JP3938981B2 - Gas recycling method for waste gasification - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas recycling method in waste gasification treatment, and particularly gasifies and burns municipal waste, sewage sludge, waste plastic, waste FRP, biomass waste, automobile waste, waste oil and other organic waste, In addition to discharging the metal contained in the waste in an unoxidized state that can be recycled, it converts it into a useful gas from a gaseous substance and turns it into a resource. At the same time, the fluidization required for the fluidized bed gasifier The present invention relates to a gas recycling method in waste gasification processing in which gas can be efficiently processed by recycling the generated gas or unnecessary components thereof.
[0002]
[Prior art]
Organic waste represented by municipal waste, sewage sludge, waste plastic, waste FRP, biomass waste, automobile waste, waste oil, etc. is generally reduced by incineration or left untreated They are disposed of in landfills, and the amount that they are recycled is very small.
In the above incineration treatment, stoker furnaces and fluidized bed furnaces have been used so far, but the amount of exhaust gas is large due to the high air ratio during combustion, and the metals discharged from the furnace are oxidized. Therefore, it was not suitable for recycling. Although an increasing number of such incineration facilities have an ash melting facility, the construction cost and operating cost of the entire system were increased.
[0003]
Japanese Patent Laid-Open No. 7-332614 was invented in order to solve these problems. Here, organic waste is supplied to a fluidized bed gasifier and gasified at a relatively low temperature to extract valuable metals and produce them. By supplying gas to the subsequent melting combustion furnace and burning it completely at a temperature higher than the melting temperature of ash, the ash content is reduced to molten slag to reduce the volume and make it a stable slag that can be landfilled. Proposals have been made on how to prolong life or recycle as earthwork materials. In the above method, combustible gas containing unburned char is generated from waste by a fluidized bed furnace in the previous stage, supplied to the molten combustion furnace in the subsequent stage, and completely burned at a high temperature, thereby completely dioxin decomposition. It is expected to make molten slag of ash.
[0004]
[Problems to be solved by the invention]
In this way, when the product gas of the fluidized bed gasification furnace is completely burned in the subsequent melting combustion furnace, in the melting combustion furnace, effective utilization of the heat held in the exhaust gas can be achieved, but the fluidized bed gas The gas produced in the chemical furnace contains a large amount of useful components that can be used as resources, and a method is proposed in which this gas is converted to synthesis gas mainly composed of H ₂ (hydrogen) and CO (carbon monoxide) and recycled as a raw material for the chemical industry. Has been. In this case, there is no need for a chimney for releasing the exhaust gas to the atmosphere. This is the so-called chemical recycling concept.
[0005]
From such a viewpoint, primary gasification is performed at a relatively low temperature in a fluidized bed gasification furnace, and the obtained gaseous matter is supplied to a high-temperature oxidation furnace to be secondary gasified at a high temperature, so that H ₂ (hydrogen), Resource conversion can be achieved by converting it into synthesis gas mainly composed of CO (carbon monoxide), but fluidized bed gasification furnaces require a large amount of gas (steam, etc.) that serves to fluidize the fluidized medium and dilute oxygen. Thus, there is a problem that the operating cost becomes high.
[0006]
In the present invention, when primary gasification by a fluidized bed gasification furnace and secondary gasification by a high temperature oxidation furnace are performed, a part of the generated secondary gas is recycled and used for fluidization gas of the fluidized bed gasification furnace. It is an object of the present invention to provide a gas recycling method in waste gasification processing that can reduce the operating cost and efficiently generate synthesis gas.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the gas recycling method in the waste gasification process according to the present invention firstly supplies organic waste to a gasification furnace using a fluidized bed to cause primary gasification. In a waste gasification process in which a gaseous substance is introduced into a high-temperature oxidation furnace to be converted into a secondary gas at a temperature higher than that of the gasification furnace, and this product gas is passed through a scrubber and then sent to a subsequent process. A part of the outlet gas of the scrubber through which the product gas discharged from the high-temperature gasification furnace passes is branchedly supplied to the fluidized bed gasification furnace and applied to the fluidization gas.
[0008]
Second, an organic waste is supplied to a gasification furnace using a fluidized bed to be primary gasified, and this gaseous substance is introduced into a high-temperature oxidation furnace at a temperature higher than that of the gasification furnace. In the waste gasification process in which the generated gas is cleaned and purified by passing through a scrubber and an acid gas removing device, and then sent to the subsequent process, the acid gas passing through the generated gas discharged from the high-temperature gasifier is passed through. A part of the CO ₂ gas separated by the gas removing device is branched and supplied to the gasification furnace so as to be applied to the fluidized gas.
