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| Just as coal and steam drove the transport revolution of the 19th century so it could also be said that coal gas drove the industrial society of the early 20th century and provided many of the raw materials for the chemical industry as well. In the later years of the 20th century coal, steam and gas were replaced in their turn by electricity. There are now only two remaining examples of coal gasification plants in the United Kingdom, one at Biggar in Lanarkshire and the other at Fakenham in Norfork. | |
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A medium sized town Gas Works at Barnstaple in the 1950's Every town had its gasworks with prominent gasholders. Remarkably, the works were often located in the middle of urban areas as the photograph shows. Nowadays the smell originating from such a plant would be considered environmentally unacceptable. Moany of the original sites survive, much reduced in size and acting as pressure-reducing stations for gas supplied from the national high pressure distribution network. |
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Biggar gasworks is the only remaining coal gas production plant in Scotland. It was built in 1837 and ceased production in 1973 when North Sea natural gas was piped to the town. It is now preserved asan industrial heritage attraction. All the original production plant is preserved and the site provides an excellent insight into the operation of a small gasworks which is representative of hundreds of many similar small town establishments which operated throughout the British Isles during the 19th and 20th centuries. Coal was brought into the gasworks by road from the local railway station and probably from small coal mines in the surrounding area. It was stacked in the yard ready for use. At larger works private railway sidings were constructed and coal was brought in by the wagonload in considerable quantities. At Harrogate gasworks (North Yorkshire), a narrow gauge railway was built to transfer coal from the nearby standard gauge line at Bilton. It operated with two small steam engines Barber and Spencer, until July 1956. |
A tonne of coal (comprising 20 cwt or hundredweights) would have produced approximately the following amounts of products: Coke : 700 kilos (14 cwt) Coal tar : 82 litres (18 gallons) Gas : 108 - 135 cubic metres (4000 - 5000 cubic feet) Ammonium Sulphate : 1.8 kilos (4 lbs) Ammoniacal liquor : 91 litres (20 gallons) The gasification yield varied according to the type of coal used, temperature conditions etc. |
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The Retort House, Biggar gasworks, Lanarkshire The retort house at Biggar gasworks. The retorts were arranged in two banks of five, set out side by side.The retort house also houses a furnace (called "the producer") into which the two banks of retorts are installed. Each retort is fitted with a cast iron door and is approx. 2' x 18" and 16' deep. Each retort is fitted with a 4" pipe located just above its front end and a battery of the 10 pipes from the retort are led up to a 2' diameter hydraulic main which runs the length of the building and is positioned approximately 4' above the top of the retort bank. The pipes from the retorts are arranged so that the gases are discharged under water into the hydraulic main. This provides both a flame trap and a place for the less volatile constituents in the coal gas to condense into. |
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The producer furnace was damped down each night but at the start of the operating shift coke was charged into the main loading hatch to provide extra heat for the retorts. (Note:The process description given here assumes that the retorts were already charged and that a "cold start-up" was not required). After the retorts were heated for between 8 and 12 hours, the operator opened the retort door slightly and applied a lighted taper to the gas issuing from the seal around the door. This controlled ignition of the coal gas prevented the possibility of a gas explosion when the door was fully opened and the proportion of oxygen increased. Once the issuing gas was ignited, the retort door was opened fully and the operator used a long iron rake to withdraw the burning coal charge into a specially designed barrow which was positioned under the retort mouth. |
| The barrow of burning coke was then wheeled outside and positioned under a water shower, which was turned on in order to quench the flames and cool the coke. The operator had to take care not to wet the coke too much as it was to be stored and later sold on as domestic or industrial fuel. After quenching, the coke was then moved to a storage area. The operator then collected a barrow load of coal with which to re-charge the retort. He wheeled the barrow load of coal up to the retort and carefully shovelled it in, distributing it directly into the still hot retort. When the charging of the retort was completed he closed the door and moved on to empty and recharge the next one. | |
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The hydraulic main. The raw coal gas from the retorts bubbled
into the hydraulic main. Coal Tar, a complex mixture of
hydrocarbons, condensed out and collected in the bottom of the
main. A discharge pipe was positioned inside the main so that
the collected tar was able to overflow into the tar well, where
it was stored. The upper watery layer of liquid ,"ammoniacal
liquor", containing about 1% of Ammonia was allowed to overflow
a weir and drain into a collecting tank. |
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The condensers at Biggar The condenser is a series of vertical cast iron pipes arranged so that the gas cooled as it passed through them. There was a water sump at the bottom of the condensers and during the cooling process some more tar collected at this point. The tar was drained into the tar well and the water sump, which became saturated with Ammonia, was drained off into the ammoniacal liquor store. The gas that left the condensers was then led to Purifiers in which the Hydrogen Sulphide present in the crude gas was removed. |
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The purifiers The purifiers were large iron chests fabricated from steel sheets and contained trays of iron oxide mixed with an inert material such as wood shavings. The impure coal gas passed through these chests and the Hydrogen Sulphide present reacted with the Iron Oxide to produce Sulphur. A close watch had to be kept on the temperature inside the purifiers because the Iron Oxide and Sulphur were liable to catch fire if any atmospheric air was allowed to leak in. At Biggar there are two purifiers. They are arranged so that,as the Iron Oxide became exhausted, a newly charged purifier could be connected up. the exhausted purifier could then be emptied and recharged. |
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| For recharging, the lid was taken off the "out of service" purifier and the spent Iron Oxide was dug out. Sulphur from the oxidation of the Hydrogen Sulphide crystallised out in the purifier bed. The spent Iron Oxide was used as a commercial source of Sulphur and this was stored for later transport away from the production site for Sulphur recovery. The purified gas was then passed through an Ammonia scrubber, which was called a "Livesey Washer". This consisted of chambers which contained water, and sets of rotating brushes used to create a spray of fine droplets (creating a large surface area). As the gas passed through these chambers the last of the Ammonia present was dissolved. | |
| The gas was then pumped through a meter into a gasholder before being held for final testing. There are many different kinds of gas holders still in existence and their evolution in terms of engineering design is a subject in itself. The calorific value of the gas was measured before the gas was released into the supply network (this distribution network was called "the district"). If the gas was satisfactory it was pumped to a second gasholder for distribution. | |
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Bibliography Harrogate Gas Works - Its railways and other transport systems, Martin P.F.Hallows and David H.Smith., Narrow Gauge Railway Society ISBN 0142 5587 |
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