Black water treatment methods

Abstract

The invention discloses a black water treatment method, which comprises the following steps: introducing black water into a first evaporative hot water tower, introducing gray water obtained after steam separation at the top of the first evaporative hot water tower into a storage container, and introducing black water at the bottom of the first evaporative hot water tower into a second evaporative hot water tower; introducing gray water obtained after steam separation at the top of the second evaporative hot water tower into a storage container, and introducing black water at the bottom of the second evaporative hot water tower into a vacuum flash tank; introducing gray water obtained after steam separation at the top of the vacuum flash tank into a storage container, and introducing black water at the bottom of the vacuum flash tank into a clarification device to obtain clarified liquid; introducing the clarified liquid in the clarification device and / or gray water in part of the storage container into the second evaporative hot water tower; introducing gray water generated by the second evaporative hot water tower into the first evaporative hot water tower. The method of the invention improves the water-gas ratio of the synthesis gas in the boundary area of ​​the gasification device, fully recovers the heat of the flash steam of the evaporative hot water tower, and reduces the consumption of circulating cooling water.

Description

Technical Field

[0001] The invention relates to a black water treatment method. Background Art

[0002] The entrained-flow gasification process has been widely used in recent years due to its high gasification temperature, wide range of raw material adaptability, large operating load, and high carbon conversion rate. It is the preferred process for large-scale gasification. The entrained-flow gasification process for carbon-containing raw materials (coal, petroleum coke and heavy oil) mainly includes three parts: entrained-flow gasification, preliminary purification of synthesis gas and black water treatment system.

[0003] Among them, in the entrained flow gasification, the carbon-containing raw materials react with the gasifying agent (air, oxygen-enriched air or oxygen) in the entrained flow gasifier with the participation of water vapor or water to produce a crude synthesis gas containing solid particles (mainly CO, H2 and CO2, etc.), the temperature of which is generally 1200-1600°C. In order to meet the requirements of the downstream CO conversion device, the solid particles in the crude synthesis gas need to be removed. Generally, the dust content of the synthesis gas from the gasification device-synthesis gas preliminary purification unit-synthesis gas washing tower is required to be less than 1mg / Nm 3 , for this purpose, a large amount of water is needed to wash the synthesis gas, especially when the raw material of the gasification unit is a carbonaceous material with a high ash content, the amount of synthesis gas washing water required is very large. The water after washing the synthesis gas generally contains a large amount of ash and has a high solid content, which is called black water. The entrained flow gasification process will produce a large amount of black water with a high temperature (generally 200-250°C). Since black water needs to be treated before it can be returned to the synthesis gas treatment unit for reuse, it is very important to improve the energy utilization efficiency in the black water treatment process, recover the heat of high-temperature black water, and reduce energy consumption.

[0004] The three-stage flash black water treatment system of patent CN101298569A will produce a large amount of low-pressure flash gas, which requires a large amount of circulating water for cooling. Specifically, its black water treatment system consists of a three-stage flash system of an evaporative hot water tower, a low-pressure flash tank and a vacuum flash tank. During the treatment process, the high-temperature black water from the gasifier quenching chamber, the cyclone separator and the bottom of the water washing tower is sent to the evaporative hot water tower for flash evaporation and direct contact with the circulating gray water for heat exchange, while allowing part of the acidic gas to be resolved. The bottom concentrated black water is further concentrated through low-pressure and vacuum flash evaporation, and then after the fine slag is separated out in the clarification tank, the clarified gray water is further recycled, and part of the gray water is discharged as wastewater. The energy utilization in this method is not sufficient, and the temperature of the gray water out of the evaporative hot water tower is still between 140°C and 170°C.

[0005] In addition, when recycled high-temperature ash water is used as washing water, if its temperature is too low, the synthesis gas temperature out of the washing tower will be correspondingly low, and its water-gas ratio will also be correspondingly low, which cannot meet the requirements of the subsequent CO conversion device.

