Steam waste heat recovery system using absorption heat pump and method for recovering steam waste heat

Abstract

A steam waste heat recovery system using an absorption heat pump and a method for recovering steam waste heat. The steam waste heat recovery system includes a second-type absorption heat pump, a water pump, an expander, a steam mixer and a separator. The second-type absorption heat pump includes a waste heat path inlet, a waste heat path outlet, a heat exchange path inlet and a heat exchange path outlet; the first steam inlet of the steam mixer is connected to the exhaust port of the expander, the second steam inlet is used to receive low-pressure medium-temperature steam to be recovered waste heat, and the steam outlet is connected to the waste heat path inlet of the second-type absorption heat pump. The inlet of the separator is connected to the waste heat path outlet of the second-type absorption heat pump, the first outlet of the separator is used to output hot water, and the second outlet of the separator is connected to the water inlet of the water pump. The heat exchange path inlet of the second-type absorption heat pump is connected to the water outlet of the water pump, and the heat exchange path outlet of the second-type absorption heat pump is connected to the air inlet of the expander. The present invention can recover the waste heat of low-pressure medium-temperature steam and improve energy utilization.

Description

Technical Field

[0001] The invention relates to a waste heat recovery technology. Background Art

[0002] There are many waste heat recovery devices for high-temperature steam on the market, but there has been a lack of efficient and low-cost energy recovery solutions for low-pressure and medium-temperature steam (0.1MPa, about 100℃). The energy grade of low-pressure and medium-temperature steam is low and cannot be used for conventional steam turbine power generation, but it contains a large amount of gaseous latent heat energy and is widely used in industry. How to effectively utilize the energy of low-pressure and medium-temperature steam and improve energy utilization is an urgent problem that technicians in this field need to solve. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a steam waste heat recovery system using an absorption heat pump and a method for recovering steam waste heat, which can recover the waste heat of low-pressure medium-temperature steam, improve energy utilization and reduce energy consumption.

[0004] According to one embodiment of the present invention, a steam waste heat recovery system using an absorption heat pump includes a second-type absorption heat pump, a water pump, an expander, a steam mixer and a separator; the second-type absorption heat pump includes a waste heat path inlet, a waste heat path outlet, a heat exchange path inlet and a heat exchange path outlet; the first steam inlet of the steam mixer is connected to the exhaust port of the expander, the second steam inlet of the steam mixer is used to receive the low-pressure medium-temperature steam to be recovered waste heat, and the steam outlet of the steam mixer is connected to the waste heat path inlet of the second-type absorption heat pump; the inlet of the separator is connected to the waste heat path outlet of the second-type absorption heat pump, the first outlet of the separator is used to output hot water, and the second outlet of the separator is connected to the water inlet of the water pump; the heat exchange path inlet of the second-type absorption heat pump is connected to the water outlet of the water pump, and the heat exchange path outlet of the second-type absorption heat pump is connected to the air inlet of the expander; the second-type absorption heat pump is used to recover the waste heat of the low-pressure medium-temperature steam flowing in from the waste heat path inlet, heat the water pump outlet water flowing into the heat exchange path inlet into high-temperature and high-pressure steam and output it from the heat exchange path outlet.

[0005] According to another embodiment of the present invention, a steam waste heat recovery system using an absorption heat pump includes a second type of absorption heat pump, a water pump, and an expander; the second type of absorption heat pump includes a first waste heat path inlet, a first waste heat path outlet, a second waste heat path inlet, a second waste heat path outlet, a heat exchange path inlet, and a heat exchange path outlet; The first waste heat path inlet of the second type absorption heat pump is connected to the exhaust port of the expander, and the first waste heat path outlet of the second type absorption heat pump is connected to the water inlet of the water pump; the second waste heat path inlet of the second type absorption heat pump is used to receive the low-pressure medium-temperature steam to be recovered waste heat, and the second waste heat path outlet of the second type absorption heat pump is used to output hot water; the heat exchange path inlet of the second type absorption heat pump is connected to the water outlet of the water pump, and the heat exchange path outlet of the second type absorption heat pump is connected to the air inlet of the expander; the second type absorption heat pump is used to recover the waste heat of the exhaust steam of the expander flowing in from the first waste heat path inlet and the waste heat of the low-pressure medium-temperature steam flowing in from the second waste heat path inlet, heat the outlet water of the water pump flowing into the heat exchange path inlet into high-temperature and high-pressure steam, and output it from the heat exchange path outlet.

