EP1187893B1

EP1187893B1 - Process for the gasification of carbonaceous material

Info

Publication number: EP1187893B1
Application number: EP00927281A
Authority: EP
Inventors: Seppo Ruottu
Original assignee: Fortum Oil Oy
Current assignee: Fortum Oil Oy
Priority date: 1999-05-14
Filing date: 2000-05-12
Publication date: 2005-02-16
Anticipated expiration: 2020-05-12
Also published as: FI112665B; WO2000069995A1; DE60018181D1; ATE289345T1; AU4571500A; FI991107A; ES2235873T3; CA2372195A1; FI991107A0; EP1187893A1; DE60018181T2

Abstract

The invention relates to a process and apparatus for the gasification of a carbonaceous material. According to the process, the carbonaceous material is gasified at an elevated temperature to produce gas, condensable compounds are separated from the gas, and the product gas thus obtained is recovered. According to the invention, in order to separate the condensable compounds the gas obtained from the gasifiers is directed to a dry scrubber (2) operating according to the fluidized bed priciple, wherein it is contacted with the bed material of the fluidized bed, the interior temperature of the dry scrubber being maintained lower than the condensation temperature of the condensable compounds in order to condense these compounds into the bed material. By means of the invention, a substantially tar-free gas can be produced which is suitable for the production of both heat and electricity.

Description

The present invention relates to a process according to the preamble of Claim 1 for the gasification of a starting material made up of a carbonaceous material.

According to such a process, the starting material is gasified at an elevated temperature in the presence of oxygen. The condensable compounds are separated from the gases obtained from the gasification, and the product gases thus obtained are recovered.

The invention also relates to an apparatus according to the preamble of Claim 12, the apparatus comprising a gasification unit and, connected to the gasification unit, a unit for the removal of condensable compounds.

Thermochemical gasification is a process wherein by a partial oxidation by elevating the temperature a carbonaceous raw material, such as biomass or coal, is converted to gaseous substances. There are many types of gasification reactors, for example, solid-bed, fluidized-bed, moving-bed and rotary-bed reactors. In addition to these, there are known, for example, cyclone and vortex reactors. The product gas obtained from the process contains carbon monoxide, carbon dioxide, hydrogen, methane, a small amount of higher hydrocarbons, water, nitrogen (if air is the oxidizing medium), as well as carbon, ashes, tars and oils.

The calorific value of the gas produced by gasification is approximately 2 - 6 MJ/m³n, and it is suitable for limited transfer in a pipe and for synthesis gas, for example, for the production of ammonia, methanol and fuel.

The competitiveness of gasification as compared with complete combustion has been weakened by the condensing of heavy hydrocarbons (tars) in connection with the cooling of the gas. By tars is generally meant a mixture of organic compounds containing both lower molar mass compounds, such as benzene, and heavy polyaromatic hydrocarbons. As "light tars" are usually regarded mixtures having boiling points of 80 - 350 °C (from benzene to pyrene), and heavy tars for their part are compounds having boiling points higher than approximately 300 °C (chrysene, coronene, etc.).

Tars, in particular light tar components, constitute on the one hand an apparatus-technology problem through the soiling of pipes and blowers and on the other hand an environmental problem, if an attempt is made to remove the tars from the gas, for example, according to the conventional technology by wet scrubbing. Experiences gained from wet scrubbing additionally indicate that the degree of separation of the fine tar mist remains poor. Even if the wet scrubbing were successful, there are formed a waste tar and a problematic effluent. The waste tar also lowers the energy economy of the process and thereby its profitability.

US 4198212 discloses a method of gasifying coal to produce a coal gasification effluent and a char residue. The char residue is cooled by indirect heat transfer in a char bed, and the coal gasification effluent is passed through the cool char bed to effect cooling of the coal gasification effluent, with tars and oil present in the effluent being absorbed by the char bed. In this manner, the gasification effluent is cooled without fouling of heat transfer surfaces, and tars and oils are effectively removed therefrom.

In WO8601822, a method of cleaning gases containing tar and other condensable components by cooling them in a circulating fluidized bed reactor provided with cooling surfaces. Into the fluidized bed reactor are led solids separated from the cooled gas in a cyclone separator and other solids. Tar and other compounds condense on the solids in a mixing chamber disposed before the cooling surface in the reactor.

