Product Code Database
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 original coal gas was produced by the coal gasification reaction,Shapley, Coal Gasification , University of Illinois. and the burnable component consisted of a mixture of carbon monoxide and hydrogen in roughly equal quantities by volume. Thus, coal gas is highly toxicity. Other compositions contain additional Calorific Value gases such as methane, produced by the Fischer–Tropsch process, and volatile hydrocarbons together with small quantities of non-calorific gases such as carbon dioxide and nitrogen.
Prior to the development of natural gas supply and transmission—during the 1940s and 1950s in the United States and during the late 1960s and 1970s in the United Kingdom and Australia—almost all gas for fuel and lighting was manufactured from coal. Town gas was supplied to households via municipally owned piped distribution systems. At the time, a frequent method of committing suicide was the inhalation of gas from an unlit oven. With the head and upper body placed inside the appliance, the concentrated carbon monoxide would kill quickly. Sylvia Plath famously ended her life with this method.
Originally created as a by-product of the coking process, its use developed during the 19th and early 20th centuries tracking the Industrial Revolution and urbanization. By-products from the production process included and ammonia, which were important raw material (or "chemical feedstock") for the dye and chemical industry with a wide range of artificial dyes being made from coal gas and coal tar. Facilities where the gas was produced were often known as a manufactured gas plant (MGP) or a gasworks.
In the United Kingdom the discovery of large reserves of natural gas, or sea gas as it was known colloquially, in the Southern North Sea off the coasts of Norfolk and Yorkshire in 1965 National Gas Museum: Gas industry timeline West Sole Gas Fields led to the expensive conversion or replacement of most of Britain's gas cookers and gas heaters, from the late 1960s onwards, the process being completed by the late 1970s. Any residual gas lighting found in homes being converted was either capped off at the meter or, more usually, removed altogether. As of 2023, some gas street lighting still remains, mainly in central London and the Royal Parks.
The production process differs from other methods used to generate fuel gas known variously as manufactured gas, syngas, Dowson gas, and producer gas. These gases are made by partial combustion of a wide variety of feedstocks in some mixture of air, oxygen, or steam, to reduce the latter to hydrogen and carbon monoxide although some destructive distillation may also occur.
The first process used was the carbonization and partial pyrolysis of coal. The off gases liberated in the high-temperature carbonization (coking) of coal in coke ovens were collected, scrubbed and used as fuel. Depending on the goal of the plant, the desired product was either a high quality coke for metallurgy use, with the gas being a side product, or the production of a high quality gas, with coke being the side product. Coke plants are typically associated with metallurgical facilities such as Smelting or , while gas works typically served urban areas.
A facility used to manufacture coal gas, carburetted water gas (CWG), and oil gas is today generally referred to as a manufactured gas plant (MGP).
In the early years of MGP operations, the goal of a utility gas works was to produce the greatest amount of illuminating gas. The illuminating power of a gas was related to amount of soot-forming hydrocarbons ("illuminants") dissolved in it. These hydrocarbons gave the gas flame its characteristic bright yellow color. Gas works would typically use oily bituminous coals as feedstock. These coals would give off large amounts of volatile hydrocarbons into the coal gas, but would leave behind a crumbly, low-quality coke not suitable for metallurgy processes.
Coal or coke oven gas typically had a calorific value between ; with values around being typical.
The advent of electric lighting forced utilities to search for other markets for manufactured gas. MGPs that once almost exclusively produced lighting gas shifted their efforts towards supplying gas for heating and cooking, and even refrigeration and cooling.
The problem of nitrogen dilution was overcome by the blue water gas (BWG) process, developed in the 1850s by Sir William Siemens. The incandescent fuel bed would be alternately blasted with air followed by steam. The air reactions during the blow cycle are exothermic, heating up the bed, while the steam reactions during the make cycle, are endothermic and cool down the bed. The products from the air cycle contain non-calorific nitrogen and are exhausted out the stack while the products of the steam cycle are kept as blue water gas. This gas is composed almost entirely of CO and H2, and burns with a pale blue flame similar to natural gas. BWG has a calorific value of .
