A multi-effect evaporation system and method for treating desulfurization wastewater by using boiler tail flue gas waste heat

Abstract

This invention discloses a multi-effect evaporation system and method for treating desulfurization wastewater using waste heat from boiler tail flue gas. The desulfurization wastewater from the desulfurization tower is connected to one end of a second-effect electric regulating valve and one end of a first-effect electric regulating valve after passing through the tube side of the preheater. The other end of the first-effect electric regulating valve is connected to the inlet of the concentrate tank and the tube side inlet of the flue gas heater. The other end of the second-effect electric regulating valve is connected to the tube side inlet of the second-effect heater and the inlet of the concentrate tank. The tube side outlet of the second-effect heater is connected to the inlet of the second-effect evaporator. The top outlet of the second-effect evaporator is connected to the inlet of the condenser via the shell side of the preheater and the tube side of the condenser. The tube side outlet of the flue gas heater is connected to the inlet of the first-effect evaporator. The top outlet of the first-effect evaporator is connected to the inlet of the condenser via the shell side of the second-effect heater. This system and method can reduce the operating cost of the multi-effect evaporation system.

Description

Technical Field

[0001] This invention belongs to the field of desulfurization wastewater treatment technology in thermal power plants, and relates to a multi-effect evaporation system and method for treating desulfurization wastewater using waste heat from boiler tail flue gas. Background Technology

[0002] Desulfurization wastewater from thermal power plants is characterized by high salinity, and traditional treatment technologies such as triple-tank systems are insufficient to remove the salt content. While bypass flue gas evaporation systems, a mature desulfurization wastewater treatment technology, achieve zero discharge through drying and evaporation, these systems often cannot completely treat the wastewater generated by thermal power units. Multi-effect evaporation systems, as a thermal concentration and volume reduction system, are increasingly being combined with bypass flue gas evaporation and drying systems as a mainstream technology for achieving zero discharge of power plant desulfurization wastewater.

[0003] Multi-effect evaporation systems offer advantages such as high heat transfer efficiency and short heating time. However, the current use of high-quality steam that has been desuperheated and depressurized as the heat source for the heater results in high operating costs, limiting the widespread application of multi-effect evaporation systems. Reducing the operating costs of desulfurization wastewater concentration and reduction has become a pressing issue for multi-effect evaporation concentration processes. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-effect evaporation system and method for treating desulfurization wastewater using waste heat from boiler tail flue gas. This system and method can reduce the operating cost of the multi-effect evaporation system.

[0005] To achieve the above objectives, this invention discloses a multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail flue gas, comprising a flue gas heater, a desulfurization tower, a preheater, a second-effect electric regulating valve, a first-effect electric regulating valve, a concentrate tank, a flue gas heater, a second-effect heater, a second-effect evaporator, a first-effect evaporator, a condenser, and a condenser tank.

[0006] The shell-side inlet of the flue gas heater is connected to the inlet flue of the desulfurization tower, and the shell-side outlet of the flue gas heater is connected to the inlet flue of the desulfurization tower. The desulfurization wastewater generated by the desulfurization tower is connected to one end of the second-effect electric regulating valve and one end of the first-effect electric regulating valve after passing through the tube side of the preheater. The other end of the first-effect electric regulating valve is connected to the inlet of the concentrate tank and the tube-side inlet of the flue gas heater. The other end of the second-effect electric regulating valve is connected to the tube-side inlet of the second-effect heater and the inlet of the concentrate tank. The tube-side outlet of the second-effect heater is connected to the inlet of the second-effect evaporator. The top outlet of the second-effect evaporator is connected to the inlet of the condenser tank via the shell side of the preheater and the tube side of the condenser. The tube-side outlet of the flue gas heater is connected to the inlet of the first-effect evaporator. The top outlet of the first-effect evaporator is connected to the inlet of the condenser tank via the shell side of the second-effect heater.

[0007] The shell-side inlet of the flue gas heater is connected to the inlet flue of the desulfurization tower via a variable frequency fan and an inlet damper.

[0008] The shell-side outlet of the flue gas heater is connected to the inlet flue of the desulfurization tower via an outlet baffle gate.

[0009] The bottom outlet of the double-effect evaporator is connected to the tube-side inlet of the double-effect heater and the inlet of the concentrate tank via a double-effect forced circulation pump.

