Gasification system and wastewater treatment method

Abstract

A gasification system according to one embodiment is equipped with a scrubber device that transfers contaminants contained in a flammable gas to wash water and discharges the contaminant-containing wash water as scrubber wastewater, a heat exchanger that vaporizes the contaminants contained in the scrubber wastewater by heating the scrubber wastewater, and a combustion furnace for incinerating the vaporized contaminants. The heat exchanger utilizes heat generated by the combustion furnace to heat the scrubber wastewater.

Description

[Technical field]

[0001] The present disclosure relates to a gasification system and a wastewater treatment method. [Background technology]

[0002] Gasification systems are used to generate combustible gas from biomass fuels, etc. The combustible gas generated by gasification systems contains contaminants such as cyanides and organic matter, so it is necessary to remove these contaminants.

[0003] As a technology for removing pollutants contained in combustible gas, for example, the system described in Patent Document 1 is known. The system described in Patent Document 1 includes a scrubber that transfers cyanide components in the reformed gas to scrubber wastewater, a pH adjustment tank that adjusts the pH of the scrubber wastewater, an aeration tank that blows fine bubbles into the scrubber wastewater to transfer the cyanide components to the gas phase, and a burner that incinerates the cyanide components in the gas phase. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-200578 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the system described in Patent Document 1, chemicals such as sulfuric acid are added to the scrubber wastewater to adjust the pH level, thereby promoting the evaporation of cyanide components, etc. This system requires a device for adding the chemicals, which makes the equipment more complicated and increases the cost of treating the wastewater.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a gasification system and a wastewater treatment method that can effectively remove pollutants while suppressing treatment costs. [Means for solving the problem]

[0007] One embodiment of the gasification system includes a scrubber device that transfers pollutants contained in combustible gas to wash water and discharges the wash water containing the pollutants as scrubber wastewater, a heat exchanger that heats the scrubber wastewater to vaporize the pollutants contained in the scrubber wastewater, and a combustion furnace that incinerates the vaporized pollutants, and the heat exchanger uses heat generated by the combustion furnace to heat the scrubber wastewater.

[0008] In the gasification system of the above embodiment, the scrubber wastewater is heated to vaporize pollutants and then incinerated in the combustion furnace, so that the pollutants contained in the scrubber wastewater can be removed without using chemicals such as a pH adjuster. Furthermore, the heat generated by the combustion furnace is reused to heat the scrubber wastewater, so that the energy efficiency of the entire system can be improved. Therefore, the pollutants can be effectively removed while suppressing the cost of treating the wastewater.

[0009] The gasification system of one embodiment may further include a microbubble supplying device that supplies microbubbles to the scrubber wastewater. By supplying microbubbles, pollutants contained in the scrubber wastewater can be decomposed, so that the pollutants contained in the scrubber wastewater can be more effectively removed. The microbubble supplying device may supply ozone microbubbles to the scrubber wastewater.

[0010] The gasification system of one embodiment further includes a gasification furnace that generates combustible gas from biomass fuel by utilizing heat generated in the combustion furnace, and a boiler that generates hot water by utilizing exhaust heat from the gasification furnace, and the heat exchanger may heat the scrubber wastewater by utilizing the hot water generated by the boiler. By utilizing the hot water generated by the exhaust heat from the gasification furnace to heat the scrubber wastewater, the energy efficiency of the entire system can be improved, and as a result, the cost of treating the scrubber wastewater can be reduced.

[0011] In one embodiment, the heat exchange device may include a hot water tank for storing hot water, a heat exchanger provided in the hot water tank for heating the scrubber wastewater by heat exchange between the hot water and the scrubber wastewater, and a retention tank for storing the heated scrubber wastewater. In this embodiment, the scrubber wastewater can be heated with high energy efficiency by exchanging heat between the hot water and the scrubber wastewater.

[0012] In one embodiment, the heat exchange device may further include an aeration device that generates air bubbles in the scrubber wastewater in the retention tank. By generating air bubbles in the scrubber wastewater and exploding the air, the vaporization of pollutants can be promoted.

