170 SECTIONAL ADDRESSES. 



according to the time and season, is less regular and more intermittent. If 

 we take as example the estimated total requirements at some future day — 

 namely, the 15,500,000 kw. and 47,000,000,000 units output— the base 

 load would represent a load of 6,000,000 kw., the output of which would 

 be 30,000,000,000 units or thereabout, while the remaining 9,500,000 kw. 

 would produce the balance of the outpiit, viz. 17,000,000,000 units, 

 at the low annual load factor of 20 per cent, or thereabout. It is 

 a fundamental requirement in the economics of electricity supply that the 

 base load or high load factor component of the total output must be 

 generated at the most economical rate that engineers can devise. What are 

 the lines along which improvements are now being made to convert the 

 highest possible thermal units available in the fuel consumed into useful 

 work for the benefit of the consumer ? 



The published Analyses and Summaries of Returns of fuel consumption 

 show that the average thermal efficiency of 1924-25 for all public generating 

 stations in this country was as low as 12.45 per cent, with an average 

 station load factor of 28.84 per cent. The highest recorded efficiency for 

 that year was at the Barton Station of the Corporation of Manchester, 

 viz. 19.85 per cent, based on units generated, the station working at an 

 average annual load factor of only 29.5 per cent. Corresponding figures 

 for the year 1925-26 show that the average thermal efficiency has been 

 raised to 21.48 per cent. — equivalent to 20.40 per cent, based on units of 

 ' output '- — with an annual station load factor of 48 per cent. 



From a paper recently presented to the Mid West Power Conference 

 in Chicago by Mr. Wm. S. Monroe, it would appear that the Crawford 

 Avenue Station of the Commonwealth Edison Company of Chicago has 

 recorded a thermal efficiency based on ' output ' of 22.24 per cent., 

 working at a station load factor of between 60 and 70 per cent. It is 

 understood that the plant at this station is not yet in full operation, and 

 therefore higher operating efficiencies may be anticipated. 



The steam pressure at Barton is 375 lb. per square inch, and at 

 Crawford Avenue 550 lb. In the former case the condensing water is 

 drawn from the Ship Canal, which has its limitations, while the Crawford 

 Avenue Station draws its condensing water from Lake Michigan, where 

 the volume is relatively inexhaustible and the average annual temperature 

 is low. A higher average percentage vacuum is therefore probable at 

 the latter station, assisting towards higher thermal efficiency. 



The published results of other American stations — notably at Philo 

 and Boston- — would appear to indicate that thermal efficiencies of the 

 order of 24 per cent, have been obtained. 



Let us examine, first, the improvements which are being tested in 

 practice to turn into useful work the highest amount of the heat available 

 in fuel, and then consider their commercial value ; having regard to the 

 capital invested. If we take a modern station as an example, working 

 at an annual load factor of 40 to 50 per cent., the total costs of generation 

 may be subdivided as follows : — 



Coal . . . . . . 46 per cent, of the total generating costs 



Capital charges . . 40 „ „ „ „ 



Other costs . . . . 14 „ „ „ „ 



100 per cent. 



