NL1039008C2 - A process and an apparatus for feeding wet biomass. - Google Patents

Description

A PROCESS AND AN APPARATUS FOR FEEDING WET BIOMASS

5 The present invention relates to a process for feeding wet biomass at high pressure. The invention also relates to an apparatus for feeding wet biomass at high pressure.

Wet biomass, such as residues from fermentation facilities and animal manures, is available in vast quantities, and needs to be disposed of. It comprises 10 organic materials which can be converted in a high-temperature gasification reaction to a methane and hydrogen-rich gas. Methane and hydrogen are both valuable fuels. In this manner, wet biomass may in principle be an environmentally friendly and sustainable source of energy, which does not contribute to the build-up of greenhouse gasses in the atmosphere.

15 In addition to the organic materials, wet biomass comprises water, and other inorganic materials, such as sand and minerals. Fibrous materials may be present in the wet biomass, such as grass, straw or small stems.

Processes for the high-temperature gasification of wet biomass into a methane and hydrogen rich gas generally operate at high pressure, requiring that the wet 20 biomass is fed into the gasification process at high pressure. It has been suggested to perform the gasification of wet biomass at conditions at which the water is present in the reaction mixture as supercritical water. These conditions comprise a temperature which is above the critical temperature of water, which is 373.946 °C, and a pressure which is above the critical pressure of water, which is 22.064 MPa 25 (220.64 bar). In E Dinjus and A Kruse, “Hot compressed water - a suitable and sustainable solvent and reaction medium” (J. Phys.: Condens. Matter 16 (2004), p.

1161-1169), the authors disclose under the heading “Gasification in supercritical water” a feeding system comprising a high-pressure pump for feeding wet biomass. However, high-pressure pumps are vulnerable to the action of fibrous material, sand 1039008 2 and other solid particles present in wet biomass which cause abrasion and/or clogging.

The present invention provides a process for feeding wet biomass, which process comprises 5 - providing a circular cylinder comprising cylinder walls, and, inside the cylinder, a piston which is movable in the axial direction of the cylinder, the cylinder having an internal cross sectional area in the range of from 80 mm2 to 20 dm2, and the stroke of the piston being in the range of from 0.1 m to 3 m, in which cylinder the cylinder walls and the piston enclose a first chamber and a second chamber, the second 10 chamber being separated from the first chamber by the piston, and - alternately feeding wet biomass at low pressure into the first chamber, and feeding hydraulic fluid into the second chamber, whereby receipt of hydraulic fluid *“ in the second chamber causes movement of the piston in the axial direction of the cylinder, which movement causes a concomitant discharge of wet biomass at high 15 pressure from the first chamber.

The wet biomass so discharged from the first chamber may be employed as feed, for example, in a gasification process.

As used in this patent document, the term “high pressure” means a pressure of at least 5 MPa, more typically at least 10 MPa, in particular at least 15 MPa, more 20 in particular at least 20 MPa, and the term “low pressure” means a pressure of less than 5 MPa, in particular at most 4 MPa, more in particular at most 3 MPa. The skilled person will appreciate that the pressure at which the hydraulic fluid may be fed to the second chamber is equal to or higher than the high pressure, typically at most 2 MPa, in particular at most 1 MPa, more in particular at most 0.5 MPa, higher 25 than the high pressure. The pressure at which the hydraulic fluid may be fed to the second chamber may typically be at least 0.001 MPa, in particular at least 0.01 MPa, higher than the high pressure.

The present invention also provides an apparatus for feeding wet biomass, which apparatus comprises 3 - a circular cylinder comprising cylinder walls, and, inside the cylinder, a piston which is movable in the axial direction of the cylinder, the cylinder having an internal cross sectional area in the range of from 80 mm to 20 dm , and the stroke of the piston being in the range of from 0.1 m to 3 m, in which cylinder the cylinder 5 walls and the piston enclose a first chamber and a second chamber, the second chamber being separated from the first chamber by the piston, and - a hydraulic pump capable of feeding a hydraulic fluid, wherein the first chamber is configured to be fluidly connected to a source of wet biomass and the second chamber is fluidly connected to the hydraulic pump and the 10 first and second chambers are configured to alternately receive wet biomass at low pressure in the first chamber, and receive hydraulic fluid in the second chamber, whereby receipt of hydraulic fluid in the second chamber causes movement of the piston in the axial direction of the cylinder, which movement causes a concomitant discharge of wet biomass at high pressure from the first chamber.

15 In a conventional high pressure piston or plunger pump the piston or plunger is driven mechanically by the action of a screw or a piston rod. A problem associated with the use of the conventional high pressure piston or plunger pump is leakage of wet biomass present in the cylinder into the very narrow space which necessarily exists between the piston or plunger and the cylinder wall. Such 20 leakage is the result of the high mechanical force exerted on the wet biomass when the mechanically driven piston or plunger moves in the axial direction of the cylinder in order to discharge wet biomass at high pressure from the cylinder. Such leakage brings dirt in the space between the piston or plunger and the cylinder wall causing problems of abrasion and also problems of fouling in mechanical parts of 25 the pump which are not intended to come in contact with wet biomass. In certain embodiments of the invention, the piston is driven by a hydraulic force using a hydraulic fluid, instead of by the conventional mechanical force using a screw or a piston rod. The associated unexpected advantage is that leakage which may occur at high pressure is leakage of the hydraulic fluid (not wet biomass) into the space 4 between the piston and the cylinder wall and subsequently into the wet biomass. Such leakage of the hydraulic fluid is generally harmless in that it does not turn into such problems of abrasion and clogging referred to hereinbefore, even it may represent the unexpected advantage that any such leakage assists in keeping the 5 space between the piston and the cylinder wall clean.

