EP0009073B1 - Process for feeding coal into a coal gasification reactor - Google Patents

Description

The invention relates to a method for introducing a coal suspension into a reactor of a coal gasification plant.

The reactor of a coal gasification plant is preferably operated with positive pressure.

To generate the excess pressure and to maintain it, locks are used at the inlet and outlet ends of the reactor. Certain locks at the end of the entry, e.g. Pumps, screws, mostly the use of a liquid as a carrier for the coal required. That is, pumps and the like devices require a pumpable mixture whose liquid content is relatively large.

Water is preferably used as the liquid, which at the same time is used to generate a gas containing CO and H ₂ .

The basis of the invention is the addition of gas to the coal suspension known from DE-A 263 1185. Above all, carbon dioxide in liquid form is used as the gas. The liquid carbon dioxide serves as a slurry agent and means of transport for the coal dust. In addition, the carbon dioxide acts as a moderator of the gasification process.

The addition of gaseous media to the coal suspension is also known from US-A 4074981, US-A 40976 and DE-A 2130120.

However, the use of liquid carbon dioxide poses significant temperature problems. with himself. For example, the temperature of the slurry must be kept above zero degrees Celsius to prevent the precipitation of water in the form of ice in the coal suspension. The structural and operational measures required to maintain the desired temperature constitute a heavy economic burden for the synthesis gas production.

According to the invention, the economy of synthesis gas production with the addition of gas to the coal suspension is considerably improved by adding an ammonium carbonate solution to the coal suspension and adding an acid and / or heating the resulting coal suspension. It is shown that even small amounts of the ammonium carbonate solution are sufficient to considerably improve the flow behavior of the coal suspension.

Phosphoric acid is preferably used as the acid for releasing carbon dioxide. According to a further feature of the invention, the released carbon dioxide comes from carbon dioxide scrubbing, which usually belongs to a synthesis gas plant of the type described at the beginning. The carbon dioxide is washed out or precipitated from the raw gas and dissolved in ammonia water and used as an ammonium carbonate solution.

In the drawing, an embodiment of the invention is shown.

A coal suspension is introduced from above into a reactor 1 of a coal gasification plant. This is done with the aid of a pump 2. Together with the coal suspension, oxygen reaches the reactor 1 through a feed line 3. The reactor 1 has an operating temperature of approximately 1,400 ° C. at an operating pressure of 30 bar.

In the exemplary embodiment, the liquid phase of the coal suspension consists of water, but it can also have a different consistency, in particular of oil or an oil residue or the like. The water of the coal suspension evaporates under the influence of the heat in the reactor. The coal reacts with the oxygen and the resulting water vapor. The reaction results in a synthesis gas with a high proportion of carbon monoxide and free hydrogen. This synthesis gas is an important chemical raw material.

At the same time, slag accumulates with the synthesis gas, which mainly collects in a water bath in the base of the reactor 1 and is discharged to the ambient air with the aid of a lock 4 while maintaining the operating pressure of 30 bar.

The lock 4 consists of a container, each with a valve at the entry and discharge ends. When the entry end is open, 4 slag collects in the container of the lock, which drops through the water bath in the base of the reactor 1. After reaching a certain filling level in the container, the valve at the end of the inlet is closed and the other valve is opened so that the slag can be removed from the container of the lock 4 without impairing the reactor operation. Then the valve at the discharge end is closed again, the lock 4 is filled with water and the valve at the discharge end is opened.

Another part of the slag obtained in the reactor 1, the flyable slag part, is discharged from the reactor 1 with the synthesis gas. The synthesis gas has optionally already been cooled by a waste heat system integrated in the reactor 1. After exiting reactor 1, further cooling may take place in a waste heat boiler, not shown, before the raw gas enters a carbon dioxide scrubber 5.

The carbon dioxide scrubber 5 consists of two pressure vessels 6 and 7, which are connected to one another by lines 8 and 9. There is a pump 10 in line 8 and a throttle 11 in line 9. Line 8 opens into the container foot at each end, while line 9 opens into container 6 at the end facing the container 6 below the bath level of a water bath 12 .

