A process and plant

Abstract

An embodiment of the present invention relates to a process for treating an absorbent solution including a desorbing step in which an acid gas is desorbed from a loaded absorbent solution, and a heating step in which the loaded absorbent solution, or at least a portion thereof, is heated before the loaded absorbent solution enters the desorbing step including control of the pressure of the absorbent solution above the bubble point of the absorbent solution at the given temperature prior to entering the desorbing step. The heating step includes a first heating step in which the loaded absorbent solution is heated to a first temperature which is less than the operating temperature of the desorbing step, and a second heating step in which the loaded absorbent solution is heated from the first temperature to a second temperature.

Description

A PROCESS AND PLANTRELATED APPLICATION

[0001] The present application claims priority to Australian provisional application number 2023904090 filed on 15 December 2023 entitled A PROCESS AND PLANT. The full contents of the specification of the provisional application are hereby incorporated into the present specification.FIELD OF THE INVENTION

[0002] The present invention relates to the process and a plant for treating an absorbent solution used for absorbing an acid gas. The absorbent solution can be recirculating between an absorber stage and a desorber stage for reuse.BACKGROUND OF THE INVENTION

[0003] Absorption and desorption processes are the main process used for the removal of CO2 and other acid gases from industrial gas streams. The processes are characterised by using a lean absorbent solution having low levels of acid gas including CO2 contacting a feed gas stream in a typically counter current arrangement, in which the feed gas rises upwardly past the downwardly flowing absorbent solution. The absorbent solution absorbs CO2 as it flows down the absorber stage, becomes enriched in CO2and leaves the absorber stage as a loaded absorbent solution.

[0004] The loaded absorbent solution is heated or otherwise treated to eventually recover CO2 gas in a desorber stage. The CO2 released from the loaded absorbent solution results in a lean absorbent solution being regenerated in the desorber stage which can be recirculated to the absorber stage in a closed loop.

[0005] A challenge faced by most processes is to heat the loaded absorbent solution. It is an objective to provide a process and / or plant for heating the loaded absorbent solution to efficiently use energy.SUMMARY OF THE INVENTION

[0006] An embodiment of the present invention relates to process for treating an absorbent solution, wherein the process includes: a desorbing step that includes desorbing an acid gas from the loaded absorbent solution to regenerate a lean absorbent solution; heating the loaded absorbent solution, or at least a portion thereof, before the loaded absorbent solution enters the desorbing step;wherein the heating step includes a first heating step in which the loaded absorbent solution is heated to a first temperature which is less than the operating temperature of the desorbing step, and a second heating step in which the loaded absorbent solution is heated from the first temperature to a second temperature, and wherein the second heating step includes transferring heat from the lean absorbent solution, and the first heating step includes transfer heat from a heat source other than the lean absorbent solution.

[0007] The heat source may be any heat source including any one or a combination of: i) heat from a rich gas stream including carbon dioxide discharged from the desorbing step after compression of the rich gas in one or more compression stages; ii) heat from a gas stream containing acid gas including carbon dioxide (fed to an absorber stage); iii) heat from a rich acid gas stream discharged from the desorbing step. iv) heat from a heating fluid, such as steam, that is condensed or partially condensed in the reboiler of the desorbing step.

[0008] In one example, the heat source may be associated with the desorbing step. That is to say, the first heating step may include transferring heat from a heat source associated with the desorbing step other than the lean absorbent solution.

[0009] Throughout this specification references to "a heat source associated with the desorbing step" embraces heat from streams discharged from the desorbing step such as acid gas streams discharged from the desorbing step, side streams discharged from the desorbing step, and waste heat that is not transferred to the desorbing step including, condensate of a reboiler of the desorbing step, uncondensed steam discharge from a reboiler of the desorbing step, saturated liquid discharged from the reboiler, gas streams discharged from the reboiler of the desorbing step.

[0010] In another example, the heat source may not be directly associated with the desorbing step, including, for example: heat generated by a compressor that compresses a rich acid gas stream discharged from the desorbing step, and / or heat from the acid gas feed stream. For instance, the rich acid gas stream discharged from the desorbing step may undergo multiple compression stages in which the rich acid gas stream is heated during the compression stages. The rich acid gas stream may be used as the heat source after each of the compression stages.

[0011] Throughout this specification, references to the "loaded absorbent", "loading of the absorbent", or variations thereof, refers to the molar proportion of the targeted species into theabsorbent stream on a scale of 0 - 1, where the loading of a totally regenerated stream is zero and loading of a totally loaded stream is 1. By way of example, when the targeted species is CO2and the absorbent is alkali carbonate, the loading of CO2incorporated into the alkali carbonate / alkali bicarbonate mixture, a loading of zero represents a solution containing only alkali carbonate and the loading of a solution containing only alkali bicarbonate is 1. In this example, the loading is equivalent to moles of CO2absorbed per mole of K2CC>3. The targeted species may be any acid gas including CO2, SOx and NOX.

[0012] The heat source associated with the desorbing step may be an acid gas discharged from the desorbing step, such that the first heating step includes transferred heat from the acid gas to the loaded absorbent solution. In an example, the first heating step may include transferring heat from the acid gas to the loaded absorbent solution after being discharged from the desorber stage. That is to say, prior to the acid stream being compressed in a compressor. In another example, the first heating step may include transferring heat from the acid gas stream to the loaded absorbent solution after the acid gas stream has been compressed in at least one compression stage, and suitably after one or more compression stage when the acid is compressed in multiple compression stages.

[0013] The heat source associated with the desorbing step may be a saturated output discharged from a reboiler of the desorbing step, such that the first heating step may include transferring heat from the saturated output of the reboiler to the loaded absorbent solution.

[0014] The first heating step may include the loaded absorbent solution receiving heat energy from at least one of or a combination of the following heat source associated with the desorbing step: i) an acid gas discharged from the desorbing step, and ii) a saturated output of a reboiler of the desorbing step.

[0015] The saturated output may include a water condensate.

[0016] The process may include splitting the loaded absorbent solution to provide first and second substreams of the loaded absorbent solution, in which the first substream is heated in the first heating step and the second heating step, and a second substream of the loaded absorbent is heated in the second heating step without the first heating step.

[0017] The second substream may initially be heated using heat energy from the regenerated lean absorbent solution and then combined with the first substream after the first substream has been heated in the first heating step.

[0018] The process may include splitting the loaded absorbent solution to provide first and second substreams of the loaded absorbent solution, in which the first substream is heated in the first heating step by heat being transferred from the acid gas discharged from the desorber, without heat being transferred from the saturated stream. Heat may be transferred from the acid gas discharged from the desorbing step prior to any compression of the acid gas stream and / or from the acid gas discharged from the desorbing step after one or each compression stage in which the acid gas is compressed.

[0019] The process may include splitting the loaded absorbent solution to provide first and second substreams of the loaded absorbent solution, in which the first substream is heated in the first heating step by heat being transferred from the saturated stream, without heat being transferred from the acid gas discharged from the desorbing step.

[0020] The heating step may include a third heating step in which the loaded absorbent is heated using steam after the second heating step.

[0021] The process may include absorbing an acid gas in the absorbing step by contacting with the absorbent solution to provide a loaded absorbent solution.

[0022] The process may include pressurising the loaded absorbent solution to suppress the vaporisation of gas from the loaded absorbent during the heating step. The step of pressurising the loaded absorbent solution may include pressurising the loaded absorbent solution to a pressure greater than the operating pressure of the absorbing step and desorbing step. Pressurising the absorbing solution during at least part of the heating step to a pressure above the operating pressure of the desorbing step enables heat energy available at higher temperatures, that is at temperatures above the bubble point of the desorbing step to be used to heat the absorbent solution without the formation of vapour, thereby also maintaining efficient heat transfer to the loaded absorbent solution. In one example, the process may include pressurising the loaded absorbent solution to a pressure from 1 to 8.5 atmospheres for a carbonate absorbent, and suitably to a pressure up to 7.7 atmospheres. In another example, the process may include pressurising the loaded absorbent solution to a pressure from 1 to 2.6 atmospheres for MEA absorbent.

[0023] The step of pressurising the loaded absorbent solution may include controlling pressurisation based on the bubble point pressure of the loaded absorbent solution.

[0024] The process may include controlling pressurisation of the loaded solvent solution so that the loaded solvent solution is pressurised to exceed the bubble point pressure of the loaded solvent solution at the second temperature. In other words, the pressurising step includes selecting thepressure to which the loaded absorbent solution is pressurised to ensure that the second temperature does not cause the loaded absorbent solution to exceed the bubble point pressure of the loaded absorbent solution, or the first substream thereof.

[0025] The process may include controlling the temperature of the heating step, including the first and second heating steps and optionally the third heating step, if present, so that the temperature of the loaded absorbent solution fed into the desorbing step is within 40 Deg C of the temperature at the bottom of the desorbing step, and suitably within 30 Deg C, and suitably within 20 Deg C, and event more suitably within 15 Deg C, and still even more suitably within 10 Deg C.

[0026] The loaded absorbent fed to the desorbing step may have a temperature in the range of 5 to 15 Deg C, and suitably 10 Deg C, less than a temperature at or toward the bottom of the desorbing step which is in the range of the 110 to 120 Deg C. The absorbent solution may be a nonprecipitating, such as an amine absorbent.

[0027] The process may include controlling the temperature of the heating step, including the first and second heating steps and optionally the third heating step, if present, so that the temperature of the loaded absorbent solution fed to the desorbing step is approximately 10 to 30 Deg C less, and suitably 15 to 25 Deg C less, and even more suitably 20 Deg C less than the temperature at, or toward, the bottom of the desorbing step is in the range of 130 to 140 Deg C. The absorbent solution may be a precipitating absorbent solution, such as a carbonate absorbent.

[0028] When the absorbent solution is a non-precipitating absorbent solution and the loading of the loaded absorbent solution is 45% or greater, and the step of pressurising the loaded absorbent solution may include pressuring the loaded absorbent solution to a pressure of at least 160kPa when heated to 105 Deg C. For example, the non-precipitating absorbent solution may be an MEA solution.

