Patent GB-772891-A (GB)
Title: Closed cycle thermal power plants
IPC: F02G1/04
Filed: 1954-04-28
Abstract: 772,891. Closed cycle thermal power plants. VILLIERS, C. P. R. De. Dec. 6, 1954 [April 28, 1954], No. 12354/54. Class 7 (1). In a thermal power plant of the closed cycle type in which the working medium is a gas having a density of between 1 and 5 times that of hydrogen at the same temperature and pressure the heating and cooling of the gas is effected under substantially constant pressure conditions while the compression and expansion of the gas is performed by reciprocating pistons. The working medium may contain substantial proportions of hydrogen or helium or both and may also include a small proportion of a chemically inert gas preferably of low density such as nitrogen, carbon dioxide or methane. The working medium may be a mixture of hydrogen and an inert gas such as nitrogen or carbon dioxide containing at least 70 per cent. by volume of hydrogen and having a density lying within the range of 1 and 5 times that of hydrogen. The working medium is compressed in a two stage compressor 22, 24 and then passes by way of a non-return valve V recuperator 3 and a thermostatically controlled heater 4 preferably to double acting engines E, F. The heater is heated externally by any fuel such as coal. The engine E drives the wheels of a locomotive either directly or through gearing and the engine F drives the compressor. Each engine exhausts to the recuperator 3 and from there passes by way of a cooler 21 back to the low pressure stage of the compressor. The inlet valves 5, 5a are operated by special cams 11 and 12 capable of varying the cut off under the action of speed sensitive governors 15, 16. A gas bottle 31 is provided with a three way cock 32 so that it may be connected at will either to a low pressure pipe at 33 or to the medium pressure pipe at 34 or to the high pressure pipe at 35. More than one bottle may be provided each with its cock 32 or the cock may be provided with closed positions between H and M and between M and L. Initially working fluid is contained in a starting bottle 1. The shaft 30 may be used to drive the cam-shaft and auxiliaries such as furnace fans, electric generators and oil pumps, but is not connected to the driving wheels of the locomotive and is therefore free to revolve at governed speed. Warm air from the coolers 21, 23 is used for combustion. The products of combustion from the heater 4 may be used in a small steam boiler for train heating more than one engine E or F and more than one heater may be used. Though the Figure shows single pistons 7 and 8 the actual plant has several pistons. The engine may have 2, 3 or 5 cylinders. The governor 15 reduces the time of admission of inlet valves 5 in accordance with locomotive speed so that the volume of hot gas taken by E per minute is substantially constant over the useful range of operation of the locomotive. On closing a cock 37 the load on the compressor may be sufficiently reduced to cause a higher speed of the shaft 30 and hence of governor 16 which may be unable to reduce the period of admission of valves 5a sufficiently to maintain normal speed. When this occurs the governor 16 causes oil to be released from above the piston 39 via the tube 40 so as to allow valve 36 to open thus allowing an escape of hot gas directly to the cooler 21. The running is controlled by the cock 32. A large proportion of the contents of the system enters the bottle when the cock is moved to the position L. Various operating pressures are quoted. In the heater the gas may be heated to about 600‹C. A fairly high mean piston speed of about 25 to 35 feet per secon may be used. Referring to Fig. 4 the surfaces of the piston are lagged by lagging material 42 which may be " Amosite " asbestos wool. The lagging is held in position by means of metal or steel shields 43 (43a, Fig. 5). Holes 45 drilled through the piston web and 46 passing down the centre of the piston rod 18 connect the lagging spaces with the crank case space below which contains air at atmospheric pressure. Spacers 47 are preferably rings of steatite or refractory cement. The lagging of the cylinder heads is accomplished by the same methods. The valve seat inserts 57, 58 are shrunk into the cylinder heads 52, 53 respectively and welded at 59 and 60 respectively. The inlet and exhaust ports are internally lagged by lagging 61, 62 which may be held in position by thin sheet metal 63, 64. The shields may be made of metal having a lower coefficient of expansion than that of the piston body 8. A space 66 may contain cool gas which cools the valve stem and adjacent valve surface. This space is connected to enclosed spaces 70 (Fig. 3) via passage 71. For rapidly closing the inlet valves 5a it appears necessary to use a bundle of torsion bars 83. A cam-shaft 92 is driven at crank-shaft speed by gearing not shown. The exhaust cam 10 and the portion 96 of the inlet cam which lifts the followers 72 is formed on the shaft 92 