A coal gasification device slag water exhaust gas three-stage coupling ultra-low emission purification device and purification method

Abstract

The application discloses a coal gasification device slag water waste gas three-stage coupling ultra-low emission purification device and purification method. The device comprises a modularized closed gas collection unit, an alkali washing sulfur removal unit, a water washing impurity removal unit, an activated carbon deep filtration unit and an intelligent monitoring and regulation unit. The purification method adopts a three-stage coupling process of "closed micro-negative pressure collection-alkali washing sulfur removal-water washing impurity removal-activated carbon deep adsorption". The modularized quick-release closed cover realizes more than 99% of waste gas full collection; the two-stage spray tower is internally provided with hollow ball fillers for layered removal of acid gases and water-soluble impurities; and the rear activated carbon adsorption tank deeply processes VOCs. The whole process is automatically matched and adjusted through sensors and PLCs. The application solves the problems of waste gas diffusion, incomplete purification, equipment corrosion and high operation and maintenance cost in the traditional process, and has the characteristics of efficient collection, complete purification, low energy consumption, convenient maintenance and strong universality.

Description

Technical Field

[0001] This invention belongs to the field of energy conservation and environmental protection in coal chemical industry and air pollution control technology. Specifically, it is applicable to the closed collection, graded purification and ultra-low emission treatment of composite waste gas from the slag and water system of fluidized bed pulverized coal gasification devices such as aerospace furnaces and Texaco. Background Technology

[0002] The slag removal, flash evaporation, and settling processes in the slag and water system of coal gasification units continuously generate highly humid mixed waste gas containing hydrogen sulfide, ammonia, volatile organic compounds, and water vapor. Currently, the industry commonly employs two main treatment methods for this type of waste gas: one involves using gas collection hoods to locally collect waste gas from some open equipment, then connecting it to a water scrubbing tower for washing, utilizing the physical absorption of water to remove some water-soluble pollutants; the other, for operating conditions with high acid gas content, involves a separate alkaline scrubbing tower, where alkaline circulating liquid reacts counter-currently with the waste gas to remove acidic components such as hydrogen sulfide. In these systems, the gas collection hoods are mostly fixed welded or bolted steel frame structures, and the scrubbing towers use conventional tray or random packing structures. During system operation, the induced draft fan volume, scrubbing liquid replenishment, and reagent dosing largely rely on manual adjustments by operators. However, the above-mentioned technical methods have the following prominent problems: the single water washing or alkaline washing process has a relatively limited function, and can only remove water-soluble impurities or acidic gases separately. It cannot achieve simultaneous deep removal of multiple pollutants such as hydrogen sulfide, ammonia, and volatile organic compounds in the same system, and the exhaust gas is difficult to stably meet the ultra-low emission limit requirements. At the same time, when acidic gases are not effectively removed, the acidic medium diffuses with the exhaust gas and comes into long-term contact with the fan, pipeline and auxiliary equipment, which accelerates the corrosion rate of the system, requires frequent equipment maintenance and replacement, and results in high operation and maintenance costs. In addition, the fixed structure gas collection hood needs to be completely removed during equipment maintenance. During the disassembly and assembly process, the amount of exhaust gas released in a short time is large, and the system has a low degree of automation. The operating parameters cannot be matched in a timely manner according to the incoming gas load and concentration fluctuations, resulting in high system energy consumption and insufficient operating economy. Summary of the Invention

[0003] The technical problem this invention aims to solve is that, in existing coal gasification plant slag and water system waste gas treatment processes, single washing methods cannot simultaneously and deeply remove multiple components of pollutants such as hydrogen sulfide, ammonia, and volatile organic compounds, making it difficult to stably meet ultra-low emission limits. Furthermore, inadequate control of upstream acidic gases leads to severe equipment corrosion, and the fixed gas collection structure is inconvenient to maintain, resulting in large-scale short-term leakage of waste gas. Additionally, the system suffers from low automation, high energy consumption, and high maintenance costs. This invention provides a three-stage coupled ultra-low emission purification device and method for coal gasification plant slag and water waste gas, which can achieve full-volume closed collection of waste gas, staged deep removal of multiple components of pollutants, intelligent and low-energy operation of the system, and convenient maintenance.