[0013] The gasification system of one embodiment may further include an adsorption reaction device that adsorbs pollutants contained in the scrubber effluent to the carbonized residue by mixing the carbonized residue remaining after generating the combustible gas from the biomass fuel with the scrubber effluent. By adsorbing the pollutants using the carbonized residue, which is a by-product of generating the combustible gas, the cost of treating the pollutants can be further reduced.

[0014] In one embodiment, the gasification system may further include a solid-liquid separator for separating the scrubber effluent treated by the adsorption reactor from the carbonized residue, and the carbonized residue containing pollutants can be removed from the scrubber effluent by the solid-liquid separator.

[0015] In one embodiment, the combustion furnace may burn the charred residue with the adsorbed pollutants. By recycling the charred residue as fuel in the combustion furnace, the energy efficiency of the entire system can be improved, and the cost of treating the pollutants can be reduced.

[0016] One embodiment of the wastewater treatment method includes a step of transferring pollutants contained in the combustible gas to the cleaning water by contacting the combustible gas with the cleaning water, a step of vaporizing the pollutants contained in the scrubber wastewater by heating the scrubber wastewater, which is the cleaning water containing the pollutants, using heat generated by a combustion furnace, and a step of incinerating the vaporized pollutants in the combustion furnace.

[0017] According to the wastewater treatment method of the above aspect, as described above, it is possible to effectively remove pollutants while suppressing the wastewater treatment cost. Effect of the Invention

[0018] In accordance with one aspect and various embodiments of the present invention, contaminants can be effectively removed while reducing processing costs. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a gasification system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference characters, and redundant description will not be repeated.

[0021] Fig. 1 is a schematic diagram of a gasification system according to an embodiment. The gasification system 1 shown in Fig. 1 generates combustible gas from biomass fuel. Note that the biomass fuel is an organic fuel derived from living organisms, such as wood biomass fuel including wood, branches, bark, etc.

[0022] As shown in Fig. 1, the gasification system 1 includes a combustion furnace 2, a gasification furnace 4, a boiler 6, and a wastewater treatment system 10. The combustion furnace 2 generates heat for obtaining combustible gas from biomass fuel. More specifically, the combustion furnace 2 burns the biomass fuel in the furnace to generate combustion gas, and supplies the generated combustion gas to the gasification furnace 4.

[0023] The gasifier 4 generates combustible gas by utilizing the heat generated in the combustion furnace 2. Biomass fuel for generating combustible gas is charged into the gasifier 4. The gasifier 4 generates combustible gas by heating the biomass fuel in the furnace to about 900°C and pyrolyzing it with the combustion gas supplied from the combustion furnace 2. The combustible gas generated by the gasifier 4 is supplied to a scrubber device 12 described later. Meanwhile, the exhaust gas containing the exhaust heat of the gasifier 4, which is supplied from the combustion furnace 2 and used for pyrolysis of the biomass fuel, is supplied to a boiler 6. After the combustible gas is generated from the biomass fuel, a carbonized residue of the biomass fuel remains in the gasifier 4. This carbonized residue is discharged from the gasifier 4 after the generation of the combustible gas.

[0024] The boiler 6 generates hot water by heating water using exhaust heat from the gasifier 4. The boiler 6 supplies the generated hot water to a hot water tank 24, which will be described later. The exhaust gas from which the exhaust heat has been recovered by generating the hot water is released into the air via, for example, an air-cooling device and a filter.

[0025] The wastewater treatment system 10 recovers pollutants contained in combustible gas into scrubber wastewater S, and purifies the scrubber wastewater S containing the pollutants. As shown in FIG. 1, the wastewater treatment system 10 includes a scrubber device 12, a microbubble supply device 14, a heat exchanger 16, an adsorption reaction device 18, and a solid-liquid separator 20.

