Croydon Harnesses Methane for Salvage Transport
Page 20
Page 21
If you've noticed an error in this article please click here to report it so we can fix it.
WASTAGE of a magnitude that is VV little short of amazing has been revealed by the campaign for economy, that is a feature of the moment. Paper, metal, bones and all sorts of funk that hitherto have not been worth the trouble of salvaging, have suddenly become precious.
-A glaring example is methane gas, of which the useless burning at sewage works has been going on for years. Valuable beat has been generated from it and wastefully dissipated for the sake of convenience. Local authorities,
with the rest, have been as profligate almost as Nature herself, treating this along with other refuse, aS refuse, seeing no possibility of economically turning it to good account.
This• useful gas, richer actually than town gas, and much superior in heat value to producer gas, is now to be harnessed. It is to he employed as-the motive power for the collection of other refuse--waste to save waste— what has hitherto been a useless. by-product, to he employed in converting rubbish to commodity.
Croydon Corporation is installing equipment for the operation of its public cleansing fleet, and, subsequently, of all its transport on the methane gas generated at its Beddington sludge-digestion plant. It is to be congratulated on this enterprise., Already some of the gas is being used for the generating of electric power, but the plant for this is, as yet, not quite complete; also the exhaust and cooling-water heat from these engines is being employed in the treatment of the sludge for which the gas was formerly used direct. In a few weeks the methane will be running a compressor for bottling the fuel for the vehicles, and thereupon it will be providing the power for transport.. Thus are multiple economies effected. It is estimated that the resultant saving will write off the outlay, in so far as the transport system is concerned, in two years.
With this " heat-exchange " scheme for the treatment of sludge in full operation, there will be available
120,000 cubic ft. of methane per day. Allowing for the fact that this contains about 30 per cent. of carbon dioxide, -200 cubic ft. are approximately the equivalent of one gallon of petrol. Therefore there will be available a daily supply of surplus gaseous fuel corresponding to 600 gallons of petrol. At present the cleansing fleet, comprising 30 vehicles,, uses 40,000 gallons a year. It is estimated that the cost of compressing, including labour an I maintenance, but excluding capital outlay, should not exceed the equivalent of 3d. per gallon of petrol. We believe that this will be the first fleet of refuse collectors to be operated on compressed gas.
About nine months ago the Corporation put into service 30 new Dennis refuse collectors of 15 cubic yds. capacity and equipped with moving floors. These are the machines which in future will run on gas. An accompanying picture shows one which has been fully equipped.
Under the frame at the sides are mounted four gas cylinders, which were supplied by the Chesterfield Tube Co., Ltd. Each has a capacity of 1.76 cubic ft. and can hold 350 cubic ft. at 3,000 lb. per sq. in. The diameter is 8 ins, and the weight 150 lb. They are made of nickel-chrome-molybdenum steel and have a minimum wall thickness of 0.24 in.
They are charged, just as in the case of compressed town-gas, from six larger cylinders at 5,990 lb. per sq. in. Each of these has a capacity of 19 cubic ft. and holds 6,330 cubic ft. For charging them a Bellis and Morcom six-stage compressor is to be used.
Incorporated in the vehicle system are a filling connection with stop valve, a pressure gauge with stop valve and a main stop valve. Gauge and three valves are mounted in compartments on the near side of the cab, accessible from the outside. The first two valves are fed from one pipe line and the main valve from another, these lines being extensions, respectively, of the two ends of the pipe fed by the four bottles. In each branch a large coil is included to allow for relative motion between frame and cab.
From the main valve, the gas is led to a reducing valve which brings the pressure down to 10 lb. per sq. in., and thence it flows to another which it leaves at just under atmospheric pressure. Thus, no gas passes unless there is suction from the engine. Both the first-stage and the second-stage pressure-reducing valves are Humber products.
The gas mixer is entirely automatic, the driver having no other engina control beyond the accelerator pedal. Compression has been raised to about 8 to 1.
With its 30 per cent, CO, content, the Croydon methane has a calorific value of 700 B.Th.U. as compared with the 675 (gross) of the local town gas. Performance, therefore, should prove to be good. There is no doubt that the behaviour of the fleet will be watched by the whole transport world with keen interest.
Another plan to which Croydon has given some thought is the use of methane by liquefaction. The time is not yet ripe to make any statement about possibilities in respect of this development, but the advantages the scheme offers are an attraction not to be ignored.
Also of importance to our industry is an experiment afoot to convert a Gardner-en gined vehicle in the Corporation's fleet. It will be operated on methane with oil injection for ignition purposes. The unit is a model 4L.K. This application of methane, we believe, also opens up new ground in • the transport field.