JPH043437B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF APPLICATION OF THE INVENTION The present invention relates to an improvement in a coal reactor suitable for use in particular as a slug tap hole in a coal gasifier. [Background of the Invention] The spouted bed gasification method, in which coal is gasified at a temperature higher than the melting temperature of ash, can produce hydrogen gas and carbon monoxide gas with high efficiency, so it is used for synthesis gas production and fuel gas production. Many gasifiers are being developed. The biggest challenge in the stable operation of a spouted bed gasifier is to stably discharge coal ash (hereinafter referred to as molten ash) melted within the gasifier to the outside of the furnace. Usually, molten ash adheres to the gasifier wall, descends along the wall, leaves the wall, and falls into the space. The fallen molten slag is cooled by some means and discharged outside the furnace. At this time, the molten ash tends to solidify at the place where it falls from the gasifier wall into the space (hereinafter referred to as the slag tap hole), and in severe cases it blocks the flow path.
In this case, stable operation of the gasifier becomes impossible. Several methods have been proposed to prevent this. A typical example is to heat the slag tap hole by some method to prevent the molten ash from solidifying.
There is a technique shown in Publication No. -76302. Further, a method of electrically heating a slug tap hole is disclosed in Japanese Patent Application Laid-Open No. 172986/1986. Although these methods are highly reliable for stable flow of molten ash, they require fuel to be supplied to the burner and electrical heating energy in addition to coal and gasifying agent, and burner operation control is required, making it difficult to gasify. Furnace operation becomes complicated. Furthermore, when heating with a burner, exhaust gas generated by combustion in the burner mixes into the gas generated by gasification, reducing the calorific value of the generated gas. Other known prevention techniques include adding CaO or Fe ₂ O ₃ to coal to lower the melting temperature of ash and the viscosity of molten slag, allowing it to flow even when the temperature of the slag tap hole is low. . This method is effective when the amount of coal used in the gasifier is limited, as the amount of additive used is limited for each type of coal, or the amount itself is large. When a variety of coals have to be treated in a coal-fired system, operation becomes complicated due to additive selection, supply amount control, etc. As described above, the conventional techniques for stably discharging molten slag have had problems such as complicated operating methods and limited types of coal to be used. [Object of the Invention] An object of the present invention is to provide a coal reactor that can stably discharge molten slag from a wide range of coals without impairing the ease of operation of the gasifier. [Summary of the Invention] For this reason, a material for the slag tap hole that does not get wet by molten ash is used, so that this material can withstand the atmosphere in the gasifier for a long time. If a material that does not get wet with molten slag is used, when the molten slag falls from the gasifier wall into the space, it will fall at a speed close to free fall because it will not adhere to the furnace wall, and the time will be shorter than the time it takes to solidify. It becomes possible to move away from the wall in time. Graphite is a suitable material for the slug tap hole. Graphite is rapidly consumed in an oxidizing atmosphere, so it is necessary to create a reducing atmosphere or an inert gas atmosphere. Therefore, the part where the graphite material comes into contact with the gas in the reactor becomes an inert gas or reducing gas atmosphere. In this way, the introduction hole through which gases flow is installed in or near the graphite refractory itself. Explain the phenomenon that motivated the invention. FIG. 5 shows an example of the flow of molten ash 9 in the spouted bed gasifier and the temperature distribution inside the furnace. Coal supplied from the coal burner 6 is gasified in the gasifier section 4. The ash melts and adheres to the gasifier wall,
Flows downward due to gravity. Furthermore, slug tap hole 7
The slag passes through and falls into the slag cooling section 5. The temperature distribution in the height direction of the gasifier when slag is rapidly cooled in the slag cooling section 5 is shown on the right side of FIG. The temperature reaches its maximum value near the coal burner 6, but because the slag cooling section 5 is located below the gasification section 4, it rapidly decreases as it goes downward. The location where the molten ash solidifies is on the slag cooling chamber side of the slag tap hole 7, because the temperature drop is most significant at this location. As soon as the molten ash reaches the slag tap hole 7, it begins to cool and its viscosity increases. As a result, the flow rate decreases and the time it stays in the low temperature region increases.
