Coal gasification black water treatment method

Abstract

The invention provides a coal gasification black water treatment method, which belongs to the technical field of coal gasification black water treatment, and comprises the following steps: introducing ash-containing crude synthesis gas discharged from a gasification furnace into pretreatment equipment, mixing the crude synthesis gas with washing water in the pretreatment equipment, and introducing the mixed crude synthesis gas and washing water into a washing tower; the method comprises the following steps: mixing high-temperature and high-pressure black water in a quenching chamber of a gasification furnace with high-temperature and high-pressure black water in a washing tower, directly introducing the mixture into a solid-liquid filtering unit, introducing thick slag slurry in the solid-liquid filtering unit into a buffer tank, and respectively introducing high-temperature and high-pressure filtrate in the solid-liquid filtering unit into the gasification furnace, the washing tower and pretreatment equipment; according to the treatment method, a high-temperature and high-pressure solid-liquid filtering mode is adopted, energy of the high-temperature and high-pressure black water is not wasted, the high-temperature and high-pressure black water can be directly introduced into the gasification furnace, the pretreatment device and the washing tower, energy waste is reduced, and the energy utilization efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of coal gasification black water treatment, and specifically relates to a coal gasification black water treatment method. Background Art

[0002] Coal gasification technology plays a pivotal role in the coal chemical industry. Domestic coal gasification technology mainly adopts pulverized coal gasification process and water-coal slurry process. Both processes will produce high-temperature and high-pressure black water containing a large amount of ash and inorganic salt solid particles in the gasifier quenching chamber and washing tower. The temperature is generally greater than 200 ºC and the pressure is about 4.0 Mpa~6.5 Mpa. In order to reuse this part of water and remove ash and inorganic salt solid particles at the same time, 2~3 levels of flash evaporation operation are generally set up to indirectly recover part of the heat energy and water. The liquid after flash evaporation is discharged from the system by sedimentation, flocculation purification and filtration.

[0003] The specific process is as follows: a part of the gray water in the gray water tank and the newly added desalted water are heated and deoxygenated in the deaerator, and then the heat is recovered through the stripping tower. It contacts with the synthesis gas in the washing tower. The water out of the washing tower is divided into two parts. Most of it is used as quenching water to the quenching chamber. The black water coming out of the quenching chamber and the other part of the black water coming out of the washing tower are sent to the high-pressure flash tower. The liquid after flashing is then sent to the low-pressure flash tower for secondary pressure reduction, cooling and concentration, and then enters the sedimentation tank. After adding flocculants for flocculation and sedimentation purification, most of the gray water is recycled, and a small part of the gray water is treated biochemically. The ash and inorganic salt solids are removed from the system by filtration.

[0004] However, after the flash evaporation treatment, the above treatment process needs to re-pressurize and heat the grey water before it can be introduced into the system to participate in the production and treatment of synthesis gas; therefore, the above process requires cooling and heating operations, resulting in energy waste. Summary of the invention

[0005] The embodiment of the present invention provides a method for treating coal gasification black water, aiming to solve the problem that the treatment process in the prior art may cause energy waste.

[0006] To achieve the above object, the technical solution adopted by the present invention is: A method for treating coal gasification black water is provided, comprising the following steps: The crude synthesis gas containing ash discharged from the gasifier is introduced into a pretreatment device, the crude synthesis gas is mixed with washing water in the pretreatment device, and the mixed crude synthesis gas and washing water are introduced into a washing tower; The high-temperature and high-pressure black water in the gasifier quenching chamber is mixed with the high-temperature and high-pressure black water in the washing tower and directly passed into the solid-liquid filtration unit. The concentrated slurry in the solid-liquid filtration unit is passed into the buffer tank. The high-temperature and high-pressure filtrate in the solid-liquid filtration unit can be respectively passed into the gasifier, the washing tower and the pretreatment equipment.

[0007] In a possible implementation, the raw synthesis gas is discharged after being washed, dust-removed, and saturated and humidified in a washing tower and introduced into a subsequent device.

