Method and plant for transferring energy from biomass raw material to at least one energy user

Abstract

A method for producing energy including: producing fuel gases from biomass raw material in a main receptacle unit (8), feeding produced fuel gas to a consumer unit (2,3), transferring energy from the consumer unit to at least one energy user (7). The method includes recovering heat and producing pressurized superheated steam, intermittently loading biomass raw material into at least one vessel (8), being included in the main receptacle unit (8), pressurizing the loaded at least one vessel (8) with pressurized superheated steam, passing pressurized superheated steam through the loaded and pressurized at least one vessel (8), thereby contacting and heat treating said biomass raw material with the pressurized superheated steam for the production of said fuel gases, supplying produced fuel gases together with still superheated steam to the consumer unit (2,3). The invention also concerns a plant.

Claims

1. Method for producing energy including: producing fuel gases from biomass raw material in a main receptacle unit, feeding produced fuel gas to a consumer unit for combustion of the fuel gases in the presence of oxygen, transferring energy from the consumer unit to at least one energy user, characterized by recovering heat in a flue gas stream downstream of the consumer unit and producing pressurized superheated steam in a steam generator using so recovered heat, intermittently loading biomass raw material into at least one vessel, being included in the main receptacle unit, pressurizing the loaded at least one vessel with pressurized superheated steam, passing pressurized superheated steam through the loaded and pressurized at least one vessel, thereby contacting and heat treating said biomass raw material with the pressurized superheated steam for the production of said fuel gases, supplying produced fuel gases together with still superheated steam to the consumer unit under essentially maintained pressure, and intermittently discharging solid biomass residues from the at least one vessel.

2. Method according to claim 1, wherein the main receptacle unit includes a plurality of vessels that are controlled for supplying an equalized stream of fuel gases and steam from the main receptacle unit to the consumer unit.

3. Method according to claim 1, characterized in that said discharged solid biomass residues are supplied to an auxiliary processing receptacle unit where they are gasified in a pressurized environment in the presence of superheated steam.

4. Method according to claim 3, characterized in that the discharged solid biomass residues are disintegrated before they are supplied to an auxiliary processing receptacle unit.

5. Method according to claim 3, characterized in that the solid biomass residues are treated in the auxiliary processing receptacle unit at a treatment temperature range exceeding a treatment temperature range in the main receptacle unit.

6. Method according to claim 3, characterized in that part of fuel gas and steam exiting the main receptacle unit is entered into the auxiliary processing receptacle unit.

7. Method according to claim 1, characterized in that at least part of solid biomass residues remaining after treatment in the main receptacle unit and at occasions in the auxiliary processing receptacle unit are passed on to a gasifier wherein they are gasified in the presence of superheated steam and an optional supply of oxygen.

8. Method according to claim 1, characterized in that flow of fuel gases to the consumer unit is regulated so as to maintain a continuous equalized supply of fuel gases to the consumer unit.

9. Method according to claim 1, characterized in that pulverized residues remaining after treatment in the main receptacle unit and at occasions in the auxiliary processing receptacle unit and after optional disintegration is entered into the consumer unit together with fuel gas.

10. Method according to claim 1, characterized in that gasification of the fuel is supported by a supply of oxygen.

11. Method according to claim 1, characterized in that the consumer unit is coupled for providing power to a compressor unit and for receiving supply of combustion air from a compressor unit.

12. Method according to claim 1, characterized in that the energy user is an electric generator for the production of electric energy.

13. Method according to claim 1, characterized in that water is recovered in the flue gas stream through a condenser supplying water to the steam generator for the production of superheated steam.

14. Method according to claim 1, characterized in that the fuel gas is led to a consumer unit including a power unit being one from the group including: a turbine arrangement, an internal combustion engine, an internal combustion engine with a turbo charger.

15. Method according to claim 1, characterized in that heat is extracted from discharged solid biomass residues for pre-treatment of solid biomass raw material.

16. Method according to claim 1, characterized in that the flue gas stream from the consumer unit upstream of the steam generator is supplied/supplemented with flue gases from an auxiliary combustor.

