JP4523563B2 - Waste gasification method - Google Patents

Description

  The present invention relates to a waste gasification method and a waste gasification apparatus.

  Conventionally, for example, as a method of treating wood chips and general waste (hereinafter referred to as waste), these wastes are put into a gasification furnace together with incombustible pellets (for example, pumice) to form a packed bed, A moving bed gasification furnace is proposed that gasifies waste by supplying an oxidant gas from the bottom of the furnace and burning it partially to form a combustion zone, reduction zone, pyrolysis zone, and drying zone in the furnace height direction. (For example, refer to Patent Document 1).

In such a moving bed type gasification furnace, for example, the waste is thermally decomposed when it reaches about 300 ° C. or higher. Therefore, in the thermal decomposition zone in this temperature region, the waste is thermally decomposed and combustible heat is generated. Cracked gas and hydrocarbon content (char) are produced. Then, the char generated in the pyrolysis zone is gasified in the reduction zone, and the remaining char flows into the combustion zone and burns to become a high temperature state of about 1000 ° C. or higher. In the reduction zone, a part of the char reacts with steam supplied from the bottom of the furnace (steam reforming) and is converted into CO and H ₂ (Equation 1). In addition, a part of CO obtained by Formula 1 is further converted to CO ₂ (Formula 2).

_{C n H m + nH 2 O} ⇒ nCO + (n + m / 2) H 2 ··· ( Equation 1)

CO + H ₂ O⇔CO ₂ + H ₂
C (S) + H ₂ O ⇒ CO + H ₂
C (S) + CO ₂ ⇒ 2CO (Formula 2)

  In this way, the product gas generated from the pyrolysis zone and the reduction zone is filtered to remove fly ash and the like in the process of rising the dry zone of the packed bed, so that a relatively clean product gas is obtained. be able to.

  On the other hand, the combustion residue and incombustible pellets that have passed through the combustion zone are cooled by an oxidant gas or water vapor supplied from the bottom of the furnace to form a cooling zone. The oxidant gas that flows up through the gap in the cooling zone filling is sufficiently formed with non-combustible pellets to prevent drift, and flows uniformly in the horizontal cross-sectional direction of the furnace and is supplied to the combustion zone. . Thereby, the temperature of the horizontal cross section of a combustion zone is equalized, and gasification efficiency is stabilized.

Japanese Patent Laid-Open No. 2004-2552

  By the way, steam reforming of hydrocarbons such as char generally exhibits high activity in a high temperature range of 1000 ° C. or higher. However, even when the combustion zone is controlled at, for example, 1000 ° C., there is a possibility that a temperature distribution in the furnace may occur (for example, ± 150 ° C.). Therefore, char or ash derived from waste may be melted by heat, and it is necessary for stable operation of the furnace to control the combustion zone to a temperature range below 1000 ° C. (for example, 800 to 900 ° C.). . However, reforming reactivity does not increase at temperatures below 1000 ° C., which is not a sufficient temperature condition in terms of gasification efficiency.

  On the other hand, in the pyrolysis zone (for example, 300 ° C. to 500 ° C.), the waste is pyrolyzed to generate pyrolysis gas, but at the same time, tar is also generated. In particular, since thermal decomposition does not proceed sufficiently in this temperature range, a large amount of heavy tar is generated. This heavy tar has a high viscosity and may flow out of the furnace and affect the piping and equipment on the rear side. Further, since these tar components are not decomposed to the pyrolysis gas, it is considered that the gasification efficiency is not improved.

  This invention makes it a subject to improve the gasification efficiency while reducing discharge | emission of a heavy tar part in a moving bed type gasification furnace.

  In the moving bed type gasification furnace, the present invention provides various non-combustible pellets, which are indispensable for uniformly supplying an oxidant gas and the like in a uniform manner, with various catalytic functions. It forms a packed bed of waste. According to this, non-combustible pellets exert the desired catalytic action while moving down the packed bed, reducing the outflow of heavy tar to the outside of the furnace and improving gasification efficiency even at low temperatures can do.

Specifically, the present invention is a vertical gasification furnace together introducing incombustible pellet and waste to form a packed bed, it supplies an oxidant gas and water vapor from below the packed bed In the waste gasification method in which a combustion zone , a reduction zone, and a pyrolysis zone are sequentially formed in the furnace height direction by partial combustion, and combustion residues and non-combustible pellets are discharged from the bottom of the furnace, the combustion zone and the reduction zone are 600 ° C. is controlled to a temperature range of to 800 ° C., a nickel-based catalyst is non-flammable pellets to promote reforming gasification reaction at this temperature range is characterized in that it is carried.