[0008] In one possible implementation, the solid removal method of the solid-liquid filtration unit is one or more of hydrocyclone separation, gravity sedimentation, filter cloth separation, metal screen screening, ceramic membrane separation, metal powder sintered filter element separation, metal organic composite membrane separation, and ceramic metal composite membrane separation.

[0009] In a possible implementation, when the desolidification method is a metal screen, the accuracy of the metal screen is 30-150 μm; When the desolidification method is a metal powder sintered filter element, the bubble point pressure of the metal powder sintered filter element is 800-10000Pa.

[0010] In a possible implementation, when the high-temperature and high-pressure filtrate in the solid-liquid filtration unit is passed into the washing tower, the high-temperature and high-pressure filtrate is directly passed into the washing tower, or the high-temperature and high-pressure filtrate is mixed with washing water and then passed into the washing tower.

[0011] In a possible implementation, conditioning water is introduced into the solid-liquid filtration unit, and the conditioning water is one or more of desalted water, steam condensate, deoxygenated water, grey water, sedimentation tank recovered water, and filtrate.

[0012] In a possible implementation, a chemical filter aid is introduced into the solid-liquid filtration unit.

[0013] In a possible implementation, the filter of the solid-liquid filtration unit includes a black water inlet, a filtrate outlet, a backwash liquid inlet, and a concentrated slurry outlet.

[0014] In a possible implementation, the filtration form of the solid-liquid filtration unit is one of dead-end filtration, cross-flow filtration and hydrocyclone filtration.

[0015] In a possible implementation, the high-temperature and high-pressure black water is pressurized before solid-liquid filtration is performed on the high-temperature and high-pressure black water; or the high-temperature and high-pressure black water is pressurized after solid-liquid filtration is performed on the high-temperature and high-pressure black water.

[0016] The present invention provides a method for treating coal gasification black water. Compared with the prior art, the treatment method in the present application adopts a high-temperature and high-pressure solid-liquid filtration method. The energy of the high-temperature and high-pressure black water is not wasted and can be directly introduced into the gasification furnace, the pretreatment device and the washing tower; therefore, the above-mentioned treatment method of the present application can reduce energy waste and improve energy utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1A schematic diagram of a process flow of a method for treating coal gasification black water provided by an embodiment of the present invention; Figure 2 A schematic diagram of a dead-end filtration method of a coal gasification black water treatment method provided by an embodiment of the present invention; Figure 3 A schematic diagram of a cross-flow filtration method of a coal gasification black water treatment method provided by an embodiment of the present invention; Figure 4 A schematic diagram of a hydrocyclone filtration method of a coal gasification black water treatment method provided by an embodiment of the present invention; Figure 5 A schematic diagram of membrane filtration and backwashing of a method for treating coal gasification black water provided by an embodiment of the present invention; Figure 6 A schematic diagram of a membrane assembly being divided into two groups when a single solid-liquid filtration unit of a coal gasification black water treatment method provided by an embodiment of the present invention is working.

[0018] Explanation of the accompanying drawings: 1. Gasification furnace; 2. Slag lock bucket; 3. Pretreatment equipment; 4. Washing tower; 5. Solid-liquid filtration unit; 5-1. Black water inlet; 5-2. Filtered liquid outlet; 5-3. Backwash liquid inlet; 5-4. Concentrated slurry outlet; 6. Buffer tank. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] See also Figures 1 to 6 Now, a method for treating coal gasification black water provided by the present invention is described. The method for treating coal gasification black water comprises the following steps: The crude synthesis gas containing ash discharged from the gasifier is introduced into the pretreatment equipment, the crude synthesis gas is mixed with washing water in the pretreatment equipment, and the mixed crude synthesis gas and washing water are introduced into the washing tower; the high-temperature and high-pressure black water in the quenching chamber of the gasifier and the high-temperature and high-pressure black water in the washing tower are mixed and directly introduced into the solid-liquid filtration unit, the concentrated slag slurry in the solid-liquid filtration unit is introduced into the buffer tank, and the high-temperature and high-pressure filtrate in the solid-liquid filtration unit can be introduced into the gasifier, the washing tower and the pretreatment equipment respectively. The filtration form of the solid-liquid filtration unit is one of dead-end filtration, cross-flow filtration and hydrocyclone filtration.

