FI122618B - Method and apparatus for gasification of solid fuel - Google Patents

Abstract

In the method the gasification of solid fuel, such as wood chips, occurs with a co-current gasifier, which has a fuel silo (14), a combustion chamber (32) and a liquid channel (19) for circulating cooling liquid. The fuel is dispensed into the fuel silo, from where it flows into the combustion chamber, where combustion of the fuel occurs. The cooling liquid circulating in the liquid channel is used to limit the transfer of heat from the combustion chamber to the fuel silo and to thus prevent the heating and drying of the fuel in the fuel silo. The cooling liquid is led from the liquid channel to the bottom of the combustion chamber and from the bottom of the combustion chamber onwards out of the combustion chamber. At the bottom of the combustion chamber there is during the gasification continuously a layer of cooling liquid, in which the ash and coal particles generated in the combustion are mixed. The product gas generated in the gasification is led out of the combustion chamber along a flow duct (74b) of the cooling liquid and contaminants are removed from the product gas in a product gas washer (100). Also the ash and coal particles generated in the gasification are led out of the combustion chamber with the cooling liquid along the flow duct. The ash is removed from the cooling liquid in a coal separator (200) and the temperature of the cooling liquid is lowered with a condenser (300), after which the liquid is directed back into the liquid channel of the co-current gasifier.

Description

Method and apparatus for gasification of solid fuel

The invention relates to a method for gasifying a solid fuel, such as wood chips, with a downstream gasifier having a fuel silo, a furnace and a fluid passage for recycling a coolant, such as water. The invention also relates to apparatus for use in the process.

Solid fuels such as wood chips can be made into flammable product gas by means of a co-gasifier. The downstream carburettor has a fuel tank and a furnace below. The fuel is fed from above through to the top of the fuel silo, from where it flows downwards by gravity into the furnace where gasification of the fuel occurs. The combustion air required for the gasification is fed to the center of the carburettor and the product gas generated is discharged from the bottom of the reactor.

In many downstream gasifiers, the heat generated in the furnace is used to heat the combustion air supplied to the gasifier and to dehydrate the fuel in the fuel silo, such as wood chips. In such gasifiers, the pyrolysis of the fuel partially occurs already in the fuel silo. The disadvantage of these carburetors is the difficulty in controlling the conditions of the pyrolysis reaction, which makes it easy to form impurities in the product gas. Also known are co-current gasifiers, which aim to make the pyrolysis reaction as short as possible. In these gasifiers, active heating and drying of the fuel in the fuel silo 20 are actively prevented so that pyrolysis occurs as close as possible to the furnace or only in the furnace.

WO 2008/145814 A1 discloses a downstream gasifier having a fuel silo and a firebox below. Between the fuel silo and the furnace is an annular air duct through which combustion air is introduced into the furnace.

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^ 25 The purpose of the air duct is to limit heat transfer from the furnace to the fuel tank. In the air duct, one or more other cooling media, such as water, can be circulated in addition to or instead of air.

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US 1524466 discloses a fuel supply device that can be used in gasifiers and furnaces. The feeder comprises three annular portions, g 30, which are superimposed. The lower annular portion has a cooling o channel for recirculating cooling water.

In the solutions described in WO 2008/145814 A1 and US 1524466, the purpose of recycling the coolant is only to prevent heat transfer from the furnace to the fuel silo.

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Prior art liquid-cooled downstream gasifiers have several disadvantages. The fuel burns in the furnace at a high temperature which causes the carburettor furnace to have a high outside temperature. High temperatures in the furnace can easily cause a fire hazard. The circulation of coolant 5 between the fuel tank and the furnace cannot solve the problem of overheating of the outside of the furnace.

The combustion of fuel generates ash, which must be removed from time to time. In order to remove ash, the furnace must be provided with an opening ash outlet which further reduces the fire safety of the carburettor. During ash removal, the fire in the 10 fireboxes must be extinguished, thereby interrupting gas production.

It is an object of the invention to provide an improved method and apparatus for gasifying biofuel which can eliminate the drawbacks and disadvantages of the prior art.

The objects of the invention are achieved by a method and apparatus which are characterized by what is disclosed in the independent claims. Certain preferred embodiments of the invention are set forth in the dependent claims.

