A two-stage vacuum flash evaporation process for gasified black water

Abstract

The present invention relates to a two-stage vacuum flash evaporation process for gasified black water, which is completed by a flash evaporation system, wherein the flash evaporation system includes a first-stage vacuum system and a second-stage vacuum system. The present invention combines the advantages of the first-stage vacuum flash evaporation and the second-stage vacuum flash evaporation. However, compared with the first-stage vacuum flash evaporation as a whole, the temperature of the discharged wastewater and the slag lock bucket flushing water of the present invention can directly meet the process requirements, reducing the configuration of the wastewater cooler and the slag lock bucket flushing water cooler, solving the problems of low online rate and large maintenance volume of the clarified water heat exchanger in the first-stage vacuum flash evaporation process, and improving the reliability of the process. Compared with the second-stage vacuum flash evaporation as a whole, the gasified black water of the present invention is graded and the reused clarified water only undergoes the first-stage vacuum flash evaporation, resulting in less heat loss and improved thermal efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, in particular to the technical field of entrained-bed chilled gasification, and specifically relates to a two-stage vacuum flash evaporation process for gasified black water. Background Art

[0002] At present, the ash water treatment process of the entrained-flow quenching gasification process is equipped with a first-stage vacuum flash evaporation system or a second-stage vacuum flash evaporation system.

[0003] Figure 1 The current single-stage vacuum flash process is shown, comprising a single-stage vacuum flash tank, a clarifier, a clarifier overflow tank, a vacuum flash separation tank, a vacuum flash gas cooler, an exhaust wastewater cooler, a slag lock hopper flushing water cooler, a vacuum pump, and a clarified water pump. The clarified water after the first stage of vacuum flash is approximately 80°C. After being pressurized by the clarified water pump, a portion is cooled to 45°C by the exhaust wastewater cooler and sent to the downstream sewage treatment unit. A portion is cooled by the slag lock hopper flushing water cooler and sent to the slag lock hopper. The remaining portion is recycled to the gasification system.

[0004] Figure 2 The existing two-stage vacuum flash evaporation process is shown, which includes a primary vacuum flash tank, a secondary vacuum flash tank, a clarifier, a clarifier overflow tank, a primary vacuum flash separation tank, a secondary vacuum flash separation tank, a primary vacuum flash gas cooler, a secondary vacuum flash gas cooler, a primary vacuum pump, a secondary vacuum jet pump, and a clarified water pump. The black water after the primary vacuum flash evaporation reaches a temperature of approximately 80°C. After the secondary flash valve further reduces the pressure, it enters the secondary vacuum flash tank. The clarified water after the secondary vacuum flash evaporation reaches a temperature below 45°C. After being pressurized by the clarified water pump, part of the water is sent to the downstream sewage treatment unit, part is sent to the slag lock hopper, and the remaining water is recycled to the gasification system.

[0005] For the above-mentioned first-stage vacuum flash evaporation system, the temperature of the clarified water after flash evaporation is high, and both the wastewater sent to the sewage treatment unit and the slag lock hopper flushing water require additional cooling. Due to the complex water quality of the gasification ash water, high hardness and soluble solids content, scaling is easy to form on the ash water side of the cooler. Moreover, due to the high ash water temperature, scaling is also easy to form on the circulating water side, resulting in a decrease in the heat exchange efficiency of the heat exchanger after a period of operation and an increase in the temperature of the external wastewater, affecting the normal operation of the downstream sewage treatment unit. For the above-mentioned second-stage vacuum flash evaporation system, since all black water enters the second-stage vacuum flash evaporation system, a large amount of flash heat is lost through the circulating water heat extraction, resulting in a lower water vapor content in the product synthesis gas than the first-stage vacuum flash evaporation process, and the overall thermal efficiency of gasification is low. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a two-stage vacuum flash evaporation process for the gasified black water portion based on the current status of the existing technology, which maintains the advantages of the one-stage vacuum flash evaporation and the two-stage vacuum flash evaporation systems, thereby achieving a high online rate of the clarified water heat exchanger, a small amount of maintenance, reduced heat loss and improved thermal efficiency.

