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Christian eschatology

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https://en.wikipedia.org/wiki/Christian_eschatology


Eschatology


Christianity

Christian eschatology, a major branch of study within Christian theology, deals with "last things". Such eschatology – the word derives from two Greek roots meaning "last" (ἔσχατος) and "study" (-λογία) – involves the study of "end things", whether of the end of an individual life, of the end of the age, of the end of the world or of the nature of the Kingdom of God. Broadly speaking, Christian eschatology focuses on the ultimate destiny of individual souls and of the entire created order, based primarily upon biblical texts within the Old and New Testaments.

Christian eschatology looks to study and discuss matters such as death and the afterlife, Heaven and Hell, the second coming of Jesus, the resurrection of the dead, the rapture, the tribulation, millennialism, the end of the world, the Last Judgment, and the New Heaven and New Earth in the world to come.

Eschatological passages appear in many places in the Bible, in both the Old and New Testaments. Many extra-biblical examples of eschatological prophecies also exist, as well as church traditions relating to the subject.

History

Eschatology within early Christianity originated with the public life and preaching of Jesus. Christian eschatology is an ancient branch of study in Christian theology, informed by Biblical texts such as the Olivet discourse, The Sheep and the Goats, and other discourses of end times by Jesus, with the doctrine of the Second Coming discussed by Paul the Apostle in his epistles, both the authentic and the disputed ones. Other escathological doctrines can be found in the Epistle of James, the First Epistle of Peter, the First Epistle of John. The Second Epistle of Peter explains that God is patient, and has not yet brought the Second Coming of Christ in order that more people will have the chance to reject evil and find salvation (3:3–9); therefore, it calls on Christians to wait patiently for the parousia and to study scripture. The First Epistle of Clement, written by Pope Clement I in ca. 95, criticizes those who had doubts about the faith because the Second Coming had not yet occurred.

Christian eschatology is also discussed by Ignatius of Antioch (c. 35–107 AD) in his epistles, then given more consideration by the Christian apologist, Justin Martyr (c. 100–165). Treatment of eschatology continued in the West in the teachings of Tertullian (c. 160–225), and was given fuller reflection and speculation soon after by Origen (c. 185–254). The word was used first by the Lutheran theologian Abraham Calovius (1612–86) but only came into general usage in the 19th century.

The growing modern interest in eschatology is tied to developments in Anglophone Christianity. Puritans in the 18th and 19th centuries were particularly interested in a postmillennial hope which surrounded Christian conversion. This would be contrasted with the growing interest in premillennialism, advocated by dispensational figures such as J. N. Darby. Both of these strands would have significant influences on the growing interests in eschatology in Christian missions and in Christianity in West Africa and Asia. However, in the 20th century, there would be a growing number of German scholars such as Jürgen Moltmann and Wolfhart Pannenberg who would likewise be interested in eschatology.

In the 1800s, a group of Christian theologians inclusive of Ellen G. White, William Miller (preacher) and Joseph Bates (Adventist) began to study eschatological implications revealed in the Book of Daniel and the Book of Revelation. Their interpretation of Christian eschatology resulted in the founding of the Seventh-day Adventist church.

Christian eschatological views

The following approaches arose from the study of Christianity's most central eschatological document, the Book of Revelation, but the principles embodied in them can be applied to all prophecy in the Bible. They are by no means mutually exclusive and are often combined to form a more complete and coherent interpretation of prophetic passages. Most interpretations fit into one, or a combination, of these approaches. The alternate methods of prophetic interpretation, Futurism and Preterism which came from Jesuit writings, were brought about to oppose the Historicism interpretation which had been used from Biblical times that Reformers used in teaching that the Antichrist was the Papacy or the power of the Roman Catholic Church.

Preterism

Preterism is a Christian eschatological view that interprets some (partial preterism) or all (full preterism) prophecies of the Bible as events which have already happened. This school of thought interprets the Book of Daniel as referring to events that happened from the 7th century BC until the first century AD, while seeing the prophecies of Revelation as events that happened in the first century AD. Preterism holds that Ancient Israel finds its continuation or fulfillment in the Christian church at the destruction of Jerusalem in AD 70.

Historically, preterists and non-preterists have generally agreed that the Jesuit Luis de Alcasar (1554–1613) wrote the first systematic preterist exposition of prophecy—Vestigatio arcani sensus in Apocalypsi (published in 1614)—during the Counter-Reformation.

Historicism

Historicism, a method of interpretation of Biblical prophecies, associates symbols with historical persons, nations or events. It can result in a view of progressive and continuous fulfillment of prophecy covering the period from Biblical times to the Second Coming. Almost all Protestant Reformers from the Reformation into the 19th century held historicist views.

Futurism

In Futurism, parallels may be drawn with historical events, but most eschatological prophecies are chiefly referring to events which have not yet been fulfilled, but will take place at the end of the age and the end of the world. Most prophecies will be fulfilled during a global time of chaos known as the Great Tribulation and afterwards. Futurist beliefs usually have a close association with Premillennialism and Dispensationalism.

Idealism

Idealism (also called the spiritual approach, the allegorical approach, the nonliteral approach, and many other names) in Christian eschatology is an interpretation of the Book of Revelation that sees all of the imagery of the book as symbols.

Jacob Taubes writes that idealist eschatology came about as Renaissance thinkers began to doubt that the Kingdom of Heaven had been established on earth, or would be established, but still believed in its establishment. Rather than the Kingdom of Heaven being present in society, it is established subjectively for the individual.

F. D. Maurice interpreted the Kingdom of Heaven idealistically as a symbol representing society's general improvement, instead of a physical and political kingdom. Karl Barth interprets eschatology as representing existential truths that bring the individual hope, rather than history or future-history. Barth's ideas provided fuel for the Social Gospel philosophy in America, which saw social change not as performing "required" good works, but because the individuals involved felt that Christians could not simply ignore society's problems with future dreams.

Different authors have suggested that the Beast represents various social injustices, such as exploitation of workers, wealth, the elite, commerce, materialism, and imperialism. Various Christian anarchists, such as Jacques Ellul, have identified the State and political power as the Beast. Other scholars identify the Beast with the Roman empire of the first century AD, but recognize that the Beast has significance beyond its identification with Rome. For example, Craig R. Koester says "the vision [of the beast] speaks to the imperial context in which Revelation was composed, but it does so with images that go beyond that context, depicting the powers at work in the world in ways that continue to engage readers of subsequent generations." And his comments on the whore of Babylon are more to the point: "The whore [of Babylon] is Rome, yet more than Rome." It "is the Roman imperial world, which in turn represents the world alienated from God." As Stephen Smalley puts it, the beast represents "the powers of evil which lie behind the kingdoms of this world, and which encourage in society, at any moment in history, compromise with the truth and opposition to the justice and mercy of God."

It is distinct from Preterism, Futurism and Historicism in that it does not see any of the prophecies (except in some cases the Second Coming, and Final Judgment) as being fulfilled in a literal, physical, earthly sense either in the past, present or future, and that to interpret the eschatological portions of the Bible in a historical or future-historical fashion is an erroneous understanding.