[0004] To achieve the above objectives, this application provides the following technical solution: First aspect: Provides a three-stage coupled ultra-low emission purification device for slag, water and waste gas of a coal gasification unit, including a gas collection unit, a waste gas conveying unit and a purification unit. The gas collection unit includes multiple modular sealed gas collection units, including detachable and separable sealed covers. Each separable sealed cover is arranged above the slag pool, sedimentation pool, ash water tank and sedimentation tank of the slag remover. Each sealed cover is connected to the main gas collection pipe of the waste gas conveying unit through a gas collection branch pipe. The purification unit consists of an alkaline washing desulfurization unit, a water washing impurity removal unit, and an activated carbon deep filtration unit connected in series along the direction of the waste gas flow. An induced draft fan is installed at the end of the waste gas conveying unit. It also includes an intelligent monitoring and control unit, which is connected to the induced draft fan, the alkaline solution supply pump and the spray circulation pump of the alkaline washing desulfurization unit. It is used to automatically adjust the frequency of the induced draft fan, the amount of reagent added and the spray flow rate according to the online collected waste gas concentration, circulating liquid pH value and system pressure difference signal.

[0005] Preferably, the modular sealed gas collection unit has a detachable and split sealed cover consisting of a fixed cover and a movable maintenance door, with the connection part adopting a snap-fit ​​quick-installation structure and inlaid with a sealing strip; Maintain a slight negative pressure state inside the sealed enclosure.

[0006] Preferably, both the alkaline washing desulfurization unit and the water washing impurity removal unit are spray towers, and the towers are respectively filled with hollow sphere packing material of polypropylene or reinforced polypropylene. The operating air velocity in the tower body is 1.0 to 1.5 m / s, and a demister made of hollow spheres is installed at the top of the tower. The alkaline washing desulfurization unit is equipped with an online pH meter and an automatic alkali replenishment system to maintain the pH value of the circulating liquid at 10.0 to 12.0.

[0007] Preferably, the activated carbon deep filtration unit is a vertical sealed adsorption tank, with two layers of porous air distribution plates inside the tank, forming an activated carbon adsorption zone between the two layers of air distribution plates. The tank is equipped with differential pressure detection instruments at both the inlet and outlet, which can be switched and replaced online.

[0008] Preferably, the spray tower is arranged from bottom to top as follows: a gas distribution layer, a packing layer, a multi-layer spray pipeline, and a hollow sphere demister.

[0009] Preferably, the intelligent monitoring and control unit is equipped with online detectors for hydrogen sulfide, ammonia, and VOCs installed at the inlet and outlet of the main gas collection pipe and each level of purification unit, a pH meter and a level gauge installed in the circulating tank of the spray tower, and a differential pressure transmitter installed in the tower body and activated carbon tank. The controller achieves fully automatic closed-loop control according to predetermined logic.

[0010] The second aspect provides a three-stage coupled ultra-low emission purification method for slag, water, and waste gas from a coal gasification unit using the purification device described above, comprising the following steps: (1) The open sludge collection tanks of the slag and water system are sealed by modular closed gas collection units, and all process waste gas is collected under negative pressure, and a slight negative pressure is maintained inside the hood. (2) The exhaust gas first enters the alkaline washing desulfurization unit, where it comes into countercurrent contact with the alkaline circulating spray liquid with pH 10.0 to 12.0 in the packing layer to remove hydrogen sulfide and simultaneously cool down and remove dust. (3) The exhaust gas after alkaline washing is introduced into the water washing and impurity removal unit, and ammonia, alkaline mist and fine dust are removed by circulating water spraying. (4) The waste gas after washing is sent to the activated carbon adsorption unit, where residual VOCs and trace amounts of sulfides are adsorbed in the activated carbon adsorption zone. (5) The clean exhaust gas after three-stage purification is transported to the chimney by the induced draft fan. The entire process is automatically matched by the intelligent monitoring and control unit based on the feedback from the online sensors to achieve stable ultra-low emissions.