Blue water gas lacked illuminants; it would not burn with a luminous flame in a simple fishtail gas jet as existed prior to the invention of the gas mantle in the 1890s. Various attempts were made to enrich BWG with illuminants from gas oil in the 1860s. Gas oil (an early form of gasoline) was the flammable waste product from kerosene refining, made from the lightest and most volatile fractions (tops) of crude oil. In 1875 Thaddeus Lowe invented the carburetted water gas process. This process revolutionized the manufactured gas industry and was the standard technology until the end of the manufactured gas era. A CWG generating set consisted of three elements; a producer (generator), carburettor and a super heater connected in series with gas pipes and valves.
During a make run, steam would be passed through the generator to make blue water gas. From the generator the hot water gas would pass into the top of the carburettor where light petroleum oils would be injected into the gas stream. The light oils would be thermocracked as they came in contact with the white hot checkerwork inside the carburettor. The hot enriched gas would then flow into the superheater, where the gas would be further cracked by more hot fire bricks.
| +UK coal production !Year !Production, million tons !Production cost, £/ton | ||
| 1947 | 197 | 2.00 |
| 1950 | 216 | 2.40 |
| 1953 | 223 | 3.05 |
| 1956 | 222 | 3.85 |
| 1959 | 206 | 4.15 |
| 1961 | 191 | 4.55 |
| 1965 | 187 | 4.60 |
| 1967 | 172 | 4.95 |
Coal-based town gas production, millions of therms
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}New technologies for manufacturing coal gas using oil, refinery tail gases, and light distillates were developed. Processes included the Lurgi Process, catalytic reforming, the catalytic rich gas process, steam reforming of rich gas, and the gas recycle Hydrogenation process. The catalytic rich gas process used natural gas as a feedstock to manufacture town gas. These facilities utilised the chemical reaction processes described above.
The rise of oil as a feedstock to manufacture town gas is shown on the graph below. The peak usage in 1968/9 and subsequent decline coincides with the availability of North Sea gas which, over the next few years, displaced town gas as a primary fuel and led to the decline of oil as a feedstock for gas making, as shown.
Oil-based town gas production, millions of therms
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"x": 1964,
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"x": 1965,
"y": 1219
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"x": 1966,
"y": 1596
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"x": 1967,
"y": 2065
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"x": 1968,
"y": 2488
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"x": 1969,
"y": 2804
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"x": 1970,
"y": 2254
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"x": 1971,
"y": 1548
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"x": 1972,
"y": 880
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"x": 1973,
"y": 795
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"x": 1974,
"y": 741
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"x": 1975,
"y": 427
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"y": 98
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In a pilot scheme customers on Canvey Island were converted from town gas to natural gas supplied from the LNG plant on Canvey.
The Fuel Policy White Paper of 1967 (Cmd. 3438) pointed the industry in the direction of building up the use of natural gas speedily to 'enable the country to benefit as soon as possible from the advantages of this new indigenous energy source'. As a result, there was a 'rush to gas' for use in peak load electricity generation and in low grade uses in industry.
The growth in availability of natural gas is shown in the graph below. Until 1968 this was from supplies of LNG from Algeria, until North Sea gas was available from 1968.
Natural gas available, millions of therms
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"y": 14612
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"x": 1978,
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The exploitation of the North Sea gas reserves, entailing landing gas at Easington, Bacton and St Fergus made viable the building of a national distribution grid, of over , consisting of two parallel and interconnected pipelines running the length of the country. This became the National Transmission System. All gas equipment in Great Britain (but not Northern Ireland) was converted (by the fitting of different-sized burner jets to give the correct gas/air mixture) from town gas to natural gas (mainly methane) over the period from 1967 to 1977 at a cost of about £100 million, including writing off redundant town gas manufacturing plants. All the gas-using equipment of almost thirteen million domestic, four hundred thousand commercial, and sixty thousand industrial customers were converted. Many dangerous appliances were discovered in this exercise and were taken out of service.
