JP2008231294A - Two-stage gasifier - Google Patents

Abstract

[Problem] To increase the diameter of a furnace body for the purpose of scaling up a two-stage gasification furnace, the low temperature region and the high temperature region are clearly defined in the furnace body without increasing the height of the furnace body. So that a desirable temperature distribution is formed, and damage to the furnace wall can be prevented, and heat loss from the furnace wall is reduced.
SOLUTION: A cylindrical furnace body 2, an upper burner group 3 disposed on the upper part of the furnace body, and a lower burner group 4 disposed on the lower part of the furnace body are provided. A gas outlet 5 from which the product gas is discharged is formed, and a molten slag outlet 7 from which molten slag is discharged is formed at the lower end portion of the furnace body 2, and an interval Lb between the upper burner group 3 and the lower burner group 4, and a gas outlet 5 is a gasification furnace in which the ratio of the distance Lu between the upper burner group 3 and the upper burner group 3 is Lb / Lu = 2-12.
[Selection] Figure 1

Description

  The present invention relates to a two-stage gasification furnace used in a coal gasification process for producing fuel gas such as carbon monoxide, hydrogen, and methane from a solid hydrocarbon fuel such as coal.

  As a process used for coal gasification, there is a two-stage gasification method. Regarding this two-stage gasification method, for example, Japanese Patent Publication No. 4-72877 and Japanese Patent Publication No. 4-55238 disclose a two-stage gasification furnace.

FIG. 1 shows an example of such a two-stage gasifier. As shown in FIG. 1A, the two-stage gasification furnace 1 includes a furnace body 2, an upper burner group 3 provided at the upper part of the furnace body 2, and a lower part provided at the lower part of the furnace body 2. The burner group 4 is schematically configured.
The furnace main body 2 has a cylindrical shape having a substantially constant cross-sectional area, and a gas outlet 5 through which a product gas such as carbon monoxide, hydrogen, and methane generated in the furnace main body 2 is led opens at the top. ing. The diameter (Dout) of the gas outlet 5 is made smaller than the diameter (D) of the furnace body 2 and is connected to the subsequent apparatus.

  An annular slag stack 6 is attached to the inner surface of the lower part of the furnace body 2, and the central opening of the slag stack 6 serves as a molten slag outlet 7 through which the molten slag flows down. The diameter of the molten slag outlet 7 is also made smaller than the diameter of the furnace body 2 so that the heat radiation from the molten slag outlet 7 is reduced.

  The upper burner group 3 is disposed at the upper part of the furnace body 2 and four burners 31, 32, 33, and 34 are each equally distributed and attached to the peripheral wall of the furnace body 2 as shown in FIG. ing. These burners 31... Are not directed toward the central axis of the furnace body 2 but are directed outward from the central axis as shown in the figure, and are ejected from the respective ejection openings. The combustion gas flows in the circumferential direction of the furnace body 2 to form a swirl flow in the furnace body 2.

The diameter of the virtual circle of the swirl flow formed by the upper burner group 3 is called “virtual swirl flow circle diameter”, and this diameter is hereinafter referred to as Du.
The “virtual swirl flow circle diameter” in the present invention does not refer to a swirl flow due to an actual gas flow, but is a virtual extension of the nozzle in the jet direction of each burner 31, 32,. It is defined as the diameter of a circle inscribed in a straight line of a book. Thereby, by determining the “virtual swirl flow circle diameter”, the arrangement of the burners 31, 32,... Is determined.
The individual burners constituting the upper burner group 3 are supplied with a fine powder of a solid hydrocarbon fuel such as coal and an oxidizer composed of an oxygen-containing gas such as air or oxygen gas, and this is injected from each injection port. It is like that. Hereinafter, the mixing ratio of oxidant and solid hydrocarbon fuel (oxidant supply amount / solid hydrocarbon fuel supply amount: weight ratio) is defined as the oxidant amount ratio.

