CN-122015545-A - Low-temperature flue gas waste heat recovery system and method based on double-safety-zone wall temperature control

CN122015545ACN 122015545 ACN122015545 ACN 122015545ACN-122015545-A

Abstract

The invention discloses a low-temperature flue gas waste heat recovery system and method based on double-safety-zone wall temperature control, and belongs to the technical field of industrial energy conservation and environmental protection. The invention provides a solution based on corrosion control theory aiming at the problems of low-temperature corrosion and low efficiency in deep waste heat recovery of acid-containing low-temperature flue gas, wherein the solution is to divide a phase-change heat exchanger into a high-temperature section and a low-temperature section along the flue gas flow, and the high-temperature section and the low-temperature section are respectively connected with independent steam drums to form two independent phase-change loops. By means of linkage control of the wall temperature measuring points and the cold source adjusting unit, the running pressure of the two loops is independently adjusted, and accurate regulation and control of partition wall temperature are achieved, wherein the high-temperature loop runs in a first safety area (higher than the acid dew point of flue gas) and the low-temperature loop runs in a second safety area (corrosion valley area). According to the material distribution with different temperature gradients, the equipment cost is reduced. The invention solves the problem of low-temperature corrosion of the flue gas, realizes safe deep cooling of the flue gas, and has the outstanding effects of high heat exchange efficiency and remarkable reduction of equipment investment.

Inventors

HE CHUNLONG
LI YU
PENG ZEJUN
WU ZHONGYONG
MA CHENGLONG
LI JUN
WANG RUI
CHEN NIAN

Assignees

重庆三峰卡万塔环境产业有限公司

Dates

Publication Date: 20260512
Application Date: 20260327

Claims (10)

