Waste heat recovery device and method for coal-fired machine

Abstract

The invention discloses a waste heat recovery device and method for a coal-fired machine, and relates to the technical field of waste heat recovery of the coal-fired machine, the waste heat recovery device is characterized in that a dust remover and an induced draft fan are introduced behind a traditional first-stage low-province device, a second-stage low-province device is connected behind the induced draft fan, and the second-stage low-province device exchanges energy with an air heater to form a second-stage low-province combined air heater system; the secondary low-province is connected with a desulfurization device; the second-stage low province exchanges energy with the air heater through a bypass; an adjusting door is arranged in the bypass and used for adjusting the water temperature of an inlet of the second-stage low-province boiler, the smoke temperature of an outlet and the air temperature of an outlet of the air heater. The air heater heats boiler secondary air based on bypass exchange energy and is connected with the air pre-heater. The two-stage low-temperature economizer is arranged in a flue behind a traditional first-stage low-temperature economizer, waste heat of boiler flue gas is further recycled, the temperature of boiler combustion-supporting secondary air and the temperature of the cold end of the air pre-heater can be increased, ammonium bisulfate blockage and low-temperature corrosion of the air pre-heater are prevented, and the boiler efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of waste heat recovery of coal-fired engines, and in particular to a waste heat recovery device and method for coal-fired engines. Background Art

[0002] Boiler economizer is a device installed in the flue at the tail of the boiler to recover the waste heat of flue gas. All boilers are designed with economizers, which are arranged in the flue before the boiler air preheater. At present, with the increasing requirements for energy conservation and emission reduction of coal-fired power generation units, heat recovery equipment is also arranged in the flue behind the air preheater, which is called "low-temperature economizer" or "low economizer" for short. The boilers of some large-scale high-efficiency and energy-saving power generation units in China have installed a first-level low economizer on the flue before the air preheater outlet to the electrostatic precipitator. The flue gas temperature at the outlet of the first-level low economizer is 90-100℃, and the average flue gas temperature is about 95℃.

[0003] It can be seen that the flue gas temperature after the first-level low-saving is still relatively high. In order to further utilize the waste heat of the flue gas after the first-level low-saving and improve the economy of the boiler, a second-level low-saving can be added after the first-level low-saving.

[0004] Our team did not design a secondary air heater, but used hot air recirculation heating, but the heating effect was not good in winter. The development of a two-stage low-energy combined heater can increase the temperature of the boiler's secondary air for combustion and the cold end temperature of the air preheater, prevent the air preheater from being blocked by ammonium bisulfate and corroded at low temperatures, and improve boiler efficiency.

[0005] Invention patent 202221163618.6 is a low-temperature economizer combined with a heater system that blocks low-temperature corrosion. Although a system with two-stage low-economizer is also provided, the one and two stages of low-economizer of this comparative invention constitute an overall system, which is not independent. Damage to one stage will affect another stage, and this comparative invention adds a dust collector after the second stage of low-economizer, which will increase the working intensity of the second stage of low-economizer (this issue is mentioned in invention patent 201911374204.0 boiler flue waste heat recovery device and recovery method), and this comparative invention only mentions some valve structures, and does not provide specific control strategies and optimization methods. Summary of the invention

[0006] In view of the above-mentioned problems, the present invention is proposed.

[0007] Therefore, the problems to be solved by the present invention are: the smoke temperature after the first-level low-energy saving is still relatively high and has recovery value; the traditional hot air recirculation heating has poor heating effect in winter; the second-level low-energy saving structure of the existing invention technology has defects, and no specific control strategy and optimization method for the second-level low-energy saving is given.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: a waste heat recovery device for a coal-fired machine, which comprises a dust collector and an induced draft fan introduced after a traditional first-level low-energy saving device, and the induced draft fan is connected to a second-level low-energy saving device, and the second-level low-energy saving device exchanges energy with a heater to form a second-level low-energy saving combined with a heater system.

[0009] As a preferred embodiment of the waste heat recovery device for a coal-fired engine described in the present invention, wherein: the traditional first-stage low-energy saving device is a structural form in which the hot flue gas from the coal gas is connected to the first-stage low-energy saving device through an air preheater; the second-stage low-energy saving is connected to a desulfurization device; the second-stage low-energy saving exchanges energy with an air heater through a bypass; the bypass contains a regulating gate for adjusting the water temperature at the inlet of the second-stage low-energy saving and the flue gas temperature at the outlet, and the wind temperature at the outlet of the heater; the air heater heats the boiler secondary air based on the energy exchanged in the bypass, and is connected to the air preheater.