The present invention relates to a process for gasification of a solid fuel such as wood chips. The gasification takes place with a downstream gasifier, which has a fuel silo, a furnace and a fluid passage for recycling the coolant. Fuel 20 is dispensed into the fuel silo, from where it drains into the furnace, where the pyrolysis and gasification of the fuel takes place. In the liquid channel, ordinary water can be used as recycled coolant. The purpose of the recycled coolant is to reduce heat transfer from the furnace to the fuel silo and thus prevent the fuel from heating and drying in the fuel silo. The method

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The coolant is discharged from the fluid passage to the bottom of the furnace and further out of the furnace from the bottom of the furnace. The bottom of the furnace thus has a continuous layer of coolant during gasification, in which the ash and carbon particles x from the combustion are mixed. Preferably, the coolant is recycled from the furnace back to the fluid passage, i.e. the same recyclable coolant is used for cooling.

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In a preferred embodiment of the process according to the invention, the product gas produced by gasification is discharged from the furnace via a coolant flow line and impurities are removed from the product gas in the product gas scrubber.

In another preferred embodiment of the process according to the invention, the ash and carbon particles from the gasification are discharged from the furnace with the coolant along a flow line. Preferably, ash and carbon are removed from the coolant in the product gas scrubber.

In a third preferred embodiment of the process according to the invention, the temperature of the coolant to be recycled is lowered by a condenser. 5 After condensing, the fluid is directed to the downstream gasifier fluid passage.

The apparatus of the invention for the gasification of biofuel has a downstream gasifier comprising a fuel silo, a furnace and a liquid channel for recycling a coolant such as water. The downstream gasifier included in the apparatus further comprises a first-to-first flow pipe from the liquid passage to the bottom of the furnace and a second flow pipe out of the furnace.

In a preferred embodiment of the apparatus according to the invention, the liquid passage is at least partially between the fuel silo and the furnace, whereby the coolant recycled in the liquid duct can effectively reduce heat transfer from the furnace to the fuel silo. Preferably, the downstream gasifier has a hole from the fuel silo to the furnace through which the fuel flows from the fuel silo to the furnace and the fluid passage is an annular channel portion surrounding said hole.

Another preferred embodiment of the apparatus according to the invention further comprises a pump and flow pipes for introducing coolant from the furnace back to the liquid-20 passage.

A third preferred embodiment of the apparatus according to the invention further comprises a product gas scrubber which is connected to the end of a second flow pipe leading out of the furnace. Preferably, the product gas scrubber has a purification layer for purifying the product gas and a product gas tube for discharging the purified product gas to cm 25, and the apparatus has means for passing coolant over the purification layer.

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| A fourth preferred embodiment of the apparatus according to the invention further comprises a co-carbon separator for removing ash and carbon particles in the coolant and a lowering of the temperature of the coolant in the condenser to be recycled.

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An advantage of the invention is that it keeps the temperature of the outer surface of the downstream carburettor at a very low temperature which reduces the risk of fire ignition.

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An advantage of one embodiment of the invention is that in cooling the furnace, the coolant is also used to remove ash from the furnace. The ash leaves the furnace with the coolant in a fire-safe manner. The furnace fire need not be extinguished during ash removal, but ash is continuously discharged during use of the boiler.

The invention will now be described in detail. Reference is made to the accompanying drawings, in which Fig. 1a is an exemplary cross-sectional view of a downstream gasifier according to the invention, Fig. 1b is a horizontal sectional view of Fig.

Fig. 1a is an exemplary cross-sectional view of a downstream gasifier and associated coolant recycling apparatus according to the invention. Fig. 1b is a horizontal cross-sectional view of the downstream gasifier of Fig. 1a from sectional plane A-A and Fig. 1c from sectional plane B-B. The co-gasifier is in the upright position as shown in Figure 1a. In the following, the directional expressions 20 used in the description of the images, such as up, down, above, below, top or bottom, refer to the directions when the carburettor is in the position shown in Figure 1a. If the carburettor is in a position other than that shown, the directional expressions will change accordingly, and the carburettor will have a cylindrical outer shell 10 with an airtight, openable lid 12 at its upwardly facing end T25. There are two substantially unidirectional with a midsole spaced apart, the upper midsole 16a and a lower midsole 16b defining a cooling space 80. The intake shell of the carburettor forms an outer wall of the cooling space. The portion o £ below the cooling space forms the gasifier 20 of the downstream gasifier, where the actual? 30 Fuel Gasification. Within the outer casing above the cooling space 80 is a cylindrical fuel silo 14, open at both ends, into which the fuel to be gasified is dispensed through the opening lid 12.