1. The low-temperature flue gas waste heat recovery system based on double-safety-zone wall temperature control is characterized by comprising a phase change heat exchanger, wherein a high-temperature phase change loop and a low-temperature phase change loop are arranged in the phase change heat exchanger in a partitioning manner along the flue gas flowing direction, the high-temperature phase change loop is positioned at the flue gas inlet side, the low-temperature phase change loop is positioned at the flue gas outlet side, phase change working mediums are arranged in the high-temperature phase change loop and the low-temperature phase change loop to form two mutually independent phase change circulation loops, and the two phase change circulation loops absorb heat in flue gas at a high temperature section and a low temperature section through the internal phase change working mediums respectively; The operating temperature of the phase-change working medium in the high-temperature phase-change loop is higher than the acid dew point of the flue gas, namely in a first safety zone, and the operating temperature of the phase-change working medium in the low-temperature phase-change loop is in the range of a corrosion valley zone, namely in a second safety zone.
2. The system of claim 1, wherein the high-temperature phase-change loop and the low-temperature phase-change loop have the same phase-change working medium, the operating pressure of the high-temperature phase-change loop is positive, the saturation temperature of the corresponding phase-change working medium under the pressure is more than or equal to 115 ℃, the wall temperature of a high-temperature heat exchange tube bundle operates in a first safety area to avoid high-temperature Duan Diwen corrosion, the operating pressure of the low-temperature phase-change loop is negative, the saturation temperature of the corresponding phase-change working medium under the pressure is 70-80 ℃, the wall temperature of the low-temperature Duan Huanre tube bundle operates in a second safety area, and the speed of low temperature Duan Fushi is reduced.
3. The system of claim 1, wherein the two phase-change circulation loops comprise a heat exchange tube bundle, a condensate water header, a steam header, a condensate water eduction tube, a condensate water preheating tube, a steam riser, a condensate water downcomer and a steam drum; The condensing water header is positioned at the lower part of the heat exchange tube bundle and connected with the lower end of the heat exchange tube bundle and used for distributing the preheated liquid phase-change working medium into the heat exchange tube bundle; One end of the steam rising pipe is connected with the steam upper header, the other end of the steam rising pipe is connected with the steam drum, a cold source heat exchange pipe is arranged in the steam drum, and a cold source is arranged in the cold source heat exchange pipe; One end of the condensate water eduction tube is connected to the bottom of the steam drum, the other end of the condensate water eduction tube is connected with the inlet of the condensate water preheating tube, the condensate water preheating tube is positioned in the steam upper header, and the condensed low-temperature liquid phase-change working medium is preheated to the saturation temperature by utilizing the gaseous phase-change working medium in the steam upper header; one end of the condensate water downcomer is connected with the condensate water preheating pipe outlet, and the other end of the condensate water downcomer is connected with the condensate water header, and is used for conveying the preheated liquid phase change working medium to the condensate water header.
4. The system of claim 3, wherein the heat exchange tube of the heat exchanger is connected with a heat exchanger supply and regulating unit for supplying heat exchanger and regulating flow.
5. The system of claim 4, further comprising a measurement and control system, wherein the measurement and control system comprises a temperature sensor and a control system, the temperature sensor is arranged on a steam rising pipe or a condensate water collecting box and is used for measuring the working medium operation temperature, the temperature sensor and the cold source supply and adjustment unit are connected with the control system, the control system drives the cold source supply and adjustment unit to adjust the cold source flow according to the feedback temperature of the temperature sensor, the condensation rate of gaseous working medium in a steam drum is controlled, the steam drum operation pressure is further adjusted, the purpose of controlling the working medium operation temperature is achieved, and the wall temperature of the heat exchange tube bundle is always in the safe area temperature.
6. The system of claim 4, wherein the two drums in the high-temperature phase-change loop and the low-temperature phase-change loop are respectively and independently connected with a set of cold source supply and regulation unit, the cold source supply and regulation unit comprises a pump and a regulating valve, the pump is positioned at the inlet side of the cold source to provide cold source conveying power, the regulating valve is positioned at the downstream of the pump and is connected with the inlet of a cold source heat exchange tube of the drum, the pump and the regulating valve are used together to regulate the flow of the cold source and control the condensation rate of the gaseous phase-change working medium in the drum, so that the operation pressure and the operation temperature of the corresponding phase-change circulation loop are dynamically maintained.
7. The system of claim 3, wherein the heat exchange tube bundles of the high temperature phase change loop are made of ND steel and are suitable for working conditions with wall temperature higher than the dew point of acid, and the heat exchange tube bundles of the low temperature phase change loop are made of 2205 duplex stainless steel and are suitable for wet flue gas environments with wall temperature in a corrosion valley area.
8. The system of claim 1, wherein the system is used for recovering waste heat of low-temperature flue gas containing acid at 230 ℃ and below, the adopted phase change working medium and cold source are desalted water, and the phase change working medium is independently supplied by the cold source supply and adjustment unit to realize absorption of condensation latent heat of the phase change working medium and cold source heating.
9. The low-temperature flue gas waste heat recovery method based on double-safety-zone wall temperature control is characterized in that the system as claimed in any one of claims 1-8 is adopted for low-temperature flue gas waste heat recovery, low-temperature flue gas enters a phase change heat exchanger and sequentially flows through a high-temperature phase change loop and a low-temperature phase change loop, heat is transferred to a phase change working medium in a pipe through a pipe wall, and the flue gas is gradually cooled to below 100 ℃ and discharged; The phase change working medium is led out from the bottom of the steam drum, enters a condensation water preheating pipe through a condensation water leading-out pipe, indirectly exchanges heat with the gaseous phase change working medium in a steam upper header, and enters a condensation water header through a condensation water reducing pipe after being preheated to be close to saturation temperature; The cold source is divided into two paths, and the cold source is supplied and adjusted by an independent cold source to flow through the steam drums of the high-temperature phase-change loop and the low-temperature phase-change loop to absorb the condensation latent heat of the phase-change working medium and output the condensation latent heat; The wall temperature is monitored through the measurement and control system, the flow of the cold source is fed back and regulated, the wall temperature of the high-temperature phase-change loop is independently controlled to be more than or equal to 115 ℃ and 70-80 ℃ so that the wall temperature of the high-temperature heat exchange tube bundle runs in a first safety area, the high temperature Duan Diwen is prevented from being corroded, the wall temperature of the low-temperature Duan Huanre tube bundle runs in a second safety area, and the speed of the low temperature Duan Fushi is reduced.
10. The method of claim 9, wherein the high temperature phase change loop maintains positive pressure, the low temperature phase change loop maintains negative pressure, the condensation rate is controlled by adjusting the flow rate of the cold source entering the steam drum, so as to adjust the operating pressure in the steam drum, correspondingly change the saturated temperature of the working medium, realize the accurate regulation and control of the operating temperature of the working medium, increase the corresponding flow rate of the cold source to accelerate the condensation to reduce the operating pressure in the steam drum when the wall temperature is higher than a set value, correspondingly reduce the saturated temperature of the working medium to a set value, reduce the flow rate of the cold source to reduce the condensation to raise the operating pressure in the steam drum when the wall temperature is lower than the set value, correspondingly raise the saturated temperature of the working medium to the set value, and realize the accurate regulation and control of the wall temperature.