  The lower burner group 4 is disposed above the slag stack 6 at the lower part of the furnace body 2, and the four burners 41, 42, 43, 44 are evenly arranged on the peripheral wall of the furnace body 2 as shown in FIG. It is arranged and attached. These burners 41 are also not directed to the central axis of the furnace body 2 but directed to the outside of the central axis as shown in the figure, and are injected from the respective injection openings. Similarly, the combustion gas forms a swirl flow in the furnace body 2. The diameter of the virtual circle of the swirl flow formed by the lower burner group 4 is also called “virtual swirl flow circle diameter”, and this diameter is hereinafter referred to as Dl. The definition of the “virtual swirl flow circle diameter” here is the same as that in the upper burner group 3.

As with the upper burner group 3, the individual burners constituting the lower burner group 4 are supplied with fine powder of solid hydrocarbon fuel and an oxidant composed of an oxygen-containing gas such as air or oxygen gas. It comes to be injected from the mouth.
The virtual swirl flow circle diameter Du by the upper burner group 3 is larger than the virtual swirl flow circle diameter Dl by the lower burner group 4, and the virtual swirl flow circle diameter Dl by the lower burner group 4 is the diameter of the gas outlet 5. It is configured to be larger than Dout (Du>Dl> Dout).

  In the two-stage gasification furnace 1 configured as described above, combustion is performed by reducing the oxidant amount ratio in the upper burner group 3 and increasing the oxidant amount ratio in the lower burner group 4 so as to cause combustion. 2 is formed, the temperature distribution in the furnace body 2 as shown in FIG. 2 is formed, and the ash content in the solid hydrocarbon fuel is not melted in the upper region, and the ash content is melted in the lower region. Is done.

Thereby, in a region near the upper burner group 3, a gas such as hydrogen, carbon monoxide, and methane is generated by a chemical reaction in the high-temperature swirling flow, and is derived as a high-temperature product gas from the upper gas outlet 5. The The temperature of this gas is lower than the melting temperature of the ash content in the solid hydrocarbon fuel.
On the other hand, in the area near the lower burner group 4, gases such as carbon dioxide and moisture are generated, and this gas rises to the area of the upper burner group 3 and is used for the reaction here. Further, the ash content in the solid hydrocarbon fuel is melted together with the ash content that is generated and descends in the upper burner group 3, and this molten ash content as a molten slag adheres to the wall surface of the furnace body 2 on the swirling flow, It travels down here and flows down from the lower molten slag outlet 7 and is discharged.
Here, the interval between the lower burner group 4 and the molten slag outlet 7 is L1, the interval between both burner groups is Lb, the interval between the upper burner group 3 and the gas outlet 5 is Lu, and the height of the furnace body 2 is When L, L = Ll + Lb + Lu.

  In the two-stage gasification method using such a two-stage gasification furnace 1, the product gas yield is high, the molten slag can be recovered well, the temperature of the product gas can be lowered, It is said that there is an advantage that the heat load on the subsequent heat recovery device is reduced, the size can be reduced, and there is no slagging, fouling, etc. to which molten slag or combustion ash adheres.

By the way, when such a two-stage gasification furnace 1 is scaled up (enhanced processing capacity) for practical use, there are the following problems.
That is, when the diameter (D) of the furnace body 2 is increased as one means for scaling up the two-stage gasification furnace 1, the height (L) of the furnace body 2 and the diameter of the furnace body 2 are increased. The ratio (L / D) to (D) is reduced, and at the same time, the ratio (Lb / D) between the distance (Lb) between the upper burner group 3 and the lower burner group 4 and the diameter (D) of the furnace body 2 is also reduced. Become.
For this reason, even if the oxidant amount ratio in the upper burner group 3 and the lower burner group 4 is appropriately set, the temperature distribution in the furnace body 2 is clearly defined as a low temperature region and a high temperature region as shown in FIG. Formation becomes difficult.

As a countermeasure against such a problem, in order to form an appropriate temperature distribution as shown in FIG. 2 in the furnace body 2, the height (L) of the furnace body 2 is set to the height of the furnace body 2 in the small furnace. It is conceivable to increase the ratio while maintaining the same ratio (L / D) between (L) and the diameter (D) of the furnace body 2.
However, when the height (L) of the furnace body 2 is increased in this way, the furnace wall area of the furnace body 2 becomes excessive, resulting in an increase in heat transfer loss from the furnace wall and oxygen for maintaining the temperature. The amount increases and the amount of product gas recovered decreases (gasification efficiency decreases). In addition, this phenomenon becomes more prominent because the coal heat input is small when the furnace load is small.

