PRODUCER GAS E
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-3TS AND FANCIES AWELL-KNOWN engineer, with whom we have been acquainted for many years, has been experimenting for some time with various types of gas producer, so we asked him to give his views on the subject. The following matter is the result. It may be somewhat caustic in parts, but at least it is constructive and not devoid of humour.
There are, he says, several answers to the question: " What is a gasproducer plant? "
The Ministry of Mines considers it is something that will enable road transport to carry on by the use of home-produced fuel, thus helping to prevent depreciation of our foreign exchange.
The producer-plant manufacturers look upon it as a means for using home-produced fuel, and one which will save two-thirds of the cost of the fuel previously employed.
The transport-vehicle operator is inclined to think of it as a device that may take longer and cause more trouble to carry 'a considerably smaller pay-load.
The answer of the Ministry of Mines is perfectly sound, and it behoves everyone concerned to fall in with its proposals, independent of the fact that there is no choice but to do so. Much can be accomplished by willing co-operation.
Early Vehicle Gas Producer
In 1826, over 100 years ago, Samuel Brown made a gas producer and screwed it on to a road carriage. Then he took one of the gas engines that he was making and selling in London and screwed that on, too. It is on record that as a result he was able to climb Shooter's Hill at quite a good speed.
No further development of gas producers for road-transport purposes took place until the beginning of the present century, although stationary producers were in use for many years for driving gas engines both large and small in industrial establishments, as in many cases they could compete in cost with town gas.
The gas-producer plant is unique in that, up to the present, it has defied evolution. If Sam Brown could review his two products—IC. engine and producer plant—to-day, after a lapse of 100 years, he would be astonished at the difference in the development of these two units. The engine of to-day has enclosed crankshaft and valve gear; in his days those parts were all exposed. It has electric or compression igni A.36
tion and rues at three or four times the speed of Sam's original engine, developing 10 times or more the horse-power for the same cylinder capacity.
The gas producer—or coal carburetter—still remains a tin can, with function control in no way connected or influenced by the engine that it serves. The argument in support of this condition of things is that the plant is simple both in operation and maintenance; that complications are
undesirable. If we point to the blatent absence of simplicity in the engine, gearbox and back axle of our transport vehicles, and to which we take no exception since they function with complete satisfaction to us, we have reason for saying, "Why not the producer also?
The development of producers has not been along the lines of general principles and the application of modem possibilities; it has attacked only details. The fear of the criticism of any departure from simplicity has outweighed the prospects of advantages accruing from the application of logical machine controls to the plant. Further, the volume of business being transacted in producer plants has been insufficient to support the experimental expenses necessary for their evolution. In this particular, it is of interest to note that one of the established plants has recently been taken over by a large engineering interest, in whose hands immediate development may be confidently expected.
Where Experimental Work Occurs
Most of the experimental work has been directed to the two holes in the side of the tin can. These have been shifted up and down, multiplied into single and double rows of concentric rings of three, five and seven; put in the centre looking upwards or downwards, or various other arrangements made.
There are two general types of plant, so far as the air supply is concerned. One uses the high-speed air stream, as in a blacksmith's hearth, by means of a tuyere with one or more holes as referred to above. This makes for a higher temperature in the fire zone than the other type, which resembles the fire grate of a stove, where the air stream is much less fierce, and the fire accordingly so.
Care of the Tuyeres
The tuyeres are very hard-worked components, and it is usually necessary to water-cool them. Some are cooled from the radiator system of the vehicle, others have a separate radiator fitted for their own use. Any interruption in the water-cooling of the tuyere spells trouble. One plant which works on the stove-type of fire grate uses a tuyere for quick starting, which tuyere is out of action when the producer gets going. It is unnecessary to water-cool this tuyere as it is made of carborundum, which stands up for the short period of time it is in work. The tuyere-type of plant is called the cross-draught, as the air passes in at one side and the gas out at the other.
The grate-type of plant has several variations, up, down, or double draught, depending upon the direction the air is made to take in its journey to the fire and from it, as gas. The double draught reverses the air current from down, and directs it upwards through a column of charcoal, to extract impurities from the gas. Most of these are Continental practices.
There are two qualities of gas produced in these plants. In one case water vapour is fed to the fire and this produces a gas of higher calorific value, • due to the production of hydrogen by the decomposition of the water. This hydrogen content amounts to about 12 per cent. as against only 5 to 7 per cent. in the case of the gas produced without water. The calorific values are respectively 145 B.Th.U.s and 135 Temperatures and Clinker Troubles Some indication of the temperatures existing in the producer are given by the fact that the combustible gas from which our power comes— carbon monoxide—is not made until the temperature reaches 1,000 degrees C. Under that temperature carbon dioxide only is formed.
