Steam boiler flue gas and waste heat recovery system and control method thereof

Abstract

The present application discloses a system for simultaneously recovering flue gas and waste heat from sewage from a steam boiler and a control method thereof, and relates to the technical field of waste heat recovery and utilization. The system includes a flue gas waste heat recovery device, a waste heat recovery device, and a control cabinet, wherein a first monitor can monitor the flue gas flow rate of the steam boiler, a second monitor can monitor the softened water flow rate of the flue gas heat exchanger, a third monitor can monitor the sewage inlet and outlet temperature of the sewage heat exchanger, and a fourth monitor can monitor the softened water inlet and outlet temperature of the sewage heat exchanger, and then the control cabinet can control the opening of the first electric regulating valve according to the flue gas flow rate of the steam boiler and the softened water flow rate of the flue gas heat exchanger, and control the opening of the second electric regulating valve according to the sewage inlet and outlet temperature of the sewage heat exchanger and the softened water inlet and outlet temperature of the sewage heat exchanger. The system of the present application can maximize the simultaneous recovery of boiler flue gas and waste heat from sewage, increase the softened water temperature injected into the steam boiler, and avoid heat waste.

Description

Technical Field

[0001] The present application relates to the technical field of waste heat recovery and utilization, and in particular to a system for simultaneously recovering flue gas and sewage waste heat from a steam boiler and a control method thereof. Background Art

[0002] Utilizing steam boiler feed water and recycling the waste heat from steam boiler flue gas can not only turn waste into treasure and reduce energy consumption such as natural gas and steam, but also reduce carbon dioxide emissions and reduce the impact of the greenhouse effect.

[0003] Currently Figure 1 As shown, the related technology recovers the waste heat of flue gas by heating the boiler feed water with a condenser, that is, the water in the water tank is injected into the condenser through a circulating pump for heating, and then transported to the steam boiler. After the sewage passes through the continuous sewage expander, a small part of it is vaporized into exhaust steam and enters the deaerator, which recovers and utilizes part of the sewage waste heat, but most of the remaining sewage with a temperature close to 100°C is directly discharged into the drain, wasting a lot of heat. Summary of the invention

[0004] In view of the above-mentioned defects or deficiencies in the related art, it is desired to provide a steam boiler flue gas and exhaust waste heat simultaneous recovery system and a control method thereof, which can maximize the simultaneous recovery of boiler flue gas and exhaust waste heat.

[0005] In a first aspect, the present application provides a system for simultaneously recovering flue gas and waste heat from exhaust gas from a steam boiler, the system comprising:

[0006] A flue gas waste heat recovery device, the flue gas waste heat recovery device comprising a flue gas heat exchanger arranged on a flue of a steam boiler, a first monitor, a second monitor located at a water side outlet of the flue gas heat exchanger, and a first electric regulating valve, wherein the outlet of the first electric regulating valve is connected to a water feed end of the steam boiler, and the water side inlet of the flue gas heat exchanger is connected to softened water, the first monitor is configured to monitor the flue gas flow rate of the steam boiler, and the second monitor is configured to monitor the softened water flow of the flue gas heat exchanger;

[0007] A waste heat recovery device for sewage discharge, the waste heat recovery device comprising a sewage heat exchanger arranged at the sewage end of the steam boiler, a third monitor located at the sewage side of the sewage heat exchanger, a fourth monitor located at the softened water side of the sewage heat exchanger, and a second electric regulating valve, the outlet of the second electric regulating valve is connected to the water feed end of the steam boiler, the inlet of the softened water side of the sewage heat exchanger is connected to softened water, the third monitor is configured to monitor the sewage inlet and outlet temperatures of the sewage heat exchanger, and the fourth monitor is configured to monitor the softened water inlet and outlet temperatures of the sewage heat exchanger;

[0008] A control cabinet, the control cabinet includes a controller, the controller is respectively connected to the first monitor, the second monitor, the third monitor, the fourth monitor and the first electric regulating valve, the second electric regulating valve, the controller is configured to control the opening of the first electric regulating valve according to the flue gas flow rate of the steam boiler and the softened water flow rate of the flue gas heat exchanger, and to control the opening of the second electric regulating valve according to the sewage inlet and outlet temperatures of the sewage heat exchanger and the softened water inlet and outlet temperatures of the sewage heat exchanger.

[0009] Optionally, in some embodiments of the present application, the steam boiler flue gas and sewage waste heat simultaneous recovery system also includes a softening water tank, the outlet of the softening water tank is connected to the steam boiler water feed end, and the softening water tank is configured to buffer and regulate the softened water flow in the steam boiler flue gas and sewage waste heat simultaneous recovery system.

