The extraction of petrol from coal by the hydrogenation process requires extremely high temperatures and pressures. The enormous plant at Billingham, Co. Durham, is the outcome of years of intensive research in this new and important industry
STORAGE TANKS at Billingham, Co. Durham, for the storage of finished petrol and of oils used in intermediate stages of the hydrogenation process. The tanks are painted with a special paint to reflect the heat of the sun and so reduce to a minimum the risk of expansion or explosion.
IN these days, when every country is striving to achieve a measure of economic self-sufficiency, it is not surprising that a great deal of research has been devoted towards the best possible use of natural resources. Great Britain is fortunate in having abundant supplies of coal, and her industrial supremacy in the past has been in no small measure due to this fact. Only in comparatively recent times, however, has intensive research been directed towards using these vast resources to further advantage.
Coal itself is an exceedingly complex substance and the chemical engineer has succeeded in extracting an enormous number of by-products from it. A huge quantity of benzole motor spirit is produced in British gasworks every year. Again, several squadrons of the Royal Air Force operate on petrol made from British coal by the low-temperature carbonization process. Petrol made from coal is of high quality and gives complete satisfaction. The vast coalfields of the world have all originated from the tropical forests of millions of years ago. Coal has been aptly described as “bottled sunshine”, for it was by the tropical sun of those remote times in the world’s history that these huge forests were formed. They were gradually submerged by the tremendous upheavals of past ages, buried under millions of tons of over-lying rock and soil and have undergone an almost incredibly slow process of carbonization.
One of the most fascinating and remarkable methods of extracting petrol from coal is the hydrogenation process, which is now employed on a commercial scale at Billingham, Co. Durham, by Imperial Chemical Industries, Ltd. The art of hydrogenation consists of choosing the correct conditions of temperature, pressure and time of reaction to yield just the right type of spirit. Briefly, the process consists of passing hydrogen through a mixture of finely ground coal and oil, the reaction taking place under tremendous pressure in the presence of a “catalyst”. A catalyst is a curious substance. It is essential for it to be present so that the reaction may take place, but the catalyst itself remains unchanged throughout the process.
The main development of the hydrogenation process was largely due to the work of the eminent German scientist Dr. Bergius, who started his experiments before the war of 1914-18, and built a small experimental plant at Rheinau, near Mannheim, Germany. This was in operation until 1927, and subsequently the I.G. Farbenindustrie, the large German chemical combine, studied the subject independently. They made a number of important discoveries and found a number of catalysts which were immune to sulphur poisoning.
HUGE REACTION VESSELS, or converters, in which the hydrogenation takes place, are forged from nickel-chrome steel. Hydrogen at high temperatures and pressures has an embrittling effect on ordinary steel, so the converters at Billingham were forged from 150-tons ingots of nickel-chrome steel.
It was in 1927 that experimental work was put in hand by the I.C.I. at Billingham, and in 1929 it was decided to build a pilot plant to treat ten tons of coal a day. This plant ran until the end of 1931. It was the first plant to hydrogenate bituminous coal on a commercial scale for any prolonged period. At this stage of development the two great chemical combines of I.C.I. and the I.G. Farbenindustrie came to an arrangement whereby they pooled all patents connected with hydrogenation through a company known as the International Hydrogenation Patents Co. Then came the stimulus which was needed to justify the building of a large-scale plant By the terms of the British Hydrocarbon Oils Production Bill, the Government guaranteed preference for a period of years on light oils made from indigenous materials.
An enormous amount of preliminary research work was carried out and between the years 1927 and 1933 the total expenditure on large-scale work amounted to £1,000,000. The present plant at Billingham owes its inception to the work of this company, and its principle of operation is founded upon the work of Dr. Bergius.
The operation can best be understood by referring to the photograph of the model of a complete hydrogenation plant reproduced on this page. This is not a model of the plant in operation at Billingham, but is merely intended to show the main features of a plant hydrogenating coal to make motor spirit. For the sake of simplicity the process is represented as being carried out in one stage, instead of the three stages actually employed. The process is known to chemists as an “exothermic” one, that is to say, heat is given out. The plant at Billingham has a number of heat exchangers and other apparatus for using this heat in the operation of the process. This extra apparatus is not shown on the model.