17. Method according to claim 1, characterized in that produced fuel gases together with still superheated steam are reheated using heat extracted from the steam generator.

18. Plant for producing energy including: a main receptacle unit for producing fuel gases from biomass raw material, means for feeding produced fuel gas to a consumer unit wherein the fuel gases are combusted in the presence of oxygen, means for transferring energy from the consumer unit to at least one energy user, characterized by a steam generator with heat exchange means for recovering heat in a flue gas stream from the consumer unit and arranged to produce pressurized superheated steam using so recovered heat, a loading arrangement for intermittently loading biomass raw material into at least one vessel, being included in the main receptacle unit, means for introducing pressurized superheated steam for pressurizing the loaded at least one vessel, means for passing pressurized superheated steam through the loaded and pressurized at least one vessel for contacting said biomass raw material with the pressurized superheated steam for heat treating the biomass raw material and production of said fuel gases, supply means for supplying produced fuel gases together with still superheated steam to the consumer unit under essentially maintained pressure, and discharge means for intermittently discharging solid biomass residues from the at least one vessel.

19. Plant according to claim 18, wherein the main receptacle unit includes a plurality of vessels that are controllable for supplying an equalized stream of fuel gases and steam from the main receptacle unit to the consumer unit.

20. Plant according to claim 18, characterized in that said discharged solid biomass residues supplied to an auxiliary processing receptacle unit wherein they are gasified in a pressurized environment in the presence of superheated steam.

21. Plant according to claim 20, characterized in that a disintegrator device is arranged for disintegrating solid biomass residues discharged from the main receptacle unit before they are supplied to the auxiliary processing receptacle unit.

22. Plant according to claim 18, characterized in that it includes a regulating device for regulating flow of fuel gases so as to maintain a continuous equalized supply of fuel gases to the consumer unit.

23. Plant according to claim 18, characterized in that the consumer unit is coupled for providing power to a compressor unit and for receiving supply of combustion air from a compressor unit.

24. Plant according to claim 18, characterized in that the energy user is an electric generator for the production of electric energy.

25. Plant according to claim 18, characterized in that a condenser is arranged for recovering water to be supplied to the steam generator for the production of superheated steam water in the flue gas stream.

26. Plant according to claim 18, characterized in that the consumer unit includes a power unit being one from the group including: a turbine arrangement, an internal combustion engine, an internal combustion engine with a turbo charger.

27. Plant according to claim 18, characterized by heat exchange means for extracting heat from discharged solid biomass residues for pre-treatment of solid biomass raw material.

28. Plant according to claim 18, characterized in that an auxiliary combustor is arranged downstream of the consumer unit and upstream of the steam generator.

29. Plant according to claim 18, characterized in that a reheater is arranged to extract from the steam generator for heating produced fuel together with superheated steam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in greater detail by way of embodiments and with reference to the annexed drawings, wherein:

(2) FIGS. 1-10 show different layouts of plants according to the present invention.

DESCRIPTION OF EMBODIMENTS

(3) In the Figs., same or similar elements are depicted with the same reference numerals. In the description, explanations of same or similar features are not repeated. In the following, see descriptions of previously explained embodiments for explanation of the reference numerals not appearing related to the specific Figs. Individual features explained in relation to different embodiments and Figs. can be combined and used in other embodiments.

(4) FIG. 1 illustrates a power generation plant where the consumer unit includes a combustor 2 and a gas turbine unit 3, wherein a means for the production of fuel gas from solid fuel, here biomass raw material, is indicated with 1. Fuel gas so produced is passed on to the combustor 2 which in a per se known manner produces flue gas which under high pressure is delivered to the gas turbine unit 3. The turbine unit 3 in turn drives a power generator 7 for the production of electric energy and also a compressor unit 4 for compressing air for combustion that is passed on to the combustor 2. An entry for air to the compressor unit 4 is indicated with 50.

(5) Solid fuel is typically passed on to a silo 12 for the intermediate collection of relatively dry solid fuel in the order of 10-20% moisture, which normally means that the solid fuel has been subjected to some kind of drying process before entering the silo 12. In the shown embodiment this is accomplished in that a conduit 54 is arranged for transferring residual heat recovered in a condenser 15 downstream of the turbine unit 3 to a dryer vessel 45 for biomass material entered through an inlet 44. Dry air can be transferred to the dryer vessel 45 over conduit 46 and be subsequently exited for the purpose of dehumidifying the biomass raw material.