[0006] Therefore, under the global low-carbon and environmentally friendly development requirements, reducing the energy and water consumption of carbon-containing raw material gasification processes and improving system energy efficiency are the inevitable choices for the development of gasification processes. It is urgent to develop a black water treatment system that can match the temperature of the high-temperature ash water circulating back to the scrubber with the requirements of the downstream CO2 shift unit for the synthesis gas water-gas ratio, while reducing the consumption of the required circulating cooling water and improving energy utilization. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the problems in the prior art that the high-temperature ash water temperature of the circulating washing tower of the black water treatment system does not match the requirements of the downstream CO conversion device for the water-gas ratio of the synthesis gas, the large amount of cooling circulating water required for the flash gas, and the high energy consumption, and provide a black water treatment method. The present invention provides a method for treating black water by arranging a plurality of separation devices in series with gradually reduced pressures and making the obtained ash water flow in reverse, thereby increasing the temperature of the circulating ash water of the gasification device, thereby improving the utilization efficiency of the high-level energy of the gasification system, increasing the water-gas ratio of the synthesis gas of the gasification device out of the existing synthesis gas washing process, and reducing the consumption of circulating cooling water of the black water treatment unit, thereby achieving the purpose of efficient utilization of materials and energy in the entrained bed gasification process.

[0008] The present invention solves the above technical problems through the following technical solutions:

[0009] The present invention provides a black water treatment method, which comprises the following steps:

[0010] The black water is introduced into the first evaporative hot water tower, the gray water obtained after the steam at the top of the first evaporative hot water tower is separated is introduced into the storage container, and the black water at the bottom of the first evaporative hot water tower is introduced into the second evaporative hot water tower;

[0011] The grey water obtained after the separation of the top vapor of the second evaporative hot water tower is introduced into the storage container, and the black water at the bottom of the second evaporative hot water tower is introduced into the vacuum flash tank;

[0012] The grey water obtained after the steam separation at the top of the vacuum flash tank is introduced into the storage container, and the black water at the bottom of the vacuum flash tank is introduced into a clarification device to obtain clarified liquid;

[0013] introducing the clarified liquid in the clarification device and / or part of the grey water in the storage container into the second evaporative hot water tower;

[0014] The grey water produced by the second evaporative hot water tower is introduced into the first evaporative hot water tower;

[0015] The pressure of the first evaporative hot water tower is 0.8-2.0 MPag;

[0016] The pressure of the second evaporative hot water tower is 0.1-0.5 MPag;

[0017] The pressure of the vacuum flash tank is -0.09 MPag to -0.05 MPag.

[0018] In the present invention, the temperatures of the first evaporative hot water tower, the second evaporative hot water tower and the vacuum flash tank can be conventional in the art. Generally, the temperature of the first evaporative hot water tower is 170-215°C; the temperature of the second evaporative hot water tower is 115-160°C; the temperature of the vacuum flash tank is 45-85°C.

[0019] In the present invention, the black water may be conventional in the art. Generally, the black water is a liquid rich in ash and may come from one or more of the gasifier quenching chamber, the cyclone separator or the bottom of the water scrubber. Specifically, the black water is a liquid containing impurities such as solid particles, suspended matter or colloids.

[0020] In the present invention, the grey water may be conventional in the art. Generally, the grey water may be a liquid obtained by flash evaporation of the black water, the solid content of which is lower than the solid content of the black water.

[0021] In the present invention, preferably, low-pressure deoxygenated water or desalted water is introduced into the top of the second evaporative hot water tower.

[0022] The low-pressure deoxygenated water may be fresh water from which oxygen is removed as is conventionally available in the art. The temperature of the low-pressure deoxygenated water may generally be 104° C., and the pressure of the low-pressure deoxygenated water may generally be 0.4 to 0.8 Mpag.

[0023] The desalted water may be water conventionally used in the art from which strong electrolytes that are easily removed are removed or reduced to a certain extent. The residual salt content in the desalted water may generally be 1 to 5 mg / L.

[0024] Adding the deoxygenated water or the desalted water into the second evaporative hot water tower is beneficial to fully utilizing the flash steam of the second evaporative hot water tower.