[0011] Preferably, the spray liquid-to-gas ratio of the alkaline washing desulfurization tower in step (2) is 2-4 L / m³; Step (3) The spray liquid-to-gas ratio of the water washing and impurity removal tower is 2-3 L / m³, the empty tower gas velocity of both towers is controlled at 1.0-1.5 m / s, and the total pressure loss of the entire purification system is 800-1500 Pa. Step (4): The space velocity of the activated carbon adsorption unit is 500–1500 h⁻¹. - ¹.

[0012] Compared with the prior art, this application has at least the following beneficial effects: The purification device and method provided in this application achieve efficient and complete collection of waste gas from pollution-generating points through a modular, sealed gas collection unit. The detachable and modular structure eliminates the need for complete dismantling during maintenance, effectively preventing the unorganized escape of waste gas during maintenance. Through a three-stage series coupling process of alkaline washing desulfurization, water washing impurity removal, and activated carbon deep filtration, multiple pollutants such as hydrogen sulfide, ammonia, volatile organic compounds, and dust are removed progressively along the flow direction of the waste gas. The comprehensive pollutant removal rate can reach over 99%, and all outlet indicators stably meet the ultra-low emission limits.

[0013] The effective removal of acidic gases by the front-end alkaline washing unit fundamentally slows down the corrosion rate of subsequent pipelines, fans, and towers, extending the overall service life of the equipment.

[0014] By forming a closed-loop linkage between the intelligent monitoring and control unit and the induced draft fan, reagent supply and spraying system, the operating parameters of each unit can be automatically matched in real time according to the fluctuation of incoming gas load and concentration. There is no need for frequent on-site manual intervention. The overall energy consumption and operation and maintenance costs of the system are significantly reduced compared with traditional processes, and the economic efficiency and stability of operation are greatly improved. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit, as proposed in an embodiment of the present invention. Figure 2 This is a logic block diagram for intelligent monitoring and control. Figure 3 This is a flow chart of the overall process for ultra-low emission purification of slag, water, and waste gas from a coal gasification unit through a three-stage coupling process.

[0016] The components include: 1. Sludge collection tank; 2. Enclosed hood; 3. Waste gas conveying unit; 4. Alkali washing desulfurization unit; 5. Water washing and impurity removal unit; 6. Activated carbon deep filtration unit; 7. Exhaust fan; 8. Chimney; 9. Packing layer; 10. Multi-layer spray pipeline; 11. Hollow ball demister; 12. Air distribution plate; and 13. Activated carbon adsorption zone.

[0017] The accompanying drawings are provided to further understand the embodiments and form part of the specification. They are used together with the embodiments for explanation and do not constitute a limitation on the embodiments. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0019] In the description of the embodiments, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments.

[0020] During the operation of the slag and water system of a coal gasification unit, open equipment in processes such as slag removal, flash evaporation, and settling continuously releases mixed waste gas containing hydrogen sulfide, ammonia, volatile organic compounds, and water vapor. Existing treatment systems generally suffer from problems such as incomplete waste gas collection, limited purification methods, severe equipment corrosion, and low automation. To address these technical issues, this application provides a three-stage coupled ultra-low emission purification device and method for slag and water waste gas from a coal gasification unit. The following detailed description of its structure and operation is provided in conjunction with specific embodiments.

[0021] like Figure 1 and Figure 2As shown in the figure, this application provides a three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit. The device includes a modular, sealed gas collection unit, a waste gas conveying unit 3, an alkaline washing desulfurization unit 4, a water washing and impurity removal unit 5, an activated carbon deep filtration unit 6, an induced draft fan 7, and a chimney 8, connected in sequence. The device also includes an intelligent monitoring and control unit for automatic control of each operating unit throughout the entire process.

[0022] The modular sealed gas collection unit consists of multiple detachable and separable sealed covers 2, which are respectively arranged above the slag collection tanks 1 of the slag removal machine, sedimentation tank, ash water tank, and settling tank. Each sealed cover 2 consists of a fixed cover and a movable inspection door. The fixed cover is constructed with a stainless steel square tube frame, covered with a 5mm thick transparent polycarbonate sheet for easy observation of the internal equipment's operating status. The movable inspection door is also made of a stainless steel frame and polycarbonate sheet. The connection between the movable door and the fixed cover is equipped with a stainless steel quick-release buckle structure. The male buckle is fixed to the movable inspection door, and the female buckle is fixed to the corresponding position on the fixed cover. After fastening, a fluororubber sealing strip is embedded at the joint to ensure the overall airtightness of the cover.

