Biomass energy power generation

Abstract

The present disclosure relates to a flue gas treatment system for a biomass energy power generation system, the flue gas treatment system comprising: a solvent cycle for absorbing carbon dioxide from the flue gas; a heat exchanger located along a flow path of the solvent for heating the solvent; and a heat transfer fluid wherein the heat transfer fluid is arranged to circulate between the heat exchanger and the biomass energy power generation system such that the heat transfer fluid absorbs heat from a heating fluid of the biomass energy power generation system and transfers the heat to the solvent cycle via the heat exchanger. The invention further relates to the raw material dryer for the biomass energy power generation system and the biomass energy power generation system.

Description

Technical Field

[0001] The present disclosure relates to a biomass power generation system, more particularly to a pyrolysis-based cogeneration system. The present disclosure also relates to a feedstock dryer for a biomass power generation system and a flue gas treatment system for removing carbon dioxide. Background Art

[0002] Biomass power generation systems use plant or animal materials, such as wood, as raw materials for producing energy. A specific type of biomass power generation system is a pyrolysis power generation system, which produces energy by pyrolyzing the raw materials. The energy generated in a biomass power generation system can be used to provide heat output, power (i.e., electricity) output, or a combined heat and power output.

[0003] Existing biomass generators produce a large amount of waste heat, which is usually released from the generator set in the form of hot flue gases or hot air. This waste heat reduces the overall efficiency of the system, which in turn increases the carbon dioxide emissions per unit of energy produced by the system.

[0004] Furthermore, while the pyrolysis process leaves some of the raw carbon in solid form, a significant amount of the carbon is released as carbon dioxide in the exhaust flue gas. Existing processes for removing carbon dioxide require significant amounts of energy, potentially offsetting the benefits of removing the carbon dioxide.

[0005] The present invention seeks to increase the efficiency of biomass power generators and the efficiency of removing carbon dioxide from the exhaust flue gases. Summary of the invention

[0006] Various aspects and embodiments of the invention are set out in the appended claims.These and other aspects and embodiments of the invention are also described herein.

[0007] According to at least one aspect described herein, there is provided a flue gas treatment system for a pyrolysis-based biomass power generation system, the flue gas treatment system comprising: a solvent cycle for absorbing carbon dioxide from the flue gas; a heat exchanger located along the flow path of the solvent for heating the solvent; and a heat transfer fluid, wherein the heat transfer fluid is arranged to circulate between the heat exchanger and the biomass power generation system so that the heat transfer fluid absorbs heat from the heating fluid of the biomass power generation system and transfers the heat to the solvent cycle via the heat exchanger. Thus, the flue gas treatment system utilizes heat from the power generation system that would otherwise be wasted, thereby improving the efficient use of the energy generated and increasing the amount of carbon dioxide removed per unit of energy output by the power generation system.

[0008] Preferably, the heated fluid is a hot air stream for driving the turbine of the biomass power generation system, and more preferably, wherein the heat transfer fluid is arranged to absorb heat from the air stream downstream of the turbine. The hot air can be discharged from the turbine (after driving the turbine) before transferring the heat to the heat transfer fluid. This arrangement means that heat is not extracted from the hot air stream until after the hot air stream drives the turbine, thereby preferentially using the hot air to generate electricity before extracting heat to power the flue gas treatment system.

[0009] Preferably, the heating fluid of the biomass power generation system is a flue gas stream from a biomass reactor of the biomass power generation system, more preferably, wherein the heat transfer fluid is arranged to absorb heat from the flue gas stream downstream of the flue gas heat exchanger to provide heat output. This arrangement means that heat is not extracted from the hot flue gas stream before the heat is extracted to provide heat output of the generator, thereby preferentially using the hot flue gas to provide heat output before extracting heat to power the flue gas treatment system.

[0010] Preferably, the heat transfer fluid is arranged to absorb heat from the heating fluid of the biomass power generation system via a further heat exchanger located along the flow path of the heating fluid, and wherein the heat transfer fluid is arranged to circulate between the heat exchanger of the flue gas treatment system and the further heat exchanger. The heat exchanger provides efficient heat transfer between fluids.

[0011] Preferably, the heat exchanger located along the flow path of the solvent is a reboiler for heating the solvent.

[0012] Preferably, the heat transfer fluid is steam, and: the reboiler is arranged to receive steam from the additional heat exchanger located along the flow path of the heating fluid of the biomass power generation system and transfer heat from the steam to the solvent, thereby forming a condensate from the steam; and the additional heat exchanger located along the flow path of the heating fluid of the biomass power generation system is arranged to receive the condensate from the reboiler and transfer heat from the heating fluid of the biomass power generation system to the condensate, thereby forming the steam. Due to the high heat capacity of water and the property of saturated steam to maintain a constant temperature during heat transfer that consumes the latent heat of vaporization, the steam-condensate cycle between the steam generator and the reboiler provides efficient heat transfer. Such a constant temperature prevents damage to the solvent.

[0013] Preferably, the solvent is an amine. However, it will be appreciated that other solvents may be used. Examples of other potential solvents include carbonates (such as potassium carbonate) and ammonia. Amine solvents are effective in absorbing carbon dioxide and are readily available.

[0014] According to another aspect described herein, there is provided a feedstock dryer for a biomass power generation system, the feedstock dryer comprising: a device for providing an air flow to the feedstock of the biomass power generation system, at least one heat exchanger located along the air flow path, and at least one coolant, the at least one coolant being arranged to flow between the at least one heat exchanger and at least one component of a gas treatment system for the biomass power generation system, wherein the at least one coolant is arranged to absorb heat from the at least one component, and wherein the at least one heat exchanger is arranged to transfer heat from the coolant to the air flow. Thus, the feedstock dryer utilizes heat from the power generation system or the flue gas treatment system that might otherwise be wasted, thereby improving the efficient use of the energy generated and increasing the amount of carbon dioxide removed per unit of energy output by the power generation system.

[0015] Preferably, the gas treatment system is a flue gas treatment system as previously described.

[0016] Preferably, the at least one component comprises a flue gas scrubber, and wherein the coolant is arranged to cool the scrubber by absorbing heat from the scrubber.

[0017] Preferably, the flue gas scrubber is located in the flue gas flow path downstream of the power and / or heat generating components of the biomass power generation system.