[0010] Optionally, in some embodiments of the present application, a fifth monitor is provided in the softened water tank, the fifth monitor is connected to the controller, the fifth monitor is configured to monitor the liquid level of the softened water tank, and the controller is further configured to correct the opening of each electric regulating valve according to the liquid level of the softened water tank.

[0011] Optionally, in some embodiments of the present application, the first monitor includes a flow rate sensor located at the flue gas inlet of the flue gas heat exchanger, a first temperature sensor, and a second temperature sensor located at the flue gas outlet of the flue gas heat exchanger.

[0012] The second monitor includes a first heat meter located at the water outlet of the flue gas heat exchanger, the first heat meter has a third temperature sensor and a fourth temperature sensor, the third temperature sensor is arranged at the water outlet pipe of the flue gas heat exchanger, and the fourth temperature sensor is arranged at the water inlet pipe of the flue gas heat exchanger.

[0013] The third monitor includes a fifth temperature sensor located at the sewage side inlet of the sewage heat exchanger and a sixth temperature sensor located at the sewage side outlet of the sewage heat exchanger. The fourth monitor includes a second heat meter located at the softened water side outlet of the sewage heat exchanger. The second heat meter has a seventh temperature sensor and an eighth temperature sensor. The seventh temperature sensor is arranged on the water outlet pipe of the sewage heat exchanger, and the eighth temperature sensor is arranged on the water inlet pipe of the sewage heat exchanger.

[0014] Optionally, in some embodiments of the present application, the third monitor also includes a water flow switch located at the sewage side outlet of the sewage heat exchanger.

[0015] In a second aspect, the present application provides a control method for a system for simultaneously recovering flue gas and waste heat from exhaust from a steam boiler as described in any one of the first aspects, the control method comprising:

[0016] Acquiring a flue gas flow rate of the steam boiler and a softened water flow rate of the flue gas heat exchanger, and controlling the opening of the first electric regulating valve based on the flue gas flow rate and the softened water flow rate;

[0017] The sewage inlet and outlet temperatures of the sewage heat exchanger and the softened water inlet and outlet temperatures of the sewage heat exchanger are obtained, and the opening of the second electric regulating valve is controlled based on the sewage inlet and outlet temperatures and the softened water inlet and outlet temperatures.

[0018] Optionally, in some embodiments of the present application, controlling the opening of the first electric regulating valve based on the flue gas flow rate and the softened water flow rate includes:

[0019] Calculating the instantaneous steam production of the steam boiler according to the flue gas flow rate;

[0020] The opening of the first electric regulating valve is controlled in a PID regulation mode according to the instantaneous steam production and the softened water flow.

[0021] Optionally, in some embodiments of the present application, controlling the opening of the second electric regulating valve based on the sewage inlet and outlet temperatures and the softened water inlet and outlet temperatures includes:

[0022] Calculating a first heat exchange temperature difference on the sewage side of the sewage heat exchanger according to the sewage inlet and outlet temperatures, and calculating a second heat exchange temperature difference on the softened water side of the sewage heat exchanger according to the softened water inlet and outlet temperatures;

[0023] The opening degree of the second electric regulating valve is controlled through a PID regulation mode according to the first heat exchange temperature difference and the second heat exchange temperature difference.

[0024] Optionally, in some embodiments of the present application, the first heat exchange temperature difference on the sewage side of the sewage heat exchanger is calculated according to the sewage inlet and outlet temperatures, and the second heat exchange temperature difference on the softened water side of the sewage heat exchanger is calculated according to the softened water inlet and outlet temperatures, further comprising:

[0025] Obtaining a correction coefficient corresponding to the periodic blowdown of the steam boiler;

[0026] The second heat exchange temperature difference is adjusted according to the correction coefficient and the first heat exchange temperature difference.

[0027] Optionally, in some embodiments of the present application, the control method further includes:

[0028] Obtaining the liquid level of the softening water tank of the steam boiler flue gas and waste heat recovery system;

[0029] If the softened water tank liquid level is higher than the upper liquid level limit, each electric regulating valve is closed until the softened water tank liquid level drops to the first liquid level, and if the softened water tank liquid level is lower than the lower liquid level limit, the opening of each electric regulating valve is adjusted to the maximum value until the softened water tank liquid level rises to the second liquid level, and the second liquid level is less than the first liquid level, wherein each time the softened water tank liquid level is lower than the second liquid level, the opening correction amount of each electric regulating valve increases by 0.2%, and each time the softened water tank liquid level is higher than the first liquid level, the opening correction amount of each electric regulating valve decreases by 0.2%.

