CN-122015158-A - Four-pipe electric drive enhanced flue gas waste heat recovery system and control method thereof

CN122015158ACN 122015158 ACN122015158 ACN 122015158ACN-122015158-A

Abstract

The application discloses a four-pipe system electric drive enhanced flue gas waste heat recovery system and a control method thereof, and relates to the field of flue gas waste heat utilization and heating. The water loops corresponding to the primary heat exchanger and the secondary heat exchanger are respectively provided with a circulating pump and a heat meter, and the water loops corresponding to the secondary heat exchanger are respectively provided with an electric heat pump, wherein the electric heat pump comprises an evaporator and a condenser. The method comprises the steps of monitoring loop information on a water loop by a heat meter, performing variable frequency control on a circulating pump by a PLC (programmable logic controller) according to the loop information, and performing gradient utilization control on flue gas waste heat based on a primary heat exchanger and a secondary heat exchanger in a heat exchanger, wherein the primary heat exchanger directly recovers the flue gas waste heat by adopting heating water backwater, the secondary heat exchanger recovers the waste heat of a low-temperature part of the flue gas by adopting an evaporator, and replaces hot water with lower temperature to serve as a heat source of an electric heat pump, and the temperature of the heating water is increased by the electric heat pump. The application can deeply recycle the waste heat of the flue gas and improve the recycling efficiency of the waste heat of the flue gas.

Inventors

YU TAO
Li Xinsuo
LU CHAOCHAO
WANG ZONGYAO
GAO SIQI
SHI XINGWANG

Assignees

北京新兴合众科技有限公司

Dates

Publication Date: 20260512
Application Date: 20260409

Claims (10)

