Coal gasification black water heat gradient utilization and residual pressure power generation integrated process

Abstract

The invention discloses a coal gasification black water heat gradient utilization and residual pressure power generation integrated process, and belongs to the technical field of coal gasification. Black water with the temperature of 200 DEG C and the pressure of 4.0 MPa sequentially passes through three stages of heat exchangers, wherein the first stage heat exchanger exchanges heat with desalted water to generate steam with the pressure of 1.0 MPa (the temperature is controlled to be 180 + / -5 DEG C The second stage exchanges heat with grey water to output grey water of 150 DEG C (the temperature is controlled to be 150 + / -2 DEG C), and the grey water is increased to 5.5 MPa and sent to a washing tower; third-stage preheating desalted water (the temperature is controlled to be 70 + / -5 DEG C); after heat exchange, the black water is subjected to power generation and pressure reduction to normal pressure through a screw expander and enters a settling tank for separation; supernate flows back to the ash water tank, and part of ash water is circulated to the second-stage heat exchanger. A traditional flash evaporation process is replaced with three-stage heat exchange, heat gradient utilization and pressure energy power generation are achieved, the number of equipment is reduced, energy consumption is reduced, and meanwhile the operation reliability is improved through the anti-blocking heat exchanger and the standby circulating pump.

Description

Technical Field

[0001] The present invention relates to the technical field of coal gasification, and in particular to an integrated process for stepwise utilization of heat from coal gasification black water and power generation with residual pressure. Background Art

[0002] In modern coal gasification technology, the mainstream process uses a downward water-quenched pressurized gasification device, and the black water is generally recycled through a two-stage, three-stage, or four-stage flash evaporation process to recover heat. Specifically, the synthesis gas produced after the gasifier reaction is quenched, separated, and scrubbed before being sent to the post-processing system. The black water (200°C, 4.0MPa) produced by quenching, separation, and scrubbing enters a high-pressure flash tank for flash evaporation (0.6MPa, 159°C). The flashed black water then enters a low-pressure flash tank for flash evaporation (0.15MPa, 127°C). The black water from the low-pressure flash tank then enters a vacuum flash tank for flash evaporation (-0.04MPa, 80°C). The black water from the vacuum flash evaporation enters a settling tank for sedimentation. The black water at the bottom of the sedimentation tank is filtered to produce coal slime and the supernatant is returned to the ash water tank. A low-pressure ash water pump is installed at the bottom of the ash water tank. Part of it is sent to sewage treatment and part is sent to the atmospheric pressure deoxygenation tank for deoxygenation. Deoxygenation is carried out using low-pressure flash steam with a temperature of ≥100°C. The deoxygenated water after deoxygenation enters the flash steam scrubber and contacts with the high-pressure flash steam in reverse to recover heat. The temperature is about 150°C. The ash water after heat recovery is pressurized as washing water for synthesis gas. Part of the washing water is sent to the high-pressure flash tank and part is sent to the gasifier for use as synthesis gas quenching water. The black water after quenching enters the high-pressure flash tank to form a cycle.

[0003] However, the above traditional process wastes the heat of the black water entering the high-pressure flash tank. Based on this, the present invention redesigns the black water heat utilization process and proposes a process that integrates the cascade utilization of coal gasification black water heat and residual pressure power generation. Summary of the Invention

[0004] The purpose of the present invention is to provide an integrated process for the cascade utilization of heat from coal gasification black water and waste pressure power generation, so as to solve the problem of imperfect black water heat utilization in the current multi-stage flash evaporation process, fully recycle and utilize the heat, and achieve the purpose of reducing energy consumption and simplifying the process.

