Biomass Energy Generation

Abstract

The present disclosure relates to an exhaust gas treatment system for a biomass energy generation system. The exhaust gas treatment system comprises a solvent circulation for absorbing carbon dioxide from the exhaust gas, a heat exchanger arranged along the flow path of the solvent for heating the solvent, and a heat transfer fluid, the heat transfer fluid being arranged to circulate between the heat exchanger and the biomass energy generation system, the heat transfer fluid absorbing heat from the heating fluid of the biomass energy generation system and transferring heat to the solvent circulation via the heat exchanger. The present disclosure also relates to a feedstock dryer for the biomass energy generation system, and the biomass energy generation system.

Description

[Technical field]

[0001] The present disclosure relates to a biomass energy generation system, more specifically to a pyrolysis type combined heat and power system. The present disclosure also relates to a feedstock dryer for a biomass energy generation system and a flue gas treatment system for carbon dioxide removal. [Background technology]

[0002] Biomass energy systems generate energy from plant or animal materials, such as wood. One type of biomass energy system, the pyrolysis energy system, generates energy through the pyrolysis of the feedstock. The energy generated by a biomass energy system can be used as thermal output, power (i.e. electricity) output, or combined heat and power output. Summary of the Invention [Problem to be solved by the invention]

[0003] Existing biomass energy generators generate large amounts of waste heat, typically released in the form of hot flue gases or hot air exhausted from the generator's chimney. This waste heat reduces the efficiency of the overall system, resulting in increased carbon dioxide emissions per unit of energy produced.

[0004] Furthermore, although the pyrolysis process leaves some of the raw carbon in a solid state, a significant amount of carbon is released as carbon dioxide in the exhaust gas. Existing processes for removing carbon dioxide require large amounts of energy, which may offset the benefits of removing the carbon dioxide.

[0005] The present invention aims to improve the efficiency of biomass energy production and the removal of carbon dioxide from exhaust gases. [Means for solving the problem]

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

[0007] According to at least one embodiment described in the present specification, there is provided an exhaust gas treatment system for a pyrolysis-type biomass energy generation system. The exhaust gas treatment system includes a solvent circulation for absorbing carbon dioxide from exhaust gas, a heat exchanger arranged along the flow path of the solvent for heating the solvent, and a heat transfer fluid. The heat transfer fluid is arranged to circulate between the heat exchanger and the biomass energy generation system, and the heat transfer fluid absorbs heat from the heating fluid of the biomass energy generation system and transfers heat to the solvent circulation via the heat exchanger. In this way, the exhaust gas treatment system can utilize the heat discharged from the energy generation system to increase the energy efficiency of the energy generation system and increase the amount of carbon dioxide removed per unit of energy discharged by the energy generation system.

[0008] Preferably, the heating fluid is a hot air stream for driving a turbine of the biomass energy production system, and more preferably, the heat transfer fluid is arranged to absorb heat from the air stream downstream of the turbine. The hot air may be exhausted from the turbine (after driving the turbine) before transferring heat to the heat transfer fluid. With this arrangement, heat is not extracted until the hot air drives the turbine, so that the hot air can be preferentially used to generate electricity before extracting heat to power the exhaust gas treatment system.

[0009] Preferably, the heating fluid of the biomass energy production system is an exhaust gas stream from a biomass reactor of the biomass energy production system, more preferably the heat transfer fluid is arranged to absorb heat from the exhaust gas stream downstream of the exhaust gas heat exchanger to provide a thermal output. This arrangement means that no heat is extracted from the hot exhaust gas stream before it is extracted to provide a thermal output for the generator, thereby prioritising the use of the hot exhaust gas for thermal output before extracting heat to power the exhaust gas treatment system.

[0010] Preferably, the heat transfer fluid is arranged to absorb heat from a heating fluid of the biomass energy production system via a further heat exchanger arranged along the flow path of said heating fluid of the biomass energy production system, said heat transfer fluid being arranged to circulate between said heat exchanger of the exhaust gas treatment system and said further heat exchanger, said heat exchanger allowing an efficient transfer of heat between the fluids.

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

[0012] Preferably, the heat transfer fluid is steam, the reboiler is arranged to receive steam from a further heat exchanger arranged along the flow path of said heating fluid of the biomass energy production system and generate condensate from the steam by transferring heat from the steam to a solvent, and the further heat exchanger arranged along the flow path of the heating fluid of the biomass energy production system is arranged to receive condensate from the reboiler and transfer heat from the heating fluid of the biomass energy production system to the condensate, thereby generating steam. The steam condensation cycle between the steam generator and the reboiler effectively transfers heat by keeping the temperature constant during the heat transfer consuming the latent heat of vaporization due to the high heat capacity of water and the properties of saturated steam. This constant temperature prevents damage to the solvent.

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

[0014] According to another aspect described herein, a feedstock dryer for a biomass energy generation system is provided. The feedstock dryer comprises a means for supplying an air flow to a feedstock for the biomass energy generation system, at least one heat exchanger disposed along the air flow path, and at least one coolant disposed to flow between the at least one heat exchanger and at least one component of a gas processing system for the biomass energy generation system, the at least one coolant disposed to absorb heat from the at least one component, and the at least one heat exchanger disposed to transfer heat from the coolant to the air flow. Thus, the feedstock dryer utilizes heat from the energy generation system or the exhaust gas processing system that may otherwise be wasted, increasing the efficient utilization of generated energy and increasing the amount of carbon dioxide removed per unit of energy output by the energy generation system.

[0015] Preferably, the gas treatment system is an exhaust gas treatment system as described above.

[0016] Preferably, the at least one component comprises an exhaust scrubbing device and the coolant is arranged to cool the exhaust scrubbing device by absorbing heat from the exhaust scrubbing device.