In these cases, an internal circulation type fluidized bed furnace is used as the fluidized bed gasification furnace, and a recycle gas to the fluidized bed gasification furnace is supplied to the fluidized bed together with a gasifying agent (oxygen) to generate a fluidized gas gas. The concentration of the agent may be adjusted.
[0009]
[Action]
The organic waste is brought into primary gasification by bringing it into contact with oxygen-containing gas at a relatively low temperature (550 to 850 ° C.) in a fluidized bed gasification furnace, and pyrolyzing it, thereby obtaining the resulting gas. The solid material and a small amount of solid material are introduced into a high-temperature oxidation furnace, where they are brought into secondary gasification by contacting with oxygen-containing gas again at a high temperature (1200 to 1600 ° C.), and CO, H as synthesis gas. _Two- synthetic synthesis gas can be generated. For these purposes, a mixed medium of oxygen and steam is usually supplied from below the dispersion plate of a fluidized bed gasification furnace to fluidize a fluid medium such as dredged sand. If you do, you will need a lot of steam. In the present invention, first, a part of the gas after separating by a scrubber a small amount of unreacted carbon contained in the secondary gas from the high temperature oxidation furnace is returned to the fluidized bed gasification furnace, and this is fluidized. Instead of steam for use. Therefore, the operating cost can be reduced as compared with the case of using steam from outside the system. Second, an acid gas such as CO ₂ (carbon dioxide) gas is further removed from the gas that has passed through the scrubber, but a part of the separated CO ₂ gas is returned and applied instead of steam. Is also possible. In this case, the production efficiency of synthesis gas can be improved by using a CO ₂ rich gas.
[0010]
In these cases, the fluidized bed gasification furnace is an internal circulation type fluidized bed furnace, so that organic waste can be supplied by pretreatment to the extent of coarse crushing, and the gasification agent (oxygen) is added to the recycle gas. ) Can be added to adjust the oxygen concentration in the fluidized gas. This lowers the oxygen concentration in the fluidized gas to prevent the agglomeration (agglomeration) of the fluidized bed contents and creates a reducing atmosphere in the layer, thereby reducing the metal contained in the waste to an unoxidized state. It becomes possible to collect by.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of a gas recycling method in waste gasification processing according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a flowchart of a waste gasification processing apparatus to which a gas recycling method according to an embodiment is applied.
The gasification apparatus is a first-stage fluidized-bed gasification furnace that is primary gasified at a relatively low temperature of 550 to 850 ° C., and a non-burned char is entrained in the primary gas. In order to produce a synthesis gas mainly composed of H2 (hydrogen) and CO (carbon monoxide). Note that both primary gasification and secondary gasification proceed by partial oxidation reaction.
[0012]
Raw materials supplied to gasification equipment include municipal waste, sewage sludge, solid fuel, slurried fuel, waste plastic, waste FRP, biomass waste, automobile waste, waste oil, and other organic waste and low grade Charcoal can be used. Organic waste is roughly crushed to about 30 mm and supplied, and solid fuel, slurry fuel and waste oil are supplied as they are. Moreover, low grade coal is crushed to about 40 mm. These are received by a pipe, and after sufficiently stirring and mixing there, they are supplied to the fluidized bed gasification furnace 10 as appropriate. In addition, if the properties (calorific value or moisture) of the waste to be gasified are not good, coal, oil coke, or the like can be supplementarily added as necessary.