[0010] In order to solve the above technical problems, the present invention provides the following technical solutions: a control method for a waste heat recovery device of a coal-fired machine, which comprises: after dust removal, the flue gas output from the first-level low-temperature economizer is sent to the second-level low-temperature economizer through an induced draft fan, the second-level low-temperature economizer exchanges energy with the air heater, and the air heater heats the boiler secondary air; by adjusting the opening of the bypass regulating door of the heater, the inlet water temperature of the second-level low-temperature economizer is controlled; by adjusting the opening of the bypass regulating door of the second-level low-temperature economizer, the outlet flue gas temperature of the second-level low-temperature economizer is controlled; by comparing the deviation between the wind temperature on both sides of the heater and the average value, the offset is adjusted to adjust the balance of the wind temperature on both sides.

[0011] As a preferred scheme of a control method for a waste heat recovery device for a coal-fired engine described in the present invention, wherein: the controlling the inlet water temperature of the secondary low-temperature economizer by adjusting the opening of the heater bypass regulating door includes: by adjusting the opening of the heater bypass regulating door, changing the water supply flow entering the heater, controlling the inlet water temperature of the secondary low-temperature economizer to reach the target value, and comparing the actually measured inlet water temperature of the secondary low-temperature economizer with the set value. When the inlet water temperature is less than the set value, the opening of the heater bypass regulating door is increased to increase the amount of water bypassing the heater, reduce the amount of water entering the heater, and increase the temperature of the water entering the secondary low-temperature economizer after mixing. When the inlet water temperature is greater than the set value, the opening of the heater bypass regulating door is reduced to reduce the amount of water bypassing the heater, increase the amount of water entering the heater, and reduce the temperature of the water entering the secondary low-temperature economizer after mixing. Add high / low value limiting function and increase / decrease limit function at the output control end to prevent the heater bypass regulating door from opening too quickly and causing impact on the system.

[0012] As a preferred embodiment of the control method for a waste heat recovery device for a coal-fired engine described in the present invention, wherein: the control of the secondary low-temperature economizer outlet flue gas temperature by adjusting the opening of the secondary low-temperature economizer bypass regulating door includes: by adjusting the opening of the secondary low-temperature economizer bypass regulating door, changing the total water supply flow entering the secondary low-temperature economizer, controlling the secondary low-temperature economizer outlet flue gas temperature to reach a target value, and by comparing the actually measured secondary low-temperature economizer outlet flue gas temperature with a set value, when the secondary low-temperature economizer outlet flue gas temperature is less than the set value, increasing the secondary low-temperature economizer outlet flue gas temperature. The opening of the economizer bypass regulating door increases the amount of water going through the bypass, reduces the amount of water entering the secondary low-temperature economizer, and increases the outlet flue gas temperature of the secondary low-temperature economizer. When the outlet flue gas temperature of the secondary low-temperature economizer is greater than the set value, the opening of the secondary low-temperature economizer bypass regulating door is reduced to reduce the amount of water going through the bypass, increase the amount of water entering the secondary low-temperature economizer, and reduce the outlet flue gas temperature of the secondary low-temperature economizer. Add high / low value limiting function and increase / decrease limit function at the output control end to prevent the secondary low-temperature economizer bypass regulating door from opening too quickly and causing impact on the system.

[0013] As a preferred embodiment of a control method for a waste heat recovery device for a coal-fired engine described in the present invention, the method comprises: adjusting the bias to adjust the balance of the wind temperatures on both sides by comparing the deviation between the wind temperatures on both sides of the heater and the average value, including: when the outlet wind temperatures of the heaters on both sides deviate, a valve adjustment bias is generated by comparing the deviation between the wind temperatures on both sides and the average value to participate in adjusting the balance of the wind temperatures on both sides; when the wind temperature on one side is lower than the average value, a positive bias is generated to open the heat medium water inlet regulating valve on the corresponding heater side, increase the amount of heat medium water entering the heater on the corresponding side, and increase the outlet wind temperature of the heater on this side; when the wind temperature on one side is higher than the average value, a negative bias is generated to close the heat medium water inlet regulating valve on the corresponding heater side, reduce the amount of heat medium water entering the heater on the corresponding side, reduce the outlet wind temperature of the heater on this side, and maintain the balance of the outlet wind temperatures on both sides; the two sides include a boiler secondary air side connected to the outlet of the blower, and a secondary low-pressure side connected to the outlet of the induced draft fan.

[0014] To solve the above technical problems, the present invention provides the following technical solutions: a heat circulation control optimization method and a heater control optimization method for a waste heat recovery device of a coal-fired machine, which include: using a heat medium water circulation pump to maintain the system heat circulation, absorbing heat at the secondary low-temperature economizer through the heat medium water, and releasing heat at the heater, thereby realizing energy recovery and recycling; the heater control optimization method includes: setting a basic opening for the hot coal water inlet regulating door of the heater, and when the hot coal water inlet regulating door of the heater has no adjustment margin, setting an override action through logic optimization, so that the hot coal water inlet regulating doors of the heaters on both sides can be manually overriden quickly and sound and light alarms are issued.