[0030] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0031] The embodiment of the present application provides a steam boiler flue gas and sewage waste heat simultaneous recovery system and a control method thereof, wherein a first monitor in a flue gas waste heat recovery device monitors the flue gas flow rate of the steam boiler, a second monitor monitors the softened water flow rate of the flue gas heat exchanger, and a third monitor in the sewage waste heat recovery device monitors the sewage inlet and outlet temperatures of the sewage heat exchanger, and a fourth monitor monitors the softened water inlet and outlet temperatures of the sewage heat exchanger. Then, a controller can use the flue gas flow rate of the steam boiler and the softened water flow rate of the flue gas heat exchanger to control the opening of the first electric regulating valve, and the sewage inlet and outlet temperatures of the sewage heat exchanger and the softened water inlet and outlet temperatures of the sewage heat exchanger to control the opening of the second electric regulating valve, thereby ensuring that the high-temperature softened water flow rate injected into the steam boiler is balanced with the flue gas evaporation amount and the sewage discharge amount, and maximizing the simultaneous recovery of boiler flue gas and sewage waste heat, thereby increasing the softened water temperature injected into the steam boiler and avoiding heat waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 It is a structural schematic diagram of a steam boiler flue gas waste heat recovery system in the related art;

[0034] Figure 2 A schematic diagram of the relationship between flue gas waste heat and the proportion of low calorific value of fuel gas corresponding to different flue gas temperatures provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of water balance of a steam boiler provided in an embodiment of the present application;

[0036] Figure 4 A schematic diagram of the structure of a system for simultaneously recovering flue gas and waste heat from exhaust from a steam boiler provided in an embodiment of the present application;

[0037] Figure 5 A flow chart of a control method for a system for simultaneously recovering flue gas and waste heat from exhaust from a steam boiler provided in an embodiment of the present application;

[0038] Figure 6 A schematic flow chart of a method for controlling the flow rate of softened water in a flue gas heat exchanger provided in an embodiment of the present application;

[0039] Figure 7 A schematic flow chart of a method for controlling the flow rate of softened water in a blowdown heat exchanger provided in an embodiment of the present application;

[0040] Figure 8 A schematic diagram of a water tank liquid level provided in an embodiment of the present application.

[0041] Reference numerals:

[0042] 1-steam boiler flue gas and waste heat recovery system, 11-flue gas waste heat recovery device, 111-flue gas heat exchanger, 112-first electric regulating valve, S-flow rate sensor, T 1 - First temperature sensor, T 2 - Second temperature sensor, Q 1 -First heat meter, T 3 - Third temperature sensor, T 4 - fourth temperature sensor, 12 - waste heat recovery device, 121 - waste heat exchanger, 122 - second electric regulating valve, T 5 -Fifth temperature sensor, T 6 -6th temperature sensor, F-water flow switch, Q 2 - Second heat meter, T 7 - Seventh temperature sensor, T 8 -8th temperature sensor, 13-control cabinet, 14-softening water tank, L-liquid level transmission. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0044] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0045] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. To facilitate a better understanding of the embodiments of the present application, the relevant background knowledge is now described.

[0046] ① Flue gas waste heat. When the natural gas steam boiler is running, the steam boiler will discharge a large amount of flue gas into the air. These flue gases contain a huge amount of heat. At different flue gas temperatures, the ratio of flue gas waste heat to the low calorific value of the gas is Figure 2 As shown in the figure, it can be seen that the waste heat of flue gas is very large. According to the production of 1 ton of water vapor, 80Nm of natural gas is consumed. 3 According to calculation, if the boiler exhaust temperature is reduced from 100℃ to 45℃, the waste heat of the flue gas that can be recycled is about 80 (Nm 3 )×8300(kcal / Nm 3 , natural gas calorific value) ÷ 860 (kcal / kWh, conversion factor) × (16.49%-7.59%) = 68.7kWh, equivalent to 7.12Nm 3 Natural gas heat.

[0047] ② Waste heat from sewage discharge. Steam boiler sewage discharge rate = steam boiler sewage discharge volume ÷ steam boiler evaporation volume. Generally, the sewage discharge rate of steam boilers exceeds 5%. According to the sewage discharge rate of 5%, for every ton of water vapor produced, about 0.05 tons of sewage is discharged. The temperature of this part of sewage is reduced from 100℃ to 30℃. The waste heat from sewage discharge that can be recycled is about 0.05×(100-30)×1.163=4.07kWh, equivalent to 0.42Nm 3 Natural gas heat.