Comparison of Futurist, Preterist and Historicist beliefs

Eschatological Topic	Futurist belief	Preterist belief	Historicist belief
	Futurists typically anticipate a future period of time when Bible prophecies will be fulfilled.	Preterists typically argue that most (Partial Preterism), or all (Full Preterism) Bible prophecies were fulfilled during the earthly ministry of Jesus and the generation immediately proceeding it, concluding with the siege and destruction of the temple in Jerusalem in 70 AD.	Historicists typically understand the prophecies to be continuous from the times of the prophets to the present day and beyond.
'The 144,000' Revelation 7	Various interpretations of a literal number of 144,000, including: 144,000 Evangelical Jews at the end of the world, or 144,000 Christians at the end of the world.	A symbolic number signifying the saved, representing completeness, perfection (The number of Israel; 12, squared and multiplied by 1,000, representing the infinite = 144,000). This symbolises God's Holy Army, redeemed, purified and complete.	A symbolic number representing the saved who are able to stand through the events of 6:17.
Locusts released from the Abyss Revelation 9	A demonic host released upon the earth at the end of the world.	A demonic host released upon Israel during the siege of Jerusalem 66–70 AD.	The Muslim Arab hordes that overran North Africa, the Near East, and Spain during the 6th to 8th centuries.
Large Army from the Euphrates, an army of 'myriads of myriads' Revelation 9:13-16	Futurists frequently translate and interpret the Greek phrase 'myriads of myriads' as meaning a 'double myriad', from which they develop the figure of 200 million. Futurists frequently assign this army of 200 million to China, which they believe will attack Israel in the future. Many Bibles employ a Futurist interpretation of the original Greek when they adopt the figure of 200 million.	Preterists hold to the original Greek description of a large army consisting of 'myriads of myriads', as a reference to the large pagan army, which would attack Israel during the Siege of Jerusalem from 66–70 AD. The source of this pagan army from beyond the Euphrates is a symbolic reference to Israel's history of being attacked and judged by pagan armies from beyond the Euphrates. Some of the Roman units employed during the siege of Jerusalem were assigned from this area.	The Muslim Arab hordes that overran North Africa, the Near East, and Spain during the 6th to 8th centuries.
'The Two Witnesses' Revelation 11:1-12	Two people who will preach in Jerusalem at the end of the world.	The two witnesses and their miracles symbolize the ministries of Moses and Elijah, who in turn symbolize 'The Law' and 'The Prophets', the Old Testament witnesses to the righteousness of God. When the armies of Rome laid siege to and destroyed Jerusalem in 70 AD, it appeared that the Two Witnesses had been killed.	The two witnesses (AKA "two olive trees" and "two candlesticks") are the Old and New Testaments.
'1260 Days' Revelation 11:3	A literal 1260 days (3.5 years) at the end of the world during which Jerusalem is controlled by pagan nations.	A literal 1260 days (3.5 years) which occurred 'at the end of the world' in 70 AD when the apostate worship at the temple in Jerusalem was decisively destroyed at the hands of the pagan Roman armies following a 3.5-year Roman campaign in Judea and Samaria. The 'Two Witnesses' appeared to be dead for 3.5 years during the siege of Jerusalem but were miraculously resurrected as the Early Church.	1260 days = forty and two months (vs. 11:2) = a time, times and the dividing of time (Dan 7:25). 1260 years during which the two witnesses are clothed in sackcloth, typically understoodto represent the time from 538 to 1798 A.D., the time of Papal authority over the Christian church.
'The Woman and the Dragon' Revelation 12:1-6	A future conflict between the State of Israel and Satan.	Symbolic of the Old Covenant Church, the nation of Israel (Woman) giving birth to the Christ child. Satan (the Dragon) was determined to destroy the Christ child. The Woman (the early church), fled Jerusalem before its destruction in 70 AD.	The Dragon represents Satan and any earthly power he uses. The woman represents God's true church before and after Christ's birth, death, and resurrection. The Woman flees to the desert away from the dominant power of the 1260 years.
'The Beast out of the Sea' Revelation 13:1-8	The future empire of the Anti-Christ, persecuting Christians	The Roman Empire, persecuting the early church during the rule of Nero. The sea symbolizing the Mediterranean and the nations of the Roman Empire.	The Beast is the earthly power supported by the Dragon (Satan). It is the Papal power during the same 42 months mentioned above.
'The Beast out of the Earth' 'The False Prophet' Revelation 13:11-18	The future empire of the Anti-Christ, persecuting Christians.	The apostate rulers of the Jewish people, who joined in union with the Roman Empire to persecute the early church.	The first is the U.S.A. The second is a future religio-political power in which everyone is forced by the first power to receive the mark of the beast.
'The Number of the Beast, 666' Revelation 13:18	The number identifying the future empire of the Anti-Christ, persecuting Christians.	In Hebrew calculations the total sum of Emperor Nero's name, 'Nero Caesar', equated to 666. The number more broadly symbolises the Roman Empire and its persecution of the early church. The number 666 also symbolises an apostate ruler as King Solomon was, who collected 666 talents of gold annually. 1 Kings 10:14	Various interpretations.
Armageddon Revelation 16:16	A future literal battle at Megiddo in the Jezreel Valley, Israel.	Megiddo is utilised as a symbol of God's complete victory over His enemies. The battle of Armageddon occurred 2000 years ago when God used the pagan armies of Rome to comprehensively destroy the apostate worship at the temple in Jerusalem. Revelation 16:16 Judges 5:19 2 Kings 9:27	A symbolic name concerning the ongoing battle between Jesus and Satan.
Mystery Babylon The Great Harlot Revelation 17:1-5	Futurists compose various interpretations for the identity of 'Mystery Babylon' such as the US, or the UN.	The corrupted city of Jerusalem, who united with pagan nations of the world in their idolatrous practices and participated in persecuting the faithful Old Covenant priests and prophets, and the early church of the New Covenant. Matthew 23:35-37	A virtuous woman represents God's true church. A whore represents an apostate church. Typically, Mystery Babylon is understood to be the esoteric apostasies, and Great Harlot is understood to be the popular apostasies. Both types of apostasies are already at work, ensnaring the unwary.
Seven heads and ten horns Revelation 17:9-11	Futurists compose various interpretations.	As the Bible text explains, the seven heads are seven mountains. This is a direct reference to the Seven hills of Rome. It is also noted that the seven hills 'refer to seven kings'. This is a reference to the Caesars of Rome. At the time of the writing of the Revelation, five Caesars had already fallen (Julius Caesar, Augustus Caesar, Tiberius Caesar, Caligula and Claudius Caesar), 'One is' (Nero, the sixth Caesar, was on the throne as John was writing the Revelation), and the seventh 'has not yet come'. (Galba, the seventh Caesar, reigned for less than 7 months).	Various interpretations.
The Thousand Years The Millennium Revelation 20:1-3	The Millennium is a literal, future 1,000-year reign of Christ following the destruction of God's enemies.	The Millennium is the current, ongoing rise of God's Kingdom. The Millennium is a symbolic time frame, not a literal time frame. Preterists believe the Millennium has been ongoing since the earthly ministry and ascension of Christ and the destruction of Jerusalem in 70 AD and is ongoing today. Daniel 2:34-35	The time period between Christ's Second Advent and the rapture of all the righteous, both living and formerly dead, from off earth and the third Advent which brings the New Jerusalem and the saints to the planet. While the saved are gone, the planet is inhabited only by Satan and his hosts, for all the wicked are dead.
'The Rapture' Revelation 4:1	The Rapture is a future removal of the faithful Christian church from earth.	Preterists generally recognize a future 'Second Coming' of Christ, as described in Acts 1:11 and 1 Thessalonians 4:16–17. However, they distinguish this from Revelation 4:1 which is construed by Futurists as describing a 'Rapture' event that is separate from the 'Second Coming'.
'The Great Tribulation' Revelation 4:1	The 'Great Tribulation' is a future period of God's judgement on earth.	The 'Great Tribulation' occurred 2000 years ago when apostate Israel was judged and destroyed by God, culminating in the destruction of the Temple in Jerusalem at the hands of the pagan armies of the Roman Empire. The early Church was delivered from this period of judgment because it heeded the warning of Jesus in Matthew 24:16 to flee Jerusalem when it saw the pagan armies of Rome approaching.	The Great Tribulation was a period of persecution for the Church for 1260 years from 538 to 1798 AD at the hands of papal authorities.
'The Abomination that causes desolation' Matthew 24:15	The Abomination that causes desolation is a future system of idolatrous worship based at the Temple Mount in Jerusalem.	The Abomination that causes desolation was the pagan armies of Rome destroying the apostate system of worship at the Temple in Jerusalem 2000 years ago.
'Gog and Magog invasion' Ezekiel 38	Ezekiel 38 refers to a future invasion of Israel by Russia and its allies, resulting in a miraculous deliverance by God.	Ezekiel 38 refers to the Maccabees miraculous defeat of the Seleucids in the 2nd century B.C. As Chilton notes, 'The word chief is, in the Hebrew, rosh, and according to this view, it does not pertain to Russia.

Preterism v. Historicism

Expositors of the traditional Protestant interpretation of Revelation known as Historicism have often maintained that Revelation was written in AD 96 and not AD 70. Edward Bishop Elliott, in the Horae Apocalypticae (1862), argues that John wrote the book in exile on Patmos "at the close of the reign of Domitian; that is near the end of the year 95 or beginning of 96". He notes that Domitian was assassinated in September 96. Elliot begins his lengthy review of historical evidence by quoting Irenaeus, a disciple of Polycarp. Polycarp was a disciple of the Apostle John. Irenaeus mentions that the Apocalypse was seen "no very long time ago [but] almost in our own age, toward the end of the reign of Domitian".

Other historicists have seen no significance in the date that Revelation was written, and have even held to an early date while Kenneth L. Gentry, Jr., makes an exegetical and historical argument for the pre-AD 70 composition of Revelation.

Historicism v. Futurism

The division between these interpretations can be somewhat blurred. Most futurists are expecting a rapture of the Church, an antichrist, a Great Tribulation and a second coming of Christ in the near future. But they also accept certain past events, such as the rebirth of the State of Israel and the reunification of Jerusalem as prerequisites to them, in a manner which the earlier historicists have done with other dates. Futurists, who do not normally use the day-year principle, interpret the Prophecy of Seventy Weeks in Daniel 9:24 as years, just as historicists do. Most historicists have chosen timelines, from beginning to end, entirely in the past, but some, such as Adam Clarke, have timelines which also commenced with specific past events, but require a future fulfillment. In his commentary on Daniel 8:14 published in 1831, he stated that the 2,300-year period should be calculated from 334 BC, the year Alexander the Great began his conquest of the Persian Empire. His calculation resulted in the year 1966. He seems to have overlooked the fact that there is no "year zero" between BC and AD dates. For example, the year following 1 BC is 1 AD. Thus his calculations should have required an additional year, ending in 1967. He was not anticipating a literal regathering of the Jewish people prior to the second coming of Christ. But the date is of special significance to futurists since it is the year of Jerusalem's capture by Israeli forces during the Six-Day War. His commentary on Daniel 7:25 contains a 1260-year period commencing in 755 AD and ending in 2015.

Major theological positions

Premillennialism

Premillennialism can be divided into two common categories: Historic Premillennialism and Dispensational Premillennialism. Historic Premillennialism is usually associated with post-tribulation "rapture" and does not see a strong distinction between ethnic Israel and the Church. Dispensational Premillennialism can be associated with any of the three rapture views but is often associated with a pretribulation rapture. Dispensationalism also sees a stronger distinction between ethnic Israel and the Church.

