FI101412B - Method for utilizing waste heat, eg in power plants - Google Patents

Description

101412

WASTE HEAT UTILIZATION 1. the power plant

The invention relates to a method for utilizing waste heat, e.g. in power plants, in which case the warm medium λ from the gas turbine process and the return medium B heat a medium B higher than the critical pressure of the process 5 according to the invention.

in parallel heat exchangers. Next, the media B coalesces and is further heated in the heat exchanger by the return medium B. The medium B is then further heated in the boiler by the medium A after the turbine or combustion chamber and expands in the turbine to a pressure below the critical pressure and returns to the above heat exchangers. The medium B is then condensed into a liquid in the condenser and pressurized by a pump to a supercritical pressure, the enthalpy difference corresponding to a certain temperature difference being greater than the post-turbine pressure. The enthalpy difference can be compensated by waste heat.

Today, electricity is produced in thermal power plants using fossil fuels or nuclear power, and in the newest plants also with solar mirrors or geothermal energy. The basic process in power plants is the gas turbine or steam power process or a combination thereof. The problems in nuclear power are radioactive waste and the high cost of basic investment, emissions that cause acidification with fossil fuels and the greenhouse effect. Both also have the risk of accidents and the consumption of non-renewable resources. In addition, all of the current 25 thermal power plants have relatively low efficiencies because they are unable to utilize low-temperature energy to generate electricity. A decisive improvement is achieved with the plant according to the invention, with which a very high electricity generation efficiency and the numerous advantages which follow can be achieved. Examples of pre-30 are lower fuel consumption, accident risk, waste and emissions, and the very easy replacement of the old plant, because then the plant according to the invention can be easily built to operate alongside the old plant using waste heat. The waste heat of the steam power process can also be utilized by increasing the intakes, whereby the mass flow through the condenser can be set to zero if necessary. The invention is particularly well suited for the use of natural gas, because the heat of condensation of the water vapor generated during combustion can be utilized most efficiently in the plant according to the invention due to the purity of the natural gas.

The invention is based on the fact that the heating of the liquefied and supercritical pressure medium B requires - mainly in the low temperature range - a greater amount of energy than the lower pressure return medium B delivers. This is a property of real gases in the vicinity of the critical temperature. In this case, the waste heat of existing thermal power plants can be utilized very efficiently in parallel heat exchangers. The difference of the invention with the ORC process (e.g. US A 3 769 789) is that the energy-intensive enthalpy increase corresponding to evaporation takes place mainly in the parallel heat exchangers after the pump (1), because the medium B is at supercritical temperature after the parallel heat exchangers (2,3). In this case, the external waste heat can also be utilized by the process according to the invention. This means that the heat exchanger (2) is not connected to the boiler. The corresponding step in the ORC process is fluid preheating. The invention is further compared to gas turbine and steam power plant processes. A closed gas turbine process with an ideal heat exchanger and a simple steam-20 power plant process are selected for comparison. The difference between these is that in the gas turbine process, the power from the turbine is equal to the thermal power introduced into the system. However, much of the power is used to pressurize the medium with a supercharger. In the steam power plant process, on the other hand, only part of the thermal power can be utilized in the turbine, because evaporation consumes a lot of energy. However, the energy requirement for pressurization is low. The process to be compared thus corresponds to the gas turbine process in terms of turbine power, taking into account the cooling need of the turbine impeller. However, the energy requirement for pressurization is significantly lower than for the gas turbine process 30 because part of the pressurization of the medium can be performed by a pump. The above applies best to the construction according to Figure 4.

The carbon dioxide, which is an excellent medium for the process, is harmless to the environment and is abundant. Even the maximum required pressure of 35 va does not impose excessive technical requirements, as a pressure of the same magnitude is already in use in the steam power process. By choosing medium B appropriately, the waste heat of the condenser can be used, for example, for district heating, while the electricity production remains high. The invention is also well suited for the gasification of solid fuel, because the process according to the invention is able to utilize low-temperature energy better than current processes, for example as a two-material process. The waste heat generated in the cooling of the supercharger can also be utilized very efficiently in the process according to the invention. The invention is also well suited for use in a plant using two different heat sources. Another advantage is the absence of a supercharger in the process according to the invention. Similarly, the size range of 10 economically viable facilities is very wide. The small size due to the moderately high pressure of the plant medium B is also relevant.

