(Page created 22/05/10)
An article by John Martin first published in the Cumbria Industrial History Society’s Bulletin
Coke is what remains when coal is heated to a fairly high temperature out of contact with air. Not all coal will form an adherent mass of coke, but that which is mined in West Cumberland can rightly be termed “coking coal”.
Prior to 1700, the production of iron from its own ores was achieved by mixing the ore with charcoal in a shaft furnace, and, after igniting, blowing air into the lower part of the furnace. The charcoal burned to provide the necessary heat and it also combined with the oxygen in the ore, leaving the metallic iron in a molten state to be collected in the base of the furnace and eventually run out into moulds to solidify.
Charcoal became scarce as the forests were denuded, and the iron makers eagerly sought a substitute. Raw coal proved quite unsuitable, but by submitting it to the same treatment which was applied to wood for the production of charcoal, they produced a coke which after many trials proved to be a satisfactory substitute.
Charcoal was made by building logs into a dome shape structure, covering it with earth and firing it, openings at the top and base being provided to create a through draught which could be regulated to avoid complete combustion.
The earliest known iron furnace in West Cumberland was erected at Little Clifton in 1723 using coal from the Frizington area. The owners were already mining coal near Clifton, and this they converted into coke on land adjacent to the furnace. They followed the charcoal burner’s practice by covering a heap of coal with earth and roasting it by controlled combustion.
In 1752 another furnace was built at Maryport and here provision was made for making coke in ovens. These were brick chambers which took the place of the earth covering in the ‘heap’ method. Otherwise the procedure was the same, some of the coal being allowed to burn to provide heat for charring the rest.
A further iron making enterprise was established at Barepot near Workington in 1763 and, here again, ovens of the type used at Maryport were erected.
These three iron making activities had all been abandoned before the days when the demand for iron and improved methods of producing it brought about the beginnings of the industry as we know it today.
The deposits of high grade iron ore in the Cleator and Egremont area had been worked for some time and shipped to other areas, notably North and South Wales and Scotland. In 1840 blast furnaces were built at Cleator Moor and in 1856/7 at Harrington and Workington. Coal was already being produced at various mines throughout the West Coast area and at several of these coke ovens of the ‘beehive’ type were erected to provide the ironworks with their requirements. As more and more ironworks were erected at Maryport, Workington, Distington, Parton and Whitehaven, more and more beehive ovens were built until every major colliery in the area had an outlet for some of its coal in this direction.
Even so coke production did not match local demand and considerable tonnages were brought in from Durham. The Durham coke proved superior to much of the local product particularly in its lower phosphorus content, a factor of considerable importance to the local hematite iron industry.
The beehive ovens were essentially coke producers. No attempt was made to recover any of the gas, tar or other by-products which were driven off from the coal when it was heated. The coal charge did not fill the oven. Space was left above the charge in which the gas liberated from the coal was burned.
An advance on the beehive ovens was made when a box like oven was designed in which the gas was led through openings in the upper part of the walls into flues where it could be burned out of contact with coal and impart its heat to the charge through the oven wall.
A battery of 24 ovens of this type was built at the St.Helen’s colliery at Siddick in 1894. Each coking chamber was 30 feet long, 6 feet 6 inches high, and 24 inches wide, and produced 4 tons of coke every 48 hours. Such ovens could not be raked out by hand as was the case with the beehive ovens, and a steam driven mechanical pusher was used which could be placed in front of each oven, and when the doors were winched up the coke was pushed out on to a flat bench where it was quenched with water before loading onto wagons.
As yet there was no recovery of any of the by-products of distillation, but in 1908 the Risehow Colliery Co. at Flimby installed a battery of 40 ovens with full by-product recovery plant. A feature of these ovens, designed by Heinrich Koppers of Essen in Germany, was the use of regenerator chambers below the ovens. Gas was taken away from the oven, cooled to condense the tar, passed through sulphuric acid to fix the ammonia and then burned in a series of flues built into the walls between the several ovens. The hot water gases were then passed through a chamber containing a chequer work of bricks before being led to the chimney. The heat absorbed by the bricks was later used to heat the air necessary for the combustion of the gas in the flues, the net result being that only some 60% of the coke oven gas was necessary for maintaining the coking process.