The UK town gas industry ended in 1987 when operations ceased at the last town gas manufacturing plants in Northern Ireland (Belfast, Portadown and Carrickfergus; Carrickfergus gas works is now a restored gasworks museum). The Portadown site has been cleared and is now the subject of a long-term experiment into the use of bacteria for the purpose of cleaning up contaminated industrial land.
As well as requiring little processing before use, natural gas is non-toxic; the carbon monoxide (CO) in town gas made it extremely poisonous, accidental poisoning and suicide by gas being commonplace. Poisoning from natural gas appliances is only due to incomplete combustion, which creates CO, and flue leaks to living accommodation. As with town gas, a small amount of foul-smelling substance (mercaptan) is added to the gas to indicate to the user that there is a leak or an unlit burner, the gas having no odour of its own.
The organisation of the British gas industry adapted to these changes, first, by the Gas Act 1965 by empowering the Gas Council to acquire and supply gas to the twelve area gas boards. Then, the Gas Act 1972 formed the British Gas Corporation as a single commercial entity, embracing all the twelve area gas boards, allowing them to acquire, distribute and market gas and gas appliances to industrial commercial and domestic customers throughout the UK. In 1986, British Gas was privatised and the government no longer has any direct control over it.
During the era of North Sea gas, many of the original cast iron gas piping installed in towns and cities for town gas were replaced by plastic.
As reported in the DTI Energy Review 'Our Energy Challenge' January 2006 North Sea gas resources have been depleted at a faster rate than had been anticipated and gas supplies for the UK are being sought from remote sources, a strategy made possible by developments in the technologies of pipelaying that enable the transmission of gas over land and under sea across and between continents. Natural gas is now a world commodity. Such sources of supply are exposed to all the risks of any import.
The German economy relied on coal gas during the Second World War as petroleum shortages forced Nazi Germany to develop the Fischer–Tropsch synthesis to produce synthetic fuel for aircraft and tanks.
/ref>
The coal used, and the town gas and by-products produced, by the major three gas companies of London are summarised in the table.
| Company ! colspan="3" | Gas, Light and Coke ! colspan="3" | South Metropolitan ! colspan="3" | Commercial | ||||||
| Year !1913 !1920 !1934 !1913 !1920 !1934 !1913 !1920 !1934 | |||||||||
| Coal carbonised, tons | 1,988,241 | 2,279,253 | 3,011,227 | 1,125,779 | 1,211,857 | 1,118,573 | 187,291 | 235,406 | 244,644 |
| Gas made, million cubic feet | 29,634 | 35,149 | 51,533 | 14,097 | 15,182 | 15,034 | 3,702 | 4,340 | 3,487 |
| Coke made, tons | 1,246,624 | 1,469,220 | 1,867,038 | 695,214 | 743,982 | 664,555 | 117,057 | 158,899 | 159,019 |
| Coke made, hundredweight per ton of coal (20 hundredweight = 1 ton) | 12.54 | 12.89 | 12.40 | 12.35 | 12.28 | 11.88 | 12.50 | 13.50 | 13.00 |
| Coal tar made, million gallons | 19.88 | 20.5 | 31.32 | 10.81 | 11.27 | 12.97 | 1.97 | 0.94 | 2.39 |
| Coal tar made, gallons per ton of coal | 10.0 | 9.0 | 10.4 | 9.6 | 9.3 | 10.7 | 10.5 | 9.4 | 9.8 |
| Ammoniacal liquor made, million gallons | 59.25 | 61.77 | 71.06 | 36.93 | 37.93 | 36.69 | 5.94 | 6.54 | 7.41 |
| Ammoniacal liquor made, gallons per ton of coal | 29.8 | 27.1 | 23.6 | 32.8 | 31.3 | 32.8 | 31.7 | 27.8 | 30.3 |
Apart from in the steel industry's coke ovens' by-products plants, coal gas is no longer made in the UK. It was replaced first by gas made from oil and later by natural gas from the North Sea.
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