https://en.wikipedia.org/wiki/Steam_reforming Illustrating inputs and outputs of steam reforming of natural gas, a process to produce hydrogen and CO2 greenhouse gas that may be captured with CCS
Steam reforming or steam methane reforming (SMR) is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The reaction is represented by this equilibrium:
The reaction is strongly endothermic (ΔHSR = 206 kJ/mol).
Hydrogen produced by steam reforming is termed 'grey hydrogen'
when the waste carbon monoxide is released to the atmosphere and 'blue
hydrogen' when the carbon monoxide is (mostly) captured and stored
geologically - see carbon capture and storage. Zero carbon 'green' hydrogen is produced by thermochemical water splitting, using solar thermal, low- or zero-carbon electricity or waste heat, or electrolysis, using low- or zero-carbon electricity. Zero carbon emissions 'turquoise' hydrogen is produced by one-step methane pyrolysis of natural gas.
Steam reforming reaction kinetics, in particular using nickel-alumina catalysts, have been studied in detail since the 1950s.
Pre-reforming
Depiction of the general process flow of a typical steam reforming plant. (PSA = Pressure swing adsorption, NG = Natural gas)
The purpose of pre-reforming is to break down higher hydrocarbons such as propane, butane or naphtha into methane (CH4), which allows for more efficient reforming downstream.
Steam reforming
The name-giving reaction is the steam reforming (SR) reaction and is expressed by the equation:
Via the water-gas shift reaction (WGSR), additional hydrogen is released by reaction of water with the carbon monoxide generated according to equation [1]:
Some additional reactions occurring within steam reforming processes have been studied. Commonly the direct steam reforming (DSR) reaction is also included:
As these reactions by themselves are highly endothermic (apart
from WGSR, which is mildly exothermic), a large amount of heat needs to
be added to the reactor to keep a constant temperature. Optimal SMR
reactor operating conditions lie within a temperature range of 800 °C to
900 °C at medium pressures of 20-30 bar.
High excess of steam is required, expressed by the (molar)
steam-to-carbon (S/C) ratio. Typical S/C ratio values lie within the
range 2.5:1 - 3:1.
Industrial practice
Global Hydrogen Production by Method
The reaction is conducted in multitubular packed bed reactors, a subtype of the plug flow reactor category. These reactors consist of an array of long and narrow tubes which are situated within the combustion chamber of a large industrial furnace,
providing the necessary energy to keep the reactor at a constant
temperature during operation. Furnace designs vary, depending on the
burner configuration they are typically categorized into: top-fired,
bottom-fired, and side-fired. A notable design is the Foster-Wheeler terrace wall reformer.
Inside the tubes, a mixture of steam and methane are put into contact with a nickel catalyst. Catalysts with high surface-area-to-volume ratio are preferred because of diffusion limitations due to high operating temperature. Examples of catalyst shapes used are spoked wheels, gear wheels, and rings with holes (see:Raschig rings). Additionally, these shapes have a low pressure drop which is advantageous for this application.
Steam reforming of natural gas is 65–75% efficient.
The United States produces 9–10 million tons of hydrogen per year, mostly with steam reforming of natural gas. The worldwide ammonia production, using hydrogen derived from steam reforming, was 144 million tonnes in 2018. The energy consumption has been reduced from 100 GJ/tonne of ammonia in 1920 to 27 GJ by 2019.
Globally, almost 50% of hydrogen is produced via steam reforming. It is currently the least expensive method for hydrogen production available in terms of its capital cost.
In an effort to decarbonise hydrogen production, carbon capture and storage (CCS) methods are being implemented within the industry, which have the potential to remove up to 90% of CO2 produced from the process.
Despite this, implementation of this technology remains problematic,
costly, and increases the price of the produced hydrogen significantly.
Autothermal reforming
Autothermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane to form syngas.
The reaction takes place in a single chamber where the methane is
partially oxidized. The reaction is exothermic. When the ATR uses carbon
dioxide, the H2:CO ratio produced is 1:1; when the ATR uses steam, the H2:CO
ratio produced is 2.5:1. The outlet temperature of the syngas is
between 950–1100 °C and outlet pressure can be as high as 100 bar.
In addition to reactions [1] – [3], ATR introduces the following reaction:
The main difference between SMR and ATR is that SMR only uses air
for combustion as a heat source to create steam, while ATR uses
purified oxygen. The advantage of ATR is that the H2:CO ratio
can be varied, which can be useful for producing specialty products.
Due to the exothermic nature of some of the additional reactions
occurring within ATR, the process can essentially be performed at a net
enthalpy of zero (ΔH = 0).
Partial oxidation (POX) occurs when a sub-stoichiometric fuel-air
mixture is partially combusted in a reformer creating hydrogen-rich
syngas. POX is typically much faster than steam reforming and requires a
smaller reactor vessel. POX produces less hydrogen per unit of the
input fuel than steam reforming of the same fuel.