Further, since the height (L) of the furnace body 2 is high, the high temperature region is unnecessarily widened, the furnace wall region exposed to the molten slag is increased, and the range of damage to the furnace wall is widened.
Further, not only the height of the furnace main body 2 but also the distance between the upper burner group 3 and the lower burner group 4 is made as long as possible so that the upper burner group 3 is brought as close to the gas outlet 5 as possible, the flame of the upper burner group 3 Will directly contact the ceiling wall of the furnace body 2 and damage the wall.
Japanese Examined Patent Publication No. 4-72977 Japanese Patent Publication No. 4-55238

  Therefore, the problem in the present invention is to increase the diameter of the furnace body for the purpose of scaling up the two-stage gasification furnace, and without increasing the height of the furnace body unnecessarily, the low temperature region in the furnace body. A high temperature region is clearly formed so that a desired temperature distribution is formed, damage to the furnace wall can be prevented, and heat loss from the furnace wall is reduced.

To solve this problem,
The invention according to claim 1 includes a cylindrical furnace body, an upper burner group that is disposed above the furnace body and that injects a mixed fluid of solid hydrocarbon fuel powder and an oxidizer, and a lower body body. A lower burner group for injecting a mixed fluid of solid hydrocarbon fuel powder and oxidant,
A gas outlet from which product gas is discharged is formed at the upper end of the furnace body,
The gasification furnace is characterized in that the ratio of the distance Lb between the upper burner group and the lower burner group and the distance Lu between the gas outlet and the upper burner group is Lb / Lu = 2-12.

According to the present invention, the ratio of the distance Lb between the upper burner group and the lower burner group and the distance Lu between the gas outlet and the upper burner group is set to Lb / Lu = 2 to 12, whereby the diameter of the furnace main body is set. Even when increasing the scale of the gasification furnace by increasing the temperature, the temperature distribution in the furnace body can be made appropriate as shown in FIG. 2 without increasing the height of the furnace body unnecessarily. .
For this reason, adverse effects such as a decrease in the amount of product gas recovered by increasing the height of the furnace body and damage to the furnace wall of the furnace body are prevented.

Hereinafter, an example of the gasification furnace of the present invention will be described with reference to FIG.
In the gasification furnace 1 of this example, the ratio (Lb / Lu) between the distance Lb between the upper burner group 3 and the lower burner group 4 and the distance Lu between the gas outlet 5 and the upper burner group 3 is 2-12. Except for this, it has the same structure as the conventional one shown in FIG.

Hereinafter, in the present invention, the ratio between the interval Lb between the upper burner group 3 and the lower burner group 4 and the interval Lu between the gas outlet 5 and the upper burner group 3, the reason or basis for setting Lb / Lu to 2-12 explain.
FIG. 3 shows the in-furnace temperature distribution (average temperature in the gasifier radial direction) of a small-scale two-stage gasifier. The vertical axis represents the relative furnace height L *, where L * = 1 represents the product gas outlet 5 and L * = 0 represents the molten slag outlet 7.
The test conditions are an oxidant amount ratio of the upper burner group 3 = 0.54 (ton / ton), an oxidant amount ratio of the lower burner group 4 = 1.11 (ton / ton), and a gasification pressure of 2.5 MPa. .
The melting temperature of the coal ash used (JIS method, pour point of oxidizing atmosphere) is 1430 ° C. The black dots in the graph indicate actual measurement values, and the solid lines indicate the results of three-dimensional heat flow analysis.

A region where L * is about 0.45 or less and exceeds the ash melting temperature, and a region where 0.4 or more and lower than the ash melting temperature are clearly formed. This is because, in the vicinity of the lower burner group 4, the high temperature gas generated by the reaction by the lower burner group 4 forms a sufficient temperature range for ash melting and slag flow, while the ash generated by the reaction by the upper burner group 3 This is because the gas below the melting temperature descends to a position facing the lower burner group 3.
The temperature distribution shown in FIG. 3 is an example of the ideal temperature distribution of the two-stage gasifier targeted by the present invention.