[0048] ③ Steam boiler water balance. Figure 3 As shown, after the steam produced by the steam boiler is output, it needs to be supplemented with corresponding new water, and the steam boiler also needs to discharge sewage, so the water supply of the steam boiler = steam production + sewage discharge. The boiler feed water may be all softened room temperature water, or it may contain some steam condensate, or other water that meets the water quality requirements. In either case, it can be used to recover boiler flue gas waste heat and sewage waste heat. This application does not analyze the source of water in the softening water tank for the time being, but only describes the use of boiler feed water to recover flue gas waste heat and sewage waste heat.

[0049] Below through Figures 4 to 8 The steam boiler flue gas and waste heat recovery system and its control method provided in the embodiment of the present application are described in detail. Please refer to Figure 4, which is a structural schematic diagram of a steam boiler flue gas and waste heat recovery system provided in an embodiment of the present application, the steam boiler flue gas and waste heat recovery system 1 includes (i) a flue gas waste heat recovery device 11, the flue gas waste heat recovery device 11 includes a flue gas heat exchanger 111 arranged on the flue of the steam boiler, a first monitor and a second monitor located at the water side outlet of the flue gas heat exchanger 111, and a first electric regulating valve 112, the outlet of the first electric regulating valve 112 is connected to the steam boiler water supply end, and the water side inlet of the flue gas heat exchanger 111 is connected to softened water, wherein the first monitor can monitor the flue gas flow rate of the steam boiler, and the second monitor can monitor the softened water flow rate of the flue gas heat exchanger 111. For example, the first monitor includes but is not limited to a flow rate sensor S located at the flue gas side inlet of the flue gas heat exchanger 111, a first temperature sensor T 1 and a second temperature sensor T located at the flue gas outlet of the flue gas heat exchanger 111 2 For example, the second monitor includes but is not limited to the first heat meter Q located at the water side outlet of the flue gas heat exchanger 111 1 etc., the first heat meter Q 1 With a third temperature sensor T 3 and the fourth temperature sensor T 4 , the third temperature sensor T 3 The fourth temperature sensor T is arranged on the water outlet pipe of the flue gas heat exchanger 111. 4 A water inlet pipe is provided at the flue gas heat exchanger 111 .

[0050] (ii) Sewage waste heat recovery device 12, which includes a sewage heat exchanger 121 disposed at the sewage end of the steam boiler, a third monitor located at the sewage side of the sewage heat exchanger 121, a fourth monitor located at the softened water side of the sewage heat exchanger 121, and a second electric regulating valve 122, the outlet of the second electric regulating valve 122 is connected to the steam boiler feed water end, and the inlet of the softened water side of the sewage heat exchanger 121 is connected to softened water, wherein the third monitor can monitor the sewage inlet and outlet temperatures of the sewage heat exchanger 121, and the fourth monitor can monitor the softened water inlet and outlet temperatures of the sewage heat exchanger 121. For example, the third monitor includes but is not limited to a fifth temperature sensor T located at the sewage side inlet of the sewage heat exchanger 121. 5 and a sixth temperature sensor T located at the sewage outlet of the sewage heat exchanger 121 6 etc.; for another example, the third monitor may also include a water flow switch F located at the outlet of the sewage side of the sewage heat exchanger 121. The advantage of such a setting is that it is convenient to monitor whether the steam boiler is discharging sewage and to open each electric regulating valve in time when discharging sewage; for another example, the fourth monitor includes but is not limited to a second heat meter Q located at the outlet of the softened water side of the sewage heat exchanger 121 2 etc., the second heat meter Q 2 With seventh temperature sensor T7 and the eighth temperature sensor T 8 , the seventh temperature sensor T 7 The eighth temperature sensor T is arranged on the outlet pipe of the sewage heat exchanger 121. 8 The water inlet pipe is arranged at the blowdown heat exchanger 121. It should be noted that after the high-temperature softened water at the softened water outlet of the flue gas heat exchanger 111 and the softened water outlet of the blowdown heat exchanger 121 are merged, they are connected between the softened water tank 14 and the deaerator water pump. For a system without a deaerator, it is connected between the softened water tank 14 and the feed water pump, thereby being able to transport the highest temperature softened water to the steam boiler feed water end, and recover the boiler flue gas waste heat and blowdown waste heat to the greatest extent.