[0005] To achieve the above objectives, the present invention provides an integrated process for cascade utilization of coal gasification black water heat and waste pressure power generation, comprising the following steps:

[0006] S1, pass 200℃, 4.0MPa black water through three-stage black water heat exchanger in sequence;

[0007] a) Exchange heat with desalted water in the first-stage black water heat exchanger, and the by-product 1.0 MPa saturated steam enters the pipe network;

[0008] b) In the secondary black water heat exchanger, the black water exchanges heat with the gray water from the low-pressure gray water pump. After the gray water is heated, it is pumped into the scrubber via the high-pressure gray water pump;

[0009] c) Exchange heat with desalted water in the three-stage black water heat exchanger, and the preheated desalted water is sent to each heat exchanger to produce steam;

[0010] S2. After heat exchange, the black water enters the residual pressure power generation device to generate electricity, and the black water pressure is reduced to normal pressure before being sent to the sedimentation tank for sedimentation;

[0011] S3. The supernatant liquid from the sedimentation tank flows back to the gray water tank, and part of the gray water is sent to the secondary black water heat exchanger through the low-pressure gray water pump to realize circulation operation.

[0012] Preferably, in step S1 a), the desalted water is 100° C. and 2.0 MPa, and the outlet temperature of the first-stage black water heat exchanger is controlled at 180±5° C. by a secondary line regulating valve.

[0013] Preferably, in step S1 b), the gray water from the low-pressure gray water pump is 0.7 MPa and 70° C., and the outlet temperature of the gray water from the secondary black water heat exchanger is controlled at 150±2° C. by a secondary line regulating valve.

[0014] Preferably, in step S1 b), the ash water is pressurized to 5.5 MPa by a high-pressure ash water pump and then fed into a washing tower.

[0015] Preferably, in step S1 c), the desalted water is at room temperature and 0.8 MPa, and the outlet temperature of the three-stage black water heat exchanger is controlled at 70±5° C. by a secondary line regulating valve.

[0016] Preferably, in step S2, the excess pressure power generation device is formed by coupling a screw expander, a gear box and a high-voltage asynchronous generator.

[0017] Preferably, an induced draft fan is provided at the top of the sedimentation tank to collect non-condensable gas and discharge it to the flare through a separation tank.

[0018] Therefore, the present invention provides an integrated process for cascade utilization of coal gasification black water heat and waste pressure power generation, which has the following beneficial effects:

[0019] (1) Increase the amount of high-quality by-product steam: By optimizing the use of black water heat, the system can produce more high-quality steam, improve energy utilization efficiency, and bring more economic benefits to the enterprise.

[0020] (2) Ensure the reuse temperature of gray water: Through reasonable process optimization, the reuse temperature of gray water is ensured, avoiding the impact of gray water temperature problems on the heat balance of the subsequent system, and ensuring the stable operation of the entire system.

[0021] (3) Realize cascade utilization of heat: By optimizing the process flow, the desalted water is preheated in advance to produce steam as a by-product, thus realizing cascade utilization of system heat, fully tapping the value of heat, and further reducing energy consumption.

[0022] (4) Fully utilize black water energy: By adding a residual pressure power generation device, the pressure energy of black water is converted into electrical energy, which realizes the full utilization of black water energy and improves the energy utilization rate of the system.

[0023] (5) The equipment operates stably and reliably: The black water heat exchanger adopts anti-blocking, anti-scouring and anti-corrosion design. The backwash device can ensure the operation cycle of the heat exchanger, reduce the equipment maintenance cost, and meet the stable operation requirements of high-pressure working conditions.

[0024] (6) The system has lower energy consumption and simpler operation: The optimized black water heat utilization process involves less equipment and a shorter process, which reduces the energy consumption of the system and makes the operation simpler. It is more in line with the current development layout of energy conservation and carbon reduction, and has good social and environmental benefits.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic flow chart of an integrated process for cascade utilization of heat from coal gasification black water and power generation using residual pressure according to the present invention;

[0027] Reference numerals:

[0028] 1. Gasifier; 2. Cyclone separator; 3. Scrubber; 4. Primary black water heat exchanger; 5. Secondary black water heat exchanger; 6. Third-stage black water heat exchanger; 7. High-pressure ash water pump; 8. Low-pressure ash water pump; 9. Residual pressure power generation device; 10. Sedimentation tank; 11. Ash water tank; 12. Induced draft fan. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below by means of the accompanying drawings and examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without violating the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the protection scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application and belong to the scope of protection of the present invention.

[0030] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0031] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0032] Unless otherwise specified in the present invention, the reagents, instruments, equipment and performance testing methods used are those commonly used by those skilled in the art.

