GB2189504A - Process and apparatus for gasification - Google Patents

Abstract

In a gasification process low-grade and high-grade fuels are fed respectively into two reactor chambers 4,5, the gas compartments of which are separate and the baths of molten metal of which are in communication with one another via passageways 3. <IMAGE>

Description

SPECIFICATION Process and apparatus for gasification The invention relates to a process of gasification and to an apparatus for carrying out the process, and especially to the gasification of low-grade fuels in a bath of molten metal which is liquid at high temperatures, particularly a bath of molten iron.

During the gasification of fuels containing carbon and/or hydrocarbons in a metal bath which is liquid at high temperatures such as molten iron for example, relatively high-grade fuels such as open-burning coal, anthracite,fossil-coal coke or lignite coke with a sufficiently high calorific value have to be used in order to be able to compensate for heat losses in the gasification plant and to keep the temperature of the iron bath at a constant height. If the calorificvalue of the fuels to be gasified sinkstoo low, a decrease in temperature and ultimately chilling ofthe iron bath can occur. This can be counteracted by using an overstoichiometric proportion of oxygen, which means that in order to introduce heat into the process, at least some ofthe high-energy process gas produced has to be burnt.

As a result, however,thequalityofthe process gas produced is impaired. If the qualitative requirements fortheproductgasarehigh,thedisturbing CO2and H20 components must be subjected to a following gas purification stage or gas scrubbing which involves costs.

A process is known from DE-OS 30 31 680 wherein the process gas produced in the iron melt of a converter and containing essentially CO and H2 is drawn into the converter space above the melt by means of an oxidizing agent, for example oxygen or air, which is additionally blown onto the surface of the molten bath and is partially burnt, the resulting heat of combustion being intended to be transmitted to the molten iron. As a result, it is supposed to be possible to gasify types of coal with a low calorific value by the known process for the gasification without the addition of other high-energy fuels such as aluminium or silicon for example. In this case, however, the product gas also contains a high proportion of CO2 and H20 as a result of which the quality ofthe gas is greatly reduced.

The present invention seeks to provide a process and an apparatus for carrying outthe process for the gasification of low-grade fuels in a bath of molten metal which is liquid at high temperatures, particularly a bath of molten iron, whereby a qualitatively high-grade gas can be produced by means originating from the metallurgical field while avoiding following gas scrubbing for the separation oF C02/H2O.

In accordance with a first aspect ofthe present invention, there is provided a processforthe gasification of low-grade fuels in a molten bath of metal which is liquid ata hightemperature,wherein low-grade fuels are introduced into a first reaction zone having a bath of molten metal and high-grade fuels are introduced into a second reaction zone having a bath of molten metal, the gas compartments of the two reaction zones being kept separate from one another and the bath of molten metal of the first reaction zone being mixed with the bath of molten of the second reaction zone.

As a result of the separate introduction of low-grade fuel into the first reaction zone and the introduction of high-grade fuels into the second reaction zone separately therefrom, a whole series of advantages are achieved: A qualitatively high-grade gas which is uncontaminated by CO2 and H20 components results as process gas from the second reaction zone. The low-energy waste gas resulting in the first reaction zone and consisting mostly of the volatile burn completely to introduce heat into the bath of molten metal and partially used for other purposes and tasks within the whole process.The carbon going into solution inthe bath of molten metalinthe first reaction zone enters, as a result of mixing the bath of molten metal from the second reaction zone, the decarbonization or gasification region of the bath of molten metal in which, in the second reaction zone, the carbon dissolved in the metal is partially oxidized to form gaseous carbon monoxide by spraying in or blowing on the gasifying agent such as oxygen or oxygen-enriched air or oxygen-enriched waste gas from the first reaction zone. The resulting high-quality product gas which draws its carbon components from high-grade and low-gradefuel, no longer needs any following gas scrubbing.

