CA1157652A

CA1157652A - Coal gasification plant

Info

Publication number: CA1157652A
Application number: CA000340910A
Authority: CA
Inventors: Josef Langhoff; Erwin Althoff; Wolfgang Kolodzey; Ulrich Gerhardus
Original assignee: Ruhrkohle AG
Current assignee: RAG AG
Priority date: 1978-11-29
Filing date: 1979-11-29
Publication date: 1983-11-29
Also published as: EP0012461B1; SU1036237A3; JPS5598294A; DE2851533A1; PL126045B1; EP0012461A1; ZA796488B; PL123992B1; AU5326479A; DE2965692D1; PL219914A1; BR7907720A; AU527886B2

Abstract

ABSTRACT
A coal gasification plant is disclosed comprising a water bath in its reaction unit, and/or a waste-heat boiler which is arranged in series, to receive the slag which is discharged together with the water. The plant is characterized in that it has a settling tank located in the flow path of the slag-carrying water for slag particles having a higher displacement weight than the water, and/or a separator for floatable slag particles.

Description

This invention relates to a coal gasification plant which comprises:
a aoal gasification reactor, a water bath in the reactor and/or in a subsequent waste heat boiler, the water bath including an inlet for receiving ccmbustible components - containing - slag which is dischargeable from the reactor together with water and a settl-ing vessel for sep æating slag particles which have higher displacement weight than water, at least one sep æ ator containing a drum screen for sep æating slag pæt-icles which æe floatable in water, and means for delivering back sep æated combustible components - containing -slag to the aoal gasification reactor.
The slag dischæ ged with water from the coal gasification plant creates a considerable disposal problem for the plant. Whether it is possible to find a solution for this problem is an important criteria during the commer-cial operation of such a plant. The only solution available so fæ i.e., to con-nect the gasification plant to existing drainage systems, entails the danger of clogging the drainage channels and the sewer system.
In accordan oe with the present invention, this is accomplished by means of a water bath including a settling tank for the slag pæticles, æ ranged in the flow path of the water for those slag particles, which, oo~pæed to the water, have a higher displacement weight, and by means of a sep æator located in the flow path of the water for the purpose of separation of floatable slag p æt-icles. me settling tank and the sepæ ator remove the buLk of the particles so that the water may, without danger, either ~e dischæged into drainage system or be recycled to the water bath of the reaction unit, or into the waste-heat boiler respectively. At the same time, the slag is colle ted in the purified fonm, namely, without other waste products. mus the collected combustible components - aontaining - slag may be used further in the coal gasification reaction.

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In detail now, the settling tank is a vessel cc~prising a water inlet belcw or above the surfa oe of the water and at least one clean-water outlet and one outlet for water carrying floatable particles, whereby both outlets are separated f m m each other by means of a wall which extends into the water. This form of construction forces the slag-containing water to move dcwnwards along a oe rtain path inside the vessel, at the sa~e time giving the floatable slag part-icles a chan oe to leave the stream of water in a oe rtain direction. This al-ready leads to a pre-separation of floatable slag particle.
The non-floatable slag particles continue, due to the flow of the water, traveling dcwnwards to the bottom of the vessel, where the direction of the stream of water is changed upwards. They accumLlate at the bottom of the vessel. The resulting clean water flows towards a certain part of the vessel where it can be tapped for any purpose, but in particular for the purpose of re-cycling into the water bath.
The water containing floatable slag arrives in a part of the vessel comprising an outlet which is constructed as an overflow or drainage. At the overflow, due to adequately slow flow of water, the floatable slag particles are retained or collected respectively. A collecting device which is indeFendent frcm the velocity of the flcw is formed for the floatable slag particles by a sieve located at the opening of the outlet of the vessel. At certain intervals, a stationary sieve requires the same maintainance given to an overflow. After some time, the sieve becomes clogged, i.e., the resistance towards the oncoming water becomes too strong and the overflow will be filled up with slag particles so that it will fail to function as a separator, thus forcing the slag particles to spill over the overflow.
An almost maintainance free construction is accomplished by means of a drum sieve. The drum sieve can be used in various ways. It makes it possible to lead the water into the interior of the drum. m ereby, the water runs through the drum to the outside, whereby the draining process due to the centi-fugal force transmitted to the water, is speeded up, thereby accGmplishing a much higher degree of drying. The slanted position of the drum ensures at the same time the flcw of the particles from one end of the drum to the other. The rotation of the drum sieve and the accomplishable degree of drying are limited by the necessary movement of the particles in axial direction of the drum. m e drum sieve should not be rotated so fast that the particles would cling to the drum due to the effect of centrifugal for oe .
In another use of this drum sieve, the slag-carrying water is charged from the outside of the drum. The water, carrying the slag particles, is charged onto the outer surfa oe of the drum. In this case, the water runs through the drum sieve into the interior of the drum, draining towards the bottom, while the slag particles on the outer surface of the drum are c~nveyed ahead and are by means of a skimmer continuously removed from the drum sieve. Due to the slanted position of the skimmer, the slag particles slide via the skimmer, which in this case acts like a chute, into the collector vessel. Preferably, the skimmer ex-tends along the sieve, parallel to the longitudinal axis thereof. m e water can be supplied by way of a similar construction, i.e., it can consist of a feed sheet which, similar to the skimmer, extends along the drum sieve. Particul æ ly favorable w~rking conditions æ e achieved if both sheets are located opposite each other at both sides of the vertical oenterline of the drum sieve, forming with respect to the centre of the drum and the points of contact at the drum sieve an angle of not more than 90. Under these circumstan oe s it is very easy for the drum to receive the slag particles and to carry them towards the skimmer, while there is ample opportunity for the water to drain off.
The water bath itself requires a particular construction in order to ., ~