[0015] As a preferred embodiment of the heat circulation control optimization method and the heater control optimization method for a waste heat recovery device for a coal-fired engine described in the present invention, the use of a heat medium water circulation pump to maintain the system heat circulation includes: determining a basic output of a heat medium water circulation pump through system calibration, and before the opening of the secondary low-temperature economizer bypass regulating door changes from closed to 0%, the heat medium water circulation pump maintains the basic output operation; after the opening of the secondary low-temperature economizer bypass regulating door is closed to 0%, when the actually measured secondary low-temperature economizer outlet flue gas temperature is greater than the set value, increasing the heat medium water circulation pump Output, so that the circulation efficiency of heat medium water is improved, so as to enhance the heat exchange at the secondary low-temperature economizer and reduce the outlet flue gas temperature of the secondary low-temperature economizer; when the outlet flue gas temperature of the secondary low-temperature economizer is lower than the set value, the output of the heat medium water circulation pump is reduced to reduce the circulation efficiency of the heat medium water, so as to reduce the heat exchange at the secondary low-temperature economizer and increase the outlet flue gas temperature of the secondary low-temperature economizer until the output of the heat medium water circulation pump is reduced to the basic output; high / low value limit function and increase / decrease limit function are added to the output control end to prevent the heat medium water circulation pump from running beyond the limit and adjusting too fast to impact the system.

[0016] As a preferred scheme of the heat circulation control optimization method and the heater control optimization method for a waste heat recovery device for a coal-fired engine described in the present invention, wherein: the setting of the basic opening includes, based on the adjustment range of the hot coal and water inlet regulating door of the heater to meet all operating conditions, selecting an intermediate opening as the basic opening; when the hot coal and water inlet regulating door of the heater is adjusted without margin, when the opening of the heater bypass regulating door reaches 100% and the inlet water temperature of the secondary low-temperature economizer is less than 72°C, the bypass adjustment has no margin at this time; the overrun action is a process of quickly closing the valve, and a timely action response is made to increase the water temperature, and an opening margin is set for the process of closing the valve to prevent the sudden interruption of the heater from impacting the equipment pipes.

[0017] In order to solve the above technical problems, the present invention provides the following technical solutions: a corrosion leakage detection device and drying method for a low-temperature economizer, which includes: the corrosion leakage detection device for the low-temperature economizer includes a humidifier, a controller with an alarm function, a water collector with a liquid level gauge inside, and a leak detection tube arranged outside the outer shell of the low-temperature economizer and connected to the inner cavity of the outer shell, a guide surface is provided in the outer shell and is located below the heat exchange component of the low-temperature economizer and is inclined, the guide surface can guide the liquid medium into the leak detection tube, the humidifier and the water collector are arranged on the leak detection tube in sequence, and the controller alarms when the humidity value detected by the humidifier is greater than the set value and the liquid level in the water collector is higher than the liquid level gauge; the drying method includes, when the low-temperature economizer completes the flushing work and needs to be dried quickly, the ash hopper gasification fan is started, and the gasification air heater connected to the outlet of the ash hopper gasification fan is controlled to start to heat the gasification air.

[0018] The beneficial effects of the present invention are as follows: the present invention arranges a secondary low-temperature economizer in the flue after the traditional primary low-temperature economizer to develop a secondary low-temperature economizer combined with a heater, further recovers the waste heat of the boiler flue gas, deeply explores the energy-saving potential of the coal-fired unit, can increase the temperature of the boiler's secondary air for combustion support and the cold end temperature of the air preheater, prevents the air preheater from being blocked by ammonium bisulfate and corroded at low temperature, and improves the boiler efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0020] Figure 1 This is a structural diagram of a two-stage low-energy combined air heater for a waste heat recovery device for a coal-fired engine in Example 1.

[0021] Figure 2 This is a diagram of the secondary low-temperature economizer inlet water temperature control strategy for a control method for a waste heat recovery device of a coal-fired machine in Example 2.

[0022] Figure 3 This is a secondary low-temperature economizer outlet flue gas temperature control strategy diagram of a control method for a waste heat recovery device of a coal-fired machine in Example 2.

[0023] Figure 4 This is a diagram of the heater outlet air temperature balance control strategy of a control method for a waste heat recovery device of a coal-fired engine in Example 2.

[0024] Figure 5 This is a heat medium water circulation pump output control optimization diagram for a heat circulation control optimization method for a waste heat recovery device of a coal-fired engine in Example 4.

[0025] Figure 6 This is a heater control optimization diagram of a heater control optimization method for a waste heat recovery device of a coal-fired engine in Example 4. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0027] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] Example 1, reference Figure 1 , which is the first embodiment of the present invention, provides a waste heat recovery device for a coal-fired machine, including an air preheater, a first-stage low-energy saving, a dust collector, an induced draft fan, a second-stage low-energy saving, a heater and a desulfurization device.