[0023] When the equipment requires routine maintenance, operators only need to manually open the corresponding movable maintenance door latch to enter the work area without disassembling the entire enclosure. Each sealed enclosure 2 has an exhaust gas suction port on its top or side wall, and a manual regulating valve is installed at the suction port. The suction ports of each sealed enclosure 2 are connected to the main exhaust gas collection pipe of the exhaust gas conveying unit 3 through a gas collection branch pipe.

[0024] The exhaust gas conveying unit 3 includes a main gas collection pipe laid along the pipe rack and branch gas collection pipes connecting the alkaline washing desulfurization unit 4, the water washing and impurity removal unit 5, the activated carbon deep filtration unit 6, and the induced draft fan 7, respectively. The induced draft fan 7 is a variable frequency speed-regulating fan, and a pressure transmitter is installed on its inlet pipe to collect the negative pressure signal in the main gas collection pipe in real time. During normal operation, the operating frequency of the induced draft fan 7 is adjusted to maintain a slight negative pressure state within each sealed enclosure, preferably -50 to -200 Pa. When the negative pressure in the main gas collection pipe deviates from the set value, the pressure transmitter feeds back the signal to the intelligent monitoring and control unit, which outputs a control signal to change the frequency of the induced draft fan 7, thereby achieving automatic matching and adjustment of the airflow.

[0025] The waste gas containing dust, sulfur, ammonia and other harmful components, collected by the modular closed gas collection unit, is sent to the three-stage coupled purification system via the waste gas conveying unit 3.

[0026] Specifically, the first stage is the alkaline washing desulfurization unit 4, which uses a spray tower. Inside the tower, from bottom to top, are arranged a packing layer 9, multiple layers of spray pipes 10, and a hollow ball demister 11. An alkaline solution circulation tank is located at the bottom of the tower. A circulation pump delivers the alkaline solution to the spray pipes, where it comes into counter-current contact with the rising exhaust gas, effectively absorbing acidic gases such as hydrogen sulfide and sulfur dioxide. An online pH monitor is installed in the alkaline solution circulation tank to monitor the pH value of the alkaline solution in real time. When the pH value of the circulating liquid is detected to be lower than the set lower limit of 10.0, the intelligent monitoring and control unit starts the metering pump to replenish the alkaline solution in the circulation tank, ensuring that the pH value of the circulating liquid is always maintained within the range of 10.0 to 12.0, thus ensuring that the alkaline solution concentration is always maintained within the high-efficiency absorption range.

[0027] The second stage is the water washing and impurity removal unit 5, which also adopts a spray tower structure, with the same tower structure as the alkaline washing desulfurization tower. The circulating medium in the water washing tower is industrial water or condensate produced by the gasification unit. The circulating liquid tank is equipped with a level controller and an automatic drain valve. During operation, part of the circulating liquid is periodically discharged into the slag water system through the automatic drain valve. At the same time, the water supply valve is opened according to the signal from the level controller to replenish fresh water, maintaining the concentration of ammonia and salts in the circulating liquid at a reasonable level, ensuring continuous and efficient absorption of ammonia. The hollow ball demister 11 installed at the top of the tower effectively intercepts droplets entrained in the airflow, preventing moisture from entering the subsequent activated carbon adsorption unit 6.

[0028] The third stage is the activated carbon deep filtration unit 6, which consists of two vertical activated carbon adsorption tanks connected in parallel. Pressure measuring points are installed at the air inlet and outlet of the tank, and the resistance of the activated carbon bed is monitored in real time through a differential pressure transmitter.

[0029] In the activated carbon adsorption tank, two layers of porous gas distribution plates 12 are set inside the tank, and an activated carbon adsorption zone 13 is formed between the two layers of gas distribution plates 12. Activated carbon adsorption material is filled in the zone. The waste gas passes through the activated carbon adsorption zone 13 from bottom to top and comes into full contact with the activated carbon. By utilizing its well-developed pore structure and surface chemical properties, the waste gas can be deeply adsorbed and purified to remove trace organic pollutants, ammonia and odor components.

