338DISCUSSION ON THE PIMLICO DISTBIUJ! Discussion M r W. B. Noddings (Chief Commercial Officer, Central Electricity Authority) said that it was well known that very great difsculty and many problems arose in allocating the costs of a combined product; for example, what was the cost of wool and what was the cost of lamb? It was clear that the particular solution must depend on the particular circumstances. The Authors had dated that in Germany more than sixty different methods of cost allocation between electricity and heat supply had been used. TheAuthors deserved sympathy in having to make the diEcult choice between all the methods available, but he thought it would be agreed that in the solution which they had adopted they were certainly not biased in favour of electricity, and it might be said that they had erred, if a t all, in the direction of showing a very favourable charge to the heat supply. They had explained that in the hypothetical scheme for the ultimate development they had credited the kilowatt outpnt of the back-pressure plant with a full kilowatt charge, on the ground that in the case in question the accumulator permitted the operation of the station in such a way that the output of the station broadly followed the requirements of the electricity supply system. That was a very fair basis of assessment in the particular case considered, but there might be other cases of district heating where those circumstances would not apply and where the output fi-om a station might in summer be less than the appropriate proportion of the winter output which was required by the seasonal variation in the electricity requirements. In that case, of course, it would be appropriate to devalue the kilowatts. Many interesting figures were given in the Paper, and others could be derived from those given. It seemed that the overall efficiency of conversion-i.e., the energy supplied by way of electricity and heat related t o the heat input in the coal-was of the order of 80%. The corresponding figure if the two supplies, of electricity and heat, were derived independently, the one by electricity production in the normal way and the other by independent central heating, was about 55%. The figure of 27% had been given by the Authors for electricity production, and a figure of 60 to 65% might be taken for independent central heating.
The paper refers to the seven years' period following the nationlaization of electricity supply. The various reasons for plant testing are stated but such work is never an end in itself. The average heat rates for 33 sets each of 30 MW. and 30 sets each of 60 MW. are stated, together with their standard deviations. Heat rates as low as 7,800 B.Th.U. per kW.-hr. may be achieved in the foreseeable future. In the seven-year period 77 per cent of new sets were tested, which yields a fair cross-section of the performance of the installed plant. It is the intention to introduce a system of routine testing for the more important machines. In dealing with the subject of boiler tests, available methods are reviewed and consideration is given to recent simplifications of the deferred efficiency test as agreed with the Watertube Boilermakers' Association (W.T.B.A.). A table of average boiler losses for stoker and for pulverized-fuel firing is presented and from this reliable estimates of boiler performance can be deduced so as to allow for several variables which could affect the answer. Water flow enters into the testing of both boilers and turbines. The paper refers to standardization of flow metering in the Central Electricity Authority (C.E.A.) and states that five hydraulic calibrating laboratories are being constructed. The Authority is constantly investigating improved means of flow measurement and hopes thereby to contribute to an improvement in technique. With regard to electrical metering, and in view of the proposal to introduce routine turbine testing, meters should be of the highest quality. N.P.L. certificates have been obtained for a super grade of instrument and results are set out in tabular form. The paper ends by a foreshadow of some possible improvements in electrical integrators.
The efficiency of the regenerative cycle may be defined as the ratio of the heat converted into work (in British Thermal Units per pound of steam) to the heat supplied to 1 lb. of steam in the boiler plant. Where feed heating is employed, however, the heat converted into work is less than the adiabatic heat drop as calculated from the initial and final states of expansion. The difference between these quantities is termed “unavailable heat” in the paper, and the efficiency is therefore given as the ratio of the adiabatic heat drop less the unavailable heat, to the heat supplied to 1 lb. of steam in the boiler plant. The object of the paper is to illustrate the advantage derived from working in terms of unavailable heat. Values of this quantity are given, and the author provides a worked example showing their use. Appendixes I and II deal with investigations of the case in which the number of feed heating stages is infinitely great, i.e. the conditions for the ideal efficiency. The relationship of the ideal efficiency to other efficiencies corresponding to various finite numbers of feed heating stages is indicated.
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