[0029] The air preheater is connected with a primary low-pressure saver, a dust collector, an induced draft fan and a secondary low-pressure saver in sequence; the secondary low-pressure saver is connected with a desulfurization device to desulfurize the flue gas and is connected to the heater through a bypass; the heater is connected to the air preheater to heat the boiler secondary air.

[0030] The reason for connecting the dust collector and the induced draft fan between the primary low-pressure pump and the secondary low-pressure pump is that this is conducive to improving the working environment of the secondary low-pressure pump and reducing the working pressure of the secondary low-pressure pump.

[0031] The secondary low-pressure heater exchanges energy with the heater through a bypass. The bypass contains a regulating door for adjusting the water temperature at the inlet of the secondary low-pressure heater, the smoke temperature at the outlet, and the wind temperature at the outlet of the heater.

[0032] The invention develops a two-stage low-energy and air heater system, which increases the flue gas heat exchange rate at the induced draft fan outlet, reduces the exhaust gas temperature to increase the supply air temperature, thereby protecting the equipment and improving the boiler efficiency. Through reasonable control logic optimization, research on the best operating mode is carried out.

[0033] The conventional arrangement of low-temperature economizers is in front of the boiler electrostatic precipitator and the induced draft fan. The present invention is the first in China to use a two-stage low-temperature economizer arranged after the boiler electrostatic precipitator and the induced draft fan to recover the waste heat of boiler flue gas. In-depth exploration of the energy-saving potential of coal-fired units. Compared with traditional boiler economizers, the arrangement of multi-stage low-temperature economizers can further explore the energy-saving potential of boilers.

[0034] Theoretically, multiple levels can be used, but the efficiency of utilization will decrease with each level. At the same time, there is no place to arrange so many low-pressure heat exchangers on site, and the heat recovered by the low-pressure heat exchangers has no place to be used. Setting too many low-pressure heat exchangers will also cause low flue gas temperature at the low-pressure heat exchanger outlet, causing low-temperature sulfur corrosion of the equipment. Therefore, the present invention chooses to arrange two levels for the best.

[0035] Example 2, reference Figure 2-Figure 4 , which is the second embodiment of the present invention, and is different from the first embodiment in that: a control method for a waste heat recovery device for a coal-fired machine includes, after dust removal, the flue gas output from the first low-pressure furnace is sent to the second low-pressure furnace through an induced draft fan, the second low-pressure furnace exchanges energy with the heater, and the heater heats the boiler secondary air, which can increase the temperature of the boiler's secondary air for combustion support and the temperature of the cold end of the air preheater, prevent ammonium bisulfate blockage and low-temperature corrosion of the air preheater, and improve the boiler efficiency.

[0036] By adjusting the opening of the heater bypass regulating door, the water flow entering the heater is changed, and the inlet water temperature of the secondary low-temperature economizer is controlled to reach the target value of 72°C (such as Figure 2 As shown), by comparing the actually measured secondary low-temperature economizer inlet water temperature with the set value, when the inlet water temperature is less than the set value, the heater bypass regulating door opening is increased to increase the amount of water bypassing the heater, reduce the amount of water entering the heater, and increase the temperature of the water entering the secondary low-temperature economizer after mixing. When the inlet water temperature is greater than the set value, the heater bypass regulating door opening is reduced to reduce the amount of water bypassing the heater, increase the amount of water entering the heater, and reduce the temperature of the water entering the secondary low-temperature economizer after mixing. In order to prevent the heater bypass regulating door from opening too quickly and causing an impact on the system, the output control adds high / low value limit function and increase / decrease limit function to facilitate further control of the output opening signal, making the equipment run more safely and reliably.

[0037] If the inlet water temperature is lower than 72°C, the SO2 in the flue gas will condense at low temperature and cause sulfur corrosion. If it is higher than 72°C, it is OK, but the efficiency of the system will decrease. 72°C is the lowest temperature under the condition of ensuring the safety of the equipment, so the target value is set to 72°C in the present invention.

[0038] By adjusting the opening of the bypass regulating door of the secondary low-temperature economizer, the total water supply flow entering the secondary low-temperature economizer is changed, and the secondary low-temperature economizer outlet flue gas temperature is controlled to reach the target value of 95°C (such as Figure 3 As shown), the actual measured secondary low-temperature economizer outlet flue gas temperature is compared with the set value. When the secondary low-temperature economizer outlet flue gas temperature is less than the set value, the secondary low-temperature economizer bypass regulating door opening is increased to increase the bypass water volume, reduce the water volume entering the secondary low-temperature economizer, and increase the secondary low-temperature economizer outlet flue gas temperature. When the secondary low-temperature economizer outlet flue gas temperature is greater than the set value, the secondary low-temperature economizer bypass regulating door opening is reduced to reduce the bypass water volume, increase the water volume entering the secondary low-temperature economizer, and reduce the secondary low-temperature economizer outlet flue gas temperature. In order to prevent the secondary low-temperature economizer bypass regulating door from opening too quickly and causing an impact on the system, the output control can add high / low value limit function and increase / decrease limit function to facilitate further control of the output opening signal and make the equipment run more safely and reliably.