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V~2 be able to function as required. One form of construction requiring little effort is characterized in that piFes are used for the water inlet and for the wall which separates the floatable slag particles from the non-floatable slag particles. Preferably, the pipes are connected to each other and/or constructed of one piece, and/or are concentrically arranged within each other. The pipe formLng the separator wall discharges into a closed catch basin which re oe ives the water that carries the floatable slag particles. The catch basin can be located within the vessel in which the separation of the floatable particles from the non-floatable particles is caused.
In another form of the invention, there are arranged several vessels in series. This makes a classification (sizing) of the slag possible. However, if several vessels are arranged parallel to each other, a much larger volume of water and slag can be processed while the size of the vessels remains the same.
The classification (sizing) of the slag particles during the process is of particul~r advantage sin oe the slag is to be recycled into the reaction unit. It permits an exact control adjustment for the particular size of the slag globules.
For the purpose of this recycling process, each vessel comprises a pipe which leads directly to the reaction l~n;t. Simple pipes are quite suitable.
The flow of the particles is controlled by means of a pump which is preferably constructed as a piston or diaphragm pump. The flcw of particles can likewise be controlled by means of control val~es arranged inside of individual pipes or inside every pipe. Suitable for control valves are simple cylindrical slide valves.
m e classification (sizing) of the slag particles as they fall on in the different ~essels is determined by means of varying screen-hole sizes or by the difference in the displa oe ment weight of the slag particles, as well as by ~, - ~

t7~2 the velocity of the water. According to the invention, the difference in the displacement weight of the slag particles in two consecutively arranged vessels amounts to at least 0,5 g/cm3. The velocity of the water is at least 2 m/sec.
For a fuller understanding of the invention, referenoe should be had to the following detailed de~cription, by way of example, in connection with the accompanying drawings, in which:
Figs. 1 and 2 show a vessel in accor~ance with the invention, where the vessel is constructed as a settling tank, Fig. 3 and 4 show another vessel in accordance with the invention, where the vessel is constructed as a settling tank~
Figs. 5 and 6 show details of a separator in accordance with the invention, Fig. 7 shows several vessels arranged in series, in accordance with Figs.
1 - 4, with the possibility to recycle the slag to the reaction unit.
Referrinq to Fiqures_l and 2, a setting vessel in accordan oe with the invention consists of a funnel 1. m e funnel 1 rests in upright position on its narrow end. B~th ends are open. At the up~er end of the funnel 1 there is oe ntrally located a pipe 2 inside the funnel. The pipe 2 is held in place by means of side wall water boxes 3 which in radial direction of the funnel abut tightly along the entire length of the pipe 2 and along the opposite inner wall of the funnel and are of equal length therewith. Preferably, the side wall water boxes 3 are welded to the inner wall of the funnel and to the pipe 2. m e side wall water boxes have a bottom 4. The bottom 4 is sQaled tightly to the side wall water boxes 3, as well as to the pipe 2, and to the inner wall of the funnel. Preferably the bottom is welded to these parts. m e bottom 4 foxms a catch basin 5, which catch basin is created by the combination of the side wall water boxes 3, the wall of the pipe enclosed by the side wall water boxes and the bottom 4 and the enclosed inner wall.