[0018] Preferably, the at least one component comprises a trim cooler in an absorption cycle for treating flue gas from the biomass power generation system, and wherein the coolant is arranged to cool the trim cooler by absorbing heat from the trim cooler.

[0019] Preferably, the at least one component comprises a reflux condenser in an absorption cycle for treating flue gas from the biomass power generation system, and wherein the coolant is arranged to cool the reflux condenser by absorbing heat from the reflux condenser.

[0020] Preferably, the at least one component comprises a plurality of components (such as two or more of a flue gas scrubber, a trim cooler and a reflux condenser as described above), and: the at least one heat exchanger comprises a separate heat exchanger for each of the components, and / or the at least one coolant comprises a separate coolant for each of the components. Preferably, the heat exchangers are arranged according to their operating temperature or the temperature of the components they cool, preferably from hottest to coldest along the air flow. In this way, efficient transfer of heat to the air flow is promoted.

[0021] Preferably, the means for providing an air flow to the feedstock comprises a fan. Preferably, the fan is powered by electricity generated by a generator; the use of a fan minimises this additional power consumption.

[0022] Preferably, the at least one coolant is water. Water provides efficient heat transfer due to its high heat capacity.

[0023] According to another aspect described herein, there is provided a biomass power generation system comprising: a biomass reactor, a turbine heat exchanger, and a flue gas heat exchanger, wherein the turbine heat exchanger is configured to transfer heat from the flue gas to a working fluid for driving a turbine to generate electricity; and wherein the flue gas heat exchanger is located along the flow path of the flue gas, downstream of the turbine heat exchanger, and is configured to transfer heat from the flue gas to a heat output end of the system. Thus, the system utilizes heat from the flue gas that would otherwise be wasted, by extracting the heat and transferring it to the heat output end of the system, thereby improving the efficient use of the generated energy and reducing carbon dioxide emissions per unit of energy output by the power generation system.

[0024] Preferably, the system includes a flue gas return duct for recycling the flue gas back into the biomass reactor. Recycling a portion of the flue gas back into the pyrolysis reactor provides a supply of inert gas within the pyrolysis reactor. These inert gases absorb some of the pyrolysis heat in the reactor and also dilute the oxygen supply in the pyrolysis reactor. Both of these factors reduce the heat of the pyrolysis reaction, thereby inhibiting the generation of undesirable nitrogen oxides, which are generated in the high temperature mixture of nitrogen and oxygen.

[0025] Preferably, the flue gas return duct is located downstream of the flue gas heat exchanger. In this way, heat is extracted from the maximum amount of flue gas before the flue gas is diverted.

[0026] Preferably, the system comprises a pump for driving the flow of the flue gas, preferably wherein the pump is located in the flue gas flow path downstream of the flue gas heat exchanger. The pump prevents the flue gas from flowing back into the reactor, the pressure in the reactor being below atmospheric pressure.

[0027] Preferably, the system comprises a working fluid heat exchanger located along the flow path of the working fluid, the working fluid heat exchanger being configured to transfer heat from the working fluid to a heat output of the system. In this way, an additional heat output from the system is provided, distinct from the output of heat extracted from the flue gases.

[0028] Preferably, the working fluid heat exchanger is located along the flow path of the working fluid downstream of the turbine. This arrangement means that heat is not extracted from the working fluid before it is used to drive the turbine, thereby giving priority to the driving of the turbine before extracting heat to provide the heat output of the system.

[0029] Preferably, the system comprises a carbon dioxide processing system, wherein the carbon dioxide processing system is arranged to receive a gas stream comprising carbon dioxide removed from the flue gas and comprises means for dehydrating the gas stream, preferably wherein the means for dehydrating the gas stream comprises at least one dehydration tower for removing water vapour from the gas stream, preferably removing water vapour from the gas stream by adsorption.

[0030] Preferably, the carbon dioxide processing system comprises a compressor downstream of the means for dehydrating water, the compressor being configured to compress the carbon dioxide, and optionally a refrigerator downstream of the compressor for cooling the carbon dioxide to a liquid state.

[0031] The carbon dioxide processing system enables the use of carbon dioxide generated in the system to be used, such as in an industrial process, thereby minimizing the release of carbon dioxide to the atmosphere and also reducing waste products of the system.

[0032] According to another aspect disclosed herein, a biomass power generation system is provided, comprising: a flue gas treatment system as described above, and / or a raw material dryer as described above, preferably, wherein the biomass power generation system is as described above. In combination, the waste heat recovery aspects of each system provide particularly efficient waste heat recovery.

[0033] Preferably, the biomass power generation system is a pyrolysis power generation system. Pyrolysis of certain raw materials can produce biochar, which acts as a carbon sink and has further uses, thereby reducing the actual waste products of the system.

[0034] As used herein, the term "flue gas" preferably refers to the collection of gases produced as a result of one or more reactions occurring in a biomass reactor, wherein the composition of the flue gas depends on the substances used in the reactor.

[0035] As used herein, the term "heat transfer" or related terms preferably refers to direct or indirect heat transfer. For example, when referring to heat transfer from flue gas to working fluid, it includes direct transfer of heat from one fluid to another, or indirect transfer of heat through intermediate components or fluids.

[0036] As used herein, the term "pyrolysis-based (biomass) power generation system" or related terms preferably refers to a power generation system that employs pyrolysis of a feedstock to generate energy, for example using a pyrolysis reactor.

[0037] Any feature in one aspect of the present invention may be applied to other aspects of the present invention in any appropriate combination. In particular, method aspects may be applied to device aspects, and vice versa. It should also be understood that the specific combination of each feature described and defined in any aspect of the present invention may be implemented and / or provided and / or used independently.

[0038] Furthermore, features implemented in hardware may generally be implemented in software, and vice versa. Any references herein to software and hardware features should be interpreted accordingly. Any device features described herein may also be provided as method features, and vice versa. As used herein, device-plus-function features may alternatively be expressed in terms of their corresponding structures, such as a suitably programmed processor and associated memory. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] One or more aspects will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0040] Figure 1 is a block diagram of an exemplary biomass power generation system and flue gas treatment system of the present disclosure;

[0041] Figure 2 is a block diagram of another exemplary biomass power generation system and an absorption cycle providing a flue gas treatment system and an exemplary feedstock dryer;

[0042] Figure 3 is a block diagram of an absorption cycle and feedstock dryer for a biomass power generation system; and

[0043] Figure 4 is a block diagram of an exemplary carbon processing system for a biomass power generation system. DETAILED DESCRIPTION

[0044] Exemplary embodiments of a biomass power generation system, a flue gas treatment system, and a feedstock dryer are described below.