[0013]
The organic waste 12 crushed in advance as necessary is supplied to the hopper, and then supplied to the fluidized bed gasification furnace 10 using a screw type quantitative supply device 14. The fluidized bed gasification furnace 10 into which the organic waste is charged is composed of a lower fluidized bed portion 16 and an upper freeboard portion 18, both of which communicate with each other via a neck portion 20. The fluidized bed portion 16 is filled with sand (eg, dredged sand, olivine sand), alumina, iron powder, limestone, dolomite, etc. as a fluidized medium 24 on a dispersion plate 22 arranged at the bottom of the furnace. The fluidizing medium 24 is fluidized by ejecting the fluidizing gas into the fluidizing medium 24. Further, the dispersion plate 22 has a cone-like shape with a conical cone protruding from the center, and the fluidizing gas is separately supplied to the central portion and the peripheral portion of the dispersion plate 22. The flow rate of the fluidized gas supplied to the central part is reduced, the gas after the high-temperature oxidation furnace 30 described later is recycled to lower the oxygen concentration in the fluidized gas, and the flow rate of the fluidized gas supplied to the peripheral part Is increased, and the oxygen concentration is set higher than the central portion. Thus, a swirling motion is generated in the fluidized bed so that the fluidized medium 24 becomes a downward flow at the center of the fluidized bed and an upward flow at the periphery of the fluidized bed. In this way, an oxygen amount of 5 to 30% of the theoretical combustion oxygen amount is consumed for partial oxidation, and primary gasification is performed.
[0014]
The fluidized gas supplied to the central part, that is, the fluidized gas in the central part is close to dry distillation in the fluidized bed formed as a downward flow in the central part of the fluidized bed because the oxygen concentration is lowered by mixing of the recycle gas. A combustible gas having a high calorific value including tar generated by gasification under conditions rises to the free board portion 18. Char, which is a solid material generated in the central fluidized bed, is transported to the peripheral fluidized bed together with the fluidized medium, partially combusted in contact with the peripheral fluidized gas having a high oxygen concentration, and CO (carbon monoxide), CO (Carbon dioxide) It becomes ₂ main combustible gas and ash, and generates heat to maintain the inside of the furnace at 550 to 850 ° C. Thus, gas, tar and char are produced in the central fluidized bed, but the production rate of tar and char increases and the gas production rate decreases as the temperature decreases. Since it is a reducing atmosphere throughout the fluidized bed, the metal contained in the waste having a melting point higher than the fluidized bed temperature is discharged together with the fluidized medium from the bottom of the gasification furnace with little oxidation. Therefore, for example, aluminum can be recovered as an unoxidized metal when the fluidized bed temperature is set lower than 660 ° C., which is the melting point of aluminum. A discharge port 26 is provided at the bottom of the fluidized bed furnace for recovering incombustibles. Therefore, if the fluidized bed temperature is 550 to 650 ° C., the aluminum contained in the waste can be recovered from the outlet 26 in a clean and unoxidized state. The crushed sand d of the fluidized medium 24 discharged together with incombustibles from the furnace bottom discharge port 26 is separated upward by a bucket conveyor or the like after separating coarse impurities by classification operation, and returned to the fluidized bed gasification furnace 10.
[0015]
The organic waste thrown into the fluidized bed portion 16 of the gasification furnace 10 becomes gas, tar and char by gasification close to dry distillation, and the gas and tar are vaporized and rise in the furnace. The char is refined by the crushing action accompanying the swirling motion of the fluidized bed portion 16 while undergoing partial oxidation. Since the refined char is porous and light, it is entrained in the upward flow of product gas. If hard dredged sand is used for the fluidized medium 24, char crushing is further promoted. The gas, tar, and char that exit the fluidized bed gasification furnace 10 are supplied to the high-temperature oxidation furnace 30 in the next stage, and a synthesis gas is generated by secondary gasification at a high temperature.
[0016]
The primary gas discharged from the top of the fluidized bed gasification furnace 10 is supplied to the next stage high temperature oxidation furnace 30 through the primary gas transfer path 32. The primary gas from which the char in the gas has been separated by the cyclone is introduced into the top of the high-temperature oxidation furnace 30 and is secondary gasified at a temperature of 1200 to 1600 ° C. together with oxygen of 20 to 40% of the theoretical combustion oxygen amount. Like to do. A reaction chamber 34 lined with a refractory is formed in the upper half of the high temperature oxidation furnace 30. In addition, a quenching chamber 36 for quenching the gas and slag from the reaction chamber 34 by directly contacting water with the water is provided at the lower portion of the high temperature oxidation furnace 30. The reaction chamber 34 and the quenching chamber 36 are provided at a throat portion 38. Communicate. A water line 40 for sending water for gas quenching is opened in the quenching chamber 36, and water is supplied at an appropriate water level. The high temperature secondary gas and slag generated in the reaction chamber 34 pass through the throat portion 38 and are blown into water in the quenching chamber 36 to be cooled. The gas after quenching is supplied from the gas discharge port 42 provided above the water surface of the quenching chamber 36 to the scrubber 56 through the gas line 44.
