Exhaust heat utilization system

Abstract

The present invention presents a technically appropriate process to utilize heat from the exhaust gas of a gas turbine by cooling it down to about 25°C by a heat pump. Another object of the present invention is to present a way to properly exhaust the exhaust gas flow to the atmosphere. This is solved by an energy efficient process to reheat / drive the low temperature dry exhaust gas through a chimney. Advantageously, the present invention provides about 20 percent surplus heat for district heating compared to the conventional WHRU (Waste Heat Recovery Unit) cycle. The increased efficiency of the present invention reduces the carbon dioxide emissions of the heat supply.

Description

[Technical field]

[0001] Heat generation in low-carbon energy systems

[0002] The present invention relates to a system for recovering heat from hot moist exhaust gases as a heat source. Furthermore, the present invention relates to the utilization of heat of condensation from exhaust gases, for example from gas turbines, by means of a heat pump, and further to the treatment of dry low temperature exhaust gases. [Background technology]

[0003] "The heating and cooling sector has been recognised by the European Commission as a priority to achieve decarbonisation and energy efficiency targets. Heating and cooling in the built environment accounts for almost 40% of Europe's final energy demand." [Kavvadias K., Jimenez-Navarro JP, Thomassen G., Decarbonising the EU heating sector - Integrating the electricity and heating sectors, EUR 29772 EN, Publications Office of the European Union, Luxembourg, 2019, ISBN 978-92-76-08386-3, doi:10.2760 / 943257, JRC114758]

[0004] Heat is supplied in very different capacities, from single-family homes to industrial sites to district heating systems. In all capacities, heat pumps are recognized as a key technology for the decarbonization of the heating sector [Sensfuss F., Bernath C., Kleinschmitt C., Resch G., Geipel J., Hiesl J., Liebmann L., Lumbreras S, Olmos L., Ramos A., Ploussard Q. - D7.8: Summary Report - Energy Systems: A Supply Perspective, http: / / www.set-nav.eu / sites / default / files / common_files / deliverables- / WP7 / D7.8_SET-Nav_SummaryReport_WP7_final.pdf last accessed: 16 October 2020]. Currently, heat supply to industrial sites and district heating systems is based on fossil fuels burned in heating and combined heat and power plants. The thermal capacity of typical units, e.g. coal-fired combined heat and power (CHP) plants, is in the range of several hundred megawatts. To replace these plants with heat pumps, a heat source of suitable capacity (>X00 MW) is needed, at a suitable temperature level (T_Source is ideally much larger than T_Ambiance) and located close to the district heating system. There are heat sources that meet both requirements, e.g. waste heat from large refineries. However, there are simply not enough of them and a cumbersome screening of potential heat sources in urban areas has started in the last years. As a result, CHP units (X00 MWth) could be replaced by a large number of heat pumps (Y0 MWth) distributed in the urban area. Distributed electricity generation in district heating systems requires suitable sites next to the heat source. It also requires enclosures for noise control, changes in the hydraulic design of the district heating system and associated works (pipes, pumps, etc.), changes in the electricity grid, proper operation adjustments of heat pumps, proper operation adjustments of distributed heat pumps, etc. All this shows that new ideas for large-scale heat sources are needed.

[0005] In this context, Blarké and Dotzauer [Blarke M., Dotzauer E., Highly efficient cogeneration for intermittent operation: operational optimization of cogeneration with compression heat pump, exhaust gas heat recovery and intermediate cold storage, Energy 36 (2011) 6867e6878] propose to use the heat from the exhaust gas of the CHP unit as a heat source for a heat pump. There, it is proposed to cool the exhaust gas to 25 °C.

[0006] At these temperatures, it is technically impossible for devices that burn fossil fuels, biofuels, or electric fuels to emit exhaust gases into the atmosphere.

[0007] The present invention proposes a process that (i) utilizes the heat of exhaust gases as a heat source and (ii) facilitates efficient emission of exhaust gases into the atmosphere, following an appropriate technological approach.

[0008] Apart from theoretical proposals and calculations, the use of waste heat from exhaust gases in heat pumps has not been put to practical use in the context of gas turbines so far.

[0009] Theoretical publications and studies have not offered a solution to properly avoid venting exhaust gases into the atmosphere.

[0010] Therefore, the aim of the present invention is to provide a comprehensive process to utilize scarce large-scale heat sources at suitable temperatures for the decarbonization of the heating sector.

[0011] While supplying heat to the heat pump, the exhaust gases from the burner / gas turbine combustion chamber are cooled to temperatures well below typical chimney temperatures (e.g. 25°C), but cannot be pumped into the chimney while maintaining the stack effect (buoyancy). To avoid a decrease in the gas turbine performance and to not affect the chimney emission profile, an adequate flow must be established at the chimney outlet.

[0012] The object of the present invention is to properly re-cut or ensure the flow of exhaust gases to the atmosphere to compensate for the additional pressure loss due to the installed heat exchanger or to generate the required exit velocity of the exhaust gases in the chimney or natural draft.