(6) In order to produce fuel gases to the combustor 2, the silo 12 is arranged to intermittently pass on material over a gate valve unit 5 which can consist of a plurality of sluices, ordinary valves, feed screws or the like to a main receptacle unit 8 which can be comprised of one or more vessels 8 being connected in parallel for sequential operation. In order to obtain an equalized, quasi continuous flow of fuel gas already from the main receptacle unit 8, two or more vessels 8 being connected in parallel for sequential operation is desired.

(7) Steam is heated in a steam generator 6 being positioned in the exhaust line downstream of the gas turbine unit 3. This provides superheated steam under pressure through conduit 22 and over a steam distributor 21, which is connected to an accumulator 14, and branch line (-s) to the main receptacle unit 8 over valves 26 in order to intermittently pressurize vessels 8 of said main receptacle unit 8.

(8) Further, a continuous supply of the superheated steam from the steam generator 6 to the vessels 8 being included in the main receptacle unit 8 when these vessels are in the pressurized and loaded state functions for heat treatment of the solid fuel. This is achieved when pressurizing to an operational pressure (in this embodiment typically of about 20-70 bar) has been reached by providing a flow of superheated steam through the vessel (-s) 8 and through the fuel to be treated therein such that a resulting temperature of about 250-350 C. and preferably about 280-300 C. is reached inside the vessels 8. Hereby the solid fuel will be carbonized through pyrolysis. At the same time a certain amount of fuel gas will be produced, which, together with the steam, over a conduit or conduits 20 will be passed on to the combustor 2 for combustion of the fuel gas. 25 indicates valves downstream the individual vessels 8. 24 indicates pressure release valves.

(9) Numeral 13 indicates an accumulator for equalizing pressure and flow into a connection 19 in the conduit downstream of the main receptacle unit 8.

(10) After completed treatment in the main receptacle unit 8 remaining, now carbonized solid fuel, will be delivered to an auxiliary processing receptacle unit 9. 27 indicates valves regulating delivery from the individual vessels 8. An optional fuel mill at the inlet of the auxiliary processing receptacle unit 9, can be arranged for disintegrating remaining, now carbonized solid fuel to get even better properties for subsequent gasification.

(11) Through a conduit 38, a fuel gas and steam mix flow can be branched off from the conduit 20 for entry into the auxiliary processing receptacle unit 9. 47 indicates a regulator unit arranged to regulate gas flow to the auxiliary processing receptacle unit 9.

(12) A conduit 31 for air feed leads compressed air from the compressor unit 4 to an air inlet in the auxiliary processing receptacle unit 9 for allowing limited combustion so as to keep up the temperature in that unit, continue the carbonization process and also make possible further formation of fuel gas, which together with steam is led over conduit 29 to conduit 20. A valve 42 is arranged in the conduit 31 for control of the compressed air flow.

(13) The gas flow over conduit 29 is mixed in a mixer with a steam and fuel gas mixture coming from the main receptacle unit 8. After mixing, the gas is filtered in a hot gas filter 11 before it is fed over conduit 20 to the combustor 2.

(14) Possible remaining solids are collected in a collecting vessel 9 for later transport for external use over conduit 52. 30 indicates a circuit for recovering remaining heat in treated and not used solid fuel, said heat being transferred to the dry silo 12 in order to enhance temperatures and reduce water contents in incoming material, thereby making the fuel gas production process more efficient. Humidity in the material can be reduced by supply of dry air.

(15) Further, in FIG. 1 there is shown a steam vessel 14 acting as an accumulator for superheated steam in the conduit 22 and steam distributor 21.

(16) The condenser 15 for heat and water recovery is positioned in the exhaust downstream of the turbine unit 3 so as to recover water contents in flue gases and recover heat during that process. An air cooler co-operating with the condenser 15 is indicated with 16. 51 indicates an flue gas exit channel. 53 indicates a conduit for leading water obtained by the condenser 15 to the steam generator 6.