DEMONSTRATION MODEL OF HYDROGENATION PLANT
This illustration shows the connexion between the different parts of a complete hydrogenation plant. It is not a model of the actual plant at Billingham, but it shows the main features of the process carried out in one stage, instead of in three stages as at Billingham. In the process heat is given out ; at Billingham the plant includes heat exchangers and
similar apparatus which, for the sake of clarity, is not shown in this model. A detailed explanation of the various stages of the hydrogenation process is given in the text. Briefly, the process consists of passing hydrogen through a mixture of finely ground coal and oil, reaction taking place in the presence of a catalyst. A Hopper ; B Conveyer ; C Storage bunkers ; D Grinding mills ; E High-pressure injectors ; F Preheater ; G Converter ; H Cooler ; I Catchpot ; J Tank ; K Pump ; L Furnace ; M Fractionating column ; N Condenser ; O Storage tanks ; P Hydrogen plant ; Q Sludge plant ; R Boilers ; S Pipe for heavy oil.
Clean coal is fed into the hopper A and raised by the conveyer B to the storage bunkers C, from which it is fed into the grinding mills D. In these mills the coal is thoroughly mixed with heavy oil, which has returned along a pipe S from a subsequent stage of the process. The whole mixture is ground into a paste consisting of coal and oil in equal proportions. The next operation consists of forcing the paste into the converter system. This is done by the high-pressure injectors E against a pressure 250 times greater than that of the atmosphere, or equal to some 3,750 lb. per sq. in. It is at this point that the coal mixture joins the hydrogen, which has already been manufactured, purified and compressed in the plant P.
Gigantic Steel Forgings
The hydrogen and the coal mixture are then heated together in the pre-heater F to the reaction temperature of 450 degrees centigrade — about four and a half times the temperature of boiling water. Then comes the hydrogenation reaction, which takes place in a gigantic heavy steel forging, or converter, the catalyst being present in the form of a fine powder and being continually agitated by the hydrogen. This converter is indicated in the illustration by the letter G. The greater part of the products and gas pass through a cooler H to a catchpot I, where there takes place a separation between the condensed oils and the uncondensed gases. The former are collected in a tank J and pumped by the pump K to a distillation unit, where they are heated in the furnace L. The cylinder M is known as a fractionating column, and in this the various grades or “fractions” of petrol are distilled off. The motor spirit is then cooled in a condenser N and washed with soda, after which the finished product is stored in tanks shown at O, ready for shipment.
HIGH-PRESSURE VESSELS, known as converters, which are used in the hydrogenation of coal. These vessels have to withstand high temperature as well as high pressure, and are forged from ingots of steel weighing more than 150 tons. The completed vessels work at a pressure of some 3,750 lb per sq in, but were tested at pressures 50 per cent in excess of this. The high test pressures were applied hydraulically, strains and stresses being carefully measured to see that no permanent distortion took place.
The heavy oils are returned to the plant through the pipes S, part being used for pasting oil in the coal mills D, and the remainder hydrogenated further so that only petrol is produced. There is a heavy sludge in the bottom of the converter, and this is led off to the sludge plant Q, where as much oil as possible is recovered and the remainder is burnt under the boilers R. The uncondensed gases in the catchpot vessel I are treated to recover all the available hydrogen and the balance, consisting chiefly of gas, is returned to the hydrogen plant P as a source of further hydrogen for use in the process.
From an engineering point of view the Billingham plant is of exceptional interest, because pressures and temperatures are so high that every item of plant had to be specially designed and built. The high-pressure technique of this process called for entirely new engineering methods, some of which were of a revolutionary nature. One of the most difficult problems confronting the engineers was the design and construction of the huge reaction vessels, or converters.
Hydrogen at high temperatures and pressures has an embrittling effect on ordinary steel. This is particularly noticeable when the pressure is between 3,000 lb. and 4,000 lb. per sq. in. and the temperature above 300 degrees centigrade, conditions found in the hydrogenation process.
Because of the wonderful advances of metallurgical science, the engineer has been provided with many different alloys which resist this hydrogen attack in normal service conditions. After a great deal of research and experiment, the final design of reaction vessel was in nickel-chrome steel. It was in the form of a simple barrel forging closed at the ends by special joints. The design of these joints required a great deal of thought and care, because at such high pressures the bolted joint becomes almost impracticable. A joint of a special type of remarkably simple construction was, therefore, developed by the English Steel Corporation. The joint is held in place by three tapering segmental clamps and a hollow steel ring acts as a sealing device. Once the joint has been made gastight this ring is automatically expanded by the gas pressure and so seals the joint.