[0007] The technical solution adopted by the present invention to solve the above technical problems is:

[0008] A two-stage vacuum flash evaporation process for gasified black water is completed by a flash evaporation system, which includes a primary vacuum system and a secondary vacuum system;

[0009] The primary vacuum system includes a primary vacuum flash tank V01, a primary vacuum flash cooler E01, a primary vacuum flash gas separation tank V03, a primary vacuum pump P03, a primary clarifier S01, a primary clarifier overflow tank T01, a clarified water pump P01, a primary vacuum flash tank V01 black water outlet level control valve LV01 and a flow control valve FV01;

[0010] The secondary vacuum system includes a secondary vacuum flash tank V02, a secondary vacuum flash cooler E02, a secondary vacuum flash gas separation tank V04, a secondary vacuum jet pump J01, a secondary clarifier S02, a secondary clarifier overflow tank T02, a secondary clarified water pump P02, a secondary vacuum flash tank V02 outlet liquid level control valve LV02, a secondary vacuum flash tank V02 pressure indicator PT01, a secondary clarified water flow monitor FT01 and a secondary vacuum jet pump J01 inlet steam flow control valve PV01;

[0011] The secondary vacuum flash evaporation process of the gasified black water portion comprises the following steps:

[0012] 1) First stage vacuum flash evaporation

[0013] (1) After flash evaporation, the black water from upstream enters the first-stage vacuum flash tank V01 for flash evaporation treatment;

[0014] (2) A portion of the black water after the first-stage vacuum flash evaporation enters the second-stage vacuum flash tank V02 through the flow control valve FV01, and the remaining portion enters the first-stage clarifier S01 through the liquid level control valve LV01;

[0015] (3) After the flash steam from the first-stage vacuum flash evaporation is cooled by the first-stage vacuum flash steam cooler E01, the non-condensable gas is extracted and sent out of the unit by the first-stage vacuum pump P03, and the condensate enters the overflow tank T01 of the first-stage clarifier;

[0016] (4) The black water is clarified in the primary clarifier S01, and the clarified overflow enters the primary clarifier overflow tank T01. The fine ash in the black water accumulates at the bottom of the primary clarifier S01 and is then sent out for liquid-solid separation;

[0017] (5) The clarified water at the overflow tank outlet of the primary clarifier is pressurized by the clarified water pump P01 and the flash steam heat is recovered before returning to the gasification washing system;

[0018] 2) Secondary vacuum flash evaporation

[0019] (1) The black water after the first-stage vacuum flash evaporation is decompressed by the flow control valve FV01 and enters the second-stage vacuum flash tank V02 for flash evaporation treatment;

[0020] (2) All the black water after the secondary vacuum flash evaporation passes through the liquid level control valve LV01 and enters the secondary clarifier S02;

[0021] (3) After the flash steam from the secondary vacuum flash evaporation is cooled by the secondary vacuum flash steam cooler E02, the non-condensable gas is extracted by the secondary vacuum jet pump J01 and sent to the inlet of the primary vacuum flash steam cooler, and the condensate enters the overflow tank T02 of the secondary clarifier;

[0022] (4) The black water is clarified in the secondary clarifier S02, and the clarified overflow enters the secondary clarifier overflow tank T02. The fine ash in the black water accumulates at the bottom of the secondary clarifier S2 and is then sent out for liquid-solid separation;

[0023] (5) The clarified water at the outlet of the overflow tank of the secondary clarifier is at a temperature of about 40°C. A portion of it is pressurized by the clarified water pump P02 and directly sent to the downstream sewage treatment device as wastewater, and the other portion is reused as slag lock hopper flushing water;

[0024] 3) Control process

[0025] (1) The black water flow from the first-stage vacuum flash tank V01 to the second-stage vacuum flash tank V02 is controlled by the clarified water flow at the outlet of the second-stage clarifier overflow tank; the black water at the first-stage vacuum outlet is the sum of the external wastewater and the slag lock hopper flushing water flow, which controls the treatment scale of the second-stage vacuum flash system;

[0026] (2) The pressure of the secondary vacuum flash tank is controlled by the steam flow rate at the inlet of the secondary vacuum jet pump J01; the temperature of the black water after the secondary vacuum flash is controlled so that the discharged wastewater can meet the temperature requirements of direct feed for sewage treatment without being cooled by a cooler.

[0027] Preferably, the first-stage vacuum flash clarified water is recycled to the gasification system, and the second-stage vacuum flash clarified water is discharged to the wastewater treatment unit and used as slag lock hopper flushing water.

[0028] Preferably, a cooler is additionally provided for the discharged wastewater to control the wastewater temperature.

[0029] Preferably, the flow rate of black water from the first vacuum flash evaporation to the second vacuum flash evaporation is controlled by the flow rate of clarified water from the second vacuum flash evaporation.

[0030] Preferably, the flash pressure of the first-stage vacuum flash tank V01 is -0.056 MPag, corresponding to a flash temperature of 80°C.

[0031] Preferably, the flash pressure of the secondary vacuum flash tank V02 is -0.09 MPag, and the corresponding flash temperature is 40°C.