Steam reforming at small scale
The
capital cost of steam reforming plants is considered prohibitive for
small to medium size applications. The costs for these elaborate
facilities do not scale down well. Conventional steam reforming plants
operate at pressures between 200 and 600 psi (14–40 bar) with outlet
temperatures in the range of 815 to 925 °C.
For combustion engines
Flared gas and vented volatile organic compounds
(VOCs) are known problems in the offshore industry and in the on-shore
oil and gas industry, since both release greenhouse gases into the
atmosphere. Reforming for combustion engines utilizes steam reforming technology for converting waste gases into a source of energy.
Reforming for combustion engines is based on steam reforming, where non-methane hydrocarbons (NMHCs) of low quality gases are converted to synthesis gas (H2 + CO) and finally to methane (CH4), carbon dioxide (CO2) and hydrogen (H2) - thereby improving the fuel gas quality (methane number).
For fuel cells
There is also interest in the development of much smaller units based on similar technology to produce hydrogen as a feedstock for fuel cells. Small-scale steam reforming units to supply fuel cells are currently the subject of research and development, typically involving the reforming of methanol, but other fuels are also being considered such as propane, gasoline, autogas, diesel fuel, and ethanol.
Disadvantages
The
reformer– the fuel-cell system is still being researched but in the
near term, systems would continue to run on existing fuels, such as
natural gas or gasoline or diesel. However, there is an active debate
about whether using these fuels to make hydrogen is beneficial while
global warming is an issue. Fossil fuel
reforming does not eliminate carbon dioxide release into the atmosphere
but reduces the carbon dioxide emissions and nearly eliminates carbon
monoxide emissions as compared to the burning of conventional fuels due
to increased efficiency and fuel cell characteristics. However, by turning the release of carbon dioxide into a point source rather than distributed release, carbon capture and storage
becomes a possibility, which would prevent the release of carbon
dioxide to the atmosphere, while adding to the cost of the process.
The cost of hydrogen production by reforming fossil fuels
depends on the scale at which it is done, the capital cost of the
reformer, and the efficiency of the unit, so that whilst it may cost
only a few dollars per kilogram of hydrogen at an industrial scale, it
could be more expensive at the smaller scale needed for fuel cells.
Challenges with reformers supplying fuel cells
There are several challenges associated with this technology:
The reforming reaction takes place at high temperatures, making
it slow to start up and requiring costly high-temperature materials.
Sulfur compounds in the fuel will poison certain catalysts, making it difficult to run this type of system from ordinary gasoline. Some new technologies have overcome this challenge with sulfur-tolerant catalysts.
Coking
would be another cause of catalyst deactivation during steam reforming.
High reaction temperatures, low steam-to-carbon ratio (S/C), and the
complex nature of sulfur-containing commercial hydrocarbon fuels make
coking especially favorable. Olefins, typically ethylene, and aromatics
are well-known carbon-precursors, hence their formation must be reduced
during steam reforming. Additionally, catalysts with lower acidity were
reported to be less prone to coking by suppressing dehydrogenation
reactions. H2S, the main product in the reforming of organic
sulfur, can bind to all transition metal catalysts to form metal–sulfur
bonds and subsequently reduce catalyst activity by inhibiting the chemisorption
of reforming reactants. Meanwhile, the adsorbed sulfur species
increases the catalyst acidity, and hence indirectly promotes coking.
Precious metal catalysts such as Rh and Pt have lower tendencies to form
bulk sulfides than other metal catalysts such as Ni. Rh and Pt are less
prone to sulfur poisoning by only chemisorbing sulfur rather than
forming metal sulfides.
Low temperature polymer fuel cell membranes can be poisoned by the carbon monoxide (CO) produced by the reactor, making it necessary to include complex CO-removal systems. Solid oxide fuel cells (SOFC) and molten carbonate fuel cells
(MCFC) do not have this problem, but operate at higher temperatures,
slowing start-up time, and requiring costly materials and bulky
insulation.
Advocates of autonomous building describe advantages that include reduced environmental impacts, increased security, and lower costs of ownership. Some cited advantages satisfy tenets of green building, not independence per se (see below). Off-grid buildings often rely very little on civil services
and are therefore safer and more comfortable during civil disaster or
military attacks. For example, Off-grid buildings would not lose power
or water if public supplies were compromised.
As of 2018, most research and published articles concerning autonomous building focus on residential homes.
It is quite possible in all parts of Australia to
construct a 'house with no bills', which would be comfortable without
heating and cooling, which would make its own electricity, collect its
own water and deal with its own waste...These houses can be built now,
using off-the-shelf techniques. It is possible to build a "house with no
bills" for the same price as a conventional house, but it would be
(25%) smaller.
History
In the 1970s, groups of activists and engineers were inspired by the warnings of imminent resource depletion and starvation. In the United States a group calling themselves the New Alchemists were famous for the depth of research effort placed in their projects. Using conventional construction techniques, they designed a series of "bioshelter" projects, the most famous of which was The Arkbioshelter community for Prince Edward Island.