The temperature distribution in the furnace main body 2 as shown in FIG. 3 shows the reaction between the solid hydrocarbon fuel powder ejected from the upper burner group 3 and the lower burner group 4 of the gasification furnace 1 and the oxidant, and their flow. Since it is determined by the state, it is influenced by the ratio L / D of the furnace height L and the furnace diameter D and the distance (Lb) between the upper burner group 3 and the lower burner group 4.
Therefore, L / D and Lb were arbitrarily changed, and the temperature distribution in the furnace was examined by the three-dimensional heat flow analysis. As a result, the temperature distribution formation in the two-stage gasification furnace was achieved by the upper burner group 3 and the lower burner group 4. It has been found that it is governed by the ratio of the distance Lb between the upper burner group 3 and the distance Lu between the gas outlet 2.

FIG. 4 shows the result.
The throughput of the gasifier considered was 20 times that of the small-scale gasifier, and the gasification conditions were the oxidant amount ratio of the upper burner group 3 = 0.54 (ton / ton), the lower burner group 4 The oxidizer amount ratio is 1.05 (ton / ton) and the gasification pressure is 3.0 MPa. The melting temperature of coal ash is 1430 ° C.
In the graph of FIG. 4, the horizontal axis is Lb / Lu, and the vertical axis is the lowest temperature in the region between the upper burner group 3 and the lower burner group 4. It can be determined whether it is formed between.
Moreover, temperature showed the average temperature of the gasifier radial direction, and the temperature of the wall vicinity. The temperature in the vicinity of the wall is a direct determination factor on whether or not a molten slag layer is formed on the gasifier wall (whether the ash is in an unmolten wall state or a molten wall state).

As a result, when Lb / Lu is small, the minimum temperature between burners exceeds the ash melting temperature, but as this ratio increases, the minimum temperature between burners becomes lower than the ash melting temperature and increases again from a certain value. .
Lb / Lu is small because the upper burner group 3 is away from the gasifier ceiling wall (Lu is large) or Lb is small (the upper burner group 3 and the lower burner group 4 are close to each other). In any case, no non-melted region of ash is formed between both burner groups.

In this state, (1) the ash melting region is long (wide), the region where the refractory is damaged by the molten slag tends to expand, (2) the amount of heat transfer loss increases, (3) the two-stage reaction function in actual operation It is not preferable for the reason that maintenance and control operations become difficult.
When Lb / Lu increases, that is, when the two burner groups are separated (Lb is large), a low temperature region is successfully formed between the two burner groups. However, if it is further increased, that is, (a) if the burner groups are separated too much (Lb is too large), the flow of the low-temperature gas generated in the upper burner group 3 to the high temperature side becomes weak, and the temperature between both burner groups If the upper burner group 3 is too close to the gasification furnace ceiling wall 6 (Lu is too small), the burners 31 of the upper burner group 3 The influence of the local high-temperature flame in the vicinity of the jet hole becomes stronger, and the minimum temperature between both burner groups becomes higher.

In the case of (b), the burner flame directly touches the gasifier ceiling wall. Normally, the gasification furnace ceiling wall has the same structure as the furnace wall or a water-cooled tube. However, if the burner flame directly hits the furnace wall, it is not preferable.
Therefore, from the result of FIG. 4, 2 ≦ Lb / Lu ≦ 12 is set as a desirable range for forming a suitable temperature in the furnace.
The interval Ll between the lower burner group 4 and the molten slag outlet 7 is determined at a position close to the molten slag outlet 7 under the condition that the molten slag is stably discharged and the gasification furnace wall and hearth are not damaged. What is necessary is just to set it as the range defined by the kind of gasifier.