In a development of the invention, it is provided that the bath of molten metal in the first reaction zone is kept free of a layer of slag or a slag forming from ash and non-combustible components ofthe low-grade fuels to be gasified is drawn off from the bath of molten metal and slag-forming constituents are introduced into the second reaction zone. In this manner, assurance is provided that a satisfactory heattransferand transfer of substances can be effected in the first reaction zone. The heat resulting from the combustion of the volatile components from the low-grade fuels can be absorbed by the bath of molten metal without a hampering layer of slag (with poor heat conductivity).The transfer of substances or the dissolving of the carbon from the low-grade fuel in the bath of molten metal is not hindered by a layer of slag and can take place sufficiently quickly as a result of the movement ofthe molten bath or ofthe constant exchange of material ofthe liquid phase between the two reaction zones.

Thesulphurcontained in the low-grade fuels mostly goes into solution in the bath of molten metal in the first reaction zone and is removed by chemical combination with the basic slag-forming constituents such as lime for example, introduced into the second reaction zone, in the slag forming there so that practically no sulphur components are contained in the product gas produced. The slag in the second reaction zone is drawn off from time to time and re-formed by added lime.

In a further development of the invention, it is providedthat brown coal, low-gradefossil coals, peat, wood, sawmill waste, sawdust, straw, agricultural waste products, tar, bitumen, pitch, waste oil, heavy oil, oil shale, household refuse, bulky refuse, waste materials, plastics materials, sewage sludge, cartyres, scrap rubberor similar materials containing carbon and hydrocarbons as weil as mixtures of these materials are introduced as low-grade fuel, in appropriately comminuted or agglomerated form, into the first reaction zone with a bath of molten metal. the range of low-grade fuels in the form listed is very advantageously extended, for the first time, by the process combination according to the invention of two reaction zone which are separate with regard to the gas phase and in communication with regard to the molten bath phase, wherein all conceivable low-grade fuels can be used in the first reaction zone and the resulting waste gas is re-used and "filtered off" in the metal bath ofthe second reaction zone.

In a further development ofthe invention it is provided,forsimplified handling and in order to equalize the quality of the most varied low-grade fuels,thatthe low-grade fuel, packed in containers, is introduced in portions into the first reaction zone, on the bath of molten metal. When containers are used for the low-grade fuels, simple transport or conveying and feed systems, such as open conveyor belts, vibrating conveyors or rotaryvane locks for example, can be used. A mixture ofthe low-grade fuels may consist, for example, of comminuted or processed oil shale, scrap rubber and bitmen or of processed household rubbish, sawdust and used oil.

In this case, it is an advantage if closable cans, buckets, crates, barrels, paper bags or sacks of material which can be melted down and/or combustible material are used as containers. The cans, buckets or barrels may vary advantageously consist of sheet metal for example which melts down in the iron bath and helps to compensateforthe losses of iron bath and helps to compensateforthe losses of iron dust discharge with the waste gas or process gas. The crates, bags or sacks may consist for example of wood, plastics material, paper jute and contribute to the introduction of heat into the first reaction zone bytheircombustion.

In afurther development ofthe invention, it is provided that at leastthe first reaction zone is operated at a pressure of 1 to 10 bar, preferably at3 bar, and the closed containers are introduced into this reaction zone by means of at least one gastight and pressure-tight lock.

The formation of dust and soot in the low-energy waste gas ofthe first reaction zone is counteracted by the pressure operation at least in the first reaction zone. As a result of the compression of the gas, more gas molecules, for example of the volatile components, are available forthe combustion in the same reaction space; the heat capacity of the gas is increased and the introduction of heat into the bath of molten metal is improved.

In a further development of the invention, it is provided that the gas constitutes escaping from the low-grade fuel, such as the volatile components for example and other pyrolysis products are caused to react witch added oxygen or are at least partially burnt in the first reaction zone. As a result ofthe combustion of the combustible gas constituents, the heat needed to maintain the constant temperature of the metal bath in the first reaction zone is very advantageously made available or compensation is provided for the heat losses.

In a further development of the invention, it is provided that the amount of waste gas from the first reaction zone is kept as low as possible and after direct cooling, preferably by means of a suspension-type heat exchange in suspension with fine-grained coal and/or limestone, the waste gas is used as agitating gas, as carriergasforthesolids such as coal, coke, lime and fine-grained slag drawn off from the first reaction zone, and/or as a gasifying agent in the second reaction zone.