[0006] According to another aspect of the present invention, there is also provided a method for recovering waste heat of steam using an absorption heat pump, comprising the following steps:

[0007] The low-pressure medium-temperature waste heat steam to be recovered and the low-pressure medium-temperature steam discharged from the expander enter the evaporator and generator of the second type absorption heat pump for heat exchange. The low-pressure medium-temperature steam is converted into low-pressure low-temperature hot water after heat exchange. Part of the low-pressure low-temperature hot water enters the water pump, and the other part of the low-pressure low-temperature hot water is discharged from the heat exchange path outlet of the second type absorption heat pump.

[0008] The high-pressure and low-temperature hot water output by the water pump is input into the second-type absorption heat pump, and is heated by the absorber of the second-type absorption heat pump to obtain high-pressure and high-temperature steam;

[0009] High-temperature and high-pressure steam is input into the expander to drive the expander to do work.

[0010] The present invention has at least the following advantages:

[0011] In the embodiment of the present invention, the second type of absorption heat pump can recover the energy of the gas discharged after the expander does work, and produce high-temperature and high-pressure steam suitable for the expander to inhale, so as to drive the expander to do work, and then drive the load or generate electricity, playing the role of pumping energy from low-grade to high-grade heat pump. In this process, the waste heat of the low-pressure and medium-temperature steam is recycled and utilized by the second type of absorption heat pump, which reduces the consumption of the driving heat source by the second type of absorption heat pump and improves the energy utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of a steam waste heat recovery system using an absorption heat pump according to a first embodiment of the present invention is shown.

[0013] Figure 2 A schematic diagram of a steam waste heat recovery system using an absorption heat pump according to a second embodiment of the present invention is shown. DETAILED DESCRIPTION

[0014] Figure 1 Schematic diagram of a steam waste heat recovery system using an absorption heat pump according to a first embodiment of the present invention is shown. Figure 1 According to the first embodiment of the present invention, a steam waste heat recovery system using an absorption heat pump includes a second type absorption heat pump 1, a water pump 2, an expander 3, a steam mixer 4 and a separator 5.

[0015] The second type absorption heat pump 1 comprises a waste heat path inlet 1A, a waste heat path outlet 1B, a heat exchange path inlet 1C and a heat exchange path outlet 1D.

[0016] The first steam inlet of the steam mixer 4 is connected to the exhaust port of the expander 3, the second steam inlet of the steam mixer 4 is used to receive the low-pressure medium-temperature steam to be recovered, and the steam outlet of the steam mixer 4 is connected to the waste heat path inlet 1A of the second type absorption heat pump 1. The inlet of the separator 5 is connected to the waste heat path outlet 1B of the second type absorption heat pump 1, the first outlet of the separator 5 is used to output hot water, and the second outlet of the separator 5 is connected to the water inlet of the water pump 2.

[0017] The heat exchange path inlet 1C of the second type absorption heat pump 1 is connected to the water outlet of the water pump 2, and the heat exchange path outlet of the second type absorption heat pump 1 is connected to the air inlet of the expander 3; the second type absorption heat pump 1 is used to recover the waste heat of the low-pressure and medium-temperature steam flowing in from the waste heat path inlet 1B, heat the water pump outlet water flowing into the heat exchange path inlet 1C into high-temperature and high-pressure steam and output it from the heat exchange path outlet 1D.

[0018] Figure 2 FIG. 2 shows a schematic diagram of a steam waste heat recovery system using an absorption heat pump according to a second embodiment of the present invention. Figure 2 A steam waste heat recovery system using an absorption heat pump according to a second embodiment of the present invention includes a second type absorption heat pump 1a, a water pump 2 and an expander 3.