[0010] The bottom outlet of the single-effect evaporator is connected to the tube-side inlet of the flue gas heater and the inlet of the concentrated water tank via the single-effect forced circulation pump.

[0011] The concentrated water tank is connected to a bypass flue evaporation system.

[0012] The condenser is connected to a vacuum system.

[0013] This invention discloses a multi-effect evaporation method for treating desulfurization wastewater using waste heat from boiler tail gas, comprising:

[0014] Hot flue gas enters the flue gas heater, and desulfurization wastewater is preheated by the preheater and then enters the flue gas heater and the second-effect heater respectively. The desulfurization wastewater output from the flue gas heater enters the first-effect evaporator for flash evaporation.

[0015] The desulfurization wastewater output from the double-effect heater enters the double-effect evaporator for flash evaporation. The steam generated by the flash evaporation in the first-effect evaporator serves as the heat source for the double-effect heater. Part of the steam output from the double-effect evaporator after flash evaporation enters the preheater as the heat source for preheating the desulfurization wastewater, while the other part of the steam enters the condenser.

[0016] The desulfurization wastewater is circulated between the double-effect evaporator and the double-effect heater by a double-effect forced circulation pump.

[0017] The desulfurization wastewater is circulated from the first-effect evaporator to the flue gas heater by a single-effect forced circulation pump.

[0018] To ensure the stability of the desulfurization wastewater concentration and reduction effect, the temperature of the first-effect evaporator is maintained within the normal range by adjusting the frequency of the variable frequency fan. The variable frequency fan frequency is adjusted to ensure that the flue gas flow rate measured by the flue gas flow meter at the inlet of the flue gas heater and the desulfurization wastewater influent flow rate are synchronized, using PID control. The formula for calculating the target value of the flue gas flow rate adjustment is as follows: In the formula, N1 is the wastewater discharge rate, and H... N1 V represents the enthalpy of wastewater discharge, and H represents the hot water volume. V F1 is the enthalpy of hot water, HF1 is the enthalpy of the input wastewater, and U is the enthalpy difference of the flue gas.

[0019] The present invention has the following beneficial effects:

[0020] The multi-effect evaporation system and method for treating desulfurization wastewater using waste heat from boiler tail gas, as described in this invention, utilizes the waste heat from boiler tail gas as the heat source for the first-effect heater, replacing the currently used high-grade live steam. This achieves the recovery and utilization of low-grade waste heat from the flue gas, significantly reducing the operating cost of the multi-effect evaporation system and demonstrating significant economic advantages. Simultaneously, the flow rate of hot flue gas drawn from the bypass flue can be flexibly adjusted by changing the frequency of the variable frequency fan, achieving coordinated control between the flue gas volume and the treated water volume.

[0021] Furthermore, by using inlet and outlet dampers, the system is isolated from the multi-effect system and the main flue of the boiler, without affecting the daily operation of the main flue and the subsequent desulfurization system, making the project implementation and maintenance flexible.

[0022] Furthermore, the hot steam from the flash steam of the double-effect evaporator is used as the preheating heat source for the desulfurization wastewater. The condensation heat released by the condensation of the steam generated by the double-effect evaporator is used to preheat the desulfurization wastewater, thereby improving the energy utilization efficiency of the system. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] Among them, 1 is the inlet flue, 2 is the desulfurization tower, 3 is the inlet damper, 4 is the outlet damper, 5 is the variable frequency fan, 6 is the flue gas heater, 7 is the first-effect evaporator, 8 is the first-effect forced circulation pump, 9 is the condenser, 10 is the second-effect heater, 11 is the second-effect evaporator, 12 is the second-effect forced circulation pump, 13 is the preheater, 14 is the condenser, 15 is the desulfurization wastewater transfer pump, 16 is the first-effect electric regulating valve, 17 is the second-effect electric regulating valve, 18 is the vacuum system, and 19 is the concentrated water tank. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0026] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0027] refer to Figure 1 The multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail flue gas as described in this invention includes an inlet flue 1, a desulfurization tower 2, an inlet baffle 3, an outlet baffle 4, a variable frequency fan 5, a flue gas heater 6, a first-effect evaporator 7, a first-effect forced circulation pump 8, a condenser 9, a second-effect heater 10, a second-effect evaporator 11, a second-effect forced circulation pump 12, a preheater 13, a condenser 14, a desulfurization wastewater transfer pump 15, a first-effect electric regulating valve 16, a second-effect electric regulating valve 17, a vacuum system 18, and a concentrated water tank 19.

