[0001] This invention relates to an electricity-generating installation, for example a combined heat and power system, or an electricity-generating plant using renewable fuels.

Background to the Invention

[0002] Combined heat and power systems typically use an internal combustion engine to drive an electricity generator producing electrical power for a building, waste heat from the engine exhaust and coolant being used to provide hot water and to heat the building. For greatest efficiency, the electricity needs and heating needs of the building are required to be matched as closely as possible so that the system produces neither in excess of requirement. However, the requirements vary, not only through the different seasons of the year, but also from day to day, and at different times of the day. The maximum require- ment for electricity may not coincide with the demand for hot water or space heating, and there may be times when the need is to maximise conversion of the energy in the fuel driving the engine into electricity.

[0003] There is also a greater need for smaller-scale power stations based on locally-produced organic material as fuel, for example the use of vegetable oil to fuel an internal combustion engine. Here, the need is simply to maximise the efficiency of conversion of the energy in the fuel into electricity.

[0004] Various proposals have been made for extracting additional energy from the exhaust gases from power generation systems. However, for CHP and smaller-scale power stations, the exhaust temperature from modern inter- nal combustion engines is relatively low, often around 500°C, and recovery of energy from the exhaust is typically limited to production of hot water or low temperature saturated steam, which does not permit the generation of further electricity using steam turbines, while the use of exhaust-driven gas turbines is again not a practical way of extracting a significant proportion of the remaining energy of combustion. Summary of the Invention

[0005] The present invention provides an electricity-generating installation, comprising an internal-combustion engine driving a primary electricity generator, the engine having an exhaust gas outlet arranged to pass exhaust gases through a pair of heat exchangers, in each of which a plurality of heat pipes are configured to transfer heat from the exhaust gases into a closed non- condensing steam circuit containing a reciprocating steam engine driving a secondary electricity generator, control means being provided to admit lower- pressure exhaust steam from the steam engine alternately to the heat exchang- ers and to pass higher-pressure steam from the heat-exchangers to an accumulator feeding higher-pressure steam to the steam engine.

[0006] Other aspects of the invention are set out in the claims.

Brief Description of the Drawings

[0007] In the drawings, which illustrate exemplary embodiments of the inven- tion schematically:

Figure 1 is a diagram of an electricity-generating installation according to one embodiment of the invention;

Figure 2 is an enlarged diagrammatic end view of a section of one heat exchanger shown in Figure 1 ;

Figure 3 is a diagram showing a bio-fuel electricity-generating installation;

Figure 4 is a front elevation of an alternative steam valve arrangement for use in the apparatus shown in Figure 1 ;

Figure 5 is an end elevation of the valve arrangement; and

Figure 6 is a detailed sectional view of one of the steam ports in the valve arrangement of Figures 4 and 5.

Detailed Description of the Illustrated Embodiment

[0008] The electricity-generating installation comprises an internal combustion engine 1 , for example a diesel engine powered by vegetable oil-derived diesel fuel or a blend thereof, driving an alternator 2 from which the electricity output is connected to an output regulator/transformer 3. The exhaust gases from the engine 1 leave via an exhaust gas outlet 4 and are directed to three heat exchangers 5, 6 and 7. As may be seen more clearly from Figure 2, which illustrates a short cross-sectional section of one exchanger, each of these heat exchangers consists of a central axial chamber 8 through which the exhaust gases flow, and a co-axial outer chamber 9 forming part of the steam circuit. Linking the two chambers 8 and 9 is a series of heat pipes 10 which pass through the wall 1 1 separating the two chambers. The heat pipes 10, which are suitably of the type consisting of a sealed tube containing a liquid which evaporates to absorb heat at one end of the tube and condenses at the other end of the tube to give out heat, the condensate then returning along the tube under capillary action, are set at varying angles along the exchanger so as to maximise contact with the gases while minimising pressure drop along the exchanger, because high back-pressure in the exhaust outlet might adversely affect performance of the engine. The heat pipes thus conduct heat from the ex- haust gases in the central chamber to the surrounding steam chamber forming part of a closed, non-condensing steam circuit.

[0009] The steam circuit comprises two of the heat exchangers 5 and 6 operating alternately in parallel to supply higher-pressure steam, for example at 130 psi, to the third heat exchanger 7, acting as a steam accumulator, in turn supplying steam to a multi-cylinder lubricant-free steam engine 12 driving a secondary alternator 13 whose electricity output is also connected to the regulator 3. Because the steam circuit is closed and non-condensing, a typical conventionally-lubricated steam engine will be unsuitable. In conventional engines, oil tends to be carried from the cylinders with the discharged steam, and this would lead to problems with the deposit of the oil in the heat exchangers, reducing their efficiency.