[0051] (iii) Control cabinet 13, control cabinet 13 includes a controller, the controller is respectively connected to the first monitor, the second monitor, the third monitor, the fourth monitor and the first electric regulating valve 112, the second electric regulating valve 122, the controller can control the opening of the first electric regulating valve 112 according to the flue gas flow rate of the steam boiler and the softened water flow rate of the flue gas heat exchanger 111, and control the opening of the second electric regulating valve 122 according to the sewage inlet and outlet temperatures of the sewage heat exchanger 121 and the softened water inlet and outlet temperatures of the sewage heat exchanger 121. It should be noted that softened water is generally obtained by softening tap water, of course there are other ways, but it usually has a pressure of more than 0.3MPa, which is sufficient to overcome the resistance of the flue gas heat exchanger 111, the sewage heat exchanger 121 and the water pipeline (generally less than 0.2MPa). For example, the controller is a programmable logic controller (PLC), and the temperature sensor, flow rate sensor, liquid level transmitter, water flow switch and electric control valve are connected to the controller through hard-wired analog signals (such as cables). For another example, the control cabinet 13 can also be configured with an Internet of Things touch screen, an Internet of Things card and an electric meter. The Internet of Things touch screen provides display and interface operation functions, and the Internet of Things card (such as a traffic card, a SIM card) provides Internet access function, which facilitates the system to connect to the cloud server and realize remote monitoring through mobile phone applications, and the electric meter measures the power consumption of the system.

[0052] Furthermore, in the embodiment of the present application, the steam boiler flue gas and waste heat recovery system 1 also includes (iiii) a softened water tank 14, the outlet of which is connected to the steam boiler water supply end. The softened water tank 14 can buffer and adjust the softened water flow in the steam boiler flue gas and waste heat recovery system 1. For example, when the boiler water supply demand flow is higher than the high-temperature softened water flow, the softened water tank 14 supplements the missing part, and when the boiler water supply demand flow is lower than the high-temperature softened water flow, the excess part flows into the softened water tank 14. Optionally, a fifth monitor is provided in the softened water tank 14, and the fifth monitor is connected to the controller. The fifth monitor can monitor the liquid level of the softened water tank. For example, the fifth monitor includes but is not limited to a liquid level transmission L, etc., and the controller can correct the opening of each electric regulating valve according to the liquid level of the softened water tank.

[0053] The embodiment of the present application provides a system for simultaneously recovering flue gas and waste heat from sewage from a steam boiler. In the system, a first monitor in a flue gas waste heat recovery device monitors the flue gas flow rate of the steam boiler, a second monitor monitors the softened water flow rate of the flue gas heat exchanger, and a third monitor in the waste heat recovery device monitors the sewage inlet and outlet temperatures of the sewage heat exchanger, and a fourth monitor monitors the softened water inlet and outlet temperatures of the sewage heat exchanger. Thus, a controller can utilize the flue gas flow rate of the steam boiler and the softened water flow rate of the flue gas heat exchanger to control the opening of the first electric regulating valve, and the sewage inlet and outlet temperatures of the sewage heat exchanger and the softened water inlet and outlet temperatures of the sewage heat exchanger to control the opening of the second electric regulating valve, thereby ensuring that the high-temperature softened water flow rate injected into the steam boiler is balanced with the flue gas evaporation rate and the sewage discharge rate, and maximizing the simultaneous recovery of boiler flue gas and waste heat from sewage, thereby increasing the softened water temperature injected into the steam boiler and avoiding heat waste.

[0054] Based on the above embodiments, the present application provides a method for Figure 4 The control method of the steam boiler flue gas and waste heat recovery system 1 in the corresponding embodiment. Please refer to Figure 5 , the control method specifically comprises the following steps:

[0055] S101, obtaining the flue gas flow rate of the steam boiler and the softened water flow rate of the flue gas heat exchanger, and controlling the opening of the first electric regulating valve based on the flue gas flow rate and the softened water flow rate.

[0056] It should be noted that the unit gas consumption (referred to as unit consumption) of the steam boiler in the embodiment of the present application refers to the amount of natural gas consumed for each ton of steam produced, which is represented by A. Usually, the unit consumption is related to the calorific value of the gas, the boiler load, and the inlet temperature and humidity. The calorific value of the gas is relatively stable, and the boiler load and the inlet temperature and humidity generally affect the unit consumption within 3%. Therefore, the unit consumption is relatively stable and fluctuates less. Even if it fluctuates, it can be corrected by the correction coefficient corresponding to the unit consumption. When the boiler is debugged, the excess air coefficient is fixed, so the amount of flue gas generated by the boiler for each cubic meter of natural gas burned is also fixed, generally around 11.6 cubic meters, represented by B. Assuming that the instantaneous steam production of the steam boiler is represented by C, the instantaneous flue gas production is represented by D, then D=A×B×C, and the cross-sectional area of ​​the boiler flue is fixed, represented by E, and the flue gas flow rate is represented by S, then D=E×S. The combined result is E×S=A×B×C. Since E, A and B are fixed values, the flue gas flow rate S is directly proportional to the instantaneous steam production C. The proportional coefficient is represented by n, then S=n×C, that is, C=S÷n. Among them, the flue gas flow rate S can be monitored in real time by the flue gas flow rate sensor, and by monitoring the flue gas flow rate S and the instantaneous steam production C in a period of time (generally steam boilers are equipped with steam flow meters), the average value of the proportional coefficient n can be calculated, so it is only necessary to set the average value of the proportional coefficient n to the control system.