The object of the present invention is to eliminate the disadvantages associated with the prior art and to provide a process for the production of a gas substantially free of incondensable compounds ("tar-free") by oxidative gasification of carbonaceous starting materials.
The invention is based on the idea that the gas produced in the gasifier is fed into a scrubbing unit (dry scrubber) operating according to the fluidized-bed principle and serving as a tar-removal device. In the dry scrubber the gases are contacted with the bed material of the fluidized bed. The interior temperature of the dry. scrubber is maintained at a level lower than the condensation temperature of the condensable substances, preferably at approximately 160 °C at maximum, in which case the tarry compounds are condensed in the dry scrubber into the bed material, and the product gases are purified. The (tar) compounds condensed into the bed material are returned with the bed material to the gasifier, where they are broken up into light gases.

The apparatus according to the invention comprises a dry scrubber operating according to the fluidized-bed principle, wherein the gasifier gases can be brought into contact with a solid material in the form of a circulating bed.

More precisely, the process according to the invention is primarily characterized in what is stated in the characterizing clause of Claim 1.

The apparatus according to the invention, for its part, is characterized in what is stated in the characterizing clause of Claim 12.

Considerable advantages are gained through the present invention. Thus, the apparatus can be used for producing a nearly tar-free gas, which is suitable for the production of both heat and in particular electricity (e.g. diesel electric power plants, boiler plants, connection to a large power plant). The gas can also be used as synthesis gas, for example, for the preparation of methanol.

Trial runs have shown that the separation of tars in the dry scrubber is so effective that no signs of tarring of the dry scrubber have been observable even after gasification runs of more than 30 hours. The sight glasses of the apparatus are completely clear, and tar is not observable on the metal surfaces, either. During the gasification of sawdust, the sawdust samples taken from the dry scrubber have been loose, readily flowing. On the basis of product gas analyses and a balance calculation it can be noted that the tars have been converted to light gases.

It should be pointed out that a high-quality fuel has been prepared from a biomass containing 80 % water with the pilot apparatus described below, without the use of external energy. The system is as such also suitable for numerous other applications, for example, to replace the hot-gas generator and drum dryer in the chipboard industry, whereby significant savings in investment and operating costs are achieved.

The invention will be discussed below in greater detail with the help of a detailed description and the accompanying drawing. The Figure shows the process flow chart of a preferred process embodiment of the invention.

The gasification apparatus according to the invention is made up of a gasifier and, linked with it, a scrubbing unit for the condensing compounds, the unit comprising a dry scrubber operating according to the fluidized-bed principle. Preferably at least either the gasifier or the dry scrubber is a device operating according to the circulating fluidized bed principle, preferably both of them.

By "device operating according to the fluidized-bed principle" is generally meant a device having a bed which contains a solid material and which is maintained in a fluid state by directing into it a flowing material, such as gas.

By "circulating fluidized bed unit" (CFB) for its part is meant in the present invention a multiple-phase flow apparatus made up of gas distribution nozzles, a riser, a cyclone separator, and a straight, uncontrolled return duct, wherein a significant proportion of the particles of the fluidized bed travel via the riser to the cyclone, from where they are returned to the lower section of the riser.

According to the present invention, a carbonaceous starting material is gasified at a temperature above 600°C, most preferably approximately 700 - 1000 °C, by using an understoichiometric amount of air, in which case the starting substance as such breaks up into gases. A gas mixture is obtained which contains at least carbon monoxide and hydrogen, and often also carbon dioxide. When air is used for oxidation, considerable amounts of nitrogen are also present in the gas mixture. Furthermore, it may contain small amounts of light hydrocarbons, such as methane, ethane, propane and n-butane. With respect to its composition, the gas is suitable, for example, for synthesis gas for the preparation of ammonia, methanol and fuel and, as was pointed out above, for the production of heat and electricity.

