JP2573046B2 - Fluidized bed gasification method and fluidized bed gasification furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gasification method and a gasification furnace using a fluidized bed.

[Conventional technology]

Lime gasifiers were put into practical use successively in the 1920s and 1950s, with moving-bed, fluidized-bed, and gas-bed reactors. Since then, many gasifiers have been developed for each gasification method.However, still operating as a commercial furnace are moving bed reactor Lurgi and gas bed reactor Koppers Totze.
We only count furnaces. Recently, Texaco, a new gas-bed reactor
A furnace is about to join in.

[Problems to be solved by the invention]

Conventionally, coal that can be used in a fluidized bed furnace has been pulverized coal of 0.5 to 3 mm. If it is larger than this, fluidization will be hindered, and if it is smaller than this, it will not be completely gasified and will be scattered outside the furnace as unreacted char with the produced gas.

In order to prevent this, in the conventional fluidized bed furnace, it was an essential element to pre-crush and size the coal using a pulverizer or the like as a pretreatment before charging the coal into the furnace.
As a result of this pretreatment, coal that does not fall within the predetermined particle size range cannot be used, and the yield of coal has to be sacrificed to some extent.

Such crushing equipment has high equipment cost, operation cost, or maintenance cost, requires labor of related work, has disadvantages such as requiring an installation space for the equipment, and also has a disadvantage that foreign matter during operation is reduced. In some cases, the crushing equipment was stopped due to damage to mechanical parts or increased power due to the bite, and furthermore, serious troubles such as when the operation of the furnace itself had to be stopped were caused.

In addition, in the conventional fluidized bed, since the entire inside of the bed was to be kept uniformly in an active fluidized state, the amount of unreacted char scattered out of the furnace accompanying the produced gas was large, and high gasification efficiency was obtained. Never Even if scattered chars are separated and collected using a cyclone or other collection device and supplied to the gasification furnace, they are scattered without reacting again, and merely increasing the load on the collection device unnecessarily increases gasification. The efficiency has not been improved yet. These phenomena were more pronounced in coals having powdering properties.

Furthermore, in the conventional fluidized-bed furnace, since the coal itself, which is the gasification raw material, was used as the fluidizing medium, the supply amount could not be balanced and the height of the fluidized bed became unstable, or when it changed to a fluidized bed mainly composed of ash. The fineness of the particle size causes bubbling, resulting in poor contact between the coal and the gasifying agent.

On the other hand, regarding the scale of the gasification furnace, each system is currently in operation and the largest is 500 to 1000 t / d, and those with larger capacities have not yet been realized. Compared to pulverized coal combustion furnaces for power generation of 8000t / d class, and considering that the future scale of coal gasification is 3,000-5000t / d, the scale up problem is It must be said that it is very large.

In order to solve such problems of the fluidized bed system, a deep fluidized bed, a two-stage fluidized bed, and agglomeration of ash by gasification or high temperature have been tried. It had disadvantages.

This is not limited to fluidized bed furnaces, but is common to all systems, but it is indispensable to carry out grinding and sizing as a pretreatment before gasification raw materials such as coal are introduced into the furnace. In addition to the cost, labor, and space loss, the operation of the furnace may be hindered due to troubles during the operation of the crushing equipment. In addition, due to such pretreatment, coal that does not fall within a predetermined particle size range cannot be used, and the yield of coal has to be sacrificed to some extent.

Deep fluidized beds, which attempt to increase the coal particle's residence time in the bed, have not been very effective in solving the problem of charring. The deep fluidized bed also increased the furnace height, increased the weight of the furnace, and increased the heat loss from the furnace wall.

Two-stage fluidized-bed gasification is to burn the char from the upper furnace in the lower furnace, guide the high-temperature combustion gas generated there to the upper furnace, and carbonize the coal supplied to the upper furnace, The feature is that a gas with a high methane concentration ratio can be obtained. 1000 for not producing tar in the upper furnace
Although it requires a temperature close to 0 ° C., it is quite difficult to cover the amount of heat required by burning the char in the lower furnace. If the temperature is increased to increase the burning rate, the problem of ash melting naturally arises. However, recent reports have overcome these problems to some extent and have led to significantly higher gasification efficiencies. However, there is a problem in that the furnace becomes higher than the deep fluidized bed due to the two-stage furnace in the upper and lower stages, and the apparatus becomes complicated.