[0039] When the flue gas temperature is lower than 90℃, SO2 will condense at low temperature and cause sulfur corrosion. Controlling at 95℃ leaves a 5℃ margin for the system. If the temperature exceeds 95℃, it means that the absorbed heat is insufficient, the discharged temperature is too high, the loss is large, and the system efficiency decreases. Therefore, the target value of the present invention is set at 95℃.

[0040] The system of the present invention is provided with two blowers and two induced draft fans, each having a corresponding channel, a heater is arranged at the outlet of the blower, and a secondary low-pressure fan is arranged at the outlet of the induced draft fan, both in two rows, so it is called two sides.

[0041] When the outlet air temperature of the heaters on both sides deviates, the valve adjustment bias is generated by comparing the deviation between the air temperature on both sides and the average value to adjust the balance of the air temperature on both sides (such as Figure 4 When the wind temperature on one side is lower than the average value, a positive bias is generated to open the heat medium water inlet regulating valve on the corresponding heater side, increase the amount of heat medium water entering the heater on the corresponding side, and increase the outlet wind temperature of the heater on that side; when the wind temperature on one side is higher than the average value, a negative bias is generated to close the heat medium water inlet regulating valve on the corresponding heater side, reduce the amount of heat medium water entering the heater on the corresponding side, and reduce the outlet wind temperature of the heater on that side, so as to maintain the balance of the outlet wind temperatures on both sides.

[0042] Embodiment 3 is the third embodiment of the present invention, which is different from the previous two embodiments in that a control method for a waste heat recovery device for a coal-fired engine also includes, in order to verify and explain the technical effects adopted in the method, comparing the test results with scientific argumentation means to verify the actual effect of the method.

[0043] Under the premise that the coal quality, ambient temperature, main reheat steam temperature and other conditions are basically maintained stable, the secondary low-temperature economizer combined with the air heater is tested and analyzed. The outlet air temperature of the heater is increased to 10, 20, and 30 °C respectively. The corresponding calculation results of the thermal characteristics recorded by the on-site measuring points and DCS data are shown in Table 1.

[0044] Table 1 Operation data and calculation results of low-energy combined heater system

[0045]

[0046]

[0047] According to various working conditions, under the premise of keeping the ambient air temperature basically the same, as the amount of heater input gradually increases, the air temperature at the air preheater inlet rises, so theoretically the exhaust gas temperature at the boiler air preheater outlet also rises. Since our company originally arranged a flue gas cooler system between the air preheater and the electrostatic precipitator, the system operates independently to perform preliminary heat exchange on the flue gas and recovers the heat in the flue gas to heat the condensate. Therefore, from the actual performance of the above data, the flue gas temperature at the inlet of the secondary low-temperature economizer has not increased significantly. However, from the above data, under low-load conditions, if the temperature rise at the heater outlet is to be maintained at a higher level, the secondary low-temperature economizer outlet flue gas temperature and inlet water temperature may not meet the safety control standards. Therefore, strictly speaking, using the heater outlet temperature rise as the overall control target is not an optimal standard.

[0048] From the perspective of the overall energy loss of the boiler system, the heat loss of flue gas is the largest of all heat losses, generally 5% to 8%. Therefore, as long as as much flue gas waste heat is recovered as much as possible to reduce the exhaust temperature, it will definitely be beneficial to the unit's economy. Taking into account the safety and economy of the secondary low-temperature economizer combined with the heater system, it is determined that the secondary low-temperature economizer outlet flue gas temperature is used as the overall control standard of the system for optimization control.

[0049] Example 4, reference Figure 5 and Figure 6 , which is the fourth embodiment of the present invention, and which is different from the first three embodiments in that: a heat cycle control optimization method for a waste heat recovery device of a coal-fired machine and a heater control optimization method include:

[0050] The present invention adopts a heat medium water circulation pump to maintain the heat circulation of the system, and the heat medium water absorbs heat at the secondary low-temperature economizer and releases heat at the heater, thereby realizing energy recovery and recycling. Since the output of the heat medium water circulation pump must first meet the requirements of overcoming the operating resistance of the system, a basic output is determined by system verification at the beginning of system design. Since the secondary low-temperature economizer has bypass regulation, the heat medium water circulation pump maintains basic output operation before the opening of the secondary low-temperature economizer bypass regulating door is closed to 0%; after the opening of the secondary low-temperature economizer bypass regulating door is closed to 0%, when the actual measured secondary low-temperature economizer outlet flue gas temperature T2 is greater than the set value, the output of the heat medium water circulation pump is increased to improve the circulation efficiency of the heat medium water, thereby enhancing the heat exchange at the secondary low-temperature economizer and reducing the secondary low-temperature economizer outlet flue gas temperature T2. On the contrary, when T2 is less than the set value, the output of the heat medium water circulation pump is reduced to reduce the circulation efficiency of the heat medium water, thereby reducing the heat exchange at the secondary low-temperature economizer and increasing the secondary low-temperature economizer outlet flue gas temperature T2 until the output of the heat medium water circulation pump is reduced to the basic output (such as Figure 5 In order to prevent the heat medium water circulation pump from running beyond the limit and adjusting too quickly to impact the system, the output control adds high / low value limit function and increase / decrease limit function to facilitate further control of the output and make the equipment run more safely and reliably.

[0051] Safety monitoring and control: The secondary low-temperature economizer combined with the heater system adopts a closed cycle. Under normal circumstances, there is no loss of the circulating medium. By continuously detecting the changes in the liquid level in the high-level water tank, when the liquid level drop rate increases abnormally and the water replenishment frequency increases abnormally, it is judged that there is a leak in the system, and the control system issues a system leakage alarm to remind the operating personnel to carry out isolation and treatment.

[0052] Considering that the increase in the output of the heat medium water circulation pump will increase the power consumption, it is necessary to calculate the economic efficiency of the entire system operation, that is, whether the increase in flue gas energy recovery achieved by increasing the output of the heat medium water circulation pump can cover the increased power consumption caused by the increase in pump output. From the operating condition data shown in Table 2, it can be seen that the more flue gas heat is recovered by increasing the pump output, the higher the overall economic efficiency of the system operation.

[0053] Table 2: Statistics on output verification of heat medium water circulation pump

[0054]

[0055] The heater control optimization method is as follows: according to the actual operation effect of the system, during the full stroke automatic adjustment process of the heater bypass, the adjustment range of the heater hot coal water inlet regulating door is 20%-50%, which can meet all operating conditions. Therefore, the middle opening (i.e. 35% opening) is selected as the basic opening to reduce the system throttling loss while ensuring the normal opening and closing of the regulating door for deviation adjustment (such as Figure 6 As shown). Considering that when the opening of the heater bypass regulating door reaches 100% and the secondary low-temperature economizer inlet water temperature is less than 72°C, there is no margin for bypass regulation at this time, and the only way is to close the heater heat medium water inlet regulating door to minimize the heat exchange in the heater area and maintain the heater outlet water temperature (i.e. the secondary low-temperature economizer inlet water temperature). In order to ensure safe operating conditions in this case, the overdrive action is set through logic optimization, so that the heat medium water inlet regulating doors of the heaters on both sides can be manually overdriven quickly and sound and light alarms are issued. Overdrive closing is a process of quickly closing the valve, which can respond in time to increase the water temperature. However, considering the impact of the heater suddenly being cut off after closing to 0%, a 10% opening margin is set. Subsequent operators can manually make further opening and closing adjustments according to the actual situation of the system.

[0056] Embodiment 5 is the fifth embodiment of the present invention, which is different from the first four embodiments in that: a corrosion leakage detection device and drying method for a low-temperature economizer includes: aiming at timely detection and positioning of corrosion leakage of a low-temperature economizer, and developing a leakage detection alarm device for a low-temperature economizer in a flue gas treatment system. It solves the problem of low detection accuracy. It includes a humidistat, a controller with an alarm function, a water collector with a liquid level gauge inside, and a leak detection tube arranged outside the shell of the low-temperature economizer and connected to the inner cavity of the shell. A guide surface located below the heat exchange component of the low-temperature economizer and inclined inside the shell is provided, and the guide surface can guide the liquid medium into the leak detection tube. The humidistat and the water collector are arranged on the leak detection tube in sequence. When the humidity value detected by the humidistat is greater than the set value and the liquid level in the water collector is higher than the liquid level gauge, the controller alarms. It has the advantages of high leak detection alarm accuracy, low modification difficulty, and a wide leak detection range.

[0057] Leak detection optimization: The water medium in the heat exchange tube of the secondary low-temperature economizer arranged in the flue is prone to dust accumulation and corrosion once a leak occurs, causing damage to the equipment. Therefore, it is particularly important to detect leaks in a timely manner and take appropriate measures as soon as possible to avoid the expansion of accidents in the application of secondary low-temperature economizers. Since the water level and water replenishment rate are often not sensitive enough in monitoring small flow leaks, a heat exchanger humidity detection is added. When a leak occurs, the humidity of the flue gas changes. Through a pair of humidity detection sampling devices before and after the heat exchange tube group, the change in humidity is detected, and the early leakage of the heat exchange tube is reliably detected. Measures can be taken in time to achieve coverage of multiple monitoring methods.