The waste gas from the first reaction zone is mostly recycled into the whole process since on the one hand it still contains valuable substances such as CO, CH4, dust containing iron and carbon for example as a result of the direct contact with fine-grained coal in the suspension-type heat exchange but on the other hand may also contain sulphur components, soot and nitric oxide which may not be released into the atmosphere with the waste gas without special separating measures.

The investment and operating costs for a dust-removing and desulphurizing or denitrogenizing device can be minimized if the amount of waste gas as a whole or the amount of waste gas to be released into the atmosphere is kept as small as possible. This is achieved in a simple and advantageous manner by recycling the greater part ofthe amount of waste gas in that the waste gas from the first reaction zone is again sprayed into the bath of molten metal of the second reaction zone, while it is used, for example, as agitating gas to produce a directional flow in the molten bath, as a carrier gas for the fuels in particleform and lime orground slag from the first reaction zone, as a coolant for oxygen blast nozzles or as a gasifying agent enriched with oxygen.

In a further development of the invention, it is provided that a horizontal flow ofthe molten metal bath between the two reaction zones is produced by appropriately directed spraying of the gasifying agentcontaining oxygenandofthehigh-gradefuels into the second reaction zone and by appropriately directed injection of combustion oxygen and/or of an agitating gas into the first reaction zone. As a result, assurance is reliably provided that a constant exchange of the metal baths in the two reaction zones is effected so that the carbon which has gone into solution in the first reaction is partially oxidized by the injection of oxygen into the second reaction zone and a high-quality production gas containing essentially CO and H2 results. Furthermore, as a result ofthe exchange of the metal baths, assurance is also providedthatthetemperature of the molten metal in the two reaction zones is equal in height and remains constant.

In a further development of the invention, it is provided that the slag drawn offfrom the first reaction zone is conveyed at least partially into the second reaction zone. As a result, on the one hand an introduction of sulphur dissolved in the bath of molten metal in the second reaction zone into these slag components can be effected almost up to the saturation limit and on the other hand any metallic oxides still contained in the slag are reduced, the metal is returned to the metal bath and so losses of metal from the second reaction zone via the slag phase drawn off are reduced.

According to a second aspect ofthe present invention, there is provided a plant for gasifying low-grade fuels in a molten metal which is liquid at high temperatures, comprising a reactorfilled with molten metal,with a partition disposed in a central region of the reactor, the partition having, at the bottom of the reactor, at least one passageforthe molten metal, and first and second reaction chambers defined by the partition, each comprising at least one feed memberforfuels and gasifying agent containing oxygen and one offtake member for molten slag and/or metal, and the first reaction chamber comprising an offlake pipe for the low-energy waste gas and the second reaction chamber comprising an off uke pipeforthe high-energy product gas.

Mixing of the two gas phases in the first and second reaction chambers is excluded by means of the partition. The recycled waste gas from the first reaction chamber is converted into high-quality gas component in the second reaction chamber. Sulphur is removed by chemical combination in the slag, nitric oxides are reduced, soot is cracked and gasified; CO2 and H20 components are reduced to CO and H2, the excess oxygen combines with the carbon dissolved in the bath of molten metal and likewise forms CO.

As a result of the coupling of the two reaction chambers with separate gas phases, all the gasifiablewaste substances and materials in question can be introduced into the first reaction chamber (this reactor portion "eats" everything) without being able to cause a negative effect, such as a deterioration in quality on the final product gas.

According to a third aspect of the present invention,there is provided a plant for gasifying low-grade fuels in a molten metal which is liquid at high temperatures, comprising two reactors separate from one another, with reaction chambers each of which comprises at least one feed member forfuels and gasifying agent containing oxygen, one offtake pipeforthewaste gas or product gas produced, one offtake member for molten slag and/or molten metal and which are in communication through at least one pipelineforthe molten metal disposed in the region of the lower side wall ofthe reaction chambers.

Such a plant, with two reactor chambers connected by at least one and preferably by two refractorily lined pipelines, represents another possibility of achieving an exchange of the metal bath or an equalization of carbon and sulphur concentration of the metal phase with separation of the gas phases. In this case, it is particularly advantageous if a shut-off device, such as a slide valveforexample, is provided in the or in each ofthe pipelines forthe molten metal between the two reaction chambers. Thus if repair work becomes necessary in the refractory masonry, the pipe connection can be closed in only one reactor and the molten metal only needs to be let out of one reactor chamber.The other reactor, for example the one with the second reaction zone, into which high-grade fuel is sprayed, can continue to be operated while the lacking low-energy waste gas is replaced by other, possibly inert, gases.