[0028] The shell-side inlet of the flue gas heater 6 is connected to the inlet flue duct 1 of the desulfurization tower 2 via the variable frequency fan 5 and the inlet damper 3. The shell-side outlet of the flue gas heater 6 is connected to the inlet flue duct 1 of the desulfurization tower 2 via the outlet damper 4. The bottom slurry outlet of the desulfurization tower 2 is connected to one end of the second-effect electric regulating valve 17 and one end of the first-effect electric regulating valve 16 after passing through the tube side of the preheater 13. The other end of the first-effect electric regulating valve 16 is connected to the inlet of the concentrated water tank 19 and the tube-side inlet of the flue gas heater 6. The other end of the valve 17 is connected to the tube-side inlet of the double-effect heater 10 and the inlet of the concentrated water tank 19. The tube-side outlet of the double-effect heater 10 is connected to the inlet of the double-effect evaporator 11. The bottom outlet of the double-effect evaporator 11 is connected to the tube-side inlet of the double-effect heater 10 and the inlet of the concentrated water tank 19 via the double-effect forced circulation pump 12. The top outlet of the double-effect evaporator 11 is connected to the inlet of the condenser tank 9 via the shell side of the preheater 13 and the tube side of the condenser 14. The condenser tank 9 is connected to the vacuum system 18.

[0029] The tube-side outlet of the flue gas heater 6 is connected to the inlet of the first-effect evaporator 7. The bottom outlet of the first-effect evaporator 7 is connected to the tube-side inlet of the flue gas heater 6 and the inlet of the concentrated water tank 19 via the first-effect forced circulation pump 8. The top outlet of the first-effect evaporator 7 is connected to the inlet of the condenser tank 9 via the shell side of the second-effect heater 10.

[0030] In this embodiment, the variable frequency fan 5 adopts a variable frequency form, which can flexibly adjust the flue gas flow rate of the inlet flue 1 by changing the frequency; the concentrated water tank 19 is connected to a bypass flue evaporation system.

[0031] refer to Figure 1The multi-effect evaporation method for treating desulfurization wastewater using waste heat from boiler tail gas, as described in this invention, includes the following steps:

[0032] Open the outlet damper 4 and the inlet damper 3 respectively, start the variable frequency fan 5, and the hot flue gas enters the flue gas heater 6 through the variable frequency fan 5. The desulfurization wastewater is preheated by the preheater and then enters the flue gas heater 6 and the second-effect heater 10 respectively. The desulfurization wastewater output from the flue gas heater 6 enters the first-effect evaporator 7 for flash evaporation. The desulfurization wastewater is circulated from the first-effect evaporator 7 to the flue gas heater 6 by the first-effect forced circulation pump 8. Start the vacuum system 18.

[0033] The desulfurization wastewater output from the double-effect heater 10 enters the double-effect evaporator 11 for flash evaporation. The double-effect forced circulation pump 12 circulates the desulfurization wastewater between the double-effect evaporator 11 and the double-effect heater 10. The steam generated by the flash evaporation in the first-effect evaporator 7 serves as the heat source for the double-effect heater 10. A portion of the steam output from the double-effect evaporator 11 after flash evaporation enters the preheater 13 as a heat source for preheating the desulfurization wastewater, while the other portion of the steam enters the condenser 14.

[0034] The vacuum system 18 draws the non-condensable gas generated by the first-effect evaporator 7, the second-effect heater 10, the second-effect evaporator 11, and the condenser 9 into the vacuum system 18 to achieve gas-liquid separation.

[0035] The condensate in condenser tank 9 is reused as flushing water for the desulfurization system or cleaning water for the chemical system.