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

[0018] Preferably, the at least one component comprises a trim cooler in an absorption cycle for treating exhaust gas from the biomass energy production system, the coolant being arranged to absorb heat from the trim cooler to cool the trim cooler.

[0019] Preferably, the at least one component includes a reflux condenser in an absorption cycle for treating exhaust gas from a biomass energy production system, and 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 the exhaust gas scrubber, trim cooler and reflux condenser as described above), and the at least one heat exchanger comprises a separate heat exchanger for each component, and / or the at least one coolant comprises a separate coolant for each component. Preferably, the heat exchangers are arranged in order of operating temperature or in order of the temperature of the components they cool, preferably from hottest to coolest along the airflow. In this way, efficient transfer of heat to the airflow is promoted.

[0021] Preferably, the means for providing an air flow to the feedstock comprises a fan, which is preferably driven by electricity generated by the generator, and the use of the fan allows this parasitic power consumption to be minimised.

[0022] Preferably, at least one coolant is water, which has a high heat capacity allowing for efficient heat transfer.

[0023] According to another aspect described herein, there is provided a biomass energy generation system comprising a biomass reactor, a turbine heat exchanger, and an exhaust gas heat exchanger. The turbine heat exchanger is configured to transfer heat from the exhaust gas to a working fluid for driving a turbine to generate electricity, and the exhaust gas heat exchanger is disposed along a flow path of the exhaust gas downstream of the turbine heat exchanger and configured to transfer heat from the exhaust gas to a thermal output of the system. Thus, the system utilizes heat from the exhaust gas that may otherwise be wasted by extracting and transferring this heat to the thermal output of the system, thereby increasing the efficient utilization of the energy generated and reducing carbon dioxide emissions per unit of energy output by the energy generation system.

[0024] Preferably, the system includes an exhaust gas return line for circulating the exhaust gas to the biomass reactor. By circulating a portion of the exhaust gas to the pyrolysis reactor, inert gases are provided in the pyrolysis reactor. These inert gases absorb a portion of the heat of pyrolysis 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 by the hot mixture of nitrogen and oxygen.

[0025] Preferably, the exhaust gas return line is arranged downstream of the exhaust gas heat exchanger, so that maximum heat is extracted from the exhaust gas before it is diverted.

[0026] Preferably, the system includes a pump for driving the flow of the exhaust gas, preferably the pump being located in the exhaust gas flow path downstream of the exhaust gas heat exchanger, the pump preventing backflow of the exhaust gas into the subatmospheric pressure reactor.

[0027] Preferably, the system comprises a working fluid heat exchanger arranged along the flow path of the working fluid, the working fluid heat exchanger being configured to transfer heat from the working fluid to a thermal output of the system, in this way providing a further thermal output from the system apart from the output of heat extracted from the exhaust gases.

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

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

[0030] Preferably, the carbon dioxide processing system comprises a compressor downstream of the dehydration means arranged to compress the carbon dioxide, and optionally a chiller downstream of the compressor for cooling the carbon dioxide to a liquid state.

[0031] The carbon dioxide processing system allows the carbon dioxide produced within the system to be used, for example, in industrial processes, minimizing carbon dioxide emissions into the atmosphere and reducing waste products from the system.

[0032] According to another aspect disclosed herein, there is provided a biomass energy generation system including the exhaust gas treatment system and / or the feedstock dryer as described above. Preferably, the biomass energy generation system is as described above. By combining the waste heat recovery aspects of the various systems, a particularly effective waste heat recovery is achieved.

[0033] Preferably, the biomass energy production system is a pyrolysis energy production system. Pyrolysis of certain feedstocks can produce biochar that acts as a carbon reservoir and has further uses, thus reducing the actual waste of the system.

[0034] The term "exhaust gas" as used herein preferably refers to the collection of gases produced as a result of the reactions carried out in the biomass reactor, the composition of the exhaust gas depending on the materials used in the reactor.

[0035] As used herein, the term "heat transfer" or related terms preferably refer to direct or indirect heat transfer. For example, reference to the transfer of heat from exhaust gas to a working fluid includes the direct transfer or heat from one fluid to another, or the indirect transfer of heat via an intermediate component or fluid.

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

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

[0038] Furthermore, functions implemented in hardware may generally also be implemented in software, and vice versa. References herein to software and hardware functions should be construed accordingly. Apparatus functions described herein may be provided as method functions, and vice versa. Means-plus-function features as used herein may alternatively be represented by corresponding structures, such as a suitably programmed processor and associated memory. [Brief description of the drawings]

[0039] [Figure 1] FIG. 1 is a block diagram of an exemplary biomass energy production system and exhaust gas treatment system of the present disclosure. [Diagram 2] FIG. 2 is a block diagram of another exemplary biomass energy production system with an absorption cycle with an exhaust gas treatment system and an exemplary feedstock dryer. [Diagram 3] FIG. 3 is a block diagram of the absorption cycle and feedstock dryer of the biomass energy generation system. [Figure 4] FIG. 4 is a block diagram of an exemplary carbon processing system for a biomass energy production system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings.

[0041] Preferred embodiments of the biomass energy generation system, the exhaust gas treatment system, and the raw material dryer are described below.

[0042] In particular, a biomass energy generation system, an exhaust gas treatment system, and a feedstock dryer are illustrated in outline with reference to FIG. 1. More detailed examples of these systems are described with reference to FIGS. 2 to 4. Here, the biomass energy generation system is illustrated as a pyrolysis energy generation system that provides cogeneration output. In particular, a more detailed exemplary biomass energy generation system, specifically a pyrolysis energy generation system, is described below with reference to FIG. 2. An exemplary exhaust gas treatment system for treating exhaust gas resulting from a pyrolysis process that utilizes waste heat is described with reference to FIG. 3. Also described is an exemplary feedstock dryer for a biomass energy generation system that recovers and utilizes waste heat in drying the feedstock. A carbon treatment system for treating carbon dioxide removed from the exhaust gas is described below with reference to FIG. 4.