In certain embodiments of the invention a feeding pump may be employed which may operate at low pressure for feeding wet biomass into the first chamber of the cylinder, and high pressure is only built up in the first chamber by the action of the piston. The feeding pump operating at low pressure may be selected from 10 commercially readily available equipment, such as a worm pump or a lobe pump. Thus, it is an unexpected advantage of the invention that it teaches the use of a combination of relatively simple and relatively robust equipment, such as comprising a conventional low-pressure pump and a cylinder with piston, for feeding wet biomass at high pressure into, for example, a high-pressure gasification 15 process.

FIG. 1 provides a scheme of an embodiment of a reaction apparatus and process for the gasification of wet biomass including an embodiment of the apparatus and process for feeding wet biomass in accordance with this invention.

FIG. 2 provides a schematic of a portion of an embodiment of the cylinder 20 with piston for use in this invention.

FIG. 3 provides a schematic of a reactor which is suitable for use in the gasification process as depicted in FIG. 1.

FIG. 4 shows temperature profiles of a reaction tube and a heating fluid over the length of the reaction tube with back-mixing and substantially without back-25 mixing in the reaction tube.

Throughout the Figures, the same objects will have the same reference numbers.

The wet biomass for use in this invention may be of various origins. The wet biomass may be, for example, residue from a fermentation facility, sewage sludge, 5 dredging sludge, algae, or animal manures. Mixtures of wet biomasses of different origins may be employed. The wet biomass may or may not be pretreated before feeding the wet biomass into the first chamber. Pretreating may involve shredding or cutting, for example, reducing the size or length of fibrous materials in the wet 5 biomass, such as grass, straw or small stems. Water may be added to the wet biomass or water may be removed from the wet biomass, for example, to achieve a desired viscosity or density. Water may be removed by centrifuging or by gravitational sedimentation. Materials may be added to the biomass. For example, the wet biomass may be fed into a gasification process and solid particles may be 10 added to the wet biomass, supplementing solid particles of a bed of solid particles present in the reactor of the gasification process.

The wet biomass as fed to the gasification process comprises water, for example in a quantity of at least 40 %w, typically at least 50 %w, more typically at least 70 %w, relative to the total weight of the wet biomass. In the normal practice 15 of this invention, the water content is at most 95 %w, on the same basis. The content of organic material is typically at least 1 %w, more typically at least 5 %w, and typically at most 60 %w, more typically at most 50 %w, on the same basis. The content of inorganic materials, other than water, is typically at least 1 %w, more typically at least 3 %w, and typically at most 80 %w, more typically at most 60 %w, 20 on the same basis. The contents of organic and inorganic materials are as determined by thermal gravimetric analysis (TGA) in accordance with ASTM El 131-08.

The invention employs a cylinder comprising a piston which is movable in the axial direction of the cylinder. The piston, together with the cylinder walls, form 25 two chambers inside the cylinder, which chambers are separated from each other by the piston. When wet biomass is fed at low pressure into the first chamber of the cylinder, and the first chamber receives wet biomass, the piston may move in the axial direction of the cylinder, away from the point of feeding wet biomass, so that the volume of the first chamber is increased. A suitable low pressure may be in the 6 range of from 0.15 MPa to 5 MPa, preferably in the range of from 0.2 MPa to 4 MPa, in particular in the range of from 0.3 MPa to 3 MPa. When subsequently a sufficiently high force is exerted onto the piston, which causes the piston to move into the opposite direction, the volume of the first chamber is decreased and wet 5 biomass is discharged from the first cylinder at high pressure. Wet biomass so discharged at high pressure may be employed as feed in a process downstream of the cylinder with piston. Such a downstream process may be a process for converting wet biomass, for example, a gasification process or an oxidation process producing syngas. The skilled person will appreciate that the force exerted onto the 10 piston, and the pressure at which the hydraulic fluid may be fed to the second chamber, will be high enough to accommodate the pressure at which the downstream process operates. A suitable high pressure may be in the range of from 5 MPa to 100 MPa, preferably in the range of from 10 MPa to 70 MPa, in particular in the range of from 15 MPa to 50 MPa, more in particular in the range of from 15 20 MPa to 35 MPa.

Biomass may be fed to the first chamber by using a feeding pump which operates at low pressure and which may be fluidly connected to the first chamber. Suitable pumps may be, for example, a worm pump or a lobe pump. The feeding pump may be equipped at the input side or at the output side with a shredder or 20 cutter for reducing the size of fibrous material which may be present in the wet biomass.

The force which may be exerted onto the piston may be a mechanical force, using a screw or a piston rod. The force is preferably a hydraulic force exerted onto the piston by using a hydraulic fluid. The hydraulic fluid may be a hydraulic oil, 25 but it is preferred to selected an aqueous liquid as the hydraulic fluid. The aqueous liquid may be filtered surface water, for example obtained from a river, a canal or a lake; or it may be tap water, drinking water, desalted water, or distilled water. Preferably, the aqueous liquid is filtered water.

7

The hydraulic fluid may be fed to the second chamber at high pressure by using a hydraulic pump which may be fluidly connected to the second chamber.