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A supply pipe 6 leads to the pipe 2, whereby pipe 6 is for the water carrying the slag particles. This water originates from the water bath of a jet unit which is connected in series to the gasification reaction unit of a coal gasification plant. The gasification reaction unit and the jet unit are hereby generally of cylindrical shaFe and are aligned and positioned on top of each other to enable the slag particles which are leaving the reaction unit to flow straight down into the jet unit where they experien oe a second cooling off. In the base of the jet unit is a water bath.
m e gas generated in a gasification process and the slag particles which æ e carried along by the gas, flow tow æ ds the surfa oe of the water bath.
Hereby, the gas is diverted at the surfa oe of the water bath, while the slag particles, which are carried along, sink down into the water bath, due to their inertia, where they accumulate.
The slag particles, together with the water, are removed from the lower end of the jet unit. In the case of coal gasification, this is carried out under atmospheric pressure and by means of a slui oe, namely, first the lower end of the jet unit is opened, which connects to the upper end of the slui oe .
This allcws the slag to flow out at the lower end of the jet unit into the slui oe. After the slag pRrticles have been removed from the water bath, the end of the water bath and the upper end of the slui oe respectively are closed again.
The amount of water disch æ ged is just equal to the amount of water needed to fill one sluice. The remaLning water of the water bath serves for safety rea-sons to block the gas. The lower end of the slui oe may ncw be opened and the slag, together with the water may under atmospheric pressure or light atmospheric pressure be removed from the slui oe .
m e sluice serves a dual purpose. It is a pressure slui oe. Because it is a pressure slui oe, it is possible to remove the slag under the atmosp~eric ~. ~

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pressure of the reaction unit and from the interior of the jet ~nit. At the same time, ~he sluice protects the gas generated in this process frcm undesired contamLnation and mixing with the surrounding atmosphere, and it protects the surrounding environment from the adverse effects of escaping synthetic gas.
me slag-carrying water from the water bath of the jet unit is pressed into the pipe 2 of the funnel 1 by means of a conveyor pump such as for instanoean impeller pump or a piston pump (not shown), via pipe 6.
Pipe 2 comprises a wall 7. The wall 7 divides the interior of the pipe into two halves and ends at the centre of the pipe 2, namely, it extends over half of the length of the pipe 2.
The slag particles which have various displacement weights, leave pipe 6 and, due to the pressure of the pump, æe foroe d to flow downwæds in the pipe