The time of use of the invention in the future is long, because the possible heat generated in the fusion is well suited for use in the plant according to Fig. 4, 15 because there are no preheating losses. In the even longer term, the renewable energy sources solar and biomass are also suitable as heat sources for the process according to the invention. The main object of the invention is to provide a new and more efficient method for utilizing waste heat in power plants. To achieve this, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The following is a detailed description of the drawings:

Figure 1: Process diagram of a plant according to the invention (gas turbine process as a waste heat source),

Figure 2: Process diagram of a plant according to the invention (steam power process as a waste heat source),

Figure 3: Process diagram of a plant used for the pressurization of natural gas according to the invention, Figure 4: Process according to the invention (heat generated in the pressurization of medium B as a waste heat source),

Figure 5: Table of state point values in Figure 1,

Figure 6: Η, Τ drawing of the heat transfer of Figure 1.

The plant of Figure 1 comprises a pump (1), heat exchangers (2, 3, 35 4), boiler (5), turbine (6), condenser (7), supercharger (8), heat exchanger (9), combustion chambers (10, 12) and a turbine (11). Medium B in this example is carbon dioxide. Medium A corresponds to an open 4 101412 gas turbine process. In principle, however, media A and B can be selected as desired to best suit the situation.

5 The compressed air from the supercharger (8) goes to the heat exchanger (9) for preheating with the exhaust gases from the gas turbine process. It then enters the combustion chamber (10) and the turbine (11). After the exhaust gases have expanded, the turbine (11) has a second combustion chamber (12), followed by a boiler (5) and a heat exchanger (9) for preheating the air. All of this is already known in practice. The novelty of the invention is that the exhaust gases from the heat exchanger (9) preheat the carbon dioxide pressurized to supercritical pressure in the heat exchanger (2) with the pump (1), while the return carbon dioxide also heats the carbon dioxide in the second parallel heat exchanger (3). The carbon dioxide at supercritical pressure then combines and is further heated in the heat exchanger (4) with lower pressure carbon dioxide. Thereafter, the carbon dioxide is further heated in the boiler (5) and expanded in the turbine (6) to a pressure below the critical pressure of 20. After expansion, the carbon dioxide returns to the heat transfer to the above-mentioned heat exchangers (4, 3). The gaseous carbon dioxide then enters the condenser (7), where it condenses into a liquid and is pressurized by a pump (1) to a supercritical pressure. The process cycle of carbon dioxide is thus closed.

Figure 2 shows a process according to the invention, in which the waste heat • is obtained from a steam power process. The carbon dioxide cycle is similar to the above, but the boiler (5) includes an air preheater. In the steam cycle from the pressure relief valve (15), the water 30 enters the feed water tank (16), where it heats up as the water vapor from the turbine (14) mixes with it. The pump (17) then pressurizes the water to the desired pressure, after which the water is heated in the heat exchanger (18) by the inlet of the turbine (14) and further by the next outlet in the heat exchanger (19). From the heat exchangers (19, 18) of the heat-3b, the return liquid flows into the feed water tank (16). After the heat exchanger (19), the water circulation branches off to the boiler (5), where it evaporates and superheats and enters the turbine (14). The rest of the water goes to the heat exchanger (2) to preheat the carbon dioxide, after which the water goes to the pressure reducing valve (15). The boiler (5) also has a carbon dioxide heating step.

Figure 3 shows a process diagram of a plant used for compressing natural gas. The process 5 using carbon dioxide as a medium is similar to Figure 1, only the boiler (5) includes an air preheater. The energy produced by the turbine (6) pressurizes the natural gas with a supercharger (20), after which the heated natural gas heats the carbon dioxide in the heat exchanger (2) and at the same time cools itself. If desired, the process can also produce electricity.

Figure 4 shows a process with two-stage expansion. Part of the pressurization of the carbon dioxide is carried out by the supercharger (25), whereby the heat of the carbon dioxide heated in the supercharger (25) can be utilized in the heat exchanger (2). The carbon dioxide cycle is otherwise as shown in Figure 1, but the boiler (5) includes, if necessary, an air preheater. The carbon dioxide heats up in the boiler (5) before the turbine (6), as well as after it, because the carbon dioxide also expands in the turbine (23). From the turbine (23), the carbon dioxide returns to the heat exchangers (4, 3) and is further cooled in the precooler (24). As the carbon dioxide expands to a pressure below the condensing temperature achievable in the turbine (23), it then enters the supercharger (25). The carbon dioxide heated in the supercharger (25) cools in the heat exchanger (2), then goes to the condenser (7), where it liquefies. After liquefaction, the carbon dioxide is pressurized with a pump (1) to a supercritical pressure. 25

Figure 5 is a table of the values of the state points of Figure 1. For simplicity, only air has been used as medium A. 90% has been used as the isentropic efficiency of the turbine, 3% as pressure losses in the heat exchangers and 90% as the recovery rate of the heat exchangers.