For example, the pump may be a positive displacement pump, such as a piston pump, which may also be referred to as a plunger pump, or a membrane pump.

5 When wet biomass is fed into the first chamber, and the piston moves in the axial direction of the cylinder, such that the volume of the first chamber increases, the volume of the second chamber decreases, with concomitant discharge of hydraulic fluid from the second chamber, for example into a reservoir which may also be used to hold a supply of hydraulic fluid as feed for the hydraulic pump.

10 A plurality of the cylinders comprising the piston, for example two, three or four cylinders with piston, may be employed in a parallel arrangement. By employing such an arrangement, a higher total feeding rate and/or an uninterrupted or continuous feed may be achieved. The skilled person will appreciate that the feeding system as described may employ valves which ensure that at any time the 15 various streams of wet biomass and hydraulic fluid, if present, come from the appropriate source and find the appropriate destination. This will be set out further in the discussion of FIGS. 1 and 2, hereinafter.

The wet biomass may be fed in accordance with this invention into a downstream process. As an example of such a downstream process, particulars of a 20 gasification process for wet biomass are provided hereinafter.

The gasification may be performed at a high temperature, typically a temperature of at least 300 °C, and more typically a temperature of at least 350 °C. Typically, the gasification is performed at a temperature of at most 900 °C, and more typically a temperature of at most 850 °C. The temperature may be selected 25 such that the gasification reactions proceed at a rate as desired. The gasification may be performed typically a pressure of at least 10 MPa, and more typically a pressure of at least 15 MPa. Typically, the gasification is performed at a pressure of at most 50 MPa, and more typically a pressure of at most 35 MPa.

8

The wet biomass fed to the gasification reactor comprises a substantial quantity of water. Supercritical water is a good solvent for many organic materials, and a poor solvent for minerals and other inorganic materials. It is therefore preferred to perform the gasification of wet biomass at conditions at which the 5 water is present in the reaction mixture as supercritical water.

As used in this patent document, supercritical water is water above its critical temperature and above its critical pressure, and subcritical water is water below its critical temperature and above its critical pressure. It is generally known that water has its critical temperature at 373.946 °C and its critical pressure at 220.64 bar 10 (22.064 MPa), cf. W. Wagner and A. Pruss, "The IAPWS Formulation 1995 for the

Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use," J. Phys. Chem. Ref. Data, 31(2):387-535,2002. As specified herein, pressure is absolute pressure. The term “fluid gasification product” is used herein in order to distinguish fluid (including gaseous and liquid) products of the gasification 15 reaction from solid products, such as tars en solidified salts.

The wet biomass may preferably be fed to the reactor at or above the critical pressure of water. In particular, the wet biomass is fed at a pressure of at least 22.5 MPa, preferably at least 23 MPa, more preferably at least 25 MPa. The pressure is typically at most 50 MPa, more typically at most 35 MPa.

20 There may be a problem in a gasification process in that the solids formed in the presence of supercritical water, such as salts, ash and char, tend to stick to the inner wall of the reactor and can cause clogging of the reactor. It has unexpectedly been found that that problem can be eliminated effectively by converting water present in the wet biomass into supercritical water in the presence of a bed of solid 25 particles suspended in a fluid. Thus, in accordance with this finding, the biomass may be fed to the reactor at a temperature below the critical temperature of water, and, subsequently, inside the reactor comprising the bed of solid particles, the temperature of the feed may be increased to above the critical temperature, so that supercritical water is formed in the presence of the bed of solid particles.

9

The wet biomass fed to the reactor comprises water, which is preferably subcritical water. The wet biomass may be preheated before feeding to the reactor. Typically, the wet biomass may be preheated to, and fed to the reactor at, a temperature of at most 370 °C, more typically at most 360 °C, in particular at most 5 350 °C. Typically, the wet biomass may be preheated to, and fed to the reactor at, a temperature of at least 250 °C, more typically at least 280 °C, preferably at least 300 °C.

In the reactor and in the presence of the bed of solid particles, the temperature of the wet biomass is typically increased to a temperature of at least 375 °C, in 10 particular at least 380 °C, to the effect that supercritical water is formed from the water present in the wet biomass. More typically the temperature of the feed is increased to a temperature of at least 400 °C, in particular at least 420 °C. Typically the temperature of the feed is increased to a temperature of at most 800 °C, more typically at most 760 °C. The temperature of at least 375 °C may be selected such 15 that the gasification reactions proceed at a rate as desired.

The bed of solid particles suspended in a fluid may preferably be a fluidised bed, typically a spouted fluidised bed or a circulating fluidised bed, and preferably a bubbling fluidised bed. In alternative embodiments of the invention the bed may be a fixed bed.

20 The fluid in which the solid particles are suspended is typically an aqueous fluid. Depending on the location in the reactor, the aqueous fluid may comprise supercritical water or subcritical water. Namely, close to a point of feeding the wet biomass, the temperature may be below the critical temperature of water, and at other points the temperature may be above the critical temperature of water. As 25 gasification proceeds in the reactor, the fluid may also comprise fluid gasification products, in particular at locations away from the point of feeding the wet biomass.