[0057] For example, Figure 6 As shown, the embodiment of the present application first calculates the instantaneous steam production C of the steam boiler according to the flue gas flow rate S, and takes the instantaneous steam production C as the set value and the softened water flow rate as the actual value, and then controls the opening of the first electric regulating valve 112 through the PID adjustment mode according to the instantaneous steam production C and the softened water flow rate, so as to achieve the softened water flow rate of the flue gas heat exchanger being equal to the evaporation amount (i.e., the instantaneous steam production C). Among them, PID adjustment is a linear adjustment method with proportional, integral and differential effects, which integrates the deviation between the actual value and the set value into a control quantity according to the dimensions of proportional, integral and differential, so as to control the controlled process more accurately.

[0058] S102, obtaining the sewage inlet and outlet temperatures of the sewage heat exchanger and the softened water inlet and outlet temperatures of the sewage heat exchanger, and controlling the opening of the second electric regulating valve based on the sewage inlet and outlet temperatures and the softened water inlet and outlet temperatures.

[0059] It should be noted that the softened water flow rate of the sewage heat exchanger is equal to the sewage discharge volume of the continuous sewage expander, which is equivalent to the same water flow rate on both sides of the sewage heat exchanger 121. According to the heat balance calculation, the heat exchange temperature difference on both sides of the sewage heat exchanger 121 should also be the same.

[0060] For example, Figure 7As shown, the embodiment of the present application first calculates the first heat exchange temperature difference on the sewage side of the sewage heat exchanger according to the sewage inlet and outlet temperatures, and calculates the second heat exchange temperature difference on the softened water side of the sewage heat exchanger according to the softened water inlet and outlet temperatures. For example, assuming that the first heat exchange temperature difference on the sewage side of the sewage heat exchanger is Tw, and the second heat exchange temperature difference on the softened water side of the sewage heat exchanger is Tr, then Tw = sewage inlet temperature of the sewage heat exchanger - sewage outlet temperature of the sewage heat exchanger, Tr = softened water outlet temperature of the sewage heat exchanger - softened water inlet temperature of the sewage heat exchanger, wherein the steam boiler discharges regularly The sewage does not pass through the sewage heat exchanger 121, so the sewage flow of the sewage heat exchanger 121 will be slightly less than the total sewage flow of the boiler. The embodiment of the present application can obtain the correction coefficient corresponding to the periodic sewage discharge of the steam boiler, and adjust the second heat exchange temperature difference according to the correction coefficient and the first heat exchange temperature difference, that is, the softened water flow of the sewage heat exchanger = (1 + correction coefficient) × sewage flow of the sewage heat exchanger, and according to the heat balance, the softened water flow of the sewage heat exchanger × Tr = sewage flow of the sewage heat exchanger × Tw, then Tr = Tw ÷ (1 + correction coefficient). Finally, the opening of the second electric regulating valve 122 is controlled by the PID adjustment mode according to the first heat exchange temperature difference and the second heat exchange temperature difference, for example, the first heat exchange temperature difference Tw is used as the set value, and the second heat exchange temperature difference Tr is used as the actual value, thereby achieving that the softened water flow of the sewage heat exchanger is equal to the sewage discharge of the continuous sewage expander. In addition, the flow rate fluctuation is small when the sewage is discharged from the continuous sewage expansion device. The embodiment of the present application can set upper and lower limits for the opening of the second electric regulating valve 122 after a certain amount of data is obtained from the trial operation, thereby greatly improving the control efficiency.