[0029] In one example, when the absorbent solution is a precipitating absorbent solution and the loading of the loaded absorbent solution is 60% or greater, and the step of pressurising the loaded absorbent solution may include pressuring the loaded absorbent solution to a pressure of at least 148kPa when heated to 105 Deg C, or to a pressure of at least 203kPa when heated to 115 Deg C, or to a pressure of at least 271kPa when heated to 125 Deg C. In another example, when the loaded absorbent solution is a precipitating absorbent solution of 40 to 50wt%, and suitably 45% carbonate and the loading of the loaded absorbent solution is 65% or greater, the step of pressurising the loaded absorbent solution may include pressuring the loaded absorbent solution to a pressure of at least 188kPa when heated to 110 Deg C, or to a pressure of at least 300kPa when heated to 125 DegC, or to a pressure of at least 441kPa when heated to 140 Deg C. For example, the precipitating absorbent solution may be alkali carbonation solution.

[0030] In one example, when the loaded absorbent solution is a precipitating absorbent and the loading of the loaded absorbent solution is 80% or greater, and the step of pressurising the loaded absorbent solution may include pressuring the loaded absorbent solution to a pressure of at least 150kPa when heated to a 90 Deg C, or to a pressure of at least 279kPa when heated to 105 Deg C, or a pressure of at least 412kPa when heated to 115 Deg C, or a pressure of at least 599kPa when heated to 125 Deg C. In another example, when the loaded absorbent solution is a precipitating absorbent solution of 40 to 50wt% carbonate, and suitably 45% carbonate and the loading of the loaded absorbent solution is 80% or greater, the step of pressurising the loaded absorbent solution may include pressuring the loaded absorbent solution to a pressure of at least 115kPa when heated to a 100 Deg C, or to a pressure of at least 280kPa when heated to 110 Deg C, or a pressure of at least 546kPa when heated to 125 Deg C, or a pressure of at least 841kPa when heated to 140 Deg C.

[0031] The process may include a flashing step that is operated at a pressure such that the vapour pressure of the loaded absorbent solution is reduced to the operating pressure of the desorbing step.

[0032] In one example, the absorbent solution may be a non-precipitating absorbent and the loading of the loaded absorbent solution is 45% or greater, the temperature of the absorbent solution is 105 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure of the loaded absorbent solution to an operating pressure of the desorbing step. For example, the flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance 1.59 times atmospheric pressure or 160kPa absolute. In another example, the absorbent solution may be a non-precipitating absorbent and the loading of the loaded absorbent solution is 42% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. For example, the flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance 1.78 times atmospheric pressure or 180kPa absolute.

[0033] In one example, the absorbent solution may be a precipitating absorbent and the loading of the loaded absorbent solution is 45% or greater, the temperature of the absorbent solution is 115 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. Forexample, the flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance 1.38 times atmospheric pressure or 147kPa absolute. In another example, the absorbent solution may be a precipitating absorbent of for example, 40 to 50 wt% carbonate, and suitably 45 wt% carbonate, and the loading of the loaded absorbent solution is 50% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. For example, the flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance 1.29 times atmospheric pressure or 131kPa absolute.

[0034] In one example, the absorbent solution may be a precipitating absorbent and the loading of the loaded absorbent solution is 60% or greater, the temperature of the absorbent solution is 105 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. For example, the flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance 1.38 times atmospheric pressure (148kPa absolute). In another example, the absorbent solution may be a precipitating absorbent solution of for example, 40 to 50 wt% carbonate, and suitably 45 wt% carbonate, and the loading of the loaded absorbent solution is 65% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution to an operating pressure of the desorbing step. For example, the flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance 1.86 times atmospheric pressure or 188kPa absolute.

[0035] In one example, the absorbent solution may be a precipitating absorbent and the loading of the loaded absorbent solution is 80% or greater, the temperature of the absorbent solution is 90 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. For example, the flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance 1.48 times atmospheric pressure or 150kPa absolute. In another example, the absorbent solution may be a precipitating absorbent solution of 45% carbonate and the loading of the loaded absorbent solution is 80% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point to an operating pressure of the desorbing step. For example, the flashing step may reduce the pressure of the loaded absorbentsolution to a pressure greater that atmospheric pressure, for instance 2.76 times atmospheric pressure or 280kPa absolute.

[0036] An embodiment of the present invention relates to a process for treating an absorbent solution, wherein the process includes: an absorbing step that includes an acid gas in the absorber stage by contacting with the absorbent; discharging a loaded absorbent from the absorbing step; and heating the loaded absorbent before the loaded absorbent enters the desorbing step; and pressurising the loaded absorbent solution during the heating step to suppress the vaporisation of gas from the loaded absorbent.

[0037] The step of pressurising the loaded absorbent may include pressurising the loaded absorbent to a pressure greater than the operating pressure of the absorber stage and desorbing step.

[0038] The step of pressurising the loaded absorbent may include controlling pressurisation based on maintaining the solution above the bubble point pressure at the maximum temperature of the heating step.

[0039] By suppressing vaporisation during the heating step, one of the advantages of the present invention is that heating step results in sensible heat rises in the loaded absorbent and avoids inefficiencies causes by the generation of a gas phases in heat transfer equipment of the heating step, including the first, second and third heating step.

[0040] An embodiment of the present invention relates to a process for treating an absorbent solution, wherein the process includes: an absorbing step that includes absorbing an acid gas with the absorbent solution to provide a loaded absorbent solution; a desorbing step that includes absorbing the acid gas from the loaded absorbent solution to regenerate a lean absorbent solution; a heating step that includes heating the loaded absorbent solution before the loaded absorbent enters the desorbing step; and a flashing step that includes flashing the loaded absorbent solution to produce a liquid phase and a gas phase;wherein the heating step includes heating the liquid phase from the flashing step to produce a hot loaded absorbent solution that can be fed to the desorbing step.

[0041] The process includes feeding the hot rich absorbent to the desorbing step.

[0042] The process includes feeding the gas phase to the desorbing step.

[0043] The heating step include heating the loaded absorbent prior to being fed to the flashing step.

[0044] It will be appreciated that the loaded absorbent undergoes a drop in pressure on entering the flashing step, which allows spontaneous volatilization of a gas phase, which results in cooling of the liquid phase in the flashing step. This in turn, provides an opportunity for the heating step to use heat energy available at a lower temperature to preheat the liquid phase prior to being fed to the desorbing step, whereas heating the loaded absorbent prior to the flashing step will require heat energy available at a higher temperature.

[0045] Moreover, the flashing step may include multiple flashing stages in which the liquid phase of a preceding stage can be fed to a next flash stage in a direction toward the desorbing step. In which case, the heating step may include heating the liquid phase discharged from one or more of the multiple flash stages. In this instance, the heating steps for heating of the liquid phases in each successive liquid phase can be carried out at a lower temperature than the preceding heating step.

[0046] The flashing step may be operated at a pressure such that the vapour pressure of the loaded absorbent solution flashes to the operating pressure of the desorbing step. For example, the operating pressure of the desorbing step may be atmospheric pressure. One of the possible benefits this can provide is that temperature of the absorbent solution will reduce as a result of volatilisation in the flashing step, which in turn reduces the operating temperature of the desorbing step which may have operating and capital cost benefits.

[0047] In one example, the absorbent solution is a non-precipitating absorbent and the loading of the loaded absorbent solution is 45% or greater, the temperature of the absorbent solution is 105 degrees C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. In another example, the absorbent solution is a non-precipitating absorbent solution of 40 to 50 wt% carbonate, and suitably 45% carbonate, and the loading of the loaded absorbent solution is 50% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. In this example, the (partial) pressure ofCO2at temperatures greater than 110 Deg C will be typically 1.58 times atmospheric pressure or 160kPa absolute.

[0048] The absorbent solution may be a precipitating absorbent and the loading of the loaded absorbent solution is 50% or greater, the temperature of the absorbent solution is 125 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step. For example, flashing step may reduce the pressure of the loaded absorbent solution to a pressure greater than atmospheric pressure, for instance to a pressure 2.01 times atmospheric pressure or 204kPa absolute.

[0049] In an example, the absorbent solution is a precipitating absorbent and the loading of the loaded absorbent solution is 60% or greater, the temperature of the absorbent solution is 105 Deg C or greater, and the flashing step operates at a pressure below the bubble point pressure of the loaded absorbent solution and evolves gas from the loaded absorbent solution. For example at a pressure up to 1.38 times atmospheric pressure or 148kPa absolute. In another example, the absorbent solution is a precipitating absorbent and the loading of the loaded absorbent solution is 65% or greater, the temperature of the absorbent solution is 115 Deg C or greater, and the flashing step operates at a pressure below the bubble point pressure of the loaded absorbent solution and evolves gas from the loaded absorbent solution. For example at a pressure up to approximately 1.86 times atmospheric pressure or 188kPa absolute. Thus avoiding the need to process the loaded absorbent solution through the desorbing step at higher temperature thereby reducing the energy usage in the desorbing step. Higher temperatures are typically used to feed the desorbing step and hence the benefits will be enhanced in practical applications.

[0050] In another example, the absorbent solution is a precipitating absorbent and the loading of the loaded absorbent solution is 80% or greater, the temperature of the absorbent solution is 90 Deg C or greater, and the flashing step operates at a pressure below the bubble point pressure of the loaded absorbent solution and evolves gas from the loaded absorbent solution. For example, at a pressure up to 1.48 times atmospheric pressure or 150kPa absolute. In yet another example, the absorbent solution is a precipitating absorbent and the loading of the loaded absorbent solution is 80% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step operates at a pressure below the bubble point pressure of the loaded absorbent solution and evolves gas from the loaded absorbent solution. For example, at a pressure up to 2.76 times atmospheric pressure or 280kPa absolute. Thus avoiding the need to process it through the desorbing step at higher temperature thereby reducing the energy usage in the desorbing step.Higher temperatures are typically used to feed the desorbing step and hence the benefits will be enhanced in practical applications

[0051] Furthermore, by removing amounts of CO2in this way the remaining stream has less ability to exert high pressures in the remainder of the heat exchange system and lessen the operational issues downstream of the final lean / rich exchanger.

[0052] The flashing step may be carried out on the loaded absorbent solution after the second heating step.

[0053] The flashing step may be carried out on the loaded absorbent solution after the first heating step.

[0054] The flashing step may be carried out on the loaded absorbent solution after the third heating step.