The cohesive discharge of ash due to high temperature has a problem that the structure and conditions of the discharge port are very difficult, and unreacted coal particles are entrained.

An object of the present invention is to provide a useful fluidized-bed gasification method and a gasification furnace that eliminate such conventional disadvantages.

[Means for solving the problem]

The present invention relates to a fluidized bed gasification method for gasifying coal or the like with a fluidized bed formed by fluidizing a fluidized medium with a fluidized gas ejected upward from a furnace bottom of a gasification furnace, The fluidized bed is held in a fluidized bed chamber having a rectangular cross section in a horizontal plane, and the fluidized gas is ejected from a gas dispersion mechanism formed with both side edges lower than a central portion, and a central portion of the furnace bottom is provided. The mass velocity of the fluidizing gas in the vicinity is 0.5 to 3 Gmf, the fluidizing gas velocity in the both side edges of the central part is 4 to 20 Gmf, and the fluidizing gas in the both side edges is upward above the fluid bed in the both sides. The flow path is blocked and turned toward the center of the furnace, forming a moving bed in which the flowing medium sinks in the center of the furnace bottom, and both side edges where the flowing medium is actively fluidized on both side edges. Forming a fluidized bed and adding the fluidized medium to the The sedimentation in the moving bed, the transition to the both side edges below the moving bed, the rising in the both side fluidized bed, and the top of the moving bed by the turning fluidized gas above the both side fluidized bed. A fluidized bed gasification method comprising supplying coal or the like to the moving bed while circulating in the furnace and gasifying the coal or the like.

〔Concrete example〕

The present invention will be described for the case where coal is gasified using oxygen and steam as gasifying agents.

FIG. 1 is an example of a flow of coal gasification using a fluidized-bed gasification furnace. The coal stored in the silo 1 is supplied to the gasification furnace 3 by the supply device 2 in a fixed amount. On the other hand, the gasifying agent composed of the mixed gas of oxygen and steam is supplied to the gasifier 3 as a fluidizing gas after being preheated by the heat exchanger 5 and reacts with the coal.

The gas generated in the gasifier 3 is a two-stage cyclone 4
Separates the solids contained in the gas. Since the solids separated by the first-stage cyclone include unreacted char, they are supplied to the gasification furnace 3 again. The solid separated in the second stage cyclone is discharged as ash and stored in the hopper 9. The temperature of the produced gas is lowered by the heat exchanger 5, then cooled and washed by the water washing tower 6, and then the hydrogen sulfide is removed by the alkali washing tower 7. The product gas thus purified is stored in the gas holder 8. The wastewater from the gas cleaning equipment is supplied to the wastewater treatment equipment 10 and detoxified.

 The gasifier 3 will be described.

As shown in FIG. 2, a dispersing plate 20 of a gasifying agent for fluidization is provided at the bottom of the gasification furnace 3. The dispersing plate 20 has both side edges lower than the central portion, and is formed in a substantially symmetrical mountain cross section with respect to the center line 36 of the furnace. Incombustibles and ash discharge ports 30 are connected to both side edges, and coarse incombustibles are discharged together with the fluid medium by a screw conveyor of 32,33.

The gasifying agent consisting of the preheated mixed gas of oxygen and steam is ejected from the dispersion plate 20 into the furnace, and hits the inclined wall 24 to form a swirling flow in a vertical plane, and the flowing medium such as silica sand flows along the swirling flow. The swirling fluidized bed 35 is formed. Further, as described later, a descending moving bed 34 is formed in the center of the furnace, and the coal is gasified by the descending moving bed 34 and the swirling fluidized bed 35 in a short time. In both cases, high gasification efficiency can be obtained without inhibiting fluidization.