(17) Valves are arranged to control the air, steam and fuel gas flows at different positions in the various supply conduits. Not all of these valves are shown in FIG. 1, and it should be noted that normally all flows are subject to regulation.

(18) The plant is also equipped with (not shown) sensors such as temperature and flow sensors in the components and in the conduits for sensing the prevailing operational conditions. A CPU receives signals from the sensors and sends regulatory signals to said valves as responses to sensed values when they are compared to pre-stored and/or calculated target values.

(19) In short, a treatment sequence in one vessel 8 can be as follows:

(20) 1. Valve in gate valve unit 5, valve 26 in steam supply branch line, valve 25 in fuel gas conduit, valve 27 for carbonized solid fuel outletall these four valves being associated with the one vessel 8 in question are all closed or closes.

(21) 2. Valve 24 opens for pressure release of vessel 8 and closes when pressure has been released.

(22) 3. Valve in gate valve unit 5 opens and solid untreated material is let into vessel 8. Valve closes when the accurate amount of material has been received.

(23) 4. Valve 26 opens for pressurizing and heating vessel 8 with superheated steam. It should be noted that during pressurizing, steam related parameters are preferably controlled in order to maintain the steam in its superheated condition. It can as an example be necessary to arrange for higher steam flow such as e.g. to slightly open valve 24 to permit additional flow of steam to pass through the vessel 8.

(24) 5. When accurate pressure has been reached and fuel gas has started to form, valve 25 opens to let a flow of steam and fuel gas be passed to the combustor 2. Two or more vessels 8 can be coupled in series connection with each other when it comes to fuel gas and steam flow, even though they are coupled in parallel when it comes to solid material flow.

(25) 6. When fuel formation has dropped below a determined level and/or carbonisation of the contained fuel is considered to have been completed or simply after a chosen time period, the valves 25 and 26 are closed, valve 27 opens for passing carbonised solid fuel to the fuel vessel 9.

(26) 7. The sequence is repeated. During non operation of one vessel 8 one or more other (-s) is/are operative. It is not excluded that plural vessels are operative at the same time.

(27) Pressure gas through the release valve 24 can be recovered and possibly at least in part be fed to the turbine or be stored in a separate container for various uses such as for re-pressurizing the main receptacle unit.

(28) FIG. 2 shows a slightly modified second embodiment of the invention. A mill 9 is arranged at the inlet of the auxiliary processing receptacle unit 9. Solid residues from the main receptacle unit are in its disintegrated state treated as is explained above in the auxiliary processing receptacle unit 9.

(29) Still solid material remaining after this treatment is controllably fed to a gasifier 10 for gasifying through partial combustion of the remaining solid fuel. It is not excluded that also pulverulent solid fuel is fed to the combustor in addition to fuel gas.

(30) A conduit 23 for gasifier air feed leads compressed air from the compressor unit 4 to an air inlet in the gasifier 10.

(31) Further, there is provided an auxiliary combustor 36 downstream of the consumer unit (in this case the turbine unit 3) as seen in the exhaust conduit. This auxiliary combustor 36 has the purpose of filling up energy requirement in the steam generator for the production of greater amounts of superheated steam and/or higher temperatures. 49 indicates a conduit for delivering fuel gas and superheated steam from the conduit 20 to the auxiliary combustor 36. 50 indicates an oxygen supply to the auxiliary combustor 36.

(32) Reference number 16 indicates a district heating device in co-operation with the condenser 15.

(33) A hot water supply is lead through a conduit 59 to a water spray device 58 arranged in the fuel feed conduit 20 upstream of the filter 11 for the purpose i.a. of cooling the gases before introducing them to the filter 11.

(34) No circuit 30 is present in the second embodiment. Otherwise the main features of the embodiment in FIG. 2 essentially correspond to the one in FIG. 1.

(35) The embodiment of FIG. 3 shows, as compared to the FIG. 1 embodiment, that the auxiliary processing receptacle unit 9 is dispensed with. Pre-treatment may be provided before the silo 12 but is not shown in FIG. 3. 41 indicates a conduit for feeding superheated steam directly to the conduit 20 (for fuel and steam feed).