  According to this configuration, first, in the thermal decomposition zone, the catalyst supported on the surface of the incombustible pellets acts to promote the decomposition of tar generated by the thermal decomposition of the waste. In particular, the concentration of heavy tar discharged from the gasification furnace can be reduced, and the influence of tar on the rear stage side can be reduced. Further, when tar is decomposed, low-molecular hydrocarbon gas is generated, so that gasification efficiency can be improved.

  On the other hand, since the catalyst of nonflammable pellets functions as a catalyst for gasification reforming reaction of char or the like at least in the reduction zone, the char reforming reaction by steam is more activated by the catalytic action in the reduction zone. Can be made. Thereby, the reaction temperature of the gasification reforming reaction can be reduced without reducing the gasification efficiency. That is, the control temperature of the combustion zone can be lowered. Incombustible pellets discharged with the combustion residue outside the furnace are separated from the combustion residue, and then the catalyst can be regenerated as needed and put back into the furnace. Can be economical.

In this case, the nickel-based catalyst supported on the nonflammable pellets has a function of promoting tar decomposition and serves as a catalyst for the gasification reforming reaction. Moreover, a nonflammable pellet is made to contain 10-20 vol% with respect to the input amount of a waste, for example. According to this, the functions of tar decomposition and steam reforming can be effectively exhibited, and in addition, the supply of oxidant gas and steam from the furnace bottom can be uniformly dispersed.

  ADVANTAGE OF THE INVENTION According to this invention, while reducing discharge | emission of a heavy tar part in a moving bed type gasification furnace, even if it controls combustion zone temperature by low temperature (for example, 700-900 degreeC), gasification efficiency is improved. Can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a main part of a waste gasifier to which the present invention is applied. Here, although the waste gasification apparatus of this embodiment is used suitably for gasification of a general waste, an industrial waste, biomass, etc., it is not limited to this.

  As shown in the figure, the updraft type waste gasifier 1 of the present embodiment (hereinafter simply referred to as the gasifier 1), for example, puts waste on the top of a cylindrical vertical container 3. A hopper 5 for storing in an appropriately dried state and a hopper 6 for storing incombustible pellets described later are provided. Double dampers 8 and 10 are provided at the inlets of the hopper 5 and the hopper 6, respectively. For example, the waste is conveyed by the screw conveyor 7 and supplied into the container 3 from the input port 9, while the non-combustible pellet is supplied from the input port 9 into the container 3 by the rotary feeder 12.

  The gasifier 1 has a gas outlet 11 for discharging a generated gas (pyrolysis gas) on the side wall at the top, and a gasifying agent for supplying an oxidizing gas (such as air or oxygen) and water vapor for combustion to the bottom. A supply port 13 is provided. The gasifying agent supply port 13 is formed at the tip of the rotary shaft 17 of the rotary extractor 15 that forms the bottom of the gasifier 1, for example. The oxidant gas and water vapor that flow through the rotary shaft 17 and are supplied into the furnace from the gasifying agent supply port 13 are supplied radially into the gasifier 1. The rotating shaft 17 of the extractor 15 is connected to the motor 21, and the rotating shaft 17 rotates so that the blades 16 cut out the combustion residue of the waste in the radial direction and discharge it from the discharge port 19. The gasifying agent supply port 13 is not limited to the present embodiment as long as the oxidizing agent and the water vapor are uniformly distributed and supplied in the horizontal cross-sectional direction of the gasifier 1, for example.

  A plurality of temperature sensors 23 are attached to the gasifier 1 at predetermined intervals in the furnace height direction of the furnace wall, and the height of the packed bed is set on the furnace wall above the temperature sensor 23 arranged at the uppermost stage. A plurality of level sensors 25 to be detected are attached in the furnace height direction. Although not shown, a pressure sensor for detecting the pressure in the upper space 27 of the packed bed is attached to the furnace wall above the level sensor 25.

  Next, the nonflammable pellets used in this embodiment will be described. The nonflammable pellets that form a packed layer together with the waste are formed, for example, by supporting a catalyst on the surface of a carrier made of a heat-resistant refractory such as alumina cement. In the present embodiment, a lashing type (diameter × length mm: φ20 × 20) carrier having, for example, 10 to 40 wt% of NiO supported as a nickel catalyst is used. It is preferable that MgO or CaO is added to the catalyst. According to this, for example, combustion of waste can be promoted in the packed bed. It is preferable that 10-20 vol% of nonflammable pellets are contained with respect to the input amount of waste.

  Next, operation | movement of the gasifier 1 comprised in this way is demonstrated.

  First, at the time of start-up, nonflammable pellets are supplied into the gasifier 1 from the inlet 9. When a predetermined amount of incombustible pellets is supplied, the waste 61 appropriately dried and pulverized is introduced into the gasifier 1 from the inlet 9 together with the incombustible pellets. The waste thrown into the furnace is filled into the furnace, for example, in a state of being uniformly mixed together with non-combustible pellets to form a packed bed.