The gasifier can be described with the words "thermochemical cracker". Fluidized-bed units known per se can be used as the gasifier. However, as was stated above, preferably a circulating fluidized bed gasifier is used, in which case an apparatus option having an annular riser and in the center of it a cylindrical dipleg is deemed to be especially preferable. The apparatus comprises, for example, a circulating-bed fluid-flow gasifier, in which the fluidization space is made up of a space annular in cross-section between two cylinders or cones one inside the other, in which space the starting material is gasified at an elevated temperature, possibly in the presence of a separate solid. Such a solid may have catalytic properties.

According to the invention, the solids are separated from the gasifier gases by means of a multi-inlet cyclone positioned directly on top of the annular duct. Owing to this structure, the residence time of gasification can be shortened, since the solids can be separated from the reaction gas stream with the multi-inlet cyclone faster and more effectively than with single-inlet cyclones. From the cyclone the solids can be returned via the space, annular in cross-section, formed by the two cylinders or cones, one inside the other, and serving as the return duct for the solids, i.e. the dipleg, possibly to a regenerator section. If a separate bed material is not used, the starting material is recycled to the riser without regeneration.

Since the aim in the gasification is not the combustion of the carbonaceous material, the gas mixture obtained from the gasifier also contains carbonaceous condensable compounds, which can be called tars. For the separation of these condensable compounds, the gas mixture is directed according to a preferred embodiment of the invention to a dry scrubber operating according to the circulating fluidized bed principle, wherein they are contacted with the bed material in order to condense the condensable compounds into the solids of the bed.

By the term "dry scrubber" is meant in this context a device wherein the separation of the condensable compounds of the gases from the gases is carried out by means of a dry or moist solid medium. In conventional wet scrubbing the scrubbing of gases is carried out, as is known, by means of liquid.

According to a preferred embodiment of the invention, the dry scrubber comprises a circulating fluidized bed reactor, which serves at the same time as the dryer of the starting material and as the scrubber of the gasifier gases. In this case the solid bed material used in the scrubber is a dryable material which will be gasified later in the process, such as biomass and refuse.

In the riser of the fluidized-bed dryer there is a riser which comprises a dry scrubber operating according to the circulating fluidized bed principle, the dry scrubber comprising a riser wherein the exit gases of the gasifier can be contacted with the bed material.

The interior temperature of the dry scrubber is maintained at a temperature lower than the condensation temperature of the condensable materials in order to condense these compounds into the biomass. When the gas arriving from the gasifier, the gas having already partially cooled (to approximately 300-400°C), and the mass flow from the tar scrubber meet, aerosols are formed at the moment of impinging. Within a certain temperature range the aerosols remain in the tar scrubber on the surface of the biomass and circulate together with the mass stream. Thus the tars are in practice in a state of equilibrium and circulate between the scrubber and the gasifier. The residence time of the starting substance in the scrubber is several minutes. The tar-free gases obtained from the dry scrubber are recovered.

In practice, there is one main stream (raw material) into the apparatus and one main stream (product gas) out. The sidestreams are gasification air in and possibly a very small ash stream out. There is hardly any ash accumulated in the gasifier or the scrubber. This, however, depends on the material to be gasified, i.e. when large amounts of inorganic compounds are gasified, the removal of ashes and dust may be necessary. For example, when sawdust is being gasified, there may be visually observed in the outlet stream some particles, the necessity of their removal being dependent on the targeted use of the gas.

For an application according to the invention, a scrubber operating according to the circulating fluidized bed principle is preferable to, for example, a bubbling bluid-ized bed unit (BFB). The advantages of the CFB are based on fluid-technology advantages. The fluid-technology operating window in the CFB (gas velocity, particle size distribution) is considerably wider than that in a bubbling fluidized bed type apparatus (BFB). In the BFB space, the gas is in the form of large bubbles, and as a consequence of this the transfer of material between the gas and the particles is poorer than in CFB. It is a further advantage of CFB that particles having a large specific surface area are concentrated in the scrubber substantially better than in BFB. Apart from what is stated above, it should be borne in mind that a CFB dry scrubber according to the invention may operate both as endothermal and as exothermal, in which case with very wet raw materials it can evaporate a considerable amount of water. The fluid technology flexibility of CFB is a crucially important prerequisite for the full-scale use of the heat exchange surfaces in the scrubber with all types of materials.