In a development of the invention with regard to apparatus, it is provided thatthefeed memberfor supplying the containers with the low-grade fuelsto the first reaction chamber is constructed in the form of rotaryvanelockordoublerockingtrap-door lock. In this mannerthe component step ofthe process in the first reaction chamber can take place separately from ortogetherwith the component steps ofthe process in the second reaction chamber, under an excess pressure beneficial to the whole process. This can also be achieved in an advantageous manner if the feed memberforthe low-grade fuels into the first reaction chamber is constructed in the form of a screw conveyor.

In a further development of the invention, it is provided that the waste-gas conduit behind the first reaction chamber is constructed in the form of a suspension-type heaterexchangerwith riser and cyclone separator, that riser comprising, in the lower region, at least one feed member for introducing solids in the form of particles, such as limestone, coal, metallic oxides or metal powder for example. In this manner, the low-energy waste gas is cooled and the thermal energy contained therein is utilized in a logical manner, for example in the suspension-type heat exchanger.On the one hand, the solids in the form of particles to be sprayed in can be preheated to as high a temperature as possible; on the other hand, heat-consuming operations such as the neutralizing of limestone orthe carbonization and partiallythe pyrolysis and/or coling of the coalsto be gasified or a reduction of metallic oxides which are introduced into the reactors to compensate for metal losses, can be moved forward into the suspension-type heat exchangerso thatthe molten bath reactors are relieved as regards heat balance or no heat is withdrawn from time for these reactions.

In another development of the invention, it is provided that the ofltake membersforthe molten slag from the two reaction chambers are in communication either together or separately from one another, with a slag granulating device through a conduit under pressure. This measure is necessary for carrying outthe process under pressure and the slag withdrawn from the process is processed in a logical manner for a further application. It is further an advantage ifthe slag granulating device is pressure-tight in construction and consists of a water tank witch lateral water nozzles, a conveyor device such as a bucket conveyor for example, conveying the fine-grained slag out of the water bath, an inclined ring separator or a conveyor worm, and of a rotary vane lock. In this manner, the granulated slag can be segregated from the pressure region of the process very simply without major circulation and purification of the water.

Preferred embodiments ofthe present invention will now be described, by way ofexample only, with reference to the accompanying drawings, ofwhich: Figure 1 shows a longitudinal section through a plant according to a first embodimentofthe present invention forthe gasification of low-grade fuels; Figure 2 shows a second embodiment of a gasification plant according to the invention, in plan view; Figure 3 shows a section through the gasification plant of Figure 2, on the line Ill-Ill; Figure 4 shows another section through the gasification plant of Figure 2, on the line IV-IV; and Figure 5shows a diagrammatic general view of a plant according to the present invention for the gasification of low-grade fuels.

In Figure 1, a reactor is designated by the reference numeral 1 which comprises, in its central region, a partition 2which is provided,atthe bottom of the reactor 1, with at least one but preferably with two passages 3 for the molten metal. The partition 2 may be equipped with an appropriate internal cooling device 17. Two reactor chambers 4 and 5 areformed in the reactor 1 by the partition 2 and each comprise at least one feed member 6,7 for the particular fuel to be gasified, at least one feed member8 and 9 forthe oxidizing or gasifying agent containing oxygen and at least one off uke member 10,10' and 11 for molten slag and/or iron.Furthermore, the first reaction chamber 4 comprises an offtake pipe 12 forthe low-energy waste gas and the second reaction chamber 5 comprises an offtake pipe 13 forthe high-energy product gas.