[0021] The present invention provides a method for treating coal gasification black water. Compared with the prior art, the treatment method in the present application adopts a high-temperature and high-pressure solid-liquid filtration method. The energy of the high-temperature and high-pressure black water is not wasted and can be directly introduced into the gasification furnace, the pretreatment device and the washing tower; therefore, the above-mentioned treatment method of the present application can reduce energy waste and improve energy utilization efficiency.

[0022] It should be noted that the main function of the pretreatment equipment is to use liquid to wash the crude synthesis gas before it enters the scrubber. There are two common equipment: one is the Venturi mixer, which mixes the liquid with the crude synthesis gas to improve the scrubbing effect of the subsequent scrubber; the other is the cyclone separator, which uses liquid to wash the crude synthesis gas. Both equipment improve the scrubbing effect of the scrubber through pretreatment methods.

[0023] Exemplarily, the crude synthesis gas containing ash from the gasifier enters the pretreatment equipment, is mixed with washing water and then enters the washing tower. The crude synthesis gas undergoes washing, dust removal, saturation-humidification processes in the washing tower and then enters the subsequent conversion device; the high-temperature and high-pressure black water exiting the gasifier quenching chamber is mixed with the high-temperature and high-pressure black water in the kettle of the washing tower, and directly enters the solid-liquid separation filtration unit without pressure reduction treatment, and the solids in the black water are intercepted. The intercepted solids enter the buffer tank in the form of slurry, and the high-temperature and high-pressure filtrate obtained by solid-liquid separation is directly returned to the washing tower, pretreatment equipment, gasifier, and slag lock hopper for recycling.

[0024] In some embodiments, Figure 1 As shown, when the high-temperature and high-pressure filtrate in the solid-liquid filtration unit is passed into the washing tower, the high-temperature and high-pressure filtrate is directly passed into the washing tower, or the high-temperature and high-pressure filtrate is mixed with washing water and then passed into the washing tower.

[0025] It should be noted that the solid-liquid filtration unit is a liquid phase operation, and the filtrate pressure of the solid-liquid filtration unit meets the requirements for entering the gasifier, pretreatment equipment and washing tower. High-temperature and high-pressure black water continuously enters the solid-liquid filtration unit, and the high-temperature and high-pressure filtrate separated by filtration selectively enters the gasifier quenching ring, pretreatment equipment and washing tower, wherein the way to return to the washing tower is to return alone or mix with washing water; preferably, the way to return the high-temperature and high-pressure filtrate to the washing tower is to return alone.

[0026] In some embodiments, Figure 1 As shown, the high-temperature and high-pressure black water is pressurized before solid-liquid filtration is performed on the high-temperature and high-pressure black water; or the high-temperature and high-pressure black water is pressurized after solid-liquid filtration is performed on the high-temperature and high-pressure black water.

[0027] Exemplarily, in order to ensure that the filtrate produced by the solid-liquid filtration unit has sufficient power to return to the gasifier quenching ring, pretreatment equipment and washing tower, a booster pump is required; preferably, a booster pump is provided before the solid-liquid separation operation.

[0028] In some embodiments, Figure 1 As shown, conditioning water is introduced into the solid-liquid filtration unit, and the conditioning water is one or more of desalted water, steam condensate, deoxygenated water, grey water, sedimentation tank recovered water, and filtrate.

[0029] Exemplarily, coal gasification ash water is a general term in coal gasification equipment and will not be elaborated here; it is necessary to add chemical filter aids and conditioning water in the solid-liquid filtration unit in order to adjust the composition and state of high-temperature and high-pressure black water; preferably, the type of chemical reagent is a flocculant or an inorganic salt dispersant; preferably, the type of conditioning water is one or more of desalted water, steam condensate, and sludge tank recovered water.