[0055] An embodiment of the present invention relates to a process for treating an absorbent solution, wherein the process includes: an absorbing step that includes absorbing an acid gas by contacting with the absorbent solution; a discharging step that includes discharging a loaded absorbent solution from the absorbing step; and a heating step that includes heating the loaded absorbent solution before the loaded absorbent solution enters the desorbing step; wherein heating step includes, a first heating step in which the loaded absorbent is heated using heat energy available in a condenser of the desorbing step, and a second heating step in which the loaded absorbent solution, or a liquid phases thereof, is heated prior to being fed to the desorbing step.

[0056] The second heating step may include using heat energy available from regenerated lean absorbent being recirculated from the desorbing step to the absorbing step.

[0057] The heating step may include a third heating step in which the loaded absorbent is heated using steam after the second heating step.

[0058] The process may also include splitting the loaded absorbent to provide first and second substreams of the loaded absorbent, in which the first substream is heated in the first heating step and the second heating step, and a second substream of the loaded absorbent is heated in thesecond heating step without the first heating step and in which the second heating step is a two stage heating step in which the second substream is initially heated using heat energy from the regenerated lean absorbent and then combined with the first substream after the first substream has been heated in the first heating step.

[0059] An embodiment of the present invention relates to a plant for treating an absorbent solution that is recirculating between an absorber stage and a desorber stage, wherein the plant includes: the absorber stage in which the absorbent solution contacts an acid gas feed to provide a loaded absorbent solution discharged from the absorber stage and a product gas lean in acid gas; the desorber stage receives the loaded absorbent solution and in which acid gas is desorbed to provide a lean absorbent and a rich acid gas product, in which the desorber stage has an operating temperature profile; a first heater in which at least a portion of the loaded absorbent solution is heated to a first temperature which is less than the operating temperature of the desorber stage; a second heater in which the at least portion of the loaded absorbent solution is heated from the first temperature to a second temperature, wherein the second heater is configured to transfer heat from the lean absorbent solution to the loaded absorbent solution; and wherein the first heater is configured to transfer heat from a heat source of the plant other than the lean absorber solution.

[0060] The first heater may be configured to transfer heat to the at least a portion of the loaded absorbent solution from any one or a combination of: i. a recuperative heat exchanger that is configured to transfer heat from the feed gas to the loaded absorbent solution, such as the first substream; ii. a condenser heat exchanger that is configured to transfer sensible and / or latent heat from the rich acid gas stream discharged from the desorber stage to the loaded absorbent solution, such as the first substream rich acid gas discharged from the disorber stage after one or more compression stage; ill. an intercooler heat exchanger that is configured to transfer heat from the rich acid gas stream, after one or more of compression stages to the loaded absorbent solution, such as the first substream; andiv. a recovery heat exchanger that is configured for transferring heat from a hot fluid discharged from a reboiler of the disrober stage, to the load absorbent solution, such as the first substream saturated output of a reboiler of the desorber stage.

[0061] The first heater may be configured to transfer heat to the at least a portion of the loaded absorbent solution from a hot stream discharged from the desorber stage other than the lean absorbent solution.

[0062] The first heater may be configured to transfer heat to the at least portion of the loaded absorbent solution from at least one of or a combination of the following heat source associated with the desorber stage: i) an acid gas discharged from the desorber stage, and ii) a saturated output of a reboiler of the desorber stage.

[0063] The plant may include a splitter that splits the loaded absorbent stream in the first and second substreams in which the first substream is heated in the first heater and the second heater, and a second substream of the loaded absorbent is heated in the second heater without being heated in the first heater.

[0064] The second substream may be initially heated using heat energy from the regenerated lean absorbent solution and the plant include a combiner in which the second substream is combined with the first substream after the first substream has been heated in the first heater.

[0065] The plant may include a splitter that splits the loaded absorbent stream into the first and second substreams in which the first substream is heated in the first heater by heat transferred from the acid gas discharged from the desorber, without heat being transferred from the saturated output of a reboiler.

[0066] The plant may include a splitter that splits the loaded absorbent stream into the first and second substreams in which the first substream is heated in the first heater by heat being transferred from the saturated stream, without heat being transferred from an acid gas discharged from the desorber stage.

[0067] The plant may include a third heater in which the loaded absorbent is heated using steam after the second heating step.

[0068] The plant may include a pump that pressurises the loaded absorbent solution to suppress the vaporisation of gas from the loaded absorbent in the first and second heaters.

[0069] The plant may include a controller that controls the pressure of the loaded absorbent solution based maintaining the loaded absorbent solution above the bubble point pressure at the maximum temperature of the loaded absorbent solution. That is the maximum temperature of the absorbent solution in the plant.

[0070] The plant may include a flashing vessel that is arranged to receive the loaded absorbent solution after being heated in either the first heater or after the second heaters, the flashing vessel discharges a liquid phase and a gas phase.

[0071] The flashing vessel may be operated at a pressure such that the pressure of the loaded absorbent solution is reduced to the operating pressure of the desorber stage.

[0072] An embodiment of the present invention relates to a plant for treating an absorbent solution that is recirculating between an absorber stage and a desorber stage, wherein the plant includes: the absorber stage in which the absorbent solution contacts an acid gas feed to provide a loaded absorbent solution discharged from the absorber stage and a product gas lean in acid gas; the desorber stage receives the loaded absorbent solution and in which acid gas is desorbed to provide a lean absorbent and a rich acid gas product, in which the desorber stage has an operating temperature profile; a heater for heating the loaded absorbent solution before the loaded absorbent enters the desorber stage; and a pump for pressurising the loaded absorbent solution during the heating step to suppress the vaporisation of the acid gas from the loaded absorbent. wherein the pump pressurises the loaded absorbent to a pressure greater than the operating pressure of the absorber stage and desorber stage.

[0073] The controller may control pressurisation of the loaded absorbent based on maintaining the loaded absorbent solution above the bubble point pressure at the maximum temperature of the loaded absorbent solution. That is the maximum temperature of the loaded absorbent solution in the plant.

[0074] The plant may include a controller that controls pressurisation of the loaded absorbent solution based on maintaining the solution above the bubble point pressure at the maximum temperature of the heating step.

[0075] An embodiment of the present invention may relate to a plant for treating an absorbent solution that is recirculating between an absorber stage and a desorber stage, wherein the plant includes: the absorber stage in which the absorbent solution contacts an acid gas feed to provide a loaded absorbent solution discharged from the absorber stage and a product gas lean in acid gas; the desorber stage receives the loaded absorbent solution and in which acid gas is desorbed to provide a lean absorbent and a rich acid gas product, in which the desorber stage has an operating temperature profile; flashing vessel into which the loaded absorbent solution is fed to flash the loaded absorbent solution to produce a liquid phase and a gas phase that are discharged from the flash vessel; a heater that heats the liquid phase from the flash vessel to produce a hot loaded absorbent solution that can be fed to the desorber stage.

[0076] The plant may include: a first preliminary heater for heating at least a portion of the loaded absorbent solution to a first temperature which is less than the operating temperature of the desorber stage; a second heater in which the at least portion of the loaded absorbent solution is heated from the first temperature to a second temperature, wherein the second heater is configured to transfer heat from the lean absorbent solution to the loaded absorbent solution; and wherein the first heater is configured to transfer heat from a heat source of the plant other than the lean absorber solution.

[0077] The flashing vessel may be operated at a pressure such that the vapour pressure of the loaded absorbent solution in the flashing vessel is reduced to the operating pressure of the desorber stage.BRIEF DESCRIPTION OF THE DRAWINGS

[0078] A preferred embodiment of the present invention will now be described with reference to the accompanying Figures, which include:

[0079] Figure 1 is a schematic flow diagram of process and a plant for absorbing an acid gas from a gas stream using an absorbent solution and desorbing the acid gas form the desorbent solution, the schematic flow diagram also illustrating some of the possible heat sources for heating the loaded solvent solution.

[0080] Figures 2 is a flow diagram of process and a plant of a preferred embodiment for absorbing an acid gas from a gas stream by an absorbent solution, desorbing an acid gas from the loaded absorbent solution in a desorber stage, and a heating step including a first step in which heat is transferred from a rich CO2 gas stream discharged from the desorber stage to the loaded solvent solution, and a second step in which heat is transferred from a lean absorbent solution discharged from the desorber stage to the loaded solvent solution.

[0081] Figures 3 is the same as Figure 2 save for the heating step. In this example, the heating step includes a first step in which heat is transferred from a heating fluid of a reboiler of the desorber stage to the loaded absorbent solution, and a second step in which heat is transferred from a lean absorbent solution to the loaded solvent solution.

[0082] Figures 4 is a flow diagram of part of a process and a plant for transferring heat between the loaded and lean absorbent solutions with pressure control.

[0083] Figures 5 and 6 are flow diagrams of part of a process and a plant for heating an loaded absorbent solution and flashing the loaded absorbent solution prior to a desorber stage. In addition, Figure 5 also illustrates pumps and control valves required to suppress evolution of carbon dioxide from the loaded absorbent solution and setting the pressure in the flashing step.

[0084] Figure 7 is a graph illustrating the heat curves of a non-precipitating absorbent solutions when lean and loaded.

[0085] Figure 8 is a graph illustrating the heat curves of a precipitating absorbent solution when lean and loaded.DETAILED DESCRIPTION

[0086] A preferred embodiment of the present invention will now be described in the following text which includes reference numerals that correspond to features illustrated in the accompanying Figures. To maintain clarity of the Figures, however, not all reference numerals are included in each Figure.

[0087] Figures 1 to 3 are flow diagrams of part of a process 9 and a plant 10 for absorbing an acid gas using an absorbent solution in an absorbing step 11 / absorber stage 46 and treating a loadedabsorbent solution 22 to form a lean absorbent solution 23 so that the absorbent solution can be recirculated between the absorbing step 11 / absorber stage 46 and a desorbing step 12 / desorber stage 47. Although the terms absorbing step 11 and desorbing step 12 may be categorised as process features, and the terms absorber stage 46 and desorber stage 47 may be categorised as plant features, it is possible these terms and the properties of these terms may be used interchangeably. For instance, it will be appreciated that the absorbing step 11 may include multiple absorber stages or substages, and that the desorbing step 12 may include multiple desorber stages or substages.