[0013] Therefore, another object of the present invention is to provide a new safe and reliable sub-process for reheating / driving the gases through a chimney in an energy efficient process to release cool and dry exhaust gases into the atmosphere.

[0014] The above mentioned object and the objects mentioned above as well as other objects which will become more apparent hereinafter are achieved by a system according to claim 1.

[0015] Advantageously, the subject invention system provides approximately 20 percent excess heat for heat supply (e.g., district heating) compared to conventional WHRU (Waste Heat Recovery Unit) cycles. The excess heat is even greater when the invention is applied to CCPP (Combined Cycle Power Plant) based cogeneration units. The increased efficiency achieved by the invention can substantially reduce the carbon dioxide emissions from heat supply.

[0016] Advantageous further embodiments of the invention are set forth in the subclaims.

[0017] The attributes, features, and advantages of the present invention, as well as the manner in which they are achieved, as set forth above, will become more apparent and better understood upon reading the following description of the embodiments of the invention in conjunction with the drawings, in which: The illustrated embodiments are intended to illustrate, but not to limit, the invention.

[0018] The invention will now be further described with reference to illustrative embodiments thereof as shown in the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 shows a first embodiment of the present invention, which is configured as a heat pump cycle. [Diagram 2] FIG. 2 shows a second embodiment of the present invention, which is configured as a heat pump cycle. [Diagram 3] FIG. 3 shows a third embodiment of the present invention, which is configured as a heat pump cycle. [Figure 4] FIG. 4 shows an exemplary diagram that demonstrates the potential of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In the drawings, numerals such as reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It will be apparent that such embodiments may be practiced without these specific details.

[0021] 1, 2, and 3 show high-temperature heat pump cycles, which are arranged from the high-temperature side of a compressor 1 to a condenser 2, subcoolers 3a and 3b, an expansion valve 4, a heat pump cycle evaporator heat exchanger 5, and then to the low-temperature side of the compressor. High-temperature wet exhaust gas 6 discharged from a gas turbine or the like is supplied from a high-temperature wet exhaust gas inlet 7 and transfers heat to the heat pump cycle evaporator heat exchanger 5, during which the high-temperature wet exhaust gas 6 is cooled to a low-temperature dry exhaust gas 8. When exhaust gas with a typical chimney temperature of, for example, 70°C is cooled to, for example, 25°C, the water vapor contained in the exhaust gas condenses in an exhaust gas compressor 14 while releasing condensation heat to the low-temperature dry exhaust gas 8, and becomes condensed water 15. The condensed water 15 is discharged outside the exhaust gas compressor 14 and reused.

[0022] According to the first embodiment of the invention shown in FIG. 1, the hot wet exhaust gas 6 transfers heat directly to the heat pump cycle evaporator heat exchanger 5, which cools it to a low temperature dry exhaust gas 8. In the pre-exhaust gas heat exchanger 9, located between the hot wet exhaust gas inlet 7 and the heat pump cycle exhaust gas heat exchanger 5, the heat from the hot wet exhaust gas 6 is transferred to the low temperature dry exhaust gas 8, which turns it into a warm dry exhaust gas 10. The warm dry exhaust gas 10 passes through the second subcooler 3b, where heat is transferred to become the reheated dry exhaust gas 11. Thus, by successive use of the heat exchanger, the low temperature dry exhaust gas 8 is efficiently reheated by transferring heat from (i) the hot wet exhaust gas 6 (~70°C → dew point) to the low temperature dry exhaust gas 8 (25°C → X°C) and (ii) from the second subcooler 3b of the heat pump cycle. The first subcooler 3a and the condenser 2 of the heat pump cycle are used to preheat the heat supply return flow 12 to a reheated heat supply feed flow 13. The heat supply flows 12, 13 pass through the subcooler 3a and then through the condenser 2 which flows in the opposite direction to the heat pump cycle flows. The heat supply flow may be provided by a district heating flow.

[0023] According to a second embodiment of the invention, shown in figure 2, the hot moist gas stream 6 is separated into two parts. The first part 6.1 is cooled and partially condensed as described above for the first embodiment. The cold dry gas stream 8 thus obtained is then reheated by mixing it with the second part 6.2 of the total exhaust gas 6. If necessary, the mixed stream is further heated using the second subcooler 3b of the heat pump.

[0024] According to a third embodiment of the invention shown in figure 3, the hot humid gas stream 6 transfers heat to a heat exchanger intermediate cycle 18 which forms an intermediate cycle together with the heat pump cycle evaporator heat exchanger 5 and the pump intermediate cycle 19. Thereby, heat from the hot humid gas stream 6 is transferred indirectly to the heat pump cycle evaporator heat exchanger 5.