The gasifying agent composed of the preheated mixed gas of oxygen and steam is ejected upward from the dispersion plate 20 through the chambers 21, 22, and 23 of the introduction section. The mass velocity of the gasifying agent ejected from the chambers 21 and 23 on both sides is large enough to form a fluidized bed, but the mass velocity of the gasifying agent ejected from the central chamber 22 is higher than the former. Is also small. For example, room 21,2
The mass velocity of the fluidizing gas ejected from 3 is 4 to 20 Gmf, preferably 6 to 12 Gmf, whereas the mass velocity of the fluidizing gas ejected from the chamber 22 is 0.5 to 3 Gmf, preferably 1 to 2.5 Gmf.
Selected as f. Here, 1 Gmf is a fluidization start mass velocity.

The oxygen concentration in the fluidizing gas ejected from the center chamber 22 may be lower than that of the fluidizing gas ejected from the chambers 21 and 23 on both side edges, or may be only steam.

The number of chambers is selected as an arbitrary number of 3 or more. Even in many cases, the mass velocity of the fluidizing gas is small for those near the center, 0.5 to 3 Gmf for those near both edges, and 4 for those near both edges.
It should be ~ 20Gmf. An inclined wall 24 is provided just above the chambers 21 and 23 at both side edges as a reflecting wall that interrupts the upward flow path of the fluidizing gas and turns the fluidizing gas toward the center of the furnace. On the upper side of the inclined wall 24, an inclined surface 25 having an inclination opposite to that of the inclined wall 24 is provided so as to prevent accumulation of the flowing medium.

A coal inlet 28 connected to the outlet 31 of the supply device 2 is provided in the furnace ceiling 27 so as to correspond to the chamber 22 in the center.

The principle of the gasifier 3 will be described. In a normal fluidized bed, the fluidized medium forms a vigorous fluidized state, such as boiling water, while the fluidized medium above chamber 22 forms a weakly fluidized moving bed. The width of the moving layer 34 is narrow at the top, but slightly wider at the bottom due to the effect of the inclination of the dispersing plate 20, where the injection of the gasifier with a high mass velocity from the chambers 21 and 23 is performed. The fluid is fluidized and blown up. This removes the fluid medium at the bottom,
The bed of fluidized medium immediately above chamber 22 descends under its own weight. Above this layer, a fluid medium from a fluidized bed 35 with a swirling flow is supplied as described later. By repeating this, the flowing medium above the chamber 22 forms the downward moving layer 34 in a weak flowing state. Room
The fluid medium that has moved above the fluidizers 21 and 23 is fluidized and blown up.However, the fluid medium is reflected and turned by the inclined wall 24, turns toward the center of the furnace, and moves to the top of the descending moving bed 34 described above, gradually It descends, reaches the bottom of the moving bed 34, is fluidized, blows up again, and circulates. Some of the fluid medium circulates in the fluidized bed 35 as a swirling flow.

The coal charged into the gasification furnace 3 in such a flowing state from the coal charging port 28 falls to the top of the descending moving bed 34.
Here, the flowing medium flows from the side edge toward the center, so that the coal is entrained in this flow and easily penetrates into the top of the descending moving bed 34. Therefore, since even fine particles can enter the descending moving bed 34, mechanical troubles such as feeding directly into the fluidized bed by the screw feeder as in the conventional fluidized bed are likely to occur. You don't have to take a method. In addition, the active fluidization can considerably prevent the unreacted particles from being scattered outside the furnace together with the generated gas.

In the descending moving bed 34, the carbonization reaction of coal is predominant,
The gasification reaction is partially performed, producing gas and char. The gas generated here escapes upward or horizontally,
The char moves together with the fluidized medium to the fluidized bed 35 on both side edges, and causes a gasification reaction with partial combustion with a gasifying agent comprising a mixed gas of oxygen and steam supplied as a fluidizing gas. The gas generated in the descending moving bed 34 is
Since the mass velocity of the gasifying agent is small, the loss due to combustion can be reduced. The gas generated in the descending moving bed 34 and the fluidized bed 35 is mixed in the freeboard section 29 above the bed,
The gasification reaction further proceeds in a high temperature atmosphere. Since the fluidization of the descending moving bed 34 is relatively gentle, even if the generated particles have a considerably small particle size, they do not scatter without being gasified as in a normal fluidized bed. Even if a part is scattered, if it is collected by the cyclone 4 outside the furnace and returned to the furnace again, it can be relatively easily gasified. As described above, in the present gasifier, a reaction very similar to the two-stage gasification described above occurs separately in the moving bed 34 and the fluidized bed 35.