[0045] Specifically, refer to Figure 1 , which summarizes an exemplary biomass power generation system, flue gas treatment system, and feedstock dryer. Figures 2 to 4 , more detailed examples of these systems are described in more detail, where, for example, a biomass power generation system is described as a pyrolysis power generation system that provides a combined heat and power output. Specifically, the following reference Figure 2 , describes a more detailed exemplary biomass power generation system, particularly a pyrolysis power generation system. Figure 3, describes an exemplary flue gas treatment system (for using waste heat to treat flue gas generated by a pyrolysis process), and an exemplary feedstock dryer for the biomass power generation system, which recovers and utilizes waste heat to dry the feedstock. Figure 4 , a carbon treatment system for treating carbon dioxide removed from flue gases is described.

[0046] System Overview

[0047] Figure 1 is a block diagram of an exemplary biomass power generation system and flue gas treatment system of the present disclosure.

[0048] In general, the biomass power generation system 10 (also referred to as a biomass generator, or simply a generator) includes: a biomass reactor 12, a turbine heat exchanger 16, and a flue gas heat exchanger 14. Broadly speaking, the turbine heat exchanger 16 is configured to transfer heat from the flue gas from the biomass reactor 12 (i.e., flue gas from a biomass reaction or a further reaction using the product of the biomass reaction) to a working fluid for driving a turbine 18 to generate electricity. The flue gas heat exchanger 14 is located along the flow path of the flue gas, downstream of the turbine heat exchanger 16, and is configured to transfer heat from the flue gas to the heat output end of the system. In this way, after the flue gas transfers the heat to the working fluid, the remaining heat in the flue gas is recovered by the flue gas heat exchanger. Otherwise, the heat may be wasted by the flue gas being carried out of the system through, for example, a chimney. Therefore, this waste heat recovery improves the efficiency of the power generation system.

[0049] Separate from the biomass power generation system 10, a flue gas treatment system 20 is provided for treating flue gas from the biomass power generation system 10. The flue gas treatment system 20 is shown as receiving flue gas from the above-mentioned biomass power generation system 10, however it should be understood that the flue gas treatment system 20 can be used to treat flue gas from any other biomass power generation system. In general, the flue gas treatment system 20 includes a solvent cycle for absorbing carbon dioxide from the flue gas, a heat exchanger 22 (for heating the solvent) located along the flow path of the solvent, and a heat transfer fluid. Broadly speaking, the heat transfer fluid is arranged to circulate between the heat exchanger 22 and the biomass power generation system 10, so that the heat transfer fluid absorbs heat from the heating fluid of the biomass power generation system 10 (for example, a working fluid for driving a turbine or a flue gas flow from a biomass reactor), and transfers the heat to the solvent cycle via the heat exchanger 22. In this way, heat that might otherwise be wasted in a biomass power generation system is recovered and used to heat the solvent in the flue gas treatment system 20 .

[0050] In addition, a feedstock dryer for a biomass power generation system (such as the system 10 described above) is also provided. In general, the feedstock dryer includes a device for providing an air flow to the feedstock 28 of the biomass power generation system, at least one heat exchanger 26 located along the air flow path, and at least one coolant, the at least one coolant being arranged to flow between the at least one heat exchanger 26 and at least one component of the biomass power generation system (such as a flue gas scrubber) or at least one component of the gas treatment system for the biomass power generation system (such as a trim cooler or a reflux condenser), wherein the at least one coolant is arranged to absorb heat from the at least one component, and wherein the at least one heat exchanger 26 is arranged to transfer heat from the coolant to the air flow. In this way, heat that would otherwise be wasted in the biomass power generation system and / or the flue gas treatment system is recovered and used to dry the feedstock of the biomass reactor.

[0051] Combined Heat and Power

[0052] Figure 2 is a block diagram of another exemplary biomass power generation system 100 of the present disclosure. Solid arrow lines are drawn between the boxes of the figure, which indicate input or output flows within the system to or from each box. Arrows point to certain boxes or dashed arrow lines are drawn away from certain boxes, indicating input or output from outside the system to the outside of the system, for example, input or output from the external environment to the output of the external environment. The boxes indicated as separated in the figures are intended to indicate separate functions, and do not necessarily mean that those functions are performed by structurally separated components; for example, the functions indicated by certain boxes can actually be provided by a single component.

[0053] The biomass generator 100 includes a pyrolysis reactor 102 (similar to Figure 1 The pyrolysis reactor 102 is configured to contain a pyrolysis reaction. The pyrolysis reactor 102 takes a biomass feedstock 104, which in this example is wood (preferably waste wood, such as waste lumber), and burns the feedstock 104 in the presence of a limited amount of oxygen to produce biochar and pyrolysis gas (also known as syngas) in a first stage of the reactor. The syngas is then burned in a second stage of the reactor (e.g., in a FLOX combustion (flameless oxidation) reaction) to produce flue gas.

[0054] The biochar produced in the pyrolysis reaction contains a considerable proportion of carbon derived from the biomass in a stable form. Therefore, the biochar acts as a carbon sink, sequestering a portion of the carbon produced in the pyrolysis reaction, thereby limiting the amount of carbon dioxide released into the atmosphere. In addition, biochar has other uses, such as spreading on farmland (CO2 sequestration), soil improvement (when combined with composting), and reducing the use of fertilizers. Therefore, the biochar produced in the generator will not be wasted.

[0055] The second stage of the reactor has a built-in high temperature turbine heat exchanger 106 (similar to Figure 1 The turbine heat exchanger 106 is arranged to transfer heat from the flue gas to a working fluid for driving a turbine. In other examples, the turbine heat exchanger may be independent of the pyrolysis reactor, and the turbine heat exchanger may be located downstream of the pyrolysis reactor. In this example, the working fluid is an air stream obtained from the external environment. The turbine heat exchanger 106 transfers heat from the flue gas to the air stream, and the heated air is used to drive a hot air turbine 108 (similar to Figure 1 The hot air turbine 108 may also include a device for compressing the air heated in the first stage of the turbine, and then the compressed heated air drives the rotation of the turbine in the second stage.