Premillennialism usually posits that Christ's second coming will inaugurate a literal thousand-year earthly kingdom. Christ's return will coincide with a time of great tribulation. At this time, there will be a resurrection of the people of God who have died, and a rapture of the people of God who are still living, and they will meet Christ at his coming. A thousand years of peace will follow (the millennium), during which Christ will reign and Satan will be imprisoned in the Abyss. Those who hold to this view usually fall into one of the following three categories:

Pretribulation rapture

Pretribulationists believe that the second coming will be in two stages separated by a seven-year period of tribulation. At the beginning of the tribulation, true Christians will rise to meet the Lord in the air (the Rapture). Then follows a seven-year period of suffering in which the Antichrist will conquer the world and persecute those who refuse to worship him. At the end of this period, Christ returns to defeat the Antichrist and establish the age of peace. This position is supported by a scripture which says, "God did not appoint us to wrath, but to obtain salvation through our Lord Jesus Christ." [1 Thess 5:9]

Midtribulation rapture

Midtribulationists believe that the Rapture will take place at the halfway point of the seven-year tribulation, i.e. after 3½ years. It coincides with the "abomination of desolation"—a desecration of the temple where the Antichrist puts an end to the Jewish sacrifices, sets up his own image in the temple, and demands that he be worshiped as God. This event begins the second, most intense part of the tribulation.

Some interpreters find support for the "midtrib" position by comparing a passage in Paul's epistles with the book of Revelation. Paul says, "We shall not all sleep, but we shall all be changed, in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised incorruptible, and we shall be changed" (1 Cor 15:51–52). Revelation divides the great tribulation into three sets of increasingly catastrophic judgments: the Seven Seals, the Seven Trumpets, and the Seven Bowls, in that order. If the "last trumpet" of Paul is equated with the last trumpet of Revelation, the Rapture would be in the middle of the Tribulation. (Not all interpreters agree with this literal interpretation of the chronology of Revelation, however.)

Posttribulation rapture

Posttribulationists hold that Christ will not return until the end of the tribulation. Christians, rather than being raptured at the beginning of the tribulation, or halfway through, will live through it and suffer for their faith during the ascendancy of the Antichrist. Proponents of this position believe that the presence of believers during the tribulation is necessary for a final evangelistic effort during a time when external conditions will combine with the Gospel message to bring great numbers of converts into the Church in time for the beginning of the Millennium.

Postmillennialism

Postmillennialism is an interpretation of chapter 20 of the Book of Revelation which sees Christ's second coming as occurring after the "Millennium", a Golden Age in which Christian ethics prosper. The term subsumes several similar views of the end times, and it stands in contrast to premillennialism and, to a lesser extent, amillennialism.

Postmillennialism holds that Jesus Christ establishes his kingdom on earth through his preaching and redemptive work in the first century and that he equips his church with the gospel, empowers her by the Spirit, and charges her with the Great Commission (Matt 28:19) to disciple all nations. Postmillennialism expects that eventually the vast majority of people living will be saved. Increasing gospel success will gradually produce a time in history prior to Christ's return in which faith, righteousness, peace, and prosperity will prevail in the affairs of men and of nations. After an extensive era of such conditions Jesus Christ will return visibly, bodily, and gloriously, to end history with the general resurrection and the final judgment after which the eternal order follows.

Postmillenialism was a dominant theological belief among American Protestants who promoted reform movements in the 19th and 20th century such as abolitionism and the Social Gospel. Postmillennialism has become one of the key tenets of a movement known as Christian Reconstructionism. It has been criticized by 20th century religious conservatives as an attempt to immanentize the eschaton.

Amillennialism

Amillennialism, in Christian eschatology, involves the rejection of the belief that Jesus will have a literal, thousand-year-long, physical reign on the earth. This rejection contrasts with premillennial and some postmillennial interpretations of chapter 20 of the Book of Revelation.

The amillennial view regards the "thousand years" mentioned in Revelation 20 as a symbolic number, not as a literal description; amillennialists hold that the millennium has already begun and is identical with the current church age. Amillennialism holds that while Christ's reign during the millennium is spiritual in nature, at the end of the church age, Christ will return in final judgment and establish a permanent reign in the new heaven and new earth.

Many proponents dislike the name "amillennialism" because it emphasizes their differences with premillennialism rather than their beliefs about the millennium. "Amillennial" was actually coined in a pejorative way by those who hold premillennial views. Some proponents also prefer alternate terms such as nunc-millennialism (that is, now-millennialism) or realized millennialism, although these other names have achieved only limited acceptance and usage.

Death and the afterlife

Jewish beliefs at the time of Jesus

There were different schools of thought on the afterlife in Judea during the first century AD. The Sadducees, who recognized only the Torah (first five books of the Old Testament) as authoritative, did not believe in an afterlife or any resurrection of the dead. The Pharisees, who not only accepted the Torah, but additional scriptures as well, believed in the resurrection of the dead, and it is known to have been a major point of contention between the two groups. The Pharisees based their belief on passages such as Daniel 12:2, which says: "Multitudes who sleep in the dust of the earth will awake: some to everlasting life, others to shame and everlasting contempt."

The intermediate state

Some traditions (notably the Seventh-day Adventists) teach that the soul sleeps after death, and will not awake again until the resurrection of the dead, while others believe the spirit goes to an intermediate place where it will live consciously until the resurrection of the dead. By "soul", Seventh-day Adventists theologians mean the physical person (monism), and that no component of human nature survives death; therefore, each human will be "recreated" at resurrection. The biblical Book of Ezekiel provides substantiation for the assertion that souls experience mortality, "Behold, all souls are Mine; The soul of the father As well as the soul of the son is Mine; The soul who sins shall die." (Ezekiel 18:4)

Purgatory

This alludes to the Catholic belief in a spiritual state, known as Purgatory, in which those souls who are not condemned to Hell, but are also not completely pure as required for entry into Heaven, go through a final process of purification before their full acceptance into Heaven.

The Catechism of the Catholic Church says:

Each man receives his eternal retribution in his immortal soul at the very moment of his death, in a particular judgment that refers his life to Christ: either entrance into the blessedness of heaven—through a purification or immediately—or immediate and everlasting damnation. (Sect. 1022)

Eastern Orthodoxy and Protestantism do not believe in Purgatory as such, though the Orthodox Church is willing to allow for a period of continued sanctification (the process of being made pure, or holy) after death. While the Eastern Orthodox Church rejects the term purgatory, it acknowledges an intermediate state after death and before final judgment, and offers prayer for the dead. In general, Protestant churches reject the Catholic doctrine of purgatory although some teach the existence of an intermediate state. The general Protestant view is that the Bible, from which Protestants exclude deuterocanonical books such as 2 Maccabees, contains no overt, explicit discussion of purgatory.

The Great Tribulation

The end comes at an unexpected time

There are many passages in the Bible, both Old and New Testaments, which speak of a time of terrible tribulation such as has never been known, a time of natural and man-made disasters on an awesome scale. Jesus said that at the time of his coming, "There will be great tribulation, such as has not been since the beginning of the world to this time, no, nor ever will be. And unless those days were shortened, no flesh would be saved; but for the elect's sake, those days will be shortened." [Mt 24:21–22]

Furthermore, the Messiah's return and the tribulation that accompanies it will come at a time when people are not expecting it:

Of that day and hour no-one knows; no, not even the angels of heaven, but My Father only. But as the days of Noah were, so also will the coming of the Son of Man be. For as in the days before the flood, they were eating and drinking, marrying and giving in marriage, until the day that Noah entered the ark, until the flood came and took them all away, so also will the coming of the Son of Man be.
— Matthew 24:36–39

Paul echoes this theme, saying, "For when they say, 'Peace and safety!' then sudden destruction comes upon them."

The abomination of desolation

The abomination of desolation (or desolating sacrilege) is a term found in the Hebrew Bible, in the book of Daniel. The term is used by Jesus Christ in the Olivet discourse, according to both the Gospel of Matthew and the Gospel of Mark. In the Matthew account, Jesus is presented as quoting Daniel explicitly.

Matthew 24:15–26 (ESV) "So when you see the abomination of desolation spoken of by the prophet Daniel, standing in the holy place (let the reader understand), then let those who are in Judea flee to the mountains."

Mark 13:14 (ESV) "But when you see the abomination of desolation standing where it ought not to be (let the reader understand), then let those who are in Judea flee to the mountains."

This verse in the Olivet Discourse also occurs in the Gospel of Luke.

Luke 21.20–21 (ESV) "But when you see Jerusalem surrounded by armies, then know that its desolation has come near. Then let those who are in Judea flee to the mountains ..."

Many biblical scholars conclude that Matthew 24:15 and Mark 13:14 are prophecies after the event about the siege of Jerusalem in AD 70 by the Roman general Titus (see Dating of the Gospel of Mark).

Preterist Christian commentators believe that Jesus quoted this prophecy in Mark 13:14 as referring to an event in his "1st century disciples'" immediate future, specifically the pagan Roman forces during the siege of Jerusalem in 70 AD.

Futurist Christians consider the "Abomination of Desolation" prophecy of Daniel mentioned by Jesus in Matthew 24:15 and Mark 13:14 as referring to an event in the end time future, when a 7-year peace treaty will be signed between Israel and a world ruler called "the man of lawlessness", or the "Antichrist" affirmed by the writings of the Apostle Paul in 2 Thessalonians.

Other scholars conclude that the Abomination of Desolation refers to the Crucifixion, an attempt by the emperor Hadrian to erect a statue to Jupiter in the Jewish temple, or an attempt by Caligula to have a statue depicting him as Zeus built in the temple.