[0088] The absorbent solution may include any suitable absorbent. The absorbent solution may be an aqueous form of: i) an alkali carbonate, ii) an amine absorbent, or iii) ammonia. In one example, the absorbent solution may be a non-precipitating, such as an amine absorbent solution having a concentration in the range of 20 to 40wt%, and suitably approximately 30wt%. Examples of amine absorbent solutions include MEA (monoethanolamine), AMP (2-Amino-2-methylpropanol), MDEA (methyldiethanolamine), DEA (diethanolamine), and PZ (Piperazine). The amine solution may or may not include promoters.

[0089] In another example, the absorbent solution may be capable forming precipitates including carbonate absorbent solutions, such as a potassium carbonate solution having a concentration in the range of 10 to 60 wt%, suitably 20 to 50 wt%, and suitably 30 to 45 wt%. The carbonate absorbent solutions may include metals such as calcium, potassium and sodium.

[0090] The absorbing step 11 / absorber stage 47 may include a lean absorbent solution 23, that is, having low levels of acid gas including CO2 contacting the acid gas in a typically counter current flow regime, in which the lean absorbent solution 23 flows downwardly and a gas including an acid gas rises upwardly past the downward flowing lean absorbent solution 23. The lean absorbent solution 23 absorbs acid gas including CCh as the absorbent flows down the absorbing step 11, and becomes enriched with acid gas including CO2 and leaves the absorbing step 11 as a loaded absorbent solution 22. The feed gas 24 may be any post combustion gas, precombustion gas, syngas and so forth.

[0091] The loaded absorbent solution 22 is heated to eventually recover pure CO2 from the desorbing step 12 as the rich CO2gas stream 21. The CO2released from the loaded absorbent stream 22 results in a lean absorbent stream 23 being regenerated in the desorbing step 12 and this can be recirculated to the absorbing step 11 in a closed loop.

[0092] Figure 1 illustrates examples of heat sources of the process 9 and plant 10 for heating the loaded absorbent solution 22. Figure 1 is a schematic flow diagram and does not include details ofvalves, pumps, flash vessels and other control equipment for controlling the flow of the loaded absorbent solution 22 between the various heat sources. The lines in Figure 1 are representative of possible flows rather than the actual pipework. The various heat sources shown in Figure 1 can be used separately, or optionally any combination of any one of the heat sources shown in Figure 1. Other heat sources not shown in Figure 1 can also be used in combination with the heat sources shown in Figure 1 for heating the load absorbent solution 22. Generally speaking, the heat sources are using a heating step 13 including a first heating step 14 and a second heating step 15 which optimise or maximise available heat energy for volatising carbon dioxide from the loaded absorbent solution 22.

[0093] As can be seen in Figure 1, the loaded absorbent solution 22, or a portion thereof, can be heated by the feed gas 24 being fed to the absorbing step 12 in a recuperative heating step 49. The entire loaded absorbent solution 22 can be heated by the feed gas 24, or either one of a first substream 17 and a second substream 18 can be heated with the feed gas 24. It is also possible that only a portion of either one of the first substream 17 or the second substream 18 can be heated using the feed gas 24. The available heat in the feed gas 24 will depending on the original or type of the feed gas 24, such as a post-combustion gas, a pre-combustion gas or a synthesis gas. In any event, heat energy of the feed gas 24 can the transferred to the loaded absorbent solution 22, for example in a recuperative heating step 49 as part of a first heating step 14 which can be carried out in a recuperative heat exchanger 45. It is also possible that the loaded absorbent solution 22 may bypass the recuperative heat exchanger 45 as represented in Figures 2 and 3.

[0094] The first heating step 14 may also include transferring heat to the loaded substream 22, or the first substream 17 thereof by transferring heat from the heating source associated with the desorbing step 12. For instance, a portion or all of the first substream 17 may be heated in the first heating step 14 by transferring heat from a rich CO2gas 21 discharged from the desorbing step 12. This may be carried out in a condenser heater exchanger 25 in which sensible and / or latent heat of condensation of a condensable portion of the rich CO2gas 21 is transferred in a condensing step 50. Optionally, the condensing step 50 and condenser heater exchanger 25 can be omitted or bypassed when the available heat from the rich CO2gas 21 is too lower temperature.

[0095] The rich CO2gas 21 may also undergo a compression step 48 to liquefy the rich CO2gas 21 to assist in long term storage of the carbon dioxide or for more efficient handling the carbon dioxide. In one example, the compression step 48 includes multiple compression stages to pressurise up to a pressure of, for example, 100 or more atmospheres. During the compression step 48, the gas stream 21 will be heated by the compression action to provide a heat source. Each compressionstep 48 may include one or more compression stages, and after the or each step or stage, the first heating step 14 may include transferring heat from the compressed rich CO2gas 21 to the first substream 17, or part thereof, in an intercooling step 42, carried out in an intercooler exchangers 43. In other words, the heat source associated with the desorbing step 12 can include the first heating step 14 having one or more intercooling steps 42, carried out in an intercooler exchangers 43 that transfers heat from the compressed rich CO2gas stream 21 to the loaded absorbent stream 22, or the first substream 17 thereof when the loaded absorbent stream is split. In other words, the first heating step 14 may include the intercooling step 42 transferring heat from the compressed rich CO2gas stream 21 to the first substream 17. As can been seen in Figure 1, the intercooling step 42 may be carried out on the first substream 17 either with or without the first substream 17 being heated by the recuperative heating step 49 and similar, the intercooling step 42 may be carried out on the first substream 17 either with or without heat being transferred to the first substream 17 in the condenser heater exchanger 25.

[0096] The first heating step 14 may also include transfer heat to the loaded absorbent solution 22, or a portion thereof, such as the first substream 17, from a heat source associated with the desorbing step 12 by way of heat from a reboiler 32 of the desorbing step 12. Typically, the reboiler 32 is supplied with a hot fluid, normally steam, to drive the carbon dioxide from the absorbent solution 22 in the desorbing step 12. The hot fluid exiting from the reboiler 32, such as water and saturated stream, may then be used in a recovery heat exchanger 34 to transfer heat to the first substream 17 in a heat recovery step 51. As can be seen in Figure 1 the loaded absorbent solution 22, or the first substream 17 thereof, can be heated in the recovery heat step 51 either with or without heat being transferred to the first substream 17 from the recuperative heat step 19, the condensing heating step 50 or the intercooling step 48.

[0097] As can be seen in Figure 1, a second substream 18 of the loaded absorbent solution 22 may also be heated in the first heating step 14 using a low level temperature heat from a lean absorbent solution 23 discharged from the desorbing step 12 in a second lean / rich heat exchanger 27. The first and second substreams 17 and 18 may then be further heated in the second heating step 15 in a first lean / rich heat exchanger 28 in which higher temperature heat is transferred to the first and second substreams 17 and 18. This may be carried out with the first and second substreams 17 and 18 being held separately from each other with the first and second substreams 17 and 18 being mixed. The heating step 13 may also include heating the first and second substreams 17 and 18 in a third heating step 16 in which heated from an external heat source such as steam in a trim heat exchanger 29 located downstream of the first lean / rich heat exchanger 28. Optionally, the trim heat exchanger 29 and the first and second lean / rich heat exchangers 27 and 28 can be used in combination withpressurisation to prevent volatisation of the loaded absorbent solution 22 in the event ensure that the first, second and third heating step do not exceed the bubble point of the loaded solution. Further details are described herein, for instance in relation to Figure 4. In addition, the process can be combined with a flashing step 20 as described herein, for instance with reference to Figure 5.

[0098] With reference to Figure 2, the heating step 13 includes heating the loaded absorbent solution 22, or at least a portion thereof, before the loaded absorbent solution 22 enters the desorbing step 12. The heating step 13 includes a first heating step 14 in which the loaded absorbent solution (or a substream thereof) is heated to a first temperature which is less than the operating temperature of the desorbing step 12, or at least the operating temperature at the base of the desorbing step 12, and a second heating step 15 in which the loaded absorbent solution 22 is heated from the first temperature to a second temperature. As can be seen, the loaded absorbent solution 22 may be split in a splitter 41 into a first substream 17 and a second substream 18. The first substream 17 is heated in the first heating step 14 to a first temperature by a heat source associated with the desorbing step 12 other than lean absorbent solution 23. Figure 2 is an example in which the heat source associated with the desorbing step 12 is the rich CO2 gas stream 21.Specifically, the first substream 17 of the loaded absorbent solution may be fed to a condenser heat exchanger 25 where heat is transferred from a rich CO2 gas stream 21 to the first substream 17 to heat the first substream 17 to a first temperature. In addition, the gas stream 21 may undergo the compression step 48 to pressurise the gas stream 21 to a suitable pressure for handling the CO2 gas stream 21, such as to liquify carbon dioxide, and suitably to pressure 100 time more than atmospheric pressure. In other words, the heat source associated with the desorbing step 12 can include the first heating step 14 having one or more intercooling steps 42, carried out in the intercooler exchangers 43, that transfers heat from the compressed rich CO2 gas stream 21 to the loaded absorbent stream 22, or the first substream 17 thereof when the loaded absorbent stream is split.

[0099] Pump 26 is used to pump the first substream 17 of the loaded absorbent solution 22 to the condenser heat exchanger 25. The second heating step 15 includes transferring heat from the lean absorbent solution 23 to the first substream 17 in a second lean / rich heat exchanger 27.

[0100] The second substream 18 of the loaded absorbent solution 22 may be heated using heating energy from regenerated lean absorbent in two stages. Initially the second substream 18 is heat using lower temperature heat energy using heat energy from regenerated lean absorbent solution 23 discharged from the desorbing step 12 in a first lean / rich heat exchanger 28. Subsequently, the first and second substreams 17 and 18 of the load absorbent solution 22 are combined in a joiner 44 andheated further using higher temperature heat energy from the regenerated lean absorbent discharged from the desorbing step 12 in the second lean / rich heat exchanger 27. The process and plant 10 may optionally also include the first and second substreams 17 and 18 of the loaded absorbent solution 22 being heated to a required temperature using a steam in a third heating step 16 after the second heating step 15. Specifically, the third heating step 13 may be carried by a trim heater 29 in which heat is transferred from steam to the loaded absorbent solution 22. In addition, a pressure control valve 31 can be used to control the pressure of the loaded absorbent solution 22 in at least the third heating step 16.

