Coal gas
Manufactured gas can be made by two processes: carbonization or gasification. Carbonization refers to the devolatilization of an organic feedstock to yield gas and char. Gasification is the process of subjecting a feedstock to chemical reactions that produce gas. 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 metallurgical 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 smelters or blast furnaces, 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 metallurgical 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 produced gas almost exclusively for lighting shifted their efforts towards supplying gas primarily for heating and cooking, and even refrigeration and cooling. Fuel gas for industrial use was made using producer gas technology. Producer gas is made by blowing air through an incandescent fuel bed (commonly coke or coal) in a gas producer. The reaction of fuel with insufficient air for total combustion produces carbon monoxide (CO); this reaction is exothermic and self-sustaining. It was discovered that adding steam to the input air of a gas producer would increase the calorific value of the fuel gas by enriching it with CO and hydrogen (H2) produced by water gas reactions. Producer gas has a very low calorific value of ; because the calorific gases CO/H2 are diluted with much inert nitrogen (from air) and carbon dioxide (CO2) (from combustion)
2C (s) + O2 → 2 CO (exothermic producer gas reaction)
C (s) + H2O (g) → CO + H2 (endothermic water gas reaction)
C + 2 H2O → CO2 + 2 H2 (endothermic)
CO + H2O → CO2 + H2 (exothermic water gas shift reaction)
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 Welsbach 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 S. C. Lowe invented the carburetted water gas process. This process revolutionized the manufactured gas industry and was the standard technology until the end of 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 fire bricks 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. Following the Second World War the slow recovery of the British coal mining industry led to shortages of coal and high prices. The decline of coal as a feedstock for town gas production using carbonisation is demonstrated in this graph. Coal-based town gas production, millions of therms<graph>{
 "version": 2,
 "width": 800,
 "height": 250,
 "data": [
 "name": "table",
 "values": [
 "x": 1951,
 "y": 2472
 {
 "x": 1952,
 "y": 2559
 {
 "x": 1953,
 "y": 2598
 {
 "x": 1954,
 "y": 2594
 {
 "x": 1955,
 "y": 2730
 {
 "x": 1956,
 "y": 2730
 {
 "x": 1957,
 "y": 2726
 {
 "x": 1958,
 "y": 2694
 {
 "x": 1959,
 "y": 2555
 {
 "x": 1960,
 "y": 2444
 {
 "x": 1961,
 "y": 2448
 {
 "x": 1962,
 "y": 2465
 {
 "x": 1963,
 "y": 2442
 {
 "x": 1964,
 "y": 2361
 {
 "x": 1965,
 "y": 2168
 {
 "x": 1966,
 "y": 1930
 {
 "x": 1967,
 "y": 1735
 {
 "x": 1968,
 "y": 1516
 {
 "x": 1969,
 "y": 1129
 {
 "x": 1970,
 "y": 797
 {
 "x": 1971,
 "y": 553
 {
 "x": 1972,
 "y": 237
 {
 "x": 1973,
 "y": 134
 {
 "x": 1974,
 "y": 64
 {
 "x": 1975,
 "y": 28
 {
 "x": 1976,
 "y": 6
 ]
 ],
 "scales": [
 "name": "x",
 "type": "ordinal",
 "range": "width",
 "zero": false,
 "domain": {
 "data": "table",
 "field": "x"
 },
 "name": "y",
 "type": "linear",
 "range": "height",
 "nice": true,
 "domain": {
 "data": "table",
 "field": "y"
 "axes": [
 "type": "x",
 "scale": "x"
 {
 "type": "y",
 "scale": "y"
 ],
 "marks": [
 "type": "rect",
 "from": {
 "data": "table"
 "properties": {
 "enter": {
 "x": {
 "scale": "x",
 "field": "x"
 "y": {
 "scale": "y",
 "field": "y"
 "y2": {
 "scale": "y",
 "value": 0
 "fill": {
 "value": "steelblue"
 "width": {
 "scale": "x",
 "band": "true",
 "offset": -1
}</graph> 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 hydrogenator 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<graph>{
 "version": 2,
 "width": 800,
 "height": 250,
 "data": [
 "name": "table",
 "values": [
 "x": 1951,
 "y": 188
 {
 "x": 1952,
 "y": 162
 {
 "x": 1953,
 "y": 149
 {
 "x": 1954,
 "y": 154
 {
 "x": 1955,
 "y": 197
 {
 "x": 1956,
 "y": 171
 {
 "x": 1957,
 "y": 123
 {
 "x": 1958,
 "y": 202
 {
 "x": 1959,
 "y": 276
 {
 "x": 1960,
 "y": 363
 {
 "x": 1961,
 "y": 428
 {
 "x": 1962,
 "y": 505
 {
 "x": 1963,
 "y": 743
 {
 "x": 1964,