2. Some of the particles are buoyant, due to their lower displaoement weight in relation to the water. These particles are continuously effected by a buoyancy force. In pipe 6, this buoyancy force is overcome by the pressure of the pump.
At the end of the dividing wall 7, these slag particles have the opportunity to break away from the flow and to rise again in the opposite half of the pipe de-signated as 8. Thereafter, the buoyant slag particles float frcm that portion of the pipe into the catch basin 5.
mose slag particles which, in relation to the water, have a higher displacement weight, exit from the pipe 2 in downward direction and continue to travel in direction of the lower end of the funnel 1. These slag p æticles accumulate at the lcwer end of the funnel 1, from which they may be removed, con-tinuously or in intervals. The water supplied via pipe 6 flows via overflow 10 into the catch basin S and via an overflow 11 located in the remaining funnel area, into outlets 12 and 13. m e water discharging via outlet 12 is not carry-ing such slag particles that have a higher displaoement weight than water and ~' `
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, t ~' 2 accumulate at the lower end 9 of funnel 1. m e water discharging via outlet 12 is also free from floatable slag particles by means of overflow 10. m e over~
flow 10 retains the floatable slag particles. m e overflow 10 and the overflow 11 are formed by a common ring inside the funnel 1 which is subdivided by means of the side wall water boxes 3.
m e elimination of the floatable slag particles by means of overflow 10 and catch basin 5 requires a repeated and discontinuous cleaning and emptying of the catch basin located above the outlet 12a. Otherwise, if the catch basin is overloaded, slag particles float, together with the water, over the overflow 10, into the outlet 12. m e outlet 12a is led tow æ ds the drum sieve in accord-an oe with Figs. 3 and 4.
Referring to Figures 3 and 4, a setting vessel in accordance with the invention consists of a funnel 29. ~he funnel 29 rests in upright position on its narrow end, pointing dcwnw æd. Both ends are open. At the upper end of the funnel 29, a pipe 38 is æ ranged inside the funnel. m e pipe 38 is located centrically inside of a separator zone 31. m e sep æ ator zone 31 is formed by a side wall water box 30, which is welded to the wall of the funnel and at the joint.
A supply pipe 32 for slag-c æ rying water leads to the pipe 38. The slag-car~ying water is by means of a conveyor pump as for instance an impeller pump or a piston pump, via supply pipe 32 pressed into the pipe 38 of the funnel 29.
The slag-c æ rying water leaving the supply pipe 32 is relieved and dis-charged via pipe 38 onto the surface of the water of the sep æ ator zone 31.
Some floatable p æticles, due to their lesser displa oe ment weight in relation to water, are continuously exposed to a buoyancy force. m is buoyancy force causes the p æ ticles to stay on the surface. As edges 35 of the side wall water boxes ,~
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z 30 æ e higher than the level of the clean-water and outlet 34, they prevent these p æ ticles from spilling over into a clean-water outlet 37.
m e slag particles which possess a higher displacement weight in rela-tion to water leave the pipe 38 and continue to move downward in the dividing zone 31 to the lower end 33 of the funnel 29. At the lower end 33 of the funnel 29, the particles accumulate. Frcm an opening provided there they may be re-moved continuously or at intervals. The water supplied via supply pipe 32 flows underneath the side wall 30 and via the overflow 34 into the outlet pipes 37.
m e water discharging frcm the outlet pipe 37 is clear, since slag particles having a higher displacement weight than water accumulate at the lower end 33 of the funnel and floatable slag particles remain within the divid-ing zone 31. The floatable particles can be removed, continuously or at inter-vals through a drain 36. It is also possible to provide a mechanically driven screen rake at the separation zone 31 which additionally removes floatable slag particles.
Figures 5 and 6 show a separator containing a drum screen for separat-ing floatable slag particles from water. The device in accordan oe with Figs. 5 and 6 consists of a box-like container 14. A drum sieve 16 is rotatably mounted into the side wall 15 of the container. m e drun sieve 16 is seated on both sides on flanges 17 and is on one side equipped with a driving motor 18. The driving motor 18 continuously turns the drum sieve 16 at a steady speed. m ere-by, the drum sieve slides along two metal sheets 19 and 20, the front sheet 19 functions as a charging sheet, while the rear sheet 20 forms a chute. The chute 20 leads to a funnel 21, on the underside of which there is a pipe 22 for the purpose of drawing-off the accumNlated slag particles. On the underside of the container 14, there is provided a pipe 23 for drawing-off the water. m e con-tainer 14 comprises furthermore a supply pipe 24 for water carrying floatable slag particles.