[0043] [System Overview] FIG. 1 is a block diagram of an exemplary biomass energy production system and exhaust gas treatment system of the present disclosure.

[0044] In overview, the biomass energy generation system 10 (also referred to as a biomass generator or simply a generator) comprises a biomass reactor 12, a turbine heat exchanger 16, and an exhaust gas heat exchanger 14. In general, the turbine heat exchanger 16 is configured to transfer heat from exhaust gas from the biomass reactor 12 (i.e., exhaust gas generated from the biomass reaction or from a further reaction using the products of the biomass reaction) to a working fluid for driving a turbine 18 to generate electricity. The exhaust gas heat exchanger 14 is disposed along the flow path of the exhaust gas downstream of the turbine heat exchanger 16 and is configured to transfer heat from the exhaust gas to a thermal output of the system. In this manner, heat remaining in the exhaust gas after transferring heat to the working fluid is recovered via the exhaust gas heat exchanger. This heat would otherwise have been wasted by being carried out of the system by the exhaust gas, such as through a flue gas stack. This waste heat recovery therefore increases the efficiency of the energy generation system.

[0045] Separate from the biomass energy generation system 10, an exhaust gas treatment system 20 is provided for treating exhaust gas from the biomass energy generation system 10. Although the exhaust gas treatment system 20 is shown as receiving exhaust gas from the biomass energy generation system 10 described above, it will be understood that the exhaust gas treatment system 20 can also be used to treat exhaust gas from other biomass energy generation systems. In summary, the exhaust gas treatment system 20 comprises a solvent circulation for absorbing carbon dioxide from the exhaust gas, a heat exchanger 22 arranged along the solvent flow path for heating the solvent, and a heat transfer fluid. In general, the heat transfer fluid is arranged to circulate between the heat exchanger 22 and the biomass energy generation system 10, and the heat transfer fluid absorbs heat from a heated fluid of the biomass energy generation system 10 (e.g., a working fluid for driving a turbine, or an exhaust gas stream from a biomass reactor) and transfers heat to the solvent circulation via the heat exchanger 22. In this manner, heat that may otherwise be wasted in the biomass energy generation system is recovered and used to heat the solvent in the exhaust gas treatment system 20.

[0046] Also provided is a feedstock dryer for a biomass energy production system such as the system 10 described above. In summary, the feedstock dryer comprises a means for providing an air flow to a feedstock 28 for the biomass energy production system, at least one heat exchanger 26 disposed along the air flow path, and at least one coolant disposed to flow between the at least one heat exchanger 26 and at least one component of the biomass energy production system (such as a flue gas scrubber) or a gas treatment system for the biomass energy production system (such as a trim cooler or reflux condenser), the at least one coolant disposed to absorb heat from the at least one component, and the at least one heat exchanger 26 disposed to transfer heat from the coolant to the air flow. In this manner, heat within the biomass energy production system and / or the flue gas treatment system that would otherwise be wasted is recovered and used to dry the feedstock for the biomass reactor.

[0047] [Combined heat and power] 2 is a block diagram of another exemplary biomass energy generation system 100 of the present disclosure. Solid arrows are drawn between blocks in the diagram to indicate input or output flows to or from various blocks within the system. Dashed arrows are drawn to or from particular blocks to indicate inputs from or outputs outside the system, e.g., from the external environment. Blocks shown as separate in the drawings are intended to indicate separate functions and do not necessarily refer to functions that are performed as structurally separate components. For example, the functionality indicated by a particular block may in fact be provided as a single component.

[0048] The biomass generator 100 includes a pyrolysis reactor 102 (similar to the biomass reactor 12 of FIG. 1). The pyrolysis reactor 102 is configured to contain a pyrolysis reaction. The pyrolysis reactor 102 receives a biomass feedstock 104, in this example wood, preferably waste wood, and combusts the feedstock 104 with limited amounts of oxygen to produce biochar and pyrolysis gas (also called syngas) in a first stage of the reactor. The syngas is then combusted in a second stage of the reactor, for example in a FLOX combustion (flameless oxidation) reaction, to produce tail gases.

[0049] The biochar produced during the pyrolysis reaction contains a significant and stable proportion of carbon from the biomass. This allows it to act as a carbon sink, sequestering some of the carbon produced during the pyrolysis reaction and limiting the amount of carbon dioxide released into the atmosphere. Furthermore, biochar has other uses, such as agricultural land application (CO2 sequestration), soil improvement (when combined with compost) and reduced fertilizer use. Therefore, the biochar produced in the generator is not wasted.

[0050] The second stage of the reactor has a built-in hot turbine heat exchanger 106 (similar to turbine heat exchanger 16 in FIG. 1) arranged to transfer heat from the exhaust gas to a working fluid for driving a turbine. In other examples, the turbine heat exchanger may be separate from and downstream of the pyrolysis reactor. In this example, the working fluid is a stream of air taken from the external environment. The turbine heat exchanger 106 transfers heat from the exhaust gas to the air stream, and the heated air is used to drive a hot air turbine 108 (similar to turbine 18 in FIG. 1) to generate electricity. Electricity is output by a power output for an external power demand, as indicated by the dashed "electric" line. The hot air turbine 108 may include a means for compressing hot air in the first stage of the turbine before the compressed hot air drives the rotation of the turbine in the second stage.

[0051] The hot air passing through the hot air turbine 108 is sent to a steam generator 110, described below with reference to FIG. 3. The hot air passing through the steam generator 110 is used for external heat demand. Because the airflow from the turbine is clean, the hot air itself may be supplied external to the system to provide thermal power (e.g., to supply hot air to a building for heating the building or to supply hot air for use in an industrial process). Alternatively, the hot air is sent to a working fluid ("WF") heat exchanger 112, where heat from the hot air is transferred to a coolant (e.g., water), which is then transferred external to the system (such as a radiator) to provide thermal power. Alternatively, the system may provide both thermal power outputs. In this case, the thermal power output from the working fluid heat exchanger provides one thermal power output, and the hot air itself provides another thermal power output.