It becomes easier to solidify. This is the reason why the eluted ash solidifies near the slag tap hole. The conventional flow down method attempts to prevent solidification by forcibly increasing the temperature of the slug tap hole 7. Contrary to conventional thinking, the present invention allows molten ash to pass through the solidifying temperature range in an extremely short time, faster than the time required for cooling and solidifying, even when the temperature of the slag tap hole 7 remains low. This is what I tried to do. In order to speed up the time it takes for the slag to pass through the tap hole 7, it is conceivable to reduce the viscous force acting in the direction opposite to the flow direction of the slag due to contact between the molten ash and the wall. If this force is zero, the slug will have a free falling velocity and will be able to pass through it the fastest. For this purpose, it is necessary to bring the contact area between the molten ash and the wall close to zero. This phenomenon is related to the wettability of molten ash to the slag tap pore material, and by using a material that is difficult to wet, the above object can be achieved. Although there is no direct mention of the relationship between molten coal ash slag and hard-to-wet materials, for example, Japanese Patent Application Laid-Open No. 126713/1983 discloses a technique for using graphite as a hard-to-wet material for removing molten steel in an electric furnace. ing. The contact angle θ is generally used as a wetting index,
It is defined as not wet when 90°<θ<180°. The contact angle is the angle between a line drawn in the tangential direction of the slag and the object at the point of contact between the slag and the object. Figure 6 shows materials that are likely to be used in current gasifiers: Al ₂ O ₃ , Cr ₂ O ₂ , ZrO ₂ , SiC, Si ₃ N ₄
This figure shows the change in θ when the temperature is raised in an inert gas atmosphere with Pacific coal ash left on a graphite plate. θ=90° (as shown in Figure 7)
is when the sample becomes hemispherical, and the temperature at this point is defined as the melting point of the ash. Beyond the melting point, everything except graphite gradually becomes flat. Graphite has θ=160° and is not wetted by Pacific coal ash. FIG. 7 shows the shapes of the samples in correspondence with the contact angles. In the case of graphite, the shape is almost spherical. In addition, Ermelo coal (melting point = 1480
℃) was measured using the same method, and it was confirmed that graphite did not get wet. Table 1 shows the composition of ash from Pacific coal and Ermelo coal.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. Coal 1 and oxidizer (oxygen or air) 2 are supplied from a coal burner 6 to a gasifier 3. Gasification section 4
The temperature is above the melting point of the ash, and most of the melted ash adheres to the inner wall of the furnace. The produced gas 11 is extracted from above the furnace. The molten ash adhering to the walls travels along the walls and flows to the lower part of the furnace. In order to collect this molten ash, a hole is made in the bottom of the gasifier 3 and the molten ash is allowed to fall into the space. This hole is called a slug tap hole 7.
In this embodiment, the slug tap hole 7 itself is made of graphite material. Graphite is commonly used artificial graphite,
Graphite materials such as natural graphite, or carbon materials can be used. In the example, isotropic graphite descended into the shape of the slag tap hole 7, with an ash content of 0.1% and a porosity of 18%, was used. A sealing gas burner 13 is provided at the bottom of the slug tap hole 7, and a sealing gas 12 such as an inert gas such as nitrogen gas or a gas generated by gasification is supplied, and this gas is caused to flow in the same direction as the generated gas 11. The structure is such that the oxidizing agent 2 supplied from the coal burner 6 does not touch the slag tap hole 7. Also, Figure 2 shows the slug tap hole 7.
This is another embodiment in which the slug tap hole 7 is not exposed to oxidizing gas, and the sealing gas is jetted out from the pores of the slug tap hole 7 itself. A plurality of minute holes are made in the graphite part of the slug tap hole, and the sealing gas 12 is introduced into the dispersion chamber 14, so that the sealing gas 12 is uniformly ejected onto the surface of the graphite that comes into contact with the gas. There is. In the embodiments shown in FIG. 1 and the second receiver, nitrogen gas is used as the sealing gas, and the pressure is 0.8 to 1.0Nm ³ /
It was supplied at a flow rate of h. The temperature of the gasifier 3 is raised by combustion gas from a gasifier starting burner (not shown) installed below the slag tap hole 7. Propane gas and air are sent to the startup burner, and combustion occurs at an excess air rate.