[0030] In some embodiments, Figure 1 As shown, the solid removal method of the solid-liquid filtration unit is one or more of hydrocyclone separation, gravity sedimentation, filter cloth separation, metal screen screening, ceramic membrane separation, metal powder sintered filter element separation, metal organic composite membrane separation, and ceramic metal composite membrane separation.

[0031] It should be noted that the above method can intercept solids in high-temperature and high-pressure black water; preferably, one or more of hydrocyclone separation, metal mesh screening, and metal powder sintered filter element separation are used.

[0032] Exemplarily, in order to ensure long-term operation of the equipment, the solid-liquid separation filtration unit is provided with an online regeneration function and an offline regeneration function; preferably, the online regeneration function is online backwashing, and the offline regeneration function is offline chemical cleaning; the cleaning liquid is one or more of HF acid aqueous solution, citric acid aqueous solution, and nitric acid solution.

[0033] In some embodiments, Figure 1 As shown, the filter of the solid-liquid filtration unit includes a black water inlet, a filtrate outlet, a backwash liquid inlet and a concentrated slurry outlet.

[0034] Exemplarily, the filter is provided with an online backflushing function: when there are at least two filters, during the normal filtering process, the filtrate outlet valve is opened, and the backflushing liquid inlet valve is closed; during the backflushing process, the corresponding filtrate outlet valve is closed, and the backflushing liquid inlet valve is opened. When there is only one filter, the filter is provided with at least two groups of filter components, each component is equipped with a filtrate outlet and a backflushing liquid inlet, during normal filtering, all filtrate outlet valves are opened, and the backflushing liquid inlet is closed, when one group of filter components is backflushed, the corresponding filtrate outlet is closed, and the backflushing liquid inlet is opened, after the backflushing is completed, the corresponding filtrate outlet is opened, and the backflushing liquid inlet is closed; the remaining filter components operate in the same manner.

[0035] It should be noted that when the solid-liquid filtration unit is in normal filtration and interception operation, the valve at the concentrated slurry outlet position at the bottom of the filter is opened, and the filter is connected to the buffer tank; when the concentrated slurry in the buffer tank reaches a certain solubility, the filtration operates normally, the valve at the concentrated slurry outlet position at the bottom of the filter is closed, and the connection with the buffer tank is disconnected; after the buffer tank is depressurized and the concentrated slurry is discharged, the buffer tank is filled with low-temperature water and the pressure is increased to normal pressure, and then the filter is reconnected to the buffer tank so that the buffer tank continues to receive the concentrated slurry in the filter.

[0036] Exemplarily, the raw syngas containing ash from the gasifier enters the venturi scrubber, is mixed with washing water and then enters the washing tower. The syngas enters the subsequent conversion device after washing, dust removal, saturation-humidification process in the washing tower; the high-temperature and high-pressure black water from the gasifier quenching chamber and the washing tower kettle is mixed and directly enters the solid-liquid filtration unit without depressurization treatment, desalted water and dispersant are added, and then the ash and inorganic salt solids in the black water are removed after multi-stage filtration through metal screens and metal filter elements, and enters the buffer tank in the form of slag slurry, and the deoxygenated water is heated and discharged from the system under pressure. The high-temperature and high-pressure filtrate is returned to the gasifier quenching ring and the venturi scrubber as quenching water and washing water respectively. Among them, the accuracy of the metal screen is 30~150 μm, the bubble point pressure of the metal filter element is 800~10000 Pa, and the obtained high-temperature and high-pressure filtered water pressure is 4 Mpa and the temperature is 200 ºC.