The member 6forfeeding the low-grade fuels into the reactorchamber3 is preferably constructed in the form of a gastight and pressure-tight rotary van lock 14, particularly if the reactor 1 is to be operated art a pressure between 1 and 10 barfor example. The feed member 6 may, however, also be constructed in the form of a doubietrap-door rocking lock. The members 7 and 9 forfeeding the high-grade fuel and the gasifying agent containing oxygen into the reaction chamber 5 may be constructed in the form of lances 15 and/or of nozzles 16, each in a multi-channel design if necessary.The oxygen nozzles 8, 16 are arranged in the side wall ofthe reactor 1, preferably close, that is to say at a distance of about 1 Oto 80 cm, abovethe surface 21 of the iron bath in the reaction chamber4 and preferably close, that is to say at a distance of about 10 to 60 cm, below the surface 21 of the iron bath in the reaction chamber 5. A fu rther feed pipe 18for primary slag from the first reaction zone can be arranged in the side wall of the reactor 1, leading into the second reactor chamber 5.Afurtherfeed pipe 18 for primary slag from the first reaction zone can be arranged in the side wall of the reactor 1, leading into the second reactor chamber 5. Afurther agitating-gas nozzle 22 is provided at the opposite side of the reactor 1, in the side wall of the reactorchamber4. Furthermore, a burner 19, directed towards the surface of the iron bath 21, is provided in the roof region ofthe reaction chamber 4.

During operation of the embodiment of the gasification reactor illustrated in Figure 1 forthe gasification of low-gradefuels, the previously appropriately prepared and mixed low-grade fuel, packed in containers 20, such as paper bags or sheet-metal buckets, isfed to the surface 21 ofthe iron bath by means of the rotary vane lock 14 situated either in the roof region or in the side wall of the reactor chamber 4. The metal bath in the reactor may, however, equally well consist of molten lead or copper. The low-gradefuel is previously prheated to a temperature of about 1200 to 250 by means ofthe heat contained in the low-energy waste gas.As soon as the low-grade fuel in the container 20 enters the reactor chamber 4through the rotary vane lock 14, it is abruptly heated to the iron-bath temperature of 1 4500for example. As a result of the carbonization and pyrolysis products, such as residual water vapour, volatile constituents and easily vaporized hydrocarbons emerging explosively, the container bursts and burns (plastic bag) or melts down (sheet metal bucket).

The carbon and sulphur contained in the low-grade fuel go into solution in the iron bath (indicated as C* and Sin Figure 1 of the drawing).

The non-gasifying or non-soluble constituents ofthe low-grade fuels are formed into slag and immediately removedfrom the reaction chamber4 through the offtake member 10. The low-energy waste gas formed in the reactor chamber 4 is conveyed, through the offtake pipe 12, into a waste-gas cooling devive, not illustrated in the drawing and a hot-gas dust-separating device which works at a temperature of 400"C for example.

Preferably the amountofwaste gas should be kept as small as possible and most of is should be recycled.

This is done, for example, in that the cooled and purified waste gas is partly used as agitating gas ata temperature ofabout3800Cthroughthe agitating-gas nozzle 22 to produce a directional horizontal flow of the iron bath through the passage 3 in the partition 2 inside both reactor chambers 4 and 5. The nozzles 7,8,9 and 16 provided in the side wall of the reactor 1 may likewise be aligned obliquely downwards, somewhat out of the horizontal, so that a bath flow equalizing concentration is reinforced. Furthermore, a iarge proportion of the low-energy waste gas is used as carrier gasfor spraying the high-grade fuels aswell as lime and fine-grained slag into the reactor chamber 5.Since the low-energy waste gas contains large proportions of CO2 and H2O, it may further be blown into the iron bath through the nozzles 9 and 16, in which case it is used as gasifying agent.

The SO2 components contained in the low-energy waste gas are "filtered off", that isto say reduced, in the iron bath in the second reaction zone or in the reactor chamber 5 during which the oxygen accumulates on the dissolved carbon and the sulphur is bound in the slag. A remaining residue of the low-energy waste gas may possibly be re-burnt as additional or auxiliary combustion gas in furnaces elsewhere.

The high-grade fuel and the gasifying agent oxygen, possibly with additions of waste gas from the first reaction zone, are blown into the reactor chamber 5 through the feed member 7, for example thetop-blowing lance 15 and/orthe nozzles 9,16.