[0010] A programmable controller 14 controls operation of the steam circuit using a number of solenoid steam valves, as follows:

[0011] Steam is exhausted from the engine 12 at approximately 15 psi and is admitted to the heat exchanger 5 or 6 through a first steam valve 15 or 19, while the outlet steam valve 16 or 20 from the exchanger is closed. In order to permit this to happen, a steam discharge valve 17 or 21 is first opened to discharge residual steam into a water top-up tank 18 where it is condensed for re-use as hereinafter described. The inlet valve 15 or 19 is then closed and the heat from the exhaust gases raises the steam temperature, and hence pressure, until the desired pressure, which is in excess of that required at the steam engine, is sensed by a pressure sensor 22 or 23 connected to the controller 14. At this stage, the outlet valve 16 or 20 is opened (it will be appreciated that, as the exchangers are operated alternately, one of these valves will be closed while the other is open), allowing higher-pressure steam to be discharged into the accu- mulator 7, which is maintained at a slightly lower pressure to ensure steam flow into it. When the pressure in the exchanger 5 or 6 has dropped to a predetermined value, the controller 14 closes the outlet valve 16 or 20, and opens the steam discharge valve 17 or 21 . When the pressure has dropped substantially to atmospheric, the steam discharge valve is closed again, and the inlet valve 15 or 19 opened again for the next cycle. Although the cycle is described as closed and non-condensing, it will be seen that a small amount of steam is discharged in each cycle, to be condensed in the tank 18. A small amount of top-up water is re-introduced from that tank in each cycle into the exchanger 5 or 6 under the control of the controller 14 through a solenoid water inlet valve 24 or 25.

[0012] Steam flowing from the accumulator 7 to the engine 12 passes through a pressure-reducing valve 26. The accumulator could be, in its simplest form, a plain pressure tank, but the use of a third heat exchanger permits additional heat to be introduced into the cycle as required by admitting, by means of a solenoid-controlled valve 27, some of the exhaust gases from the exhaust outlet 4.

[0013] Figure 3 depicts the installation of the present invention adapted for the generation of electricity via a range of renewable fuel production that will in turn drive a series of electrical generators from an internal combustion engine and supported by a steam engine. The system will also recover heat from waste fluids and gases from the process of the aforementioned primary generation equipment and thus provide heating and cooling other than the conven- tional methods in a conventional residential or commercial building. Such buildings generally contain a boiler or furnace 100, a central space-heating/cooling system 101 , a hot water tank 102 and a plurality of hot water needs such as for bathing 103 and for laundering 104. In order to recycle this valuable source of energy, the present invention incorporates a plurality of heat recovery modules (heat exchangers) throughout the building. Specifically, the system recaptures heat from the hot exhaust gases of the general combustion processes and exhausts from the engine and furnace equipment 105, 106, 107, 108, and 109.

[0014] The installation compromises a controller 1 10, a distribution manifold 1 1 1 , a plurality of heat recovery modules 105, 106, 107, 108, and 109. Figure 3 depicts the integration of the system of the present invention with the complete process comprising with the commencement of a bio-fuel system which ultimately provides the combustion material to drive the two generators numbers 1 12 and 1 13 which are an internal combustion generator and a steam engine generator respectively.

[0015] The system shown in Figure 3 as an operation commences with the delivery of renewable fuel raw materials in the form of an oil seed - fruit - food waste by a delivery vehicle number (not shown). This delivery will deliver the raw material via a vertical elevator number 1 15 to a series of independent stor- age hoppers 1 16, 1 17, and 1 18. Prior to these hoppers discharging into a screw press number 1 19 each hopper will have placed in its outlet a heat exchanger working in reverse cycle from the control manifold numbers 120, 121 and 122. These heat exchangers 120, 121 and 122 are of the heat pipe configuration working on a liquid to liquid heat transfer characteristic.

[0016] When hopper 1 16 is discharging oil seed into the screw press 1 19 two products thus emit from the screw press, one being pure vegetable oil via discharge pipe 123 and passing an oil filter 124 before being stored in a vegetable oil fuel silo 125. This tank is also heated from the waste heat manifold as shown 1 1 1 .