The solid particles suspended in the fluid may be particles comprising, for example, a mineral or an aggregate of minerals, such as sand, crushed rock or crushed stone; a salt, for example a salt originating from wet biomass; metal, such 10 as stainless steel, copper or aluminum; or a crystalline or non-crystalline ceramic, such as a glass, a clay, an alumina, a silica, a silica-alumina, or mixtures thereof. The material of the solid particles may have a density in a wide range, for example, in the range of from 1.5* 10J kg/m3 to 10x 103 kg/m3, more typically in the range of 5 from 2* 10 kg/m to 9x10 kg/m . The particles may typically comprise particles having a size in the range of from 20 pm to 1 mm, in particular in the range of from 50 pm to 0.5 mm, wherein the size of the particles is as determined by ISO 13320:2009. Preferably, all particles have a size in the range as specified. The suspended solid particles may have a dual function in the gasification process, in 10 that they assist in preventing solids from depositing on the inner wall of the reactor, and in addition they may act as a catalyst in the gasification reaction.

The solid particles may be fed into the reactor together with the wet biomass. For example, at least a portion of the solid particles may be sand which may inevitably be present in the wet biomass as one of its components. Alternatively, 15 solid particles may be added to the wet biomass before feeding the wet biomass to the reactor. Dissolved salts which are present in the wet biomass may solidify in the reactor upon and/or after the formation of supercritical water, and such solidified salts may then constitute a portion of the bed of suspended solid particles. As another alternative, solid particles may be introduced into the reactor separate 20 from the wet biomass.

The bed of suspended particles may have a void fraction which is selected from a wide range. Typically, the void fraction of the fluidised bed is in the range of from 0.05 to 0.95 v/v, relative to the total volume of the bed. When the bed is a bubbling fluidised bed, the void fraction may typically be in the range of from 0.25 25 to 0.8 v/v, more typically in the range of from 0.35 to 0.7 v/v, relative to the total volume of the bed. When the bed is a spouted fluidised bed, the void fraction may typically be in the range of from 0.05 to 0.2 v/v, relative to the total volume of the bed. When the bed is a circulating fluidised bed, the void fraction may typically be in the range of from 0.8 to 0.95 v/v, relative to the total volume of the bed. As used 11 herein, the total volume of the bed is the volume of the bed at the conditions of temperature and pressure of the bed, and is as determined from the reactor dimensions and/or the dimensions of the portion of the reactor which holds the bed. The void volume is as determined by subtracting the particles volume from the bed 5 volume. The particles volume may be as determined by submersing the particles present in the bed in water and determining the displaced volume of water.

The size of the reactor is not essential. Preferably, the residence time in the reactor is high enough for obtaining a sufficient yield of fluid gasification products. Thus, when the gasification process is operated in a continuous mode, the 10 dimensions of the reactor are preferably such that at a desired throughput a sufficiently long residence time is achieved. It is also desired, for avoidance of the formation of tars, that in the reactor, or in the portion of the reactor which holds the bed of solid particles, the rate of temperature increase of the feed is high. Typically, the rate of temperature increase is at least 1.5 °C/s, preferably at least 2 °C/s. In the 15 normal practice of the gasification process, the rate of temperature increase will frequently be at most 80 °C/s, more frequently at most 50 °C/s. The rate of temperature increase is as determined by calculating the quotient of the temperature increase and the average residence time of the fluid in the reactor or in the portion of the reactor which holds the bed of solid particles. The average residence time is 20 determined from experiments using a tracer material.

The fluid gasification product may be withdrawn from the reactor together with supercritical water formed in the reactor. The fluid gasification product may also comprise entrained solid particles. A portion of the solid particles may remain in the reactor. Solid particles entrained in the fluid gasification product leaving the 25 reactor may be removed. The fluid gasification product may be cooled and depressurised, resulting in a gas/aqueous liquid mixture, and gaseous gasification products may subsequently be recovered from the gas/aqueous liquid mixture.

In a preferred embodiment, prior to cooling, the fluid gasification product withdrawn from the reactor may be further heated. The further heated fluid 12 gasification product may be used as a heating fluid (“first heating fluid”, hereinafter) for heating the reactor. It is generally sufficient to further heat fluid gasification product as to increase its temperature typically by at most 200 °C, more typically by at most 150 °C, for example 100 °C. The temperature increase is 5 typically at least 10 °C, more typically at least 20 °C. Electrical energy may be applied to accomplish the further heating. Preferably, the fluid gasification product withdrawn from the reactor is further heated by heat exchange with a second heating fluid. The second heating fluid may be a hot gas produced in a hot-gas producing unit. The hot-gas producing unit may be, for example, a gas burner, a 10 gas turbine, a gas engine or a fuel cell.

For optimisation purposes, the further heated fluid gasification product may be kept at a high temperature for some time before the further heated fluid gasification product is used as the first heating fluid, as this will have the advantageous effect of increasing the methane content of the fluid gasification product. In this 15 embodiment, the process may comprise as an additional step maintaining the temperature of the further heated fluid gasification product, typically for a period of at least 5 minutes, in particular at least 10 minutes, and typically for a period of at most 1 hour, in particular at most 40 minutes. This may be accomplished by using a vessel, preferably an insulated vessel or a heated vessel, which may hold the further 20 heated fluid gasification for the time as specified. Herein, “maintaining the temperature” means maintaining the temperature typically within a margin of plus or minus 50 °C, more typically within a margin of plus or minus 40 °C, in particular within a margin of plus or minus 30 °C.