[0030] In actual operation, one adsorption tank is in operation during normal operation, while the other is on standby. When the pressure difference of the operating tank reaches the set upper limit of 1200 Pa or the online VOCs detector at the outlet shows a concentration close to the emission limit, the waste gas flow is switched to the standby tank by switching the inlet and outlet valves, and the activated carbon in the old tank is replaced or regenerated. A drain port is provided at the bottom of the tank to periodically discharge any trace amounts of moisture that may condense due to gas cooling, preventing the activated carbon from becoming damp and ineffective.

[0031] The core of the intelligent monitoring and control unit is a PLC programmable controller. The controller is connected to the induced draft fan 7, the alkali metering pump, various circulating pumps, and valves via communication connections, including but not limited to wired signal line connections and wireless communication connections. Regarding sensor configuration, online detectors for hydrogen sulfide, ammonia, and VOCs are installed at the inlet and outlet of the main gas collection pipe and each stage of the purification unit; pH meters and level gauges are installed in the circulation tanks of the alkali washing desulfurization unit 4 and the water washing impurity removal unit 5; differential pressure transmitters are installed in each tower and activated carbon tank; and temperature sensors and pressure transmitters are installed on the main gas collection pipe.

[0032] The controller incorporates a built-in PID control algorithm. Its operating logic includes: comparing the negative pressure of the main gas collection pipe with the set value of -150Pa and outputting a signal to adjust the frequency of the induced draft fan 7; comparing the pH value of the alkaline washing circulating liquid with the set range of 10.0–12.0, and starting the metering pump to replenish alkali when it falls below the lower limit; opening the water supply valve when the water washing tower level is below the set value; issuing a cleaning alarm when the pressure difference of any section of the packing layer 9 exceeds 1.5 times the normal value; and automatically adjusting the spray pump flow rate to maintain the liquid-to-gas ratio within the design range when the concentration of pollutants in the incoming gas changes. Through this closed-loop linkage control, the entire system achieves fully automatic regulation throughout the entire process.

[0033] In existing technologies, the exhaust gas from coal gasification slag water systems often cannot be effectively collected during maintenance due to the limitations of the gas collection hood structure, and multiple component pollutants are difficult to remove simultaneously and deeply under a single washing process. To address this problem, this application provides a three-stage coupled ultra-low emission purification method for slag water exhaust gas from coal gasification units using the aforementioned device.

[0034] like Figure 3 As shown, the method includes step one: negative pressure collection section. Each wastewater pool 1 is sealed by a modular, detachable, and sealed cover 2. The variable frequency induced draft fan 7 is started to maintain a slight negative pressure of -50 to -200 Pa inside each sealed cover 2. External air can only flow into the cover in one direction through the necessary openings of the equipment. All the waste gas that escapes from the wastewater pool 1 is sucked into the gas collection pipe of the waste gas conveying unit 3, with a collection rate of ≥99%.

[0035] In practical operation, modular sealed hoods of corresponding specifications are customized and installed according to the geometric dimensions and maintenance requirements of the slag pit, sedimentation pit, ash water tank, and settling tank of the slag remover. The suction port of each sealed hood is connected to the main gas collection pipe through a gas collection branch pipe. After starting the induced draft fan 7, the suction effect creates a stable micro-negative pressure of about -150 Pa inside each sealed hood. External air can only flow unidirectionally into the hood through the necessary openings of the equipment. All the exhaust gas escaping from the equipment is sucked into the gas collection pipe and will not diffuse into the surrounding environment. After on-site testing, the concentration of fugitive VOCs around each hood opening is less than 0.5 ppm, and the exhaust gas collection rate reaches 99.5%.

[0036] Step Two: Primary Purification Section The exhaust gas first enters the alkaline washing and desulfurization unit 4 through the gas collection branch pipe. In the packing layer 9, it comes into counter-current contact with the alkaline circulating spray liquid with pH 10.0~12.0 to remove hydrogen sulfide and simultaneously cool down and remove dust.