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Within the gasification section is a furnace 32 having a three-layer wall structure comprising an inner sheath 34, a central sheath 36 and an outer sheath 38. The inner mantle forming the inner wall surface of the furnace is a cylindrical portion having an upper edge in the plane of the upper intermediate floor 16a and extending through concentric holes 30 passing through the upper intermediate floor, manifold 5 16c and lower intermediate floor 16b close to the bottom of the furnace. The inner sheath is secured to the edges of the midsole and manifold holes by welding, thereby forming one wall of the air channel 18 and the liquid channel 19. At the lower edge of the inner mantle is a circular grate 40 supported at its edge to the lower edge of the inner mantle. On the inner surface of the inner sheath, just below the height of the lower midsole 16b, there is a horizontal fire ring 50 which forms a narrowing reduction in the upper part of the furnace. The fire ring is supported in a manner allowing thermal movement by attaching the lower support ring and the upper support ring to the inner wall of the inner sheath and fitting the fire ring into the gap between the support rings.

The inner sheath is surrounded by a central sheath 36 which forms a closed wall surface outside the cylindrical side wall of the inner sheath and below the grate 40. The central mantle curves at its upper edge inwards and connects to the inner mantle just above the fire ring. Preferably, the center sheath is made of steel and secured at its upper edge to the inner sheath by welding. Around the center sheath is an outer sheath 20 which forms the outer shell of the furnace. A space is formed between the outer jacket and the central jacket, which acts as a preheat space for the gasification air. The upper surface of the preheating space is formed by the lower midsole 16b.

The cooling space 80 between the fuel silo and the gasification section acts as a structural element that reduces heat transfer from the gasification section to the fuel silo. The cooling-25 space is divided by a manifold plate 16c in the direction of the upper and lower midsole so that an air passage 18 is formed above the manifold and a liquid passage 19 is formed below the manifold. The air passage 18 is the annular passage for gasifying the gas.

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the carburetor. Inside the air duct is a baffle plate 48 (Fig. 1b) which completely closes the duct £ 30 at one point. On the first side of the baffle there is an inlet 57 in the outer edge of the duct through which gassing air can enter g into the air duct and on the other side of the baffle there is an outlet 58 for venting o from the duct to the air duct 64. The gasification The other end of the air tube is guided through a hole made in the outer sheath head 35 to the space between the outer sheath and the central sheath. Through the outlet, gasification air can flow from the air duct to the air duct 64 and further through the duct to the preheating space. At the portion between the lower midsole and the upper edge of the central jacket, the preheating space is limited to the inner jacket 34. Air-nozzles 60 are provided on the wall portion of the annular preheating space adjacent to the inner jacket through which the gasification air is led

Figure 1c shows a downstream gasifier according to the invention in a horizontal cross-sectional view of the plane B-B. The fluid duct 19 below the air duct is an annular duct portion defined by an outer sheath 38, an inner sheath 34, a distribution plate 16c, and a lower midsole 16b. The outer jacket has an inlet 70 for a coolant si-10 for the weather flow and an outlet 72 for the coolant outflow. Water is preferably used as the coolant. The inlet hole opens through the outer sheath 38 to the outside of the carburetor and the outlet hole opens through the lower midsole 16b to the space between the outer sheath and the middle sheath. The inlet and outlet are located at opposite edges of the annular fluid passage. The outlet hole 72 is extended by a first flow tube 74a, the downwardly facing second end of which is guided through a hole in the center slot 36 below the grate 40. The first flow pipe thus forms the coolant inflow path from the fluid passage into the furnace below the grate. There is another hole in the wall of the central jacket which is extended by a second flow tube 74b. The second flow tube passes through the outer jacket 38 to the outside of the carburettor 20, i.e. it forms the coolant outflow path from the furnace to the outside of the carburettor. The holes in the center jacket for connecting the first flow pipe and the second flow pipe are located at opposite edges of the furnace at a distance from the lowest point of the central jacket. Thus, there is always some coolant, preferably 25 water, at the bottom of the furnace when the carburettor is being used.

The downstream gasifier according to the invention naturally includes an ignition mechanism for igniting the gas to be gasified (the ignition mechanism is not ci, shown in the figures). A variety of prior art can be used in the carburettor

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which are not described in further detail herein. Preferably, the ignition mechanism is an automatic, LPG or electric § mechanism.