[0025] In the present invention, the separation of the top vapor of the first evaporative hot water tower, the top vapor of the second evaporative hot water tower, and the top vapor of the vacuum flash tank before entering the storage container can be conventional in the art, and generally, the top vapor can be separated into gas and liquid independently.

[0026] The gas-liquid separation device can be a conventional gas-liquid separation device in the art. Preferably, the gas-liquid separation operation is performed in a separation tank.

[0027] In the present invention, preferably, before separating the top vapor of the first evaporative hot water tower, the top vapor of the second evaporative hot water tower, and the top vapor of the vacuum flash tank, the top vapor of the first evaporative hot water tower, the top vapor of the second evaporative hot water tower, and the top vapor of the vacuum flash tank are cooled independently.

[0028] In the present invention, preferably, 10-30% of the grey water in the storage container is discharged as waste water after cooling, and the percentage is volume percentage.

[0029] In the present invention, the cooling device can be a conventional device for reducing temperature in the art. Preferably, the cooling operation is performed in a heat exchanger.

[0030] Preferably, the cooling medium is each independently water.

[0031] In the present invention, preferably, the sediment at the bottom of the clarification device is introduced into a downstream processing device.

[0032] In the present invention, preferably, the black water treatment method further comprises introducing the grey water generated by the first evaporative hot water tower into a synthesis gas washing unit.

[0033] In the present invention, preferably, the equipment for introducing the sediment at the bottom of the clarification device into the downstream processing device, the equipment for introducing part of the gray water in the storage container into the second evaporative hot water tower, the equipment for introducing the gray water generated by the second evaporative hot water tower into the first evaporative hot water tower, and the equipment for introducing the gray water generated by the first evaporative hot water tower into the synthesis gas washing unit are each independently a pump.

[0034] In the present invention, the storage container can be a conventional container for storing substances in the art. Preferably, the storage container is a tank.

[0035] In the present invention, the clarification device can be a conventional device in the art for removing suspended matter and colloids in water. Preferably, the clarification device is a clarification tank.

[0036] In the present invention, preferably, the number of the evaporative hot water towers is 2 to 3.

[0037] In the present invention, preferably, the number of the vacuum flash tanks is 1 to 2.

[0038] In the present invention, preferably, the pressure difference between the successive evaporation hot water towers is ≥ 0.5 MPa. This is conducive to increasing the temperature difference between the gray water from the next stage evaporation hot water tower and the steam in the previous stage evaporation hot water tower, so that the two can fully exchange heat and further utilize the flash steam capacity of the evaporation hot water tower.

[0039] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0040] The positive and progressive effects of the present invention are:

[0041] (1) The present invention provides a series of separation devices with gradually reduced pressure in the black water treatment unit, and makes the separated gray water countercurrently rise in the evaporation hot water tower step by step to increase the temperature of the gray water, thereby improving the water-gas ratio of the synthesis gas in the boundary area of ​​the gasification device (i.e., the volume ratio of water vapor to dry gas in the synthesis gas), which is beneficial to the operation of the downstream conversion unit.

[0042] (2) In the present invention, the pressure of the first evaporative hot water tower is higher than that of the second evaporative hot water tower. When the gray water in the storage container flows back to the second evaporative hot water tower, the flash steam in the tower is first preheated; the gray water then enters the first evaporative hot water tower, and the flash steam in the tower reheats it; this is beneficial to recover the heat of the flash steam in the evaporative hot water tower.

[0043] (3) In the present invention, the amount of steam at the top of the tower is reduced, the flash steam is fully utilized, and the consumption of circulating cooling water is greatly reduced. The method can fully utilize the energy of the evaporation device, reduce consumption, and achieve energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the process of the black water treatment system in Example 1 of the present invention.