[0037] In operation, the collected waste gas enters through the lower inlet of the tower and passes sequentially from bottom to top through the packing layer 9, the multi-layer spray pipe 10, and the hollow sphere demister 11. A circulating pump delivers an alkaline circulating spray liquid with a pH of 10.0–12.0 to the multi-layer spray pipe 10, where the liquid is sprayed downwards in a mist form, with a liquid-to-gas ratio controlled at 2–4 L / m³. On the surface of the hollow sphere packing, the waste gas undergoes sufficient gas-liquid contact and mass transfer with the alkaline liquid film. Hydrogen sulfide and sodium hydroxide undergo a neutralization reaction to produce sodium sulfide and water, achieving desulfurization. Simultaneously, the waste gas temperature drops from 45–60℃ at the inlet to below 35℃, and coarse particulate dust in the waste gas is captured by the liquid and enters the circulating liquid. A demister consisting of 2–4 layers of Φ25 polypropylene hollow spheres, with a thickness of 200 mm, is installed at the top of the tower. Droplets and mist in the rising airflow are intercepted and removed through inertial collisions between the hollow spheres, ensuring a low liquid content in the exiting gas.

[0038] Step 3: Secondary purification stage The exhaust gas after alkaline washing is introduced into water washing and impurity removal unit 5, where clean water is used to spray and remove ammonia, alkaline mist and fine dust.

[0039] In actual operation, the exhaust gas from the alkaline scrubbing tower enters through the lower inlet of the water scrubbing tower. The circulating clean water liquid comes into countercurrent contact with the rising exhaust gas through the multi-layer spray pipe 10 in the packing layer 9. The liquid-to-gas ratio is controlled at 2.5 L / m³, and the empty tower gas velocity is 1.2 m / s. Ammonia is easily soluble in water and is absorbed by the circulating water on the packing surface to form dilute ammonia water. The trace amounts of alkaline mist that may be entrained in the alkaline scrubbing section are diluted and neutralized in the water scrubbing section. Even finer dust particles are further captured by the circulating water.

[0040] During operation, the circulating liquid is partially discharged through an automatic drain valve at regular intervals, while fresh water is added to prevent the ammonia concentration in the aqueous phase from reaching saturation and affecting the mass transfer driving force, thus maintaining a stable ammonia removal efficiency.

[0041] Step 4: Three-stage deep purification section The low-temperature clean exhaust gas after water washing is sent into the activated carbon deep filtration unit 6, where residual VOCs and trace amounts of sulfides are adsorbed in the hydrophobic activated carbon bed.

[0042] In actual operation, the low-temperature clean exhaust gas from the outlet of the water washing tower enters an activated carbon adsorption tank that is in operation, and the adsorption space velocity is controlled at 1000 h⁻¹. -¹. The hydrophobic coal-based activated carbon filled in the tank has a well-developed microporous structure with a specific surface area greater than 1000 m² / g. Residual volatile organic compounds and trace amounts of hydrogen sulfide in the waste gas are adsorbed onto the inner surface of the activated carbon pores through van der Waals forces, achieving deep removal. Two adsorption tanks are used, one in operation and one on standby, with online switching achieved through pressure difference and outlet concentration monitoring to ensure uninterrupted adsorption treatment.

[0043] Step 5: Emission Section The clean exhaust gas, purified through three stages, is conveyed to the chimney 8 by the induced draft fan 7 for emission. The intelligent monitoring and control unit automatically matches the operating conditions of each unit based on feedback from online sensors. The purified exhaust gas, after testing, shows hydrogen sulfide concentration below 0.5 mg / m³, ammonia concentration below 1.0 mg / m³, and non-methane total hydrocarbon concentration below 10 mg / m³, all exceeding the ultra-low emission limits stipulated by relevant standards. The overall system energy consumption is reduced by more than 15% compared to traditional single-stage scrubbing processes, and the annual equipment maintenance cost is reduced by more than 30%.