[0017] The secondary product from the screw press 1 19 can be discharged via a conveying tube 126 and as in the form of a grain particulate. At this point as it is passing through delivery pipe 126 it will pass a divert valve 127 and can be proportionately distributed to become a pelletized direct fuel product in a pel- letizer 128 or continue in convey pipe line 129 to be prepared to be converted into a renewable fuel alcohol process and be delivered into a preparation mash tub 130.

[0018] The distillation process of converting materials in the mash tub which can also be added to fruit from tub 1 17 and food waste from food tub 1 18 via the similar process and be prepared for fermentation within the mash tub. During this process and at the right amount of time water will be added from tank number 131 via pipe work 132 into mash tub 130 and at various points through the fermentation process yeast will be added via the yeast tub 132 and a further molasses/sugar will come from tub 133. The pipe work delivery to the fermentation will be delivered by pipe work 134 and 135 respectively. As the fermentation process occurs the resultant "beer" will travel via pipe work 136 into the dis- tillation column 137 commonly known as "still". From the still and via pipe work 138 the vapour from the still will enter the condenser section via water from water tank 131 and through pipe work 139 into the condenser. As condensation occurs alcohol of circa 85-90% proof will be stored in an alcohol fuel tank 140.

[0019] The system now has two sources of renewable fuel processed and ready for application at the point of combustion but with the further processing of a water addition from water tank 131 in a percentage by volume of between 30-50% into what is known as an emulsification unit 141 . This blended multi fuelled vessel will be the combined fuel tank 142. This fuel tank will then provide direct primary renewable fuel via pipe work 143 split into pipe work 144 and 145 to combust into furnace boiler number 100 and internal combustion engine 1 12.

[0020] The furnace boiler can also be fuelled directly via valve 146 and through pipe work 147 into the furnace boiler 100. In the event of an over capacity or over production of pelletized the fuel the divert valve 146 can convert pelletized fuel through pipe work 148 and into an intermediate storage of 149 for use in combustion off site into other satellite generation systems. Similarly the emulsified combined renewable fuel delivering down pipe work 144 can also be fed via porting valve 150 and be delivered either to the furnace boiler as an after burner or into storage tank 151 for once again off site storage or further satellite generators.

[0021] Figure 3 shows two primary electrical generating sets number 1 12 is a traditional internal combustion engine fired on emulsified fuel being delivered down pipe work 145. This generating set drives a traditional alternating unit generating 415 volts and being delivered into the electrical distribution system for the building 152. In the event of any over production for the building or process the power generated can be exported into the National Grid distribution network 153. At the point of generation in the engine 1 12 two normal losses would occur, one would be the coolant system of the engine 1 12 usually in the order of 30% of the growth input and the other loss would be the exhaust system. In addressing the recovery of the waste energy in the cooling system from engine 1 12 we have via flow and return pipe work 154 and 155 delivered water into a liquid to liquid heat recovery unit 105 which in return delivers a separate flow and return pipe work to manifold 1 1 1 via pipe work 156 and 157.

[0022] The exhaust pipe work of engine 1 12 number 158 will combine with the exhaust of the furnace boiler 100 the pipe work being 159. The combined pipe work joining in a "Y" piece configuration to become 160. At this point the hot exhaust gases varying between 560°C and 900°C have the ability to generate considerable useful low pressure steam via heat exchangers 107, 108 and 109 and valves 161 , 162 and 163 divert the energy controlled accordingly to heat exchangers 107, 108 and 109.

[0023] The steam generating engine 1 13 will operate at a pressure of 150 psi and receive its primary operational steam from heat exchanger 109. This steam will be delivered from heat exchanger 109 down pipe work 164 to the inlet steam port on the steam engine 1 13. The steam pressure gauge 165 on heat exchanger 109 will operate and control the steam pressure. The present invention is able to maximise the full use of the benefits of heat exchangers 107 and 108 be taking the low pressure steam exhaust port on steam engine 1 13 and through pipe work 166 deliver into either heat exchanger 107 or 108 via steam solenoid valves 167 or 168. Once heat exchanger 107 now called accumulator 1 and controlled by its steam pressure gauge 169 when the maximum pressure is obtained by pressure 169 from exhaust pipe work 166 steam pressure valve 170 will close along with steam pressure valve 168 and maximum flow through exhaust gas valve 161 will increase the pressure to a level of 160 psi. When this pressure is reached steam valve 169 will open and discharge the steam in almost in its entirety through pressure differential into heat exchanger 109. At the point of maximum discharge steam solenoid valve 169 will close, solenoid valve 168 will open and the whole process will commence once again. The previous description will be followed in absolute exact accordance on accumulator 2 which is heat exchanger 108 and its exhaust solenoid valve 171 and again controlled by its steam regulation valve 172. This present invention allows with this heat exchangers 107, 108 and 109 in sequence as described is able to recover the full benefit of the latent heat of the steam from exhaust pipe work 166 to be super heated by heat exchangers 107, 108 and 109 and therefore maximising complete steam usage efficiency.