[0033] Example

[0034] like Figure 1 As shown, this embodiment provides an integrated process for cascade utilization of coal gasification black water heat and waste pressure power generation, including the following steps:

[0035] (1) The black water from the gasifier 1, which has been quenched, separated by the cyclone separator 2, and washed in the scrubber 3, enters the primary black water heat exchanger 4 at 200°C and 4.0 MPa. At the same time, the desalted water in the pipe network at 2.0 MPa and 100°C also enters the primary black water heat exchanger 4. In the primary heat exchanger, the black water exchanges heat with the desalted water. The black water releases heat and its temperature drops, while the desalted water absorbs heat, its temperature rises, and it vaporizes into saturated steam at 1.0 MPa and 184°C. The steam production is regulated by controlling the outlet temperature of the primary black water heat exchanger 4. This is achieved by setting a bypass temperature regulating valve on the heat exchanger. When the steam production needs to be increased, the bypass valve can be appropriately closed to increase the flow of black water through the heat exchanger, thereby increasing the heat exchange rate. Conversely, when the steam production needs to be reduced, the bypass valve can be opened.

[0036] (2) The black water coming out of the first-stage black water heat exchanger 4 has its temperature reduced to 180°C, while its pressure remains at 4.0 MPa, and enters the second-stage black water heat exchanger 5. At the same time, the gray water coming out of the outlet of the low-pressure gray water pump 8, with a pressure of 0.7 MPa and a temperature of 70°C, also enters the second-stage black water heat exchanger 5 to exchange heat with the black water. During the heat exchange process, the black water continues to release heat, and its temperature further decreases. The gray water absorbs heat, and its temperature rises to 150°C. After heat exchange, the gray water is pressurized to 5.5 MPa by the high-pressure gray water pump 7 and then sent to the washing tower 3 as washing water. In order to accurately control the outlet temperature of the gray water, a secondary line temperature regulating valve is set at the second-stage black water heat exchanger 5. The opening of the valve is adjusted according to the outlet temperature of the low-pressure gray water to ensure that the gray water temperature is stable at 150°C.

[0037] (3) The black water exiting the secondary black water heat exchanger 5 enters the tertiary black water heat exchanger 6, where it exchanges heat with the normal-temperature, 0.8 MPa desalted water from the pipeline network. In this heat exchanger, the black water transfers its remaining heat to the desalted water, raising its temperature. The desalted water then enters the various heat exchangers, producing steam as a byproduct. After heat exchange, the black water's temperature drops to 70°C. To control this outlet temperature, a secondary line temperature regulating valve is installed at the tertiary black water heat exchanger 6. The valve opening is adjusted to maintain a stable black water outlet temperature of 70°C.

[0038] (4) The black water coming out of the tertiary black water heat exchanger 6 enters the residual pressure power generation device 9, which is composed of a screw expander, a gear box and a high-voltage asynchronous generator coupled. After the black water enters the screw expander, the pressure decreases and the volume expands, which drives the screw to rotate, and drives the high-voltage asynchronous generator to generate electricity through the gear box. After passing through the residual pressure power generation device 9, the black water pressure drops to normal pressure and is then sent to the sedimentation tank 10 for sedimentation treatment. During the operation of the residual pressure power generation device 9, the operating status of the equipment, including the speed of the screw expander, the output power of the generator, etc., needs to be checked regularly to ensure stable operation of the device and achieve effective recovery of black water pressure energy.

[0039] (5) The black water entering the sedimentation tank 10 is precipitated and separated in the sedimentation tank 10. The black water slurry at the bottom of the sedimentation tank 10 is sent to the filter press device for filtration. The coal slime produced after filtration can be sold for disposal. The supernatant at the top of the sedimentation tank 10 flows back to the gray water tank 11. The low-pressure gray water pump 8 set at the bottom of the gray water tank 11 divides the gray water into two parts: one part is sent to sewage treatment, and the other part is sent to the secondary black water heat exchanger 5 to exchange heat with the black water to achieve the recycling of gray water. During the gray water circulation process, it is necessary to pay attention to controlling the liquid level of the gray water tank 11 to ensure the normal operation of the low-pressure gray water pump 8. At the same time, the water quality of the gray water should be monitored regularly to avoid the normal operation of the system being affected by water quality problems.

