A HEAT AND POWER CO-GENERATION PLANT

Abstract: A heat and power plant includes an internal combustion engine (10) driving an electric generator (11) and having its exhaust gases conveyed to a CFB-boifler (12) as primary fluidizing gas. The boiler supplies steam to a turbine (13) driving a further electric generator (14). The exhaust steam from the turbine is condensed in a heat exchanger (15) forming part in a district heating plant (16). A heat exchanger (31) heats the feed water to the boiler by means of waste heat from the internal combustion engine (10).

Description: There is often an obvious need of simultaneous production of heat and electricity, and many different production plants have been proposed. An internal combustion engine for instance a low speed diesel engine, will operate with a satisfactory efficiency, but produ­ ces large volumes of exhaust gases, which contain components which are detrimental to the environment. In circulating fluid bed boiler, a CFB-boiler, various kinds of fuel may be burnt with a high efficiency and with a low content of environmental contaminants in its exhaust. The operation will however require large quantities of fluidizing gas, usually air, and necessitates a big fan power input. The exhaust gases from an internal combustion engine will con­ tain a sufficient amount of oxygen for maintaining a combus­ tion, at least partly, and by conducting the engine exhaust gases to the CFB-boiler as fluidization gas. The fan work at the boiler as well, as the air preheating arrangements are reduced. Furthermore a destruction of environmentally detrimen­ tal constituents in the exhaust gases is obtained, in the first hand NOx and unburnt hydrocarbons. A co-generation plant according to the invention accordingly comprises an internal combustion engine and a CFB-boiler, each connected to an electric generator, and the invention is cha­ racterized by means for conducting the exhaust gases from the internal combustion engine as fluidizing gas to the CFB-boiler, the steam generating parts of which are connected to a steam turbine driving one of the electric generators, and by a heat exchanger connected to a heat consumer outside the plant for condensing the exhaust steam from the turbine into feed water for the boiler. The plant further includes a heat exchanger for heating the feed water to the boiler by waste heat from the internal combustion engine. The plant advantageously includes means for conveying combus­ tion residues from the CFB-boiler to a heat exchanger, forming part of a circuit comprising a heat exchanger in the feed water supply conduit. The invention will below be described with reference to the accompanying drawing, which schematically shows a heat and power co-generation plant according to the invention. The heat and power co-generation plant shown in the drawing includes a diesel engine 10, which drives a first electric generator 11, as well as a steam boiler 12, having a combustion part operating according to the circulating bed principle (CFB), and which delivers steam to a turbine 13, driving a second electric generator 14. The plant further includes a heat exchanger 15, which operates as a condensor for the steam tur­ bine 13, and is connected to a heat consumer outside the plant, for instance a district heating circuit 16. The CFB-boiler, in a conventional manner, includes a combustion reactor 17, the upper end of which is connected to a particle separator 18 of the cyclone type. From the latter the purified gases are conducted through a shaft 19 containing heat absor­ bing surfaces to a smoke stack 20. Particles separated out in the cyclone 18 are collected in a lock 21, and transferred back to the reactor 17. The reactor may be designed to burn fuels of arbitrary kind. The drawing shows a conveyor 22 for feeding fuel from a hopper 23, and inert bed material (sand), and possibly crushed lime­ stone from a hopper 24 into the reactor. Finely divided garbage and household waste can advantageously be burnt in a circula­ ting fluid bed reactor. The hot exhaust gases from the diesel engine 10 are fed through a conduit 25 and a fan 26 to the CFB-boiler, to serve in the first hand as primary fluidizing gas. The oxygen content is sufficient to maintain at least a partial combustion. Means 27 are provided for supplying secondary gas, either from the con­ duit 25, or from the ambient atmosphere, suitable pre-heating means (not shown) being provided. An efficient destruction of the content of NOx and other contaminant in the diesel exhaust gases will occur in the reactor. The conduit 25 includes valve means 28, through which the diesel exhaust gases may be conveyed directly to the smoke stack 20, by way of a branch conduit 29, for instance when the engine is to be started. A second valve means 30 permits the fan 26 to draw air directly from the atmosphere, when the diesel engine is not running, or as addition to the diesel exhaust gases. The steam passing through the turbine 13, will be condensed in the heat exchanger 15, and is re-introduced in the CFB-boiler as feed water. The feed water will first pass a heat exchanger 31, heated by the cooling water of the diesel engine 10. Combustion residues withdrawn from the reactor 17 contain a large amount of heat, and are collected in a receptacle 33 enclosing a heat exchanger 34. This forms part of a closed circuitry 35, including a second heat exchanger 36 in the feed water conduit 37. The latter finally passes a heating coil 38 in the shaft 19, and the feed water is, by way of a de-aerator 39, conveyed to a steam generating coil 40 in the shaft 19. This coil is connec­ ted to the steam drum 41 of the boiler. A circuit 43 including a circulation pump 42 contains further heating coils 44 in shaft 17. Steam from the drum 41 is by way of a conduit 45, a heat ex­ changer 46 in the particle lock 21 and a superheating coil 47 in the shaft 19, conveyed to the turbine 13. The plant described above and shown in the drawing may be modi­ fied in many ways within the scope of the appended claims. It is evident for a man skilled in the art, that, depending upon expected variation in the power requirements, two or more engines may be connected to the boiler, and that the plant will include control and supervision devices which are not mentioned here.

Claims: 1. A heat and power co-generation plant including an internal combustion engine (10) and a CFB-boiler (12) each connected to an electric generator (11, 14), characterized by means (25) for conducting the exhaust gases from the internal combustion engine as fluidizing gas to the CFB-boiler (12). The steam generating parts (40, 41, 44, 46, 47) of which are con­ nected to a steam turbine (13) driving one of the electric generators (14), and by a heat exchanger (15) connected to a heat consumer (16) outside the plant for condensing the exhaust steam from the turbine (13) into feed water for the boiler. 2. A heat and power plant according to claim 1, charac­ terized in that it includes a heat exchanger (31) for heating the feed water to the boiler (12) by waste heat from the internal combustion engine (10). 3. A heat and power plant according to either of claims 1 or 2 characterized in means (33) for conveying combus­ tion residues from the CFB-boiler to a heat exchanger (34), forming part of a circuit (35) comprising a heat exchanger (36) in the feed water supply conduit (37).

Inventors: STENHEDE, THOMAS
Applicants: PPS PROJECT PROMOTION SERVICES AB
Application year: 1988
Main classification: F01K23
IPC codes: F01K23