[0036] Example 1

[0037] The liquid level in the first-effect evaporator 7 and the second-effect evaporator 11 is 1.8 meters. The vacuum system 18 is started, and the first-effect forced circulation pump 8 and the second-effect forced circulation pump 12 are started. The outlet damper 4 and the inlet damper 3 are opened respectively. The variable frequency fan 5 is started. The hot flue gas with a pressure of 103 kPa and a temperature of 95°C enters the flue gas heater 6 through the variable frequency fan 5. The frequency of the variable frequency fan 5 is adjusted to gradually adjust the flue gas flow rate to match the desulfurization wastewater influent flow rate and heat the desulfurization wastewater. After the hot flue gas passes through the flue gas heater 6, the flue gas temperature in the outlet flue is 53°C. After merging into the inlet flue duct 1, the flue gas temperature in the main flue is... The temperature is 86℃. When the temperature of the desulfurization wastewater in the first-effect evaporator 7 reaches 78℃ and the upper pressure is -61kPa, the steam generated by the flash evaporation in the first-effect evaporator 7 enters the second-effect heater 10 as a heat source to gradually heat the wastewater. When the temperature at the top of the second-effect evaporator 11 reaches 62℃ and the upper pressure is -84kPa, the steam generated by the flash evaporation in the second-effect evaporator 11 enters the preheater 13 to preheat the desulfurization wastewater transported by the desulfurization wastewater pump 15, and then flows into the condenser 14. The condensate generated in the condenser 14 enters the condenser tank 9, and the condensate in the condenser tank 9 is reused as flushing water for the desulfurization system. When the density of the desulfurization wastewater solution in the second-effect evaporator 11 reaches 1200kg / m³, the temperature is gradually increased. 3 During this process, a portion of the desulfurization wastewater solution in the second-effect evaporator 11 is discharged into the concentration tank 19. The desulfurization wastewater in the concentration tank 19 is then transported to the bypass flue evaporation system for evaporation, achieving zero discharge of desulfurization wastewater. After being preheated by the preheater 13, the desulfurization wastewater is continuously transported to the first-effect evaporator 7 and the second-effect evaporator 11. The desulfurization wastewater in the multi-effect evaporation system is concentrated and reduced in volume, forming a dynamic balance.

[0038] Example 2

[0039] The liquid level in the first-effect evaporator 7 and the second-effect evaporator 11 is 2.0 meters. The vacuum system 18 is started, as are the first-effect forced circulation pump 8 and the second-effect forced circulation pump 12. The outlet damper 4 and the inlet damper 3 are opened respectively. The variable frequency fan 5 is started. Hot flue gas with a pressure of 102 kPa and a temperature of 92°C enters the flue gas heater 6 through the variable frequency fan 5. The frequency of the variable frequency fan 5 is adjusted to gradually regulate the flue gas flow rate to match the influent flow of desulfurization wastewater, thus heating the desulfurization wastewater. When the temperature of the desulfurization wastewater in the first-effect evaporator 7 reaches 75°C and the upper pressure is -60 kPa, the first-effect evaporation... The steam generated by the flash evaporator 7 enters the double-effect heater 10 as a heat source and is gradually heated. When the temperature at the top of the double-effect evaporator 11 is 60℃ and the pressure at the top is -85kpa, the steam generated by the flash evaporator 11 enters the preheater 13 to heat the desulfurization wastewater transported by the desulfurization wastewater transfer pump 15. The steam then flows into the condenser 14. The condensate generated in the condenser 14 enters the condenser tank 9. The condensate in the condenser tank 9 is reused as flushing water for the desulfurization system. After being preheated by the preheater 13, the desulfurization wastewater is continuously transported to the first-effect evaporator 7 and the second-effect evaporator 11 to form a dynamic balance.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail gas, characterized in that, It includes a flue gas heater (6), a desulfurization tower (2), a preheater (13), a double-effect electric regulating valve (17), a single-effect electric regulating valve (16), a concentrated water tank (19), a double-effect heater (10), a double-effect evaporator (11), a single-effect evaporator (7), a condenser (14), and a condenser tank (9). The shell-side inlet of the flue gas heater (6) is connected to the inlet flue (1) of the desulfurization tower (2), and the shell-side outlet of the flue gas heater (6) is connected to the inlet flue (1) of the desulfurization tower (2). The desulfurization wastewater outlet generated by the desulfurization tower (2) is connected to one end of the double-effect electric regulating valve (17) and one end of the first-effect electric regulating valve (16) after passing through the tube side of the preheater (13). The other end of the first-effect electric regulating valve (16) is connected to the inlet of the concentrated water tank (19) and the tube-side inlet of the flue gas heater (6). The other end of the double-effect electric regulating valve (17) is connected to the inlet of the concentrated water tank (19) and the tube-side inlet of the flue gas heater (6). One end is connected to the tube side inlet of the second-effect heater (10) and the inlet of the concentrated water tank (19). The tube side outlet of the second-effect heater (10) is connected to the inlet of the second-effect evaporator (11). The top outlet of the second-effect evaporator (11) is connected to the inlet of the condenser tank (9) via the shell side of the preheater (13) and the tube side of the condenser (14). The tube side outlet of the flue gas heater (6) is connected to the inlet of the first-effect evaporator (7). The top outlet of the first-effect evaporator (7) is connected to the inlet of the condenser tank (9) via the shell side of the second-effect heater (10). The shell-side inlet of the flue gas heater (6) is connected to the inlet flue (1) of the desulfurization tower (2) via a variable frequency fan (5) and an inlet damper (3); The shell-side outlet of the flue gas heater (6) is connected to the inlet flue (1) of the desulfurization tower (2) via the outlet baffle gate (4); To ensure the stability of the concentration and reduction effect of desulfurization wastewater, the temperature of the first-effect evaporator is maintained within the normal range by adjusting the frequency of the variable frequency fan. The variable frequency fan ensures that the flue gas flow rate measured by the flue gas flow meter at the inlet of the flue gas heater and the influent flow rate of desulfurization wastewater are matched in a coordinated manner.