[0056] The hot air that has passed through the hot air turbine 108 is directed through a steam generator 110, which will be referred to below. Figure 3 Explanation. After passing through the steam generator 110, the hot air is used for an external heat demand end. When the air flow from the turbine is clean, the hot air itself can be supplied to the outside of the system to provide heat output (for example, supplying the hot air to a building to heat the building, or supplying the hot air for use in an industrial process). Alternatively, the hot air is directed through a working fluid ("WF") heat exchanger 112 so that heat from the hot air is transferred to a coolant (e.g., water), which is then transferred to the outside of the system (such as to a radiator) to provide heat output. Alternatively, the system can provide both heat outputs at the same time; in this case, the heat output from the working fluid heat exchanger provides one heat output and the hot air itself provides another heat output.

[0057] Flue gas from the pyrolysis process is directed to a flue gas ("FG") heat exchanger 114 (similar to Figure 1 The flue gas heat exchanger 114 is arranged to transfer heat from the flue gas to a coolant (such as water) which is transferred to the outside of the system to provide a further heat output from the system.

[0058] Thus, the system provides combined heat and electricity through three energy outputs: an electrical output from the hot air turbine 108, a first heat output from the working fluid heat exchanger 112, and a second heat output from the flue gas heat exchanger 114. Optionally, there is also a third heat output, which is the hot air itself after having passed through the working fluid heat exchanger 112. The heat outputs from the system are at different temperatures and can therefore be used to meet different heat requirements. In particular, the hot working fluid heat exchanger 112 provides a heat output of approximately 70 to 80 degrees Celsius, while the heat output provided by the flue gas heat exchanger 114 is much hotter.

[0059] Advantageously, these heat outputs utilize heat that would otherwise be wasted, thereby increasing the efficiency of the system, which in turn reduces the amount of carbon dioxide produced per unit of energy generated by the system. In particular, the system utilizes heat in the flue gas, extracting this heat via the flue gas heat exchanger 114 and providing a heat output; otherwise, this heat from the flue gas would be wasted by the flue gas being carried out of the system via the flue gas chimney. At the same time, heat in the working fluid (which drives the turbine 108) is also extracted via the working fluid heat exchanger 112 to provide another heat output; otherwise, this heat may also be wasted.

[0060] The pump 116 located downstream of the flue gas heat exchanger 114 in this example draws the flue gas from the pyrolysis reactor through the turbine heat exchanger 106 and the flue gas heat exchanger 114, and then drives the flue gas along its further flow path, as described below. The pump 116 is provided because the pyrolysis reaction occurs in the reactor 102 at a pressure below atmospheric pressure; therefore, the pump 116 prevents the flue gas from flowing back into the reactor 102.

[0061] In this example, the flue gas is split downstream of the pump 116 such that a portion of the flue gas is diverted and recycled back to the pyrolysis reactor, while the remainder of the flue gas is directed to a flue gas scrubber 118 .

[0062] Recirculation of a portion of the flue gas back to the pyrolysis reactor provides a supply of inert gases within the pyrolysis reactor. These inert gases absorb some of the pyrolysis heat in the reactor and also dilute the oxygen supply in the pyrolysis reactor. Both of these factors reduce the heat of the pyrolysis reaction, thereby suppressing the production of undesirable nitrogen oxides, which are produced in the high temperature mixture of nitrogen and oxygen.

[0063] The remaining portion of the flue gas that is not recycled to the pyrolysis reactor 102 is directed to a flue gas scrubber 118. The flue gas scrubber 118 treats the flue gas to remove pollutants such as sulfur dioxide (which may be formed particularly during low temperature pyrolysis that occurs under start-up conditions of the generator), or other pollutants depending on the feedstock and the pyrolysis system.

[0064] After passing through the flue gas scrubber, the scrubbed flue gas is directed to and processed by a carbon dioxide absorption cycle 200 to remove carbon dioxide from the flue gas, as described below with reference to Figure 3 After the carbon dioxide is removed from the flue gas in the absorption cycle, the remaining flue gas is released from the system via the chimney of the generator (e.g., a flue gas chimney). The carbon dioxide removed in the absorption cycle is directed to a carbon dioxide processing system 300, which processes the carbon dioxide for storage and / or use, as described below with reference to Figure 4 described.

[0065] As reference below Figure 3 Described in more detail, the absorption cycle 200 is powered by waste heat recovered by the steam generator 110 from the working fluid (i.e., the hot air stream) of the hot air turbine 108. Heat is transferred from the steam generator 110 to the absorption cycle 200 by the circulation of steam and condensate between the steam generator 110 and the reboiler of the absorption cycle. In addition, when the flue gas scrubber 118 and the various components of the absorption cycle 200 become hot due to the treatment of flue gas or the heating of solvent, these components are cooled by one or more coolants (e.g., water) circulating between these components and the coolant heat exchanger 120. The coolant heat exchanger 120 is arranged to transfer heat from the circulating coolant to the air stream (taken from the external environment). The air heated by the coolant heat exchanger 120 is driven by a fan 122 to the feedstock 104. Thus, the coolant heat exchanger 120 and the fan 122 together form a feedstock dryer 124 that uses waste heat from the flue gas scrubber and absorption cycle to dry the feedstock 104 before it is used in the pyrolysis reactor.

[0066] Absorption cycle

[0067] Figure 3 is a block diagram of a carbon dioxide absorption cycle 200 used as a flue gas treatment system for the power generator 100. The absorption cycle is arranged to receive a gas stream from the flue gas scrubber 118, the gas stream comprising the portion of the flue gas that is not recycled to the pyrolysis reactor 102. The gas stream is composed of Figure 3 1. The "flue gas" arrow in FIG. 1 is indicated by the "flue gas" arrow leaving the flue gas scrubber 118. As described above, the flue gas scrubber 118 processes the gas stream (before it is received in the absorption cycle) to remove pollutants, such as sulfur dioxide. The absorption cycle 200 then further processes the gas stream to remove carbon dioxide from the gas stream.