(36) The consumer unit has been changed in that the turbine-compressor unit 3, 4 has been supplemented with an intermediate turbine-compressor unit 3, 4. This intermediate turbine-compressor unit 3, 4 is a so called top-spool arrangement which serves to increase efficiency. The intermediate turbine-compressor unit 3, 4 drives an auxiliary generator 7. For further explanation of the top-spool arrangement it is referred to U.S. Pat. No. 7,721,552 (B2) (Euroturbine AB).

(37) Produced fuel gas is here entered into a compressor circuit before the high pressure compressor of the intermediate turbine-compressor unit 3, 4. This makes it possible for the entire means for the production of fuel gas 1 as well as for the superheated steam generator 6 to operate at lower pressures that what prevails at an inlet of the combustor 2.

(38) A conduit 31 for controlled (through valves 32) air feed leads compressed air from the compressor unit 4 to (an) air inlet (-s) in the main receptacle unit 8. Hereby limited combustion can take place already in the main receptacle unit 8 resulting in rising temperature.

(39) In FIG. 4 is shown an embodiment like the one in FIG. 3 but with a turbocharged (with a turbine-compressor unit 3, 4) internal combustion engine 3. In this embodiment, like in the FIG. 3 embodiment, the pressure in the circuit including the main receptacle unit 8 can be relatively lower. 55 indicates a mixer for mixing compressed air from the compressor unit of the turbo charger with fuel gas prior to injection into the engine 3.

(40) 7 indicates an optional auxiliary electric generator being powered by the turbine of the turbine-compressor unit 3, 4.

(41) According to the embodiment in FIG. 5, which is a further development of the FIG. 4 embodiment, there is provided means for delivering fuel gases produced in the main receptacle unit 8 for external use through a conduit 33. This embodiment covers plants wherein produced gases in respect of the treatment in the main receptacle unit 8 being in excess of what is required for the consumer unit.

(42) FIG. 6 shows a simplified version of the embodiment shown in FIG. 2. The gasifier 10, the filter 11, the water spray device 58 and the dryer vessel 45 have been dispensed with. Solid pulverulent coal from the auxiliary processing receptacle unit 9 is directly entered into the combustor 2.

(43) The FIG. 6 embodiment also features a connection from the fuel conduit 20 close to the auxiliary processing receptacle unit 9 for delivering part of the fuel gas produced in the main receptacle unit 8 and the auxiliary processing receptacle unit 9 for external use through a conduit 33.

(44) 37 indicates a conduit for delivering fresh superheated steam directly to the auxiliary processing receptacle unit 9.

(45) In the FIG. 7 embodiment there is provided a connection from the fuel conduit 20 downstream of the gasifier 10 for delivering part of the fuel gas produced in the main receptacle unit 8, in the auxiliary processing receptacle unit 9 and in the gasifier 10 for external use through a conduit 33.

(46) A reheater 56 for steam/fuel gas is included as a part of the (superheated) steam generator 6 and is arranged to extract heat from the (superheated) steam generator 6 and to raise the temperature in the mix of superheated steam and produced fuel gas. For that purpose, a first reheater conduit 60 is branched off from said connection 19 in the fuel gas conduit 20 downstream of the main receptacle unit 8 so as lead the gas mix to be reheated to the steam generator 6 and to reintroduce the reheated gas mix into the fuel gas conduit 20 at a position where the conduit 38 is branched off from the conduit 20 for entry into the auxiliary processing receptacle unit 9. As an alternative, or also, a second reheater conduit 61 is branched off from the fuel gas conduit 20 at or adjacent to the inlet from the auxiliary processing receptacle unit 9 into the fuel gas conduit 20 so as lead the gas mix to be reheated to the steam generator 6 and to reintroduce the reheated gas mix into the fuel gas conduit 20 at a position further downstream in the fuel gas conduit 20 but upstream of the gasifier 10. As another alternative a separate reheater unit (not shown) being arranged in the fuel gas conduit 20 for reheating the gas mix upstream of the auxiliary processing receptacle unit 9 and/or the gasifier 10 can have a connection for extracting heat from the steam generator 6 or from another process heat source, e.g. a fuel gas flow for external use.