[0052] The exhaust gas from the pyrolysis process passes through turbine heat exchanger 106, where heat is transferred from the exhaust gas to an air stream, before being sent to a exhaust gas ("FG") heat exchanger 114 (similar to exhaust gas heat exchanger 14 of FIG. 1). The exhaust gas heat exchanger 114 is positioned to transfer heat from the exhaust gas to a coolant (such as water), which is sent external to the system to provide additional heat output from the system.

[0053] Thus, the system provides cogeneration with three energy outputs: an electrical output from the hot air turbine 108, a first thermal output from the working fluid heat exchanger 112, and a second thermal output from the exhaust gas heat exchanger 114. There is also an optional third thermal output, which is the hot air itself after passing through the working fluid heat exchanger 112. The thermal outputs from the system are at different temperatures and can therefore be used to meet different heat demands. In particular, the working fluid heat exchanger 112 provides a thermal output of about 70-80°C, while the exhaust gas heat exchanger 114 provides a thermal output at a much higher temperature.

[0054] Advantageously, these thermal outputs utilize heat that would otherwise be wasted, improving the efficiency of the system and resulting in reduced carbon dioxide emissions per unit of energy produced by the system. In particular, the system utilizes heat from the exhaust gases, extracting it via exhaust gas heat exchanger 114 to provide thermal outputs that would otherwise be wasted as the exhaust gases are transported out of the system via the exhaust gas stack. At the same time, heat from the working fluid (which drives the turbine 108) is also extracted via working fluid heat exchanger 112 to provide another thermal output that may otherwise be wasted.

[0055] In this example, a pump 116 located downstream of the exhaust heat exchanger 114 draws exhaust gas from the pyrolysis reactor through the turbine heat exchanger 106 and the exhaust heat exchanger 114, and then drives the exhaust gas along its subsequent flow path, as described below. The pump 116 is provided because the pyrolysis reaction takes place in the reactor 102 at subatmospheric pressure, and therefore the pump 116 prevents the exhaust gas from flowing back into the reactor 102.

[0056] In this example, downstream of the pump 116 the exhaust gas is split so that a portion of it is diverted for recycle to the pyrolysis reactor and the remaining portion is sent to an exhaust gas scrubber 118 .

[0057] By recycling a portion of the exhaust gas to the pyrolysis reactor, an inert gas is supplied to the reactor, which absorbs a portion of the heat of pyrolysis in the reactor and dilutes the oxygen supply in the pyrolysis reactor, reducing the heat of the pyrolysis reaction and thus suppressing the production of undesirable nitrogen oxides, which are produced by the high temperature mixing of nitrogen and oxygen.

[0058] The remaining flue gas that is not recycled to the pyrolysis reactor 102 is sent to a flue gas scrubber 118, which treats the flue gas to remove pollutants such as sulfur dioxide that may be produced during low temperature pyrolysis, particularly during generator start-up, or other pollutants depending on the feedstock and pyrolysis system.

[0059] After passing through the flue gas scrubbing system, the scrubbed flue gas is sent to a carbon dioxide absorption cycle 200 for processing 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 vented outside the system through the generator chimney (e.g., stack). The carbon dioxide removed in the absorption cycle is sent to a carbon dioxide processing system 300 for processing for storage and / or utilization, as described below with reference to Figure 4.

[0060] As will be explained in more detail below with reference to FIG. 3, the absorption cycle 200 is powered by waste heat recovered from the working fluid (i.e., hot air stream) of the hot air turbine 108 by the steam generator 110. Heat is transferred from the steam generator 110 to the absorption cycle 200 by circulation of steam and condensate between the steam generator 110 and the reboiler of the absorption cycle. In addition, since the exhaust gas scrubber 118 and various components of the absorption cycle 200 become hot due to processing the exhaust gas or heated 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 a flow of air (taken from the outside environment). The air heated by the coolant heat exchanger 120 is sent to the feed 104 by a fan 122. Thus, the coolant heat exchanger 120 and the fan 122 together form a feedstock dryer 124, which utilizes waste heat from the flue gas scrubber and absorption cycle to dry the feedstock 104 before it is used in the pyrolysis reactor.

[0061] [Absorption cycle] Figure 3 is a block diagram of a carbon dioxide absorption cycle 200 that functions as an exhaust gas treatment system for the generator 100. The absorption cycle is arranged to receive a gas stream from the flue gas scrubber 118 that includes the portion of the exhaust gas that is not recycled to the pyrolysis reactor 102. This gas stream is indicated in Figure 3 by the "exhaust" arrow exiting the flue gas scrubber 118. As discussed above, the flue gas scrubber 118 treats this gas stream (prior to receipt by the absorption cycle) to remove pollutants such as sulfur dioxide. The absorption cycle 200 then further treats this gas stream to remove carbon dioxide from the gas stream.

[0062] The absorption cycle 200 includes circulation of a solvent for absorbing carbon dioxide in the 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 that has absorbed carbon dioxide, and the term "lean amine solution" (or solvent) is used to refer to the amine solution after the absorbed carbon dioxide has been driven off from the amine solution. It will be appreciated that other solvents, such as carbonates (e.g., potassium carbonate) or ammonia, may be used in place of the amine.