[0061] Furthermore, due to the boiler control system, the boiler evaporation, blowdown and boiler feed water cannot be completely matched in real time, and the softened water volume of the flue gas heat exchanger 111, the softened water volume of the blowdown heat exchanger 121 and the boiler feed water cannot be completely matched in real time. Water volume errors will inevitably occur, resulting in an imbalance between the boiler evaporation, blowdown and boiler feed water. Therefore, the softened water tank 14 can be used for buffering and adjustment. Figure 8As shown, the water tank level includes four different levels, namely, an upper limit, a first limit, a second limit and a lower limit. The second level is lower than the first level. Thus, the embodiment of the present application can obtain the softening water tank level of the steam boiler flue gas and the waste heat recovery system 1 at the same time. If the softening water tank level is higher than the upper limit, each electric regulating valve is closed and water replenishment is suspended until the softening water tank level drops to the first level. If the softening water tank level is lower than the lower limit, the opening of each electric regulating valve is adjusted to the maximum value, that is, water replenishment at the maximum flow rate, until the softening water tank level rises to the second level. Each time the softening water tank level is lower than the second level, the opening correction amount G of each electric regulating valve increases by 0.2%, and each time the softening water tank level is higher than the first level, the opening correction amount G of each electric regulating valve decreases by 0.2%. That is to say, the opening of each electric regulating valve = PID output opening + G, thereby realizing the softening water flow regulation of the entire waste heat recovery system.

[0062] The control method for a system for simultaneously recovering flue gas and waste heat from sewage from a steam boiler provided in an embodiment of the present application controls the opening of a first electric regulating valve by utilizing the flue gas flow rate of the steam boiler and the softened water flow rate of a flue gas heat exchanger, and controls the opening of a second electric regulating valve by utilizing the sewage inlet and outlet temperatures of a sewage heat exchanger and the softened water inlet and outlet temperatures of the sewage heat exchanger, thereby ensuring that the high-temperature softened water flow rate injected into the steam boiler is balanced with the flue gas evaporation rate and the sewage discharge rate, and maximizing the simultaneous recovery of boiler flue gas and waste heat from sewage, thereby increasing the softened water temperature injected into the steam boiler and avoiding heat waste.

[0063] As another aspect, the present application provides a computer-readable storage medium for storing program code, the program code for executing the aforementioned Figures 5 to 8 The steps of the control method of the corresponding embodiment.

[0064] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and modules described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0065] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the modules is only a logical function division. There may be other division methods in actual implementation, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or modules, which can be electrical, mechanical or other forms. The modules described as separate components may or may not be physically separated, and the components displayed as modules may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment.

[0066] In addition, each functional module in each embodiment of the present application may be integrated into a processing unit, or each module may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of a software functional unit. If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it may be stored in a computer-readable storage medium.

[0067] Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or the whole or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the control method of each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0068] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A system for recovering flue gas and waste heat from a steam boiler, characterized in that: The steam boiler flue gas and waste heat recovery system (1) comprises: A flue gas waste heat recovery device (11), the flue gas waste heat recovery device (11) comprising a flue gas heat exchanger (111) arranged on a flue of a steam boiler, a first monitor, a second monitor located at a water side outlet of the flue gas heat exchanger (111), and a first electric regulating valve (112), the outlet of the first electric regulating valve (112) being connected to a water feed end of the steam boiler, the water side inlet of the flue gas heat exchanger (111) being connected to softened water, the first monitor being configured to monitor a flue gas flow rate of the steam boiler, and the second monitor being configured to monitor a softened water flow rate of the flue gas heat exchanger (111); A waste heat recovery device (12), the waste heat recovery device (12) comprising a waste heat exchanger (121) arranged at a waste water end of a steam boiler, a third monitor located at a waste water side of the waste heat exchanger (121), a fourth monitor located at a softened water side of the waste heat exchanger (121), and a second electric regulating valve (122), the outlet of the second electric regulating valve (122) being connected to a water feed end of the steam boiler, the inlet of the softened water side of the waste heat exchanger (121) being connected to softened water, the third monitor being configured to monitor the waste inlet and outlet temperatures of the waste heat exchanger (121), and the fourth monitor being configured to monitor the softened water inlet and outlet temperatures of the waste heat exchanger (121); A control cabinet (13), the control cabinet (13) comprising a controller, the controller being connected to the first monitor, the second monitor, the third monitor, the fourth monitor, the first electric regulating valve (112), and the second electric regulating valve (122) respectively, the controller being configured to control the opening of the first electric regulating valve (112) according to the flue gas flow rate of the steam boiler and the softened water flow rate of the flue gas heat exchanger (111), and to control the opening of the second electric regulating valve (122) according to the sewage inlet and outlet temperatures of the sewage heat exchanger (121) and the softened water inlet and outlet temperatures of the sewage heat exchanger (121); A softened water tank (14), wherein the outlet of the softened water tank (14) is connected to the water supply end of the steam boiler, and the softened water tank (14) is configured to buffer and adjust the softened water flow in the steam boiler flue gas and waste heat recovery system (1), wherein a fifth monitor is provided in the softened water tank (14), and the fifth monitor is connected to the controller, and the fifth monitor is configured to monitor the liquid level of the softened water tank, and the controller is further configured to correct the opening of each electric regulating valve according to the liquid level of the softened water tank.