[0101] Figure 2 illustrates the condenser heat exchanger 25 located externally of the desorbing step 12. However, it will be appreciated that the condenser heat exchanger 25 may be located within or inside the desorbing step 12.

[0102] It will also be appreciated that the process and plant 10 may not include splitting the loaded absorbent solution 22, in which case all or most of the loaded absorbent solution 22 is fed to the first heating step 14, and thereafter to the second heating step 15. That is say, the loaded absorbent solution 22 may be pressurised by the pump 26 to avoid the bubble point of the loaded solution 22 so that vapourisation of a gas phase from the loaded absorbent solution 22 is minimised. Optionally, the loaded absorbent solution 22 may also be heated in the third heating step 16 after the first and second heating steps 14 and 15.

[0103] Figure 3 illustrates a process 9 and plant 10 that is similar to the process 9 and plant 10 shown in Figure 2 and includes heating the loaded absorbent solution 22, or at least a portion thereof, in a heating step 13 before the loaded absorbent solution 22 enters the desorbing step 12. The loaded absorbent solution 22 is split in a splitter 41 into the first substream 17 and second susbstream 18 and the first substream 17 is heated in the first heating step 14 to a first temperature by a heat source associated with the desorbing step 12 other than lean absorbent solution 22. Figure 3 is an example in which the heat source associated with the desorbing step 12 includes a heating medium 33, such a saturated steam and / or condensation discharged from a reboiler 32 of a desorbing step 12. The heating medium 33 may include at different times, superheated steam, saturated steam, steam and condensate, or condensate. In any event, the heating medium 33 discharged from the reboiler 32 is used to heat the loaded absorbent solution 22 in a first heating step 14 in a recovery heat exchanger 34 to a first temperature. The heating step 13 then includes the first substream 17 being heated in a second heating step 15 that includes transferring heat from the lean absorbent solution 22 to the first substream 17 in second lean / rich heat exchanger 27 to a second temperature.

[0104] In Figure 3, the second substream 18 may also be heated using heating energy from regenerated lean absorbent solution 23 in two stages. Initially the second substream 18 is heated using lower temperature heat energy using heat energy from regenerated lean absorbent solution 23 discharged from the desorbing step 12 in first lean / rich heat exchanger 28. Subsequently, the first and second substreams 17 and 18 of the load absorbent solution 22 are combined in the joiner 44 and heated together in the second lean / rich heat exchanger 27. In addition, the heating step 13 may include the third heating step 16 using a steam as a heating medium in trim heat exchanger 29. Similarly, pressure control valve 31 can be used to control the pressure of the loaded absorbent solution 22 being heated in the second and / or third heating steps 15 and 16.

[0105] In the case of amine based absorbent solutions, the absorbent solution is purely a liquid phase that will not form precipitants. In this situation, the absorbent solution can be loaded to their rich limit with CO2dictated by the vapour pressure exerted by the CO2in the absorbent solution. This results in the absorbing step 11 being operated with liquid to gas ratios (L / G) determined by the liquid solvent chemistry and the gas concentrations in and out of the absorbing step 11.

[0106] The inclusion of CO2in the loaded absorbent solution 22 increases the mass of loaded absorbent solution 22 above that of the lean absorbent solution 23, and as such the heat capacities of the lean and rich will also vary. Figure 7 is a graph illustrating the heat curves of loaded and lean amine absorbent solutions 22 and 23. The heat curves are effectively linear with similar gradients. As a result, heat integration between the lean absorbent solution 23 and the loaded absorbent solution 23 is closely matched.

[0107] However, as the loaded absorbent solution 22 is heated, the vapour pressure of CO2also increases and there may be some vapour evolution. To maintain efficiency of the heating step 13, suppression of vapour evolution may be required. The pressure required to do so is typically relatively small and is only manifested at the exit of the heating step 13 and the pressure of the absorbent solution at the desorber inlet 35.

[0108] When the absorbent solution is a precipitating solvent, such as a carbonate based solvent, the process can be operated under different conditions which provides different opportunities for heat integration. Specifically, precipitating solvents have a lower recirculation flow rate compared to the non-precipitating absorbent solvents which impacts the heat load, heat capacity and solvent vapour pressure characteristics of the loaded absorbent solution. As a result the amount of CO2contained in the loaded stream, in the form of bicarbonate precipitates, is considerably larger than conventional liquid solvents. As can be seen in Figure 8, the gradient of the lean absorbent solution 23 and the loaded absorbent solution 22 curves of a bicarbonate solvent solution are dramaticallydifferent, and the loaded absorbent solution 22 is non-linear and does not follow well with the lean absorbent solution 23 curve from a heat duty perspective.

[0109] Another difference between precipitating and non-precipitating absorbent solutions is in the loading and the vapour pressures produced at various temperatures across the temperature ranges in the absorber stage 11 through to the desorber inlet 35 for the loaded absorbent solution 22 of the desorbing step 12 / desorber stage 47.

[0110] The temperature of the loaded absorbent solution 22 at the desorber inlet 35 is typically maximised to a close approach between the temperature at that the desorber inlet 35 and the temperature at the bottom of the desorbing step 12 / desorber stage 47. For example, the process may include controlling the temperature of the heating step 13, including the first and second heating steps 14 and 15, and the optionally the third heating step 16 if present, so that the temperature of the loaded absorbent solution 22 fed into the desorbing step 12 via inlet 35 is within 40 Deg C of the temperature at the bottom of the desorbing step 12, and suitably within 30 Deg C, and suitably within 20 Deg C, and event more suitably within 15 Deg C, and still even more suitably within 10 Deg C. That is to say, for example, to operate with a temperature differential of approximately 10 Deg C. This maximises heat recovery while minimising heat exchange area in the first and second lean / rich exchanger 28 and 27. Moreover, it will be appreciated that the desorbing step 12 may operate over a temperature range of 100 to 140C, where the bottom of the desorbing step stage 12 will have a higher operating temperature than the top of the desorbing step 12.

[0111] Differences exist between non-precipitating and precipitating absorbent solutions of various types in this regard and Tables 1 and 2 below are presented to exemplify these differences. Table 1 shows the significant difference in carbon dioxide that can be evolved from highly loaded precipitating systems versus amines when each are operated under their respective typical operating conditions. In the case of non-precipitating absorbent solutions, Table 1 includes MEA at a concentration of 30%wt. As mentioned above, the concentration of the MEA solution may range from 20 to 40wt%, and suitably approximately 30wt%. The loading of the loaded absorbent solution may, range from 30% to 50%. As MEA and other amine base absorbents tend to degrade at high temperatures and allowing for a 10 Deg C difference between the desorber inlet 35 and the temperature at the bottom of the desorbing step 12 may, for example, be approximately 120 Deg C. As such the desorbing step 12 may be operated predominantly at temperature ranging from 90 to 105 Deg C. Operating temperatures of 115 and 125 Deg C result in higher degradation of the amine absorbent and therefore a temperature of 110 Deg C is considered upstream of any valve leading into the desorber. Moreover, by operating the desorbing step 12 / desorber 47 at pressures ofapproximately 180kPa, flashing of the amine loaded absorbent solution at the desorber inlet will be suppressed or minimal. The table shows the relative amounts of CO2flashed at the top of the desorber.

[0112] In precipitating systems higher concentrations, loadings and temperatures can be tolerated and hence for a concentration of 45 % carbonate at 80% loading and a temperature of 125 Deg C upstream of the valve entering the desorbing step 12 / desorber stage 47 are used for comparison. The desorbing step 12 / desorber stage 47 pressure is maintained in the Table 1 example at 180 kPa for comparative purposes, thus resulting in significant flashing occurring alongside the pressure drop (with minor temperature drops evident). The resulting flash vapour at the top of the desorbing step 12 / desorber stage 47 is both of a higher concentration of CO2(54% v 38%) and of much higher quantity (20 kg CO2 / t solvent v 5.7 kg CO2 / t solvent) for the precipitating carbonate versus the amine. The larger CO2evolution rates are greater for precipitating systems even when the larger circulation rates for amines (approximately twice) are factored in, demonstrating the benefits of this process 9. Table 2 shows the best currently available data on the bubble point pressure for each absorbent solution, at different concentration, loadings and temperatures taken from both internal models and open literature sources as noted. The bubble point pressure indicates the pressure required to suppress vapour formation in kPa absolute. It also includes the bubble point pressure at selected data points the percentage of CO2in the gas phase at those conditions is provided in brackets.Table 1: Potassium carbonate vs MEA solvent flash at typical stripper entry operating conditions, (results from an ASPEN simulation)Table 2: Solvent bubble point pressures (Ptotin kPa) and flash vapour composition (mol % CO2)for potassium carbonate vs MEA solventa. Xu, Q. and G. Rochelle 2011. Total pressure and C02solubility at high temperatures in aqueous amines. Energy Procedia 4:117-124 b. KC8 Capture internal thermodynamic modelling of potassium carbonate / potassium bicarbonate / water ternary system c. Zhang, S., X. Ye and Y. Lu 2014. Development of a Potassium Carbonate-Based Absorption Process with Crystallization-Enabled High-Pressure Stripping for C02 Capture: Vapor-Liquid Equilibrium Behavior and C02 Stripping Performance of Carbonate / Bicarbonate Aqueous Systems. Energy Procedia 63:665-75.

[0113] In the case of non-precipitating absorbent solutions, Table 1 includes MEA at a concentration of 30%wt. As mentioned above, the concentration of the solution may range from 20 to 40wt%, and suitably approximately 30wt%. The loading of the loaded absorbent solution may, for example, range from 30% to 80%. As MEA and other amine base absorbents tend to degrade at high temperatures and allowing for a 10 Deg C difference between the desorber inlet 35 and the temperature at the bottom of the desorbing step 12 may, for example, be approximately 120 Deg C. As such the desorbing step 12 may be operated predominantly at temperature ranging from 90 to 110 Deg C. The temperature at the desorber inlet 35 may be operating at temperature of 120 and above, resulting in higher degradation of the amine absorbent and therefore no applicable operating pressures are provided in Table 2 greater than 110 Deg C. Moreover, by operating the desorbing step 12 at pressures of approximately 180kPa, flashing of the amine loaded absorbent solution at the desorber inlet 35 will be suppressed or minimal. In addition, the height of the desorber inlet 35 is typically elevated compared to the second lean / rich heat exchanger 27, namely the second heating step 15, which means that adequate pressure head can be maintained in the second lean / rich heat exchanger 27 to suppress vapour generation therein. As mentioned above, the pressure control valve 31 between the desorber inlet 35 and the second and third heating steps 15 and 16 can be used to control vapour generation suppression. As such, ideally the process includespressure control of the loaded absorbent solution fed to the desorbing step 12 when a nonprecipitating absorbent solution is used.