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In commercial use, the water carrying the slag particles is led into the vessel 14 by means of a pump via supply pipe 24. Thereby, the water carry-ing the slag particles is charged via the charging sheet 19 onto the outer cir-cumference of the drum sieve which slowly turns in clockwise direction.
The drum sieve 16 transports the slag particles frcm the charging sheet 19 to the chute 20, while the water flows through the drum sieve to the bottLxn of the vessel, and is drawn off through the pipe 23.
The slag p æ ticles arriving at the chute 20 are skimmed off the drum sieve and slide along the chute 20 into the funnel 21. There they are stored 10 and can be remDved, oontinuously or at intervals, via pipe 22, for any further use.
In order to strip the arriving slag particles off the drum sieve, the chute 20 is so arranged that it may slide along the drum sieve and the toleran oe between the chute and the drun sieve may be as small as possible. m e same applies to the charging sheet 19, in order to prevent undesired passing of slag particles onto the bottom of the vessel.
The turning speed of the drum sieve and the conveying velocity of the water and the slag p æ ticles æ e so adjusted that the water level at the charg-ing end lies below the upper limit dictated by the drum sieve.
In order to achieve the highest possible degree of dryness of the slag p æ ticles during the separation prooe ss, there æ e provided screen holes in the chute 20, at random, which Fermit additional drainage of water.
Furthermore the drum seive 16 can also be charged with slag-carrying water from the inside instead frcm the outside. In such an æ rangem~ent, the drum sieve is constructed like a hollcw cylinder and the slag-c æ rying water isfed into the interior of the drum sieve via a ooaxially æ ranged supply pipe.
There, the water flows through the drum sieve into the surrounding vessel. m e rota~ion of the drum sieve accellerates the separation of the water from the slag particles. The disch æ ged water is thrown against the walls of the vessel 14, which for that purpose is suitably d osed on all sidesr flows to the bottom of the vessel and is drawn off via pipe 23.
m e separation inside the drum sieve is a continuous process, which means, the slag from which the water has been removed as much as possible is con-tinuously discharged at the other end of the drum sieve. The vessel which CQ~r prises the drum sieve is in a slanted position, and an indirect driving motor is provided which is operated via a suitable transmission, as for instance a belt or a cogwheel, to turn the drum sieve 16, instead a direct drive by a motor mLunted on the same shaft as the drum sieve, as shown in Fig. 6. If a belt or oogwheel drive is used, the drum sieve can be supported at its outer circumfer-ence and can ccmpris a drive wheel which would be located on the outside of the vessel 14, having an opening equal in size to the inner diameter of the drum sieve. In this manner, the slag particles are able to discharge from the drum sieve 16 and through the drive wheel along a smooth surfa oe and without hindrance. m e slag-carrying water w~uld be supplies via a borehole in the shaft of the flange seat 17.
Where the slag-carrying water is applied from the inside, the speed of rotation of the drum sieve is limited due to the oe ntrifugal force effecting the slag particles and due to the slanted position of the drum sieve 16 and the vessel 14 respectively.
For the purpose of sizing of the slag material, the vessel 14 is pro-vided in pla oe of the catch basin 5. In this case the supply pipe 24 is con-nected to portion 8 of the pipe, and the slag particles with the higher displace-ment weight accumulate in the funnel 1, while the slag particles with the lcwer displacement weight accumulate in funnel 21. A further classification of the ~ , , : .
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3 1 7~ ~z slag material can be accomplished by changing the velocity of the water flow and/or the change of the size of the openings in the drum sieve, and in the chute 20, respectively. m e increase of the velocity of the water flcw causes smaller slag particles to be dragged along to overflow 10. Where several col-lecting and separating vessels are arranged in series, these slag particles accumulate in a collector or separator tank located at the end, which means that the principle of continuous sizing rests upon a lack of functionability of these æ parator and collector devices. Too high velocity of the water flow decreases the collecting and separating capacity of the devices in this process.
Independent from the velocity of the water flow, the sizing can be con-trolled by varying the size of the holes of the sieve. When a sieve having l æ ge openings is used as the first devi oe in the series, the small slag part-icles may float with the water through the drum sieve 16 and through the chute 20 respectively. The collecting and separating devices located first in the series are then concerned only with the large particles. Those small particles floating in the water can subsequently be separated in one or more additional collecting and separating devices æ ranged in series. If the openings of the sieve are graded frcm devi oe to devi oe, the slag particles will be sorted to their size.
~ shows more than one separating and collecting devi oe s connected in series. m e schema shown is hereafter described in det~ls in connectian with vessel 14. According to this emkodiment, inside of each supply pipe 24 there is provided a control valve 25 which is constructed as a cylindrical slide valve.
Each vessel 14 is oonnected via its supply pipe 24 to the outlet pipe 23 of the vessel 14 preceeding thereto. From pipes 23 and 24 a pipe 27 comprising control valves 26 leads to a p æ allel running pipe 28. Valves 25 control the water flow to the vessel 14. Depending on the position of the valves, more or less slag-.

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carrying water is Fermitted to enter vessel 14. m e water, restricted by each valve from entering the vessel 14, flows, together with the slag particles via pipe 27 and control valve 26 into the parallel running pipe 28. The stream of liquid in the pipes 27 can on the other hand also be controlled by adjustment of the cantrol valves 26.
Where the size of the holes of the sieve differs in each vessel 14, in such a manner that the first sieve has the largest holes and the hole size de-creases fram sieve to sieve, the water will carry smaller and smaller slag part-icles as it leaves each vessel 14. This water and these slag particles can be entirely or partially led via pipe 27 which branches off in front of valve 25 which belongs to it into the parallel pipe 28 by adjusting the control valve 25.
After branching off, the remaining stream of water and particles enter-ing vessel 14 following in the series, is again freed from slag particles of a oe rtain size, i.e. of those which cling to the holes of the sieve of vessel 14.
m e smaller particles which are floating in the water exit via pipes 23 and can again either entirely or partially be led towards parallel pipe 28. m is is accomplished by means of the control valve 25 which is located in front of the vessel 14 following in the series.
m e particles sifted out of all of the vessels 14 æ e transported off via pipes 22 for further use as desired.
The slag particles which are c æ ried by water into the parallel pipe 28 may, with reg æ d to their globular size, be sized in such a manner, and the control valves 25 and 26 may accordingly be adjusted in such a manner, that the slag p æ ticles combine perfectly with the coal supply, where the slag from parallel pipe 28 is recycled, into the coal supply, in particular into the mixer for the processing of the coal, which is arranged in front of the gasification plant. This optimal adjustment can be determ m ed by manual test adjustment of the control valve 25.