Here an excess supply of heat generally prevails which, as a result ofthe flow of the iron bath inside the two reactor chambers, compensates for the heat losses in the first reaction zone. A high-quality, high-energy product gas which is almost free of sulphur and is formed essentially of CO and H2, is drawn offthrough the offtake pipe 13 and after cooling in an indirect heat exchanger and being freed of dust, is supplied for further use.

Another embodiment of a plant according to the invention is illustrated in Figure 2, the reference numerals already used in Figure 1 being used for equivalent parts.

The low-gradefuels are introduced, intheform of a pasty mixture, for example a mixture of heavy oil, tar, sawdust, household rubbish and sewage sludge, into the reactor chamber 4through the feed member 6 which is provided in the roof ofthe reactor 1 ' and in this case is constructed in the form of a screw conveyor 31. Oxygen or oxygen-enriched airfor burning the volatile components and other pyrolysis products from the low-grade fuels, is injected through the feed member 8, a nozzle provided in the sidewall ofthe reactor 1 above the level ofthe iron bath. The low-energy waste gas formed is drawn off through the offtake pipe 12, cooled down, freed of dust and at least partially re-used in the reactor 1".

The two reactors are connected to one another through two refractorily lined pipelines 30, 30'. If necessary, the pipelines 30, 30' can be disconnected by means of shut-off devices 37, 37', for a possible disturbance, for example in the reactor chamber 4, only this reactor chamber has to be emptied while the separate gasification of high-grade fuels, blown in through the multi-material nozzle 7 orthe lance 5, could be continued in the reactor chamber 5.

Asa result of the special alignmentofthefeed members 7,8 for fuels and gasifying agent and the agitating-gas nozzle 22, a horizontally aligned circulating flow of the iron bath is caused between the two reactors 1' and 1".

The carbon which has gone into solution in the reactor chamber 4 is gasified to form carbon monoxide and is drawn off, as high-energy product gas, from the offtake pipe 13 in the roof region of the reactor 1". The corresponding slags are removed from the process as intermediate products or by-products, through the offlake members 10, 10'. In ordertocompensateforheatlossesorto maintain thethermal economy,the burner 19 maybe provided in the sidewall of the reactor land may preferably be constructed in the form of a combined fuel burnerforfuel gas/solid (or oil/coal dust) and is fired, for example, with recycled low-energy waste gas, with blast-furnace gas and coal dust.

In Figures 3 and 4, cross-sections of the reactors 1' and 1" of Figure 2 are illustrated. In this case, the passages 3,3' of the pipelines 30, 30' between the reactors 1', " as well as the screw conveyor 31 as a feed member 6 for the low-grade fuel on the reactor 1' are particularly clear. The arrangement in heightof the fuel feed member 7 and of the agitating-gas nozzle 22 can likewise be seen. The feed member7 and the agitating-gas nozzle 22 essentially cause the flow of the iron bath circulating horizontally through the passages 3 and 3' between the two reactors 1 ' and 1".

According to the diagrammatic general view of Figure 5, low-grade fuels in a bulky form such as household refuse, bulky refuse, straw or cartyres for example, enter a comminuting device 50 such as a spikedcrusheroran impact hammer mill and are then mixed, in comminuted form, possibly with the addition of other low-grade fuels such as sawdust, sewage sludge and pitch for example (indicated by the arrows 55,56) in a mixing and granulating device 51, for example a rotary drum, and formed into granulated material or agglomerates.The mixture of various low-gradefuelsthus prepared can be fed, in a pasty consistency directly into the reactor chamber 4 of the reactor 1 by a screw conveyor or it is compressed in a briquetting machine 52, for example a roll press, and conveyed into the reactor chamber4via a conveyor belt 53 by means ofthe rotary vane lock 14. If the low-grade fuels are to enter the gasification reactor 1 in portions, packed in containers, the prepared mixture travels through a filling and packing station 54 before it enters the molten iron bath via the conveyor belt 53 and the rotary vane lock 14.