In preferred embodiments, the further heated fluid gasification product may be 25 used for the purpose of heating, by heat exchange, the wet biomass. In these embodiments, the temperatures of the wet biomass and the further heated fluid gasification product may be selected in accordance with the prevailing pressures, to the effect that an unexpected improvement in the heat integration of the gasification process is achieved. In the improved heat integration, the relatively large amount of 13 heat released around the critical temperature when cooling down gasification product comprising supercritical water is used to satisfy the relatively large heat requirement around the critical temperature when heating wet biomass.

Accordingly, in these embodiments the gasification process comprises 5 - heating wet biomass at a pressure Pp in the range of from 22.1 MPa to 35 MPa from a temperature of at most Ti to a temperature of at least T2 by heat exchange with a first heating fluid, upon which heating the fluid gasification product is obtained, - further heating the fluid gasification product, and 10 - using the further heated fluid gasification product as the first heating fluid, upon which use the further heated fluid gasification product is cooled down at a pressure Ps in the range of from 22.1 MPa to 35 MPa from a temperature of at least T3 to a temperature of at most T4, wherein Ti, T2, T3 and T4 are temperatures in °C which can be calculated by using the mathematical formulae 15 Tj = 3.2 xPp + 301.6, T2 = 3.8 xPp + 292.4, T3 = 3.8 *PS + 292.4, and T4 = 3.2 xPs + 301.6, wherein Pp and Ps denote the pressures Pp and Ps, respectively, in MPa. Preferably, 20 Ti, T2, T3 and T4 are temperatures in °C which can be calculated by using the mathematical formulae T, = 2.9 x Pp + 306.2, T2 - 4.1 xpp + 287.8, T3=4.1 xps +287.8, and 25 T4 - 2.9 x Ps + 306.2, wherein Pp and Ps denote the pressures Pp and Ps, respectively, in MPa having values in the range of from 22.1MPa to 33 MPa. More preferably, Ti, T2, T3 and T4 are temperatures in °C which can be calculated using the mathematical formulae Ti =2.6 x Pp + 310.8, 14 T2 = 4.4 x Pp+ 283.2, T3 = 4.4 x ps + 283.2, and T4 = 2.6 xps + 310.8, wherein Pp and Ps denote the pressures Pp and Ps, respectively, in MPa having 5 values in the range of from 22.1MPa to 32 MPa.

Typically the increase from the temperature of at most T] to the temperature of at least T2 is at least 10 °C, more typically at least 20 °C, in particular at least 30 °C.

/

Typically the increase from the temperature of at most T] to the temperature of at least T2 is at most 450 °C, more typically at most 400 °C, in particular at most 10 350 °C. Typically the temperature of the feed is increased to a temperature of at least T2 of at least 377 °C, more typically at least 380 °C, in particular at least 400 °C, more in particular at least 420 °C. Typically the temperature of the feed is increased to a temperature of at least T2 of at most 800 °C, more typically at most 760 °C. At the temperature of at least T2, as defined herein, water is present in the 15 wet biomass as supercritical water. The temperature of at least T3 may typically be at least 425 °C, in particular at least 440 °C, and typically at most 900 °C, more typically at most 850 °C. The decrease from the temperature of at least T3 to the temperature of at most T4 typically amounts to at least 10 °C, more typically at least 20 °C, in particular at least 30 °C. Typically the decrease from the temperature of at 20 least T3 to the temperature of at most T4 is at most 450 °C, more typically at most 400 °C, in particular at most 350 °C. The further heated gasification product may be cooled down typically to a temperature of at most 390 °C, in particular at most 380 °C, more in particular at most 370 °C, or even at most 360 °C. Typically, it may be cooled down to a temperature of at least 300 °C, more typically at least 25 320 °C.

When, as in preferred embodiments, the gasification process is carried out as a continuous process, cooling down gasification product proceeds downstream from heating the wet biomass, in which case the pressure Ps is generally lower than the pressure Pp. Typically, the pressure Ps is at least 0.001 MPa, more typically at least 15 0.01 MPa, lower than the pressure Pp. Typically, the pressure Ps is at most 10 MPa, more typically at most 8 MPa, in particular at most 5 MPa, lower than the pressure Pp-

In an embodiment, the heat exchange may comprise heat exchange between a 5 flow of the wet biomass and a flow of the further heated fluid gasification product which is co-current with the flow of the wet biomass. In such an embodiment, the temperature of at least T3 and the temperature of at most T4 are preferably both selected higher than the temperature of at least T2. In a preferred embodiment, the heat exchange comprises heat exchange between a flow of the wet biomass and a 10 flow of the further heated fluid gasification product which is counter-current with the flow of the wet biomass. The latter embodiment is preferred as the temperature of at least T3 may be selected higher than the temperature of at least T2 and the temperature of at most T4 may be selected higher than the temperature of at most Ti, which makes the latter embodiment more energy efficient that the primer 15 embodiment.

Now turning to the Figures, FIG. 1 provides a scheme of an embodiment of a reaction apparatus and process for the gasification of wet biomass including an embodiment of the apparatus and process for feeding wet biomass in accordance with this invention. The reaction apparatus may comprise feeding system 10, 20 heating and reaction system 30 and recovery system 60.