Therefore, before igniting the starting burner, nitrogen gas is flowed into the slug tap hole 7, and this state is maintained thereafter. Coal is supplied when the temperature inside the gasifier reaches a predetermined value, and after the coal is ignited, the starting burner is stopped. Oxygen was supplied from a coal burner at a ratio of 0.76 to 1 weight of coal. The temperature directly above the slug tap hole 7 is 1680 to 1720°C.
The temperature directly below it was 1100-1140℃. Under these conditions, the molten slag was stably dropped without solidifying. At this time, the nitrogen concentration in the generated gas is 1.0 to 1.4%
(volume ratio), with an amount of sealing gas that has almost no effect on the quality of the generated gas.
can withstand sufficiently in the gasifier. In the examples shown in FIGS. 1 and 2 above, Pacific coal was used as the coal. When a slag tap made of graphite material was used, molten ash could be dripped into the slag tap hole without solidifying even if the temperature fell below the ash melting temperature. In other materials, the molten ash solidified and plugged the slug tap holes. Next, an example of Ermelo coal will be described. Into the gasifier shown in Figure 2, 1 liter of Ermelo coal was added.
Oxygen was supplied at a weight ratio of 0.79. The sealing gas was nitrogen gas and was supplied at a rate of 1Nm ³ /h. The temperature directly above the slug tap hole 7 was 1,760 to 1,780°C, and the temperature directly below the slag tap hole was 1,120°C, and under these conditions, the molten ash dripped stably. When a 95% Al ₂ O ₃ refractory was used in the slag tap hole, the temperature immediately above and below the slag tap at the beginning of coal supply was almost the same as in the previous example, but over time molten ash solidified in the slag tap hole. However, the temperature directly below the slug tap hole dropped rapidly. Graphite is also effective in the case of Ermelo coal.
Moreover, since the melting point of Ermelo coal is 1480℃,
It will flow through a temperature range 350°C lower than this without solidifying. In the case of Pacific coal, the difference is 200
℃, it is more effective for coal with a high melting point. Figure 3 shows the case where the generated gas 11 and molten ash 9 both flow vertically downward, and Figure 4 shows the generated gas 1.
This is the case of a furnace structure in which molten ash 9 flows horizontally and molten ash 9 flows vertically downward. In either case, by using a slug tap hole 7 made of graphite material at a location where the molten ash 9 separates from the furnace wall into the space, smooth extraction of the molten ash is possible. [Effects of the Invention] As described above, according to the present invention, by using graphite as the material for the slag tap hole and covering it with non-oxidizing gas, wear and tear can be significantly reduced. It has the effect of allowing smooth extraction of molten ash without complication. Furthermore, since the slag tap hole itself allows dripping even if the temperature is below the melting temperature of coal ash, a wide variety of coal types can be treated.

[Brief explanation of drawings]

1 to 4 are longitudinal cross-sectional views of the slag tap portion of a gasifier, which is one of the coal reactors of the present invention, and FIG.
The figure is a general temperature distribution diagram in the gasifier, FIG. 6 is a diagram showing the relationship between the contact angle and temperature of molten coal ash with respect to various materials, and FIG. 7 is an explanatory diagram showing the shape of molten ash. 1... Coal, 2... Oxidizer, 3... Gasifier,
4... Gasification section, 5... Slag cooling section, 6... Coal burner, 7... Slag tap hole, 9... Molten ash, 11... Produced gas, 12... Sealing gas,
13... Burner for seal gas, 14... Dispersion chamber.

Claims (1)

[Claims] 1. A coal reaction system that has a coal gasification section at the top that heats and decomposes coal to gasify it, a slag cooling section that cools the molten coal slag produced during gasification at the bottom, and a slag tap hole at the boundary between the two. In the furnace, the inner wall of the slag tap hole is made of a graphite refractory, and an inert gas or reducing gas ejection hole for maintaining the surface of the graphite refractory in an inert gas or reducing gas atmosphere is formed by the graphite refractory itself. A coal reactor characterized by being installed at or near the coal reactor.