G.— ENGINEERING. 171 



The two principal items in which economies must be sought are 

 obviously a reduction in the consumption of coal per unit generated, and 

 a reduction in the capital expenditure. 



Many refinements can be employed which may economise coal, but at 

 the expense of an undue capital expenditure. Broadly speaking, the 

 employment of bigger stations and an increase in the size of plant employed 

 reduces the capital employed per kw. of plant installed. Interconnection 

 of stations fiirther reduces the percentage of reserve plant, and thus 

 reduces the capital employed per kw. of plant demanded. 



The employment of higher steam-pressures, reheating the steam in the 

 later turbine stages, so as to reduce its total volume and minimise the diffi- 

 culties of design experienced in the vacuum stages of the turbine, stage 

 feed-water heating through ' bleeding ' the turbine, and thus utilising the 

 latent heat in the steam, are all producing higher thermal eSiciencies 

 between the electricity generated and the fuel consumed. 



Sir Charles Parsons, to whom the world owes so much, has shown that 

 with a steam-pressure of 500 lb. per square inch and a 97.5 per cent, 

 vacuum we may hope to reach a full-load thermal efficiency (steam to 

 electricity) of 33i per cent., while with an initial steam-pressure of 1,000 lb, 

 per square inch we may obtain a thermal efficiency of 35 per cent. 



Assuming a boiler-plant efficiency of 83 per cent., the equivalent 

 efl&ciencies (fuel to electricity) are 27.97 per cent, at 500 lb. pressure, and 

 29.2 per cent, at 1,000 lb., which are figures comparable with the best 

 realised results claimed from internal-combustion engines. The equivalent 

 heat consumptions per kw.h. are 12,200 and 11,685 B.Th.U. respectively, 

 or, assuming coal as fired to have a value of 11,500 B.Th.U. per lb., the 

 coal consumed is 1.16 lb. and 1.11 lb. per kw.h. 



The development and steady improvement of the steam-using plant 

 at the generating station is proceeding satisfactorily, and we are certainly 

 within sight of a heat consumption not exceeding 12,000 B.Th.U. per 

 kw.h. generated at base-load stations. Where a group of stations is 

 interconnected the peak-load stations with annual load factors of only 

 about 20 per cent, woidd, cceteris paribus, require a fuel consumption of 

 about 20,000 B.Th.U. per kw.h. generated. Although the annual load 

 factor is low, the programme for running the plant can be so arranged 

 that the plant load factor is high. There is a probability that fewer 

 refinements would be commercially justified in peak-load stations, and in 

 the estimates which follow the heat consumption at such stations is 

 advisedly taken at 22,000 B.Th.U. per unit generated. The average 

 B.Th.U. per imit sent out or available for transmission would thus be 

 16,500, at a station load factor of 35 per cent., and representing a thermal 

 efficiency all round of 20.6 per cent., which would be a notable advance 

 on the last recorded figure of 12.45 per cent, for the whole country. 



There is also the steam-raising plant to be considered, and it may be 

 well to review briefly the economic developments which may be looked for. 



With the coming of the larger turbine, a demand has arisen for larger 

 boiler units and higher evaporative capacities. The present general land 

 practice is some 7 to 8 lb. of water evaporated per square foot of heating 

 surface, but in marine practice, and in naval practice particularly, 

 evaporations up to 20 lb. per square foot are normally called for. 