[0019] The second type absorption heat pump 1a includes a first waste heat path inlet 1E, a first waste heat path outlet 1F, a second waste heat path inlet 1G, a second waste heat path outlet 1H, a heat exchange path inlet 1I and a heat exchange path outlet 1J.

[0020] The first waste heat path inlet 1E of the second type absorption heat pump 1a is connected to the exhaust port of the expander 3, and the first waste heat path outlet 1F of the second type absorption heat pump 1a is connected to the water inlet of the water pump 2; the second waste heat path inlet 1G of the second type absorption heat pump is used to receive low-pressure medium-temperature steam to be recovered waste heat, and the second waste heat path outlet 1H of the second type absorption heat pump 1a is used to output hot water; the heat exchange path inlet 1I of the second type absorption heat pump 1a is connected to the water outlet of the water pump 2, and the heat exchange path outlet 1J of the second type absorption heat pump 1a is connected to the air inlet of the expander 3.

[0021] The second type absorption heat pump 1a is used to recover the waste heat of the expansion machine exhaust steam flowing in from the first waste heat path inlet 1E and the waste heat of the low-pressure medium-temperature steam flowing in from the second waste heat path inlet 1G, heat the outlet water of the water pump flowing into the heat exchange path inlet 1I into high-temperature and high-pressure steam and output it from the heat exchange path outlet 1J.

[0022] In the second embodiment, the first waste heat path and the second waste heat path of the second type absorption heat pump 1a are independent of each other and are arranged in parallel.

[0023] Optionally, in the first and second embodiments, the expander 3 is a screw expander or a steam turbine. When the expander intake pressure is 0.27 MPa, a steam turbine is preferred, and when the expander intake pressure is 0.9 MPa, a screw expander is preferred.

[0024] The steam waste heat recovery system of the first embodiment is an open system, and the low-pressure medium-temperature steam to be recovered is mixed with the exhaust steam of the expander, and then input into the second type absorption heat pump 1a together. In the whole system, the steam circulating in the expander is connected to the outside (the low-pressure medium-temperature steam to be recovered), and the expander cycle belongs to an open cycle.

[0025] The steam waste heat recovery system of the second embodiment is a closed system. The low-pressure medium-temperature steam to be recovered is separated from the exhaust steam of the expander and enters the second absorption heat pump 1a respectively. In the whole system, the cycle of the expander is independent of the outside world (the low-pressure medium-temperature steam to be recovered), and the expander cycle is a closed cycle.

[0026] The open cycle system is relatively simple, but it has high requirements for the cleanliness of the waste heat steam, otherwise it may cause damage to the expander. The expander part of the closed system has high reliability, but it needs to use a second-type absorption heat pump with two sets of heat exchange pipelines, which increases the complexity of the system.

[0027] According to another embodiment of the present invention, a method for recovering waste heat of steam using an absorption heat pump comprises the following steps:

[0028] The low-pressure medium-temperature waste heat steam to be recovered and the low-pressure medium-temperature steam discharged from the expander 3 enter the evaporator and generator of the second type absorption heat pump 1 or 1a for heat exchange. The low-pressure medium-temperature steam is converted into low-pressure low-temperature hot water after heat exchange. A part of the low-pressure low-temperature hot water enters the water pump, and the other part of the low-pressure low-temperature hot water is discharged from the heat exchange path outlet of the second type absorption heat pump 1 or 1a.

[0029] The high-pressure and low-temperature hot water output by the water pump 2 is input into the second type absorption heat pump 1 or 1a, and is heated by the absorber of the second type absorption heat pump 1 or 1a to obtain high-pressure and high-temperature steam;

[0030] The high-temperature and high-pressure steam is input into the expander 3 to drive the expander to do work.