[0068] The absorption cycle 200 includes a solvent cycle for absorbing carbon dioxide in a gas stream. In this example, the solvent is an amine solvent, also referred to as an amine solution. The term "rich amine solution" (or solvent) is used to refer to the amine solution when carbon dioxide has been absorbed, while the term "lean amine solution" (or solvent) is used to refer to the amine solution when the absorbed carbon dioxide has been discharged from the amine solution. It should be understood that other solvents can be used instead of amines, such as carbonates (e.g., potassium carbonate) and ammonia.

[0069] The gas stream including the flue gas enters the amine cycle 200 by entering at least one absorber 202. The absorber 202 in this example is an absorption tower. The lean amine solution is pumped into the absorption tower 202 from a mixing tank 212, which will be described below. The lean amine solution and the gas stream (including the flue gas) enter the absorption tower 202 from opposite ends of the tower 202; in particular, the lean amine solution enters the absorption tower 202 at the top of the tower, while the gas stream enters the absorption tower 202 from the bottom of the tower (it should be noted in this regard that Figure 3 2 is a block diagram showing the interaction between the various blocks, rather than a true representation of the relative structural position and positioning of the various blocks and fluid flows). Therefore, the lean amine solution and the gas flow flow in relative directions along the absorption tower (the solution flows from top to bottom and the gas flow flows from bottom to top). The absorption tower 202 is arranged to allow the gas flow to flow through the amine solution so that carbon dioxide in the gas flow is absorbed into the amine solution. In order to optimize the absorption of carbon dioxide into the amine solution, the tower 202 operates in a temperature range of 40 to 50 degrees Celsius and at a pressure of about 1.15 bar (absolute pressure). The remaining gas in the gas flow that is not absorbed into the amine solution is discharged from the generator via the chimney of the generator 100 (e.g., a flue gas chimney).

[0070] After absorbing the carbon dioxide, the amine solution (now a rich amine solution having absorbed the carbon dioxide) is collected in a sump of the absorber 202 and then pumped out of the absorber 202 and passed through an amine heat exchanger 204 to a stripper 206, which in this example is a stripper. The amine heat exchanger 204 is arranged to transfer heat from the heated lean amine solution leaving the reboiler 208 (described below) to the rich amine solution as the rich amine solution is pumped from the absorber 202 to the stripper 206. By the amine heat exchanger 204, the rich amine solution is heated to about 100 degrees Celsius before being received by the stripper 206. The heated rich amine solution is received by the stripper 206 via a perforated plate of the stripper 206, wherein the carbon dioxide and water vapor discharged from the amine solution are flashed by the heat from the amine heat exchanger 204.

[0071] In this stripping column 206, the absorption reaction occurring in the absorption column is reversed so that the carbon dioxide absorbed in the amine solution is discharged from the amine solution in the gas phase (i.e., stripped from the amine solution), as described below. The rich amine solution enters the stripping column 206 and flows downward through the column 206, while the heated carbon dioxide and water vapor entering the stripping column 206 from the reboiler as described below flows upward through the column 206 and through the downwardly flowing rich amine solution. The contact between the countercurrent rich amine solution and the heated carbon dioxide and water vapor causes heat to be transferred from the heated carbon dioxide and water vapor to the rich amine solution, thereby heating the rich amine solution, which releases the carbon dioxide absorbed in the solution.

[0072] The carbon dioxide released from the amine solution travels upward through the stripper 206 along with the carbon dioxide and water vapor from the reboiler and passes through a (preferably internal) demister (not shown) which removes water droplets entrained in the gas stream before it exits the top of the stripper and is directed to the reflux condenser 122. At the same time, the amine solution (which is now a lean amine solution that has been stripped of its absorbed carbon dioxide) flows downward through the stripper 206 and is collected in a sump of the stripper 206 from where it is pumped out of the stripper and to the reboiler 208.

[0073] The reflux condenser 122 is arranged to receive the output gas stream from the top of the stripping tower 206. The output gas stream from the stripping tower 206 mainly includes carbon dioxide stripped from the amine solution; however, it may also contain some steam from the amine solution, which is undesirable. Therefore, the reflux condenser 122 (a partial reflux condenser in this example) is configured to cool the gas stream it receives from the stripping tower. The cooling is achieved by transferring heat from the gas stream to the water coolant through the reflux condenser 122, as described below with reference to the raw material dryer. This cooling causes most of the steam (e.g., water vapor) in the gas stream to condense, thereby partially dehydrating the gas stream and increasing the concentration of carbon dioxide in the gas stream. The partially dehydrated gas stream obtained is transferred to the carbon dioxide treatment system 300, which includes a dehydrator for removing steam from the gas stream that is not removed by the reflux condenser 122. The condensate formed by cooling the steam in the gas stream by the reflux condenser 122 is returned to the stripping tower 206.

[0074] The lean amine solution collected in the sump of the stripping column 206 is extracted from the column 206 to the reboiler 208 by a transfer pump. In the reboiler 208, the lean amine solution is heated to about 115 degrees Celsius using waste heat from the biomass power generation system 100, as described below. Heating the lean amine solution in the reboiler 208 causes more carbon dioxide to be released from the amine solution. The carbon dioxide released from the solution in the reboiler is returned to the stripping column 206, as described below. Figure 3206. The returned carbon dioxide flows upward through the stripper, causing carbon dioxide to be released from the rich amine solution in the stripper 206 (as described above), and then the returned carbon dioxide is extracted into the reflux condenser 122 together with the released carbon dioxide as described above.

[0075] Reboiler 208 uses waste heat from biomass power generation system 100 to heat the lean amine solution (reboiler is similar to Figure 1 Heat exchanger 22 of ). In particular, the heat transfer fluid is arranged to circulate between the reboiler and the biomass power generation system so that the heat transfer fluid absorbs heat from the heating fluid of the biomass power generation system (in this case, the heated turbine working fluid) and transfers the heat to the circulating amine solution via the reboiler. In this example, this is achieved by arranging the steam generator 110 along the flow path of the working fluid (i.e., hot air) driving the turbine 108. In this example, the heat transfer fluid is water (liquid phase or gas phase, i.e., steam). The reboiler 208 is arranged to receive steam from the steam generator 110 and acts as a heat exchanger along the path of the amine solution circulation to transfer heat from the steam to the amine solution, thereby heating the amine solution to about 115 degrees Celsius. The heat transfer causes the steam to condense to form a condensate (i.e., water), which is directed to the steam generator 110. The steam generator is arranged to receive condensate from the reboiler 208 and act as a heat exchanger along the path of the turbine working fluid to transfer heat from the turbine working fluid to the condensate, thereby heating the condensate to form steam, which is circulated to the reboiler as described herein.