Fig. 6 is a h, T-drawing of points A, B, C and D in Fig. 1. The heat exchangers (2, 3, 4) and the boiler (5) have been converted into a single heat exchanger for the sake of clarity.

Among some embodiments of the invention, mention may be made of the process in which, after the heat exchanger (4), the medium B is no longer heated in the boiler room (5). In this case, the heating of the medium B to the maximum temperature '101412 takes place naturally with the waste heat of the medium A in the heat exchanger (4), which is then in fact a boiler. Some other process components can also be omitted if necessary. The carbon dioxide sides of the heat exchangers (2, 3, 4) can also be combined, thus reducing the number of heat exchangers. Expansion in the turbine (6) can also take place in several stages, as well as compression in the pump (1), whereby there is cooling between the compression stages. The plant according to the invention also has, if necessary, the components necessary for achieving a pressure level higher than the ambient pressure of the medium B. The carbon dioxide in the process cycle decomposes at a sufficiently high temperature into carbon monoxide and oxygen, which can be burned in a closed loop before the turbine (6). In this case, as the maximum process temperature increases, the efficiency also improves. Medium A or B can also consist of several substances, in which case the desired heat transfer properties can be achieved with the mixture.

The process according to the invention can also be connected to an existing combined heat and power plant, for example by adding steam turbine intakes as shown in Figure 2, whereby a very high electricity generation efficiency can be achieved, especially if the condensing heat of combustion water is utilized in the process.

The application examples of the invention have been described only to illustrate the invention and do not constitute any limitation on the use of the invention, as details which are not necessary for an understanding of the invention have been omitted for the sake of clarity. Thus, the invention is not limited to the embodiments shown, but includes everything within the scope of the following claims.

Claims (9)

1. Process for utilizing waste heat e.g. in power plants, in which process a heat carrier B with a pressure higher than the critical pressure is heated in a parallel heat exchanger (2, 3) located at a pump (1) with waste heat and with a pressure lower in a turbine (6). than the critical pressure expanded return heat carrier B of which at least some of it is condensed to liquid in a condenser (7) and is pressurized with the pump (1) to a pressure higher than the critical pressure, characterized in that the heat carrier B is heated to the supercritical temperature. or in the supercritical temperature of the parallel heat exchangers (2, 3), the enthalpy difference corresponding to a certain temperature difference being greater than that of the pressure after the turbine (6), so that the enthalpy difference is equalized with the waste heat. 2. A method according to claim 1, characterized in that the rising ring corresponding to a boiler (5) in the temperature of the heat carrier B is carried out in the desired manner. 3. A method according to claims 1-2, characterized in that the condenser (7) and / or a radiator (24) functions, for example, as a heat exchanger connected to a district heating network. 4. A method according to claims 1-3, characterized in that the waste heat A's waste heat is obtained from cooling of a compressor, from a combined power plant, from a meadow power plant for example by increasing the number of turbine (14) outlets or from another pour from the desired object. , and that the process has one or more different heat sources. •. Process according to claims 1-4, characterized in that • the heat carriers A and B consist of one or more substances and that the substances that arise where the heat carrier B is carbon dioxide and where it is decomposed in carbon monoxide and oxygen in the high temperature of the process may react with each other saying that they burn in a closed process circulation. 101412 10 Method according to claims 1-5, characterized in that the heat surfaces of the heat exchangers (2, 3, 4) are joined to each other with respect to the heat carrier B. 7. A method according to claims 1-6, characterized in that the condensation heat from the water vapor produced by the combustion is used in the heat exchanger (2, 3), after which there is a heat exchanger (4) before a boiler (5) or equivalent if desired. ie, in which heat exchanger (4) at least part of the supercritical heat carrier B is heated with the return heat carrier B. Process according to claims 1-7, characterized in that the expansion in the turbine (6, 23) occurs even at a pressure lower than the pressure corresponding to the condensation temperature which can be attained, whereby in the process, before the condenser (7), a compressor is provided. -sor (25) where the heat of the heated heat carrier B is utilized in the heat exchanger (2) before the condenser (7), whereby more work is carried out from the turbines (6, 23) - in which or between which there are one or more outlets if the be desired. Method according to claims 1-8, characterized in that one or more heat exchangers (2, 3, 4), boilers (5), turbines (6), pumps (1), condensers (7), compressors (25) can be used. ), combustion chamber (10), radiator (24) and / or process heat carrier. «