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? The apparatus of the invention further comprises a product gas scrubber 100, a carbon separator 200, a condenser 300 and a pump 400. The product gas scrubber is a device for removing impurities from the gas stream process gas such as soot from the downstream gasifier. The washer comprises an upright cylindrical container 108 having an internally mounted horizontal grid 102 that divides the inner portion into an upper portion 104 and a lower portion 106. The upper portion includes a plurality of substantially circular bodies 110 deposited as a cleaning layer 122 over the net 102. The pieces may be made of, for example, metal or some organic material such as wood or carbon. The size and shape of the pieces are selected such that a plurality of labyrinthine flow paths are formed between them for the flow of product gas and coolant. A tube 114 is provided through the container lid 112 with a spout 116 at its end. The spreader distributes the coolant coming through the tube into a uniform droplet of jet on the surface of the cleaning layer. A product gas tube 124 is conducted through the tank lid 10, along which product gas purged of impurities is sucked out of the tank. At the other end of the product gas tube, a vacuum may be provided or may be connected to a motor which, when running, provides a suitable suction to remove product gas (the vacuum and motor are not shown).

At the bottom of the lower part 106 of the reservoir is a fluid chamber 118, in which the liquid coming from the sprinkler and passing through the cleaning layers 15 is collected. The other end of the second flow tube 74b from the co-gasifier is passed through the tank wall to the lower portion of the tank. The entry point of the second flow pipe is at a distance from the bottom of the tank. In the vicinity of the container bottom 120, there is a hole passing through the container wall, which is extended by a third flow pipe 74c leading out of the container. The product gas generated in the co-current 20 gasifier flows into the container through a second flow tube 74a and rises inside the container by suction upwardly through the purification layer toward the first end of the product gas tube. At the same time, a liquid is flowing down through the cleaning layer, which freezes the product gas and removes the impurities you have. Impurities run into the liquid space with the liquid.

The coolant flows from the inside of the furnace 32 along the second flow pipe 74b into the scrubber g 100 to the liquid space 118. The ash from the combustion of the fuel is mixed with the coolant in the combustion chamber, whereby the ash leaves the furnace with the coolant. Thus, a separate ash removal system is not needed in the co-gasifier,

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The ash is removed from the furnace with the coolant recycled in the plant. At the end of the third flow pipe 74c from the scrubber is a pump g 400. Preferably, the pump is electric. A fourth flow pipe g 74d is connected to the pump, the other end of which is connected to the inlet 70 of the downstream gasifier fluid passage 19. The flow pipes 74a, 74b, 74c, and 74d and the pump 400 thus form a liquid passage to a firebox, a conductive coolant flow path maintaining coolant circulation via pump 400. The pipe 114 leading to the upper part 104 of the scrubber is connected at one end to the fourth flow pipe 74d via a valve 126. By means of the valve, a portion of the coolant to be recycled is directed through the conduit 114 onto the purification layer.

The portion of the flow pipe 74d between the pump 400 and the valve 126 has a carbon separator 5200 and a condenser 300. The carbon separator removes the mixed ash and fine carbon therefrom. The carbon separator can be any separator which can be used to separate small solid particles from the liquid. The coolant recycled in the condenser removes heat energy, allowing the temperature of the coolant to be maintained at the desired level. The capacity of the condenser is dimensioned 10 so that the temperature of the coolant after condensation is about 30 ° C. The structure and function of the carbon separator and the condenser are well known in the art and will not be further described herein.

The downstream gasifier according to the invention functions as follows. The lid 12 of the fuel silo 14 is opened and a suitable amount of fuel 15 is dispensed into the fuel silo, whereby a portion of the fuel is discharged into the furnace 32. Almost any biofuel, such as shelled pine, birch, spruce, willow or other wood species, can be used. The wood chips may be air-dried, whereby their moisture content may be 30-40% by weight. After fueling, the lid will be hermetically closed.

20 A vacuum is connected to the product gas pipe 124 and the fuel in the furnace 32 is ignited. Due to the vacuum created by the vacuum, gasification air flows into the air duct 18 and through the air duct 64 into the preheating space between the central shroud 36 and the outer sheath 38, from where it is led through the air nozzles 60 above the fire ring 50. The fuel gasifies in a fire-5 chamber at a high temperature of 1100-1300 ° C. Because of the fuel temperature

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^ the fuel pre-mix is low, virtually no pyrolysis occurs at the fuel silo. Also, no significant drying of the fuel occurs in the fuel blade, but upon arrival at the furnace, the fuel is approximately in its original humid space. Pyrolysis is thus carried out at a very short distance between the upper midsole 16a and 30 of the firing ring 50,