[0114] In the case of precipitating absorbent solutions, Table 2 shows the details of pressure, temperature and loadings for a carbonate absorbent at a concentration of 40 to 50wt% and with loadings from 50 to 80wt%. However, it would be recognised that different combinations of these parameters would result in different concentrations of carbon dioxide held within the absorbent. For example, as mentioned above, a carbonate absorbent, such as potassium carbonate may have a concentration ranging from 10 to 60 wt%, suitably 20 to 50 wt%, and suitably 30 to 50 wt%. The loadings may also range from 45 to 80% for the different concentrations. The increased loading and concentration for precipitating carbonate systems allow for considerably more carbon dioxide to be absorbed within the loaded solutions, approximately twice that of amines.

[0115] An advantage in using an alkali carbonate absorbent solution is that precipitates of the loaded species can be formed in the loaded absorbent solution 22. In other words, the loaded absorbent solution 22 may be a slurry. In addition, these absorbents have a benefit of not degrading in same manner as amine based absorbents and can therefore be used at higher temperatures.When the temperature of the loaded absorbent solution 22 at the desorber inlet 35 is approximately 120 to 125 Deg C, the temperature at or toward the bottom of the desorbing step 12 is likely to be approximately 130 to 140 Deg C, and the pressure to suppress the vapourisation of absorbent solution at a higher loading of say 75wt% is much higher than for the amine absorbent. As a result, the head of liquid from the heating steps 13, including the first and second heating steps 14 and 15, and at the outlet of the second lean / rich exchanger 27 and the desorber inlet 35 may be, without pressure control, insufficient to suppress vapourisation. Without pressure control there may be vaporisation and pulsing at the desorber inlet 35, in lines to the desorber inlet 35, and in the heating steps 13, including the first, second and third heating steps 14, 15 and 16 causing inefficient heat transfer and flow instabilities that affect operability. The bubble point pressures for practical operating ranges of precipitating carbonate absorbents shown in Table 2 are substantially higher than that of amines. The higher carbon dioxide carrying capacity of the precipitating system operating at a higher temperature means that if suppressed through this work the operability of the process is enhanced. Furthermore, once the loaded stream is let down to the lower desorber pressure considerable carbon dioxide will be evolved and separated at the top of the desorbing step 12 / desorber 47 rather than requiring extra energy input of the reboiler 32 located at the bottom of the desorber. This, in part, provides a pressure swing desorption mechanism than the wholly temperature swing desorption mechanism for traditional post combustion capture applications. This reduces energy usage, improves process economics and represents the benefits of this work. Assuch, ideally the process includes pressure control of the loaded absorbent solution 22 fed to the desorbing step 12 when a precipitating absorbent solution is used.

[0116] In terms of pressure control, Figure 4 is an example of a flow diagram of part of a process and a plant 10 for absorbing an acid gas using an absorbent solution and treating the absorbent solution to suppress vaporisation of the absorbent solution or an absorbed gas from therefrom during the heating step 13.

[0117] The loaded absorbent solution 22 is discharged from the absorbing step 11 (not shown in Figure 4) and the heating step 13 of the process 9 includes preheating the loaded absorbent solution 22 prior to the loaded absorbent solution 22 being conveyed to the desorbing step 12. An improvement being provided by a pressurising step 19 that pressurises the loaded absorbent solution 22 during the heating step 13 to suppress the evolution of gases, including acid gases such as carbon dioxide and water from the loaded absorbent solution 22 during the heating step 13, including the first and second heating steps 14 and 15, and if the present the third heating step 16. This means that heat transferred to the loaded absorbent solution 22 results in a sensible heat change in the loaded absorbent solution 22, and maintains efficiency in the heating step 13.

[0118] It will be appreciated that the pressurisation step 19 may include controlling the pressure of the loaded absorbent solution 22 in the process 9 illustrated in Figures 2 and 3. That is to say, the process 9 and plant 10 in Figures 2 and 3 may include the pressuring step 19 in which the heating step 13 heats the loaded absorbent solution 22, including the first substream 17, using a heating source associated the desorbing step 12 other than the lean absorbent solution 23. As mentioned herein, the heating source associated with the desorbing step 12 may include heat from the rich CO2 gas stream 21 discharge from the desorber step 12 and / or heating medium discharged from the reboiler 32 of the desorbing step 12. Heat from the rich CO2 gas stream 21 may include heat from the gas stream 21 prior to any compression of the gas stream 21 and / or after one or more of the compression stages when the gas stream 21 is subjected to compression. The heating step 13 may also include the second substream 18 of the loaded absorbent solution 22 being heated using a lower temperature level of the lean / regenerated stream 23 in the first lean / rich heat exchanger 28 in Figures 2 and 3. The heating step 13 may also include the third heating step 16 in which the combined first and second substreams 17 and 18, may be heated using the trim heat exchanger 29. The pressurising step 19 may include controlling pressurisation of the loaded absorbent solution 22 in the heating step 13 can include adjusting operating speed of the first and second pumps 26 and 30. Controlling pressurisation of the loaded absorbent solution 22 may also include operation a pressure control valve down stream of the pumps 26 and 30, such as controlling operation ofpressure control valve 31 downstream of the heating step 13. Moreover, the pressurising step 19 can be controlled based on the bubble point pressure of the loaded absorbent solution 22 as described above to achieved in the heating step 10.

[0119] Finally, after the heating step 10 the pressure of the loaded sorbent solution 22 can be released by the pressure control valve 31 prior to the desorbing step 12, or inside the desorbing step 12. In the case of a non-precipitating absorbent solution, the pressure control step may include controlling the pressure to a pressure of approximately 180kPa in the heating step to suppress vapourisation. In the case of the precipitating absorbent solutions, the pressure control step may include controlling the pressure to a pressure of approximately 230 kPa for an absorbent solution having a loading of approximately 60wt% prior to either one or both of the desorbing step 12 or a flashing step 20.

[0120] Figures 5 and 6 are flow diagrams of part of a process 9 and a plant 10 for absorbing an acid gas using an absorbent solution including a flashing step 20 of the loaded absorbent solution 22 prior to being fed to the desorbing step 12.

[0121] The flashing step 20 may optionally be carried out after heating in heating step 13, including the first heating step 14 and the second heating step 15 in Figures 2 and 3. The flash drum 40 is operated at a pressure that is less than the pressure at which the loaded absorbent is fed to the heat step 13. This pressure differential spontaneously volatizes a gas phase, including acid gas such as CO2 from the loaded absorbent to produce a gas phase and a liquid phase rich in absorbed acid gases. Generally speaking, the liquid phase has been cooled by heats of vapourisation of the gas phase.

[0122] It will be appreciated that the bubble point of the loaded absorbent solution 22 being the temperature and pressure at which vapour (carbon dioxide and water) is evolved from the loaded absorbent solution 22 will be a function of several factors, including: the type of absorbent, the concentration of the absorbent in the absorbent solution, and the loading of the absorbent solution. It will be appreciated that the loading of the absorbent solution 22 should reduce as CO2 is volatilised from the absorbent solution 22 in the flashing step 20.

[0123] The bubble point of the loaded absorbent solution 22 in the flashing step 20 may approximate the bubble point of the loaded absorbent solution at the top of the desorbing step 12 / desorber stage 11. However, the bubble point of the loaded absorbent solution in the flashing step may differ from the bubble point of the absorbent solution at the bottom of the desorbing step 12 / desorber stage 47 because the loading of the solution at the bottom of the desorbing step 12 / desorber stage 47 will be, or approximately equal to the loading of the lean absorbent solution, and may be hotter than the absorbent solution at the top of the desorbing step 12 / desorber stage 47.

[0124] In one example, the process 9 and plant 10 shown in Figures 5 and 6 may include the first heating step 14, and the second heating step 15 described with refer to Figures 2 and 3 before the loaded absorbent solution 22 goes to the flashing step 20. In another example, the process 9 and plant 10 shown in Figures 5 and 6 may include only the first heating step 14 in Figures 2 and 3 being carried out on the loaded absorbent solution 22 before being sent to the flashing step 20.Specifically, when the flashing step 20 is incorporated into the process and plant 10 shown in Figures 2 and 3, the first heating step 14 may include heating the loaded absorbent solution 22 using a heating source associated the desorbing step 12 other than the lean absorbent solution 23, such as heat from the rich CO2gas stream 21 discharge from the desorbing step 12 / desorbing stage 47 and / or heating medium discharged from the reboiler 32 of the desorber step 12 / desorber stage 47. The first heating step 14 may also include a loaded absorbent solution 22 being heated using a lower temperature level of the lean / regenerated solution 23 such as the first lean / rich heat exchange 28 in Figures 1 and 2. Following the flashing step 20, the process 10 may include heating the liquid phase to produce a hot loaded absorbent solution that can then be fed to the desorbing step 12 / desorber stage 47 or to a further flashing stage (not illustrated). Heating the liquid phase after the flashing step 20 may be carried by the second and / or third heating steps 15 and 16, namely by the second lean / rich heat exchanger 27 and the trim heat 29 shown in Figures 2 and 3.

[0125] With reference to the Figure 6, the loaded absorbent solution 22 is pumped through the first heating step 14 and pressure controlled in the first heating step 14 to suppress vaporisation using upstream valve 36. Pressure of the gas stream discharged from the flashing step 20 is used to control the pressure of the flashing step 20, which includes operating first downstream pressure valve 37. The liquid phase discharged from the flashing step 20 is drawn by pump 39 and second downstream valve 38 is used to control the pressure of the loaded absorbent solution 22 in the heating step 10 downstream of the flashing step 20 to suppress vaporisation, such as the second heating steps 15 and / or the third heating step 16 described in relation to Figures 2 and 3.