They published the plans for all of these, with detailed design
calculations and blueprints. The Ark used wind-based water pumping and
electricity and was self-contained in food production. It had living
quarters for people, fish tanks raising tilapia for protein, a greenhouse watered with fish water, and a closed-loop sewage reclamation system that recycled human waste
into sanitized fertilizer for the fish tanks. As of January 2010, the
successor organization to the New Alchemists has a web page up as the
"New Alchemy Institute". The PEI Ark has been abandoned and partially renovated several times.
The 1990s saw the development of Earthships,
similar in intent to the Ark project, but organized as a for-profit
venture, with construction details published in a series of 3 books by Mike Reynolds. The building material is tires filled with earth. This makes a wall that has large amounts of thermal mass (see earth sheltering). Berms
are placed on exposed surfaces to further increase the house's
temperature stability. The water system starts with rain water,
processed for drinking, then washing, then plant watering, then toilet
flushing, and finally black water is recycled again for more plant watering. The cisterns are placed and used as thermal masses. Power, including electricity, heat and water heating, is from solar power.
1990s architects such as William McDonough and Ken Yeang
applied environmentally responsible building design to large commercial
buildings, such as office buildings, making them largely
self-sufficient in energy production. One major bank building (ING'sAmsterdam headquarters) in the Netherlands was constructed to be autonomous and artistic as well.
Advantages
As
an architect or engineer becomes more concerned with the disadvantages
of transportation networks, and dependence on distant resources, their
designs tend to include more autonomous elements. The historic path to
autonomy was a concern for secure sources of heat, power, water and
food. A nearly parallel path toward autonomy has been to start with a
concern for environmental impacts, which cause disadvantages.
Autonomous buildings can increase security and reduce
environmental impacts by using on-site resources (such as sunlight and
rain) that would otherwise be wasted. Autonomy often dramatically
reduces the costs and impacts of networks that serve the building,
because autonomy short-circuits the multiplying inefficiencies of
collecting and transporting resources. Other impacted resources, such as
oil reserves and the retention of the local watershed, can often be
cheaply conserved by thoughtful designs.
Autonomous buildings are usually energy-efficient
in operation, and therefore cost-efficient, for the obvious reason that
smaller energy needs are easier to satisfy off-grid. But they may
substitute energy production or other techniques to avoid diminishing
returns in extreme conservation.
An autonomous structure is not always environmentally friendly.
The goal of independence from support systems is associated with, but
not identical to, other goals of environmentally responsible green building. However, autonomous buildings also usually include some degree of sustainability through the use of renewable energy and other renewable resources, producing no more greenhouse gases than they consume, and other measures.
Disadvantages
First and fundamentally, independence is a matter of degree. For
example, eliminating dependence on the electrical grid is relatively
easy. In contrast, running an efficient, reliable food source can be a
chore.
Living within an autonomous shelter may also require sacrifices
in lifestyle or social opportunities. Even the most comfortable and
technologically advanced autonomous homes could require alterations of
residents' behavior. Some may not welcome the extra chores. The Vails
described some clients' experiences as inconvenient, irritating,
isolating, or even as an unwanted full-time job. A well-designed
building can reduce this issue, but usually at the expense of reduced
autonomy.
An autonomous house must be custom-built (or extensively retrofitted) to suit the climate
and location. Passive solar techniques, alternative toilet and sewage
systems, thermal massing designs, basement battery systems, efficient
windowing, and the array of other design tactics require some degree of
non-standard construction, added expense, ongoing experimentation and maintenance, and also have an effect on the psychology of the space.
Systems
This
section includes some minimal descriptions of methods, to give some feel
for such a building's practicality, provide indexes to further
information, and give a sense of modern trends.
Water
A domestic rainwater harvesting systemA concrete under-floor cistern being installed.
There are many methods of collecting and conserving water. Use reduction is cost-effective.
Greywater systems reuse drained wash water to flush toilets or to water lawns and gardens.
Greywater systems can halve the water use of most residential
buildings; however, they require the purchase of a sump, greywater
pressurization pump, and secondary plumbing. Some builders are installing waterless urinals and even composting toilets that eliminate water usage in sewage disposal.
The classic solution with minimal life-style changes is using a well. Once drilled,
a well-foot requires substantial power. However, advanced well-foots
can reduce power usage by twofold or more from older models. Well water
can be contaminated in some areas. The Sono arsenic filter eliminates unhealthy arsenic in well water.
However drilling a well is an uncertain activity, with aquifers depleted in some areas. It can also be expensive.
In regions with sufficient rainfall, it is often more economical to design a building to use rainwater harvesting, with supplementary water deliveries in a drought.
Rain water makes excellent soft washwater, but needs antibacterial
treatment. If used for drinking, mineral supplements or mineralization
is necessary.
Most desert and temperate climates get at least 250 millimetres (9.8 in) of rain per year. This means that a typical one-story house with a greywater system can supply its year-round water needs from its roof alone. In the driest areas, it might require a cistern
of 30 cubic metres (7,900 US gal). Many areas average 13 millimetres
(0.51 in) of rain per week, and these can use a cistern as small as 10
cubic metres (2,600 US gal).