[0025] The second embodiment of the present invention shown in FIG. 2 can be combined with the first embodiment of the present invention shown in FIG. 1 or the third embodiment of the present invention shown in FIG. 3 without any creative effort by a person skilled in the art.

[0026] In another embodiment, a fan 16 is positioned in the path of the exhaust gases to exhaust the dry, cool exhaust gases through a chimney.

[0027] In yet another embodiment, a jet nozzle 17 is used to remove dry, cool exhaust gases through the chimney.

[0028] Figure 4 shows an example of a conventional cycle consisting of an (open cycle) gas turbine GT and a heat recovery unit WHRU in the first row, and an example of the present invention consisting of a gas turbine GT, a heat recovery unit WHRU, and a heat pump HP in the second row. It is clear that the system according to the present invention provides 22 percent surplus heat for district heating (DH) compared to the conventional cycle.

[0029] According to the invention, the exhaust gas is cooled to a temperature in the range of 10° C. to 40° C. In a preferred embodiment, the exhaust gas is cooled to 25° C.

[0030] When the exhaust gas is cooled, for example from a typical stack temperature of 70° C. to 25° C., the water vapor contained in the exhaust gas condenses, releasing heat of condensation. In this specification, the terms "hot wet exhaust gas 6" and "cold dry exhaust gas 8" are used to describe the exhaust gas at different points in the process.

[0031] Although preferred embodiments have been illustrated and described in detail, the invention is not limited to the disclosed examples: a person skilled in the art can make other variations without departing from the scope of protection of the claimed invention.

Claims

1. A system that utilizes heat from exhaust gas as a heat source for heat supply, a heat pump cycle, which runs from the hot side of a compressor (1) through a condenser heat pump cycle (2), an expansion valve (4) and a heat pump cycle evaporator heat exchanger (5) to the cold side of the compressor; - the hot wet exhaust gas (6) supplied by the hot wet exhaust gas inlet (7) transfers heat to the heat pump cycle evaporator heat exchanger (5) and is cooled to a low temperature dry exhaust gas (8); - Heat from the system is used to turn the cold dry exhaust gas (8) into warm dry exhaust gas (10); a heat supply return flow (12) through said condenser heat pump cycle (2) in which said transferred heat is used as a heat source for a heat supply feed flow (13); A system that provides.

2. The transfer of heat of the hot wet exhaust gas (6) to the heat pump cycle evaporator heat exchanger (5) is realized by a heat exchanger intermediate cycle (18) which dissipates heat from the hot wet exhaust gas (6) and forms an intermediate cycle together with the heat pump cycle evaporator heat exchanger (5). The system of claim 1 further comprising:

3. The heat from the system for transforming the low temperature dry exhaust gas (8) into the warm dry exhaust gas (10) is utilized by separating the hot wet exhaust gas (6) into a first portion of hot wet exhaust gas (6.1) and a second portion of hot wet exhaust gas (6.2) complementary to the first portion, the first portion being fed to a heat pump cycle evaporator heat exchanger (5) where it is cooled to a low temperature dry exhaust gas (8), and the low temperature dry exhaust gas (8) is mixed with the second portion of hot wet exhaust gas (6.2) to provide the warm exhaust gas (10).

3. The system of claim 1, further comprising:

4. The heat from the system for transforming the low temperature dry exhaust gas (8) into a warm dry exhaust gas (10) is utilized by a pre-exhaust gas heat exchanger (9) installed between the high temperature wet exhaust gas inlet (7) and the heat pump cycle evaporator heat exchanger (5), so that heat from the high temperature wet exhaust gas (6) is transferred to the low temperature dry exhaust gas (8) and transforms the low temperature dry exhaust gas (8) into the warm dry exhaust gas (10).

3. The system according to claim 1 or 2, further comprising:

5. a first subcooler (3a) located in the heat pump cycle between the expansion valves (4) of the heat pump cycle and directly adjacent to the condenser heat pump cycle (2); the heat supply return flow (12) passing first through the first subcooler (3a) and then through the condenser heat pump cycle (2); The system according to any one of the preceding claims, further comprising:

6. a second subcooler (3b) disposed in the heat pump cycle between the condenser heat pump cycle (2) and the expansion valve (4) and directly adjacent to the expansion valve (4), the warm dry exhaust gas (10) passes through the second subcooler (3b) and becomes a reheated dry exhaust gas (11) by the transferred heat; The system according to any one of the preceding claims, further comprising:

7. A fan (16) for driving the warm exhaust gas (10) through the chimney. The system according to any one of the preceding claims, further comprising:

8. A jet nozzle (17) for discharging the warm exhaust gas (10) through the chimney. The system according to any one of the preceding claims, further comprising:

9. The hot wet exhaust gas discharged by the gas turbine (6). The system according to any one of the preceding claims, further comprising:

10. said heat supply return flow (12) being provided by a district heating return flow and said heat supply feed flow (13) being provided by a district heating feed flow; The system according to any one of the preceding claims, further comprising:

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