1. The four-pipe electric drive enhanced flue gas waste heat recovery system is characterized by being applied to a natural gas hot water boiler scene, and comprises a control cabinet, a circulating pump, a heat exchanger and a heat meter, wherein the control cabinet comprises a PLC (programmable logic controller); The heat exchanger comprises a primary heat exchanger and a secondary heat exchanger, wherein the water loops corresponding to the primary heat exchanger and the secondary heat exchanger are respectively provided with a circulating pump and a heat meter, and the water loops corresponding to the secondary heat exchanger are provided with an electric heat pump; the heat meter is used for monitoring loop information on the water loop, wherein the loop information comprises temperature, temperature difference, flow, thermal power and heat; The PLC is used for performing variable frequency control on the circulating pump according to loop information and performing gradient utilization control on flue gas waste heat in a natural gas hot water boiler scene based on a primary heat exchanger and a secondary heat exchanger in the heat exchanger, wherein the primary heat exchanger directly recovers the flue gas waste heat by adopting heating water backwater, the secondary heat exchanger recovers the waste heat of a low-temperature part of the flue gas by adopting an evaporator and replaces hot water with lower temperature to serve as a heat source of the electric heat pump, the temperature of the heating water is increased by the electric heat pump, the low-temperature part of the flue gas is the flue gas after the waste heat recovery by the primary heat exchanger, and the lower temperature is lower than the waste heat temperature of the low-temperature part of the flue gas.
2. The four-pipe electric drive enhanced flue gas waste heat recovery system according to claim 1, wherein the primary heat exchanger and the secondary heat exchanger adopt heat exchangers with different end differences; The end difference is determined based on the flue gas outlet temperature and the heat exchanger inlet water temperature.
3. The four-pipe electric drive enhanced flue gas waste heat recovery system according to claim 1, wherein a buffer water tank is arranged between the secondary heat exchanger and the evaporator; the buffer water tank is used for buffering the residual heat quantity change of the flue gas, and the water quantity of the buffer water tank corresponds to the circulating flow of the secondary heat exchanger and the evaporator with set time duration.
4. The four-pipe electric drive enhanced flue gas waste heat recovery system according to claim 3, wherein the buffer water tank is supplemented with heating water backwater and is controlled by a float valve.
5. The four-pipe electric drive enhanced flue gas waste heat recovery system according to claim 1, wherein when the electric heat pump is not one-to-one with a boiler in a natural gas hot water boiler scenario, the four-pipe electric drive enhanced flue gas waste heat recovery system further comprises an electric valve and a temperature sensor; the temperature sensor is used for monitoring the outlet water temperature of the heat exchanger.
6. The four-pipe electric drive enhanced flue gas waste heat recovery system according to claim 1, wherein the control cabinet further comprises a touch screen, a frequency converter and a smart meter; The touch screen, the frequency converter and the intelligent ammeter are all connected with the PLC.
7. The four-pipe electric drive enhanced flue gas waste heat recovery control method is characterized by being realized by adopting the four-pipe electric drive enhanced flue gas waste heat recovery system according to any one of claims 1-6, and comprises the following steps: Loop information on a water loop is acquired, wherein the loop information comprises temperature, temperature difference, flow, thermal power and heat; The method comprises the steps of performing variable frequency control on a circulating pump according to loop information, and performing gradient utilization control on flue gas waste heat in a natural gas hot water boiler scene based on a primary heat exchanger and a secondary heat exchanger in a heat exchanger, wherein the primary heat exchanger directly recovers the flue gas waste heat by adopting heating water backwater, the secondary heat exchanger recovers the waste heat of a low-temperature part of the flue gas by adopting an evaporator and replaces hot water with lower temperature to serve as a heat source of an electric heat pump, the temperature of the heating water is increased by the electric heat pump, the low-temperature part of the flue gas is flue gas after the waste heat recovery by the primary heat exchanger, and the lower temperature is lower than the waste heat temperature of the low-temperature part of the flue gas.
8. The four-pipe electric drive enhanced flue gas waste heat recovery control method according to claim 7, wherein the method is characterized by performing variable frequency control on the circulating pump according to loop information and performing gradient utilization control on flue gas waste heat in a natural gas hot water boiler scene based on a primary heat exchanger and a secondary heat exchanger in the heat exchangers, and specifically comprises the following steps: determining the upper and lower limits of the frequency of a circulating pump corresponding to the primary heat exchanger according to the flow in the loop information corresponding to the primary heat exchanger, and controlling according to the end difference of the primary heat exchanger by adopting a PID control method, wherein the end difference is determined based on the flue gas outlet temperature and the water inlet temperature of the heat exchanger; When the frequency-reducing condition is met, controlling a circulating pump corresponding to the primary heat exchanger to start frequency-reducing operation, and when the frequency-reducing condition is not met, keeping the operating frequency unchanged, wherein the frequency-reducing condition comprises that the outlet water temperature of the evaporation side corresponding to the evaporator is lower than a preset temperature, and the heat power of the secondary heat exchanger is lower than the set proportion of the rated heat power of the electric heating pump; determining the upper and lower limits of the frequency of the circulating pump corresponding to the secondary heat exchanger according to the flow rates of the secondary heat exchanger and the evaporation side of the electric heating pump, and controlling according to the end difference of the secondary heat exchanger by adopting a PID control method; The method comprises the steps of determining a frequency adjusting range of an electric heat pump according to flow of a condensing side of the electric heat pump, and determining a water inlet and outlet temperature difference of the condensing side of the electric heat pump by adopting a PID control method, wherein the water inlet temperature of the condensing side of the electric heat pump is heating backwater temperature, the water outlet temperature of the condensing side of the electric heat pump is automatically matched according to thermal power, and the condensing side of the electric heat pump is the side, close to a condenser, of the electric heat pump.
9. The four-pipe electric drive enhanced flue gas waste heat recovery control method according to claim 7, wherein the control modes corresponding to the gradient utilization control comprise a refrigeration mode and a heating mode; The heating mode is used for controlling the outlet water temperature of the condensing side, and the refrigerating mode is used for controlling the outlet water temperature of the evaporating side.
10. The four-pipe electric drive enhanced flue gas waste heat recovery control method according to claim 9, wherein in a heating mode, the condensation side water outlet temperature is controlled, specifically comprising: The initial setting value of the water outlet temperature of the condensing side is determined based on the water inlet temperature of the condensing side and the preset temperature difference of the condensing side; acquiring the outlet water temperature of the evaporation side in real time according to a preset time interval, wherein the evaporation side is the side, close to the evaporator, of the water loop corresponding to the secondary heat exchanger; The initial setting value of the water outlet temperature of the condensing side is adjusted according to the water outlet temperature of the evaporating side, wherein the initial setting value of the water outlet temperature of the condensing side is not adjusted when the water outlet temperature of the evaporating side is in a preset threshold range, the initial setting value of the water outlet temperature of the condensing side is gradually reduced when the water outlet temperature of the evaporating side is smaller than the lower limit of the preset threshold range, and the initial setting value of the water outlet temperature of the condensing side is gradually increased when the water outlet temperature of the evaporating side is larger than the upper limit of the preset threshold range.