 "y": 870
 {
 "x": 1965,
 "y": 1219
 {
 "x": 1966,
 "y": 1596
 {
 "x": 1967,
 "y": 2065
 {
 "x": 1968,
 "y": 2488
 {
 "x": 1969,
 "y": 2804
 {
 "x": 1970,
 "y": 2254
 {
 "x": 1971,
 "y": 1548
 {
 "x": 1972,
 "y": 880
 {
 "x": 1973,
 "y": 795
 {
 "x": 1974,
 "y": 741
 {
 "x": 1975,
 "y": 427
 {
 "x": 1976,
 "y": 98
 ]
 ],
 "scales": [
 "name": "x",
 "type": "ordinal",
 "range": "width",
 "zero": false,
 "domain": {
 "data": "table",
 "field": "x"
 },
 "name": "y",
 "type": "linear",
 "range": "height",
 "nice": true,
 "domain": {
 "data": "table",
 "field": "y"
 "axes": [
 "type": "x",
 "scale": "x"
 {
 "type": "y",
 "scale": "y"
 ],
 "marks": [
 "type": "rect",
 "from": {
 "data": "table"
 "properties": {
 "enter": {
 "x": {
 "scale": "x",
 "field": "x"
 "y": {
 "scale": "y",
 "field": "y"
 "y2": {
 "scale": "y",
 "value": 0
 "fill": {
 "value": "steelblue"
 "width": {
 "scale": "x",
 "band": "true",
 "offset": -1
}</graph> By the 1960s, manufactured gas, compared with its main rival in the energy market, electricity, was considered "nasty, smelly, dirty and dangerous" (to quote market research of the time) and seemed doomed to lose market share still further, except for cooking where its controllability gave it marked advantages over both electricity and solid fuel. The development of more efficient gas fires assisted gas to resist competition in the market for room heating. Concurrently a new market for whole house central heating by hot water was being developed by the oil industry and the gas industry followed suit. Gas warm air heating found a market niche in new local authority housing where low installation costs gave it an advantage. These developments, the realignment of managerial thinking away from commercial management (selling what the industry produced) to marketing management (meeting the needs and desires of customers) and the lifting of an early moratorium preventing nationalised industries from using television advertising, saved the gas industry for long enough to provide a viable market for what was to come. In 1959 the Gas Council in Great Britain demonstrated that liquid natural gas (LNG) could be transported safely, efficiently and economically over long distances by sea. The "Methane Pioneer" shipped a consignment of LNG from Lake Charles, Louisiana, USA, to a new LNG terminal on Canvey Island, in the Thames estuary in Essex, England. A long high-pressure trunk pipeline was built from Canvey Island to Bradford. The pipeline and its branches provided Area Gas Boards with natural gas for use in reforming processes to make town gas. A large-scale LNG reception plant was commissioned on Canvey in 1964, which received LNG from Algeria in two dedicated tankers, each of 12,000 tonnes. The slow decline of the town gas industry in the UK was signalled by the discovery of natural gas by the drilling rig "Sea Gem", on 17 September 1965, some forty miles off Grimsby, over below the seabed. Subsequently, the North Sea was found to have many substantial gas fields on both sides of the median line defining which nations should have rights over the reserves. 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 effects on the coal industry were very significant; not only did coal lose its market for town gas production, it came to be displaced from much of the bulk energy market also. 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<graph>{
 "version": 2,
 "width": 700,
 "height": 250,
 "data": [
 "name": "table",
 "values": [
 "x": 1958,
 "y": 3
 {
 "x": 1959,
 "y": 8
 {
 "x": 1960,
 "y": 15
 {
 "x": 1961,
 "y": 13
 {
 "x": 1962,
 "y": 14
 {
 "x": 1963,
 "y": 21
 {
 "x": 1964,
 "y": 32
 {
 "x": 1965,
 "y": 133
 {
 "x": 1966,
 "y": 314
 {
 "x": 1967,
 "y": 315
 {
 "x": 1968,
 "y": 634
 {
 "x": 1969,
 "y": 1232
 {
 "x": 1970,
 "y": 2697
 {
 "x": 1971,
 "y": 4639
 {
 "x": 1972,
 "y": 7632
 {
 "x": 1973,
 "y": 10242
 {
 "x": 1974,
 "y": 11600
 {
 "x": 1975,
 "y": 13236
 {
 "x": 1976,
 "y": 14241
 {
 "x": 1977,
 "y": 14612
 {
 "x": 1978,
 "y": 15945
 {
 "x": 1979,
 "y": 16765
 {
 "x": 1980,
 "y": 17373
 ]
 ],
 "scales": [
 "name": "x",
 "type": "ordinal",
 "range": "width",
 "zero": false,
 "domain": {
 "data": "table",
 "field": "x"
 },