2. The multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail gas as described in claim 1, characterized in that, The bottom outlet of the double-effect evaporator (11) is connected to the pipe-side inlet of the double-effect heater (10) and the inlet of the concentrated water tank (19) via the double-effect forced circulation pump (12).

3. The multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail gas as described in claim 1, characterized in that, The bottom outlet of the single-effect evaporator (7) is connected to the pipe-side inlet of the flue gas heater (6) and the inlet of the concentrated water tank (19) via the single-effect forced circulation pump (8).

4. The multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail gas as described in claim 1, characterized in that, The concentrated water tank (19) is connected to a bypass flue evaporation system.

5. The multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail gas as described in claim 1, characterized in that, The condenser (9) is connected to a vacuum system (18).

6. A multi-effect evaporation method for treating desulfurization wastewater using waste heat from boiler tail gas, characterized in that, The multi-effect evaporation system for treating desulfurization wastewater using waste heat from boiler tail flue gas as described in claim 1 includes: Hot flue gas enters the flue gas heater (6), and desulfurization wastewater is preheated by the preheater and then enters the flue gas heater (6) and the second-effect heater (10) respectively. The desulfurization wastewater output from the flue gas heater (6) enters the first-effect evaporator (7) for flash evaporation. The desulfurization wastewater output from the double-effect heater (10) enters the double-effect evaporator (11) for flash evaporation. The steam generated by the flash evaporator (7) of the first-effect evaporator serves as the heat source for the double-effect heater (10). A portion of the steam output from the double-effect evaporator (11) after flash evaporation serves as the heat source for preheating the desulfurization wastewater and enters the preheater (13), and then enters the condenser (14).

7. The multi-effect evaporation method for treating desulfurization wastewater using waste heat from boiler tail gas according to claim 6, characterized in that, The desulfurization wastewater is circulated between the double-effect evaporator (11) and the double-effect heater (10) by a double-effect forced circulation pump (12).

8. The multi-effect evaporation method for treating desulfurization wastewater using waste heat from boiler tail gas according to claim 6, characterized in that, The desulfurization wastewater is circulated between the first-effect evaporator (7) and the flue gas heater (6) by a single-effect forced circulation pump (8); To ensure the stability of the concentration and reduction effect of desulfurization wastewater, the temperature of the first-effect evaporator is maintained within the normal range by adjusting the frequency of the variable frequency fan. The variable frequency fan frequency is adjusted to ensure that the flue gas flow rate measured by the flue gas flow meter at the inlet of the flue gas heater and the influent flow rate of the desulfurization wastewater are matched in PID control. The formula for calculating the target value of the flue gas flow rate adjustment is as follows: , in the formula, Wastewater discharge volume The enthalpy value of wastewater discharge. This refers to the amount of hot water. This is the enthalpy value of hot water. Wastewater input volume To input the enthalpy value of the wastewater, This represents the difference in enthalpy of the flue gas.

Images