[0024] The steam engine 1 13 alternating generation equipment as described in internal combustion 1 12 will follow the same line of operational duty.

[0025] The hot water tank 102 provides hot water via flow pipe 173 to a multitude of hot water needs such as a tub 103 and a laundry machine 104. The hot water tank 102 receives its water through a flow pipe 173 from a supplement tank 174 which, in turn, receives its water from the cold water main 175. A release valve 176 and control device 177 (such as a float) are provided to shut off the cold water supply when the supplement tank 174 is filled to predefined level. The supplement tank 174 is a substantially L-shaped container with two additional inlet points. One inlet point receives heated water from the waste water heat recovery module 178 via flow pipe 179 this water being delivered from the twin manifold 1 1 1 .

[0026] Finally, a controller 1 1 1 monitors the "loading" within the building and responds by matching the demand with the most cost effective heat generating source. Loading is defined as the sum total of the various demands for heated water within the building. The controller 1 10 calculates loading by gathering information from plurality of temperature sensors 180, 181 ,182, 183, 184 and, 185 a plurality of thermostats 186 (space heating/cooling) and 187 (water tank) flow sensor 188, and a plurality of sensors controls 189, 190, 191 and 192. The controller 1 10 is programmed to calculate the instantaneous energy need of the building. The controller 1 10 takes into account the temperature of all water circuits (supply circuits and demand circuits), the flow of water within the distribution manifold 1 1 1 , the settings of the thermostats, historical energy consumption patterns, programmed settings ad hoc commands for determining and predicting the most cost effective method of meeting the energy demands of the building. When recovered heat is available from one plurality of heat recovery modules, the controller 1 10 will channel the recovered heat to meet a particular energy need. The loading matching feature enhances the thermal efficiency of the present invention. Furthermore, although Figure 3 depicts four supply circuits and two demand circuits, those skilled in art will realise that a multitude of supply and demand circuits can be employed within a building.

[0027] Optionally, a modem 193 and an energy meter 194 are coupled to the controller for providing off-site monitoring capabilities. A remote station 195 in communication with the controller 1 10 will be able to monitor the energy demands of the building and the performance of the various heat generating components within the building. This configuration permits off-site detection of the failures and enhances billing functions.

[0028] Referring now to Figures 4 to 6, a potential problem with the use of solenoid-operated steam valves 15-21 in the embodiment illustrated in Figure 1 is long-term reliability. An alternative valve arrangement is proposed having a pair of parallel plates 200 and 201 , spaced apart by a distance sufficient to accommodate a swinging valve plate 202 carried on an axle 203 mounted between the upper parts of the plates 200 and 201 . A lever 204 extends from the lowermost edge of the swinging valve plate 202 and is connected via a spherical bearing 205 to a pneumatic cylinder 206. The motion of the cylinder 206 is controlled by the controller 14 (Figure 1 ). The plates 200 and 201 have aligned holes passing therethrough, the uppermost pairs of holes 207 and 208 connecting on one side to the exhaust steam line from a respective one of the steam engines and on the other side to a respective one of the heat exchangers 5 and 6. A hole 209 through the swinging valve plate 202 aligns alternately with the pair of holes 207 and the other pair 208, allowing passage of steam therethrough, or blocking the line. Ring seals 210 and 21 1 (Figure 6) are mounted in grooves 212 and 213 in the opposed faces of the plates 200 and 201 extending around the inwardly-facing mouths of the aligned holes in a pair 208 or 209. Similarly, aligned pairs of holes 214 and 215 extend through the lower part of the plates 200 and 201 and are connected on one side to the accumulator heat exchanger 7 and on the other side to outlets from the first and second heat exchangers 5 and 6 respectively, a hole 216 through the swinging plate 202 alternately connecting these outputs to the accumulator 7 as the swinging plate 202 is reciprocated by the cylinder 206.

[0029] It would also be possible to use some of the electricity generated to electrolyse water to produce a hydrolysis gas mixture of oxygen and hydrogen which could then be supplied to a combustion chamber (not shown) provided in the exhaust line from the engine 1 , thus raising the exhaust temperature before the gases pass through the heat exchangers 5 and 6, thereby increasing the output of high temperature steam from the exchangers for supply to the steam engine.