The Risehow battery was among the earliest by-product ovens in the country and was the first to use the ‘semi-direct’ process for the recovery of ammonia.
A similar plant was installed at the St.Helen’s colliery a year later, followed between 1911 and 1913 with installations at Lowca, Whitehaven, Moresby, Allerdale and Oughterside, until there were 409 such ovens in West Cumberland producing 12,000 tons of coke and using 18,000 tons of local coal per week. Meanwhile, as a result of a decline in the demand for hematite iron, the amalgamation of local iron making companies and improved efficiencies in the use of coke in blast furnaces, the consumption of coke in the area had substantially decreased. These factors eventually resulted in iron production being concentrated at the works of Workington Iron and Steel Company, with three blast furnaces of high operating capacity. In 1936 a battery of 53 Becker ovens was commissioned adjacent to the blast furnaces producing sufficient coke to meet their requirements and, one by one, the older batteries of ovens in the area were closed down.
The coke produced in the so-called ‘patent’ by-product ovens was quite different in character from that from the beehive ovens, and it was received with a certain amount of prejudice by the furnacemen. It was smaller, no piece being larger that half the width of the 20″ wide ovens, whereas the beehive coke could be up to 20-24″ long. Its appearance was also different, lacking the graphitic lustre of that to which the furnace operators were accustomed. There was an uninformed suspicion that the recovery of by-products had “taken something out of the coke”.
It took some time for this prejudice to die down, but in the course of time furnacemen learned to use the new material to advantage, until eventually they were producing good quality iron with a consumption of only 11 cwts. of coke per ton compared with a figure of 20-22 cwts. in the ‘beehive days’. This very marked economy was due to several factors, not all related to coke quality although this was materially improved as a better understanding of furnace requirements was reached. Larger furnaces, grading the size of ore and coke, the sintering of fine ore and the blending of various qualities of coal for use in the ovens, all contributed to the production of cheaper iron.
One of the attractions to the colliery companies of installing the early by-product coke ovens was their ability to use the small coal left after the run-of-mine coal had been screened. Such fine coal was always contaminated with shale, clay and stone from the floor and roof of the seams which obviously could not be hand separated as in the case of the larger coal. The impurities could, however, be separated by washing, but this added a cost which the cleaned coal could not always carry if used as an ordinary fuel.
The new coke ovens were, however, designed to use crushed coal of about a quarter of an inch down, and the economics of the process enabled it to absorb the cost of washing and crushing. Consequently a coal washery became a feature at all the collieries where the new ovens were installed. The washed small coal was allowed to drain either in bunkers or on slow moving draining conveyors until its moisture content was reduced to 9 or 10% and then crushed.
It was considered that the local coals produced better coke if the coal was stamped into a cake before charging to the ovens, and a feature of all the local plants was a stamping machine which prepared a solid cake of coal, the full length of the oven but slightly narrower and sitting on a peel which was mechanically propelled into the coking chamber. Whilst a large measure of mechanisation had been applied to the ovens designed and built in the first 20 years of the present century, there was still much manual labour necessary. For example the coke, after being discharged from the ovens and quenched with water, was loaded into wagons by men using large forks with tines three quarters of an inch apart to separate the fines or breeze. In a normal eight hour shift three men manhandled 100 tons of coke.
Other manual jobs consisted of winching the oven doors up and down as required for pushing and charging, hand operating the gas reversing valves, and keeping the gas collecting main free from pitch deposits by hand poking.
In the early 1920s there were many developments by the oven designers and builders which were to result in larger ovens operated at higher temperatures, with mechanical aids to eliminate the particularly heavy manual work associated with the earlier plants. The Workington battery of 1936 incorporated the most up-to-date techniques of this nature.
Today there are few relics left of the earlier coke making activities. Until quite recently there were traces of the ‘heaps’ where coke was made for the Little Clifton furnace. It was possible to identify the base of the heaps by the carbon impregnated earth and stones on which they had been built. At Maryport there is still the remains of an oven, probably the oldest in the country. The (other? Ed.) beehive ovens have long been demolished. The last visible ones were buried under the spoil heaps of the Risehow collliery alongside the road on the north side of Flimby. There are (were? Ed.) considerable remains at William Pit, Whitehaven, of the old beehives. The earlier by-product ovens have all gone, but there are records of their design in the text books and catalogues of the builders.