in the usual way. A sleeve 12 is bored so as to be a sliding fit on the shaft 92 and about a quarter of the circumference of the sleeve is removed so as to give a helical slot which may slide past similar helical surfaces 98, 99 milled on the sides of the portion 96. When the sleeve is moved axially it also moves circumferentially so that the port of cut-off is altered. The governor comprises an outer cylinder 16 containing a stepped piston 104. The cylinder cover 105 is firmly shrunk on the end of shaft 92 and is screwed to the cylinder 16 so that both piston and cylinder rotate with the shaft at engine speed. Piston 104 is attached to rod 95 by means of a freely fitting screw thread 106. A broad leaf spring 107 of suitable shape and stiffness is fixed to the outside of the cylinder and carries a weight 108 having a shaped profile 109. A needle valve 110 slides against the weight as shown in Fig. 2. Lubricating oil under pressure is fed to all camshaft bearings 93, 94. Some of this oil passes via drilled passages to the right hand cylinder space 111 through the orifice 112 and into the left hand cylinder space 113. A stud 117 is used as a guide to locate piston 104. If the engine speed should be too great the movement of weight 108 allows valve 110 to open thus allowing oil to flow from space 113 via hole 114. The oil pressure developed across the orifice 112 then causes piston 104 to move leftward thus moving rod 95 and sleeves 12 leftward and causing the inlet valves to close earlier. This tends to reduce the engine speed. If the speed reduction is insufficient when the piston 104 has moved into its leftmost position then the port 115 allows lubricating oil to escape from hole 115a, port 116 and tube 40, Fig. 1, allowing the safety valve to be lifted. Ports 115, 116 are shown on second bearing here for convenience but would normally be located at the left hand end of the cam-shaft. The engine F may be governed at an almost constant speed at all loads and may therefore be used to drive an electric generator. Alternatively the governor may alter the cut-off so that the engine E consumes the same volume of hot gas per minute over a wide range of locomotive speeds. The cam mechanism may also be used upon engine E but in this case a mechanical reversing gear may be required between the engine and wheels. Alternatively a known type of cam mechanism (for example type RR, Engineering, Vol. 168, p. 291), may be used on engine E so as to obtain reverse operation as well as suitable variation of cutoff which may be done automatically by means of a governor as described above. Referring to Fig. 8 the oil in tank 121 which is above the level of groove 160 is able to prevent gas leakage to the crank case 120 during storage. The circles marked R are pressure release valves and those marked P are oil pumps for example of gear wheel type. The pressure in 121 is maintained at exhaust pressure. Pump 128 feeds oil to various engine parts such as the crank and cam-shaft bearings to ports 130 and to the exhaust valve and safety valve stems at ports 131. Valve 132 is set to maintain the oil from 128 at a pressure above that of the exhaust 20. Hence the valve stems are oil sealed the packing 133 round the stems merely serving to prevent oil entering the hot gas space. Pump 128 also delivers oil to port 134 surrounding rod 18 (Figs. 4, and 8) whence it flows via pipe 135, holes 136 drilled within the piston web to the cooled part of the cylinder walls for lubrication purposes. Surplus oil is returned via the circumferential slots 137, holes 138, 139 to the radial hole 140 in the piston rod. When the piston rod arrives near the bottom of its stroke the oil with any gas which has escaped past the piston rings passes via port 142 and returns to the tank 121. Further oil from pump 128 flows via valve 145 to cylinder 146 containing a small spring loaded piston 147. An inwardly acting scraper ring 148 is fitted. When under pressure some of the gas in the cylinder space 150 passes with oil to the back of the scraper ring and thence above the piston where it assists the spring in lowering the piston and thus forcing oil at still higher pressure along pipe 151 to groove 152 and causing the piston rod to be oil sealed. Surplus oil from ring 148 may pass the upper end of the piston and return to the tank. Pump 154 returns surplus oil via valve 155 to tank 121. This valve is set to give an oil pressure above that in the intercooler 23. This oil is fed to groove 156 continuously for gas sealing the lower end of the piston rod and for lubricating piston 40. Also this oil is fed via valve 157 to spring loaded piston 158 in cylinder 159 which feeds oil to groove 160 surrounding the cross head piston 28 thus sealing and lubricating piston 28 which thus requires no rings. The action of piston 158 is similar to that of 147. Further oil from cylinder 159 which rises intermittently above maximum gas pressure is fed via valve 161 and pipe 161a to ports 162 for oil sealing the inlet va