[0032] Preferably, the temperature of clarified water at the outlet of the overflow tank of the primary clarifier is 75-85°C.

[0033] Preferably, the temperature of the black water after the first-stage vacuum flash evaporation is 45-90°C, and the temperature of the black water after the second-stage vacuum flash evaporation is ≤45°C.

[0034] Compared with the prior art, the advantages of the present invention are: the present invention combines the advantages of primary vacuum flash evaporation and secondary vacuum flash evaporation, but compared with the full primary vacuum flash evaporation, the temperature of the discharged wastewater and slag lock bucket flushing water of the present invention can directly meet the process requirements, reducing the configuration of the wastewater cooler and the slag lock bucket flushing water cooler, solving the problems of low online rate and large maintenance volume of the clarified water heat exchanger in the primary vacuum flash evaporation process, and improving the reliability of the process; compared with the full secondary vacuum flash evaporation, the present invention performs graded treatment of gasified black water, and the reused clarified water only undergoes primary vacuum flash evaporation, resulting in less heat loss and improved thermal efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A process flow chart of the background technology of the present invention;

[0036] Figure 2 Another process flow chart for the background technology of the present invention;

[0037] Figure 3 is a process flow chart of an embodiment of the present invention;

[0038] V01 first-stage vacuum flash tank, V02 second-stage vacuum flash tank, V03 first-stage vacuum flash gas separation tank, V04 second-stage vacuum flash gas separation tank, E01 first-stage vacuum flash cooler, E02 second-stage vacuum flash cooler, S01 first-stage clarifier, S02 second-stage clarifier, T01 first-stage clarifier overflow tank, T02 second-stage clarifier overflow tank, P01 clarified water pump one, P02 clarified water pump two, P03 first-stage vacuum pump, J01 second-stage vacuum jet pump, LV01 first-stage vacuum flash tank black water outlet liquid level control valve, FV01 flow control valve, LV02 second-stage vacuum flash tank outlet liquid level control valve, PT01 second-stage vacuum flash tank V02 pressure indicator, FT01 clarified water second flow monitor, PV01 second-stage vacuum jet pump inlet steam flow control valve. DETAILED DESCRIPTION

[0039] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0040] like Figure 3 As shown, the secondary vacuum flash evaporation process of the gasified black water portion of this embodiment is completed by a flash evaporation system, which includes a primary vacuum system and a secondary vacuum system.

[0041] The primary vacuum system includes a primary vacuum flash tank V01, a primary vacuum flash cooler E01, a primary vacuum flash gas separation tank V03, a primary vacuum pump P03, a primary clarifier S01, a primary clarifier overflow tank T01, a clarified water pump P01, a primary vacuum flash tank V01 black water outlet level control valve LV01 and a flow control valve FV01;

[0042] The secondary vacuum system includes a secondary vacuum flash tank V02, a secondary vacuum flash cooler E02, a secondary vacuum flash gas separation tank V04, a secondary vacuum jet pump J01, a secondary clarifier S02, a secondary clarifier overflow tank T02, a secondary clarified water pump P02, a secondary vacuum flash tank V02 outlet liquid level control valve LV02, a secondary vacuum flash tank V02 pressure indicator PT01, a secondary clarified water flow monitor FT01 and a secondary vacuum jet pump J01 inlet steam flow control valve PV01.

[0043] The secondary vacuum flash evaporation process of the gasified black water portion of this embodiment comprises the following steps:

[0044] 1) First stage vacuum flash evaporation

[0045] (1) After flash evaporation, the black water from upstream enters the first-stage vacuum flash tank V01 for flash evaporation treatment;

[0046] (2) A portion of the black water after the first-stage vacuum flash evaporation enters the second-stage vacuum flash tank V02 through the flow control valve FV01, and the remaining portion enters the first-stage clarifier S01 through the liquid level control valve LV01;

[0047] (3) After the flash steam from the first-stage vacuum flash evaporation is cooled by the first-stage vacuum flash steam cooler E01, the non-condensable gas is extracted and sent out of the unit by the first-stage vacuum pump P03, and the condensate enters the overflow tank T01 of the first-stage clarifier;

[0048] (4) The black water is clarified in the primary clarifier S01, and the clarified overflow enters the primary clarifier overflow tank T01. The fine ash in the black water accumulates at the bottom of the primary clarifier S01 and is then sent out for liquid-solid separation;

[0049] (5) The clarified water at the overflow tank outlet of the primary clarifier is pressurized by the clarified water pump P01 and the flash steam heat is recovered before returning to the gasification washing system;