[0026] The scrubber unit 12 is a wet-type cleaning device that removes pollutants contained in the combustible gas. As described above, the combustible gas generated by the gasifier 4 is introduced into the scrubber unit 12. The scrubber unit 12 has a plurality of water sprinklers 12a, and the cleaning water sprayed from the plurality of water sprinklers 12a is brought into contact with the combustible gas, thereby transferring the pollutants contained in the combustible gas to the cleaning water. Examples of the pollutants transferred to the cleaning water include hydrogen cyanide, benzene, and phenol.

[0027] The combustible gas from which the pollutants have been removed by the scrubber unit 12 is supplied to a power generation device such as a gas engine by the operation of the fan F1, and is used as fuel for power generation in the power generation device. Meanwhile, the wash water containing the pollutants is discharged as scrubber wastewater S to a wastewater tank 22. In one embodiment, a partition wall 22a defining a flow path for the scrubber wastewater S may be formed inside the wastewater tank 22. The scrubber wastewater S discharged by the scrubber unit 12 is supplied to the upstream part of the flow path formed by the partition wall 22a, and flows toward the downstream part of the flow path. A conduit C1 is connected to the downstream part of the flow path. The scrubber wastewater S that has reached the downstream part of the flow path of the wastewater tank 22 is returned to the multiple sprinklers 12a through the conduit C1 by the operation of the pump P1, and is reused as wash water.

[0028] The microbubble supply device 14 generates microbubbles and supplies them to the scrubber wastewater S in the wastewater tank 22. The microbubbles supplied by the microbubble supply device 14 eventually disappear in the scrubber wastewater S. When the microbubbles are generated, hydrodynamic cavitation generates hydroxyl radicals, and the generated hydroxyl radicals decompose the pollutants in the scrubber wastewater S. In one embodiment, the microbubbles supplied from the microbubble supply device 14 may be ozone microbubbles. For example, the microbubble supply device 14 releases minute ozone bubbles having an average particle size of 10 μm to 100 μm into the scrubber wastewater S at the upstream part of the flow path of the wastewater tank 22. The ozone microbubbles oxidize and decompose hydrogen cyanide, benzene, phenol, and the like contained in the scrubber wastewater S, thereby reducing the pollutants contained in the scrubber wastewater S.

[0029] The heat exchange device 16 heats the scrubber wastewater S treated by the microbubble supply device 14 to vaporize pollutants contained in the scrubber wastewater S. As shown in FIG. 1, the heat exchange device 16 includes a hot water tank 24, a heat exchanger 26, and a retention tank 28.

[0030] The hot water tank 24 is connected to the boiler 6 via conduits C2 and C3. Water supplied by the water supply device 32 is stored in the hot water tank 24. The water stored in the hot water tank 24 is supplied to the boiler 6 via the conduit C2 by operation of the pump P2. The water supplied to the boiler 6 is heated by the exhaust heat of the gasifier 4 to become hot water, and is returned to the hot water tank 24 via the conduit C3. In this way, water circulates between the hot water tank 24 and the boiler 6, so that the temperature of the water in the hot water tank 24 is maintained at a temperature of, for example, 60°C to 90°C.

[0031] The hot water tank 24 is also connected to the drain tank 22 via a conduit C5. A part of the hot water in the hot water tank 24 is supplied to the drain tank 22 via the conduit C5 by operation of the pump P4. This maintains the water level in the drain tank 22 at a substantially constant level. Furthermore, a cooling device 33 is connected to the hot water tank 24. When the temperature in the hot water tank 24 becomes higher than a predetermined temperature, the pump P5 is operated to circulate the hot water in the hot water tank 24 between the hot water tank 24 and the cooling device 33. This cools the hot water in the hot water tank 24.

[0032] The heat exchanger 26 is disposed in the hot water tank 24 and is connected to the wastewater tank 22 via a conduit C4. The scrubber wastewater S in the wastewater tank 22 is introduced into the heat exchanger 26 via the conduit C4 by the operation of the pump P3. The scrubber wastewater S introduced into the heat exchanger 26 is heated by heat exchange with the hot water stored in the hot water tank 24. That is, the heat exchanger 16 indirectly uses the heat generated by the combustion furnace 2 to heat the scrubber wastewater S. The heated scrubber wastewater is supplied to the retention tank 28.