[0058] Low-temperature economizer drying technology: In view of the long drying time after water flushing of low-temperature economizer after maintenance, a shorter drying method after water flushing of low-temperature economizer is developed. It solves the problems of low air drying efficiency and poor air drying effect. When the low-temperature economizer needs to be dried quickly after the flushing work is completed, the ash hopper gasification fan is started, and the gasification air heater connected to the outlet of the ash hopper gasification fan is controlled to start to heat the gasification air. It has the advantages of high air drying efficiency, good air drying effect, and easy operation.

[0059] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A waste heat recovery device for a coal-fired machine, characterized in that: include, A dust collector and induced draft fan are introduced after the traditional first-level low-energy saving device, and the induced draft fan is connected to the second-level low-energy saving. The second-level low-energy saving exchanges energy with the heater to form a second-level low-energy saving combined with heater system.

2. A waste heat recovery device for a coal-fired engine according to claim 1, characterized in that: The conventional first-stage low-pressure saving device is a structural form in which the hot flue gas from the coal gas saver is connected to the first-stage low-pressure saving device through an air preheater; The secondary low-pressure desulfurization device is connected to the back of the device; The secondary low-voltage power plant exchanges energy with the heater via a bypass; The bypass contains an adjusting door for adjusting the water temperature at the inlet of the secondary low-pressure furnace, the smoke temperature at the outlet, and the wind temperature at the outlet of the heater; The air heater heats the boiler secondary air based on the energy exchanged through the bypass and is connected to the air preheater.

3. A control method for a waste heat recovery device of a coal-fired machine, characterized in that: include, After dust removal, the flue gas output from the first-stage low-pressure boiler is sent to the second-stage low-pressure boiler through the induced draft fan. The second-stage low-pressure boiler exchanges energy with the heater, and the heater heats the boiler secondary air. By adjusting the opening of the heater bypass regulating door, the inlet water temperature of the secondary low-temperature economizer is controlled; By adjusting the opening of the bypass regulating door of the secondary low-temperature economizer, the outlet flue gas temperature of the secondary low-temperature economizer is controlled; By comparing the deviation between the wind temperature on both sides of the heater and the average value, the offset is adjusted to adjust the balance of the wind temperature on both sides.

4. The control method for a waste heat recovery device for a coal-fired machine according to claim 3, characterized in that: The method of controlling the inlet water temperature of the secondary low-temperature economizer by adjusting the opening of the heater bypass regulating door includes: By adjusting the opening of the heater bypass regulating door, the water supply flow entering the heater is changed, and the inlet water temperature of the secondary low-temperature economizer is controlled to reach the target value. By comparing the actually measured inlet water temperature of the secondary low-temperature economizer with the set value, when the inlet water temperature is less than the set value, the opening of the heater bypass regulating door is increased to increase the amount of water passing through the heater bypass, reduce the amount of water entering the heater, and increase the temperature of the water entering the secondary low-temperature economizer after mixing. When the inlet water temperature is greater than the set value, the opening of the heater bypass regulating door is reduced to reduce the amount of water passing through the heater bypass, increase the amount of water entering the heater, and reduce the temperature of the water entering the secondary low-temperature economizer after mixing. Add high / low value limit function and increase / decrease limit function to the output control end to prevent the heater bypass regulating door from opening too quickly and causing impact on the system.

5. The control method for a waste heat recovery device for a coal-fired machine according to claim 4, characterized in that: The method of controlling the flue gas temperature at the secondary low-temperature economizer outlet by adjusting the opening of the secondary low-temperature economizer bypass regulating door comprises: By adjusting the opening of the secondary low-temperature economizer bypass regulating door, the total water supply flow entering the secondary low-temperature economizer is changed, and the secondary low-temperature economizer outlet flue gas temperature is controlled to reach the target value. By comparing the actually measured secondary low-temperature economizer outlet flue gas temperature with the set value, when the secondary low-temperature economizer outlet flue gas temperature is less than the set value, the opening of the secondary low-temperature economizer bypass regulating door is increased to increase the amount of water going through the bypass and reduce the amount of water entering the secondary low-temperature economizer, so that the secondary low-temperature economizer outlet flue gas temperature increases; when the secondary low-temperature economizer outlet flue gas temperature is greater than the set value, the opening of the secondary low-temperature economizer bypass regulating door is reduced to reduce the amount of water going through the bypass and increase the amount of water entering the secondary low-temperature economizer, so that the secondary low-temperature economizer outlet flue gas temperature decreases; Add high / low value limit function and increase / decrease limit function at the output control end to prevent the secondary low-temperature economizer bypass regulating door from opening too quickly and causing impact on the system.