[0063] A gas stream, including flue gas, enters the amine cycle 200 by entering at least one absorber 202. The absorber 202 in this example is an absorption column. A lean amine solution is pumped into the absorption column 202 from a mixing tank 212, described below. The lean amine solution and the gas stream (including the flue gas) enter the absorption column 202 at opposite ends of the absorption column 202. In particular, the lean amine solution enters the absorption column 202 at the top and the gas stream enters the absorption column 202 at the bottom (it should be noted in this regard that FIG. 3 is a block diagram illustrating the interaction between the various blocks and is not a realistic representation of the relative structural positions and locations of the various blocks and fluid streams). Thus, the lean amine solution and the gas stream flow in opposite directions through the absorption column (the solution from top to bottom and the gas stream from bottom to top). The absorption column 202 is arranged such that the gas stream flows through the amine solution, which causes carbon dioxide in the gas stream to be absorbed by the amine solution. To optimize the absorption of carbon dioxide into the amine solution, the absorption column 202 operates at a pressure of approximately 1.15 bar(a) at a temperature range of 40° C. to 50° C. Remaining gas in the gas stream that is not absorbed into the amine solution is discarded from the generator via a chimney (e.g., a flue gas stack) of the generator 100.

[0064] The carbon dioxide-absorbed amine solution (carbon dioxide-absorbed rich amine solution) is collected in the sump of the absorber column 202 and then pumped out of the absorber column 202 and transferred through an amine heat exchanger 204 to a stripper 206, which in this example is a stripper column. The amine heat exchanger 204 is positioned to transfer heat from the heated lean amine solution exiting the reboiler 208 (as described below) to the rich amine solution as it passes from the absorber 202 to the stripper 206. The amine heat exchanger 204 heats the rich amine solution to about 100° C. before passing it to the stripper column 206. The heated rich amine solution is received by the stripper column 206 through an orifice plate in the stripper column 206 where the carbon dioxide and water vapor displaced from the amine solution by the heat from the amine heat exchanger 204 are flashed.

[0065] In the stripper column 206, the absorption reaction that occurred in the absorption column is reversed, and the carbon dioxide absorbed in the amine solution is stripped from the amine solution in the gas phase. The rich amine solution enters the stripper column 206 and flows downward through the column 206. Meanwhile, the heated carbon dioxide and water vapor that enter the stripper 206 from the reboiler, as described below, flows upward through the column 206 and into the rich amine solution flowing downward. Contact between the counterflowing rich amine solution and the heated carbon dioxide and water vapor transfers heat from the heated carbon dioxide and water vapor to the rich amine solution, which results in the rich amine solution being heated and the carbon dioxide absorbed in the solution being released.

[0066] The carbon dioxide released from the amine solution, along with the carbon dioxide and water vapor from the reboiler, travels upward through the stripper column 206 and passes through a (preferably built-in) demister (not shown) which removes any water droplets entrained in the gas stream before it exits the top of the stripper column and is sent to the reflux condenser 122. Meanwhile, the amine solution (now lean, having had its absorbed carbon dioxide stripped away) flows downward through the stripper column 206 and collects in the sump of the stripper column 206 where it is pumped out of the stripper column to the reboiler 208.

[0067] The reflux condenser 122 is positioned to receive the output gas stream from the top of the stripper column 206. The output gas stream from the stripper column 206 is primarily composed of carbon dioxide removed from the amine solution, but may also contain some undesirable vapors from the amine solution. Thus, the reflux condenser 122 (a partial reflux condenser in this example) is configured to cool the gas stream it receives from the stripper column. This cooling is accomplished by the reflux condenser 122 transferring heat from the gas stream to cooling water, as will be described below with reference to the feed dryer. This cooling condenses much of the vapor (e.g., water vapor) in the gas stream, partially dehydrating the gas stream and increasing the concentration of carbon dioxide in the gas stream. The resulting partially dehydrated gas stream is sent to the carbon dioxide processing system 300, which includes a dehydrator to remove any vapors from the gas stream that were not removed by the reflux condenser 122. The condensate formed by cooling the vapors in the gas stream by the reflux condenser 122 is returned to the stripper column 206.

[0068] The lean amine solution accumulated in the sump of the stripper column 206 is extracted from the column 206 by a transfer pump to a reboiler 208. In the reboiler 208, the lean amine solution is heated to about 115° C. using waste heat from the biomass energy production system 100, as described below. As the lean amine solution is heated in the reboiler 208, more carbon dioxide is released from the amine solution. The carbon dioxide released from the solution in the reboiler is returned to the stripper column 206, as shown in FIG. 3 by the “CO2” arrow from the reboiler 208 to the stripper 206. This returned carbon dioxide flows upward through the stripper column, causing the release of carbon dioxide from the rich amine solution in the stripper column 206 (as described above), and then this returned carbon dioxide is extracted along with the released carbon dioxide into the reflux condenser 122, as described above.

[0069] The reboiler 208 heats the lean amine solution using waste heat from the biomass energy generation system 100 (the reboiler is similar to the heat exchanger 22 of FIG. 1). In particular, a heat transfer fluid is arranged to circulate between the reboiler and the biomass energy generation system, the heat transfer fluid absorbing heat from the heated fluid of the biomass energy generation system (in this case, the heated turbine working fluid) and transferring the heat to the circulating amine solution via the reboiler. In this example, this is accomplished by providing a steam generator 110 along the flow path of the working fluid (i.e., hot air) that drives the turbine 108. In this example, the heat transfer fluid is water (liquid 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 circulation path of the amine solution, transferring heat from the steam to the amine solution to heat the amine solution to approximately 115° C. This heat transfer causes the steam to condense to form condensate (i.e., water) that is sent to the steam generator 110. The steam generator is positioned to receive the condensate from the reboiler 208 and acts as a heat exchanger along the path of the turbine working fluid to transfer heat from the turbine working fluid to the condensate, heating the condensate to form steam which is circulated to the reboiler as previously described.

[0070] In this example, the steam generator 110 is positioned along the path of the turbine working fluid downstream of the hot air turbine and upstream of the working fluid heat exchanger 112. This positioning is advantageous because the steam generator requires the working fluid to be relatively hot to heat the condensate to produce steam, whereas the working fluid heat exchanger 112 does not require the working fluid to be as hot to provide a heat output suitable for the heat demand.

