CN102537935A - Heat regenerative system adopting jet-type heat pumps - Google Patents

Abstract

A heat recovery system using a jet heat pump, including several stages of heaters connected in sequence, the heaters of each stage are respectively connected with the steam extraction pipeline of the stage, and the heaters of each adjacent stage are provided with the said An indirect heater connected to two adjacent heaters is provided between the steam extraction pipelines of the adjacent two-stage heaters, which communicates with the steam extraction pipelines of the adjacent two-stage heaters and communicates with this stage. The jet heat pump corresponding to the indirect heater, the outlet of the jet heat pump is connected with the inlet of the indirect heater. The present invention introduces a jet heat pump into the heat recovery system, utilizes the higher-pressure steam extraction to inject the next-stage steam extraction with a lower pressure, and generates mixed steam with a pressure between the two-stage steam extraction pressures, and adds one more The mixed steam acts as an indirect regenerative heater for heating the steam source, thereby reducing the irreversible loss in the regenerative process and improving the thermal efficiency of the unit.

Description

A heat recovery system using jet heat pump

technical field

The invention relates to a heat recovery system, in particular to a heat recovery system using a jet heat pump.

Background technique

Modern large-scale thermal power units all use heat recovery to improve their thermal economy. From a thermodynamic point of view, the more heat recovery stages, the higher the thermal efficiency of the unit. However, due to the constraints of the steam turbine structure and other factors, the increase in the heat recovery stages is limited. Currently, large thermal power units generally use 7-9 stage heat recovery. hot. The regenerative heater of thermal power plant uses steam to heat the feed water, and there is an irreversible loss due to the temperature difference between the steam and the feed water. The greater the temperature difference between steam and feed water, the greater its irreversible loss.

Contents of the invention

The purpose of the present invention is to provide a heat recovery system using a jet heat pump that can reduce the irreversible loss in the heat recovery process, improve the thermal efficiency of the unit, and save energy and reduce emissions.

In order to achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: comprising several stages of heaters connected in sequence, the heaters of each stage are respectively connected with the steam extraction pipelines of the stage, and there is a set between each adjacent two-stage heater. The indirect heaters connected to the two adjacent heaters are provided between the steam extraction pipelines of the adjacent two-stage heaters and communicate with the steam extraction pipelines of the adjacent two-stage heaters. This level of indirect heater corresponds to the ejector heat pump, and the outlet of the ejector heat pump is connected to the inlet of the indirect heater.

Each of the adjacent two-stage heaters is defined as the current-stage heater and the next-stage heater. The high-pressure nozzle of the jet heat pump is connected to the extraction pipeline of the current-stage heater, and the low-pressure nozzle of the jet heat pump is connected to the next-stage heater. The extraction steam pipeline of the heater is connected, and the medium-pressure nozzle of the jet heat pump is connected with the indirect heater of this stage through the pipeline.

The present invention introduces a jet heat pump into the heat recovery system, utilizes the higher-pressure steam extraction to inject the next-stage steam extraction with a lower pressure, and generates mixed steam with a pressure between the two-stage steam extraction pressures, and adds one more The mixed steam acts as an indirect regenerative heater for heating the steam source, thereby reducing the irreversible loss in the regenerative process and improving the thermal efficiency of the unit. Calculation shows that the adoption of this technology for 1000MW units can increase the thermal efficiency by about 1%, and the benefits of energy saving and emission reduction are obvious.

Description of drawings

Figure 1 is a schematic diagram of the principle of a heat recovery system using a jet heat pump;

Fig. 2 is the temperature-enthalpy diagram of the reheating heating process;

Figure 3 is a schematic diagram of a jet heat pump.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Since the regenerative heater of thermal power plant uses steam to heat the feed water, there is an irreversible loss due to the temperature difference between the steam and the feed water. The greater the temperature difference between steam and feed water, the greater its irreversible loss. Figure 2 shows the temperature-enthalpy diagram of the regenerative heating process. It can be seen from this figure that increasing the number of regenerative stages can reduce the temperature difference in the regenerative process and thus reduce the regenerative process when the end difference of the heater remains unchanged. irreversible loss. However, in reality, limited by factors such as the structure of the steam turbine, currently large coal-fired generating units generally use 7-9 stages of regenerative steam extraction, and the corresponding regenerative heater stages are also 7-9 stages. In order to increase the number of stages of the regenerative heater, the present invention proposes the use of jet heat pumps, using the extraction steam with higher pressure to inject the extraction steam with lower pressure in the next stage, so as to generate steam with a pressure between these two stages of extraction steam. The mixed steam is used as the heating steam source of the newly added regenerative heater, so that the number of stages of the regenerative heater can be increased without increasing the number of steam extraction stages of the steam turbine.

