Water gas is a kind of fuel gas, a mixture of carbon monoxide and hydrogen. It is produced by "alternately hot blowing a fuel layer [coke] with air and gasifying it with steam". [1] [2] The caloric yield of this is about 10% of a modern syngas plant. Further making this technology unattractive, its precursor coke is expensive, whereas syngas uses cheaper precursor, mainly methane from natural gas.
Synthesis gas is made by passing steam over a red-hot carbon fuel such as coke: [3]
The reaction is endothermic, so the fuel must be continually re-heated to maintain the reaction. To do this, an air stream, which alternates with the vapor stream, is introduced to combust some of the carbon:
Theoretically, to make 6 L of water gas, 5 L of air is required. Alternatively, to prevent contamination with nitrogen, energy can be provided by using pure oxygen to burn carbon into carbon monoxide.
In this case, 1 L of oxygen will create 5.3 L of pure water gas.
The water-gas shift reaction was discovered by Italian physicist Felice Fontana in 1780. Water gas was made in England from 1828 by blowing steam through white-hot coke. [4]
Hydrocarbonate is an archaic term for water gas composed of carbon monoxide and hydrogen generated by passing steam through glowing coke. Hydrocarbonate was classified as a factitious air and explored for therapeutic properties by eighteenth-century physicians including: Thomas Beddoes and James Watt. [5] The term hydrocarbonate was coined by Thomas Beddoes in 1794. It should not be confused with the modern name "hydrogen carbonate" for bicarbonate ion.
Between 1794 and 1802, physicians such as Tiberius Cavallo and Davies Gilbert experimented with hydrocarbonate as an analgesic and anesthetic. [6] Humphry Davy infamously inhaled three quarts of hydrocarbonate at the Pneumatic Institution and nearly died upon "sinking into annihilation"; Davy recovered two days later and concluded inhalation of more hydrocarbonate could have "destroyed life immediately without producing any painful sensations". [7] He was right: carbon monoxide poisoning can be fatal.
Diseases treated by hydrocarbonate included: tuberculosis, inflammation, asthma, expectoration, hemoptysis, pneumonia, hydrothorax, spasm and other indications. [5] [6] Many of the diseases treated with hydrocarbonate, whose active ingredient was carbon monoxide, are now being investigated using modern biomedical research methods to determine the therapeutic potential of carbon monoxide. For example, James Lind recognized hydrocarbonate to effectively treat lung inflammation; [5] delivery of carbon monoxide via inhalation protocol or carbon monoxide-releasing molecules has significant preclinical data indicating an effective treatment for inflammation. [8] The pioneering work of exploratory medicinal application of hydrocarbonate is an important origin for modern drug development.
James Watt suggested hydrocarbonate could act as "an antidote to the oxygen in blood" in 1794 and cautioned about the toxicity of an overdose prior to the discoveries of carbon monoxide (1800) and hemoglobin (1840). [5] Despite Watt's observation, it is widely accepted that Claude Bernard had first described the mechanism for carbon monoxide poisoning by describing carbon monoxide's affinity for hemoglobin displacing oxygen to induce asphyxia circa 1857. [9]
In 1873, Thaddeus S. C. Lowe developed and patented the water gas process by which large amounts of hydrogen gas could be generated for residential and commercial use in heating and lighting. This gas provided a more efficient heating fuel than the common coal gas, or coke gas, which was used in municipal service. The process used the water-gas shift reaction:
The process was discovered by passing high-pressure steam over hot coal, the major source of coke gas. Lowe's process improved upon the chimney systems by which the coal could remain superheated, thereby maintaining a consistently high supply of the gas. The reaction produced carbon dioxide and hydrogen, which, after a process of cooling and "scrubbing", produced hydrogen gas.
The process spurred on the industry of gas manufacturing, and gasification plants were established quickly along the Eastern seaboard of the United States. Similar processes, like the Haber–Bosch process, led to the manufacture of ammonia (NH3) by the combining of nitrogen, found in air, with hydrogen. This spurred on the refrigeration industry, which long used ammonia as its refrigerant. Prof. Lowe also held several patents on artificial ice making machines and was able to run successful businesses in cold storage, as well as products which operated on hydrogen gas.
Water gas has a lower heat of combustion than coal gas, so the calorific value was often boosted by passing the gas through a heated retort, into which oil was sprayed. The resulting mixed gas was called carburetted water gas. The average composition of carburated water gas is as follows: H2=34-38%; CO=23-28%; saturated hydrocarbon=17-21%; unsaturated hydrocarbon=13-16%; CO2=0.2-2.2%; N2=2.5-5.0%. It is used as a source of heat since it has a high calorific value
Semi-water gas is a mixture of water gas and producer gas made by passing a mixture of air and steam through heated coke. The heat generated when producer gas is formed keeps the temperature of the coke high enough to allow water gas to be formed.
Pure hydrogen can be obtained from water gas by using the Water–gas shift reaction, after subsequent removal of the carbon dioxide formed when carbon monoxide reacts with water.
Completely displaced by syngas, water gas could be applied to certain fuel cells. Used in Fischer–Tropsch process. It reacts with producer gas to produce fuel gas. It could also be used to gain pure hydrogen for synthesis of ammonia.