[0017]
In this case, it is desirable to supply the primary gas to the high-temperature oxidation furnace 30 so as to make a swirl flow in the reaction chamber 34 so that the residence time of the unburned char becomes long. As a result, the unburned char descends while circling along the furnace wall, and is rapidly oxidized at a high temperature of 1200 to 1600 ° C. while being mixed in a swirling flow with oxygen by radiant heat from the combustion flame and the furnace wall. As a result of this secondary gasification, the ash contained in the char becomes slag mist, is captured by the molten slag phase on the furnace wall of the reaction chamber 34 by the centrifugal force of the swirling flow, flows down the furnace wall and enters the quenching chamber 36, The water is crushed in the quenching chamber 36 to form slag particles, discharged to the outside through the lock hopper 46, and separated into coarse slag and fine slag by the screen 48.
[0018]
In this way, valuable metals are recovered in an unoxidized state in accordance with the primary gasification by the fluidized bed gasification furnace 10 in the previous stage, and the primary gas and the unburned char are secondary gas by high-speed oxidation in the high temperature oxidation furnace 30 in the subsequent stage. Can be In the subsequent high-temperature oxidation furnace 30, hydrocarbons, tar, and char are completely decomposed by high-temperature gasification at 1200 to 1600 ° C., and the generated gases are H ₂ (hydrogen), CO (carbon monoxide), CO ₂ (carbon dioxide). ), A composition gas composed of H ₂ O (water vapor). Further, the slag granulated ash is discharged from the bottom of the high temperature oxidation furnace 30. Thereby, while recovering valuable metals and slag from organic waste, synthesis gas can be generated.
[0019]
In order to recover the synthesis gas, a gas discharge port 42 provided in the upper part of the quenching chamber 36 of the high-temperature oxidation furnace 30 is connected to a scrubber 56 by a gas line 44, and fine unreacted carbon contained in the secondary gas. And ash and hydrogen chloride are removed. In this method, the produced gas is washed by bringing the secondary gas into direct contact with water and separating the solid content from the gas. In addition, an acid gas removing device 58 is disposed at the subsequent stage of the scrubber 56 to remove acid gases such as CO ₂ (carbon dioxide), H ₂ S (hydrogen sulfide), and COS (carbonyl sulfide) accompanying the product gas, Purify for use as synthesis gas. Further, the purified gas is sent to the cold box 60, and the remaining H ₂ is supplied to, for example, an ammonia production facility by deeply cooling CO.
[0020]
In such a two-stage gasifier, in the present embodiment, a part of the outlet gas of the scrubber 56 is branched and supplied to the gas chamber 64 below the dispersion plate 22 of the fluidized bed gasification furnace 10 as a fluidized gas. Used. For this reason, a branch pipe 62 is provided in the middle of the gas path from the scrubber 56 to the acid gas removal device 58, and this is connected to the gas chamber 64 of the fluidized bed gasifier 10. The gas chamber 64 is divided into two chambers (compartment chambers 64A and 64B) so as to supply a fluidized gas separately into a central portion of the furnace and a concentric peripheral portion, and the branch pipe 62 has a central portion. It is made to open separately in a peripheral part, and a part of scrubber 56 exit gas is supplied here.
[0021]
Oxygen gas as a gasifying agent supplied to the fluidized bed gasification furnace 10 and the high temperature oxidation furnace 30 is supplied after being pressurized by an oxygen blower 68. The fluidized bed gasification furnace 10 is supplied to the central compartment 64 </ b> A and the peripheral compartment 64 </ b> B of the gas chamber 64 through the fluidized gas supply path 70. Apart from the oxygen gas supplied from these oxygen blowers 68, the branch pipe 62 from the scrubber 56 is connected to the central compartment 64A and the peripheral compartment 64B, and the scrubber 56 outlet gas is connected thereto via the recycle gas blower 72. Part of it. The fluid medium of the fluidized bed gasification furnace 10 is set so that the oxygen concentration is low in the central portion and the oxygen concentration is relatively higher in the peripheral portion than in the central portion. By controlling the linear velocity of the fluidized gas, which is a combination of oxygen and recycle gas into the bed, to be lower in the central part than in the peripheral part, the fluid medium 24 becomes a downward flow at the central part and an upward flow at the peripheral part. A swivel motion occurs.