When a large coal of about several tens of mm is dropped and supplied to the descending moving bed 34, the coal does not fall instantly onto the chamber 22, but gradually descends with the flow of the fluid medium in the descending moving bed 34. Furthermore, since there is no partition wall separating the descending moving bed 34 and the fluidized bed 35, even the coal having a large particle diameter can be smoothly moved from the descending moving bed 34 to the fluidized bed 35 without being attracted to the partition wall. Also, it does not hinder the flow of the fluid medium.

Therefore, even if the coal is quite large,
The carbonization is performed while gradually descending in the
By the time it reaches the both ends of 34, most of it will be in the form of fragmented char, so that it does not hinder the formation of the fluidized bed 35 on both side edges. Therefore, coal does not need to be crushed and sized in advance with a crusher or the like, and not only can the crushing equipment be omitted, but also trouble in the crushing process may cause serious problems in the operation of the gasifier. Can be prevented. Further, since the reaction in the moving bed 34 proceeds more smoothly than in a normal fluidized bed, even if coal having a large particle diameter is supplied, pressure fluctuation due to rapid gas generation does not occur. For this reason, the operation of the gasification furnace becomes extremely easy.

Since crushing equipment is not required, biomass raw materials such as waste wood and waste plastic which cannot be easily crushed like coal can be used as gasification raw materials. Since the amount of waste wood generated varies seasonally, it is possible to diversify gasification raw materials and reduce raw material costs by mixing and using it with coal. Further, for example, unburnable waste that is currently disposed in landfill and that contains coarse incombustible materials that are difficult to crush can also be used as a gasification raw material.

It is considered that the capacity of the gasifier is determined by the settling speed of the descending moving bed. According to the study of the inventors, if the mass velocity of the fluidizing gas ejected from the chamber 22 is too low, the descending moving bed 34
Loses fluidity to cause accumulation, while if too large, it becomes an active fluidized bed and the downward moving layer 34 is not formed. At the mass velocity during this time, if the amount of the fluidizing gas to the chamber 22 is increased, the descending moving bed 34 increases the fluidity and the sedimentation velocity becomes large. A high sedimentation velocity means that the circulation amount of the fluid medium is large, and the gasification capacity is increased.

In the present gasifier, inspection and repair become extremely easy because there are no obstacles such as partition plates in the furnace. Also, since the shape of the horizontal cross section of the gasification furnace holding the fluidized bed is rectangular, it is only necessary to change the width in the same cross section to design gasification furnaces with different capacities, making it easier to design or manufacture . According to the study by the inventors, even if the furnace width is largely changed, the swirling effect of the fluidized medium does not change much.

According to the present invention, it is possible to provide a fluidized-bed gasification method and a gasification furnace having the following extremely large practical effects.

Even a raw material having a large particle diameter can be quickly diffused in the moving bed and a sufficient gasification efficiency can be increased, so that it is not necessary to crush and size the raw material in advance.

Since the raw material can be supplied without crushing, all crushing equipment is not required, which not only saves cost, labor and space, but also operates the furnace such as shutting down the furnace due to trouble in the crushing process. It is possible to prevent the occurrence of a serious problem with respect to.

Similarly, since the raw material is dropped from the upper part of the furnace, the mechanical trouble of the supply device can be reduced as much as possible in comparison with the conventional method of directly supplying the fluidized bed.

Similarly, the yield of the raw materials used can be improved.

Similarly, it is possible to use a method of mixing coal with waste wood and waste plastic, thereby diversifying raw materials and reducing raw material costs. Further, it is possible to use a material containing incombustible substances which is a problem in crushing as a gasification raw material.

Similarly, since the ratio of fine powder contained in the raw material is reduced, and the fine powder is formed by dry distillation in the inactive fluidization of the moving bed, the amount of scattered unreacted char is small, and the gasification efficiency is accordingly reduced. Can be higher. Even if scattered, the relatively easy regasification after collection also leads to an improvement in gasification efficiency.

The sedimentation velocity of the fluidized medium in the moving bed can be increased, the amount of circulation in the furnace can be increased, and the gasification capacity can be increased. Further, the control width of the settling speed of the moving bed can be increased.