The Prophecy of Seventy Weeks

Many interpreters calculate the length of the tribulation at seven years. The key to this understanding is the "seventy weeks prophecy" in the book of Daniel. The Prophecy of Seventy Septets (or literally 'seventy times seven') appears in the angel Gabriel's reply to Daniel, beginning with verse 22 and ending with verse 27 in the ninth chapter of the Book of Daniel, a work included in both the Jewish Tanakh and the Christian Bible; as well as the Septuagint. The prophecy is part of both the Jewish account of history and Christian eschatology.

The prophet has a vision of the angel Gabriel, who tells him, "Seventy weeks are determined for your people and for your holy city (i.e., Israel and Jerusalem)." [Dan 9:24] After making a comparison with events in the history of Israel, many scholars have concluded that each day in the seventy weeks represents a year. The first sixty-nine weeks are interpreted as covering the period until Christ's first coming, but the last week is thought to represent the years of the tribulation which will come at the end of this age, directly preceding the millennial age of peace:

The people of the prince who is to come will destroy the city and the sanctuary. The end of it will be with a flood, and till the end of the war, desolations are determined. Then he will confirm a covenant with many for one week. But in the middle of the week, he will bring an end to sacrifice and offering. And on the wing of abominations will be one who makes desolate, even until the consummation which is determined is poured out on the desolate. [Dan 9:26–27]

This is an obscure prophecy, but in combination with other passages, it has been interpreted to mean that the "prince who is to come" will make a seven-year covenant with Israel that will allow the rebuilding of the temple and the reinstitution of sacrifices, but "in the middle of the week", he will break the agreement and set up an idol of himself in the temple and force people to worship it—the "abomination of desolation". Paul writes:

Let no-one deceive you by any means, for that day will not come unless the falling away comes first, and the man of sin is revealed, the son of perdition, who opposes and exalts himself above all that is called God or that is worshiped, so that he sits as God in the temple of God, showing himself that he is God. [2 Thess 2:3–4]

Rapture

The rapture is an eschatological term used by certain Christians, particularly within branches of North American evangelicalism, referring to an end time event when all Christian believers—living and dead—will rise into Heaven and join Christ. Some adherents believe this event is predicted and described in Paul's First Epistle to the Thessalonians in the Bible, where he uses the Greek harpazo (ἁρπάζω), meaning to snatch away or seize. Though it has been used differently in the past, the term is now often used by certain believers to distinguish this particular event from the Second Coming of Jesus Christ to Earth mentioned in Second Thessalonians, Gospel of Matthew, First Corinthians, and Revelation, usually viewing it as preceding the Second Coming and followed by a thousand-year millennial kingdom. Adherents of this perspective are sometimes referred to as premillennialist dispensationalists, but amongst them there are differing viewpoints about the exact timing of the event.

The term "rapture" is especially useful in discussing or disputing the exact timing or the scope of the event, particularly when asserting the "pre-tribulation" view that the rapture will occur before, not during, the Second Coming, with or without an extended Tribulation period. The term is most frequently used among evangelical and fundamentalist Christians in the United States. Other, older uses of "rapture" were simply as a term for any mystical union with God or for eternal life in Heaven with God.

There are differing views among Christians regarding the timing of Christ's return, such as whether it will occur in one event or two, and the meaning of the aerial gathering described in 1 Thessalonians 4. Many Christians do not subscribe to rapture-oriented theological views. Though the term "rapture" is derived from the text of the Latin Vulgate of 1 Thess. 4:17—"we will be caught up", (Latin: rapiemur), Catholics, as well as Eastern Orthodox, Anglicans, Lutherans and most Reformed Christians, do not generally use "rapture" as a specific theological term, nor do any of these bodies subscribe to the premillennialist dispensationalist theological views associated with its use, but do believe in the phenomenon—primarily in the sense of the elect gathering with Christ in Heaven after his Second Coming. These denominations do not believe that a group of people is left behind on earth for an extended Tribulation period after the events of 1 Thessalonians 4:17.

Pre-tribulation rapture theology originated in the eighteenth century, with the Puritan preachers Increase and Cotton Mather, and was popularized extensively in the 1830s by John Nelson Darby and the Plymouth Brethren, and further in the United States by the wide circulation of the Scofield Reference Bible in the early 20th century. Some, including Grant Jeffrey, maintain that an earlier document called Ephraem or Pseudo-Ephraem already supported a pre-tribulation rapture.

The Second Coming

Icon of the Second Coming. Greek, ca. 1700 A.D.

Signs of Christ's return

The Bible states:

Now when He had spoken these things, while they watched, He was taken up, and a cloud received Him out of their sight. And while they looked steadfastly toward heaven as He went up, behold, two men stood by them in white apparel, who also said, "Men of Galilee, why do you stand gazing up into heaven? This same Jesus, who was taken up from you into heaven, will so come in like manner as you saw Him go into heaven." [Acts 1:9-11]

Many, but not all, Christians believe:

The coming of Christ will be instantaneous and worldwide. "For as the lightning comes from the east and flashes to the west, so also will the coming of the Son of Man be." ~ Matthew 24:27
The coming of Christ will be visible to all. "Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory." Matthew 24:30
The coming of Christ will be audible. "And He will send His angels with a great sound of a trumpet, and they will gather together His elect from the four winds, from one end of heaven to the other." Matthew 24:31
The resurrection of the righteous will occur first. "For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first." ~ 1 Thessalonians 4:16
In one single event, the saved who are alive at Christ's coming will be caught up together with the resurrected to meet the Lord in the air. "Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord." ~ 1 Thessalonians 4:17

Last Day Counterfeits

In Matthew 24 Jesus states:

For then there will be great tribulation, such as has not been since the beginning of the world until this time, no, nor ever shall be. For false christs and false prophets will rise and show great signs and wonders to deceive, if possible, even the elect. [Matthew 24:21, 24 NKJV]

These false Christs will perform great signs and are no ordinary people "For they are spirits of demons, performing signs, which go out to the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty." (Revelation 16:14) Satan's angels will also appear as godly clergymen, and Satan will appear as an angel of light. "For such are false apostles, deceitful workers, transforming themselves into apostles of Christ. And no wonder! For Satan himself transforms himself into an angel of light. Therefore it is no great thing if his ministers also transform themselves into ministers of righteousness, whose end will be according to their works." (2 Corinthians 11:13–15)

The Marriage of the Lamb

After Jesus meets his followers "in the air", the marriage of the Lamb takes place: "Let us be glad and rejoice and give him glory, for the marriage of the Lamb has come, and his wife has made herself ready. And to her was granted that she should be arrayed in fine linen, clean and bright, for the fine linen is the righteous acts of the saints" [Rev 19:7–8]. Christ is represented throughout Revelation as "the Lamb", symbolizing the giving of his life as an atoning sacrifice for the people of the world, just as lambs were sacrificed on the altar for the sins of Israel. His "wife" appears to represent the people of God, for she is dressed in the "righteous acts of the saints". As the marriage takes place, there is a great celebration in heaven which involves a "great multitude" [Rev 19:6].

Resurrection of the dead

Doctrine of the resurrection predates Christianity

The word resurrection comes from the Latin resurrectus, which is the past participle of resurgere, meaning to rise again. Although the doctrine of the resurrection comes to the forefront in the New Testament, it predates the Christian era. There is an apparent reference to the resurrection in the book of Job, where Job says, "I know that my redeemer lives, and that he will stand at the latter day upon the earth. And though... worms destroy this body, yet in my flesh I will see God" [Job 19:25–27]. Again, the prophet Daniel writes, "Many of those who sleep in the dust of the earth shall awake, some to everlasting life, some to shame and everlasting contempt" [Dan 12:2]. Isaiah says: "Your dead will live. Together with my dead body, they will arise. Awake and sing, you who dwell in dust, for your dew is like the dew of herbs, and the earth will cast out the dead" [Isa. 26:19].

This belief was still common among the Jews in New Testament times, as exemplified by the passage which relates the raising of Lazarus from the dead. When Jesus told Lazarus' sister, Martha, that Lazarus would rise again, she replied, "I know that he will rise again in the resurrection at the last day" [Jn 11:24]. Also, one of the two main branches of the Jewish religious establishment, the Pharisees, believed in and taught the future resurrection of the body [cf Acts 23:1–8].

Two resurrections

An interpretation of the New Testament is the understanding that there will be two resurrections. Revelation says: "Blessed and holy is he who has part in the first resurrection. Over such, the second death has no power, but they will be priests of God and of Christ, and will reign with him a thousand years" [Rev 20:6]. The rest of the dead "did not live again until the thousand years were finished" [Rev 20:5].

Despite this, there are various interpretations:

According to the premillennial post-tribulational position there will two physical resurrections, separated by a literal thousand years (one in the Second Coming along with the Rapture; another after a literal 1,000 year reign).

According to premillennial pre-tribulationists, there will be three further physical resurrections (one in the Rapture at the beginning of tribulation; another in the Second Coming at the final tribulation; and the last one after a literal 1,000 year reign). They claim that the first resurrection includes the resurrection in the Rapture, and that the resurrection in the Second Coming, the second resurrection, would be after the 1,000 year reign.

According to premillennial mid-tribulationists, too, there will be three physical resurrections (one in the rapture at the middle of tribulation; another in the Second Coming at the end of the tribulation; and the last one after a literal 1,000 year reign). And the first resurrection would be the resurrection in the Rapture, and the resurrection in the Second Coming, the second resurrection, would be after the 1,000 year reign.