[0022]
Separately from the above embodiment, the high-concentration CO ₂ gas separated by the acid gas removing device 58 described above may be returned to the fluidized bed gasification furnace 10. In the acid gas removal device 58, it is relatively easy to separate the CO ₂ gas contained in the product gas, and by recycling a part of the separated CO ₂ gas near normal temperature as a fluidized gas, steam is removed. The running cost required for generation can be greatly reduced. However, it is inevitable that the capacity of the acid gas removal equipment 58 is increased by the amount of CO2 that is recycled.
[0023]
As described above, according to the present embodiment, the primary gas generated in the fluidized bed gasification furnace 10 is supplied to the high-temperature oxidation furnace 30, where secondary gas is generated, and the scrubber 56 and the acid gas removal device 58 are used. When cleaning and purifying, by recycling a part of the outlet gas of the scrubber 56 or a part of the CO ₂ gas separated by the acid gas removing device 58 as the fluidized gas of the fluidized bed gasification furnace 10, The required amount of fluidizing gas can be ensured. At the same time, by adjusting the oxygen concentration by mixing the recycle gas with oxygen, it becomes possible to prevent the occurrence of agglomeration (agglomeration) due to local high temperature. Further, the running gas of the entire system can be significantly reduced by recycling the outlet gas of the scrubber 56 or the CO ₂ gas separated by the acidic gas removing device 58.
[0024]
【The invention's effect】
As described above, according to the gas recycling method in the waste gasification treatment according to the present invention, the organic waste is supplied to the gasification furnace using the fluidized bed to be primary gasified at a relatively low temperature, The gaseous substance obtained by the primary gasification is introduced into a high-temperature oxidation furnace having a higher temperature condition than the gasification furnace to be converted into secondary gas, and the resulting product gas is passed through a scrubber to be washed to a subsequent process. In the waste gasification process to be supplied, a part of the outlet gas of the scrubber through which the product gas discharged from the high-temperature gasification furnace passes is branched and supplied to the gasification furnace, or applied to the fluidized gas, or By constituting a part of the CO ₂ gas separated by the acid gas removal device that passes the product gas discharged from the high-temperature gasification furnace to the gasification furnace and applying it to the fluidized gas, Necessary for fluidized bed gasifier Such small to effect the supply equipment burden such as steam is obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart of a waste gasification apparatus according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Fluidized bed gasification furnace 12 Organic waste 14 Fixed quantity supply apparatus 16 Fluidized bed part 18 Free board part 20 Neck part 22 Dispersion board 24 Fluidized medium (sand sand)
26 discharge port 30 high temperature oxidation furnace 32 primary gas transfer path 34 reaction chamber 36 quenching chamber 38 throat section 40 water line 42 gas discharge port 44 gas line 46 lock hopper 48 screen 56 scrubber 58 acid gas removal device 60 cold box 62 branch pipe 64 Gas chamber 68 Oxygen blower 70 Fluidizing gas supply path 72 Recycle gas blower

Claims (3)

Organic gas is supplied to a gasification furnace using a fluidized bed to be primary gasified, and this gas is introduced into a high-temperature oxidation furnace to produce a secondary gas at a higher temperature than the gasification furnace, In the waste gasification process in which the generated gas is passed through a scrubber and then sent to a subsequent process, a part of the outlet gas of the scrubber through which the generated gas discharged from the high-temperature gasifier is passed is the fluidized bed gasifier. A gas recycling method in waste gasification processing, wherein the gas is branched and supplied to fluidized gas. Organic waste is supplied to a gasification furnace using a fluidized bed to be primary gasified, and this gaseous substance is introduced into a high-temperature oxidation furnace to be secondary gasified at a temperature higher than that of the gasification furnace. In the waste gasification process in which the product gas is washed and purified through a scrubber and acid gas removal device and then sent to the subsequent process, it is separated by the acid gas removal device that passes the product gas discharged from the high-temperature gasification furnace. A gas recycling method in waste gasification processing, characterized in that a part of the generated CO ₂ (carbon dioxide) gas is branched and supplied to the gasification furnace and applied to fluidized gas. An internal circulation type fluidized bed furnace is used for the fluidized bed gasification furnace, and the recycle gas to the fluidized bed gasification furnace is supplied to the fluidized bed together with the gasifying agent to adjust the gasifying agent concentration of the fluidized gas. The gas recycling method in the waste gasification process according to claim 1 or 2.

Images