[0040] Furthermore, during the blackwater treatment process, non-condensable gases may precipitate due to temperature and pressure fluctuations. To prevent non-condensable gases from accumulating within the system, this embodiment also includes an induced draft fan 12 at the top of the settling tank 10. This fan collects the non-condensable gases precipitated within the settling tank 10 and delivers them to a separator tank for gas-liquid separation. The separated non-condensable gases are then discharged to a flare for combustion, thus preventing environmental pollution. During operation of the non-condensable gas treatment system, the operating status of the induced draft fan 12 and the separation efficiency of the separator tank must be regularly checked to ensure effective treatment of the non-condensable gases.

[0041] The flow chart is a schematic diagram of the principle, which only shows the connection of the core equipment and does not reflect the details of the auxiliary subsystem. In addition to the core equipment shown in the figure, the black water heat exchanger used in the present invention adopts an anti-blocking, anti-scouring and anti-corrosion design. During operation, in order to ensure the operating cycle of the heat exchanger, the heat exchanger can be backwashed regularly. By backwashing, impurities and dirt that may accumulate in the heat exchanger can be removed to avoid the occurrence of blockage and corrosion problems. In addition, a desalted water supply pipe and two circulating water pumps are provided. During operation, by monitoring the steam production and pressure, the desalted water supply and the operating status of the circulating water pump are adjusted in time to ensure stable steam generation. When the operating pump fails, the standby pump can start automatically to ensure the normal operation of the system.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A process for integrated utilization of coal gasification black water heat in stages and waste pressure power generation, characterized in that: The following steps are involved: S1, pass 200℃, 4.0MPa black water through three-stage black water heat exchanger in sequence; a) Exchange heat with desalted water in the first-stage black water heat exchanger, and the by-product 1.0 MPa saturated steam enters the pipe network; b) In the secondary black water heat exchanger, the black water exchanges heat with the gray water from the low-pressure gray water pump. After the gray water is heated, it is pumped into the scrubber via the high-pressure gray water pump; c) Exchange heat with desalted water in the three-stage black water heat exchanger, and the preheated desalted water is sent to each heat exchanger to produce steam; S2. After heat exchange, the black water enters the residual pressure power generation device to generate electricity, and the black water pressure is reduced to normal pressure before being sent to the sedimentation tank for sedimentation; S3. The supernatant liquid from the sedimentation tank flows back to the gray water tank, and part of the gray water is sent to the secondary black water heat exchanger through the low-pressure gray water pump to realize circulation operation.

2. The integrated process for cascade utilization of coal gasification black water heat and residual pressure power generation according to claim 1 is characterized by: In step S1 a), the desalted water is at 100° C. and 2.0 MPa, and the outlet temperature of the first-stage black water heat exchanger is controlled at 180±5° C. by a secondary line regulating valve.

3. The integrated process for cascaded utilization of coal gasification black water heat and residual pressure power generation according to claim 1 is characterized by: In step S1 b), the gray water from the low-pressure gray water pump is 0.7 MPa and 70° C., and the outlet temperature of the gray water from the secondary black water heat exchanger is controlled at 150±2° C. by a secondary line regulating valve.

4. The integrated process for cascaded utilization of coal gasification black water heat and residual pressure power generation according to claim 1 is characterized by: In step S1 b), the high-pressure grey water pump raises the pressure to 5.5 MPa and sends it to the washing tower.

5. The integrated process for cascade utilization of coal gasification black water heat and waste pressure power generation according to claim 1 is characterized by: In step S1 c), the desalted water is at room temperature and 0.8 MPa, and the outlet temperature of the three-stage black water heat exchanger is controlled at 70±5° C. by a secondary line regulating valve.

6. The integrated process for cascade utilization of coal gasification black water heat and residual pressure power generation according to claim 1 is characterized by: In step S2, the residual pressure power generation device is formed by coupling a screw expander, a gear box and a high-voltage asynchronous generator.

7. The integrated process for cascade utilization of coal gasification black water heat and residual pressure power generation according to claim 1 is characterized by: An induced draft fan is installed at the top of the sedimentation tank to collect non-condensable gas and discharge it to the flare through a separation tank.

Images