6. A control method for a waste heat recovery device for a coal-fired machine according to claim 5, characterized in that: The step of comparing the deviation between the wind temperature on both sides of the heater and the average value and adjusting the offset to adjust the balance of the wind temperature on both sides includes: When the outlet air temperature of the heaters on both sides deviates, the valve adjustment bias is generated by comparing the deviation between the air temperature on both sides and the average value to participate in adjusting the balance of the air temperature on both sides. When the air temperature on one side is lower than the average value, a positive bias is generated to open the heat medium water inlet regulating valve on the corresponding heater side, increase the amount of heat medium water entering the heater on the corresponding side, and increase the outlet air temperature of the heater on that side; when the air temperature on one side is higher than the average value, a negative bias is generated to close the heat medium water inlet regulating valve on the corresponding heater side, reduce the amount of heat medium water entering the heater on the corresponding side, and reduce the outlet air temperature of the heater on that side, so as to maintain the balance of the outlet air temperature on both sides; The two sides include a boiler secondary air side connected to the outlet of the blower, and a secondary low-pressure side connected to the outlet of the induced draft fan.

7. A heat cycle control optimization method and a heater control optimization method for a waste heat recovery device of a coal-fired machine, characterized in that: include, A heat medium water circulation pump is used to maintain the heat circulation of the system. The heat medium water absorbs heat at the secondary low-temperature economizer and releases heat at the heater, thereby realizing energy recovery and recycling. The heater control optimization method includes setting a basic opening for the heater hot coal water inlet regulating door, and when the heater hot coal water inlet regulating door has no adjustment margin, setting an override action through logic optimization, so that the heat medium water inlet regulating doors of the heaters on both sides are manually overrun and sound and light alarms are issued.

8. A heat cycle control optimization method and a heater control optimization method for a waste heat recovery device of a coal-fired engine as claimed in claim 7, characterized in that: The use of a heat medium water circulation pump to maintain the heat circulation of the system includes: determining a basic output of the heat medium water circulation pump through system calibration, and before the opening of the secondary low-temperature economizer bypass regulating door is closed to 0%, the heat medium water circulation pump maintains the basic output operation; after the opening of the secondary low-temperature economizer bypass regulating door is closed to 0%, when the actually measured secondary low-temperature economizer outlet flue gas temperature is greater than the set value, increasing the output of the heat medium water circulation pump to improve the circulation efficiency of the heat medium water, so as to enhance the heat exchange at the secondary low-temperature economizer and reduce the secondary low-temperature economizer outlet flue gas temperature; When the flue gas temperature at the secondary low-temperature economizer outlet is lower than the set value, the output of the heat medium water circulation pump is reduced to reduce the circulation efficiency of the heat medium water, thereby reducing the heat exchange at the secondary low-temperature economizer and increasing the flue gas temperature at the secondary low-temperature economizer outlet until the output of the heat medium water circulation pump is reduced to the basic output; Add high / low value limit function and increase / decrease limit function to the output control end to prevent the heat medium water circulation pump from running beyond the limit and adjusting too quickly to impact the system.

9. A heat cycle control optimization method and a heater control optimization method for a waste heat recovery device of a coal-fired engine as claimed in claim 8, characterized in that: The setting of the basic opening includes selecting an intermediate opening as the basic opening based on the adjustment range of the hot coal water inlet regulating door of the heater when it meets all operating conditions; The heater hot coal water inlet regulating door has no margin when the heater bypass regulating door opening reaches 100% and the secondary low-temperature economizer inlet water temperature is less than 72°C, at which time the bypass regulation has no margin; The overrun action is a process of quickly closing the valve, and a timely action response is made to increase the water temperature. An opening margin is set for the process of closing the valve to prevent the sudden interruption of the heater from impacting the equipment pipes.

10. A corrosion leakage detection device and drying method for a low-temperature economizer, characterized in that: The corrosion leakage detection device for the low-temperature economizer includes a humidifier, a controller with an alarm function, a water collector with a liquid level gauge inside, and a leak detection tube arranged outside the shell of the low-temperature economizer and connected to the inner cavity of the shell, a guide surface located below the heat exchange component of the low-temperature economizer and inclined inside the shell is provided, the guide surface can guide the liquid medium into the leak detection tube, the humidifier and the water collector are arranged on the leak detection tube in sequence, and the controller alarms when the humidity value detected by the humidifier is greater than the set value and the liquid level in the water collector is higher than the liquid level gauge; The drying method includes starting the ash hopper gasification fan when the low-temperature economizer needs to be quickly dried after the flushing work is completed, and controlling the gasification air heater connected to the outlet of the ash hopper gasification fan to start to heat the gasification air.

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