2. The system for recovering flue gas and waste heat from exhaust from a steam boiler according to claim 1 is characterized in that: The first monitor comprises a flow rate sensor (S) located at a flue gas inlet of the flue gas heat exchanger (111), a first temperature sensor (T1), and a second temperature sensor (T2) located at a flue gas outlet of the flue gas heat exchanger (111). The second monitor comprises a first heat meter (Q1) located at the water outlet of the flue gas heat exchanger (111), the first heat meter (Q1) having a third temperature sensor (T3) and a fourth temperature sensor (T4), the third temperature sensor (T3) being arranged at the water outlet pipe of the flue gas heat exchanger (111), the fourth temperature sensor (T4) being arranged at the water inlet pipe of the flue gas heat exchanger (111), The third monitor comprises a fifth temperature sensor (T5) located at the sewage side inlet of the sewage heat exchanger (121) and a sixth temperature sensor (T6) located at the sewage side outlet of the sewage heat exchanger (121); the fourth monitor comprises a second heat meter (Q2) located at the softened water side outlet of the sewage heat exchanger (121); the second heat meter (Q2) comprises a seventh temperature sensor (T7) and an eighth temperature sensor (T8); the seventh temperature sensor (T7) is arranged at the water outlet pipe of the sewage heat exchanger (121), and the eighth temperature sensor (T8) is arranged at the water inlet pipe of the sewage heat exchanger (121).

3. The system for recovering flue gas and waste heat from exhaust from a steam boiler according to claim 2 is characterized in that: The third monitor also includes a water flow switch (F) located at the sewage side outlet of the sewage heat exchanger (121).

4. A control method for a steam boiler flue gas and waste heat recovery system as claimed in any one of claims 1 to 3, characterized in that: The control method comprises: Acquiring a flue gas flow rate of the steam boiler and a softened water flow rate of the flue gas heat exchanger, and controlling the opening of the first electric regulating valve based on the flue gas flow rate and the softened water flow rate; The sewage inlet and outlet temperatures of the sewage heat exchanger and the softened water inlet and outlet temperatures of the sewage heat exchanger are obtained, and the opening of the second electric regulating valve is controlled based on the sewage inlet and outlet temperatures and the softened water inlet and outlet temperatures.

5. The control method according to claim 4, characterized in that: The controlling the opening of the first electric regulating valve based on the flue gas flow rate and the softened water flow rate comprises: Calculating the instantaneous steam production of the steam boiler according to the flue gas flow rate; The opening of the first electric regulating valve is controlled in a PID regulation mode according to the instantaneous steam production and the softened water flow.

6. The control method according to claim 4, characterized in that: The controlling the opening of the second electric regulating valve based on the sewage inlet and outlet temperatures and the softened water inlet and outlet temperatures includes: Calculating a first heat exchange temperature difference on the sewage side of the sewage heat exchanger according to the sewage inlet and outlet temperatures, and calculating a second heat exchange temperature difference on the softened water side of the sewage heat exchanger according to the softened water inlet and outlet temperatures; The opening degree of the second electric regulating valve is controlled through a PID regulation mode according to the first heat exchange temperature difference and the second heat exchange temperature difference.

7. The control method according to claim 6, characterized in that: The method of calculating the first heat exchange temperature difference on the sewage side of the sewage heat exchanger according to the sewage inlet and outlet temperatures, and calculating the second heat exchange temperature difference on the softened water side of the sewage heat exchanger according to the softened water inlet and outlet temperatures, further includes: Obtaining a correction coefficient corresponding to the periodic blowdown of the steam boiler; The second heat exchange temperature difference is adjusted according to the correction coefficient and the first heat exchange temperature difference.

8. The control method according to any one of claims 4 to 7, characterized in that: The control method further comprises: Obtaining the liquid level of the softening water tank of the steam boiler flue gas and waste heat recovery system; If the softened water tank liquid level is higher than the upper liquid level limit, each electric regulating valve is closed until the softened water tank liquid level drops to the first liquid level, and if the softened water tank liquid level is lower than the lower liquid level limit, the opening of each electric regulating valve is adjusted to the maximum value until the softened water tank liquid level rises to the second liquid level, and the second liquid level is less than the first liquid level, wherein each time the softened water tank liquid level is lower than the second liquid level, the opening correction amount of each electric regulating valve increases by 0.2%, and each time the softened water tank liquid level is higher than the first liquid level, the opening correction amount of each electric regulating valve decreases by 0.2%.

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