In many areas, it is difficult to keep a roof clean enough for drinking. To reduce dirt and bad tastes, systems use a metal collecting-roof and a
"roof cleaner" tank that diverts the first 40 liters. Cistern water is
usually chlorinated, though reverse osmosis systems provide even better quality drinking water.
In the classic Roman house ("Domus"), household water was
provided from a cistern (the "impluvium"), which was a decorative
feature of the atrium, the house's main public space. It was fed by
downspout tiles from the inward-facing roof-opening (the "compluvium").
Often water lilies were grown in it to purify the water. Wealthy
households often supplemented the rain with a small fountain fed from a
city's cistern. The impluvium always had an overflow drain so it could
not flood the house.
Modern cisterns are usually large plastic tanks. Gravity tanks on
short towers are reliable, so pump repairs are less urgent. The least
expensive bulk cistern is a fenced pond or pool at ground level.
Reducing autonomy reduces the size and expense of cisterns. Many
autonomous homes can reduce water use below 10 US gallons (38 L) per
person per day, so that in a drought
a month of water can be delivered inexpensively via truck.
Self-delivery is often possible by installing fabric water tanks that
fit the bed of a pick-up truck.
It can be convenient to use the cistern as a heat sink or trap for a heat pump or air conditioning system; however this can make cold drinking water warm, and in drier years may decrease the efficiency of the HVAC system.
Solar stills can efficiently produce drinking water from ditch water or cistern water, especially high-efficiency multiple effect humidification designs, which separate the evaporator(s) and condenser(s).
New technologies, like reverse osmosis can create unlimited amounts of pure water from polluted water, ocean water, and even from humid air. Watermakers are available for yachts that convert seawater and electricity into potable water and brine. Atmospheric water generators extract moisture from dry desert air and filter it to pure water.
Composting toilets use bacteria to decompose human feces
into useful, odourless, sanitary compost. The process is sanitary
because soil bacteria eat the human pathogens as well as most of the
mass of the waste. Nevertheless, most health authorities forbid direct
use of "humanure" for growing food.
The risk is microbial and viral contamination, as well as heavy metal
toxicity. In a dry composting toilet, the waste is evaporated or
digested to gas (mostly carbon dioxide) and vented, so a toilet produces
only a few pounds of compost every six months. To control the odor,
modern toilets use a small fan to keep the toilet under negative
pressure, and exhaust the gasses to a vent pipe.
Some home sewage treatment systems use biological treatment,
usually beds of plants and aquaria, that absorb nutrients and bacteria
and convert greywater and sewage to clear water. This odor- and
color-free reclaimed water
can be used to flush toilets and water outside plants. When tested, it
approaches standards for potable water. In climates that freeze, the
plants and aquaria need to be kept in a small greenhouse space. Good
systems need about as much care as a large aquarium.
Electric incinerating toilets
turn excrement into a small amount of ash. They are cool to the touch,
have no water and no pipes, and require an air vent in a wall. They are
used in remote areas where use of septic tanks is limited, usually to
reduce nutrient loads in lakes.
NASA's bioreactor
is an extremely advanced biological sewage system. It can turn sewage
into air and water through microbial action. NASA plans to use it in the
crewed Mars mission. Another method is NASA's urine-to-water distillation system.
A big disadvantage of complex biological sewage treatment systems
is that if the house is empty, the sewage system biota may starve to
death.
Waste
Sewage handling is essential for public health. Many diseases are transmitted by poorly functioning sewage systems.
The standard system is a tiled leach field combined with a septic tank. The basic idea is to provide a small system with primary sewage treatment. Sludge settles to the bottom of the septic tank, is partially reduced by anaerobic digestion,
and fluid is dispersed in the leach field. The leach field is usually
under a yard growing grass. Septic tanks can operate entirely by
gravity, and if well managed, are reasonably safe.
Septic tanks have to be pumped periodically by a vacuum truck
to eliminate non reducing solids. Failure to pump a septic tank can
cause overflow that damages the leach field, and contaminates ground
water. Septic tanks may also require some lifestyle changes, such as not
using garbage disposals, minimizing fluids flushed into the tank, and
minimizing non-digestible solids flushed into the tank. For example,
septic safe toilet paper is recommended.
However, septic tanks remain popular because they permit standard plumbing fixtures, and require few or no lifestyle sacrifices.
Composting or packaging toilets
make it economical and sanitary to throw away sewage as part of the
normal garbage collection service. They also reduce water use by half,
and eliminate the difficulty and expense of septic tanks. However, they
require the local landfill to use sanitary practices.
Incinerator systems are quite practical. The ashes are
biologically safe, and less than 1/10 the volume of the original waste,
but like all incinerator waste, are usually classified as hazardous
waste.
Traditional methods of sewage handling include pit toilets, latrines, and outhouses. These can be safe, inexpensive and practical. They are still used in many regions.
Storm drains
Drainage
systems are a crucial compromise between human habitability and a
secure, sustainable watershed. Paved areas and lawns or turf do not
allow much precipitation to filter through the ground to recharge
aquifers. They can cause flooding and damage in neighbourhoods, as the
water flows over the surface towards a low point.