 "name": "y",
 "type": "linear",
 "range": "height",
 "nice": true,
 "domain": {
 "data": "table",
 "field": "y"
 "axes": [
 "type": "x",
 "scale": "x"
 {
 "type": "y",
 "scale": "y"
 ],
 "marks": [
 "type": "rect",
 "from": {
 "data": "table"
 "properties": {
 "enter": {
 "x": {
 "scale": "x",
 "field": "x"
 "y": {
 "scale": "y",
 "field": "y"
 "y2": {
 "scale": "y",
 "value": 0
 "fill": {
 "value": "steelblue"
 "width": {
 "scale": "x",
 "band": "true",
 "offset": -1
}</graph> 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 burning town gas to burn natural gas (mainly methane) over the period from 1967 to 1977 at a cost of about £100 million including the writing off of 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 died 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 dismembered 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 pipes 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. Monty Python parodied the conversion from coal to North Sea gas, and the jumping through hoops some encountered, in their "New Cooker Sketch," as part of the episode that began its second series in 1970. It was used to power several historic balloon ascents in the 19th Century (see "The Aeronauts"). In many ways, Germany took the lead in coal gas research and carbon chemistry. With the labours of August Wilhelm von Hofmann, the whole German chemical industry emerged. Using the coal gas waste as feedstock, researchers developed new processes and synthesized
natural organic compounds such as Vitamin C and aspirin. 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. The Pacific coast process has significant problems with lampblack. 20 to 30 lb/1000 ft3 (300 to 500 g/m3) of oily soot can be created during combustion. Major pollution problems led to the passage of early state-level environmental legislation. CWG tar is full of lighter polycyclic aromatic hydrocarbons, good for making pitch, but poor in chemical precursors. In British usage, coal gas specifically means gas made by the destructive distillation of coal. It was more commonly known as town gas. Coal gas is not applied to other coal-derived gases, such as water gas, producer gas and syngas. United States usage may be different. Coal gas was introduced in the UK in the 1790s as an illuminating gas by the Scottish inventor William Murdoch and became very widely used for lighting, cooking, heating and powering gas engines. Coal was heated in a retort and the crude gas was passed through a condenser to remove tar and a scrubber to remove other impurities. The residue remaining in the retort was coke. The composition of coal gas varied according to the type of coal and the temperature of carbonisation. Typical figures were:


In a plain burner, only the ethylene produced a luminous flame but the light output could be greatly increased by using a gas mantle. The by-products of coal gas manufacture included coke, coal tar, sulfur and ammonia and these were all useful products. Dyes, medicines such as sulfa drugs, saccharine, and dozens of organic compounds are made from coal tar. The coal used, and the town gas and by-products produced, by the major 3 gas companies of London are summarised in the table. Coke is used as a smokeless fuel and for the manufacture of water gas and producer gas. Coal tar was subjected to fractional distillation to recover various products, including Used in the manufacture of sulfuric acid Used in the manufacture of fertilisers Coal gas was initially manufactured by independent companies but in the United Kingdom many of these later became municipal services. In 1948 there was a total of 1,062 gas undertakings. Both the private companies, about two-thirds of the total, and the municipal gas undertakings, about one-third, were nationalised under the Gas Act 1948. Further re-structuring took place under the Gas Act 1972. For further details see British Gas plc. 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.
Terminology in the UK ; By-products
By-products from the production process included coal tars and ammonia, which were important chemical feedstock for the dye and chemical industry with a wide range of artificial dyes being made from coal gas and coal tar.