[0045] Reference numerals:

[0046] 1- the first evaporation hot water tower;

[0047] 2- Second evaporation hot water tower;

[0048] 3-Vacuum flash tank;

[0049] 4- Clarification tank;

[0050] 5-Gray water tank;

[0051] 6-separation tank; 61-first separation tank; 62-second separation tank; 63-third separation tank;

[0052] 7-heat exchanger; 71-first heat exchanger; 72-second heat exchanger; 73-third heat exchanger; 74-fourth heat exchanger;

[0053] 8-pump; 81-first pump; 82-first pump; 83-third pump; 84-fourth pump;

[0054] S1-black water; S11-first black water; S12-second black water; S13-third black water; S14-fourth black water;

[0055] S2-flash steam; S21-first flash steam; S22-second flash steam; S23-third flash steam;

[0056] S3-uncondensed gas; S31-first uncondensed gas; S32-second uncondensed gas; S33-third uncondensed gas;

[0057] S4-condensed liquid; S41-first condensed liquid; S42-second condensed liquid; S43-third condensed liquid;

[0058] S5-grey water; S51-first grey water; S52-second grey water; S53-third grey water;

[0059] S6-deoxygenated water;

[0060] S7-clarified liquid;

[0061] S8 - Slurry. DETAILED DESCRIPTION

[0062] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0063] Example 1

[0064] Embodiment 1 of the present invention provides a black water treatment method, wherein the flow diagram of the black water treatment system is as follows: Figure 1 shown.

[0065] The first black water S11 from the gasifier and the washing unit is introduced into the first evaporation hot water tower 1, the pressure of the first black water S11 is 6.5MPag, the operating pressure of the first evaporation hot water tower 1 is 1.28MPag, and the operating temperature of the first evaporation hot water tower 1 is 189°C. After flash evaporation in the first evaporation hot water tower 1, the first flash gas S21 at the top of the tower is cooled by the first heat exchanger 71 and separated in the first separation tank 61, wherein the first condensed liquid S41 enters the gray water tank 5, and the first uncondensed gas S31 goes to the flare; the second black water S12 flashed and concentrated by the first evaporation hot water tower 1 is introduced into the second evaporation hot water tower 2 for flash evaporation, the operating pressure of the second evaporation hot water tower 2 is 0.25MPag, and the operating temperature of the second evaporation hot water tower 2 is 139°C, The second flash gas S22 at the top of the tower is cooled by the second heat exchanger 72 and separated in the second separation tank 62, wherein the second condensed liquid S42 enters the gray water tank 5, and the second uncondensed gas S32 goes to the flare; the third black water S13 further concentrated after flashing in the second evaporation hot water tower 2 is passed into the vacuum flash tank 3 for flashing, the operating pressure of the vacuum flash tank 3 is -0.056MPag, and the operating temperature of the vacuum flash tank 3 is 79°C. The third flash gas S23 at the top is cooled by the third heat exchanger 73 and separated in the third separation tank 63, wherein the third condensed liquid S43 enters the gray water tank 5, and the third uncondensed gas S33 goes to the vacuum extractor; the fourth black water S14 at the bottom of the vacuum flash tank is passed into the clarification tank 4 for clarification. The upper clarified liquid S7 in the clarification tank 4 is passed into the gray water tank 5, and the bottom precipitated and concentrated slurry S8 is sent to the downstream treatment device through the third pump 83. 70-90% (volume percentage) of the third gray water S53 in the gray water tank 5 is circulated back to the second evaporative hot water tower 2 through the fourth pump 84, and 10-30% (volume percentage) of the third gray water S53 is discharged as waste water after being cooled by the fourth heat exchanger 74. In all the above heat exchangers, the cooling medium is water. In order to maintain the water balance of the system, deoxygenated water S6 is introduced into the second evaporative hot water tower 2. The temperature of the deoxygenated water is 104°C and the pressure is 0.5MPag. The second gray water S52 produced by the second evaporative hot water tower 2 is pressurized by the second pump 82 and circulated back to the first evaporative hot water tower 1. The first gray water S51 produced after flash evaporation in the first evaporative hot water tower 1 is circulated back to the upstream synthesis gas washing unit through the first pump 81. The pressure of the first gray water S51 is 6.8MPag.

[0066] The present invention arranges separation equipment in series and with gradually reduced pressure in a black water treatment system, so that the black water is evaporated to obtain gray water, and then the gray water is countercurrently directed into a second evaporation hot water tower and a first evaporation hot water tower in sequence, so as to achieve step-by-step temperature increase of the gray water, thereby increasing the water-gas ratio of the synthesis gas in the boundary area of ​​the gasification device, which is beneficial to the operation of the downstream conversion unit; recovering the heat of the flash steam in the evaporation hot water tower; and reducing the consumption of circulating cooling water.