Typically, elaborate, capital-intensive storm sewer networks are engineered to deal with stormwater. In some cities, such as the Victorian era London sewers or much of the old City of Toronto,
the storm water system is combined with the sanitary sewer system. In
the event of heavy precipitation, the load on the sewage treatment plant
at the end of the pipe becomes too great to handle and raw sewage is
dumped into holding tanks, and sometimes into surface water.
Autonomous buildings can address precipitation in a number of ways. If a water-absorbing swale for each yard is combined with permeable concrete
streets, storm drains can be omitted from the neighbourhood. This can
save more than $800 per house (1970s) by eliminating storm drains.
One way to use the savings is to purchase larger lots, which permits
more amenities at the same cost. Permeable concrete is an established
product in warm climates, and in development for freezing climates. In
freezing climates, the elimination of storm drains can often still pay
for enough land to construct swales (shallow water collecting ditches)
or water impeding berms instead. This plan provides more land for
homeowners and can offer more interesting topography for landscaping.
Additionally, a green roof
captures precipitation and uses the water to grow plants. It can be
built into a new building or used to replace an existing roof.
Electricity
Wind turbine on the roof in Manchester, UKA PV-solar system
Since electricity is an expensive utility, the first step towards autonomy is to design a house and lifestyle to reduce demand. LED lights, laptop computers and gas-powered refrigerators save electricity, although gas-powered refrigerators are not very efficient.
There are also superefficient electric refrigerators, such as those
produced by the Sun Frost company, some of which use only about half as
much electricity as a mass-market energy star-rated refrigerator.
Using a solar roof, solar cells
can provide electric power. Solar roofs can be more cost-effective than
retrofitted solar power, because buildings need roofs anyway. Modern
solar cells last about 40 years, which makes them a reasonable
investment in some areas. At a sufficient angle, solar cells are cleaned
by run-off rain water and therefore have almost no life-style impact.
Many areas have long winter nights or dark cloudy days. In these
climates, a solar installation might not pay for itself or large battery
storage systems are necessary to achieve electric self-sufficiency. In stormy or windy climates, wind turbines can replace or significantly supplement solar power. The average autonomous house needs only one small wind turbine,
5 metres or less in diameter. On a 30-metre (100-foot) tower, this
turbine can provide enough power to supplement solar power on cloudy
days. Commercially available wind turbines use sealed, one-moving-part
AC generators and passive, self-feathering blades for years of operation
without service.
The main advantage of wind power
is that larger wind turbines have a lower per-watt cost than solar
cells, provided there is wind. Turbine location is critical: just as
some locations lack sun for solar cells, many areas lack enough wind to
make a turbine pay for itself. In the Great Plains
of the United States, a 10-metre (33-foot) turbine can supply enough
energy to heat and cool a well-built all-electric house. Economic use in
other areas requires research, and possibly a site survey.
Some sites have access to a stream with a change in elevation. These sites can use small hydropower systems
to generate electricity. If the difference in elevation is above 30
metres (100 feet), and the stream runs in all seasons, this can provide
continuous power with a small, inexpensive installation. Lower changes
of elevation require larger installations or dams, and can be less
efficient. Clogging at the turbine intake can be a practical problem.
The usual solution is a small pool and waterfall (a penstock) to carry
away floating debris. Another solution is to utilize a turbine that
resists debris, such as a Gorlov helical turbine or Ossberger turbine.
During times of low demand, excess power can be stored in
batteries for future use. However, batteries need to be replaced every
few years. In many areas, battery expenses can be eliminated by
attaching the building to the electric power grid and operating the power system with net metering. Utility permission is required, but such cooperative generation is legally mandated in some areas (for example, California).
A grid-based building is less autonomous, but more economical and
sustainable with fewer lifestyle sacrifices. In rural areas the grid's
cost and impacts can be reduced by using single-wire earth return systems (for example, the MALT-system).
In areas that lack access to the grid, battery size can be
reduced with a generator to recharge the batteries during energy
droughts such as extended fogs. Auxiliary generators are usually run
from propane, natural gas, or sometimes diesel.
An hour of charging usually provides a day of operation. Modern
residential chargers permit the user to set the charging times, so the
generator is quiet at night. Some generators automatically test
themselves once per week.
Recent advances in passively stable magnetic bearings may someday permit inexpensive storage of power in a flywheel in a vacuum. Research groups like Canada's Ballard Power Systems are also working to develop a "regenerative fuel cell", a device that can generate hydrogen and oxygen when power is available, and combine these efficiently when power is needed.
Earth batteries tap electric currents in the earth called telluric current. They can be installed anywhere in the ground. They provide only low voltages and current. They were used to power telegraphs in the 19th century. As appliance efficiencies increase, they may become practical.
Microbial fuel cells and thermoelectric generators
allow electricity to be generated from biomass. The plant can be dried,
chopped and converted or burned as a whole, or it can be left alive so
that waste saps from the plant can be converted by bacteria.