[0033] The retention tank 28 is disposed in the hot water tank 24 and stores the scrubber wastewater S heated by the heat exchanger 26. The scrubber wastewater S in the retention tank 28 is maintained at a temperature of, for example, 80°C or higher. Here, the boiling point of hydrogen cyanide contained in the scrubber wastewater S is room temperature (25°C), and the boiling point of benzene is 80°C. Therefore, the contaminants including hydrogen cyanide and benzene contained in the scrubber wastewater S are vaporized in the retention tank 28. The vaporized contaminants are sent to the combustion furnace 2 through the conduit C6 by the operation of the fan F2. The contaminants sent to the combustion furnace 2 are incinerated by the heat of the combustion furnace 2. This reduces the amount of contaminants contained in the scrubber wastewater S. The heat exchanger 16 may further include an air diffuser 30 that generates air bubbles in the scrubber wastewater S in the retention tank 28. The air diffuser 30 generates air bubbles in the scrubber wastewater S, which promotes the vaporization of the contaminants.

[0034] The retention tank 28 is connected to the adsorption reaction device 18 via a conduit C7. The scrubber wastewater S from which pollutants have been vaporized by the retention tank 28 is sent to the adsorption reaction device 18 via the conduit C7.

[0035] The carbonized residue discharged from the gasifier 4 is fed into the adsorption reaction device 18. The adsorption reaction device 18 stirs the scrubber wastewater S treated by the heat exchanger 16 and the carbonized residue by the operation of the stirrer 34. This causes organic matter (e.g., tar, benzene, phenol, etc.) contained in the scrubber wastewater S to be adsorbed by the carbonized residue, further reducing the pollutants contained in the scrubber wastewater S. The scrubber wastewater S treated by the adsorption reaction device 18 is supplied to the solid-liquid separation device 20 via the conduit C8. Meanwhile, the carbonized residue to which the pollutants have been adsorbed is discharged from the adsorption reaction device 18 and fed into the combustion furnace 2 as fuel.

[0036] The solid-liquid separator 20 separates the scrubber wastewater S treated by the adsorption reaction device 18 from the carbonized matter residue. For example, the solid-liquid separator 20 is a precoat filter device that recovers the particulate carbonized matter remaining in the scrubber wastewater S with a filter aid. The scrubber wastewater S from which the carbonized matter residue has been removed is discharged outside the wastewater treatment system 10.

[0037] Next, a description will be given of a wastewater treatment method using the above-mentioned wastewater treatment system 10. When the combustible gas generated by the gasification furnace 4 is introduced into the scrubber unit 12, the scrubber unit 12 sprays cleaning water from the sprinkler 12a to bring the combustible gas into contact with the cleaning water, thereby transferring contaminants contained in the combustible gas to the cleaning water.

[0038] Next, the microbubble supplying device 14 supplies microbubbles to the scrubber wastewater S discharged from the scrubber device 12. As a result, pollutants contained in the scrubber wastewater S are oxidized and decomposed. The microbubbles supplied by the microbubble supplying device 14 may be ozone microbubbles.

[0039] Next, the scrubber wastewater S in the wastewater tank 22 is introduced into the heat exchanger 26 of the heat exchanger 16. The heat exchanger 26 heats the scrubber wastewater S with thermal energy of hot water generated by the combustion gas in the combustion furnace 2, and supplies the heated scrubber wastewater S to the retention tank 28. Next, the air diffuser 30 generates air bubbles in the scrubber wastewater S. This vaporizes the pollutants contained in the scrubber wastewater S. Next, the combustion furnace 2 incinerates the vaporized pollutants.

[0040] Next, the scrubber wastewater S treated by the heat exchanger 16 is introduced into the adsorption reaction device 18. The adsorption reaction device 18 then agitates the scrubber wastewater S treated by the heat exchanger 16 and the carbonized residue discharged from the gasifier 4, thereby adsorbing the pollutants contained in the scrubber wastewater S to the carbonized residue. Next, the carbonized residue to which the pollutants are adsorbed is removed from the adsorption reaction device 18 and fed into the combustion furnace 2. As a result, the carbonized residue is used as fuel in the combustion furnace 2, and the pollutants adsorbed to the carbonized residue are incinerated.