[0126] A possible benefit provided by the flashing step 20 is that the loaded absorbent solution can be heated using heat energy available at different temperatures. Specifically, heat energy available at lower temperatures can be used to heat the liquid phase discharged from the flashing step / drum 20, 40, whereas heat used for heating the loaded absorbent solution 22 before the flashing step / drum 20, 40 must be provided at a higher temperature.

[0127] Although not illustrated in Figures 4 and 5, multiple flash drums 40 can be incorporated in the process and plant 10, in which liquid phases produced in each flashing drum 40 can be heated from a chosen heat source. The gas phase from each flashing step 20 can then be fed to the desorbing step 12, such as a condenser 25 of the desorbing step 12.

[0128] The plant 10 shown in Figures 1 to 3, and the parts thereof shown in Figures 4 to 6 relate to a plant 10 for treating an absorbent solution that is recirculating between an absorber stage 46 and a desorber stage 47. A feed gas 24 containing carbon dioxide and other acid gases enters the bottom of the absorber stage 46 and flows upward therein and an absorbent solution flow in counter current from the top of the absorber stage 46 and a loaded absorbent solution 22 is discharged from the bottom. The desorber stage 47 receives the loaded absorbent solution 22 at the to of the desorber stage 47 and carbon dioxide is desorbed therein so that the desorber stage 47 discharges a lean absorbent solution 23 from the bottom and a rich CO2gas 21 from the top. The plant 10 may include a splitter 41 that splits the loaded absorbent solution 23 into first and second substreams 17 and 18 respectively, although the first and second substreams 17 and 18 do not need to be of equal flows. The splitter 41 when the first and second substreams 17 and 18 are not required.

[0129] The plant 10 also include a first heater 52 for heating at least a portion of the loaded absorbent solution 22, such as the first substream 17, to a first temperature that may be is less than the operating temperature of the desorber stage 47. The first heater 52 can be configured to transfer heat from a heat source of the plant 10 other than the lean absorber solution 23. The plant 10 also includes a second heater 53 for heating the at least portion of the loaded absorbent solution 22 from the first temperature to a higher second temperature. The first heater 52 may include any one or a combination of the following heat exchangers: i) A recuperative heat exchanger 45 that is configured to transfer heat from the feed gas 24 to the loaded absorbent solution 22, such as the first substream 17, prior to the feed gas24 entering the absorber stage 46. ii) A condenser heat exchanger 25 for transfer sensible or latent heat from the rich CO2gas stream 21 discharged from the desorber stage 47 to the loaded absorbent solution 22, such as the first substream 17. Any condensate formed in the condenser heat exchanger25 may be separated from rich CO2gas stream 21. iii) An intercooler heat exchanger 43 and a multi-stage compressor 54 in which the intercooler heat exchanger 43 is configured to transfer heat from the rich CO2gas stream 21, after oneor more of compression stages of the compressor 54, to the loaded absorbent solution 22, such as the first substream 17. The compressor 54 can be operated to liquefy the rich CO2gas stream 21. iv) A recovery heat exchanger 34 and a reboiler 32 in which the reboiler 32 is arranged to receive a first hot fluid such as steam for volatising carbon dioxide from the absorbent solution 22 in the desorber stage 47. A second hot fluid, typically hot water and saturated steam is discharged from the reboiler 32 and supplied to the recovery heat exchanger 34 which is configured for transferring heat from the second hot fluid to the load absorbent solution 22, such as the first substream 17. v) A first lean / rich heat exchanger 28 that is configured to transfer heat from the lean absorbent solution 22 such as the second substream 18.

[0130] The plant 10 may also include a joiner 44 for combining the first and second substreams 17 and 18 back into a single stream of the loaded absorbent solution 22. As can be seen in Figures 1 to 3, the joiner 44 may be located to combine the first and second substreams 17 and 18 after the substreams 17 and 18 have been heated by one or a combination of the heat exchangers of the first heater 52 mentioned in paragraphs i) to v) above.

[0131] The second heater 53 of the plant 10 may include a second lean / rich heat exchanger 27 for transferring heat from the lean absorbent solution 23 discharged from the desorber stage 47 to the loaded absorbent solution 22 after the loaded absorbent solution has been heated in the first heater 52. In addition, the second heater 53 may include a trim heat exchanger 29 that is configured for transferring heat from a hot fluid such as steam to the desorber stage 47 prior to the loaded absorbent solution being fed to the desorber stage 47.

[0132] The plant 10 also include one or more pump 26, 30 for pressurising the first and second substreams 17 and 18 to suppress volatization in the first and second heaters 52 and 53 mentioned above. With reference to Figure 4, the plant 9 this may include a controller for operating the pressure control valve 31 to maintain the required pressure throughout the operation of the first and second heaters 52 and 53, and in particular the trim heat exchanger 29 and the first lean / rich heat exchanger 28 and the second lean / rich heat exchanger 27.

[0133] Figure 5 illustrates a flash drum 40 or flashing vessel that is arranged to receive the loaded absorbent solution after being heated in either one or both of the first heater 52 or after the second heater 53, in which the flash drum 40 discharges a liquid phase and a gas phase. The flash drum 40 may be operated at a pressure such that the vapour pressure of the loaded absorbent solutionapproximates the operating pressure of the desorber stage 47. The liquid phase can be further heated as either one or a combination of the first and / or second substreams 17 and 18 , such in the trim heat exchanger 29.

[0134] Figure 6 schematically illustrates a plant 9 including a combination of pressurising and heating the loaded absorbent solution 22 using first and second pumps 26 and 30 for pressuring the first and second substreams 17 and 18 to a pressure above the operating pressure of the desorber stage 46. That is to say, the pumps 26 and 30 can be operated to pressurise the absorbent solution 22 to a pressure above the bubble point of the heat sources of the plant 9 to enable heat energy available at higher temperatures, that is a temperatures above the bubble point in the desorber 47, to be used in either one or a combination of the firsts and second heaters 52 and 53. The controller can be used to operate the first and second pumps 26 and 30 and control valve 36 upstream of the flash drum 40 and control valve 37 downstream of the flash drum 40. Figure 6 shows that the gas phase discharged from flash drum 40 can be fed to the desorber stage 47 to join the rich CO2 gas 21. The liquid phase discharged from the flash drum 40 can also be further pressurised using pump 39 and heated further in another heater, for example, in the trim heat exchanger 16 that can heat the loaded absorbent solution 22 to a temperature and pressure above the bubble point pressure and temperature of desorber stage 47. Thereby enable further flashing of carbon dioxide from the loaded absorbent solution 22, such as on entering the desorber stage 47. Alternatively, the loaded absorbent solution 22 can be fed directly to the desorber stage 47

[0135] Those skilled in the art of the present invention will appreciate that many variations and modification can be made to the example described herein without departing from the spirit and scope of the present invention.

[0136] For instance, it will be recognised by those skilled in the art that in the case of the examples shown in Figures 1 to 7, the specific steps or items of equipment may in included or excluded. For example, operating pressures may be set to eliminate the need for pumps in certain cases and the requirement for trim heaters may be eliminated through improved heat recovery or different reboiler configurations that may be used. In another example, heating the loaded absorbent solution by receiving heat from the rich CO2 gas discharged from the desorber may be through indirect means as shown in Figures 1 and 2, or through direct contact with the gas stream. Engineering methods to optimise the heat recovery may dictate such process variations.Reference numeral table

Claims

CLAIMS1. A process for treating an absorbent solution, wherein the process includes: a desorbing step that includes desorbing the acid gas from the loaded absorbent solution in at least one desorber stage to regenerate a lean absorbent solution that can be fed to the absorbing step; and a heating step that includes heating the loaded absorbent solution, or at least a portion thereof, before the loaded absorbent solution enters the desorbing step; wherein the heating step includes a first heating step in which the loaded absorbent solution, or a substream thereof, is heated to a first temperature which is less than the operating temperature of the desorber step, and a second heating step in which the loaded absorbent solution is heated from the first temperature to a second temperature, and wherein the second heating step includes transferring heat from the lean absorbent solution, and the first heating step includes transfer heat from a heat source other than the lean absorbent solution.

2. The process according to claim 1, wherein the heat source is heat available from including any one or a combination of: i) heat from a rich gas stream including carbon dioxide discharged from the desorbing step after compression of the rich gas in one or more compression stages; ii) heat from a gas stream containing acid gas including carbon dioxide (fed to an absorbing step); iii) heat from a rich acid gas stream discharged from the desorbing step prior to compression; iv) heat from a heating fluid such as steam that is condensed or partially condensed in the reboiler of the desorbing step.

3. The process according to claims 1, wherein the heat source is associated with the desorbing step other than the lean absorbent solution.

4. The process according to claim 3, wherein the heat source associated with desorbing step is an acid gas discharged from the desorbing step, such that the first heating step includes transferred heat from the acid gas discharged from the desorbing step to the loaded absorbent solution.

5. The process according to claim 3 or 4, wherein heat source associated with desorbing step is a saturated output discharged from a reboiler of the desorbing step, such that the first heating step includes transferring heat from the saturated output of the reboiler to the loaded absorbent solution.

6. The process according to claim 1, wherein the first heating step includes the loaded absorbent solution receiving heat energy from at least one of or a combination of the following heat source associated with the desorbing step: i) an acid gas discharged from the desorbing step, and ii) a saturated steam of a reboiler of the desorbing step.

7. The process according to claim 5 or 6, wherein the saturated output includes a water condensate.

8. The process according to claim 1, wherein the heat source is not directly associated with the desorbing step, namely one or both of: heat from a rich gas stream including carbon dioxide discharged from the desorbing step after compression of the rich gas in one or more compression stages, heat from the acid gas stream fed to the absorbing step.

9. The process according to any one of the preceding claims, wherein the process includes splitting the loaded absorbent solution to provide first and second substreams of the loaded absorbent solution, in which the first substream is heated in the first heating step and the second heating step, and a second substream of the loaded absorbent solution is heated in the second heating step without the first heating step.

10. The process according to claim 9, wherein the second substream is initially heated using heat energy from the regenerated lean absorbent solution and then combined with the first substream after the first substream has been heated in the first heating step.