According to amillennial position there will be only two resurrections. The first resurrection would be in a spiritual sense (the resurrection of the soul), according to Paul and John as participation, right now, in the resurrection of Christ through faith and baptism, according to Colossians 2:12 and Colossians 3:1 as occurring within the millennium interpreted as an indefinite period between the foundation of the Church and the Second Coming of Christ, the second resurrection would be the general resurrection (the resurrection of the body) that would occur at the time of Jesus' return.

The resurrection body

The Gospel authors wrote that our resurrection bodies will be different from those we have now. Jesus said, "In the resurrection, they neither marry nor are given in marriage, but are like the angels of God in heaven" [Mt 22:30]. Paul adds, "So also is the resurrection of the dead: the body ... is sown a natural body; it is raised a spiritual body" [1 Co. 15:42–44].

According to the Catechism of the Catholic Church the body after resurrection is changed into a spiritual, imperishable body:

Christ is raised with his own body: "See my hands and my feet, that it is I myself"; but he did not return to an earthly life. So, in him, "all of them will rise again with their own bodies which they now bear," but Christ "will change our lowly body to be like his glorious body," into a "spiritual body".

In some ancient traditions, it was held that the person would be resurrected at the same spot where they died and were buried (just as in the case of Jesus' resurrection). For example, in the early medieval biography of St Columba written by Adomnan of Iona, Columba at one point prophesies to a penitent at the monastery on Iona that his resurrection would be in Ireland and not in Iona, and this penitent later died at a monastery in Ireland and was buried there.

Other views

Although Martin Luther personally believed and taught resurrection of the dead in combination with soul sleep, this is not a mainstream teaching of Lutheranism and most Lutherans traditionally believe in resurrection of the body in combination with the immortal soul.

Several churches, such as the Anabaptists and Socinians of the Reformation, then Seventh-day Adventist Church, Christadelphians, Jehovah's Witnesses, and theologians of different traditions reject the idea of the immortality of a non-physical soul as a vestige of Neoplatonism, and other pagan traditions. In this school of thought, the dead remain dead (and do not immediately progress to a Heaven, Hell, or Purgatory) until a physical resurrection of some or all of the dead occurs at the end of time. Some groups, Christadelphians in particular, consider that it is not a universal resurrection, and that at this time of resurrection that the Last Judgment will take place.

Armageddon

Megiddo is mentioned twelve times in the Old Testament, ten times in reference to the ancient city of Megiddo, and twice with reference to "the plain of Megiddo", most probably simply meaning "the plain next to the city". None of these Old Testament passages describes the city of Megiddo as being associated with any particular prophetic beliefs. The one New Testament reference to the city of Armageddon found in Revelation 16:16 also makes no specific mention of any armies being predicted to one day gather in this city, but instead seems to predict only that "they (will gather) the kings together to .... Armageddon". The text does however seem to imply, based on the text from the earlier passage of Revelation 16:14, that the purpose of this gathering of kings in the "place called Armageddon" is "for the war of the great day of God, the Almighty". Because of the seemingly highly symbolic and even cryptic language of this one New Testament passage, some Christian scholars conclude that Mount Armageddon must be an idealized location. R. J. Rushdoony says, "There are no mountains of Megiddo, only the Plains of Megiddo. This is a deliberate destruction of the vision of any literal reference to the place." Other scholars, including C. C. Torrey, Kline and Jordan argue that the word is derived from the Hebrew moed (מועד), meaning "assembly". Thus, "Armageddon" would mean "Mountain of Assembly," which Jordan says is "a reference to the assembly at Mount Sinai, and to its replacement, Mount Zion."

The traditional viewpoint interprets this Bible prophecy to be symbolic of the progression of the world toward the "great day of God, the Almighty" in which the great looming mountain of God's just and holy wrath is poured out against unrepentant sinners, led by Satan, in a literal end-of-the-world final confrontation. Armageddon is the symbolic name given to this event based on scripture references regarding divine obliteration of God's enemies. The hermeneutical method supports this position by referencing Judges 4 and 5 where God miraculously destroys the enemy of His elect, Israel, at Megiddo, also called the Valley of Josaphat.

Christian scholar William Hendriksen says:

For this cause, Har Magedon is the symbol of every battle in which, when the need is greatest and believers are oppressed, the Lord suddenly reveals His power in the interest of His distressed people and defeats the enemy. When Sennacherib's 185,000 are slain by the Angel of Jehovah, that is a shadow of the final Har-Magedon. When God grants a little handful of Maccabees a glorious victory over an enemy which far outnumbers it, that is a type of Har-Magedon. But the real, the great, the final Har Magedon coincides with the time of Satan's little season. Then the world, under the leadership of Satan, anti-Christian government, and anti-Christian religion—the dragon, the beast, and the false prophet—is gathered against the Church for the final battle, and the need is greatest; when God's children, oppressed on every side, cry for help; then suddenly, Christ will appear on the clouds of glory to deliver his people; that is Har-Magedon.

The Millennium

Millennialism (from millennium, Latin for "a thousand years"), or chiliasm (from the Greek equivalent), is the belief that a Golden Age or Paradise will occur on Earth prior to the final judgment and future eternal state of the "World to Come".

Christian millennialism developed out of a Christian interpretation of Jewish apocalypticism. Christian millennialist thinking is primarily based upon the Book of Revelation, specifically 20:1–6, which describes the vision of an angel who descended from heaven with a large chain and a key to a bottomless pit, and captured Satan, imprisoning him for a thousand years:

He seized the dragon, that ancient serpent, who is the Devil and Satan, and bound him for a thousand years and threw him into the pit and locked and sealed it over him, so that he would deceive the nations no more, until the thousand years were ended. After that, he must be let out for a little while.
— Rev. 20:2–3

The Book of Revelation then describes a series of judges who are seated on thrones, as well as his vision of the souls of those who were beheaded for their testimony in favor of Jesus and their rejection of the mark of the beast. These souls:

came to life and reigned with Christ a thousand years. (The rest of the dead did not come to life until the thousand years were ended.) This is the first resurrection. Blessed and holy are those who share in the first resurrection. Over these the second death has no power, but they will be priests of God and of Christ, and they will reign with him a thousand years
— Rev. 20:4–6

Thus, Revelation characterizes a millennium where Christ and the Father will rule over a theocracy of the righteous. While there are an abundance of biblical references to such a kingdom of God throughout the Old and New Testaments, this is the only reference in the Bible to such a period lasting one thousand years. The literal belief in a thousand-year reign of Christ is a later development in Christianity, as it does not seem to have been present in first century texts.

The End of the World and the Last Judgment

Satan released

According to the Bible, the Millennial age of peace all but closes the history of planet Earth. However, the story is not yet finished: "When the thousand years have expired, Satan will be released from his prison and will go out to deceive the nations which are in the four corners of the earth, Gog and Magog, to gather them together to battle, whose number is as the sand of the sea." [Rev 20:7–8]

There is continuing discussion over the identity of Gog and Magog. In the context of the passage, they seem to equate to something like "east and west". There is a passage in Ezekiel, however, where God says to the prophet, "Set your face against Gog, of the land of Magog, the prince of Rosh, Meshech, and Tubal, and prophesy against him." [Ezek 38:2] Gog, in this instance, is the name of a person of the land of Magog, who is ruler ("prince") over the regions of Rosh, Meshech, and Tubal. Ezekiel says of him: "You will ascend, coming like a storm, covering the land like a cloud, you and all your troops and many peoples with you..." [Ezek 38:2]

Despite this huge show of force, the battle will be short-lived, for Ezekiel, Daniel, and Revelation all say that this last desperate attempt to destroy the people and the city of God will end in disaster: "I will bring him to judgment with pestilence and bloodshed. I will rain down on him and on his troops, and on the many peoples who are with him: flooding rain, great hailstones, fire and brimstone." [Ezek 38:22] Revelation concurs: "Fire came down from God out of heaven and devoured them." [Rev 20:9] It may be that the images of fire raining down are an ancient vision of modern weapons, others would say a supernatural intervention by God, yet others that they refer to events in history, and some would say they are symbolic of larger ideas and should not be interpreted literally.

The Last Judgment

Following the defeat of Gog, the last judgment begins: "The devil, who deceived them, was cast into the lake of fire and brimstone where the beast and the false prophet are, and they will be tormented day and night forever and ever" [Rev 20:10]. Satan will join the Antichrist and the False Prophet, who were condemned to the lake of fire at the beginning of the Millennium.

Following Satan's consignment to the lake of fire, his followers come up for judgment. This is the "second resurrection", and all those who were not a part of the first resurrection at the coming of Christ now rise up for judgment:

I saw a great white throne and him who sat on it, from whose face the earth and the heaven fled away, and there was found no place for them. And the sea gave up the dead who were in it, and Death and Hades delivered up the dead who were in them. And they were judged, each one according to his works. And Death and Hades were cast into the lake of fire. This is the second death. And anyone not found written in the Book of Life was cast into the lake of fire. [Rev 20:11,13-15]

John had earlier written, "Blessed and holy is he who has part in the first resurrection. Over such the second death has no power" [Rev 20:6]. Those who are included in the Resurrection and the Rapture are excluded from the final judgment, and are not subject to the second death. Due to the description of the seat upon which the Lord sits, this final judgment is often referred to as the Great White Throne Judgment.

A decisive factor in the Last Judgement will be the question, if the corporal works of mercy were practiced or not during lifetime. They rate as important acts of charity. Therefore, and according to the biblical sources (Mt 5:31–46), the conjunction of the Last Judgement and the works of mercy is very frequent in the pictorial tradition of Christian art.