[0031] In this embodiment, the exhaust pressure of the expander is the pressure of the low-pressure medium-temperature waste heat steam to be recovered, preferably, it is set to 0.1MPa; the exhaust temperature of the expander is the saturation temperature under the exhaust pressure, which is about 100°C, and the actual operation can be higher than 100°C; the inlet temperature of the expander is set to the saturation temperature under the inlet pressure, which is about 130°C at 0.27MPa. The heat source temperature and pressure of the second type of absorption heat pump are the temperature and pressure of the low-pressure medium-temperature steam to be recovered; the heating temperature of the second type of absorption heat pump is the inlet temperature of the expander plus the heat exchange temperature difference, which is about 135°C; the cooling temperature of the second type of absorption heat pump is preferably 40°C. In theory, the lower the temperature, the higher the energy that can be recovered. The pressure before the water pump is the exhaust pressure of the expander, and the pressure after the pump is the suction pressure of the expander.

[0032] The following combination Figure 2 The second embodiment shown describes the working principle and process of the present invention in detail. In the second embodiment, 0.27MPa is high pressure, 0.10MPa is low pressure; 130℃ is high temperature, 100℃ is medium temperature, and 40℃ is low temperature. The pressure of the low-pressure medium-temperature steam to be recovered is 0.1MPa and the temperature is 100℃; the pressure of the low-pressure low-temperature hot water is 0.1MPa and the temperature is 40℃; the pressure of the high-pressure low-temperature hot water is 0.27MPa and the temperature is 40℃; the pressure of the high-pressure high-temperature steam is 0.27MPa and the temperature is 130℃. The expander adopts a twin-screw expander.

[0033] See also Figure 2. The low-pressure medium-temperature steam (flow Q2) discharged from the expander 3 enters the first waste heat path inlet 1E of the second type absorption heat pump 1a, and the low-pressure medium-temperature steam (flow Q1) to be recovered from the waste heat enters the second waste heat path inlet 1G of the second type absorption heat pump 1a. In the second type absorption heat pump 1a, the condensed water flowing into the evaporator from the condenser absorbs the heat of the two low-pressure medium-temperature steams and then vaporizes. The generated water vapor is transported to the absorber to dilute the lithium bromide solution in the absorber. The dilute lithium bromide solution enters the generator through the throttle valve. In the generator, the dilute lithium bromide solution absorbs the heat of the low-pressure medium-temperature steam discharged from the expander 3 and the heat of the low-pressure medium-temperature steam to be recovered from the waste heat, and becomes a concentrated lithium bromide solution. The low-pressure medium-temperature steam releases heat and condenses into water. The lithium bromide concentrated solution is sent to the absorber, and the negative pressure water vapor circulating inside the lithium bromide is sent to the condenser and condensed into water in the condenser (this part is the internal circulation of the lithium bromide absorption heat pump, which will not be further explained in this patent). The low-pressure and low-temperature hot water generated by the low-pressure and medium-temperature steam to be recovered after heat exchange is directly discharged through the second waste heat path outlet 1H, and the low-pressure and low-temperature hot water generated by the low-pressure and medium-temperature steam discharged from the expander 3 after heat exchange is output to the water pump 2 through the first waste heat path outlet 1F, and the water pump 2 is pressurized. The heat generated by the lithium bromide solution in the absorber during the absorption process heats the high-pressure and low-temperature hot water output by the water pump 2 to obtain high-pressure and high-temperature steam, which is then discharged through the second heat exchange path outlet 1J of the second type absorption heat pump 1a, enters the expander 3, drives the expander 3 to do work, and then drives the load or drives the generator to generate electricity. The gas discharged from the expander 3 becomes low-pressure and medium-temperature steam, and then passes into the second type absorption heat pump 1a to complete the cycle.

[0034] In the embodiment of the present invention, the second type of absorption heat pump can recover the energy of the gas discharged after the expander does work, and produce high-temperature and high-pressure steam suitable for the expander to inhale, so as to drive the expander to do work, and then drive the load or generate electricity, playing the role of pumping energy from low-grade to high-grade heat pump. In this process, the waste heat of the low-pressure and medium-temperature steam is recycled and utilized by the second type of absorption heat pump, which reduces the consumption of the driving heat source by the second type of absorption heat pump and improves the energy utilization rate.