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In the pyrolysis reaction, the furnace 32 produces product gas containing hydrogen, carbon monoxide, carbon dioxide, nitrogen and water vapor. The product gas exits the furnace by suction through a second flow tube 74b to the lower portion 106 of the product gas scrubber 100, from where it flows upwardly to the upper portion 35 104 and further along the product gas tube 124 out of the scrubber. The product gas is purged 9 of the impurities contained therein as it flows through the purification layer. During operation of the carburettor, the coolant, preferably water, is circulated in the apparatus by means of a pump 400 included in the apparatus. The pump draws coolant from the product gas scrubber fluid space 118 and passes it through the carbon separator 200 and condenser 300 5 to the downstream gasifier fluid passage 19. The coolant cooled in the condenser enters the fluid passage at a temperature of about 30 ° C. The coolant flowing in the fluid passage absorbs heat and prevents the transfer of heat generated in the furnace to the fuel silo 14 and the fuel in the silo. From the fluid passage, the coolant flows along the first flow pipe 74a below the grate 10 40 to the bottom of the furnace. The hot coals and humps generated by the combustion of the fuel fall directly through the grate into the coolant, where they quickly quench. It is believed that dropping glowing fuel grills into the water may increase hydrogen gas production. The ash from combustion is mixed with the coolant in the fire chamber. The coolant flows from the furnace 32 along the second flow 15 pipe 74b to the scrubber of the product gas from where it is sucked back into the circulation by the pump. Part of the circulating coolant is directed through valve 126 and conduit 114 onto the purification layer.

The downstream gasifier for the apparatus may be a single firebox carburettor as described above or may have multiple fireboxes as disclosed in Applicant's previous application WO 2008/145814 A1. Further, the individual devices included in the apparatus, such as a carbon separator, a product gas scrubber, a condenser, a pump, and a downstream gasifier, may be located along a coolant flow path in a sequence other than that described above. The apparatus may also include a separate Fifth Flow 25e 74e located above the second flow tube 74b for the flow of product gas.

Certain preferred embodiments of the method and apparatus of the invention have been described above. The invention is not limited to the solutions just described, but the inventive concept can be applied in numerous ways within the scope of the claims.

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Claims (14)

A method for solid fuel gasification, such as wood chips, with a co-stream gasifier having a fuel silo (14), a fire hearth (32) and a liquid duct (19) for circulating cooling liquid, such as the water, characterized in that method, the cooling liquid is conducted from the liquid duct to the bottom of the hearth under a rust and from the bottom of the hearth to the hearth. Process according to claim 1, characterized in that in the process the cooling liquid from the hearth (32) is fed back into the liquid duct (19). 3. A method according to claim 1 or 2, characterized in that product gas which arises in the gasification is discharged from the hearth (32) along the flow tube (74b) of the cooling liquid and the product gas is purified from impurities in a product gas washer (100). Method according to any one of claims 1-3, characterized in that ash and carbon particles rising in the gasification are discharged from the hearth (32) together with the cooling liquid along the flow pipe (74b). Process according to Claim 4, characterized in that ash and koi are removed from the cooling liquid (100) from the cooling liquid. Process according to any of claims 1-5, characterized in that the temperature of the circulating cooling liquid is lowered by a condenser (200). Apparatus for solid fuel gasification, such as wood chips, which apparatus has a co-stream gasifier which includes a fuel silo (14), a fire hearth (32) and a 71 liquid duct (19) for circulating coolant, such as water, characterized in that the co-current carburetor comprises a first flow tube (74a) Y which leads from the liquid channel to the bottom of the hearth and a second flow tube g (74b) which leads from the hearth. X 8. Apparatus according to claim 7, characterized in that the liquid channel (19) is at least partially between the fuel jet (14) and the fire hearth (32). t'- m Apparatus according to claim 7 or 8, characterized in that the co-current carburetor has a heel (30) which leads from fuel silo (14) to the fire hearth (32) and the liquid duct (19) is an annular duct part which surrounds said heel. 13 Apparatus according to any one of claims 7-9, characterized in that it further comprises a pump (400) and flow tubes (74b, 74c, 74d) for directing cooling liquid from the hearth (32) back to the liquid duct (19). Apparatus according to any of claims 7-10, characterized in that it further comprises a product gas washer (100), which washer is connected to the end of the second flow tube (74b) which leads from the hearth (32). 12. Apparatus according to claim 11, characterized in that the product gas washer has a purification layer (122) for purifying the product gas, a product gas pipe (124) for discharging the purified product gas and the apparatus has means (126, 114, 116) for conducting the cooling liquid. outside the purification layer. Apparatus according to any of claims 7-12, characterized in that it further comprises a carbon separator (200) for removing ash and charcoal particles in the cooling liquid. Apparatus according to any one of claims 7-13, characterized in that it further comprises a condenser (300) for lowering the temperature of the circulating cooling liquid. δ CM CM 05 CM T cc CL CO o LO o δ CM