The low-energy waste gases resulting from partial combustion ofvolatile components and other carbonization and pyrolysis products in the reactor chamber4 are conveyed through a waste-gas pipe 32 into a prel imi nary separating cyclone 58 for the separationofsoot,dustand iron particles.These particlesseparatred outarethen admixed with low-gradefuelsto be gasified and recycled into the reactor chamber4.The preliminary separating cyclone 58 is followed by a suspension-type heat exchanger 33 consisting of riser 34 and cyclone separator 35, in order to cool the hot waste gas, while two pipelines 59,60 discharge at the lower end ofthe riser 34 for the introduction of powdered limestone CaCO3 and/or granulated coal orfinely divided low-grade fuels. In this advantageous manner, the waste gas can be cooled to about 450"C, in that the thermal energy contained in the waste gas heats the added solids, dissociates the limestone to CaO and dewaters (bound water of crystallization) carbonizes and cokes the carbonaceous materials.

The heat-treated particles are separated out ofthe stream of waste gas in the cycline separator 35. The burnt lime and the coke dust produced are then blownintothereactor5throughthelance 15 orthe nozzles. 7,9,16in ordertoform slag ortobind sulphur and forthe gasification into high-quality product gas. The low-energy waste gas is completely purified, at waste-gas temperatures of about 300'C, in a following electrostatic filter 61 and is partially recycled into the reactor as preheated carrier gas, agitating gas and gasifying agent. Another portion of the waste gas can be after-burnt and drawn off into the atmosphere.

The slag formed in the reactor chamber 4 is introduced into a slag granulating device 38 and blown by means of at least one water nozzle 40 into a fine-grained granulated slag (slag sand). The slag granules are removed from the watertank 39, which is at the same pressure as the reactor 1, for example 5 bar, by means of a conveyor device 41, for example a screw conveyor, through a pressure-tight rotary vane lock 42. The slag discharged from the reactor chamber 4can, if it still has an adequate suiphur-binding capacity, be recylced into the reactor chamber 5. Thefinal slag discharged from the reactor chamber 5 is processed in an appropriate manner and supplied for use, for example in road building or in the cement industry.

Thus all carbonaceous materials, particularly household refuse or similar waste materials containing carbon, can be converted into a valuable product gas consisting of CO and H2 which is almost free of sulphurand which is cooled in the usual manner, for example in an indirect heat exchanger, with the gasification plants according to the present invention.

Claims (27)

1. A processforthe gasification of low-grade fuels in a molten bath of metal which is liquid art a hightemperature,wherein low-grade fuels are introduced into afirst reaction zone having a bath of molten metal and high-grade fuels are introduced into a second reaction zone having a bath of molten metal, the gas com partments of the two reaction zones being kept separate from one another and the bath of molten metal of the first reaction zone being mixed with the bath of molten metal of the second reaction zone.

2. A process as claimed in claim 1 wherein the molten metal is iron.

3. A process as claimed in claim 1 or 2,wherein the bath of molten metal in the first reaction zone is kept free of a layer of slag or a slag forming from ash and non-combustible components ofthe low-grade fuels to be gasified is drawn offfrom the bath of molten metal and slag-forming constituents are introduced into the second reaction zone.

4. A process as claimed in claim 1 or 2, wherein a slag forming from ash and non-combustible products ofthe low-grade fuels to be gasified is drawn offfrom the bath of molten metal in the first reaction zone and slag-forming constituents are introduced into the second reaction zone.

5. A process as claimed in any preceding claim, wherein brown coal, low-grade bituminous coal, peat, wood, sawmill waste, sawdust, straw, agricultural waste products, tar, bitumen, pitch, waste oil, heavy oil, oil shale, household refuse, bulky refuse, waste materials, plastics materials, sewage sludge, cartyres, scrap rubber or similar materials containing carbon and hydrocarbons, ora mixture of one or more of these materials are introduced in appropriately comminuted or agglomerated form, as low-grade fuels, into the first reaction zone.

6. A process as claimed in any preceding claim, wherein the low-grade fuel is introduced, into the bath of molten metal ofthe first reaction zone packed in individual containers.

7. A process as claimed in claim 6, wherein closable cans, buckets, crates, barrels, paper bags or sacks of a material which can be melted down and/or combustible material are used as containers.

8. A process as claimed in any preceding claim, wherein at leastthefirst reaction zone is operated at a pressure from 1 to 10 bar, andtheclosed containers are introduced into this reaction zone by means of at least one gastightand pressure-tight lock.