[0067] The specific data of the main logistics of this embodiment 1 are shown in Table 1.

[0068] Table 1 Main logistics data of Example 1

[0069]

[0070] When the amount of quenching water, washing water and waste water remains basically unchanged, the temperature, pressure and flow rate of the first black water S11 obtained are also basically the same. From the data in Table 1, it can be seen that the temperature of the first gray water S51 leaving the first evaporation hot water tower is 189°C; after the first gray water S51 leaving the first evaporation hot water tower is introduced into the upstream synthesis gas washing tower, the water-gas ratio of the synthesis gas finally obtained is 0.94; the amount of uncondensed steam generated by the three-stage flash evaporation (the total flow rate of S21, S22 and S23) is 14.5t / h.

[0071] Comparative Example 1

[0072] To further illustrate the effects of the present invention in terms of increasing the ash water temperature, increasing the water-gas ratio of the synthesis gas, and reducing the energy consumption, comparative example 1 adopts a traditional three-stage flash evaporation treatment method, wherein, during the traditional three-stage flash evaporation treatment, the operating temperature of the first evaporation hot water tower is 164°C, and the operating pressure is 0.66Mpg; the operating temperature of the second evaporation hot water tower is 139°C, and the operating pressure is 0.25Mpg; the operating temperature of the vacuum flash tank is 79°C, and the operating pressure is -0.056Mpg.

[0073] The specific data of the main logistics of this comparative example 1 are shown in Table 2.

[0074] Table 2 Main logistics data of comparative example 1

[0075]

[0076] When the amount of quenching water, washing water and waste water remains basically unchanged, the temperature, pressure and flow rate of the first black water S11 obtained are also basically the same. It can be seen from the data in Table 2 that the temperature of the first gray water S51 out of the first evaporative hot water tower is 164°C, which is 25°C lower than that of Example 1; after the first gray water S51 out of the first evaporative hot water tower is introduced into the upstream synthesis gas washing tower, the water-gas ratio of the synthesis gas finally obtained is 0.81, which is 0.13 lower than that of Example 1; the amount of uncondensed steam generated by the three-stage flash evaporation (the total flow rate of S21, S22 and S23) is 22.1t / h, which is 7.6t / h higher than that of Example 1, greatly increasing the use of circulating cooling water.

[0077] As can be seen from the above, compared with Comparative Example 1, Example 1 increases the gray water temperature out of the first evaporative hot water tower, increases the water-gas ratio of the synthesis gas, and reduces the amount of tower top steam and the amount of circulating cooling water used.

[0078] Comparative Example 2

[0079] To further illustrate the effects of the present invention in terms of increasing the ash water temperature, increasing the water-gas ratio of the synthesis gas, and reducing the energy consumption, this comparative example 2 is still carried out according to the following method: Figure 1 The system process shown is for black water treatment, and only the operating pressures of the first evaporation hot water tower and the vacuum flash tank are changed, and the other conditions are the same as those in Example 1.

[0080] Specifically, the operating pressure of the first evaporative hot water tower is 0.66 MPag, the operating pressure of the second evaporative hot water tower is 0.25 MPag, and the operating pressure of the vacuum flash tank is -0.056 MPag.

[0081] The specific data of the main logistics of this comparative example 2 are shown in Table 3.

[0082] Table 3 Main logistics data of comparative example 2

[0083]

[0084] When the amount of quenching water, washing water and waste water remains basically unchanged, the temperature, pressure and flow rate of the first black water S11 obtained are also basically the same. It can be seen from the data in Table 3 that the temperature of the first gray water S51 out of the first evaporative hot water tower is 169°C, which is 20°C lower than that of Example 1; after the first gray water S51 out of the first evaporative hot water tower is introduced into the upstream synthesis gas washing tower, the water-gas ratio of the synthesis gas finally obtained is 0.84, which is 0.10 lower than that of Example 1; the amount of uncondensed steam generated by the three-stage flash evaporation (the total flow rate of S21, S22 and S23) is 20.7t / h, which is 6.2t / h higher than that of Example 1, and the use of circulating cooling water is increased.