The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. The German chemists Fritz Haber and Carl Bosch developed it in the first decade of the 20th century. The process converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using an iron metal catalyst under high temperatures and pressures. This reaction is slightly exothermic (i.e. it releases energy), meaning that the reaction is favoured at lower temperatures and higher pressures. It decreases entropy, complicating the process. Hydrogen is produced via steam reforming, followed by an iterative closed cycle to react hydrogen with nitrogen to produce ammonia.
Coke is a grey, hard, and porous coal-based fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air—a destructive distillation process. It is an important industrial product, used mainly in iron ore smelting, but also as a fuel in stoves and forges when air pollution is a concern.
Producer gas is fuel gas that is manufactured by blowing through a coke or coal fire with air and steam simultaneously. It mainly consists of carbon monoxide (CO), hydrogen (H2), as well as substantial amounts of nitrogen (N2). The caloric value of the producer gas is low (mainly because of its high nitrogen content), and the technology is obsolete. Improvements over producer gas, also obsolete, include water gas where the solid fuel is treated intermittently with air and steam and, far more efficiently synthesis gas where the solid fuel is replaced with methane.
Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.
Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.
Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous fuels produced for sale to consumers and municipalities.
The Fischer–Tropsch process (FT) is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatures of 150–300 °C (302–572 °F) and pressures of one to several tens of atmospheres. The Fischer–Tropsch process is an important reaction in both coal liquefaction and gas to liquids technology for producing liquid hydrocarbons.
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:
In industrial chemistry, coal gasification is the process of producing syngas—a mixture consisting primarily of carbon monoxide (CO), hydrogen, carbon dioxide, methane, and water vapour —from coal and water, air and/or oxygen.
The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures and pressures in the presence of a nickel catalyst. It was discovered by the French chemists Paul Sabatier and Jean-Baptiste Senderens in 1897. Optionally, ruthenium on alumina makes a more efficient catalyst. It is described by the following exothermic reaction:
The water–gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen:
An integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the electricity generation cycle. Some of these pollutants, such as sulfur, can be turned into re-usable byproducts through the Claus process. This results in lower emissions of sulfur dioxide, particulates, mercury, and in some cases carbon dioxide. With additional process equipment, a water-gas shift reaction can increase gasification efficiency and reduce carbon monoxide emissions by converting it to carbon dioxide. The resulting carbon dioxide from the shift reaction can be separated, compressed, and stored through sequestration. Excess heat from the primary combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine. This process results in improved thermodynamic efficiency, compared to conventional pulverized coal combustion.
Hydrogen gas is produced by several industrial methods. In 2022 less than 1% of hydrogen production was low-carbon. Fossil fuels are the dominant source of hydrogen, for example by steam reforming of natural gas. Other methods of hydrogen production include biomass gasification and methane pyrolysis. Methane pyrolysis and water electrolysis can use any source of electricity including renewable energy. Underground hydrogen is extracted.
A methane reformer is a device based on steam reforming, autothermal reforming or partial oxidation and is a type of chemical synthesis which can produce pure hydrogen gas from methane using a catalyst. There are multiple types of reformers in development but the most common in industry are autothermal reforming (ATR) and steam methane reforming (SMR). Most methods work by exposing methane to a catalyst at high temperature and pressure.
PROX is an acronym for PReferential OXidation, that refers to the preferential oxidation of carbon monoxide in a gas mixture by a catalyst. It is intended to remove trace amounts of CO from H2/CO/CO2 mixtures produced by steam reforming and water-gas shift. An ideal PROX catalyst preferentially oxidizes carbon monoxide (CO) using a heterogeneous catalyst placed upon a ceramic support. Catalysts include metals such as platinum, platinum/iron, platinum/ruthenium, gold nanoparticles as well as novel copper oxide/ceramic conglomerate catalysts.
Reactive flash volatilization (RFV) is a chemical process that rapidly converts nonvolatile solids and liquids to volatile compounds by thermal decomposition for integration with catalytic chemistries.
The first time a catalyst was used in the industry was in 1746 by J. Roebuck in the manufacture of lead chamber sulfuric acid. Since then catalysts have been in use in a large portion of the chemical industry. In the start only pure components were used as catalysts, but after the year 1900 multicomponent catalysts were studied and are now commonly used in the industry.
The Kim reformer is a type of syngas plant invented by Hyun Yong Kim. It is a high temperature furnace, filled with steam and/or carbon dioxide gas and maintaining a thermal equilibrium at a temperature just above 1200 °C, in which the reforming reaction is at its thermodynamic equilibrium and carbonaceous substance is reformed with the highest efficiency.
Factitious airs was a term used for synthetic gases which emerged around 1670 when Robert Boyle coined the term upon isolating what is now understood to be hydrogen. Factitious means "artificial, not natural", so the term means "man-made gases".
Chemical looping reforming (CLR) and gasification (CLG) are the operations that involve the use of gaseous carbonaceous feedstock and solid carbonaceous feedstock, respectively, in their conversion to syngas in the chemical looping scheme. The typical gaseous carbonaceous feedstocks used are natural gas and reducing tail gas, while the typical solid carbonaceous feedstocks used are coal and biomass. The feedstocks are partially oxidized to generate syngas using metal oxide oxygen carriers as the oxidant. The reduced metal oxide is then oxidized in the regeneration step using air. The syngas is an important intermediate for generation of such diverse products as electricity, chemicals, hydrogen, and liquid fuels.
 | This article includes a list of general references, but it lacks sufficient corresponding inline citations .(January 2017) |
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