The other end of the line 9 opens above the bath level of a water bath 1.3 in the container 7.

The water bath 13 is under the same or a slightly lower pressure than the interior of the reactor 1.

As a result of this pressure, a substantial part of the carbon dioxide contained in the raw gas dissolves in the water. The water thus enriched with carbon dioxide penetrates due to a large pressure gradient between the two containers 6 and 7 through the line 9 into the throttle 11 in the container 7. The water pressure is reduced to a desired level by means of the throttle 11, the pressure in the container 7 , reduced. During and after the pressure drop, the carbon dioxide contained in the water bubbles out.

The water collecting in the pressure vessel 7 is drawn off with the aid of the pump 10 and returned to the pressure vessel through the line 8.

So that the raw gas flowing through the water bath 12 in the container 6 does not enter the line 9, the bath level of the water bath 12 must be above the confluence of the line 9 and the pressure container 6. This is achieved by regulating the throttle 11 and / or the pump 10. The necessary adjustment of the. Throttle 11 1 and / or the pump 10 causes a float (not shown) in the pressure vessel 6, which is connected to the throttle 11 and / or the pump 10 via a lever linkage and / or a hydraulic system.

A loss of water is compensated for from a feed line 14 via a slide 15 that is operated automatically or at intervals by hand.

Slag washed out of the raw gas together with the carbon dioxide is collected and discharged in a thickener (not shown) connected into line 8.

So-called precipitation can also take the place of carbon dioxide washing. In the event of precipitation, only the carbon dioxide is deliberately removed from the raw gas, while the usual carbon dioxide scrubbing usually also results in undesired washing out of other constituents. A base in the container 6 is then used to precipitate the carbon dioxide. By reaction of the carbon dioxide with the base, a salt is formed which is drawn off from the container 6 and then subjected to water and heat, so that free carbon dioxide is produced.

The carbon dioxide collecting in the container 7 above the water bath 13 penetrates through a line 16 with an interposed check valve 17 into a container 18. Concentrated ammonia water is located in the container 18. When flowing through the container 18 ^Q and the ammonia water, a substantial part of the carbon dioxide is dissolved in the ammonia water or converted to ammonium carbonate. The remaining carbon dioxide exits through a line 19. Ammonia water is drawn off by means of a pump 20 at the foot of the container 18 and fed to the coal entry 21. The amount of ammonia water withdrawn is continuously replaced via a feed line 22 and an intermediate valve 23 with the aid of a pump 24.

The coals entering the coal entry 21 together with the ammonia water containing dissolved carbon dioxide are wet-ground in a mill 25. The ammonia water can also be fed behind the mill 25 after the coal has been dry-ground. In the feed line to the reactor 1, the carbon dioxide is released again by heating the coal-liquid suspension. The ammonium carbonate breaks down after the addition of small amounts of phosphoric acid. The dosing required for this takes place from a feed line 26. A dosing pump is connected into the feed line 26 for dosing. This can be both a pump delivering continuously via a suitable control valve and an intermittently injecting pump.

The carbon dioxide released in the delivery line is created in many small bubbles, which significantly improve the flow behavior of the carbon-liquid suspension.

The small bubbles have a lower ascent rate than large bubbles and keep the three-substance mixture created by the addition of gas largely stable.

Claims (3)

1. Process for feeding a suspension of coal into a reactor of a coal gasification plant, characterised in that an ammonium carbonate solution is mixed into the suspension of coal, and the resulting suspension of coal has an acid added to it, and/or is heated.

2. Process according to claim 1, characterised in that phosphoric acid is employed as acid.

3. Process according to claim 1, characterised in that carbon dioxide is scrubbed or precipitated out of the crude gas resulting after the coal gasification, and the scrubbed-out carbon dioxide is dissolved in ammonia water and employed as ammonium carbonate solution.

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