(47) The measure of this way reheating the gas mix in the fuel gas conduit 20 advantageously eliminates or at least reduces the requirements for supply of oxygen to the auxiliary processing receptacle unit 9 and/or to the gasifier 10 respectively since it gives the opportunity to reach very high temperatures in the gas mix through such reheating arrangement. For that reason, no air supply to the gasifier 10 is indicated in FIG. 7.

(48) Reheating is thus, in general, highly preferred, since it results in several advantages: 1. Less NO.sub.X gas contents in the exhaust gases. 2. Cleaner fuel gases with lower N gas contents, specially preferred for fuel gas/syncgas export. 3. Lower requirements for compressed air in the process, which in turn reduces compressor work requirements and, as a consequence, better electricity production efficiency and overall plant economy. As is indicated above, reheating is particularly valuable together with an auxiliary combustor positioned downstream of the consumer unit. See the above discussion.

(49) The embodiment in FIG. 8 is further developed in respect of the FIG. 7 embodiment in that the gasifier 10 is supplied with hot water from a particular water exit from the steam generator. The water is mixed with solids from the auxiliary processing receptacle unit 9 before entering the gasifier 10 which is also supplied with compressed air via conduit 23 and superheated steam through a conduit 40 from the steam generator 6. Also the auxiliary processing receptacle unit 9 is supplied with compressed air via conduit 28 and superheated steam through a conduit 40 from the steam generator 6.

(50) A compressed air supply to the main receptacle unit 8 is also provided in order to enhance the carbonisation and fuel gas forming process in the main receptacle unit 8. See FIG. 3 and the above.

(51) In the embodiment in FIG. 9, the consumer unit is simply a combustor 2 being directly associated with the superheated steam generator. An overpressure is provided in the circuit including the means 1 for the production of fuel gas from solid fuel. 31 indicates a conduit for supply of air to the auxiliary processing receptacle unit 9 over the valve 42. 48 indicates a pressure or flow regulating means.

(52) FIG. 10 shows a simplified version of the FIG. 9 embodiment, wherein i.a the auxiliary processing receptacle unit 9 has been dispensed with. It is arranged for leading excess fuel gas over the conduit 33 for external use.

(53) A further condenser 34 is arranged for heat exchange with fuel gases for external use. Extracted heat and water is transferred for steam generation in the plant. Numeral 35 indicates an air cooler co-operating with the condenser 34.

(54) The invention can be modified within the scope of the following claims. I.a. it is possible to supply gas from an independent oxygen source to the gasifier 10 in order to avoid problems with nitrogen contents. The turbine and compressor units can each be comprised of one or more single steps.

(55) Superheated steam from the steam generator 6 can be delivered in optional order to the main receptacle unit, the auxiliary processing receptacle unit 9 and to the gasifier 10. It is thus possible to introduce superheated steam from the steam generator 6 directly to either one of these units and pass gas mix discharged therefrom to any one of the other units. It is also possible to introduce superheated steam from the steam generator 6 directly to each one of these units.

(56) It is important to realize that, in case fuel gas is produced for external use, see FIGS. 5-8 and 10 and the associated text paragraphs, these fuel gases are very hot. It is highly preferred that these fuel gases are subjected to heat recovery and that the recovered heat is brought back into the processis used in the inventive plant.

(57) For that reason, the conduits 33, 33 and 33 (see FIGS. 5-8 and 10) are lead firstly through heat exchange devices in order to extract heat and secondly through a condenser in order to extract heat and water from these fuel gases. This can be carried out at different pressures as desired. So extracted heat is thereupon advantageously reintroduced into the process by leading heat transfer medium, such as steam, to a heating device for heating one or more of: 1. Compressed air from a compressor unit. 2. Fuel-steam gas mix in the conduit 20 leading to the consumer unit. 3. Water to be introduced into the steam generator for the production of superheated steam. 4. Fuel drying conduit. 5. District heating conduit.

(58) The different devices, measures and method steps can be used either separately or in combination.