New Heaven and New Earth

A new heaven and new earth Collection

But, in accordance with his promise, we wait for new heavens and a new earth, where righteousness is at home.

The basic difference with the promises of the Old Testament is that in Revelation they also have an ontological value and no longer just gnosiological.

New Jerusalem

The focus turns to one city in particular, the New Jerusalem. Once again, we see the imagery of the marriage: "I, John, saw the holy city, New Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband" [Rev 21:2]. In the New Jerusalem, God "will dwell with them, and they will be his people, and God himself will be with them and be their God..." [Rev 21:3]. As a result, there is "no temple in it, for the Lord God Almighty and the Lamb are its temple." Nor is there a need for the sun to give its light, "for the glory of God illuminated it, and the Lamb is its light" [Rev 21:22–23]. The city will also be a place of great peace and joy, for "God will wipe away every tear from their eyes. There will be no more death, nor sorrow, nor crying; and there will be no more pain, for the former things have passed away" [Rev 21:4].

Description

The city itself has a large wall with twelve gates in it which are never shut, and which have the names of the twelve tribes of Israel written on them. Each of the gates is made of a single pearl, and there is an angel standing in each one. The wall also has twelve foundations which are adorned with precious stones, and upon the foundations are written the names of the twelve apostles. The gates and foundations are often interpreted as symbolizing the people of God before and after Christ.

The city and its streets are pure gold, but not like the gold we know, for this gold is described as being like clear glass. The city is square in shape, and is twelve thousand furlongs long and wide (fifteen hundred miles). If these are comparable to earthly measurements, the city will cover an area about half the size of the contiguous United States. The height is the same as the length and breadth, and although this has led most people to conclude that it is shaped like a cube, it could also be a pyramid.

The Tree of Life

The tree of life, a print from the Phillip Medhurst Collection of Bible illustrations in the possession of Revd. Philip De Vere at St. George's Court, Kidderminster, England.

The city has a river which proceeds "out of the throne of God and of the Lamb" Next to the river is the tree of life, which bears twelve fruits and yields its fruit every month. The last time we saw the tree of life was in the Garden of Eden [Gen 2:9]. God drove Adam and Eve out from the garden, guarding it with cherubim and a flaming sword, because it gave eternal life to those who ate of it. In the New Jerusalem, the tree of life reappears, and everyone in the city has access to it. Genesis says that the earth was cursed because of Adam's sin, but the author of John writes that in the New Jerusalem, "there will be no more curse."

The Evangelical Dictionary of Theology (Baker, 1984) says:

The rich symbolism reaches beyond our finest imaginings, not only to the beatific vision but to a renewed, joyous, industrious, orderly, holy, loving, eternal, and abundant existence. Perhaps the most moving element in the description is what is missing: there is no temple in the New Jerusalem, 'because the Lord God Almighty and the Lamb are its temple.' Vastly outstripping the expectations of Judaism, this stated omission signals the ultimate reconciliation.

Thermal power station

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Thermal_power_station

Nantong Power Station, a coal-fired power station in Nantong, China

Grafenrheinfeld Nuclear Power Plant in Bavaria

Geothermal power station in Iceland

Drax Power Station, the world's largest biomass power station, in England

PS10 solar power plant, concentrated solar thermal power station in Andalusia, Spain

A thermal power station is a power station in which heat energy is converted to electricity. Typically, fuel is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam turbine connected to an electrical generator. The low-pressure exhaust from the turbine passes through a steam condenser and is recycled to where it was heated. This is known as a Rankine cycle. Natural gas can also be burnt directly in a gas turbine similarly connected to a generator.

Water power stations (which generate hydroelectricity) are excluded from this category, since they convert the potential energy of water into electricity via a water turbine.

The design of thermal power stations depends on the intended energy source: fossil fuel, nuclear and geothermal power, solar energy, biofuels, and waste incineration are all used. Certain thermal power stations are also designed to produce heat for industrial purposes; for district heating; or desalination of water, in addition to generating electrical power.

Types of thermal energy

Almost all coal-fired power stations, petroleum, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as all natural gas power stations are thermal. Natural gas is frequently burned in gas turbines as well as boilers. The waste heat from a gas turbine, in the form of hot exhaust gas, can be used to raise steam by passing this gas through a heat recovery steam generator (HRSG). The steam is then used to drive a steam turbine in a combined cycle plant that improves overall efficiency. Power stations burning coal, fuel oil, or natural gas are often called fossil fuel power stations. Some biomass-fueled thermal power stations have appeared also. Non-nuclear thermal power stations, particularly fossil-fueled plants, which do not use cogeneration are sometimes referred to as conventional power stations.

Commercial electric utility power stations are usually constructed on a large scale and designed for continuous operation. Virtually all electric power stations use three-phase electrical generators to produce alternating current (AC) electric power at a frequency of 50 Hz or 60 Hz. Large companies or institutions may have their own power stations to supply heating or electricity to their facilities, especially if steam is created anyway for other purposes. Steam-driven power stations have been used to drive most ships in most of the 20th century. Shipboard power stations usually directly couple the turbine to the ship's propellers through gearboxes. Power stations in such ships also provide steam to smaller turbines driving electric generators to supply electricity. Nuclear marine propulsion is, with few exceptions, used only in naval vessels. There have been many turbo-electric ships in which a steam-driven turbine drives an electric generator which powers an electric motor for propulsion.

Cogeneration plants, often called combined heat and power (CHP) facilities, produce both electric power and heat for process heat or space heating, such as steam and hot water.

History

Interior of the Toledo Edison Steam Plant, Toledo, Ohio, approximately 1900

The reciprocating steam engine has been used to produce mechanical power since the 18th century, with notable improvements being made by James Watt. When the first commercially developed central electrical power stations were established in 1882 at Pearl Street Station in New York and Holborn Viaduct power station in London, reciprocating steam engines were used. The development of the steam turbine in 1884 provided larger and more efficient machine designs for central generating stations. By 1892 the turbine was considered a better alternative to reciprocating engines; turbines offered higher speeds, more compact machinery, and stable speed regulation allowing for parallel synchronous operation of generators on a common bus. After about 1905, turbines entirely replaced reciprocating engines in almost all large central power stations.

The largest reciprocating engine-generator sets ever built were completed in 1901 for the Manhattan Elevated Railway. Each of seventeen units weighed about 500 tons and was rated 6000 kilowatts; a contemporary turbine set of similar rating would have weighed about 20% as much.

Thermal power generation efficiency

A Rankine cycle with a two-stage steam turbine and a single feed water heater.

The energy efficiency of a conventional thermal power station is defined as saleable energy produced as a percent of the heating value of the fuel consumed. A simple cycle gas turbine achieves energy conversion efficiencies from 20 to 35%. Typical coal-based power plants operating at steam pressures of 170 bar and 570 °C run at efficiency of 35 to 38%, with state-of-the-art fossil fuel plants at 46% efficiency. Combined-cycle systems can reach higher values. As with all heat engines, their efficiency is limited, and governed by the laws of thermodynamics.

The Carnot efficiency dictates that higher efficiencies can be attained by increasing the temperature of the steam. Sub-critical pressure fossil fuel power stations can achieve 36–40% efficiency. Supercritical designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures above 4400 psi (30.3 MPa) and multiple stage reheat reaching 45-48% efficiency. Above the critical point for water of 705 °F (374 °C) and 3212 psi (22.06 MPa), there is no phase transition from water to steam, but only a gradual decrease in density.

Currently most nuclear power stations must operate below the temperatures and pressures that coal-fired plants do, in order to provide more conservative safety margins within the systems that remove heat from the nuclear fuel. This, in turn, limits their thermodynamic efficiency to 30–32%. Some advanced reactor designs being studied, such as the very-high-temperature reactor, Advanced Gas-cooled Reactor, and supercritical water reactor, would operate at temperatures and pressures similar to current coal plants, producing comparable thermodynamic efficiency.

The energy of a thermal power station not utilized in power production must leave the plant in the form of heat to the environment. This waste heat can go through a condenser and be disposed of with cooling water or in cooling towers. If the waste heat is instead used for district heating, it is called cogeneration. An important class of thermal power station is that associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas, and in these plants freshwater production and electricity are equally important co-products.

Other types of power stations are subject to different efficiency limitations. Most hydropower stations in the United States are about 90 percent efficient in converting the energy of falling water into electricity while the efficiency of a wind turbine is limited by Betz's law, to about 59.3%, and actual wind turbines show lower efficiency.

Electricity cost

The direct cost of electric energy produced by a thermal power station is the result of cost of fuel, capital cost for the plant, operator labour, maintenance, and such factors as ash handling and disposal. Indirect social or environmental costs, such as the economic value of environmental impacts, or environmental and health effects of the complete fuel cycle and plant decommissioning, are not usually assigned to generation costs for thermal stations in utility practice, but may form part of an environmental impact assessment.

Boiler and steam cycle

Pressurized water reactor simplified schematic

In the nuclear plant field, steam generator refers to a specific type of large heat exchanger used in a pressurized water reactor (PWR) to thermally connect the primary (reactor plant) and secondary (steam plant) systems, which generates steam. In a boiling water reactor (BWR), no separate steam generator is used and water boils in the reactor core.

In some industrial settings, there can also be steam-producing heat exchangers called heat recovery steam generators (HRSG) which utilize heat from some industrial process, most commonly utilizing hot exhaust from a gas turbine. The steam generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine that drives the electrical generator.