The circulating bed used in the dry scrubber is the starting material to be gasified, in which case a moist biomass is dried in the dry scrubber before it is fed to gasification. In terms of fluidization, the material to be gasified may contain at the same time both coarse and fine fractions, since a portion of the bed material will, nevertheless, remain in place and the finer fraction will circulate along with the gases.

The temperature in the dry scrubber is maintained at <160 °C, preferably at 80 - 120 °C, and especially preferably at approximately 90 - 110 °C. The tar scrubber according to a preferred embodiment of the invention is recuperative by its operating principle, i.e. its temperature is regulated by indirect heat exchange (by indirect heating or cooling). The scrubber serves as a drying scrubber when, for example, a slurry is being treated with steam, and as a cooling scrubber when, for example, a dry sawdust is being treated. Thus, in general, heat is introduced into the dry scrubber if its interior temperature drops substantially below the condensation temperature of the gases and, respectively, heat is removed from the dry scrubber if its interior temperature rises substantially above the condensation temperature of the gases.

The heat-exchange surface is located inside the tar scrubber, whereby a more effective heat exchange is produced than if the surface were outside. The fluidization gas used is, at least in the main, post-scrubber gas. "Post-scrubber gas" comprises at least in part the gases obtained from the gasification, which gases are combined with the circulating gas stream of the dry scrubber. There is namely produced in the dry scrubber a significant circulating gas return stream, which is directed to the lower section of the scrubber via the return duct. The function of the circulating gas is to produce fluidization conditions, and constant conditions are aimed at in the circulation gas stream. In this case the scrubber is controlled by controlling the temperature difference.

The scrubber preferably comprises an elongate reactor mantle having three sections, i.e. a lower section, a riser section and an upper section, which has a cyclone for separating solids from the gases. The cyclone may be a conventional single-inlet cyclone or a multi-inlet cyclone. The cyclone has a separation chamber for the separation of solids from the gases, a gas outlet pipe connected to the separation chamber, and a solids dipleg connected to the riser for returning to the riser the solids separated from the gases. The riser of the dry scrubber and/or the dipleg of the cyclone are/is preferably connected to the feed connection of the gasification unit in order to feed the bed material from the dry scrubber to the gasifier.

There is further arranged in the scrubber a gas recycling duct, which may be arranged outside the reactor mantle. The outlet connection for the gaseous exit material of the gasification unit may be connected to this gas recycling line.

In, for example, the conical lower section of the scrubber there are separate feed connections for the starting material to be dried and, respectively, for the tar-containing product gas to be purified. The lower section further has withdrawal connections, i.e. outlet connections, for the dried biomass. In the lower section there is arranged a grate which serves as a distribution plate for the circulating gas. The riser duct section has, fitted inside the reactor mantle, at least one riser pipe. Around the pipe there is a heat-exchange mantle to provide indirect heat exchange. However, the riser may have several parallel pipes (e.g. 2 - 15) in order to increase the heat-exchange surface.

The starting material, such as biomass or refuse fractions, is gasified and circulated without a separate bed material both in the gasifier and in the scrubber. It is, however, possible to use on the gasifier side an outside bed material or a catalyst acting in the manner of a bed material, for example, a fluidized-bed cracking catalyst. Bed materials usable in this case are various silicate materials (sand) and similar fine materials withstanding heat sufficiently well. The advantages of gasification without a foreign fluid material include the elimination of the erosion problem and the reduction of the internal consumption. In this case there are also not formed any dust emissions causing additional problems in terms of gas purification. The costs of investment and operation are reduced, the risk of sintration caused by a foreign fluid material is eliminated, whereby a higher concentration of coke in the gasifier is achieved and, consequently, the quality of the gas is improved.

Starting materials of many types can be used as the feed in the reactor system. The common nominator of the materials used as starting materials is that they contain carbon or are carbonaceous. These materials can be divided into two principle groups: biomass and refuse.

The biomass starting materials are preferably selected from among the forest industry residues and thinning residues; agricultural residues such as straw, residues from olive thinning or collection; energy plants such as willow and energy hay, Miscan- thus and peat.

