CS220057B1 - A method for coal gasification and apparatus for carrying out this process - Google Patents

Abstract

The invention relates to the field of coal gasification into synthesis or fuel gas and solves the problem of cost-effective conversion. Coal is dosed in powder form into the upper part of the reaction zone, where it is heated to the reaction temperature and the resulting mixture proceeds cocurrently through the reaction zone downwards, with intensive heat exchange between the gas and the solid phase occurring along the entire length of the reaction zone. The reactor and the separator form a single body, the reactor is separated from the separator by a partition provided with a connecting pipe. The gas outlet from the separator is located higher than the lower end of the connecting pipe.

Description

The invention relates to a process for the gasification of coal by means of an oxygen-containing gas and to an apparatus for carrying out the process for the production of hydrogen and carbon monoxide which can be used for chemical or heating purposes.

Coal gasification is particularly suitable for less valuable lignite or brown coal, while the gasification itself takes place in an autothermal reactor at temperatures of 1300 - 2200 ° C and pressures of 0.1 - 6 MPa. Under these conditions, a gas with a high H 2 and CO 2 content is produced, free of tarry substances and a very low methane content. The gasification process involves thermally almost neutral pyrolysis reactions, strongly exothermic combustion reactions and strongly endothermic gasification reactions.

Basically, two processes are used for the gasification of coal under the above reaction conditions.

In the first process, the coal is fed into the reactor as a liquid mixture with water. The reaction mixture then flows down the reactor, leaving the reactor at the bottom and passing through an apparatus in which the ash is separated and the gas is cooled indirectly.

This type of gasification has the thermodynamic disadvantage that the evaporation of water takes away so much heat that it is not possible to maintain the preferred reaction temperature range for less heating coal types without enormous oxygen consumption and carbon loss.

In the second process, the coal is fed to the reactor as a powder. The coal inlet is located in the center or at the bottom of the reactor.

The area around and below the feed is used to carry out pyrolysis and combustion reactions, and the area above the feed is used to carry out gasification reactions.

At the inlet of the coal, the gaseous and solid phase (i.e., ash) separates, which falls down and flows out of the reactor in the form of molten high-temperature slag, leaving the reactor rising and leaving the reactor at the top.

This arrangement has the significant disadvantage that in this arrangement it is not possible to utilize the apparent heat of the slag to carry out endothermic gasification reactions. Since the apparent heat of the gas in the upper part is not sufficient to cover this need with heat, the velocity of the flowing gas must be selected so that the rising gas entrains about 20-50% by weight of the solid phase (based on the injected coal) forming the heat carrier. it contains unreacted carbon and must therefore be separated and returned to the reactor in subsequent stages.

The above-mentioned disadvantages are substantially eliminated by the gasification process according to the invention, which is characterized in that the coal in the form of powder is pneumatically metered into the upper part of the reaction zone where it is heated to the reaction temperature. there is an intense heat exchange between the gas and the solid phase. The invention can be carried out by removing the vast majority of the ash from the reaction gas by accelerating the reaction mixture by narrowing the flow profile and then subsequently changing the gas direction by 180 °. The invention can also be carried out by cooling the reaction gas by admixing the cooler water vapor produced by the evaporation of water into which the hot ash falls, the water being located in the water part of the separation zone.

Driven bed reactors are most preferred for gasification in which both the gas phase and the solid phase pass through the reactor at high speed, with some of the solid phase leaving the reactor gas out of the reactor and must be returned.

Achieving the most intensive heat exchange and separating the vast majority of the solid phase is accomplished by a reactor and separator device according to the invention, characterized in that the reactor and the separator form a single body, the reactor being separated from the separator by a baffle and the separator is located higher than the lower end of the connecting pipe.

The method and apparatus of the invention have the following advantages:

since, on the one hand, pulverized coal is used for the reaction and not the mixture of coal and water, and, on the other hand, it utilizes the thermal content of the molten ash to the maximum extent by contacting all of it with the gas phase over the reactor; the reaction not only of the apparent heat of the gas, but also of the apparent heat of all the ash from the coal, and high gas outlet temperatures are achieved which cause high yields of hydrogen and carbon monoxide.

Theoretical analysis of coal gasification has shown that the presence of a solid phase is of great importance for reaching the final temperature of the reaction mixture, which must be sufficiently high (about 1300 - 1600 ° C) to achieve optimum yield of hydrogen and carbon monoxide. According to the invention, the solid phase in the vicinity of the burner is heated to a high temperature (approx. 1800 to 200 ° Cj) and in the zone of endothermic gasification reactions it transfers heat of gas, ie acts as a heat carrier. The lowering of the maximum temperature even makes it unnecessary to use cooling steam for less valuable coal, and it is natural that the greatest effect is achieved when the heat of all ash is utilized and over the length of the reactor. if both the gaseous and solid phases co-flow from top to bottom and are in contact over the entire length of the reactor.