Description

Low-temperature flue gas waste heat recovery system and method based on double-safety-zone wall temperature control Technical Field The invention belongs to the technical field of industrial energy conservation and environmental protection, and particularly relates to a low-temperature flue gas waste heat recovery system and method based on double-safety-zone wall temperature control, in particular to a phase change heat exchange process system and method for realizing efficient, safe and deep recovery of flue gas waste heat by setting a wall temperature safety zone through zoning and independently regulating and controlling on the basis of a corrosion control theory. Background In the field of industrial waste heat recovery, particularly for low-temperature flue gas at 230 ℃ and below, a dividing wall type heat exchanger (such as a shell-and-tube heat exchanger and a plate heat exchanger) is the heat exchange technology which is most widely applied and mature at present. The principle is that the heat of the flue gas is indirectly transferred to working media (such as water and air) to be heated through the metal wall surface, and the flue gas heating device is simple in structure and high in reliability. Although widely used, the traditional dividing wall type heat exchange technology has the following problems when deeply recovering waste heat of acid-containing low-temperature flue gas: 1. In the dividing wall type heat exchanger, low-temperature working medium to be heated enters from an inlet, and the temperature of the metal wall surface of the heat exchange tube at the inlet section is close to the temperature of the working medium at the inlet and is far lower than the acid dew point of flue gas. The sulfuric acid vapor in the flue gas is quickly condensed into high-concentration liquid sulfuric acid on the low-temperature wall surface, and electrochemical corrosion reaction is carried out on the high-concentration liquid sulfuric acid and metal, so that the corrosion rate of the area is extremely high, and the high-concentration liquid sulfuric acid becomes a main part of perforation leakage of equipment. 2. The inherent heat exchange efficiency is low, and the traditional wall-dividing type heat exchange technology mainly relies on convection and heat conduction for heat transfer. Under the specific working condition of low-temperature flue gas waste heat recovery, the overall heat transfer coefficient is generally low due to small heat transfer temperature difference (end difference), so that the overall heat exchange efficiency is low. 3. The equipment investment is huge, and because the low-temperature flue gas energy grade is low, the available heat exchange temperature difference between the low-temperature flue gas energy grade and the cold working medium is small, and the heat transfer coefficient is low, so that in order to cool the flue gas to the target flue gas temperature, an extremely huge heat exchange area is required to be configured. Disclosure of Invention In view of the above, the invention aims to solve the above-mentioned defects existing in the prior dividing wall type heat exchange technology when recovering the waste heat of acid-containing low-temperature flue gas, and provides a low-temperature flue gas waste heat recovery system and method based on double-safety-zone wall temperature control. In order to achieve the above purpose, the present invention provides the following technical solutions: The low-temperature flue gas waste heat recovery system based on double-safety-zone wall temperature control comprises a phase change heat exchanger, wherein a high-temperature phase change loop and a low-temperature phase change loop are arranged in the phase change heat exchanger along the flue gas flowing direction in a partitioning mode, the high-temperature phase change loop is positioned at the flue gas inlet side, the low-temperature phase change loop is positioned at the flue gas outlet side, phase change working mediums are arranged in the high-temperature phase change loop and the low-temperature phase change loop to form two mutually independent phase change circulation loops, and the two phase change circulation loops absorb heat in flue gas in a high-temperature section and a low-temperature section through the internal phase change working mediums respectively; The operating temperature of the phase-change working medium in the high-temperature phase-change loop is higher than the acid dew point of the flue gas, namely in a first safety zone, and the operating temperature of the phase-change working medium in the low-temperature phase-change loop is in the range of a corrosion valley zone, namely in a second safety zone. The high-temperature phase-change loop and the low-temperature phase-change loop are the same in phase-change working medium, the operating pressure of the high-temperature phase-change loop is positive pressure, the saturation temperature of the c