Heating
Schematic of an active solar heating system
Most autonomous buildings are designed to use insulation, thermal
mass and passive solar heating and cooling. Examples of these are trombe walls and other technologies as skylights.
Passive solar heating
can heat most buildings in even the mild and chilly climates. In colder
climates, extra construction costs can be as little as 15% more than
new, conventional buildings. In warm climates, those having less than
two weeks of frosty nights per year, there is no cost impact.
The basic requirement for passive solar heating is that the solar collectors must face the prevailing sunlight (south in the Northern Hemisphere, north in the Southern Hemisphere), and the building must incorporate thermal mass to keep it warm in the night.
A recent, somewhat experimental solar heating system "Annualized geo solar heating" is practical even in regions that get little or no sunlight in winter. It uses the ground beneath a building for thermal mass. Precipitation can carry away the heat, so the ground is shielded with 6 m
skirts of plastic insulation. The thermal mass of this system is
sufficiently inexpensive and large that it can store enough summer heat
to warm a building for the whole winter, and enough winter cold to cool
the building in summer.
In annualized geo solar systems, the solar collector is often
separate from (and hotter or colder than) the living space. The building
may actually be constructed from insulation, for example, straw-bale construction.
Some buildings have been aerodynamically designed so that convection
via ducts and interior spaces eliminates any need for electric fans.
A more modest "daily solar" design is practical. For example, for about a 15% premium in building costs, the Passivhaus
building codes in Europe use high performance insulating windows, R-30
insulation, HRV ventilation, and a small thermal mass. With modest
changes in the building's position, modern krypton- or argon-insulated
windows permit normal-looking windows to provide passive solar heat
without compromising insulation or structural strength. If a small
heater is available for the coldest nights, a slab or basement cistern
can inexpensively provide the required thermal mass.
Passivhaus building codes, in particular, bring unusually good interior
air quality, because the buildings change the air several times per
hour, passing it through a heat exchanger to keep heat inside.
In all systems, a small supplementary heater increases personal
security and reduces lifestyle impacts for a small reduction of
autonomy. The two most popular heaters for ultra-high-efficiency houses
are a small heat pump, which also provides air conditioning, or a central hydronic (radiator) air heater with water recirculating from the water heater. Passivhaus designs usually integrate the heater with the ventilation system.
Earth sheltering and windbreaks
can also reduce the absolute amount of heat needed by a building.
Several feet below the earth, temperature ranges from 4 °C (39 °F) in
North Dakota to 26 °C (79 °F), in Southern Florida. Wind breaks reduce the amount of heat carried away from a building.
Rounded, aerodynamic buildings also lose less heat.
Houses designed to cope with interruptions in civil services generally incorporate a wood stove, or heat and power from diesel fuel or bottled gas, regardless of their other heating mechanisms.
Electric heaters and electric stoves may provide pollution-free
heat (depending on the power source), but use large amounts of
electricity. If enough electricity is provided by solar panels, wind
turbines, or other means, then electric heaters and stoves become a
practical autonomous design.
Hot water heat recycling
units recover heat from water drain lines. They increase a building's
autonomy by decreasing the heat or fuel used to heat water. They are
attractive because they have no lifestyle changes.
Current practical, comfortable domestic water-heating systems combine a solar preheating system with a thermostatic gas-powered flow-through heater,
so that the temperature of the water is consistent, and the amount is
unlimited. This reduces life-style impacts at some cost in autonomy.
Solar water heaters
can save large amounts of fuel. Also, small changes in lifestyle, such
as doing laundry, dishes and bathing on sunny days, can greatly increase
their efficiency. Pure solar heaters are especially useful for
laundries, swimming pools and external baths, because these can be
scheduled for use on sunny days.
The basic trick in a solar water heating system is to use a well-insulated holding tank. Some systems are vacuum- insulated, acting something like large thermos
bottles. The tank is filled with hot water on sunny days, and made
available at all times. Unlike a conventional tank water heater, the
tank is filled only when there is sunlight. Good storage makes a
smaller, higher-technology collector feasible. Such collectors can use
relatively exotic technologies, such as vacuum insulation, and
reflective concentration of sunlight.
Cogeneration systems produce hot water from waste heat. They usually get the heat from the exhaust of a generator or fuel cell.
Heat recycling, cogeneration
and solar pre-heating can save 50–75% of the gas otherwise used. Also,
some combinations provide redundant reliability by having several
sources of heat.
Some authorities advocate replacing bottled gas or natural gas with biogas.
However, this is usually impractical unless live-stock are on-site. The
wastes of a single family are usually insufficient to produce enough methane for anything more than small amounts of cooking.
Cooling
Annualized
geo solar buildings often have buried, sloped water-tight skirts of
insulation that extend 6 metres (20 ft) from the foundations, to prevent
heat leakage between the earth used as thermal mass, and the surface.
Less dramatic improvements are possible. Windows can be shaded in
summer. Eaves can be overhung to provide the necessary shade. These
also shade the walls of the house, reducing cooling costs.