The refuse is preferably organic, solid or liquid, and it is selected from among refuse derived fuel (RDF), sawmill waste, plywood, furniture and other residues of the mechanical forest industry; waste plastic; and waste slurries (including industrial and community effluents).

Especially advantageous starting materials include wood chips, wood shavings, sawdust, peat, lumbering residues and chips, community refuse, briquettes, straw, and energy plants.

Applications of the invention to be mentioned include the gasification of so-called opportunity fuel type fuel batches. These include fuel batches, not always available, containing large amounts of volatile compounds. Some examples are thinning wood, snag wood chips, REF, RDF, automobile tires and other waste rubber and plastic, timber offcuts from building sites, wood from demolishing, etc. The gas obtained from these starting substances can be used to replace the principal fuel, such as carbon, of the principal process. When a gasification plant is connected to a larger natural-gas or coal power plant, the proportion of product gas of the total fuel is typically small. In this case, any incidentally available fuel batches can be exploited at only a marginal conversion cost. Investment in a turbine/generator/converter is thus not needed. The gasification apparatus in this application serves as a kind of 'waste grinder' by means of which the said starting materials can be disposed of advantageously. The fact that the gases are nearly devoid of tar promotes the transfer of chemical heat from this sidestream process to the principal process. It also reduces the maintenance costs. The_ash of the secondary fuel in this manner also remains separate from the ash of the principal fuel.

According to another embodiment, the product gas is used as fuel for smallish spark-ignition gas engines and as additional fuel for largish heavy oil diesel engines. For this application, the starting materials selected for the gasifier are primarily wood-based biomass fractions.

The use of the gasifier as a producer of synthesis gas is also possible. In this case the gasifier feed is again wood-based biomass.

The gases obtained from the process and the apparatus do not contain condensable compounds (they are "tar-free"), which means that they do not contain substantial amounts of hydrocarbon compounds which have, in terms of the use of the gases, a detrimentally high saturated-state vapor pressure at above 200°C. In general the concentration of such compounds in the gases is lower than 0.1 % by volume, in particularly lower than 0.01 % by volume.

The invention is examined below in greater detail on the basis of the Figure.

The following reference numerals are used in the Figure.

1. Silo

2. Dry scrubber

3. Inverter

4. Gravity pipe

5. Gasifier

6. Screw conveyor

7. Inverter

8. Dryer chamber

9'. Feed connection

9". Outlet connection

10. Grate plate

11. Recycle cyclone

12. Return pipe

13. Fuel feed connection

14. Product gas outlet connection

From the silo 1 the material to be gasified is fed into the dry scrubber 2 via the gravity pipe 4 so that a significant amount of oxygen cannot pass into the dry scrubber via the feed devices. The control of the feed of the material to be gasified is most preferably carried out by control of the rotation speed of the feed screw by means of the inverter 3.

In the dry scrubber 2 the material to be gasified comes into contact with the tarry gas coming from the gasifier 5, whereupon the tars are condensed into the material to be gasified. The energy balance of the dry scrubber in general needs to be controlled by either direct or indirect cooling or heating in order for the temperature to be maintained within the desired operating window (70-120 °C). Since direct cooling has several disadvantages, the riser of the dry scrubber is made up of a plurality of parallel pipes 8, inside which the gas and the material to be gasified rise upwards and outside which there flows a heating or cooling liquid or gas. The said space thus constitutes a heat-exchange mantle. The lower section 10 of the riser is a continuous, usually upwardly expanding cone. The upper section of the dry scrubber is made up of a cyclone 11 above the heat exchange section. The material to be gasified, separated in the cyclone, is returned to the lower section of the dry scrubber.

The gasifier 5 is preferably a light-structured CFB reactor made from refractory steel and equipped with a multi-inlet cyclone and a simple return duct. The operating temperature of the gasifier is 700-900 °C, suitable for refractory steels. Especially if the gasification is carried out without an abrasive circulating material, ceramic abrasion shields are not needed. The gasification air or oxygen-enriched gas mixture is introduced into the lower section of the gasifier via the grate plate, and the gasification air flow is controlled according to the gasifier temperature so that if the temperature tends to rise above the upper limit, the air flow is reduced and vice versa. The material to be gasified, which has accumulated tar compounds in the dry scrubber 2, is fed via the feed connection 13 into the gasifier 5, preferably with the help of a smallish (not shown) intermediate silo and a screw feeder 6. The rotation speed of the feeding screw 6 is controlled by means of the inverter 7. To prevent the flow of hot product gases from the gasifier to the dry scrubber, a portion of the gasification air is directed to between the screw and the gasifier.