Geothermal plants do not need boilers because they use naturally occurring steam sources. Heat exchangers may be used where the geothermal steam is very corrosive or contains excessive suspended solids.

A fossil fuel steam generator includes an economizer, a steam drum, and the furnace with its steam generating tubes and superheater coils. Necessary safety valves are located at suitable points to protect against excessive boiler pressure. The air and flue gas path equipment include: forced draft (FD) fan, air preheater (AP), boiler furnace, induced draft (ID) fan, fly ash collectors (electrostatic precipitator or baghouse), and the flue-gas stack.

Feed water heating

The boiler feed water used in the steam boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinning steam turbine. The total feed water consists of recirculated condensate water and purified makeup water. Because the metallic materials it contacts are subject to corrosion at high temperatures and pressures, the makeup water is highly purified before use. A system of water softeners and ion exchange demineralizers produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter. The makeup water in a 500 MWe plant amounts to perhaps 120 US gallons per minute (7.6 L/s) to replace water drawn off from the boiler drums for water purity management, and to also offset the small losses from steam leaks in the system.

The feed water cycle begins with condensate water being pumped out of the condenser after traveling through the steam turbines. The condensate flow rate at full load in a 500 MW plant is about 6,000 US gallons per minute (400 L/s).

Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal water storage section).

The water is pressurized in two stages, and flows through a series of six or seven intermediate feed water heaters, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Typically, in the middle of this series of feedwater heaters, and before the second stage of pressurization, the condensate plus the makeup water flows through a deaerator that removes dissolved air from the water, further purifying and reducing its corrosiveness. The water may be dosed following this point with hydrazine, a chemical that removes the remaining oxygen in the water to below 5 parts per billion (ppb). It is also dosed with pH control agents such as ammonia or morpholine to keep the residual acidity low and thus non-corrosive.

Boiler operation

The boiler is a rectangular furnace about 50 feet (15 m) on a side and 130 feet (40 m) tall. Its walls are made of a web of high pressure steel tubes about 2.3 inches (58 mm) in diameter.

Fuel such as pulverized coal is air-blown into the furnace through burners located at the four corners, or along one wall, or two opposite walls, and it is ignited to rapidly burn, forming a large fireball at the center. The thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter. The water circulation rate in the boiler is three to four times the throughput. As the water in the boiler circulates it absorbs heat and changes into steam. It is separated from the water inside a drum at the top of the furnace. The saturated steam is introduced into superheat pendant tubes that hang in the hottest part of the combustion gases as they exit the furnace. Here the steam is superheated to 1,000 °F (540 °C) to prepare it for the turbine.

Plants that use gas turbines to heat the water for conversion into steam use boilers known as heat recovery steam generators (HRSG). The exhaust heat from the gas turbines is used to make superheated steam that is then used in a conventional water-steam generation cycle, as described in the gas turbine combined-cycle plants section.

Boiler furnace and steam drum

The water enters the boiler through a section in the convection pass called the economizer. From the economizer it passes to the steam drum and from there it goes through downcomers to inlet headers at the bottom of the water walls. From these headers the water rises through the water walls of the furnace where some of it is turned into steam and the mixture of water and steam then re-enters the steam drum. This process may be driven purely by natural circulation (because the water is the downcomers is denser than the water/steam mixture in the water walls) or assisted by pumps. In the steam drum, the water is returned to the downcomers and the steam is passed through a series of steam separators and dryers that remove water droplets from the steam. The dry steam then flows into the superheater coils.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers, water lancing, and observation ports (in the furnace walls) for observation of the furnace interior. Furnace explosions due to any accumulation of combustible gases after a trip-out are avoided by flushing out such gases from the combustion zone before igniting the coal.

The steam drum (as well as the superheater coils and headers) have air vents and drains needed for initial start up.

Superheater

Fossil fuel power stations often have a superheater section in the steam generating furnace. The steam passes through drying equipment inside the steam drum on to the superheater, a set of tubes in the furnace. Here the steam picks up more energy from hot flue gases outside the tubing, and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves before the high-pressure turbine.

Nuclear-powered steam plants do not have such sections but produce steam at essentially saturated conditions. Experimental nuclear plants were equipped with fossil-fired superheaters in an attempt to improve overall plant operating cost.

Steam condensing

The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases.

Diagram of a typical water-cooled surface condenser.

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low-pressure turbine enters the shell, where it is cooled and converted to condensate (water) by flowing over the tubes as shown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-driven exhausts for continuous removal of air and gases from the steam side to maintain vacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100 °C where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented.

Typically the cooling water causes the steam to condense at a temperature of about 25 °C (77 °F) and that creates an absolute pressure in the condenser of about 2–7 kPa (0.59–2.07 inHg), i.e. a vacuum of about −95 kPa (−28 inHg) relative to atmospheric pressure. The large decrease in volume that occurs when water vapor condenses to liquid creates the low vacuum that helps pull steam through and increase the efficiency of the turbines.

The limiting factor is the temperature of the cooling water and that, in turn, is limited by the prevailing average climatic conditions at the power station's location (it may be possible to lower the temperature beyond the turbine limits during winter, causing excessive condensation in the turbine). Plants operating in hot climates may have to reduce output if their source of condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air conditioning.

The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through cooling (OTC) water from a river, lake or ocean. In the United States, about two-thirds of power plants use OTC systems, which often have significant adverse environmental impacts. The impacts include thermal pollution and killing large numbers of fish and other aquatic species at cooling water intakes.

A Marley mechanical induced draft cooling tower

The heat absorbed by the circulating cooling water in the condenser tubes must also be removed to maintain the ability of the water to cool as it circulates. This is done by pumping the warm water from the condenser through either natural draft, forced draft or induced draft cooling towers (as seen in the adjacent image) that reduce the temperature of the water by evaporation, by about 11 to 17 °C (20 to 30 °F)—expelling waste heat to the atmosphere. The circulation flow rate of the cooling water in a 500 MW unit is about 14.2 m³/s (500 ft³/s or 225,000 US gal/min) at full load.

The condenser tubes are made of brass or stainless steel to resist corrosion from either side. Nevertheless, they may become internally fouled during operation by bacteria or algae in the cooling water or by mineral scaling, all of which inhibit heat transfer and reduce thermodynamic efficiency. Many plants include an automatic cleaning system that circulates sponge rubber balls through the tubes to scrub them clean without the need to take the system off-line.

The cooling water used to condense the steam in the condenser returns to its source without having been changed other than having been warmed. If the water returns to a local water body (rather than a circulating cooling tower), it is often tempered with cool 'raw' water to prevent thermal shock when discharged into that body of water.

Another form of condensing system is the air-cooled condenser. The process is similar to that of a radiator and fan. Exhaust heat from the low-pressure section of a steam turbine runs through the condensing tubes, the tubes are usually finned and ambient air is pushed through the fins with the help of a large fan. The steam condenses to water to be reused in the water-steam cycle. Air-cooled condensers typically operate at a higher temperature than water-cooled versions. While saving water, the efficiency of the cycle is reduced (resulting in more carbon dioxide per megawatt-hour of electricity).

From the bottom of the condenser, powerful condensate pumps recycle the condensed steam (water) back to the water/steam cycle.

Reheater

Power station furnaces may have a reheater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high-pressure turbine is passed through these heated tubes to collect more energy before driving the intermediate and then low-pressure turbines.

Air path

External fans are provided to give sufficient air for combustion. The Primary air fan takes air from the atmosphere and, first warms the air in the air preheater for better economy. Primary air then passes through the coal pulverizers, and carries the coal dust to the burners for injection into the furnace. The Secondary air fan takes air from the atmosphere and, first warms the air in the air preheater for better economy. Secondary air is mixed with the coal/primary air flow in the burners.

The induced draft fan assists the FD fan by drawing out combustible gases from the furnace, maintaining slightly below atmospheric pressure in the furnace to avoid leakage of combustion products from the boiler casing.

Steam turbine generator

A steam turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft.

Steam turbine

Rotor of a modern steam turbine, used in a power station

There is usually a high-pressure turbine at one end, followed by an intermediate-pressure turbine, and finally one, two, or three low-pressure turbines, and the shaft that connects to the generator. As steam moves through the system and loses pressure and thermal energy, it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy. The entire rotating mass may be over 200 metric tons and 100 feet (30 m) long. It is so heavy that it must be kept turning slowly even when shut down (at 3 rpm) so that the shaft will not bow even slightly and become unbalanced. This is so important that it is one of only six functions of blackout emergency power batteries on site. (The other five being emergency lighting, communication, station alarms, generator hydrogen seal system, and turbogenerator lube oil.)

For a typical late 20th-century power station, superheated steam from the boiler is delivered through 14–16-inch (360–410 mm) diameter piping at 2,400 psi (17 MPa; 160 atm) and 1,000 °F (540 °C) to the high-pressure turbine, where it falls in pressure to 600 psi (4.1 MPa; 41 atm) and to 600 °F (320 °C) in temperature through the stage. It exits via 24–26-inch (610–660 mm) diameter cold reheat lines and passes back into the boiler, where the steam is reheated in special reheat pendant tubes back to 1,000 °F (540 °C). The hot reheat steam is conducted to the intermediate pressure turbine, where it falls in both temperature and pressure and exits directly to the long-bladed low-pressure turbines and finally exits to the condenser.