Wet biomass 11 may be pressurised and introduced into heating and reaction system 30 by using a pumping system. It has been found advantageous to employ feeding pump 12 which is fluidly connected to the first chamber, for pumping a portion of wet biomass 11 at low pressure into the first chamber of cylinder with 25 piston 14, via valve 16. As an alternative to the use of feeding pump 12, wet biomass may be fed hydrostatically from a storage tank. Subsequently, valve 16 may be closed. Then, the wet biomass may be discharged at high pressure from cylinder with piston 14 via valve 18 into heating and reaction system 30, by using a hydraulic system comprising hydraulic pump 20 and valves 22 and 24. Flydraulic 16 pump 20 may pump a hydraulic fluid via valve 22 into the second chamber of cylinder with piston 14, valves 16 and 24 being closed. After discharging the wet biomass into heating and reaction system 30, valve 18 may be closed, valves 16 and 24 may be opened and a further portion of wet biomass may be pumped from 5 feeding pump 12 into cylinder 14. A plurality of cylinders with pistons 14 and a plurality of valves 16,18,22 and 24 may be placed in parallel arrangement.

FIG. 2 shows cylinder with piston 14, comprising cylinder wall 60. Piston 64 is located inside cylinder 62, and is movable in the axial direction AD of cylinder 62. Piston 64 divides the space inside cylinder 62 into first chamber 66 and second 10 chamber 68. Piston 64 may be oriented generally perpendicülarly relative to axial direction AD. Conduits may fluidly connect first chamber 66 via valve 16 to feeding pump 12 (FIG. 1) and via valve 18 to heating and reaction system 30 (FIG. 1). In addition, conduits may fluidly connect second chamber 68 via valve 22 to hydraulic pump 20 (FIG. 1) and via valve 24 to an outlet (not drawn) for hydraulic 15 fluid or to a reservoir (not drawn) for holding a supply of hydraulic fluid.

The shape and size of circular cylinder 62 may be selected in accordance with the pumping capacity desired. The internal cross sectional area of the cylinder may in particular be in the range of from 7 cm to 3.2 dm . The stroke of piston 64 may in particular be in the range of from 0.2 m to 2.5 m. The wall thickness of the 20 cylinder may typically be in the range of from 1 mm to 10 cm, in particular in the range of from 1.5 mm to 2 cm. The thickness of piston 64 may typically be in the range of from 1 mm to 30 cm, in particular in the range of from 1 cm to 20 mm. Cylinder 62 and piston 64 may typically be made of cast iron or steel, or a combination thereof. Cylinder with piston 14 may typically operate at a frequency 25 in the range of from 0.1 strokes/minute to 50 strokes/minute, in particular a frequency in the range of from 0.2 strokes/minute to 20 strokes/minute, in which one stroke is a complete movement of the piston, which includes a movement towards the point of feeding wet biomass and a movement away from the point of feeding wet biomass.

17

Now turning again to FIG. 1, in heating and reaction system 30, heat exchanger 29 may be, for example, a double tube heat exchanger or a shell and tube heat exchanger. In heat exchanger 29, the wet biomass may be preheated to a temperature below the critical temperature of water, as set out hereinbefore. Then 5 the preheated wet biomass may be introduced into reactor 32 comprising bed 31 of solid particles suspended in a fluid. In reactor 32 the wet biomass may be further heated to a temperature above the critical point of water, as set out hereinbefore.

For the purpose of heating the wet biomass, reactor 32 comprises a heating device, for example a heating jacket and/or internal heating pipes through which a heating 10 fluid may flow. A plurality of reactors 32 may be employed in parallel, to increase the total capacity of the reaction system.

Stream 34 of fluid gasification product leaving reactor 32 may preferably be treated to remove entrained solids, mainly comprising solid salts. In this preferred embodiment, the reaction apparatus comprises additionally a separation unit, in 15 particular a cyclone, a gravity separator, or a device comprising impactor plates, positioned in the fluid connection connecting the reaction tube with the heater, which separation unit is configured to remove entrained solids from the fluid gasification product. Suitably, the removal may be achieved by using cyclone 37. Solids 36 may be discharged from cyclone 37, for example, via a lock chamber (not 20 drawn). Removing solids at this point has an advantage that less heat is required when the fluid gasification product is further heated in a next heating step, as described hereinafter.

The heating fluid for use in reactor 32 may be any heating fluid which is high enough in temperature for sufficient heating of the wet biomass in the reactor. The 25 heating fluid may be hot gas produced in a hot-gas producing unit. However, it has been found particularly advantageous to further heat fluid gasification product in heat exchanger 35 using the heat of, for example, hot gas 38 produced in a hot-gas producing unit (not drawn), and to use the further heated fluid gasification product as first heating fluid 40 in reactor 32. The hot-gas producing unit may be, for 18 example, a gas burner, a gas turbine, a gas engine or a fuel cell. For optimisation purposes, vessel 39, for example a tube or an arrangement of parallel tubes, may be incorporated receiving further heated fluid gasification product from heat exchanger 35. Vessel 39 provides that further heated fluid gasification product will have an 5 increased residence time at the highest temperature prevailing in heating and reaction system 30, which will have the advantageous effect of increasing the methane content of the fluid gasification product. In this embodiment, the reaction apparatus comprises additionally a vessel fluidly connected to the heater to receive further heated fluid gasification product from the heater and fluidly connected to the 10 heating device to feed the further heated fluid gasification product into the heating device for use as the first heating fluid, which vessel is configured to hold the further heated fluid gasification product for a period of time.