[0041] Next, the scrubber wastewater S treated by the adsorption reaction device 18 is introduced into the solid-liquid separation device 20. Then, the solid-liquid separation device 20 separates the scrubber wastewater S from the carbonized residue remaining in the scrubber wastewater S. Next, the scrubber wastewater S from which the carbonized residue has been separated is discharged outside the wastewater treatment system 10.

[0042] In the above-mentioned gasification system 1, the scrubber wastewater is heated to vaporize and incinerate the pollutants, so that the pollutants contained in the scrubber wastewater can be removed without using chemicals such as a pH adjuster. Furthermore, the heat generated by the combustion furnace is reused to heat the scrubber wastewater, so that the energy efficiency of the entire system can be improved. Therefore, according to this gasification system 1, the pollutants can be effectively removed while suppressing the treatment cost of the scrubber wastewater S.

[0043] In addition, in the gasification system 1, pollutants are adsorbed by the carbonized residue, which is a by-product of the generation of combustible gas, using the adsorption reaction device 18, so that the processing cost can be reduced compared to the case where activated carbon is used as an adsorbent. Furthermore, the carbonized residue to which the pollutants are adsorbed is returned to the combustion furnace 2 and reused as fuel, so that the operating cost of the gasification system 1 can be reduced.

[0044] Furthermore, in the gasification system 1, the scrubber wastewater S is treated in the order of the microbubble supply device 14, the heat exchange device 16, and the adsorption reaction device 18, so that the pollutants contained in the scrubber wastewater S can be removed in stages. Therefore, the pollutants contained in the scrubber wastewater S can be efficiently removed.

[0045] Although the gasification system according to various embodiments has been described above, various modifications can be made without being limited to the above-described embodiments without changing the gist of the invention. For example, in the above-described embodiments, an example in which woody biomass fuel is used as biomass fuel has been described, but flammable gas may be generated from a biomass fuel other than woody biomass fuel.

[0046] In the above-described embodiment, the scrubber wastewater S is treated in the order of the microbubble supply device 14, the heat exchange device 16, and the adsorption reaction device 18. However, the microbubble supply device 14, the heat exchange device 16, and the adsorption reaction device 18 may treat the scrubber wastewater S in any order. [Explanation of symbols]

[0047] Reference Signs List: 1...gasification system, 2...combustion furnace, 4...gasification furnace, 6...boiler, 12...scrubber equipment, 14...microbubble supply device, 16...heat exchanger, 18...adsorption reaction device, 20...solid-liquid separation device, 24...hot water tank, 26...heat exchanger, 28...retention tank, 30...aeration device, S...scrubber wastewater.

Claims

1. A scrubber device that transfers pollutants contained in the combustible gas to wash water and discharges the wash water containing the pollutants as scrubber wastewater; A heat exchange device that heats the scrubber wastewater to vaporize the pollutants contained in the scrubber wastewater; a combustion furnace for incinerating the vaporized pollutants; a gasification furnace that generates the combustible gas from biomass fuel by utilizing heat generated in the combustion furnace; a boiler for generating hot water by utilizing exhaust heat from the gasification furnace; an adsorption reaction device that adsorbs the pollutants contained in the scrubber wastewater onto the carbonized residue by stirring the carbonized residue remaining after generating the combustible gas from the biomass fuel and the scrubber wastewater; Equipped with The heat exchanger heats the scrubber wastewater by utilizing the heat generated by the combustion furnace and the hot water generated by the boiler. Gasification system.

2. The gasification system according to claim 1 , further comprising a solid-liquid separator that separates the scrubber effluent treated by the adsorption reaction device from the char residue.

3. The gasification system according to claim 1 or 2, wherein the combustion furnace combusts the char residue to which the pollutants are adsorbed.

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