Tested to Destruction
It is remarkable to think that these huge forgings have been produced from ingots weighing more than 150 tons. The handling of such ingots is in itself a tremendous task. Throughout the process of forging and finishing the converters, careful inspection was given to the work at every stage. Test pieces were cut from ingots and forgings, examined under powerful microscopes and tested to destruction in huge testing machines. The completed vessels were then subjected to a high test pressure applied by hydraulic means, equivalent to one and a half times the normal working pressure, or 5,625 lb. per sq. in. During this test the strains and stresses were carefully measured, to make sure that no permanent distortion of the metal took place at this high pressure.
IN THE CONTROL ROOM of each section of the hydrogenation plant at Billingham instruments record the temperatures, pressures and gas flew. Here, too, are the valves regulating operating conditions of the plant.
In connexion with the building of the hydrogenation plant as a whole, a remarkable machine for doing heavy electric welding has been designed and built at Billingham. For certain parts of the process it was necessary to have tubes in lengths longer than those which could ordinarily be supplied by the makers. For this reason it was decided to weld lengths of tube together by what is known as “butt resistance” welding (see the chapter “The Craft of the Welder”). This consists of bringing the two pieces to be welded together end to end, and passing a heavy electric current through them at the same time as pressure is applied to them.
Since the current has to overcome great resistance the temperature at the junction is raised considerably — so much so that the two pieces become white hot and can be welded together with ease and certainty while pressure is applied. In this machine the pressure is applied by hydraulic power, and some idea of its capacity can be gauged from the fact that it has been designed to weld an area of 30 sq. in. of metal. The. total weight of the machine is 25 tons and it was in full working order after eighteen weeks. The operation of the machine is entirely automatic, after it has been set in accordance with the particular part to be welded. This machine is one of the key points in the plant and it is believed to be some three and a half times the size of any previous welding machine built in Great Britain. Each section of the hydrogenation plant is provided with its own control room. Here are located all the valves and control mechanism for exact adjustment of operating conditions.
For successful operation of the process it is absolutely essential to use coal which is as clean as possible. The coal is therefore cleaned by a special method, known as the Chance process, in which a suspension of sand in water is used for separating the dirt from the clean coal. By this means it is possible to obtain coal which contains only 2½ per cent of ash. The clean coal is stored in bunkers near the plant, and there is always sufficient reserve for two days’ operation.
The reaction itself takes place in the huge converters of the hydrogenation “stall”. All parts of similar items of plant are interchangeable. A huge repair shop is provided for the maintenance of the plant, and the equipment includes a giant 170-tons crane.
The hydrogen gas is made from coke in a special plant and the total raw coal consumption at Billingham for the 100,000 tons of petrol made directly from coal each year is 500,000 tons.
Petrol from Carbon Monoxide
This great plant is much more than a mere factory for producing petrol. It is an example of the wonderful way in which scientific research is being applied to the solution of an industrial problem. From the early days, when Dr. Bergius first started his classic experiments, this wonderful process has been developed at great expense.
Another process which has recently come into prominence for the production of oil from coal is the Fischer-Tropsch process. It consists of using carbon monoxide as the raw material for making the petrol. This gas is easily obtained from what is known as “water gas”, a mixture of carbon monoxide and hydrogen. This is produced by the gasification of coal or coke. After the gases so produced have been submitted to a purifying process they are passed through a reaction chamber. Here the necessary chemical reaction is brought about by a catalyst.
LIFTING A CONVERTER INTO POSITION at Billingham. A Titan crane with a capacity of 170 tons is used for handling equipment in the hydrogenation plant. The huge converter is a simple barrel forging closed at the ends by special joints sealed automatically by the pressure of the gas.
The Fischer-Tropsch process employs a temperature of only 200 degrees centigrade and takes place at the same pressure as the atmosphere. It is claimed that the petrol produced by this process is of a high quality and good diesel oil can also be produced without difficulty. An enormous amount of research work was undertaken by Dr. Franz Fischer and his collaborators to discover the best possible catalyst. Some thousands of experiments were carried out before the ideal substance was found.