With or without vessel 39 installed, additional heat exchanger 42 may be incorporated, transferring heat from further heated fluid gasification product to fluid 15 gasification product before the latter enters heat exchanger 35. Alternatively, vessel 39 may be incorporated in the fluid connection between heat exchanger 42 and heat exchanger 35. In these embodiments, the reaction apparatus comprises additionally a heat exchanger positioned in the fluid connection connecting the heater with the heating device, and in the fluid connection connecting the reaction 20 tube and with the heater, which heat exchanger is configured to exchange heat between the further heated fluid gasification product and the fluid gasification product.

It has been found particularly advantageous to employ as reactor 32 a reactor as shown in FIG. 3. Reactor 32 shown in FIG. 3 may comprise reaction tube 46, 25 distribution plate 47, and the heating device, for example heating jacket 48 and/or in internal heating pipes (not drawn). Inlet pipe 50 for wet biomass may be fluidly connected with heat exchanger 29 (FIG. 1). Outlet pipe 52 for fluid gasification product may be fluidly connected to heat exchanger 35, optionally via heat exchanger 42 and/or cyclone 37 and/or vessel 39. Inlet pipe 54 for heating fluid 19 may be fluidly connected with heat exchanger 35, optionally via heat exchanger 42 and/or vessel 39. Outlet pipe 56 for heating fluid may be fluidly connected with heat exchanger 29. The bed of suspended solid particles in the form of a fluidised bed 44 may be contained in reaction tube 46, downstream of distribution plate 47.

5 An excess of solid particles may be withdrawn from reactor 32 via overflow pipe 58. Reaction tube 46 is adapted to allow wet biomass to pass in the longitudinal direction of the reaction tube, and counter-currently with the heating fluid flowing in heating jacket 48 and/or in internal heating pipes. Reactor 32 may be fluidly connected with lock chamber 59 for the purpose of introducing solid particles into 10 the reactor.

Fluidised bed 44 has typically a length of at least 0.5 m, more typically at least 1 m. Fluidised bed 44 has typically a length of at most 10 m, more typically at most 5 m. For example, the length of fluidised bed 44 may suitably be 3 m. The cross sectional area of fluidised bed 44 is typically at most 1.8 m2, more typically at most 15 20 dm . The cross sectional area of fluidised bed 44 is typically at least 1 cm , more typically at least 2 cm2. For example, the cross sectional area of fluidised bed 44 may suitably be 4.5 cm2. Preferably, fluidised bed 44 has the shape of a circular cylinder, typically having a length to diameter ratio in the range of from 5 to 50, more typically in the range of from 8 to 30. For example, the length to diameter 20 ratio of fluidised bed 44 may suitably be 20. In fluidised bed 44, when having dimensions as specified in this paragraph, there is relatively little back-mixing, so that there is a temperature gradient over the length of the bed. A single reactor tube comprising a fluidised bed having dimensions as specified may be installed. Alternatively, a plurality of reaction tubes comprising a fluidised bed having 25 dimensions as specified may be installed in parallel. The number of reaction tubes and fluidised beds may be in the range of from 2 to 20 (inclusive), in particular in the range of from 3 to 10 (inclusive).

An advantage of having fluidised bed 44 in which there is relatively little back-mixing is shown in FIG. 4. FIG. 4 shows the profiles of temperature t over 20 length L of the bed and the heating fluid, substantially without back-mixing in the bed (situation A) and, for comparison, with substantial back-mixing in the bed (situation B). In situation A, there is a temperature gradient C in the bed, which extends from an inlet temperature tj to an outlet temperature t^ In situation B, there 5 is, as a consequence of back-mixing, virtually the same temperature over the length of the bed (D), except for a steep temperature gradient E near the inlet. F and G depict the temperature profiles of the heating fluids which can accommodate the heating profiles of the reaction tubes in situations A and B, respectively. In both cases At depicts the minimum temperature difference between the reaction tube and 10 the heating fluid. With At being equal in situations A and B, temperature difference AtA at the inlet of the heating fluid in situation A is substantially less than temperature difference AtB at the inlet of the heating fluid inlet in situation B. This implies for the process depicted in FIG. 1 that in heat exchanger 35 fluid gasification product needs heating to achieve a smaller temperature increase in 15 situation A than in situation B, which means that in situation A less heat is supplied from the hot-gas producing unit than in situation B.

Returning again to FIG. 1, further heated fluid gasification product may be used as first heating fluid 40 in heating jacket 48 and/or in internal heating pipes (not drawn) of reactor 32. When the fluid gasification product leaves reactor 32 20 through outlet pipe 56 it may typically have a temperature in the range of from 300 °C to 450 °C, more typically in the range of from 350 °C to 400 °C, for example 380 °C. The fluid gasification product may be cooled down further in heat exchanger 29 against wet biomass. The fluid gasification product leaving heat exchanger 29 may typically have a temperature in the range of from 20 °C to 25 150 °C, more typically in the range of from 40 °C to 120 °C, for example 90 °C.

The extensive recovery of heat as it may take place in any of heat exchangers 42 and 29 and in reactor 32 renders the process depicted in FIG. 1 a very energy efficient process in that the recovery of heat reduces the net energy supply to the 21 process, in particular the energy supply in heat exchanger 35 by means of the hot gas 38.

When entering recovery system 60, the fluid gasification product may be depressurized over valve 61 to a pressure typically in the range of from 0.1 MPa to 5 20 MPa, more typically in the range of from 0.2 MPa to 15 MPa.