[0037] Exemplarily, the raw synthesis gas containing ash and slag from the gasifier is mixed with washing water in the hydrocyclone separator and then enters the washing tower. The synthesis gas enters the subsequent conversion device after washing, dust removal, saturation-humidification process in the washing tower; the high-temperature and high-pressure black water from the gasifier quenching chamber and the washing tower kettle is mixed and directly enters the solid-liquid filtration unit without depressurization treatment, and desalted water and dispersant are added. After multi-stage filtration through metal screen and metal filter element, the ash and inorganic salt solids in the black water are removed, and the black water enters the buffer tank in the form of slag slurry, and the deoxygenated water is heated and discharged from the system under pressure. A part of the high-temperature and high-pressure filtrate enters the gasifier quenching ring as non-quenching water, a part enters the hydrocyclone separator, and a part enters the washing tower as washing water. Among them, the accuracy of the metal screen is 30~150 μm, the bubble point pressure of the metal filter element is 800~10000 Pa, and the obtained high-temperature and high-pressure filtered water pressure is 4 Mpa and the temperature is 200 ºC.

[0038] Exemplarily, the raw synthesis gas containing ash from the gasifier is mixed with washing water in the cyclone separator and then enters the washing tower. The synthesis gas enters the subsequent conversion device after washing, dust removal, saturation-humidification process in the washing tower; the high-temperature and high-pressure black water from the gasifier quenching chamber and the washing tower kettle is mixed and directly enters the solid-liquid filtration unit without depressurization treatment, desalted water and flocculant are added, and the ash and inorganic salt solids in the black water are removed after filtering through the metal filter element, and enter the buffer tank in the form of slag slurry, and the deoxygenated water is heated and discharged from the system under pressure. A part of the high-temperature and high-pressure filtrate does not enter the gasifier quenching ring as quenching water, and the high-temperature and high-pressure filtrate returns to the gasifier quenching ring and the Venturi scrubber as quenching water and washing water respectively. Among them, the bubble point pressure of the metal filter element is 3000-5000 Pa, and the obtained high-temperature and high-pressure filtered water pressure is 4 Mpa and the temperature is 200 ºC.

[0039] The above configuration of this application has the following beneficial effects: 1. After sufficient separation and purification of high-temperature and high-pressure black water, ultra-low or even zero discharge of black water is achieved, thus avoiding waste of water resources. At the same time, the water quality of the filtrate is greatly improved compared with the gray water obtained by the original technology, thus improving the operation and washing effect of the gasifier and washing tower, and avoiding serious damage to the internal structure of the equipment and pipelines.

[0040] 2. Compared with the treatment methods in the prior art, this application reduces the usage of chemical drugs such as flocculants and dispersants, saving operating costs.

[0041] 3. Compared with the existing black water treatment technology that undergoes multi-stage flash evaporation, cooling and pressure reduction before solid-liquid separation, the black water treatment unit has simple equipment, continuous and stable operation, and low operating costs.

[0042] 4. It is universally applicable to the entrained-bed coal gasification process.

[0043] Embodiment 1: As shown in Table 1, the filtration accuracy of the metal mesh is 30 μm, the filtration method is dead-end filtration, the filtration temperature is 180° C., and the nephelometric turbidity unit (NTU) of the filtrate after filtration is 1.79.

[0044] Comparative Example 1: As shown in Table 1, the filtration accuracy of the metal screen is 200 μm, the filtration method is dead-end filtration, the filtration temperature is 180° C., and the scattering turbidity of the filtrate after filtration is greater than 500.

[0045] Comparative Example 2: As shown in Table 1, the filtration accuracy of the metal screen is 200 μm, the filtration method is dead-end filtration, the filtration temperature is 210° C., and the scattering turbidity of the filtrate after filtration is greater than 500.

[0046] Therefore, when the filtration accuracy of the metal screen is 200μm, no matter the filtration temperature is 180℃ or 210℃, the scattering turbidity of the filtrate after filtration cannot meet the requirements; when the metal screen is 30μm, the scattering turbidity of the filtrate after filtration can meet the requirements.

[0047] Embodiment 2: As shown in Table 1, the bubble point pressure of the metal powder sintered filter element is 5000 Pa, the filtration method is cross-flow filtration, the filtration temperature is 180°C, and the scattering turbidity of the filtrate after filtration is 1.12.