[0071] The steam generator 110, reboiler 208, and heat transfer fluid (i.e., the same steam and condensate) thus provide a means to use waste heat from the biomass energy generation system to power the amine cycle. In this example, the waste heat is extracted from the turbine working fluid, but in other examples, heat extracted from the exhaust gas, for example by the exhaust gas scrubber 118, can be used to extract heat from other parts of the generator, for example, the exhaust gas. This heat would otherwise have been wasted or an external heat supply would have been required to provide heat to the reboiler 208. This system configuration therefore increases the efficiency of the system, resulting in increased carbon dioxide removal per unit of energy produced by the system.

[0072] The lean amine solution heated in the reboiler is then sent from the boiler to a trim cooler 210 via an amine heat exchanger 204, where heat from the heated lean amine solution is transferred to the rich amine solution, which is also sent through the amine heat exchanger 204 between the absorber column 202 and the stripper column 206, as previously described. The heat transfer to the rich amine solution cools the lean amine solution to about 60° C. The trim cooler 210 is positioned to receive the cooled lean amine solution from the amine heat exchanger 204 and is configured to further cool the lean amine solution to about 40° C. Further cooling of the lean amine solution is achieved by the trim cooler 210 transferring heat from the lean amine solution to a coolant (such as water), as described below with reference to the feed dryer.

[0073] From the trim cooler 210, the lean amine solution passes through a filter to remove any particulates or heat stable solids (or heat stable salts) that may have formed in the solution due to partial decomposition of the amine in the reboiler. After filtration, the lean amine solution is returned to the mixing tank 212 and fed to the absorption column 202. In the mixing tank, the amine solution is dosed with crude amine, promoters, and pH adjusters to maintain the proper ratios. Small amounts of make-up water are constantly added to the mixing tank 212, and the liquid in the mixing tank is constantly drained at similarly small rates, so that the solution is gradually and constantly renewed. Nitrogen gas is flooded above the liquid in the mixing tank 212 to drive out any oxygen that would degrade the amine, as well as to maintain a slight positive pressure in the tank. To restart the amine cycle 200, liquid is fed from the mixing tank 212 to the absorber 202, which absorbs carbon dioxide from the tail gas as previously described.

[0074] It should be noted that the energy required to remove carbon dioxide from the exhaust gas in the exhaust gas treatment system is primarily heat, which is provided by waste heat recovery from the working fluid of the turbine. Negligible electricity is required for both the exhaust gas treatment system and other parasitic loads, such as the pump 116 of the generator 100, and therefore the energy penalty for power generation in the disclosed system is minimal. In contrast, electricity-based carbon capture technologies are approximately 25% less efficient due to the need to use electricity to generate steam for the carbon capture system.

[0075] [Raw material dryer] FIG. 2 also shows a feedstock dryer 124 for the biomass energy production system 100 that utilizes waste heat from the flue gas scrubber and absorption cycle to dry the feedstock 104 before it is used in the pyrolysis reactor 102.

[0076] In overview, the feedstock dryer 124 comprises a means for providing an airflow over the feedstock 104 (in this example a fan 122) and at least one coolant heat exchanger 120 (similar to heat exchanger 26 of FIG. 1) disposed along the flow path of the air, with the coolant arranged to flow between the at least one coolant heat exchanger 120 and at least one component of the biomass energy generation system 100, the coolant absorbing heat from the at least one component of the biomass energy generation system and the at least one coolant heat exchanger 120 configured to transfer heat from the coolant to the airflow. In this way, waste heat from the components of the biomass energy generation system can be used to heat the airflow over the feedstock and the waste energy can be utilized for drying the feedstock 104.

[0077] More specifically, in this example, waste heat is extracted from components such as the flue gas scrubber 118, the trim cooler 210, and the reflux condenser 122 of the flue gas treatment system of the biomass energy production system. Each of these three components is provided with a coolant circuit, with each component configured to transfer heat to the coolant. Each component is provided with a respective heat exchanger configured to transfer heat from the coolant to an air stream, whereby the air is heated before being used to dry the feedstock. Each of these three components will be described in turn.

[0078] The flue gas scrubber 118 is arranged to receive the flue gas and treat it to remove pollutants such as sulphur dioxide. As the flue gas is therefore hot as it comes from the pyrolysis reactor 102, the flue gas scrubber also becomes hot during use and needs to be cooled. Cooling of the flue gas scrubber 118 is achieved by circulating a coolant (water in this example) between the flue gas scrubber 118 and the flue gas scrubber heat exchanger 214. The flue gas scrubber 118 is arranged to transfer heat from the flue gas to the cooling water, which is then recirculated to the flue gas scrubber heat exchanger 214. The flue gas scrubber heat exchanger 214 is arranged to transfer heat from the coolant to an air stream.

[0079] The trim cooler 210 is arranged to cool the lean (amine) solution before it enters the mixing tank 212. There is therefore provided a circulation of a coolant, in this example water, between the trim cooler 210 and the trim cooler heat exchanger 216. The trim cooler 210 is arranged to transfer heat from the lean (amine) solution to the cooling water to cool the (amine) solution. The coolant is then recirculated to the trim cooler heat exchanger 216 which is arranged to transfer heat from the coolant to an air stream.

[0080] The reflux condenser 122 is arranged to cool the gas stream received from the stripper column to partially dehydrate the gas stream output from the stripper 206 before transferring it to the carbon dioxide processing system 300. To dehydrate the gas stream, the reflux condenser is arranged to cool the gas stream to condense the steam present in the gas stream. Thus, between the reflux condenser 122 and the reflux condenser heat exchanger 218, a circulation of a coolant, which in this example is water, is provided. The reflux condenser 122 is arranged to transfer heat from the gas stream to the cooling water to cool the gas stream. The coolant is then recirculated to the reflux condenser heat exchanger 218, which is arranged to transfer heat from the coolant to the air stream.