[0044] In the specific operating parameter control of the above method, the spray liquid-to-gas ratio of the alkaline washing desulfurization unit 4 is 2~4 L / m³, and 3.3 L / m³ is taken in this embodiment; the spray liquid-to-gas ratio of the water washing and impurity removal unit 5 is 2~3 L / m³, and 2.5 L / m³ is taken in this embodiment; the empty tower gas velocity of both towers is controlled at 1.2 m / s, which is within the preferred range of 1.0~1.5 m / s. Within this gas velocity range, the tower pressure drop is moderate, the mass transfer efficiency is high, and it is not easy for flooding or packing blockage to occur.

[0045] The total pressure loss of the entire purification system from the inlet of the main gas collection pipe to the outlet of the induced draft fan 7 was measured to be approximately 1100 Pa, which is within the design range of 800~1500 Pa. The induced draft fan 7 can meet the system's airflow and pressure head requirements by operating at a frequency of 38 Hz. The space velocity of the activated carbon adsorption unit 6 is 500~1500 h⁻¹. - ¹, In this embodiment, 1000 h is used. - ¹ At this space velocity, the waste gas has sufficient contact time with the activated carbon bed, and the adsorption capacity is fully utilized.

[0046] After the device in this embodiment is put into operation, the concentration of hydrogen sulfide in the purified exhaust gas is below 0.5 mg / m³, the concentration of ammonia is below 1.0 mg / m³, and the concentration of non-methane total hydrocarbons is below 10 mg / m³. After long-term operation, all pollutant indicators have consistently met the standards. Compared with the traditional process of using a local gas collection hood combined with a single alkali scrubbing tower, the overall energy consumption of the system is reduced by 18%, and the annual operation and maintenance cost of the equipment is reduced by more than 30%. Moreover, no obvious signs of corrosion were found in the equipment and pipelines during operation, and the system operates stably and reliably with a significantly reduced failure rate.

[0047] To verify the technical effectiveness of this invention, a comparative experiment was conducted in the slag and water system of a pulverized coal gasification unit. Under the same operating conditions, three purification processes were run: Scheme A is the three-stage coupling process described in the embodiments of this invention (closed collection + alkaline washing + water washing + activated carbon adsorption + intelligent control).

[0048] Option B is a single alkaline washing process, while Option C is an alkaline washing plus water washing process. Both options are equipped with sealed gas collection hoods, achieving a waste gas collection rate of ≥99%.

[0049]

[0050] Experimental results show that while a single alkaline washing process can partially remove hydrogen sulfide, its removal effect on ammonia and VOCs is limited, and the outlet emissions cannot meet the ultra-low emission limits. Furthermore, the unremoved acidic gases cause severe corrosion of pipelines and fans. The alkaline washing + water washing process can effectively remove hydrogen sulfide and ammonia, but its VOCs removal efficiency is insufficient. Moreover, the high humidity gas after water washing entering subsequent equipment easily causes the activated carbon adsorption capacity to decay rapidly, with a replacement cycle of only 4 months. The three-stage coupling process of this invention protects the equipment through alkaline washing for acid removal, water washing for ammonia removal and alkaline mist protection for activated carbon, and deep adsorption of VOCs by activated carbon. The three stages work synergistically and complementarily, achieving a comprehensive pollutant removal rate of over 99%. The emission concentrations of all pollutants are consistently below the ultra-low emission limits, the equipment corrosion rate is reduced by over 85%, and the service life of activated carbon is extended to 12 months, which is 3 times longer than that of the alkaline washing + water washing process.

[0051] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0052] The embodiments have been described above, and such description is not restrictive. The figures shown are only one embodiment, and the actual structure is not limited to this. In short, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the inventive spirit, such design should fall within the scope of protection.

Claims

1. A three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit, comprising a gas collection unit, a waste gas conveying unit, and a purification unit, characterized in that: The gas collection unit includes multiple modular sealed gas collection units, including detachable and separable sealed covers. Each separable sealed cover is arranged above the slag pool, sedimentation pool, ash water tank, and sedimentation tank of the slag remover. Each sealed cover is connected to the main gas collection pipe of the exhaust gas conveying unit through a gas collection branch pipe. The purification unit consists of an alkaline washing desulfurization unit, a water washing impurity removal unit, and an activated carbon deep filtration unit connected in series along the direction of the waste gas flow. An induced draft fan is installed at the end of the waste gas conveying unit. It also includes an intelligent monitoring and control unit, which is connected to the induced draft fan, the alkaline solution supply pump and the spray circulation pump of the alkaline washing desulfurization unit. It is used to automatically adjust the frequency of the induced draft fan, the amount of reagent added and the spray flow rate according to the online collected waste gas concentration, circulating liquid pH value and system pressure difference signal.