The starting of the plant is carried out so that the storage silo 1 for the material to be gasified is filled, the circulation gas blower is started, and the feeding of the material to be gasified into the dry scrubber is started. When the pressure difference of the riser duct of the dry scrubber is at its setting value, the starting igniter of the gasifier is ignited. When the temperature in the gasifier has exceeded the minimum limit (approximately 600 °C), the feeding of the material to be gasifier into the gasifier is started and the starting igniter power is reduced as the stream of material to be gasified increases. When the gasifier temperature is at its target value, the starting igniter is switched off, and the shifting to the gasifying run is carried out by rapidly increasing the feeding in of material to be gasified. Gas is removed from the gasifier 5 via the outlet connection 14, and the gas stream is connected to the recycle line 12 of the dryer, i.e. the return pipe, from which it travels via the feed connection 9' to the dryer. In the dryer the gases produce the required fluidization gas flow. The separation of solids and tar from the gases takes place in the manner described above, and the product gases are removed via the outlet connection and are recovered.

The storage capacity of the dry scrubber 2 is sufficient for controlling, in a rapid change of power, primarily the stream of material to be gasified fed into the gasifier, and the stream fed into the dry scrubber follows with a delay, taking its control quantity from the pressure difference of the riser of the dry scrubber. The stopping of the plant is carried out by first discontinuing the feeding of gasification air into the gasifier, and when the temperature in the gasifier has begun to decrease, the feeding in of material to be gasified is discontinued. At this time the temperature in the dry scrubber also begins to decrease, whereupon the feeding of material to be gasified into the dry scrubber can be discontinued. Last, the circulation gas blower is stopped and any valves possibly causing air leaks are closed.

Example

In the example case, a gasification apparatus was constructed which comprised a scrubber and a gasifier connected to it.

The most important components of the scrubber were:

Cyclone: a coaxial multi-inlet cyclone having a height of approximately 1 m and having 16 inlets on the cyclone circumference and a blade height of 40 mm. The cyclone had a 110 mm diameter central pipe upwards. The return duct had natural circulation, the diameter of the return duct was 85 mm, and its height was 2000 mm. The riser duct comprised 6 parallel riser pipes the diameters of which were 85 mm and which were arranged inside a pipe mantle having a diameter of 320 mm and a height of 2000 mm. The height of the upper section of the scrubber was 1000 mm, and in its lower section the pipe mantle was conical and equipped with feeding and outlet connections. The grate at the bottom of the scrubber had a nozzle having a diameter of 100 mm.

The circulating fluidized bed gasifier was an uncooled, steel-structured CFB reactor capable of being used with both over- and understoichiometric air feed. The most important parts of the gasifier were: A coaxial multi-inlet cyclone having a height of 500 mm, 16 tangential inlets on the cyclone circumference and a blade height of 100 mm. The cyclone had a 110 mm diameter central pipe downwards. The circulation flow had been arranged as natural circulation in an annular return duct (d_ul50 mm, d_s100 mm) having a height of 1200 mm.

The outer diameter of the riser duct was 300 mm and height 2000 mm.

Only two blowers were used in the apparatus; one was used for operating the dryer and the gasifier, the other provided the air required by the pneumatic transport.

The following analyses were made during the trial runs:

Sawdust was gasified in the apparatus. The moisture contents of the sawdust were determined by weighing and drying the samples in an oven at approximately 110 °C until the weight of the sample no longer changed. Samples of the gas were taken into bags, and the gas compositions were measured at Neste.

On the basis of the balance calculation, the thermal losses in the gasifier were for both runs approximately 3.9 kW, and the thermal losses of the dryer and the circulation gas duct were estimated at 2.1 kW in total.