[0050] 2) Secondary vacuum flash evaporation

[0051] (1) The black water after the first-stage vacuum flash evaporation is decompressed by the flow control valve FV01 and enters the second-stage vacuum flash tank V02 for flash evaporation treatment;

[0052] (2) All the black water after the secondary vacuum flash evaporation passes through the liquid level control valve LV01 and enters the secondary clarifier S02;

[0053] (3) After the flash steam from the secondary vacuum flash evaporation is cooled by the secondary vacuum flash steam cooler E02, the non-condensable gas is extracted by the secondary vacuum jet pump J01 and sent to the inlet of the primary vacuum flash steam cooler, and the condensate enters the overflow tank T02 of the secondary clarifier;

[0054] (4) The black water is clarified in the secondary clarifier S02, and the clarified overflow enters the secondary clarifier overflow tank T02. The fine ash in the black water accumulates at the bottom of the secondary clarifier S2 and is then sent out for liquid-solid separation;

[0055] (5) The clarified water at the outlet of the overflow tank of the secondary clarifier is at a temperature of about 40°C. A portion of it is pressurized by the clarified water pump P02 and directly sent to the downstream sewage treatment device as wastewater, and the other portion is reused as slag lock hopper flushing water;

[0056] 3) Control process

[0057] (1) The black water flow from the first-stage vacuum flash tank V01 to the second-stage vacuum flash tank V02 is controlled by the clarified water flow at the outlet of the second-stage clarifier overflow tank; the black water at the first-stage vacuum outlet is the sum of the external wastewater and the slag lock hopper flushing water flow, which controls the treatment scale of the second-stage vacuum flash system;

[0058] (2) The pressure of the secondary vacuum flash tank is controlled by the steam flow rate at the inlet of the secondary vacuum jet pump J01; the temperature of the black water after the secondary vacuum flash is controlled so that the discharged wastewater can meet the temperature requirements of direct feed for sewage treatment without being cooled by a cooler.

[0059] The first-stage vacuum flash evaporation clarified water is recycled to the gasification system, and the second-stage vacuum flash evaporation clarified water is discharged to the wastewater treatment unit and used as slag lock hopper flushing water.

[0060] In this embodiment, a cooler is additionally provided for the discharged wastewater to control the wastewater temperature.

[0061] The flow rate of black water from the first vacuum flash evaporation to the second vacuum flash evaporation is controlled by the flow rate of clarified water from the second vacuum flash evaporation.

[0062] The flash pressure of the first-stage vacuum flash tank V01 is -0.056 MPag, and the corresponding flash temperature is 80°C.

[0063] The flash pressure of the secondary vacuum flash tank V02 is -0.09 MPag, and the corresponding flash temperature is 40°C.

[0064] The temperature of clarified water at the outlet of the overflow tank of the first-stage clarifier is 75-85℃.

[0065] The black water temperature after the first-stage vacuum flash evaporation is 45-90°C, and the black water temperature after the second-stage vacuum flash evaporation is ≤45°C.

[0066] Taking a nominal capacity of 1500 tons / day weathering furnace, low-pressure flash evaporation (corresponding to flash pressure 0.15MPaG) followed by vacuum flash evaporation of black water, and part of the two-stage vacuum flash evaporation as an example, the material balance is as follows:

[0067]

[0068]