2. The three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit according to claim 1, characterized in that: The modular sealed gas collection unit has a detachable and split sealed cover consisting of a fixed cover and a movable maintenance door. The connection part adopts a snap-on quick-installation structure and is inlaid with a sealing strip. Maintain a slight negative pressure state inside the sealed enclosure.

3. The three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit according to claim 1, characterized in that: Both the alkaline washing desulfurization unit and the water washing impurity removal unit are spray towers, and the towers are respectively filled with hollow sphere packing material of polypropylene or reinforced polypropylene. The operating air velocity in the tower body is 1.0 to 1.5 m / s, and a demister made of hollow spheres is installed at the top of the tower. The alkaline washing desulfurization unit is equipped with an online pH meter and an automatic alkali replenishment system to maintain the pH value of the circulating liquid at 10.0 to 12.

0.

4. The three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit according to claim 1, characterized in that: The activated carbon deep filtration unit is a vertical sealed adsorption tank with two layers of porous air distribution plates inside the tank, forming an activated carbon adsorption zone between the two layers of air distribution plates. The tank is equipped with differential pressure detection instruments at both the inlet and outlet, which can be switched and replaced online.

5. The three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit according to claim 3, characterized in that: The spray tower is arranged from bottom to top as follows: a gas distribution layer, a packing layer, a multi-layer spray pipeline, and a hollow sphere demister.

6. The three-stage coupled ultra-low emission purification device for slag, water, and waste gas from a coal gasification unit according to claim 1, characterized in that: The intelligent monitoring and control unit is equipped with online detectors for hydrogen sulfide, ammonia, and VOCs installed at the inlet and outlet of the main gas collection pipe and each level of purification unit, a pH meter and a level gauge installed in the circulating tank of the spray tower, and a differential pressure transmitter installed in the tower body and activated carbon tank. The controller achieves fully automatic closed-loop control according to predetermined logic.

7. A method for ultra-low emission purification of slag, water, and waste gas from a coal gasification unit using the purification device described in claim 1, characterized in that, Includes the following steps: (1) The open sludge collection tanks of the slag and water system are sealed by modular closed gas collection units, and all process waste gas is collected under negative pressure, and a slight negative pressure is maintained inside the hood. (2) The exhaust gas first enters the alkaline washing desulfurization unit, where it comes into counter-current contact with the alkaline circulating spray liquid with pH 10.0 to 12.0 in the packing layer to remove hydrogen sulfide and simultaneously cool down and remove dust. (3) The exhaust gas after alkaline washing is introduced into the water washing and impurity removal unit, and ammonia, alkaline mist and fine dust are removed by circulating water spraying. (4) The waste gas after washing is sent to the activated carbon adsorption unit, where residual VOCs and trace amounts of sulfides are adsorbed in the activated carbon adsorption zone. (5) The clean exhaust gas after three-stage purification is transported to the chimney by the induced draft fan. The entire process is automatically matched by the intelligent monitoring and control unit based on the feedback from the online sensors to achieve stable ultra-low emissions.

8. The three-stage coupled ultra-low emission purification method for slag, water, and waste gas from a coal gasification unit according to claim 7, characterized in that: Step (2) The spray liquid-to-gas ratio of the alkaline washing desulfurization tower is 2-4 L / m³; Step (3) The spray liquid-to-gas ratio of the water washing and impurity removal tower is 2-3 L / m³, the empty tower gas velocity of both towers is controlled at 1.0-1.5 m / s, and the total pressure loss of the entire purification system is 800-1500 Pa. Step (4): The space velocity of the activated carbon adsorption unit is 500–1500 h⁻¹. - ¹.

Images