[0048] Comparative Example 3: As shown in Table 1, the bubble point pressure of the metal powder sintered filter element is 400 Pa, the filtration method is dead-end filtration, the filtration temperature is 180°C, and the scattering turbidity of the filtrate after filtration is 325.

[0049] Comparative Example 4: As shown in Table 1, the bubble point pressure of the metal powder sintered filter element is 400 Pa, the filtration method is cross-flow filtration, the filtration temperature is 210 ° C, and the scattering turbidity of the filtrate after filtration is 431.

[0050] Therefore, when the bubble point pressure of the metal powder sintered filter element is 400Pa, the filtration method and filtration temperature have little effect on the filtration effect, and the scattering turbidity of the filtrate after filtration cannot meet the requirements; when the bubble point pressure of the metal powder sintered filter element is 5000Pa, the scattering turbidity of the filtrate after filtration can meet the requirements.

[0051] Table 1 Comparative test of metal screen and metal sintered filter element

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating coal gasification black water, characterized in that: The following steps are involved: The crude synthesis gas containing ash discharged from the gasifier is introduced into a pretreatment device, the crude synthesis gas is mixed with washing water in the pretreatment device, and the mixed crude synthesis gas and washing water are introduced into a washing tower; The high-temperature and high-pressure black water in the gasifier quenching chamber is mixed with the high-temperature and high-pressure black water in the washing tower and directly passed into the solid-liquid filtration unit. The concentrated slurry in the solid-liquid filtration unit is passed into the buffer tank. The high-temperature and high-pressure filtrate in the solid-liquid filtration unit can be respectively passed into the gasifier, the washing tower and the pretreatment equipment.

2. A method for treating coal gasification black water according to claim 1, characterized in that: The raw synthesis gas is discharged from the scrubbing tower after being scrubbed, dust-removed, saturated and humidified, and then introduced into subsequent devices.

3. A method for treating coal gasification black water according to claim 1, characterized in that: The solid removal method of the solid-liquid filtration unit is one or more of hydrocyclone separation, gravity sedimentation, filter cloth separation, metal screen screening, ceramic membrane separation, metal powder sintered filter element separation, metal organic composite membrane separation, and ceramic metal composite membrane separation.

4. A method for treating coal gasification black water as claimed in claim 3, characterized in that: When the desolidification method is a metal screen, the accuracy of the metal screen is 30~150 μm; When the desolidification method is a metal powder sintered filter element, the bubble point pressure of the metal powder sintered filter element is 800 to 10,000 Pa.

5. The method for treating coal gasification black water according to claim 1, characterized in that: When the high-temperature and high-pressure filtrate in the solid-liquid filtration unit is passed into the washing tower, the high-temperature and high-pressure filtrate is directly passed into the washing tower, or the high-temperature and high-pressure filtrate is mixed with washing water and then passed into the washing tower.

6. A method for treating coal gasification black water according to claim 1, characterized in that: Conditioning water is introduced into the solid-liquid filtration unit, and the conditioning water is one or more of desalted water, steam condensate, deoxygenated water, grey water, sedimentation tank recovered water, and filtrate.

7. A method for treating coal gasification black water according to claim 1 or 6, characterized in that: A chemical filter aid is introduced into the solid-liquid filtration unit.

8. The method for treating coal gasification black water according to claim 1, characterized in that: The filter of the solid-liquid filtration unit includes a black water inlet, a filtrate outlet, a backwash liquid inlet and a concentrated slurry outlet.

9. A method for treating coal gasification black water according to claim 1, characterized in that: The filtration form of the solid-liquid filtration unit is one of dead-end filtration, cross-flow filtration and hydrocyclone filtration.

10. The method for treating coal gasification black water according to claim 1, characterized in that: Before the high-temperature and high-pressure black water is subjected to solid-liquid filtration, the high-temperature and high-pressure black water is pressurized; or after the high-temperature and high-pressure black water is subjected to solid-liquid filtration, the high-temperature and high-pressure black water is pressurized.

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