Referring to Figures 1 and 3, the present invention includes several stages of heaters connected in sequence, the heaters of each stage are respectively connected to the steam extraction pipeline of the stage, and the two-stage heater is arranged between each adjacent two-stage heater. The indirect heater 4 connected to adjacent heaters is provided between the extraction pipelines of adjacent two-stage heaters, which communicates with the extraction pipelines of the adjacent two-stage heaters and is indirect with the stage. The heater 4 corresponds to the ejector heat pump 2 , and the outlet of the ejector heat pump 2 is connected to the inlet of the indirect heater 4 . Each of the adjacent two-stage heaters is defined as the heater 1 of the current stage and the heater 3 of the next stage. The high-pressure nozzle 7 of the jet heat pump 2 is connected to the steam extraction pipeline 5 of the heater of the present stage. The low-pressure nozzle 8 is connected with the steam extraction pipeline 6 of the next-stage heater, and the medium-pressure nozzle 9 of the jet heat pump 2 is connected with the indirect heater 4 of the stage through the pipeline.

Since jet heat pumps are widely used in many fields. The high-pressure steam expands through the high-pressure nozzle to form a high-speed airflow, mixes with the low-pressure steam, and forms a medium-pressure steam with a pressure between the high-pressure steam and the low-pressure steam after passing through the mixing chamber 10. The essence is to use the kinetic energy of the high-pressure steam to increase the pressure of the low-pressure steam . Compared with other types of heat pumps, this heat pump has a simple structure, no moving parts, and a safe and reliable working process. The invention uses the heat pump in the heat recovery heating system of a large thermal power unit, which can reduce the irreversible loss in the heat recovery process and improve its thermal efficiency.

A preliminary calculation is made on the improvement scheme of the heat recovery system of a 1000MW supercritical unit by using the present invention. Consider using the eighth-stage steam extraction to eject the seventh-stage steam extraction. Under the design condition, the steam pressure of the eighth-stage heater is 8.19MPa, and the steam pressure in the seventh-stage heater is 4.73MPa. When the injection ratio ( When the mass flow ratio of high-pressure steam to low-pressure steam) is 0.7, the mixed steam pressure can reach 5.49MPa, the thermal efficiency of the unit can be increased by about 0.14%, the coal consumption rate of the unit for power generation can be reduced by 0.4g/kWh, and more than 3,000 tons of standard coal can be saved every year. It has significant energy saving and emission reduction benefits.

The invention can be widely used in heat recovery systems of thermal power plants and heating systems of heating networks, and can also be used in technological processes requiring multi-stage steam for heating in industries such as petroleum, chemical industry, metallurgy, and light industry.

Claims (2)

1. A heat recovery system using a jet heat pump, characterized in that it includes several stages of heaters connected in sequence, and each stage of heaters is respectively connected to the steam extraction pipeline of the stage, and between each adjacent two stages of heaters An indirect heater (4) communicating with the two-stage adjacent heaters is arranged between them, and an extraction pipe connected to the adjacent two-stage heaters is provided between the extraction pipelines of the adjacent two-stage heaters. The steam pipeline is connected with the injection heat pump (2) corresponding to the indirect heater (4) of this stage, and the outlet of the injection heat pump (2) is connected with the inlet of the indirect heater (4). 2. The heat recovery system using jet heat pump according to claim 1, characterized in that: each of the adjacent two-stage heaters is defined as the current-stage heater (1) and the next-stage heater (3) , the high-pressure nozzle (7) of the jet heat pump (2) is connected to the steam extraction pipeline (5) of the current stage heater, and the low pressure nozzle (8) of the jet heat pump (2) is connected to the steam extraction pipeline of the next stage heater ( 6) are connected, and the medium-pressure nozzle (9) of the jet heat pump (2) is connected with the indirect heater (4) of this stage through a pipeline.

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