  Next, the gasifier 1 filled with waste is ignited by supplying an oxidizing agent from the gasifying agent supply port 13 and blowing hot air (for example, 400 ° C. or more) from the hot air generator 14 for ignition. Let And the supply amount of an oxidizing agent is adjusted, the waste 61 is partially burned, and a combustion zone is formed in a packed bed. When the waste is pyrolyzed by the combustion heat in the combustion zone, pyrolysis gas is generated. This pyrolysis gas rises in the gasifier 1 through the gap between the wastes and is discharged from the gas outlet 11 to the outside of the furnace.

  When the partial combustion and thermal decomposition of the waste become stable, a stable combustion zone 51 is formed in the vicinity of the bottom of the furnace, and the char generated by the thermal decomposition is reduced until the transition to the combustion zone 51. 52 is produced, reformed and gasified. A pyrolysis zone 53 is formed above the reduction zone 52, and a waste drying zone 55 is further formed above the reduction zone 52.

In the pyrolysis zone 53, the waste is pyrolyzed to generate combustible pyrolysis gas and char. Further, the char generated in the thermal decomposition zone 53 reacts with water vapor in the reduction zone 52 and is converted into a reformed gas such as CO or H ₂ . The remaining part of the char flows down to the combustion zone 51 and is burned. The flow rate of the oxidant and water vapor supplied into the furnace is adjusted so that most of the generated char becomes combustion gas and reformed gas.

  When the oxidant gas and water vapor supplied from the bottom of the furnace flow and rise through the gaps in the filling of the cooling zone 57, there are sufficient gaps formed by the non-combustible pellets, so that the drift is suppressed. The temperature of the horizontal section of the gas is made uniform, and gasification efficiency is stabilized.

  The generated gas, which is a mixture of the pyrolysis gas and the reformed gas generated in this way, passes through the drying zone 55 while exchanging heat in the process of flowing through the gaps between the upper-layer wastes, and removes the wastes 61. dry. The product gas is reduced in temperature (for example, about 100 ° C.) by drying the waste 61, and is discharged from the gas outlet 11 through the upper space 27 formed at the top of the gasifier 1. Even if fly ash generated in the combustion zone 51 accompanies the product gas, the waste layer filled in the dry zone 55 collects as a filter, so that the fly ash flowing out from the gas outlet 11 is collected. The amount of ash can be reduced.

  On the other hand, the waste dried in the drying zone 55 gradually moves to the thermal decomposition zone 53 and undergoes a thermal decomposition reaction. Then, it moves to the combustion zone 51 and the reduction zone 52 and is gasified and reformed and burned to become ash (combustion residue). These are cooled by exchanging heat with the oxidant gas supplied from the bottom of the furnace in the process of flowing down the cooling zone 57 formed in the lower layer of the combustion zone 51, and the discharge port 19 together with the incombustible pellets by the rotation of the extractor 15. Is cut out and discharged out of the furnace. The non-combustible pellets discharged to the outside of the furnace are returned to the hopper 6 and repeatedly used.

  In this way, the waste in the packed bed moves downward when the extractor 15 extracts the waste 61 from the bottom. On the other hand, the furnace height position at which the combustion zone 51, the reduction zone 52, and the thermal decomposition zone 53 are formed is controlled to a height range set by, for example, the waste extraction speed and the oxidant supply speed. Can do.

  By the way, although steam reforming of hydrocarbons such as char in the reduction zone 52 shows high activity in a high temperature region of 1000 ° C. or higher, for example, even when the combustion zone 51 is controlled at 1000 ° C., the temperature distribution in the furnace ( For example, ± 150 ° C.) occurs, and char or ash may be melted by heat. Therefore, the combustion zone 51 needs to be controlled in a low temperature range (for example, 800 to 900 ° C.). Further, in the pyrolysis zone 53, for example, a large amount of tar is generated due to the relatively low temperature of 300 ° C to 500 ° C. In particular, if heavy tar is discharged outside the furnace without being decomposed, gasification efficiency is lowered, and there is a risk of affecting downstream piping and equipment.

  FIG. 2 is a diagram for explaining the operation from the introduction of waste and incombustible pellets into the gasifier 1 until the discharge. The nonflammable pellets used here carry a catalyst.

  The waste 61 thrown into the furnace forms a packed bed together with the incombustible pellets 63. In the thermal decomposition zone 53 of the packed bed, the catalyst supported on the surface of the noncombustible pellet 63 acts to promote the decomposition of tar generated when the waste 61 is thermally decomposed. Thereby, the density | concentration of the tar discharged | emitted from the gasification apparatus 1, especially a heavy tar can be reduced, and the influence of the tar to a back | latter stage side can be reduced. Further, since tar is decomposed, a low-molecular hydrocarbon gas is generated, so that the gasification efficiency can be improved.

