174 SECTIONAL ADDRESSES. 



The late Sir George Beilby, in his James Forrest Lecture at the Institu- 

 tion of Civil Engineers in 1921, said : ' When coal is used for steam- raising 

 under the best known conditions, it is obvious there is little to be gained 

 in thermal efficiency by any preliminary sorting out of the thermal units 

 of the coal into fuels of liigher availability. It is well known that an 

 efficiency of 75 to 80 per cent, is attainable in steady practice,' and he went 

 on to quote the results from two power stations — namely, the Central 

 Electric Supply Company at St. John's Wood, where the average boiler 

 efficiency was 75.5 per cent, although the average ash content in the coal 

 fired was 18.4 per cent., and the Southern Railway Company's power 

 station at Wimbledon, where the average boiler efficiency was 78 per cent, 

 with an ash content of 16 per cent. 



Sir George Beilby also said : 'Supposing the coal used at these stations 

 had been submitted for preliminary carbonisation and its thermal units 

 sorted out into the forms of gas, tar, and coke, how would this have affected 

 the evaporative capacity ? Of the thermal units of coal 



Per Cent. 

 The coke would contain . . . . . . . . 70 



The gas „ „ 12 



The oils „ „ . . . . . . . . 11 



93 



Per Cent. 



Intrinsic thermal loss . . . . . . 7 



Heat for carbonisation . . . . . . 6 



— 13 



Net thermal value . . . . . . . . 80 



' The high thermal availability of the rich gas would be thrown away if 

 it were used for steam- raising, the fuel oil would be a boiler fuel decidedly 

 superior to the original coal, and the coke would not be of more than equal 

 value to the coal. Solely from a steam-raising point of view, therefore, 

 a thermal loss and not a gain would result from the operation. I am quite 

 prepared to admit that in special cases this thermal loss might be compen- 

 sated for if a local market for the rich gas were available. In most cases, 

 however, the margin of profit would be much too small to justify the extra 

 capital expenditure which would be required.' 



The additional capital cost of low-temperature carbonisation plant 

 appears to be from £0.9 to £1.1 per ton of coal carbonised, which is equiva- 

 lent to £4 per kw.i. additional capital expended, or 28 per cent, addition 

 to the normal capital expended upon a modern power station. It has 

 been claimed that, after allowance for the extra capital charges on the 

 station and crediting the cost of production with the marketable value of 

 the fuel oils recovered by the process, the net cost of electrical energy 

 delivered (not only the net cost of the fuel consumed) would be reduced 

 by more than 50 per cent. One may be sceptical about the realisation of 

 so great an improvement, but until the matter has been put thoroughly 

 to the test it is impossible to say whether this method of treating coal will 

 really be a source of economy in the generation of electricity. 



Whatever the future may bring forth in the application of coal 