Turbo generator

The generator, typically about 30 feet (9 m) long and 12 feet (3.7 m) in diameter, contains a stationary stator and a spinning rotor, each containing miles of heavy copper conductor. There is generally no permanent magnet, thus preventing black starts. In operation it generates up to 21,000 amperes at 24,000 volts AC (504 MWe) as it spins at either 3,000 or 3,600 rpm, synchronized to the power grid. The rotor spins in a sealed chamber cooled with hydrogen gas, selected because it has the highest known heat transfer coefficient of any gas and for its low viscosity, which reduces windage losses. This system requires special handling during startup, with air in the chamber first displaced by carbon dioxide before filling with hydrogen. This ensures that a highly explosive hydrogen–oxygen environment is not created.

The power grid frequency is 60 Hz across North America and 50 Hz in Europe, Oceania, Asia (Korea and parts of Japan are notable exceptions), and parts of Africa. The desired frequency affects the design of large turbines, since they are highly optimized for one particular speed.

The electricity flows to a distribution yard where transformers increase the voltage for transmission to its destination.

The steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily and safely. The steam turbine generator, being rotating equipment, generally has a heavy, large-diameter shaft. The shaft therefore requires not only supports but also has to be kept in position while running. To minimize the frictional resistance to the rotation, the shaft has a number of bearings. The bearing shells, in which the shaft rotates, are lined with a low-friction material like Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated.

Stack gas path and cleanup

As the combustion flue gas exits the boiler it is routed through a rotating flat basket of metal mesh which picks up heat and returns it to incoming fresh air as the basket rotates. This is called the air preheater. The gas exiting the boiler is laden with fly ash, which are tiny spherical ash particles. The flue gas contains nitrogen along with combustion products carbon dioxide, sulfur dioxide, and nitrogen oxides. The fly ash is removed by fabric bag filters in baghouses or electrostatic precipitators. Once removed, the fly ash byproduct can sometimes be used in the manufacturing of concrete. This cleaning up of flue gases, however, only occurs in plants that are fitted with the appropriate technology. Still, the majority of coal-fired power stations in the world do not have these facilities. Legislation in Europe has been efficient to reduce flue gas pollution. Japan has been using flue gas cleaning technology for over 30 years and the US has been doing the same for over 25 years. China is now beginning to grapple with the pollution caused by coal-fired power stations.

Where required by law, the sulfur and nitrogen oxide pollutants are removed by stack gas scrubbers which use a pulverized limestone or other alkaline wet slurry to remove those pollutants from the exit stack gas. Other devices use catalysts to remove nitrous oxide compounds from the flue-gas stream. The gas travelling up the flue-gas stack may by this time have dropped to about 50 °C (120 °F). A typical flue-gas stack may be 150–180 metres (490–590 ft) tall to disperse the remaining flue gas components in the atmosphere. The tallest flue-gas stack in the world is 419.7 metres (1,377 ft) tall at the Ekibastuz GRES-2 Power Station in Kazakhstan.

In the United States and a number of other countries, atmospheric dispersion modeling studies are required to determine the flue-gas stack height needed to comply with the local air pollution regulations. The United States also requires the height of a flue-gas stack to comply with what is known as the "good engineering practice" (GEP) stack height. In the case of existing flue gas stacks that exceed the GEP stack height, any air pollution dispersion modeling studies for such stacks must use the GEP stack height rather than the actual stack height.

Auxiliary systems

Boiler make-up water treatment plant and storage

Since there is continuous withdrawal of steam and continuous return of condensate to the boiler, losses due to blowdown and leakages have to be made up to maintain a desired water level in the boiler steam drum. For this, continuous make-up water is added to the boiler water system. Impurities in the raw water input to the plant generally consist of calcium and magnesium salts which impart hardness to the water. Hardness in the make-up water to the boiler will form deposits on the tube water surfaces which will lead to overheating and failure of the tubes. Thus, the salts have to be removed from the water, and that is done by a water demineralising treatment plant (DM). A DM plant generally consists of cation, anion, and mixed bed exchangers. Any ions in the final water from this process consist essentially of hydrogen ions and hydroxide ions, which recombine to form pure water. Very pure DM water becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw water input. However, some storage is essential as the DM plant may be down for maintenance. For this purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-up. The storage tank for DM water is made from materials not affected by corrosive water, such as PVC. The piping and valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with air. DM water make-up is generally added at the steam space of the surface condenser (i.e., the vacuum side). This arrangement not only sprays the water but also DM water gets deaerated, with the dissolved gases being removed by a de-aerator through an ejector attached to the condenser.

Fuel preparation system

Conveyor system for moving coal (visible at far left) into a power station.

In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next pulverized into a very fine powder. The pulverizers may be ball mills, rotating drum grinders, or other types of grinders.

Some power stations burn fuel oil rather than coal. The oil must kept warm (above its pour point) in the fuel oil storage tanks to prevent the oil from congealing and becoming unpumpable. The oil is usually heated to about 100 °C before being pumped through the furnace fuel oil spray nozzles.

Boilers in some power stations use processed natural gas as their main fuel. Other power stations may use processed natural gas as auxiliary fuel in the event that their main fuel supply (coal or oil) is interrupted. In such cases, separate gas burners are provided on the boiler furnaces.

Barring gear

Barring gear (or "turning gear") is the mechanism provided to rotate the turbine generator shaft at a very low speed after unit stoppages. Once the unit is "tripped" (i.e., the steam inlet valve is closed), the turbine coasts down towards standstill. When it stops completely, there is a tendency for the turbine shaft to deflect or bend if allowed to remain in one position too long. This is because the heat inside the turbine casing tends to concentrate in the top half of the casing, making the top half portion of the shaft hotter than the bottom half. The shaft therefore could warp or bend by millionths of inches.

This small shaft deflection, only detectable by eccentricity meters, would be enough to cause damaging vibrations to the entire steam turbine generator unit when it is restarted. The shaft is therefore automatically turned at low speed (about one percent rated speed) by the barring gear until it has cooled sufficiently to permit a complete stop.

Oil system

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator. It supplies the hydraulic oil system required for steam turbine's main inlet steam stop valve, the governing control valves, the bearing and seal oil systems, the relevant hydraulic relays and other mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takes over the functions of the auxiliary system.

Generator cooling

While small generators may be cooled by air drawn through filters at the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses. This system requires special handling during start-up, with air in the generator enclosure first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in the air.

The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress, and up to about two atmospheres pressure to improve heat transfer efficiency. The hydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage to atmosphere.

The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV, an insulating barrier such as Teflon is used to interconnect the water line and the generator high-voltage windings. Demineralized water of low conductivity is used.

Generator high-voltage system

The generator voltage for modern utility-connected generators ranges from 11 kV in smaller units to 30 kV in larger units. The generator high-voltage leads are normally large aluminium channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminium bus ducts and are supported on suitable insulators. The generator high-voltage leads are connected to step-up transformers for connecting to a high-voltage electrical substation (usually in the range of 115 kV to 765 kV) for further transmission by the local power grid.

The necessary protection and metering devices are included for the high-voltage leads. Thus, the steam turbine generator and the transformer form one unit. Smaller units may share a common generator step-up transformer with individual circuit breakers to connect the generators to a common bus.

Monitoring and alarm system

Most of the power station operational controls are automatic. However, at times, manual intervention may be required. Thus, the plant is provided with monitors and alarm systems that alert the plant operators when certain operating parameters are seriously deviating from their normal range.

Battery-supplied emergency lighting and communication

A central battery system consisting of lead–acid cell units is provided to supply emergency electric power, when needed, to essential items such as the power station's control systems, communication systems, generator hydrogen seal system, turbine lube oil pumps, and emergency lighting. This is essential for a safe, damage-free shutdown of the units in an emergency situation.

Circulating water system

To dissipate the thermal load of main turbine exhaust steam, condensate from gland steam condenser, and condensate from Low Pressure Heater by providing a continuous supply of cooling water to the main condenser thereby leading to condensation.

The consumption of cooling water by inland power stations is estimated to reduce power availability for the majority of thermal power stations by 2040–2069.

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Thursday, February 10, 2022

Christian eschatology

History

Christian eschatological views

Preterism

Historicism

Futurism

Idealism

Comparison of Futurist, Preterist and Historicist beliefs

Preterism v. Historicism

Historicism v. Futurism

Major theological positions

Premillennialism

Pretribulation rapture

Midtribulation rapture

Posttribulation rapture

Postmillennialism

Amillennialism

Death and the afterlife

Jewish beliefs at the time of Jesus

The intermediate state

Purgatory

The Great Tribulation

The end comes at an unexpected time

The abomination of desolation

The Prophecy of Seventy Weeks

Rapture

The Second Coming

Signs of Christ's return

Last Day Counterfeits

The Marriage of the Lamb

Resurrection of the dead

Doctrine of the resurrection predates Christianity

Two resurrections

The resurrection body

Other views

Armageddon

The Millennium

The End of the World and the Last Judgment

Satan released

The Last Judgment

New Heaven and New Earth

New Jerusalem

Description

The Tree of Life

Thermal power station

Types of thermal energy

History

Thermal power generation efficiency

Electricity cost

Boiler and steam cycle

Feed water heating

Boiler operation

Boiler furnace and steam drum

Superheater

Steam condensing

Reheater

Air path

Steam turbine generator

Steam turbine

Turbo generator

Stack gas path and cleanup

Auxiliary systems

Boiler make-up water treatment plant and storage

Fuel preparation system

Barring gear

Oil system

Generator cooling

Generator high-voltage system

Monitoring and alarm system

Battery-supplied emergency lighting and communication

Circulating water system

Operator (computer programming)