Another trick is to cool the building's thermal mass at night, perhaps with a whole-house fan
and then cool the building from the thermal mass during the day. It
helps to be able to route cold air from a sky-facing radiator (perhaps
an air heating solar collector with an alternate purpose) or evaporative
cooler directly through the thermal mass. On clear nights, even in
tropical areas, sky-facing radiators can cool below freezing.
If a circular building is aerodynamically smooth, and cooler than
the ground, it can be passively cooled by the "dome effect." Many
installations have reported that a reflective or light-colored dome
induces a local vertical heat-driven vortex that sucks cooler overhead
air downward into a dome if the dome is vented properly (a single
overhead vent, and peripheral vents). Some people have reported a
temperature differential as high as 8 °C (15 °F) between the inside of the dome and the outside. Buckminster Fuller discovered this effect with a simple house design adapted from a grain silo, and adapted his Dymaxion house and geodesic domes to use it.
Refrigerators and air conditioners operating from the waste heat
of a diesel engine exhaust, heater flue or solar collector are entering
use. These use the same principles as a gas refrigerator. Normally, the
heat from a flue powers an "absorptive chiller". The cold water or brine from the chiller is used to cool air or a refrigerated space.
Cogeneration is popular in new commercial buildings. In current cogeneration systems small gas turbines or stirling engines powered from natural gas produce electricity and their exhaust drives an absorptive chiller.
A truck trailer refrigerator operating from the waste heat of a tractor's diesel exhaust was demonstrated by NRG Solutions, Inc. NRG developed a hydronic ammonia
gas heat exchanger and vaporizer, the two essential new, not
commercially available components of a waste heat driven refrigerator.
A similar scheme (multiphase cooling) can be by a multistage
evaporative cooler. The air is passed through a spray of salt solution
to dehumidify it, then through a spray of water solution to cool it,
then another salt solution to dehumidify it again. The brine has to be
regenerated, and that can be done economically with a low-temperature
solar still. Multiphase evaporative coolers can lower the air's
temperature by 50 °F (28 °C), and still control humidity. If the brine
regenerator uses high heat, it also partially sterilises to the air.
If enough electric power is available, cooling can be provided by conventional air conditioning using a heat pump.
Food production
Food production has often been included in historic autonomous projects to provide security.
Skilled, intensive gardening can support an adult from as little as 100 square meters of land per person,possibly requiring the use of organic farming and aeroponics. Some proven intensive, low-effort food-production systems include urban gardening (indoors and outdoors). Indoor cultivation may be set up using hydroponics, while outdoor cultivation may be done using permaculture, forest gardening, no-till farming, and do nothing farming.
Greenhouses are also sometimes included. Sometimes they are also outfitted with irrigation systems or heat sink
systems which can respectively irrigate the plants or help to store
energy from the sun and redistribute it at night (when the greenhouses
starts to cool down).
A hydrogen station is a storage or filling station for hydrogen fuel. The hydrogen is dispensed by weight. There are two filling pressures in common use: H70 or 700 bar, and the older standard H35 or 350 bar. As of 2021, around 550 filling stations were available worldwide.
Delivery methods
Hydrogen
fueling stations can be divided into off-site stations, where hydrogen
is delivered by truck or pipeline, and on-site stations that produce and
compress hydrogen for the vehicles.
As of 2019, 98% of hydrogen is produced by steam methane reforming, which emits carbon dioxide. The bulk of hydrogen is also transported to fueling stations in trucks, so pollution is also emitted in its transportation.
Volatility
Hydrogen fuel is hazardous because of its low ignition energy, high combustion energy, and because it easily leaks from tanks. Explosions at hydrogen filling stations have been reported.
Supply
Hydrogen
fuelling stations generally receive deliveries by truck from hydrogen
suppliers. An interruption at a hydrogen supply facility can shut down
multiple hydrogen fuelling stations due to an interruption of the supply
of hydrogen.
There are far fewer Hydrogen filling stations than gasoline fuel stations, which in the US alone numbered 168,000 in 2004. Replacing the US gasoline infrastructure with hydrogen fuel infrastructure is estimated to cost a half trillion U.S. dollars. A hydrogen fueling station costs between $1 million and $4 million to build.
In comparison, battery electric vehicles can charge at home or at
public chargers. As of 2023, there are more than 60,000 public charging
stations in the United States, with more than 160,000 outlets.
A public Level 2 charger, which comprise the majority of public
chargers in the US, costs about $2,000, and DC fast chargers, of which
there are more than 30,000 in the U.S., generally cost between $100,000 and $250,000, although Tesla superchargers are estimated to cost approximately $43,000.
Freezing of the nozzle
During
refueling, the flow of cold hydrogen can cause frost to form on the
dispenser nozzle, sometimes leading to the nozzle becoming frozen to the
vehicle being refueled.
Locations
Consulting firm Ludwig-Bölkow-Systemtechnik tracks global hydrogen filling stations and publishes a map.
Asia
In 2019, there were 178 publicly available hydrogen fuel stations in operation.
As of May 2023, there are 167 publicly available hydrogen fuel
stations in operation, and there are projected to be 181 locations by
the end of this fiscal year.