[0076] The steam generator 110 is located along the path of the turbine working fluid, in this example, downstream of the hot air turbine but upstream of the working fluid heat exchanger 112; this arrangement is advantageous because the steam generator requires the working fluid to be relatively hot in order to be able to heat the condensate to produce steam, while the working fluid heat exchanger 112 does not require the working fluid to be equally hot in order to provide a heat output suitable for use with the thermal demand.

[0077] Thus, the steam generator 110, reboiler 208, and heat transfer fluid (i.e., the same steam and condensate) together provide a means for using waste heat from the biomass power generation system to power the amine cycle. In this example, the waste heat is taken from the turbine working fluid, however, the heat in other examples can be taken from another part of the generator, such as from the flue gas, using heat extracted from the flue gas by, for example, the flue gas scrubber 118. This heat would otherwise be wasted, and an external heat supply would be required to provide heat for the reboiler 208; therefore, this system configuration improves the efficiency of the system, which in turn increases the amount of carbon dioxide removed per unit of energy produced by the system.

[0078] The lean amine solution heated in the reboiler is then transferred from the reboiler to a trim cooler 210 via an amine heat exchanger 204. In the amine heat exchanger 204, heat from the heated lean amine solution is transferred to a rich amine solution, wherein the rich amine solution is also directed through the amine heat exchanger 204 on the way between the absorber 202 and the stripper 206 as described above. Transferring heat to the rich amine solution results in the lean amine solution being cooled to approximately 60 degrees Celsius. The trim cooler 210 is arranged to receive the cooled lean amine solution from the amine heat exchanger 204 and is configured to further cool the lean amine solution to approximately 40 degrees Celsius. Further cooling of the lean amine solution is achieved by the trim cooler 210 transferring heat from the lean amine solution to a coolant (e.g., water), as described below with reference to the feed dryer.

[0079] The lean amine solution passes from the trim cooler 210 through a filter to remove any particles and heat-stable solids (or heat-stable salts) that may be formed in the solution due to partial degradation of the amine in the reboiler. After filtration, the lean amine solution returns to the mixing tank 212, which supplies the absorber 202. In the mixing tank, the amine solution is mixed with the raw amine, promoter and pH regulator fluids in order to maintain the correct proportions. A small stream of make-up water is continuously added to the mixing tank 212, and a similarly small proportion of liquid in the mixing tank is continuously purged so that the solution is gradually and continuously renewed. Nitrogen is blanketed above the liquid in the mixing tank 212 to displace the oxygen of the degraded amine and provide a small positive pressure in the tank. In order to restart the amine cycle 200, the liquid from the mixing tank 212 is supplied to the absorber 202 to absorb carbon dioxide from the flue gas as described above.

[0080] It should be noted that the energy required by the flue gas treatment system to remove carbon dioxide from the flue gas is primarily heat, and this heat is supplied by recovering waste heat from the working fluid of the turbine. Only negligible amounts of electricity are required for both the flue gas treatment system and other parasitic loads (such as the pump 116 of the generator 100), and therefore there is only minimal energy demand for the production of electricity in the system of the present disclosure. In contrast, the efficiency of electrical-based carbon capture technology is reduced by about 25% due to the need to use electricity to generate steam for the carbon capture system.

[0081] Raw material dryer

[0082] Figure 2 Also shown is a feedstock dryer 124 for the biomass power generation system 100 that uses waste heat from the flue gas scrubber and absorption cycle to dry the feedstock 104 before it is used in the pyrolysis reactor 102 .

[0083] In general, the feedstock dryer 124 includes a device for providing an air flow to the feedstock 104 (in this example, a fan 122) and at least one coolant heat exchanger 120 (similar to Figure 1 The at least one coolant heat exchanger 120 is configured to heat the air flow through the feedstock, wherein the coolant is arranged to flow between the at least one coolant heat exchanger 120 and at least one component of the biomass power generation system 100, so that the coolant absorbs heat from the at least one component of the biomass power generation system, and the at least one coolant heat exchanger 120 is configured to transfer heat from the coolant to the air flow. In this way, waste heat from one or more components of the biomass power generation system can be used to heat the air flow flowing through the feedstock, so as to utilize the waste heat energy when drying the feedstock 104.

[0084] More specifically, in this example, waste heat is taken from the following components: flue gas scrubber 118 of the biomass power generation system, temperature trim cooler 210 of the flue gas treatment system, and reflux condenser 122. A coolant cycle is provided for each of these three components, and each component is configured to transfer heat to the coolant. A corresponding heat exchanger is provided for each component, and each component is configured to transfer heat from the coolant to the air flow, thereby heating the air before it is used to dry the raw material. As described below, each of these three components is considered in turn.

[0085] The flue gas scrubber 118 is arranged to receive flue gas and treat the flue gas to remove pollutants such as sulfur dioxide. Therefore, since the flue gas is hot from the pyrolysis reactor 102, the flue gas scrubber also becomes hot during use and must be cooled. This cooling of the flue gas scrubber 118 is achieved by providing a circulation of a coolant between the flue gas scrubber 118 and the flue gas scrubber heat exchanger 214, which is water in this example. The flue gas scrubber 118 is arranged to transfer heat from the flue gas to a water coolant, which is then recycled back to the flue gas scrubber heat exchanger 214. The flue gas scrubber heat exchanger 214 is then arranged to transfer heat from the coolant to the air flow.

[0086] The trim cooler 210 is arranged to cool the lean (amine) solution before it enters the mixing tank 212. Therefore, between the trim cooler 210 and the trim cooler heat exchanger 216, a circulation of a coolant (water in this example) is provided. The trim cooler 210 is arranged to transfer heat from the lean (amine) solution to the water coolant, thereby cooling the (amine) solution. The coolant is then recirculated back to the trim cooler heat exchanger 216, and the trim cooler heat exchanger 216 is arranged to transfer heat from the coolant to the air flow.