[0081] An air stream is drawn in from the external ambient environment and then driven through flue gas scrubber heat exchanger 214, trim cooler heat exchanger 216, and reflux condenser heat exchanger 218, absorbing heat from each heat exchanger along the way. The heated air is then directed over the feedstock 104 to dry it before being used in the pyrolysis reactor 102. A fan 122 provides a means for driving the air stream, and in this example is positioned downstream of heat exchangers 214, 216, 218 (collectively 120) such that the fan draws air through the heat exchangers and forces the air against the feedstock.

[0082] 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 the feedstock dryer 124, which dries the feedstock using heat from the generator 100 that would otherwise be wasted. Because this heat would otherwise be wasted and a separate power source would be required to power the feedstock dryer, the feedstock dryer of the present disclosure increases the efficiency of the biomass energy generation system 100, and as a result reduces the carbon dioxide emissions per unit of energy produced by the system.

[0083] It should be noted that while three waste heat sources are used in Figure 3 (exhaust gas scrubber 118, trim cooler 210, reflux concentrator 122), in other examples only one waste heat source or any number of waste heat sources may be used, and these waste heat sources may be provided by other components or systems of generator 100. For example, steam generator 110 may instead provide heat for a feedstock dryer.

[0084] 3 further illustrates three heat exchangers 214, 216, 218 arranged in series with the airflow passing through each heat exchanger. This arrangement is advantageous as it maximizes the heating of the airflow. Furthermore, the arrangement of the heat exchangers 214, 216, 218 from coldest to hottest (along the direction of the airflow) improves the efficiency of the heat transfer from the heat exchangers to the air. However, in other examples, the heat exchangers may be arranged in parallel such that the airflow is provided with parallel airflows passing through the heat exchangers.

[0085] [Carbon dioxide processing] 4 is a flow diagram of a carbon dioxide processing system 300 for a biomass energy production system. The carbon dioxide processing system 300 is arranged to receive the carbon dioxide removed from the flue gas by the absorption cycle 200 and process it for utilization or storage. This carbon dioxide can be used, for example, in the food and beverage industry to minimize carbon dioxide emissions in the power generation process, eliminate the need to separately generate carbon dioxide for other purposes, thereby preventing unnecessary release of carbon dioxide into the atmosphere, and increase the efficiency of biomass utilization.

[0086] First, the gas stream from the reflux concentrator 122 (containing carbon dioxide and having been partially dehydrated by the reflux concentrator 122) is sent from the reflux concentrator of the absorption cycle 200 to the carbon dioxide dehydrator 302. The carbon dioxide dehydrator 302 removes residual water vapor remaining in the gas stream (i.e., water not removed by the reflux concentrator 122), thereby "drying" the gas stream. The dehydrator 302 includes columns for removing water vapor from the gas stream by adsorption. The columns operate in a temperature swing adsorption circuit in the dehydrator 302, where one of the columns (the "dehydration column") is actively dehydrating the gas stream while another one of the columns (the "regeneration column") is regenerating. Preferably, the dehydrator 302 includes two such columns, one column dehydrates the gas stream and the other column regenerates it. To facilitate water vapor adsorption, the gas stream from the reflux concentrator 122 is cooled before entering the dehydration columns of the dehydrator 302.

[0087] Adsorption of water vapor from the gas stream is accomplished by trapping water on adsorbent beads (preferably made of 3A zeolite) within the column. This removes water from the gas stream, leaving a dehydrated carbon dioxide gas stream. The dehydrated carbon dioxide leaves the dehydration column at the bottom of the column via a network of pipes, with a series of valves controlling the exit of the carbon dioxide from the dehydration column. The exiting carbon dioxide is also filtered to remove debris generated as the adsorbent decomposes within the column.

[0088] To regenerate an inactive column (a column that is not actively dehydrating a gas stream), a portion of the dehydrated carbon dioxide leaving the dehydration column (approximately 10%) is returned to the regeneration column via a compressor and heater. The heated carbon dioxide flowing back through the regeneration column releases the adsorbent water from the adsorbent beads, regenerating the column. Regeneration of the column releases a stream of water vapor along with the heated carbon dioxide. This stream is cooled and separated in the knock-out drum. The carbon dioxide gas recovered from the knock-out drum is returned to the dehydrator for reuse in increasing the carbon dioxide yield, while the liquid condensate (i.e., condensed water) is discarded.

[0089] The portion of the dehydrated carbon dioxide from the dehydrator 302 that is not recirculated through the regeneration column may simply be exhausted from the system. However, to reduce unwanted emissions, the carbon dioxide is preferably utilized. For example, the carbon dioxide may be used in an industrial process co-located with the generator 100, or may be stored for later use or transport.

[0090] Accordingly, a carbon dioxide extraction system is provided to process the dehydrated carbon dioxide from the dehydrator 302 so that it can be used immediately or stored or transported for later use. The carbon dioxide extraction system includes a carbon dioxide compressor 304 and an optional carbon dioxide chiller 306. The carbon dioxide compressor 304 is positioned to receive the dehydrated carbon dioxide from the dehydrator 302 and is configured to compress the carbon dioxide to pipeline pressure for export from the generator 100 to an associated (i.e., "on-site") industrial process. The carbon dioxide is preferably sequestered by the industrial process to minimize release of carbon dioxide to the atmosphere. The pressure to which the carbon dioxide is compressed will vary depending on the requirements of the industrial process used.

[0091] If the carbon dioxide is not used immediately, or is used off-site and requires transportation, it is sent from compressor 304 to chiller 306 where it is cooled and stored for transportation or later use. The chiller is configured to cool the compressed carbon dioxide to a liquid phase and store it in situ (i.e., near generator 100) for later use in cryogenic storage, or to store it during normal delivery for transportation to a tanker.