Depressurised fluid gasification product may be degassed in degasser 62, yielding a gas fraction and a liquid fraction. The gas fraction comprising high value gases, such as hydrogen and methane may be split into a methane-rich stream and a hydrogen-rich stream in, for example, membrane separator 64. The liquid fraction 10 from degasser 62 may be depressurized further over valve 66, and further degassed in degasser 68, producing a gaseous fraction which may comprise carbon dioxide, methane, hydrogen, and hydrocarbons other than methane. The pressure downstream of valve 66 may typically be in the range of from 0.1 MPa to 5 MPa, more typically in the range of from 0.2 MPa to 3 MPa. The liquid product obtained 15 in degasser 68 is an aqueous residue comprising salts. The aqueous residue may be treated in membrane separator 70 yielding water and an aqueous residue being enriched in salts.

1039008

Claims (17)

5 A method for feeding wet biomass, the method comprising - providing a circular cylinder that has cylinder walls and, within the cylinder, a piston movable in the axial direction of the γ cylinder, the cylinder having a has a cross-section in the range of 80 mm to 10 20 dm, and the stroke of the piston is in the range of 0.1 m to 3 m, in which cylinder the cylinder walls and the piston enclose a first chamber and a second chamber, the second chamber from the first chamber is separated by the piston, and - feeding wet biomass at a low pressure of less than 5 MPa to the first chamber alternately with feeding a hydraulic fluid to the second chamber, entering the chamber hydraulic fluid in the second chamber causes a movement of the piston in the axial direction of the cylinder, which movement causes a simultaneous discharge of wet biomass from the first chamber at a high pressure of at least 5 MPa. A method according to claim 1, characterized in that the high pressure is a pressure in the range of 15 MPa to 50 MPa and the low pressure is a pressure in the range of 0.2 MPa to 4 MPa, and in particular the high pressure a pressure in the range of 20 MPa to 35 MPa and the low pressure a pressure in the range of 0.3 MPa to 3 MPa. A method according to claim 1 or 2, characterized in that the hydraulic fluid is fed to the second chamber with a pressure equal to the high pressure, or at most 2 MPa, in particular at most 1 MPa, more in particularly at most 0.5 MPa, higher than the high pressure. 1039008 A method according to any one of claims 1-3, characterized in that the wet biomass is selected from fermentation residues, sewage sludge, dredging sludge, algae, animal manure, and mixtures thereof, and in that the wet biomass comprises at least 40% by weight of water based on the total weight of the wet biomass. Receive 5 MPa in the first chamber and receive hydraulic fluid in the second chamber, the arrival of the hydraulic fluid in the second chamber causing movement of the piston in the axial direction of the cylinder, which movement causes simultaneous discharge of wet biomass from the first chamber 5 at a high pressure of at least 5 MPa. A method as claimed in one or more of claims 1-4, characterized in that the wet biomass contains fiber material and that the method additionally comprises reducing the size or length of the fiber material before the wet biomass is fed to the first room. A method according to one or more of claims 1-5, characterized in that the hydraulic fluid is an aqueous liquid. A method according to one or more of claims 1-6, characterized in that the method additionally includes the use of the wet biomass emitted from the first chamber as a feed in a gasification process. A method according to one or more of claims 1-7, characterized in that the cylinder has a cross-section in the range of 7 cm to 3.2 dm, and the stroke of the piston in the range of 0.2 m to 2.5 m. 9. A device for feeding wet biomass, which device comprises - a circular cylinder that has cylinder walls and, within the cylinder, a piston 20 that is movable in the axial direction of the cylinder, the cylinder having a cross section in the region from 80 mm to 20 dm, and the stroke of the piston is in the range of 0.1 m to 3 m, in which cylinder the cylinder walls and the piston enclose a first chamber and a second chamber, the second chamber being the first chamber separated by the piston, and - a hydraulic pump capable of feeding a hydraulic fluid, the first chamber being arranged to have a fluid connection with a supply of wet biomass and the second chamber a fluid connection with the hydraulic pump, and the first chamber and the second chamber are arranged to alternate wet biomass at a low pressure of less than An apparatus according to claim 9, characterized in that the apparatus additionally includes a feed pump that has a fluid communication with the first chamber for pumping wet biomass to the first chamber. An apparatus according to claim 10, characterized in that the feed pump is a worm pump or a lobe pump. An apparatus according to claim 10 or 11, characterized in that the feed pump is provided with a shredder or a cutter on the supply side or on the discharge side. 13. An apparatus according to one or more of claims 9-12, characterized in that the first chamber is adapted to expel the biomass to a heating and reaction system of an apparatus for gasifying wet biomass. An apparatus according to claim 13, characterized in that the apparatus comprises additional conduits and valves, which conduits and valves are adapted to provide the first chamber with a fluid connection to the feed pump and via a second valve to provide a fluid connection to the heating and reaction system. 15. An apparatus according to one or more of claims 9-14, characterized in that the apparatus additionally comprises conduits, valves and an outlet for the hydraulic fluid or a storage reservoir for the hydraulic fluid, the conduits passing the second chamber through a giving a third valve a fluid connection to the hydraulic pump, and providing a fluid connection to the outlet or reservoir via a fourth valve. An apparatus according to one or more of claims 9-15, characterized in that the apparatus comprises a plurality of piston cylinders in a parallel arrangement. An apparatus according to one or more of claims 9-16, characterized in that the cylinder has a cross-section in the range of 7 cm to 3.2 dm, and the stroke of the piston in the range of 0.2 m to 2.5 m lies. 1039008