FIGS. 5 and 6 show examples in which the temperature distribution of the two-stage reaction can be formed without setting the furnace height L excessively by setting Lb / Lu of the present invention in the range of 2 ≦ Lb / Lu ≦ 12.
The gasification furnace 1 shown in (a) of FIG. 5 is a conventional furnace, that is, a large-sized furnace that maintains L / D equal to L / D in a small-scale gasification furnace and has a processing capacity of 20 times. Further, the gasification furnace 1 shown in (b) uses the method of the present invention, Lb / Lu = 4.8, and the height (L) of the furnace is 0.38 times that of the gasification furnace of (a). And a large furnace with a processing capacity of 20 times.

FIG. 6 shows the temperature distribution in the two types of gasification furnaces obtained by a three-dimensional heat flow analysis. Curve (a) in FIG. 6 is the temperature distribution for the gasification furnace shown in FIG. 5 (a), and curve (b) is also the temperature distribution for the gasification furnace shown in FIG. 5 (b). . As a result, it was found that the gas distribution furnace (b) according to the present invention can form a temperature distribution similar to that of the conventional gasification furnace (a), and the present invention does not require an unnecessarily high furnace height. .
As described above, by optimizing the arrangement positions of both burner groups, it is possible to form an appropriate temperature distribution even if the size of the furnace is increased.

FIG. 7 shows the effect of heat transfer loss due to the furnace height. The graph of FIG. 7 shows the relationship between the relative height and the relative heat transfer loss amount when the furnace height of the gasification furnace 1 in FIG. 5B and the heat transfer loss amount from the furnace wall at that time are respectively 1. It is a thing.
If the furnace height L of the large furnace is determined by the conventional design method, it is necessary to make the furnace height 1 / 0.38≈2.6 times higher than the furnace height according to the present invention. .1x. In order to prevent the gasification temperature from being lowered due to this, the amount of oxygen used is increased by 3.7%, thereby reducing the amount of CO and H ₂ produced by 2.0%.

In the above-described embodiment, oxygen is used as the oxidizing agent, but air or a mixed gas of air and oxygen is used as the oxidizing agent. In addition, once the coal type is determined, the temperature (ash melting, non-melting temperature) at which an appropriate two-stage reaction is performed is determined according to the elemental composition, ash composition, ash melting temperature, etc., and any oxidant is used. Also, determine the supply ratio of oxidizer and coal to maintain such temperature.
Moreover, solid hydrocarbon fuels other than coal, for example, solid wastes such as petroleum residue oil, solid biomass, and plastics are used as the solid hydrocarbon fuel. In the case where the solid hydrocarbon fuel does not contain ash in a certain amount or more, an inorganic substance having a composition corresponding to the ash can be added to the raw material from the viewpoint of protecting the gasifier wall.

It is a schematic block diagram which shows the example of the two-stage gasifier in this invention. It is a graph which shows the temperature distribution in the furnace main body of the two-stage gasifier in this invention. It is a graph which shows the temperature distribution in the furnace main body in a small-scale furnace. It is a graph which shows the relationship between Lb / Lu and the minimum temperature between burner groups in this invention. It is explanatory drawing which shows the model furnace by this invention and the conventional method for confirming the effect in this invention. It is a graph which shows the temperature distribution in two types of model furnaces shown in FIG. It is a graph which shows the relationship between the furnace height of a gasification furnace, and a furnace wall heat-transfer loss.

Explanation of symbols

1 ... Gasification furnace 2 ... Furnace body 3 ... Upper burner group 4 ... Lower burner group 5 ... Gas outlet 7 ... Melt slag outlet

Claims (1)

A cylindrical furnace body that generates gas by the reaction of the solid hydrocarbon fuel powder and the oxidant, and a fluid mixture of the solid hydrocarbon fuel powder and the oxidant that is disposed in the upper part of the furnace body is injected into the furnace body. An upper burner group, and a lower burner group disposed in the lower part of the furnace body and injecting a mixed fluid of solid hydrocarbon fuel powder and oxidant into the furnace body,
A gas outlet from which product gas is discharged is formed at the upper end of the furnace body,
A two-stage gasification furnace characterized in that the ratio between the distance Lb between the upper burner group and the lower burner group and the distance Lu between the gas outlet and the upper burner group is Lb / Lu = 2-12.

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