  Next, in the combustion zone 51 and the reduction zone 52 of the packed bed, the waste is combusted and reformed by the oxidant gas and water vapor supplied from the bottom of the furnace, and is controlled in a temperature range of 600 to 800 ° C. Even at this low temperature, the catalyst of the non-combustible pellet 63 acts, so that the reforming reaction of hydrocarbons such as char by steam is more activated, so that the gasification efficiency can be improved.

  Drawing 3 is a mimetic diagram showing an example of a filling mode of incombustible pellets in a packed bed of a gasifier.

  (1) of a figure shows the state which the nonflammable pellet 63 is uniformly disperse | distributed three-dimensionally in the packed bed. This filling mode can be realized by simultaneously putting the waste 61 and the incombustible pellets 63 into the furnace. However, the waste 61 and the incombustible pellets 63 may be introduced after being uniformly mixed in advance. On the other hand, (2) in the figure shows a state in which the incombustible pellets 63 are formed in layers in the packed bed. This filling mode can be realized by alternately putting the waste 61 and the incombustible pellets 63 into the furnace.

  FIG. 4 is a configuration diagram showing a subsequent configuration for processing the generated gas discharged from the gasifier.

  As shown in the figure, the product gas discharged from the gasifier 1 to the outside of the furnace is cooled to a predetermined temperature via the gas cooling tower 71 and then guided to the gas cleaning tower 73. The generated gas introduced into the gas cleaning tower 73 is cooled to a predetermined temperature by contacting with the mist of the cooling water, whereby the water vapor in the gas is drained and removed from the bottom as condensed water, and the tar content in the gas is also reduced. Is separated and recovered. Subsequently, the product gas from which the water vapor and tar content has been separated is further subjected to a predetermined cleaning process as necessary, and then stored as a reformed gas in a gas holder (not shown). The reformed gas obtained here can be used as a fuel for a gas engine, for example.

  As described above, according to the present embodiment, by supporting the catalyst having various functions on the nonflammable pellet 63, first, the tar content is decomposed in the thermal decomposition zone 53, and then the char content is reduced in the reduction zone 52. Steam reforming can be more activated. Thereby, the gasification efficiency can be improved even at low temperatures (about 700 ° C.), and the concentration of heavy tar can be reduced. That is, with the activation of the reforming reaction by the catalyst, high gasification efficiency can be obtained even when the temperature of the combustion zone 51 is 1000 ° C. or lower, so that melting of, for example, ash can be reliably avoided and the gasifier 1 The life of the refractory material can be improved. Moreover, since the discharge concentration of heavy tar can be reduced, the clogging of the piping due to tar condensation can be suppressed on the rear stage side, and in addition, the increase in gas cleaning water COD can be suppressed and the load of the cleaning process can be reduced. it can.

  In addition, since the non-combustible pellets 63 discharged together with the combustion residue are separated from the combustion residue and can be reused after regenerating the catalyst as necessary, the conventional equipment can be used as it is. There is an advantage that you can. A moving bed type vertical furnace as in the present invention is inferior in contact efficiency with a catalyst as compared with, for example, a fluidized bed type, but is not economically deteriorated (wear, etc.) in the furnace. It is.

  In this embodiment, a nickel-based reforming catalyst is used as the catalyst supported on the nonflammable pellet 63, but the catalyst is not limited to this as long as it has the same function.

It is a block diagram which shows the principal part of the waste gasification apparatus formed by applying this invention. It is a figure explaining operation | movement until it discharges | emits after throwing a waste and a nonflammable pellet in a gasifier. It is a schematic diagram which shows an example of the filling aspect of the nonflammable pellet in the packed bed of a gasifier. It is a block diagram which shows the structure of the back | latter stage which processes the product gas discharged | emitted from the gasifier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gasifier 11 Gas discharge port 13 Gasifying agent supply port 19 Discharge port 51 Combustion zone 52 Reduction zone 53 Pyrolysis zone 55 Drying zone 57 Cooling zone 61 Waste 63 Nonflammable pellet

Claims (2)

A vertical gasification furnace together introducing incombustible pellet and waste to form a packed bed, required for the gasification reaction by partial combustion by supplying the oxidant gas and water vapor from the bottom of the packed bed Waste gasification that sequentially forms a combustion zone that generates combustion heat, a reduction zone that gasifies char, etc., and a pyrolysis zone in the furnace height direction, and discharges combustion residues and non-combustible pellets from the bottom of the furnace In the method
It said combustion zone and said reducing zone is controlled to a temperature range of 600 ° C. to 800 ° C., wherein the non-combustible pellets, nickel-based catalyst that promotes reforming gasification reaction at this temperature range is carried Waste gasification method. 2. The waste gasification method according to claim 1, wherein the incombustible pellets are contained in an amount of 10 to 20 vol% with respect to the input amount of the waste.

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