The attached drawing shows an exemplary embodiment of the device according to the invention.

The reactor 8 provided with pulverized coal inlet 1, oxygen inlet 2 or oxygen-rich air and the burner 7 forms, with a separator 10 provided with gas outlet 3, ash outlet, water part 11 with inlet 5 and water outlet 6, one body. The two parts are separated from one another by a partition 12 with a connecting channel 9.

The process of the invention is explained in detail in the following example of gasification of lignite with oxygen.

Example

The method of the invention is operated on the apparatus of the invention shown in the accompanying drawing.

Powdered lignite is conveyed pneumatically by carbon dioxide inlet 1 to a burner 7 located at the top of the reactor 8. In the burner, coal is partially oxidized by oxygen supplied through inlet 2. Specifications for lignite and oxygen, and their relative ratios are shown in Table 1.

At the outlet of the burner 7 pyrolysis and combustion reactions occur, during which the temperature around the flame rises to 1800 to 2000 ° C. High temperature causes melting of ash and greatly accelerates pyrolysis and combustion reactions. The heated reaction mixture then flows down the reactor 8, with intense heat exchange between the gaseous and solid phases. The slag cools and, by its apparent heat, helps both accelerate and carry out the desired endothermic reactions to the required extent and at the required rate. Using the conditions given in Table 1, a temperature of about 1400 ° C is achieved.

The reaction mixture leaves the reactor zone 8 at the bottom thereof and passes through a connecting line 9 to a slag separator 10 immediately adjacent to the reaction zone and located with the reaction zone in a single body and separated from the reaction zone by partition 12. and to cool the gas.

The slag separation of about 95% by weight is preferably carried out by combining the acceleration of the gas in the connecting pipe 9 and changing its direction by 180 ° by placing the end of the connecting pipe 9 lower than the gas outlet 3. Substantially different cross-sections of the connecting pipe 9 and the separator 10, which lead to a reduction in the gas velocity in the direction of the outlet throat, further cause more intense ash separation.

The bulk of the slag falls in the separator 10 into the water located in the water portion 11 of the separator 10, in which it is granulated and periodically discharged through line 4. On contact with water, the slag cools and causes water evaporation to assist in cooling the reaction mixture. Low water temperature (approx. 200 ° C) is ensured by water circulation through inlet 5 and outlet 6.

Using the coal described in Table 1, the yield and efficiency shown in Table 2 can be achieved as described.

T a b u 1 k a 1

Specification of coal, oxygen and weight ratios

Coal composition:

combustible - 59.73% by weight humidity - 8.00% by weight ash - 32.37% by weight

Composition of combustible material:

carbon - 68,00% hydrogen - 5,5% oxygen - 22,00% sulfur - 3,0% nitrogen - 1,5%

Oxygen composition:

oxygen - 98.0% by weight

Oxygen to coal ratio: - 0.48: 1

Table 2

Yields and gasification efficiency yield H2 + CO - 1 Nm ³ / t coal

Dry gas composition

H2 - 27.5 mol%

CO - 59.5 mol%

CO2 - 10.5 mol%

CH4 - 0.1 mole% carbon conversion> 98% chemically bound heat efficiency 78% max.

Claims (4)

Subject Process for gasifying coal using an oxygen-containing gas in an autothermal reactor at temperatures of 1300-2200 ° C and a pressure of 0.1-6 MPa using, in the case of less calorific coal, to control the maximum temperature in the reaction zone of moisture contained in the coal and as transport gas using carbon dioxide, characterized in that the coal in the form of powder is pneumatically metered into the upper part of the reaction zone, where it is heated to the reaction temperature and the resulting mixture moves downstream, while intensive heat exchange between the gas and the solid phases. 2. A process according to claim 1, wherein most of the ash is removed from the reaction gas by accelerating the reaction mixture by narrowing the flow profile and then changing the gas direction by 180 [deg.]. 3. A process as claimed in claim 1, wherein the reaction gas is cooled by admixing the colder water vapor produced by evaporation of water into which the hot, separated ash falls. 4. Apparatus according to claim 1, characterized in that the reactor (8) and the separator (10) form a single body, wherein the reactor (8) is separated from the separator (10) by a partition (12) provided with a connection. and the gas outlet (3) from the separator (10) is located higher than the lower end of the connecting pipe (9).