Japan built hydrogen filling stations under the JHFC project from
2002 to 2010 to test various technologies of hydrogen generation. By the end of 2012 there were 17 hydrogen stations. In 2021, there were 137 publicly available hydrogen fuel stations in operation.
China
By the end of 2020, China had built 118 hydrogen refueling stations.
South Korea
In 2019, there were 33 publicly available hydrogen fuel stations in operation.
As of 2018, approximately 18,000 fuel cell electric vehicles (FCEV) had been produced in Korea (domestic demand: 9,000 vehicles).
Europe
In 2019, there were 177 stations in Europe.
Germany
As of June 2020, there were 84 publicly available hydrogen fuel stations in operation.
France
As of June 2020, there were 5 publicly available hydrogen fuel stations in operation.
Iceland
As of June 2020, there were 3 publicly available hydrogen fuel stations in operation.
Italy
As of June 2020, there was one publicly available hydrogen fuel stations in operation.
Netherlands
As of June 2020, there are 4 publicly available hydrogen fuel stations in operation.
Denmark
As of June 2020, there were 6 publicly available hydrogen fuel stations in operation.
Everfuel, the only operator of hydrogen stations in Denmark, announced
in 2023 that it is closing all of its public hydrogen stations in the
country.
Belgium
As of June 2020, there were 2 publicly available hydrogen fuel stations in operation.
Norway
As of June 2021, there were 2 publicly available hydrogen fuel stations in operation, both in the Oslo area. Since the explosion at the hydrogen filling station in Sandvika in June 2019, the sale of hydrogen cars in Norway has halted.
In 2023, Everfuel announced that it is closing its two public hydrogen
stations in Norway and cancelling the opening of a third.
Sweden
As of June 2020, there were 4 publicly available hydrogen fuel stations in operation.
Switzerland
As of June 2020, there were 3 publicly available hydrogen fuel stations in operation.
United Kingdom
As of June 2020, there were 11 publicly available hydrogen fuel stations in operation, but as of 2023, the number decreased to 5.
In 2011 the first public hydrogen station opened in Swindon. In 2014 the London Hatton Cross station opened.
In 2015, the London Hydrogen Network Expansion project opened the first
supermarket-located hydrogen refuelling station at Sainsbury's in
Hendon. As of 2015, there were two publicly accessible hydrogen refuelling stations in Aberdeen.
In 2022, Shell closed its three hydrogen stations in the UK.
North America
Canada
As of July 2023, there were 10 fueling stations in Canada, 9 of which were open to the public:
British Columbia: Five stations in the Greater Vancouver Area
and Vancouver Island, with one station in Kelowna. All six stations are
operated by HTEC (co-branded with Shell and Esso).
Ontario: One station in Mississauga, which is operated by Hydrogenics Corporation. The station is only available to certain commercial customers.
Quebec: Three stations in the Greater Montreal area, which is
operated by Shell, and one station in Quebec City, operated by Harnois
Énergies (co-branded with Esso).
United States
As of December 2023,
there were 58 publicly accessible hydrogen refueling stations in the
US, 57 of which were located in California, with one in Hawaii.
Arizona: A prototype hydrogen fuelling station was built in
Phoenix to demonstrate that they could be built safely in urban areas. As of November 2023, no publicly accessible stations were in operation in Arizona.
California: As of December 2023, there were 57 retail stations. Continued state funding for hydrogen refueling stations is uncertain.
In September 2023, Shell announced that it had closed its hydrogen
stations in the state and discontinued plans to build further stations.
Hawaii opened its first hydrogen station at Hickam in 2009. In 2012, the Aloha Motor Company opened a hydrogen station in Honolulu. As of April 2023, however, only one publicly accessible station was in operation in Hawaii.
Massachusetts: The French company Air Liquide built a hydrogen fuelling station in Mansfield, Massachusetts
in 2018, one of four stations they built as part of a plan to expand
the hydrogen fuelling infrastructure in the Northeastern U.S. As of April 2016 a hydrogen fuelling station was located at the Billerica, Massachusetts headquarters of fuel cell manufacturer Nuvera. As of November 2023, no publicly accessible stations were in operation in Massachusetts.
Michigan: In 2000, the Ford Motor Company and Air Products & Chemicals opened the first hydrogen station in North America in Dearborn, MI. As of November 2023, no publicly accessible stations were in operation in Michigan.
Missouri's only hydrogen filling station is located at the Missouri University of Science and Technology campus. As of November 2023, no publicly accessible stations were in operation in Missouri.
Ohio: A hydrogen filling station opened in 2007 on the campus of Ohio State University at the Center for Automotive Research. This station is the only one in Ohio. As of November 2023, no publicly accessible stations were in operation in Ohio.
Vermont: A hydrogen station was built in 2004 in Vermont in Burlington, Vermont, partially funded through the United States Department of Energy's Hydrogen Program. As of November 2023, no publicly accessible stations were in operation in Vermont.
Oceania
Australia
In March 2021, the first Australian publicly available hydrogen fuel station opened in Canberra operated by ActewAGL.
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