Description

Four-pipe electric drive enhanced flue gas waste heat recovery system and control method thereof Technical Field The application relates to the field of flue gas waste heat utilization and heating, in particular to a four-pipe system electric drive enhanced flue gas waste heat recovery system and a control method thereof. Background During use, the gas-fired boiler generates a large amount of flue gas, which contains a large amount of heat, especially latent heat of condensation. Although most boilers perform flue gas waste heat recovery, the recovery is not thorough, and a large amount of heat is still wasted in the flue gas. The prior gas boiler mostly performs flue gas waste heat recovery, the conventional finned tube flue gas heat exchanger is used for the type of project, the general flue gas temperature is still above 60 ℃, the efficient plate type flue gas heat exchanger is used for the type of project, the flue gas temperature can be reduced lower, the flue gas temperature is still above 40 ℃ generally, and energy-saving space is still provided. The boiler room adopts a mode of the flue gas waste heat recovery and the heat pump operation, and takes all the recovered flue gas waste heat as a heat source of a heat pump unit, so that the system can reduce the flue gas temperature to about 30 ℃. The conventional operation mode of the flue gas waste heat recovery and the heat pump has the following defects: 1) The recovered flue gas waste heat is heated by the heat pump, so that the heat pump has larger shape selection and higher investment. 2) Because the heat pump has larger selection, more distribution capacity and larger installation space are required, and the implementation in the existing project is difficult. 3) The boiler load change is larger, the severe cold period of the boiler load is more than 3 times of the initial and final cold periods generally, the smoke temperature in the severe cold period is higher, the load of smoke waste heat is more than 5 times of the initial and final cold periods, the heat pump type selection is difficult, the heat pump type selection is easy to cause the initial and final cold periods to be opened due to the fact that the load is too low (the heat pump unit has minimum operation load requirement), and the heat pump type selection is easy to cause the heat pump type selection in the initial and final cold periods to be insufficient. 4) The coefficient of performance (Coefficient of Performance, COP) of the heat pump is not high enough and the economy is poor. 5) When the boiler operates under low load, the load change of the boiler is frequent and even standby, so that the heat taking quantity at the evaporation side is small and even no heat is preferable, and the electric heat pump is stopped, and the electric heat pump is started again after stopping for more than 10 minutes, so that three problems are caused, namely, the waste of the flue gas waste heat caused by the fact that the flue gas waste heat of the boiler cannot be recovered in the time interval of stopping and starting the electric heat pump, the power consumption is increased when the electric heat pump is started frequently, the power consumption is high in the starting process of the heat pump, the efficiency is low, and the service life of the heat pump is short and the maintenance cost is high because the number of times of starting and stopping the electric heat pump is high. 6) Because the condensation side water of the electric heat pump is heating water, the temperature change of the heating water is large in daytime, at night and under the influence of weather, and the load change is frequent, so that the electric heat pump is difficult to control, particularly the load control, and the actual running electric heat pump has low efficiency. Therefore, how to realize the deep recovery of the flue gas waste heat so as to improve the flue gas waste heat recovery efficiency is of great importance. Disclosure of Invention The application aims to provide a four-pipe electric drive enhanced flue gas waste heat recovery system and a control method thereof, which can deeply recover flue gas waste heat and improve the flue gas waste heat recovery efficiency. In order to achieve the above object, the present application provides the following solutions: The application provides a four-pipe electric drive enhanced flue gas waste heat recovery system which is applied to a natural gas hot water boiler scene, and comprises a control cabinet, a circulating pump, a heat exchanger and a heat meter, wherein the control cabinet comprises a PLC (programmable logic controller); The heat exchanger comprises a primary heat exchanger and a secondary heat exchanger, wherein the water loops corresponding to the primary heat exchanger and the secondary heat exchanger are respectively provided with a circulating pump and a heat meter, and the water loops corresponding to the secondary heat exchanger are provided wit