[0092] It will be understood that the invention has been described above purely by way of example and modifications of detail are possible within the scope of the invention.

[0093] Each feature disclosed in this specification, and (where applicable) the claims and drawings, may be provided individually or in any suitable combination.

[0094] Any reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

1. An exhaust gas treatment system for a pyrolysis-type biomass energy generation system, comprising: Circulation of a solvent to absorb carbon dioxide from the exhaust gas; a heat exchanger disposed along a flow path of the solvent for heating the solvent; A heat transfer fluid; Equipped with The heat transfer fluid is arranged to circulate between the heat exchanger and the biomass energy production system, the heat transfer fluid absorbing heat from a heating fluid of the biomass energy production system and transferring heat to the solvent circulation via the heat exchanger. Exhaust gas treatment system.

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

3. 2. The system of claim 1, the heating fluid of the biomass energy production system is an exhaust gas stream from a biomass reactor of the biomass energy production system; system.

4. 3. The system according to claim 1 or 2, the heat transfer fluid is arranged to absorb heat from a heating fluid of the biomass energy production system via a further heat exchanger arranged along a flow path of the heating fluid of the biomass energy production system, and the heat transfer fluid is arranged to circulate between the heat exchanger of the exhaust gas treatment system and the further heat exchanger. system.

5. 5. The system according to claim 1, The heat exchanger disposed along the flow path of the solvent is a reboiler for heating the solvent. system.

6. In the system according to claim 4 or 5, the heat transfer fluid is steam; the reboiler is positioned to receive steam from the further heat exchanger disposed along a flow path of the heating fluid of the biomass energy production system and to generate a condensate from the steam by transferring heat from the steam to the solvent; the additional heat exchanger disposed along a flow path of the heating fluid of the biomass energy production system is configured to receive the condensate from the reboiler and to transfer heat from the heating fluid of the biomass energy production system to the condensate to produce the steam. system.

7. 7. The system according to claim 1, The solvent is an amine. system.

8. A feedstock dryer for a biomass energy generation system, comprising: The raw material dryer is a means for providing an air flow to the feedstock for the biomass energy production system; at least one heat exchanger disposed along the air flow path; 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 energy production system; the at least one coolant is positioned to absorb heat from the at least one component; the at least one heat exchanger is positioned to transfer heat from the coolant to the airflow. Raw material dryer.

9. 9. The raw material dryer according to claim 8, At least one component comprises an exhaust gas scrubbing device; the coolant is arranged to cool the exhaust gas scrubbing apparatus by absorbing heat from the exhaust gas scrubbing apparatus. Raw material dryer.

10. 10. The raw material dryer according to claim 9, The exhaust gas scrubbing device is disposed in an exhaust gas flow path downstream of a power and / or heat generating component of the biomass energy production system; Raw material dryer.

11. In the raw material dryer according to any one of claims 8 to 10, the at least one component comprises a trim cooler in an absorption cycle for treating exhaust gas from the biomass energy production system; the coolant is positioned to absorb heat from the trim cooler to cool the trim cooler. Raw material dryer.

12. In the raw material dryer according to any one of claims 8 to 11, At least one component comprises a reflux condenser in an absorption cycle for treating exhaust gas from the biomass energy production system; the coolant is arranged to absorb heat from the reflux condenser to cool the reflux condenser. Raw material dryer.

13. In the raw material dryer according to any one of claims 8 to 12, The at least one component comprises a plurality of components, the at least one heat exchanger comprises a separate heat exchanger for each component; and / or the at least one coolant comprises a separate coolant for each component; Raw material dryer.

14. In the raw material dryer according to any one of claims 8 to 13, The means for providing air flow to the raw material comprises a fan. Raw material dryer.

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

16. A biomass reactor; A turbine heat exchanger; An exhaust gas heat exchanger, the turbine heat exchanger is configured to transfer heat from the exhaust gas from the biomass reactor to a working fluid for driving a turbine to generate electricity; the exhaust gas heat exchanger is disposed downstream of the turbine heat exchanger along a flow path of the exhaust gas and configured to transfer heat from the exhaust gas to a thermal output of a system. Biomass energy generation system.

17. 17. The system of claim 16, A flue gas return pipe is provided for recirculating the flue gas to the biomass reactor. system.

18. 20. The system of claim 17, The exhaust gas return pipe is disposed downstream of the exhaust gas heat exchanger. system.

19. 19. The system according to any one of claims 16 to 18, a pump for driving the flow of the exhaust gas; Preferably, the pump is disposed in the exhaust gas flow path downstream of the exhaust gas heat exchanger. system.

20. 20. The system according to any one of claims 16 to 19, a working fluid heat exchanger disposed along a flow path of the working fluid; the working fluid heat exchanger is configured to transfer heat from the working fluid to a thermal output of the system; system.

21. 21. The system of claim 20, the working fluid heat exchanger is disposed along a flow path of the working fluid downstream of the turbine; system.

22. 22. The system according to any one of claims 16 to 21, Equipped with a carbon dioxide treatment system; 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 said gas stream, preferably said means for dehydrating said gas stream comprising at least one dehydration column for removing water vapour from said gas stream, preferably by adsorption. system.

23. 23. The system of claim 22, the carbon dioxide processing system comprising a compressor downstream of the dehydration means, the compressor configured to compress the carbon dioxide, and optionally a cooling device downstream of the compressor for cooling the carbon dioxide to a liquid state; system.

24. An exhaust gas treatment system according to any one of claims 1 to 7, and / or a raw material dryer according to any one of claims 8 to 15, Preferably, the biomass energy generation system according to any one of claims 16 to 23, Biomass energy generation system.

25. A feedstock dryer or biomass energy generation system according to any one of claims 8 to 24, The biomass energy generation system is a pyrolysis type energy generation system. Feedstock dryers or biomass energy generation systems.

Images