[0085] It can be seen that, compared with Example 1, Comparative Example 2 reduces the pressure of the first-stage evaporative hot water tower, so that the amount of steam flashed by the first-stage evaporative hot water tower is large, but it is not fully utilized. At the same time, the low pressure also thermodynamically limits the temperature of the gray water generated by the first-stage evaporative hot water tower, resulting in poor effects in increasing the gray water temperature, increasing the water-gas ratio of the synthesis gas, and reducing energy consumption.

Claims

1. A method for treating black water, characterized in that: It includes the following steps: The black water is introduced into the first evaporative hot water tower, the gray water obtained after the steam at the top of the first evaporative hot water tower is separated is introduced into the storage container, and the black water at the bottom of the first evaporative hot water tower is introduced into the second evaporative hot water tower; The grey water obtained after the separation of the top vapor of the second evaporative hot water tower is introduced into the storage container, and the black water at the bottom of the second evaporative hot water tower is introduced into the vacuum flash tank; The grey water obtained after the steam separation at the top of the vacuum flash tank is introduced into the storage container, and the black water at the bottom of the vacuum flash tank is introduced into a clarification device to obtain clarified liquid; introducing the clarified liquid in the clarification device and / or part of the grey water in the storage container into the second evaporative hot water tower; The grey water produced by the second evaporative hot water tower is introduced into the first evaporative hot water tower; The pressure of the first evaporative hot water tower is 0.8-2.0 MPag; the temperature of the first evaporative hot water tower is 170-215°C; The pressure of the second evaporative hot water tower is 0.1-0.5 MPag; the temperature of the second evaporative hot water tower is 115-160°C; The pressure of the vacuum flash tank is -0.09MPag~-0.05Mpag; the temperature of the vacuum flash tank is 45~85℃; Before separating the top vapor of the first evaporative hot water tower, the top vapor of the second evaporative hot water tower, and the top vapor of the vacuum flash tank, the top vapor of the first evaporative hot water tower, the top vapor of the second evaporative hot water tower, and the top vapor of the vacuum flash tank are cooled independently; the cooling operation is carried out in a heat exchanger; and the cooling medium is independently water.

2. The black water treatment method according to claim 1, characterized in that: Low-pressure deoxygenated water or desalted water is introduced into the top of the second evaporative hot water tower; And / or, the sediment at the bottom of the clarification device is introduced into a downstream processing device.

3. The black water treatment method according to claim 1, characterized in that: The top vapor of the first evaporation hot water tower, the top vapor of the second evaporation hot water tower, and the top vapor of the vacuum flash tank are each independently subjected to gas-liquid separation before entering the storage container; The gas-liquid separation operation is carried out in a separation tank.

4. The black water treatment method according to claim 1, characterized in that: 10-30% of the grey water in the storage container is discharged as waste water after cooling, and the percentage is volume percentage.

5. The black water treatment method according to claim 1, characterized in that: The black water treatment method further includes introducing the grey water generated by the first evaporative hot water tower into a synthesis gas scrubbing unit.

6. The black water treatment method according to claim 5, characterized in that: The device for introducing the sediment at the bottom of the clarification device into the downstream processing device, the device for introducing part of the gray water in the storage container into the second evaporative hot water tower, the device for introducing the gray water produced by the second evaporative hot water tower into the first evaporative hot water tower, and the device for introducing the gray water produced by the first evaporative hot water tower into the synthesis gas washing unit are each independently a pump.

7. The black water treatment method according to claim 1, characterized in that: The storage container is a tank; And / or, the clarification device is a clarification tank.

8. The black water treatment method according to claim 1, characterized in that: The number of the evaporative hot water towers is 2 to 3; And / or, the number of the vacuum flash tanks is 1 to 2.

9. The black water treatment method according to claim 1, characterized in that: The pressure difference between the step-by-step evaporation hot water towers is ≥0.5MPa.

Images