Claims

1. A steam waste heat recovery system using an absorption heat pump, characterized in that: It includes a second type absorption heat pump, a water pump, an expander, a steam mixer and a separator; The second type absorption heat pump comprises a waste heat path inlet, a waste heat path outlet, a heat exchange path inlet and a heat exchange path outlet; The first steam inlet of the steam mixer is communicated with the exhaust port of the expander, the second steam inlet of the steam mixer is used to receive low-pressure medium-temperature steam to be recovered waste heat, and the steam outlet of the steam mixer is communicated with the waste heat path inlet of the second type absorption heat pump; The inlet of the separator is communicated with the outlet of the waste heat path of the second type absorption heat pump, the first outlet of the separator is used to output hot water, and the second outlet of the separator is communicated with the water inlet of the water pump; The heat exchange path inlet of the second type absorption heat pump is connected to the water outlet of the water pump, and the heat exchange path outlet of the second type absorption heat pump is connected to the air inlet of the expander; the second type absorption heat pump is used to recover the waste heat of the low-pressure and medium-temperature steam flowing in from the waste heat path inlet, heat the water pump outlet water flowing into the heat exchange path inlet into high-temperature and high-pressure steam, and output it from the heat exchange path outlet.

2. The steam waste heat recovery system using an absorption heat pump according to claim 1, characterized in that: The expander is a screw expander or a steam turbine.

3. A steam waste heat recovery system using an absorption heat pump, characterized in that: It includes a second type absorption heat pump, a water pump and an expander; The second type absorption heat pump comprises a first waste heat path inlet, a first waste heat path outlet, a second waste heat path inlet, a second waste heat path outlet, a heat exchange path inlet and a heat exchange path outlet; The first waste heat path inlet of the second type absorption heat pump is communicated with the exhaust port of the expander, and the first waste heat path outlet of the second type absorption heat pump is communicated with the water inlet of the water pump; the second waste heat path inlet of the second type absorption heat pump is used to receive low-pressure medium-temperature steam to be recovered waste heat, and the second waste heat path outlet of the second type absorption heat pump is used to output hot water; the heat exchange path inlet of the second type absorption heat pump is communicated with the water outlet of the water pump, and the heat exchange path outlet of the second type absorption heat pump is communicated with the air inlet of the expander; The second type of absorption heat pump is used to recover the waste heat of the expansion machine exhaust steam flowing in from the inlet of the first waste heat path and the waste heat of the low-pressure and medium-temperature steam flowing in from the inlet of the second waste heat path, heat the outlet water of the water pump flowing into the inlet of the heat exchange path into high-temperature and high-pressure steam and output it from the outlet of the heat exchange path.

4. The steam waste heat recovery system using an absorption heat pump according to claim 3, characterized in that: The expander is a screw expander or a steam turbine.

5. A method for recovering waste heat from steam using an absorption heat pump, characterized in that: The following steps are involved: The low-pressure medium-temperature waste heat steam to be recovered and the low-pressure medium-temperature steam discharged from the expander enter the evaporator and generator of the second type absorption heat pump for heat exchange. The low-pressure medium-temperature steam is converted into low-pressure low-temperature hot water after heat exchange. Part of the low-pressure low-temperature hot water enters the water pump, and the other part of the low-pressure low-temperature hot water is discharged from the heat exchange path outlet of the second type absorption heat pump. The high-pressure and low-temperature hot water output by the water pump is input into the second type absorption heat pump, and is heated by the absorber of the second type absorption heat pump to obtain high-pressure and high-temperature steam; The high-temperature and high-pressure steam is input into the expander to drive the expander to do work.

6. The method for recovering waste heat of steam using an absorption heat pump according to claim 5, characterized in that: The pressure of the low-pressure medium-temperature steam is 0.1MPa and the temperature is 100°C; the pressure of the low-pressure low-temperature hot water is 0.1MPa and the temperature is 40°C; the pressure of the high-pressure low-temperature hot water is 0.27MPa and the temperature is 40°C; the pressure of the high-pressure high-temperature steam is 0.27MPa and the temperature is 130°C.

7. The method for recovering waste heat of steam using an absorption heat pump according to claim 5, characterized in that: The inlet air temperature of the expander is the saturation temperature under the inlet air pressure.

Images