9. A process as claimed in claim 8 wherein the first reaction zone is operated at a pressure of 3 bar.

10. A process as claimed in any preceding claim wherein combustible gas constituents escaping from the low-grade fuel, such as the volatile constituents and other pyrolysis products, are caused to react with added oxygen or are at least partially burnt in the first reaction zone.

11. A process as claimed in any preceding claim, wherein the amount of waste gas from the first reaction zone is kept as low as possible and the waste gas, after direct cooling, is used as agitating gas, as carrier gas for the solids, such as coal, coke, lime and fine-grained slag drawn offfrom the first reaction zone, to be introduced into the second reaction zone, and/or as a gasifying agent in the second reaction zone.

12. A process according to claim 11, wherein the direct coding ofthe waste gas is by means of a suspension-type heat exchange in suspension with fine-grained coal and/or limestone.

13. A process as claimed in any preceding claim, wherein a horizontal flow of the molten bath of metal between the two reaction zones is produced by appropriately directed spraying of the gasifying agent containing oxygen and of the high-grade fuels in the second reaction zone and by appropriately directed spraying of combustion oxygen and/or of an agitating gas into the first reaction zone.

14. A process as claimed in any preceding claim, wherein slag drawn off from the first reaction zone is at least partially recycled into the second reaction zone.

15. A plantfor gasifying low-grade fuels in a molten which is liquid at high temperatures, comprising a reactorfilled with molten metal, with a partition disposed in a central region ofthe reactor, the partition having, at the bottom ofthe reactor, at least one passage for the molten metal, and first and second reaction chambers defined by the partition each comprising at least one feed memberforfuels and gasifying agent containing oxygen and one oake mem berfor molten slag and/or metal, and the first reaction chamber comprising an offtake pipe forthe low-energywaste gas andthesecond reaction chamber comprising an offtake pipe forthe high-energy product gas.

16. Aplantforgasifying low-grade fuels in a molten metal which is liquid at high temperatures, comprising two reactors separate from one another, with reaction chambers each of which comprises at least one feed memberforfuels and gasifying agent containing oxygen, one offtake pipe forthe waste gas or product gas produced, one offtake member for molten slag and/or molten metal and which are in communication through atleast one pipelineforthe molten metal disposed in the region ofthe lower side wall ofthe reaction chambers.

17. Aplantasclaimed in claim 16,whereintwo said pipelines are provided.

18. A plant as cliamed in anyofclaims 15to 17, wherein a feed memberforfeeding containers with low-grade fuels into the first reaction chamber is constructed in the form of a rotary vane lock or of a double rocking trap-door lock.

19. A plant as claimed in any of claims 15 to 17, wherein the feed memberforthe low-grade fuels in the first reaction chamber is constructed in the form of a screw conveyor.

20. A plant as claimed in any of claims 15to 19, wherein a waste-gas conduit behind the first reaction chamber is constructed in the form of a suspension-type heat exchanger with a riser and cyclone separator, and the riser comprises, in the lower region, at least one feed memberforthe introduction of solids in the form of particles.

21. A plant as claimed in claim 20 wherein the particles are limestone, coal, low-gradefuels, metallic oxides and/or metal powder.

22. A plant as claimed in claim 16, or in claim 16 and any of claims 17 to 20, wherein a shut-off device is provided in the pipeline or in each of the pipelines forthe molten metal between the two reaction chambers.

23. A plant as claimed in any of claims 15to22, wherein offtake members for molten slag from the two reaction chambers are in communication, either together or separately from one another, through a conduit under pressure, with a slag granulating device.

24. A plant as claimed in claim 23, wherein the slag granulating device is of pressure-tight construction and consists of a watertankwith water nozzles, a conveyor device conveying the fine-grainedslag outofthewater bath, an inclined ring separatorora conveyorworm, and of a rotary vane lock.

25. A plant as claimed in claim 24, wherein the conveyor device is a bucket conveyor.

26. A gasification process substantially as herein described with reference to Figure 1, Figure 2 to 4, or Figure 5 of the accompanying drawings.

27. A gasification plant substantially as herein described with reference to Figure 1, Figure 2 to 4, or Figure 5 ofthe accompanying drawings.