Ash fuses and becomes clinker, stopping gas production, at between 1,300 and 1,400 degrees C. As these temperatures, and, indeed, much higher ones, are attained in the fire zone, ash which remains in the hot zone is fused and must be poked out of tuyeres and firebox by an iron rod.
It is of considerable interest to note that the recent patent issued to T. Hurley, of the Fuel Research Station, as reviewed in our issue of January 13, adopts a mechanical means for ash ejection from the fire zone, by means of moving grate bars. His patent aims at the use of fuels of wider specification, and claims for his producer the ability to eliminate from the fuel much greater tar content than can existing producers.
The Mining Association has just issued specifications of suitable fuels for use in small portable producer plants. The chief brands are Progasite, Suncole and Motor Coalite; others are in course of development. It is important to note that fuels that do not come within these specifications will inevitably cause trouble in the plant and in the engine. Fuel for 150 to 200 miles is stored in the firebox, from which tars will be dis
tilled out, and clinkers formed to obstruct the gas-forming operation of the fire. The engine will gum up and the lubricating oil will deteriorate. The time will come when producers will be able to use such fuels, but this is not yet.
Sam Brown must have had lots of trouble with fuel in his day, and yet we are still doing the same things to-day as he did so long ago.
Sam harnessed the roughness of the roads to form the automatic feed of fuel to his fire; we still do the same thing in our producers. He also used this same roughness to shake the ashes out of his fire; we still do the same. I expect Mr. Brown used a similar iron rod to the one we use.
It is difficult to understand why we still expect the irregularities of the roads to carry out the duties they did for Mr. Brown 100 years ago.
It is illogical. Why do we not use machinery to do these jobs for us? Why not connect up the control of the functions of the producer to the engine for the particular benefit of which they are performed? Why let a stretch of rough road force a burst of gas on the engine when it does not want it? What happens on a hill-. climb when the road is beautifully smooth and no gas is " shaken" into the engine? Give the engine self-determination and let it tell the producer when it wants gas, and how much it wants. What is the use of letting the producer ask the road what the engine wants?
Automatic Plant 25 Years Ago These facts were all found out 25 years ago when Lieut.-Colonel D. J. Smith, a pioneer in producer plants and known to many readers of this journal, patented a plant which did all the things indicated above, which patents were bought by the late Major Tulloch The controls of the Smith producer or coal carburetter (known finally as the Tulloch-Reading) were mechanically operated from the engine, which metered the fuel to the fire, eliminated the ash by means of moving fire bars, which also prevented the formation of clinker; it also supplied to the fire the correct quantity of steam, which it raised from water. The bulk of fuel was not stored in the firebox, and was not subject to the heat of the fire until the proper time arrived for its combustion, so that tars should be produced only in a temperature high enough to destroy them.
The firebox was fire-brick lined, the water supply heated, as was also the incoming air, by the gas, outgoing at 900 degrees C. This heat regeneration increased the efficiency.
The Smith plant was capable of dealing with a wide range of fuels of various kinds found in different countries of the world. Peat, rice straw, coconut shells, bagasse and others. Also the range of anthracite it could successfully use was much wider than the recently published specification provides for, and—a point of great importance—it did not require that the fuel should be dry, a stipulation made by some plant makers, which calls for special preparation and consequent expense and stocking difficulties.
Reasons for Power Losses The theoretical difference between the values of explosive mixtures is that producer gas is 25 per cent. weaker than petrol. This assumes that each is used in its appropriate engine. When, therefore, gas is used in a petrol engine, and not in a gas engine, the efficiency falls short of the theoretical possibilities.
The results of calorific-value tests on the road indicate that gas supplied to the engine instead of being of the order of 135 B.Th.U.s per cubic ft., falls short of this value by 15 per cent. Power tests confirm these figures, and show losses of 35 to 50 per cent., as compared with petrol.
The first loss is basic; it can be regained in a large measure by carburetting the gas with a small quantity (about 5 per cent.) of petrol.
The second loss is inefficiency in the conversion of the heat value of the fuel into mechanical energy, and depends for its cure on the improvement of functioning of the producer plant with a view to obtaining a gas of higher calorific value, and a quick response to demands made upon it by the engine for the performance of the duties required.