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This is achieved either by way of correspondingly redu oe d dischargability of the water or by adding portions of discharged water after it has left the separator.
Preferably floatable particles only are recycled, since floatable part-icles still contain combustible carbon material owing to incomplete burning.
Where the addition of totally burnt-out slag particles wDuld be of advantage for influencing the temperature in the reaction unit, an additional supply pipe would be provided for slag particles originating from funnel 1, i.e.
from its lcwer end, leading into parallel pipe 28. The additional supply would be delivered by a suitable conveyor aggregate such as a screw- or worm conveyor.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A coal gasification plant which comprises:
a coal gasification reactor, a water bath in the reactor and/or in a subsequent waste heat boiler, the water bath including an inlet for receiving combustible components -containing - slag which is dischargeable from the reactor together with water and a settling vessel for separating slag particles which have higher displacement weight than water, at least one separator containing a drum screen for separating slag particles which are floatable in water, and means for delivering back separated combustible components - containing -slag to the coal gasification reactor.

2. A coal gasification plant according to claim 1, wherein the drum screen is constructed in a rotatable manner and arranged horizontally, and is provided with a feed plate for subjecting the exterior of the drum screen to water carrying slag, a chute for the slag particles retained on the screen, and a collecting vessel for the slag particles skimmed off the screen through the chute.

3. A coal gasification plant according to claim 1, wherein the drum screen is arranged inclinedly, and is provided with an axial supply of the water carrying slag, an axial outlet for the slag particles, and also a receiving container for the water emerging in a radial direction from the drum screen.

4. A coal gasification plant according to claim 1, wherein the water bath comprises a plurality of the separators arranged in succession.

5. A coal gasification plant according to claim 4, wherein each successive separator has a conduit leading directly to the gasification reactor.

6. A coal gasification plant according to claim 5, which comprises control valves in the conduits.

7. A coal gasification plant according to claim 1, wherein the settling vessel includes a supply conduit for water carrying the slag particles, a discharge for clear water and an input to the separator for water containing slag particles floatable in the water while the discharge and the input are separated from each other by a wall extending into the water consisting of side cheeks and a bottom.

8. A coal gasification plant according to claim 7, wherein the clear water discharge is formed as an overflow.

9. A coal gasification plant according to claim 7, wherein the supply conduit has an opening below the water level.

10. A coal gasification plant according to claim 7, wherein the space defined by the side cheeks, with which the discharge is associated, is open downwards for discharge of the non-buoyant slag particles, and that the discharge at the bath level has an opening for free outflow of the slag particles floatable in the water.

11. A coal gasification plant which comprises:
a gasification reactor;
a water bath in the reactor and/or in a subsequent waste heat boiler, the water bath including an inlet for receiving combustible components containing - slag which is dischargeable from the reactor together with water, a settling vessel for separating slag particles which have a higher dis-placement weight than water, the settling vessel comprising a supply conduit for water carrying the slag particles, a discharge for clear water and a discharge for the slag particles accumulating at the bottom of the vessel;
at least one separator containing a drum screen for separating from water slag particles which are floatable in water, the drum screen being constructed in a rotatable manner, being arranged horizontally, and being provided with a feed plate for subjecting the exterior of the drum screen to water carrying slag particles floatable in water, a chute for the slag particles retained on the screen and a vessel for collecting the slag particles skimmed off the screen through the chute; and means for delivering back separated combustible components-containing slag particles to the coal gasification reactor.

12. A coal gasification plant according to claim 1 or 11, wherein the settling vessel and the separator or the separators are connected in series.