Claims

1. A two-stage vacuum flash evaporation process for gasified black water, characterized by: This is accomplished through a flash evaporation system, which includes a primary vacuum system and a secondary vacuum system; The primary vacuum system comprises a primary vacuum flash tank (V01), a primary vacuum flash cooler (E01), a primary vacuum flash gas separation tank (V03), a primary vacuum pump (P03), a primary clarifier (S01), a primary clarifier overflow tank (T01), a clarified water pump (P01), a black water outlet level control valve (LV01) and a flow control valve (FV01) of the primary vacuum flash tank (V01); The secondary vacuum system comprises a secondary vacuum flash tank (V02), a secondary vacuum flash cooler (E02), a secondary vacuum flash gas separation tank (V04), a secondary vacuum jet pump (J01), a secondary clarifier (S02), a secondary clarifier overflow tank (T02), a secondary clarified water pump (P02), a secondary vacuum flash tank (V02) outlet liquid level control valve (LV02), a secondary vacuum flash tank (V02) pressure indicator (PT01), a secondary clarified water flow monitor (FT01) and a secondary vacuum jet pump (J01) inlet steam flow control valve (PV01); The secondary vacuum flash evaporation process of the gasified black water portion comprises the following steps: 1) First stage vacuum flash evaporation (1) After flash evaporation, the black water from upstream enters the first-stage vacuum flash tank (V01) for flash evaporation treatment; (2) A portion of the black water after the first-stage vacuum flash evaporation enters the second-stage vacuum flash tank (V02) through the flow control valve (FV01), and the remaining portion enters the first-stage clarifier (S01) through the liquid level control valve (LV01); (3) After the flash steam from the first-stage vacuum flash evaporation is cooled by the first-stage vacuum flash steam cooler (E01), the non-condensable gas is extracted and sent out of the unit by the first-stage vacuum pump (P03), and the condensate enters the overflow tank (T01) of the first-stage clarifier; (4) The black water is clarified in the primary clarifier (S01), and the clarified overflow enters the primary clarifier overflow tank (T01). The fine ash in the black water accumulates at the bottom of the primary clarifier (S01) and is then sent out for liquid-solid separation; (5) The clarified water at the overflow tank outlet of the primary clarifier is pressurized by the clarified water pump (P01) and the flash steam heat is recovered before returning to the gasification and washing system; 2) Secondary vacuum flash evaporation (1) The black water after the first-stage vacuum flash evaporation is decompressed by the flow control valve (FV01) and enters the second-stage vacuum flash tank (V02) for flash evaporation treatment; (2) All the black water after the secondary vacuum flash evaporation passes through the liquid level control valve (LV02) and enters the secondary clarification tank (S02); (3) After the flash steam from the secondary vacuum flash evaporation is cooled by the secondary vacuum flash steam cooler (E02), the non-condensable gas is extracted by the secondary vacuum jet pump (J01) and sent to the inlet of the primary vacuum flash steam cooler, and the condensate enters the overflow tank of the secondary clarifier (T02); (4) The black water is clarified in the secondary clarifier (S02), and the clarified overflow enters the secondary clarifier overflow tank (T02). The fine ash in the black water accumulates at the bottom of the secondary clarifier (S2) and is then sent out for liquid-solid separation; (5) The clarified water at the outlet of the overflow tank of the secondary clarifier is at a temperature of about 40°C. After being pressurized by the clarified water pump (P02), part of it is directly sent to the downstream sewage treatment device as wastewater, and the other part is reused as slag lock hopper flushing water; 3) Control process (1) The black water flow from the first vacuum flash tank (V01) to the second vacuum flash tank (V02) is controlled by the clarified water flow at the outlet of the second clarifier overflow tank; the black water at the first vacuum outlet is the sum of the external wastewater and the slag lock hopper flushing water flow, which controls the treatment scale of the second vacuum flash system; (2) The pressure of the secondary vacuum flash tank is controlled by the steam flow rate at the inlet of the secondary vacuum jet pump (J01); the temperature of the black water after the secondary vacuum flash is controlled so that the discharged wastewater can meet the temperature requirements of direct feed for sewage treatment without being cooled by a cooler.

2. The two-stage vacuum flash evaporation process for gasified black water according to claim 1, characterized in that: The first-stage vacuum flash evaporation clarified water is recycled to the gasification system, and the second-stage vacuum flash evaporation clarified water is discharged to the wastewater treatment unit and used as slag lock hopper flushing water.

3. The two-stage vacuum flash evaporation process for gasified black water according to claim 1, characterized in that: An additional cooler is installed for the discharged wastewater to control the wastewater temperature.

4. The two-stage vacuum flash evaporation process for gasified black water according to claim 1, characterized in that: The flow rate of black water from the first vacuum flash evaporation to the second vacuum flash evaporation is controlled by the flow rate of clarified water from the second vacuum flash evaporation.

5. The two-stage vacuum flash evaporation process for gasified black water according to any one of claims 1 to 4, characterized in that: The flash pressure of the first-stage vacuum flash tank (V01) is -0.056 MPag, and the corresponding flash temperature is 80°C.

6. The two-stage vacuum flash evaporation process for gasified black water according to any one of claims 1 to 4, characterized in that: The flash pressure of the secondary vacuum flash tank (V02) is -0.09 MPag, and the corresponding flash temperature is 40°C.

7. The two-stage vacuum flash evaporation process for gasified black water according to any one of claims 1 to 4, characterized in that: The temperature of clarified water at the outlet of the overflow tank of the first-stage clarifier is 75-85℃.

8. The two-stage vacuum flash evaporation process for gasified black water according to any one of claims 1 to 4, characterized in that: The black water temperature after the first-stage vacuum flash evaporation is 45-90°C, and the black water temperature after the second-stage vacuum flash evaporation is ≤45°C.

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