Gas analyses

Gasifier sample
Component	Calibration, % by vol.	In the sample, % by vol.
CO₂	15.70	12.02
H₂	10.00	10.66
O₂	3.90	0.41
N₂		52.45
CO	9.63	18.80
Hydrocarbons total		5.67
CH₄		(4.38)
Ethane		(0.03)
Ethene		(1.04)
Propane		(0.01)
n-Butane		(0.02)
C₆		(0.00)
C₇		(0.19)
Total		100.00

Dryer sample
Component	Calibration, % by vol.	In the sample, % by vol.
CO₂	15.70	10.90
H₂	10.00	8.04
O₂	3.90	4.09
N₂		60.28
CO	9.63	11.94
Hydrocarbons total		4.76
CH₂		(3.71)
Ethane		(0.04)
Ethene		(0.87)
Propane		(0.01)
n-Butane		(0.01)
C₇		(0.12)
Total		100.01

The most essential results of the trial runs can be summarized as follows:

The separation of tars in the dry scrubber succeeded very well. In the steady state the tars did not cause problems of process or apparatus technology. The CFB gasification of sawdust without a foreign fluidization material succeeded well. The apparatus can be used for producing from biomasses a tar-free, high quality gas with a low calorific value, which gas is a technically suitable fuel, for example, for boilers, furnaces, piston engines and gas turbines.

In the trial runs, tar did not accumulate in the dry scrubber, the pipe systems or the circulation gas blower. The sawdust remained throughout completely loose and capable of being fluidized.

Claims

A process for the gasification of a carbonaceous material, according to which process

a carbonaceous material is gasified (5) at an elevated temperature in order to produce gas,

condensable compounds are separated (2) from the gas, and

the product gas thus obtained is recovered,

characterized in that

in order to separate the condensable compounds, the gas obtained from the gasifiers is fed into a dry scrubber (2) operating according to the fluidized bed principle, wherein it is contacted with the bed material of the fluidized bed, the interior temperature of the dry scrubber being maintained at a temperature below the condensation temperature of the condensable compounds in order to condense these compounds into the bed material,

the bed material of the dry scrubber (2) is at least in part made up of the carbonaceous material to be gasified, and the fluidization gas used in the dry scrubber (2) is at least in the main the exit gas of the scrubber (2), a portion of it being recycled to the lower section of the scrubber.
A process according to Claim 1, characterized in that the bed material containing condensed compounds is directed from the dry scrubber (2) to the gasification (5).
A process according to Claim 1 or 2, characterized in that the dry scrubber (2) used is an apparatus operating according to the circulating fluidized bed principle.
A process according to any of the above claims, characterized in that the gases obtained from the gasification (5) are combined with the fluidization gas stream of the dry scrubber (2).
A process according to any of Claims 1 - 4, characterized in that the material to be gasified is dried in the dry scrubber (2) before being fed to gasification (5).
A process according to Claim 5, characterized in that the temperature in the dry scrubber (2) is maintained at <160 °C, preferably at approximately 80 - 120 °C.
A process according to Claim 5 or 6, characterized in that the temperature in the dry scrubber (2) is controlled by indirect heat exchange.
A process according to Claim 7, characterized in that heat is introduced into the dry scrubber (2) if its interior temperature drops substantially below the condensation temperature of the gases.
A process according to Claim 7, characterized in that heat is removed from the dry scrubber (2) if its interior temperature rises substantially above the condensation temperature of the gases.
A process according to any of the above claims, characterized in that the carbonaceous starting material is gasified at a temperature of 600 - 1000 °C.
A process according to any of the above claims, characterized in that from a biomass to be gasified there is produced a gas mixture containing at least carbon monoxide and hydrogen.
A process according to any of the above claims, characterized in that the carbonaceous starting substance used is biomass or refuse.
A process according to Claim 10, characterized in that thinning wood, lumbering waste chips, REF, RDF, waste plastic or rubber, or construction site offcut is used for producing a gas usable for the production of heat and/or electricity.
A process according to Claim 12, characterized in that a wood-based biomass is gasified for producing a gas usable as fuel for spark ignition gas engines and as supplementary fuel for heavy oil diesel engines.
A process according to Claim 12, characterized in that a wood-based wood biomass is gasified for producing a synthesis gas.