[0087] Reflux condenser 122 is arranged to cool the gas stream it receives from stripping tower, so that the gas stream output from stripping tower 206 is partially dehydrated before the gas stream is transferred to carbon dioxide treatment system 300. In order to dehydrate the gas stream, the reflux condenser is configured to cool the gas stream to condense the steam present in the gas stream. Therefore, between reflux condenser 122 and reflux condenser heat exchanger 218, a circulation of coolant (water in this example) is set. Reflux condenser 122 is arranged to transfer heat from the gas stream to the water coolant, thereby cooling the gas stream. The coolant is then recirculated back to the reflux condenser heat exchanger 218, and the reflux condenser heat exchanger 218 is arranged to transfer heat from the coolant to the air stream.

[0088] The air flow is taken from the external ambient environment and then driven through the flue gas scrubber heat exchanger 214, the trim cooler heat exchanger 216, and the reflux condenser heat exchanger 218, so that it absorbs heat from each heat exchanger along the way. The heated air is then directed to flow through the feedstock 104, thereby drying the feedstock before it is used in the pyrolysis reactor 102. The fan 122 provides a means for driving the air flow, and in this example, the fan 122 is located downstream of the heat exchangers 214, 216, 218 (collectively: 120) so that the fan draws air through the heat exchangers and then pushes the air onto the feedstock.

[0089] Thus, the coolant heat exchanger 120 (including the flue gas scrubber heat exchanger 214, the trim cooler heat exchanger 216, and the reflux condenser heat exchanger 218) together with the means for providing air flow (in this example, the fan 122) form a feedstock dryer 124 that uses heat from the generator 100 (which would otherwise be wasted) to dry the feedstock. Since this heat would otherwise be wasted and a separate power source is required to power the feedstock dryer, the feedstock dryer of the present disclosure improves the efficiency of the biomass power generation system 100, which in turn reduces the amount of carbon dioxide produced per unit of energy generated by the system.

[0090] It should be noted that although Figure 3 The use of three waste heat sources (flue gas scrubber 119, trim cooler 210, and reflux condenser 122) is shown, but in other examples, only one or any other number of waste heat sources may be used, and these sources may be provided by any other component of generator 100 or system used with generator 100; for example, steam generator 110 may alternatively provide heat for the feed dryer.

[0091] also, Figure 3Three heat exchangers 214, 216, 218 are shown arranged in series so that the air flow passes through each heat exchanger. This arrangement is advantageous because it provides maximum heating of the air flow. It is further advantageous to arrange the heat exchangers 214, 216, 218 in a sequence from the coldest to the hottest (in the direction of air flow) so as to improve the efficiency of heat transfer from the heat exchanger to the air. However, in other examples, the heat exchangers can be arranged in parallel so that the air flow is provided in parallel air flows through the heat exchangers.

[0092] Carbon dioxide treatment

[0093] Figure 4 is a flow diagram of a carbon dioxide processing system 300 for a biomass power generation system. The carbon dioxide processing system 300 is arranged to receive carbon dioxide removed from flue gases by the absorption cycle 200 and process it for use or storage. The use of such carbon dioxide, for example in the food and beverage industry, increases the efficiency of the use of biomass because it prevents unnecessary carbon dioxide from being released into the atmosphere, both by minimizing carbon dioxide emissions during power generation and by avoiding the need for separate carbon dioxide production for these other purposes.

[0094] First, the gas stream from the reflux condenser 122 (which includes carbon dioxide and has been partially dehydrated by the reflux condenser 122) is directed from the reflux condenser of the absorption cycle 200 to the carbon dioxide dehydrator 302. The carbon dioxide dehydrator 302 removes the residual water vapor still remaining in the gas stream (i.e., the water not removed by the reflux condenser 122), thereby "drying" the gas stream. The dehydrator 302 includes a tower for removing water vapor from the gas stream by adsorption. The tower operates within a temperature swing adsorption loop in the dehydrator 302 so that when one of the towers (the "dehydration tower") is actively dehydrating the gas stream, the other tower (the "regeneration tower") is regenerated. Preferably, the dehydrator 302 includes two such towers, one of which dehydrates the gas stream and the other tower regenerates. In order to promote the adsorption of water vapor, the gas stream from the reflux condenser 122 is cooled before entering the dehydration tower of the dehydrator 302.

[0095] The adsorption of water vapor from the gas stream is achieved by capturing water on the adsorbent beads (preferably made of 3A zeolite) within the tower. Thus, water is removed from the gas stream, leaving a dehydrated carbon dioxide gas stream. The dehydrated carbon dioxide leaves the dehydration tower at the bottom of the tower via a network of pipes, with a series of valves controlling the outflow of carbon dioxide from the tower. The outflowing carbon dioxide is also filtered to remove any debris generated by the decomposition of the adsorbent material within the tower.

[0096] To regenerate an inactive tower (i.e., a tower that does not actively dehydrate a gas stream), a portion (about 10%) of the dehydrated carbon dioxide leaving the dehydration tower is directed, via a compressor and a heater, back through the regeneration tower. The heated carbon dioxide refluxed through the regeneration tower causes the adsorbed water to be released from the adsorbent beads, thereby regenerating the tower. The regeneration of the tower causes a stream of water vapor to be released along with the heated carbon dioxide. The stream is then cooled and separated in a knock-out drum. The carbon dioxide gas recovered from the knock-out drum is recycled back to the dehydrator to increase the carbon dioxide yield, while the liquid condensate (i.e., condensed water) is discarded.

[0097] The portion of the dehydrated carbon dioxide from the dehydrator 302 that is not recycled through the regeneration tower can simply be vented from the system. However, preferably, the carbon dioxide is utilized in order to reduce unnecessary emissions. For example, the carbon dioxide can be used in an industrial process that is co-located with the generator 100, or it can be stored for later use or transportation.

[0098] Therefore, a carbon dioxide discharge system is provided to process the dehydrated carbon dioxide from the dehydrator 302 so that it can be used immediately or stored for later use or transportation. The carbon dioxide discharge system includes a carbon dioxide compressor 304 and an optional carbon dioxide refrigerator 306. The carbon dioxide compressor 304 is arranged to receive the dehydrated carbon dioxide from the dehydrator 302, and is configured to compress the carbon dioxide to a pipeline pressure for output from the generator 100 to a co-located (i.e., "on-site") industrial process. Preferably, the carbon dioxide is sealed by the industrial process to minimize the emission of carbon dioxide to the atmosphere. The pressure to which the carbon dioxide is compressed depends on the requirements of the industrial process in which it will be used.