Since the reaction in the moving bed is relatively mild, even if a raw material having a large particle diameter is charged, the pressure fluctuation is small, and the operation is extremely easy.

Since the gasification furnace is a single chamber and has a shallow fluidized bed, the furnace height is reduced, and heat loss from the furnace wall can be reduced. The advantages of construction costs are also great.

Since silica sand is used as the fluid medium, the bed height is stable,
The contact between the raw material and the gasifying agent is also good.

By extending the furnace in the width direction (perpendicular to the plane of FIG. 2), the fluidized bed is rectangular in shape, and the capacity of one furnace can be reduced without changing the operating conditions of the fluidized bed and moving bed. Can increase.

Since the gas dispersing mechanism is formed so that both side edges are lower than the center, the movement of the fluid medium at the foot of the moving bed is smooth, and the circulation of the fluid medium is promoted. In addition, it enables smooth discharge of coarse incombustibles.

[Brief description of the drawings]

FIG. 1 is a flow chart of coal gasification, and FIG. 2 is a sectional view of a coal gasification furnace. 1 ... silo, 2 ... supply device, 3 ... gasifier, 4 ...
... cyclone, 5 ... heat exchanger, 6 ... water washing tower, 7 ...
... Alkaline washing tower, 8 ... Gas holder, 9 ... Ash hopper, 10 ... Waste water treatment equipment, 20 ... Dispersion plate, 21,22,23 ...
… Room, 24 …… inclined wall, 25 …… inclined wall, 26 …… furnace wall, 27…
... Ceiling wall, 28 ... Coal inlet, 29 ... Free board, 30
…… Incombustibles outlet, 31… Supply device, 32,33… Screw conveyor, 34… Downward moving bed, 35 …… Fluidized bed, 36…
… Center line.

Claims (6)

(57) [Claims] 1. A fluidized bed gasification method for gasifying coal or the like with a fluidized bed formed by fluidizing a fluidized medium with a fluidized gas ejected upward from the bottom of the gasification furnace, The fluidized bed is held in a fluidized-bed chamber having a rectangular cross section in a horizontal plane, and the fluidized gas is ejected from a gas dispersion mechanism having both side edges lower than a central portion, The mass velocity of the fluidizing gas near the
0.5 to 3 Gmf, the fluidizing gas velocity at both side edges on both sides of the central portion is 4 to 20 Gmf, and above the both side edges, the upward flow path of the fluidizing gas on both side edges is blocked, and Turning toward the center, forming a moving bed in which the fluidized medium settles at the center of the furnace bottom, and forming both-sided fluidized beds in which the fluidized medium is actively fluidizing at both side edges; The medium is allowed to settle in the moving bed, migrate to the side edges at the lower part of the moving bed, and rise in the both side fluidized beds, and the turning fluidizing gas is used at the upper part of the both side fluidized beds. A fluidized-bed gasification method, comprising turning coal toward the top of a moving bed and circulating it in a furnace to supply coal or the like to the moving bed and gasifying the coal or the like. 2. The fluidized bed gasification method according to claim 1, wherein said fluidizing gas is a mixture of air and steam or a mixture of oxygen and steam. 3. The method for gasifying a fluidized bed according to claim 1, wherein said fluidized medium is silica sand. 4. A fluidized bed chamber having a rectangular cross section in a horizontal plane is provided at a lower portion in the furnace, and a fluidizing gas dispersion mechanism is provided at a bottom portion of the furnace, and the dispersion mechanism is formed so that both side edges are formed lower than the center. Yes,
The gas dispersing mechanism is configured such that the fluidized gas mass velocity at both side edges is 4 to 20 Gmf, and the fluidized gas mass velocity at the center is 0.5 to 3 Gmf, and the fluidization is performed just above the both side edges. A fluidized-bed gasification furnace comprising an inclined wall for intercepting an upward flow gas and redirecting the fluidized gas toward the center of the furnace, and a gasification material inlet at an upper part of the furnace. . 5. The fluidized-bed gasifier according to claim 4, wherein ash discharge ports are connected to the both side edges of the gas dispersion mechanism. 6. The fluidized-bed gasification furnace according to claim 4, wherein a supply port for a char, which is a gasification product, is connected to a furnace wall in contact with said moving bed portion.