THE PLACE OF THE GAS TURBINE IN FUTURE ELECTRICITY GENERATION*By B. V. POULSTON, Graduate.f

(ABSTRACT of a paper read before the NORTH-WESTERN STUDENTS' SECTION 6th October, 1945.)

During the past thirty years, the process of mechanicalsimplification by which the steam turbine evolved from thereciprocating steam engine, has been applied with increasingsuccess to the internal-combustion engine and has resulted in thegas turbine. Briefly, the simple gas turbine consists of a com-pressor inspiring air, which it delivers to a combustion chamberan which fuel is injected and burnt, the gaseous products of com-bustion driving turbines which, in turn, drive the compressor andthe external load.

APPLICATIONS OF THE SIMPLE GAS TURBINEThis simple gas turbine has a theoretical efficiency of about

17% and so is immediately applicable only where its othercharacteristics are of more value.

Its most important applications are, first, in chemical and otherprocesses, when the process may be supercharged to advantage bymeans of a compressor driven by the turbine, which utilizes thehot exhaust gases from the process; secondly, in standby plants,where compactness, self-sufficiency and quick-starting propertiesoutweigh low efficiency; and thirdly, for traction purposes, whereagain compactness and lightness are of importance.

IMPROVEMENTS IN EFFICIENCYThe efficiency of the thermodynamic cycle is increased by

raising the maximum temperature, but this is limited by the per-missible working temperature of the turbine blading. However,other methods are available, such as recovering some of the heatin the exhaust gases by means of heat exchangers and using inter-coolers to make the compression process more nearly the efficientisothermal one. Also, the output can be efficiently boosted bysub-dividing the expansion stages and interjecting reheaters.

ECONOMIC CONSIDERATIONSTo obtain some idea of the comparison on an economic basis

between a large modern steam station and a possible high-efficiency gas-turbine station, it is useful to consider the com-ponents item by item from the point of view of capital andrunning costs, as well as technically.

Capital Costs.—The relative types of component are as follows:—Steam Station. Gas Turbine Station.

(a) Coal storage and handling. Coal or oil storage and handling.(b) Boiler house with the auxiliary Compressors with their driving

firing and draught equip- turbines and high- and low-ment. pressure combustion cham-

bers.(c) Ash handling. —(d) Engine house. Turbines and generators.(e) Condenser plant and cooling Heat-exchanger plant and inter-

towers, coolers.(./") House supply for auxiliaries. Smaller house supply for starting

and fuel-handling.(g) Control. Control.

(a) There should be no difficulty in developing a gas turbineto run on pulverized coal, in which event the required handlingand pulverizing plant would be similar in the two cases. If oilis used as fuel, the pumping plant should be simpler and cheaper.

• The original paper, of which this is an abstract, was awarded a Students' Premiumby the Council.

t Metropolitan-Vickers Electrical Co., Ltd.

VOL. 93, PART I.

(b) Broadly, the bulky boiler equipment of a steam stationwould be replaced by rotating machines and by compact com-bustion chambers, and would result in saving in the size and costof the buildings, if not in the total cost of machinery, the com-ponents of which might be relatively more expensive.

(c) The problem of ash-handling depends on the firing systemin use, but with the air quantities and pressures available it shouldbe easier and less costly of solution than with the present steamstation.

(d) Here there should be a small saving in size and weight ofthe turbine, since higher stage-temperature drops can be used,and a further saving in the simplification of control and governing.

(e) The heat exchangers and intercoolers are not strictly com-parable in function with condensers and cooling plant, but may becompared in size and cost in an approximate analysis such as this.Based on present knowledge of heat transfer, the heat exchangersare likely to be larger than the condensers in a steam station, butnot necessarily higher in cost: while the intercoolers and theirassociated extra pumping and cooling equipment are not dealingwith the heat'quantities involved in the condensers, and so wouldbe smaller and less costly than the normal water-cooling plant.

(g) Control of the gas turbine is effected primarily on the fuelsupply to the combustion chambers, and its complexity andsensitivity again depend on the design of the firing system.However, the gear should not be as bulky as that required forcontrol of the steam supply to a steam-driven turbine.

The main tendency is for the size and capital cost of the build-ings for a gas-turbine station to be less than for the familiar steamstation, although in sum the machinery cost would be similar.

Running Costs.—The predominant item, fuel costs, is influencedby the thermal efficiency of the plant and by the price of the fuel.It seems likely that large gas-turbine plants can soon be built tohave efficiencies approaching those of the best steam plants whileburning efficiently cheap low-grade coal and bunker oil. Thusfuel bills should be similar for the two types of station. Lubrica-tion costs should be similar, but water costs should be less sincethe quantities of water would be less.

In general, the difference in maintenance between the twoplants is that the cleaning and maintenance of boilers, economizers,etc., would be replaced by that of rotating machines and com-bustion chambers. The maintenance costs may therefore beslightly higher for the gas turbine.

The total running costs of this type of plant would thus appearlikely to be comparable with those of the normal steam-turbineprime mover.

CONCLUSIONSThere is little evidence that drastic economies would be

obtained with gas turbines, unless great improvements in com-pressor and turbine and heat-exchanger efficiencies enabledadvantage to be taken of the inherently higher efficiencies of thecycle at high temperatures, and unless the required heat transfercould be obtained with much smaller apparatus. Nevertheless,there exists at present a large field for the use of the gas turbinein small local peak-load and standby stations, where quickstarting and small water demand are advantageous.

577 ] 35