[0099] If the carbon dioxide is not used immediately, or if the carbon dioxide is to be used off-site so that it must be transported, it is directed from the compressor 304 to the chiller 306 for cooling and storage for transportation or later use. The chiller is configured to cool the compressed carbon dioxide into a liquid phase so that it can be stored cryogenically on-site (i.e., local to the generator 100) for later use or stored in tank trucks for transportation between scheduled discharges.

[0100] It will be appreciated that the present invention has been described above purely by way of example and that modifications of detail may be made within the scope of the invention.

[0101] Each feature disclosed in the description and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

[0102] Reference signs appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

1. A flue gas treatment system for a biomass power generation system based on pyrolysis, the flue gas treatment system include: a solvent cycle for absorbing carbon dioxide from the flue gas; a heat exchanger, located along a flow path of the solvent, for heating the solvent; and Heat transfer fluid, The heat transfer fluid is arranged to circulate between the heat exchanger and the biomass power generation system, so that the heat transfer fluid absorbs heat from the heating fluid of the biomass power generation system and transfers the heat to the solvent cycle via the heat exchanger.

2. The system according to claim 1, in, The heating fluid is a hot air flow for driving a turbine of the biomass power generation system, preferably wherein the heat transfer fluid is arranged to absorb heat from the air flow downstream of the turbine.

3. The system according to claim 1, in, The heating fluid of the biomass power generation system is a flue gas stream from a biomass reactor of the biomass power generation system.

4. A system according to any one of the preceding claims, in, The heat transfer fluid is arranged to absorb heat from the heating fluid of the biomass power generation system via a further heat exchanger located along the flow path of the heating fluid, and wherein the heat transfer fluid is arranged to circulate between the heat exchanger of the flue gas treatment system and the further heat exchanger.

5. A system according to any one of the preceding claims, in, The heat exchanger located along the flow path of the solvent is a reboiler for heating the solvent.

6. The system according to claim 4 and 5, in, The heat transfer fluid is steam, and wherein: the reboiler being arranged to receive steam from the further heat exchanger located along the flow path of the heating fluid of the biomass power generation system and to transfer heat from the steam to the solvent, thereby forming condensate from the steam; and The further heat exchanger located along the flow path of the heating fluid of the biomass power generation system is arranged to receive the condensate from the reboiler and transfer heat from the heating fluid of the biomass power generation system to the condensate, thereby forming the steam.

7. A system according to any one of the preceding claims, in, The solvent is an amine.

8. A raw material dryer for a biomass power generation system, the raw material dryer include: A device for providing an air flow to the feedstock of the biomass power generation system; at least one heat exchanger located along the air flow path; and at least one coolant arranged to flow between the at least one heat exchanger and at least one component of a gas processing system for the biomass power generation system, wherein the at least one coolant is arranged to absorb heat from the at least one component, and wherein the at least one heat exchanger is arranged to transfer the heat from the coolant to the air flow.

9. The raw material dryer according to claim 8, in, The at least one component comprises a flue gas scrubber, and wherein the coolant is arranged to cool the scrubber by absorbing heat from the scrubber.

10. The raw material dryer according to claim 9, in, The flue gas scrubber is located in the flue gas flow path downstream of the power generation and / or heat generation components of the biomass power generation system.

11. The raw material dryer according to any one of claims 8 to 10, in, The at least one component comprises a trim cooler in an absorption cycle for treating flue gas from the biomass power generation system, and wherein the coolant is arranged to cool the trim cooler by absorbing heat from the trim cooler.

12. The raw material dryer according to any one of claims 8 to 11, in, The at least one component comprises a reflux condenser in an absorption cycle for treating flue gas from the biomass power generation system, and wherein the coolant is arranged to cool the reflux condenser by absorbing heat from the reflux condenser.

13. A raw material dryer according to any one of claims 8 to 12, in, The at least one component comprises a plurality of components, and wherein: said at least one heat exchanger comprises a separate heat exchanger for each said component, and / or The at least one coolant includes a separate coolant for each of the components.

14. A raw material dryer according to any one of claims 8 to 13, in, The means for providing an air flow to the feedstock may include a fan.

15. A raw material dryer according to any one of claims 8 to 14, in, The at least one coolant is water.

16. A biomass power generation system, include: Biomass reactor; Turbine heat exchangers; and Flue gas heat exchangers, wherein the turbine heat exchanger is configured to transfer heat from the flue gas of the biomass reactor to a working fluid for driving a turbine to generate electricity; and wherein the flue gas heat exchanger is located along a flow path of the flue gas, downstream of the turbine heat exchanger, and is configured to transfer heat from the flue gas to a heat output end of the system.

17. The system of claim 16, comprising a flue gas return duct for recycling the flue gas back into the biomass reactor.

18. The system according to claim 17, in, The flue gas return pipe is located downstream of the flue gas heat exchanger.

19. A system according to any one of claims 16 to 18, comprising a pump for driving the flue gas flow, preferably in, The pump is located in the flue gas flow path downstream of the flue gas heat exchanger.

20. The system of any one of claims 16 to 19, comprising a working fluid heat exchanger located along a flow path of a working fluid, the working fluid heat exchanger being configured to transfer heat from the working fluid to a heat output of the system.

21. The system according to claim 20, in, The working fluid heat exchanger is located along the flow path of the working fluid downstream of the turbine.

22. The system of any one of claims 16 to 21, comprising a carbon dioxide processing system; in, The carbon dioxide processing system is arranged to receive a gas stream comprising carbon dioxide removed from the flue gas, and comprises means for dehydrating the gas stream, preferably wherein the means for dehydrating the gas stream comprises at least one dehydration tower for removing water vapour from the gas stream, preferably removing water vapour from the gas stream by adsorption.

23. The system according to claim 22, in, The carbon dioxide processing system comprises a compressor downstream of the means for dehydrating water, the compressor being configured to compress the carbon dioxide, and optionally a refrigerator downstream of the compressor for cooling the carbon dioxide to a liquid state.

24. A biomass power generation system, include: A flue gas treatment system according to any one of claims 1 to 7; and / or The raw material dryer according to any one of claims 8 to 15, Preferably, the biomass power generation system is the biomass power generation system according to any one of claims 16 to 23.

25. The raw material dryer or biomass power generation system according to any one of claims 8 to 24, in, The biomass energy power generation system is a power generation system based on pyrolysis.

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