11. The process according to claim 6, wherein the process includes splitting the loaded absorbent solution to provide first and second substreams of the loaded absorbent solution, in which the first substream is heated in the first heating step by heat being transferred from the acid gas discharged from the desorber, without heat being transferred from the saturated stream.

12. The process according to claim 6, wherein the process includes splitting the loaded absorbent solution to provide first and second substreams of the loaded absorbent solution, in which the first substream is heated in the first heating step by heat being transferred from the saturated stream, without heat being transferred from the acid gas discharged from the desorber.

13. The process according to any one of the preceding claims, wherein the heating step includes a third heating step in which the loaded absorbent solution is heated using steam after the second heating step to a third temperature.

14. The process according to any one of the preceding claims, wherein the process includes a step of pressurising the loaded absorbent solution to suppress the vaporisation of gas from the loaded absorbent solution during the heating step.

15. The process according to claim 14, wherein the step of pressurising the loaded absorbent solution, or the first substream thereof, includes pressurising the loaded absorbent solution to a pressure greater than the operating pressure of the absorbing step and desorbing step.

16. The process according to claim 14 or 15, wherein the step of pressurising the loaded absorbent solution, or the first substream thereof, includes controlling pressurisation based on maintaining the loaded absorbent solution above the bubble point pressure at the maximum temperature of the heating step.

17. The process according to any one of claims 14 to 16, wherein the process includes pressurising the loaded absorbent solution to a pressure from 1 to 8.5 atmospheres for a carbonate absorbent, and suitably to a pressure up to 7.7.

18. The process according to any one of claims 14 to 16, wherein the process includes pressurising the loaded absorbent solution to a pressure from 1 to 2.6 atmospheres for MEA absorbent.

19. The process according to any one of claims 16 to 18, wherein the process includes controlling pressurisation of the loaded solvent solution so that the loaded solvent solution is pressurised to exceed the bubble point pressure of the loaded solvent solution at the second temperature.

20. The process according to any one of the preceding claims, wherein the process includes controlling the temperature of the heating step, including the first and second heating steps and optionally the third heating step, if present, so that the temperature of the loaded absorbent solution fed into the desorbing step is within 40 Deg C of the temperature at the bottom of the desorbing step, and suitably within 30 Deg C, and suitably within 20 Deg C, and event more suitably within 15 Deg C, and still even more suitably within 10 Deg C.

21. The process according to any one of the preceding claims, wherein the loaded absorbent solution fed to the desorbing step has a temperature in the range of 5 to 15 Deg C, and suitably 10Deg C, less than a temperature at or toward the bottom of the desorbing step which is in the range of the 110 to 120 Deg C.

22. The process according to claim 20 or 21, wherein the loaded absorbent solution is a nonprecipitating, such as an amine absorbent.

23. The process according to any one of the preceding claims, wherein the process includes controlling the temperature of the heating step, including the first and second heating steps and optionally the third heating step, if present, so that the temperature of the loaded absorbent solution fed to the desorbing step is approximately 10 to 30 Deg C less, and suitably 15 to 25 Deg C less, and even more suitably 20 Deg C less than the temperature at, or toward, the bottom of the desorbing step is in the range of 130 to 140 Deg C.

24. The process according to claim 23, wherein the absorbent solution is a precipitating absorbent solution, such as a carbonate absorbent.

25. The process according to any of claims 14 to 24, wherein the absorbent solution is a nonprecipitating absorbent MEA solution of 25 to 35 wt% concentration, and suitably 30 wt% concentration, and the loading of the loaded absorbent solution is 42% or greater, and the step of pressurising the loaded absorbent solution includes pressuring the loaded absorbent solution to a pressure of at least 176kPa when heated to 100 Deg C.

26. The process according to any one of claims 14 to 24, wherein the absorbent solution is a precipitating absorbent solution having a concentration of 40 to 50wt% carbonate, and suitably 40 wt%, and the loading of the loaded absorbent solution is 65% or greater, and the step of pressurising the loaded absorbent solution includes pressuring the loaded absorbent solution to a pressure of at least 188kPa when heated to HOC, or to a pressure of at least 300kPa when heated to 125 Deg C, or to a pressure of at least 441kPa when heated to 140 Deg C.

27. The process according to any one of clams 14 to 24, wherein the absorbent solution is a precipitating absorbent having a concentration of 40 to 50wt% carbonate, and suitably 40 wt%, and the loading of the loaded absorbent solution is 80% or greater, and the step of pressurising the loaded absorbent solution includes pressuring the loaded absorbent solution to a pressure of at least 115kPa when heated to a 100 Deg C, or to a pressure of at least 280kPa when heated to 110 Deg C, or a pressure of at least 560kPa when heated to 125 Deg C, or a pressure of at least 841kPa when heated to 140 Deg C.

28. The process according to any one of the preceding claims, wherein the process includes a flashing step that includes flashing the loaded absorbent solution to produce a liquid phase and a gas phase after either one or a combination of the first heating step or after the second heating step.

29. The process according to claim 28, wherein the heating step includes heating the liquid phase from the flashing step prior to the liquid phase entering the desorbing step.

30. The process according to claim 28 or 29, wherein the flashing step is operated at a pressure such that the vapour pressure of the loaded absorbent solution is reduced to the operating pressure of the desorbing step.

31. The process according to claim 29, wherein the loaded absorbent solution is a nonprecipitating MEA absorbent solution of 25 to 35 wt%, and suitably 30wt%, and the loading of the loaded absorbent solution is 42% or greater, the temperature of the loaded absorbent solution is 100 degrees C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step , preferably to a pressure of 1.74 times atmospheric pressure or 176kPa absolute.

32. The process according to claim 29, wherein the loaded absorbent solution is a precipitating absorbent where the concentration is from 40 to 50 wt% carbonate, and suitably 45wt% carbonate, and the loading of the loaded absorbent solution is 65% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step, preferably up to a pressure up to approximately 1.86 times atmospheric pressure or 188kPa absolute.

33. The process according to claim 29, wherein the loaded absorbent solution is a precipitating absorbent where the concentration is from 40 to 50 wt% carbonate, and suitably 45wt% carbonate, and the loading of the loaded absorbent solution is 80% or greater, the temperature of the loaded absorbent solution is 100 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step, at a pressure up to approximately 1.13 times atmospheric pressure or 115kPa absolute.

34. A process for treating an absorbent solution, wherein the process includes: an absorbing step that includes absorbing an acid gas by contacting with the absorbent solution to provide a loaded absorbent solution;a desorbing step that includes desorbing the acid gas from the loaded absorbent solution in the desorbing step to regenerate a lean absorbent solution; a heating step that includes heating the loaded absorbent solution before the loaded absorbent enters the desorbing step; and a pressurising step that includes pressurising the loaded absorbent solution during the heating step to suppress the vaporisation of the acid gas from the loaded absorbent.

35. The process according to claim 34, wherein the step of pressurising the loaded absorbent includes pressurising the loaded absorbent to a pressure greater than the operating pressure of the absorbing step and the desorbing step.

36. The process according to claim 34 or 35, wherein the step of pressurising the loaded absorbent solution includes controlling pressurisation based on maintaining the loaded absorbent solution above the bubble point pressure at a maximum temperature of the heating step.

37. The process according to any one of claims 34 to 36, wherein the process includes controlling the temperature of the heating step so that the temperature of the loaded absorbent solution fed into the desorbing step is within 40 Deg C of the temperature at the bottom of the desorbing step, and suitably within 30 Deg C, and suitably within 20 Deg C, and event more suitably within 15 Deg C, and still even more suitably within 10 Deg C.

38. The process according to any one of claims 34 to 37, wherein the loaded absorbent fed to the desorbing step has a temperature in the range of 5 to 15 Deg C, and suitably 10 Deg C, less than a temperature at or toward the bottom of the desorbing step which is in the range of the 110 to 120 Deg C.

39. The process according to any one of claims 34 to 38, wherein the absorbent solution is a non-precipitating, such as an amine absorbent.

40. The process according to any one of claim 34 to 39, wherein the process includes controlling the temperature of the heating step, including the first and second heating steps and optionally the third heating step, if present, so that the temperature of the loaded absorbent solution fed to the desorbing step is approximately 10 to 30 Deg C less, and suitably 15 to 25 Deg C less, and even more suitably 20 Deg C less than the temperature at, or toward, the bottom of the desorbing step is in the range of 130 to 140 Deg C41. The process according to any one claims 34 to 40, wherein the absorbent solution is a precipitating absorbent solution, such as a carbonate absorbent.

42. The process according to any one of claims 34 to 36, wherein the absorbent solution is a non-precipitating MEA absorbent solution having a concentration in the range of 25 to 35 wt%, and suitably 30wt%, and the loading of the loaded absorbent solution is 42% or greater, and the step of pressurising the loaded absorbent solution includes pressuring the loaded absorbent solution to a pressure of at least 176kPa when heated to 100C.

43. The process according to any one of claims 34 to 41, wherein the absorbent solution is a precipitating absorbent solution where the concentration is 40 to 50 wt% carbonate, and suitably 45wt% carbonate, and the loading of the loaded absorbent solution is 65% or greater, and the step of pressurising the loaded absorbent solution includes pressuring the loaded absorbent solution to a pressure of at least 188kPa when heated to 110 Deg C, or to a pressure of at least 300kPa when heated to 125Deg C, or to a pressure of at least 441kPa when heated to 140 Deg C.

44. The process according to any one of claims 34 to 41, wherein the absorbent solution is a precipitating absorbent solution where the concentration is 40 to 50 wt% carbonate, and suitably 45wt% carbonate, and the loading of the loaded absorbent solution is 80% or greater, and the step of pressurising the loaded absorbent solution includes pressuring the loaded absorbent solution to a pressure of at least 115kPa when heated to a 100 Deg C, or to a pressure of at least 280kPa when heated to 110 Deg C, or a pressure of at least 546kPa when heated to 125 Deg C, or a pressure of at least 841kPa when heated to 140 Deg C.

45. A process for treating an absorbent solution, wherein the process includes: an absorbing step that includes absorbing an acid gas by contacting with the absorbent solution to provide a loaded absorbent solution; a desorbing step that includes desorbing the acid gas from the loaded absorbent solution to regenerate a lean absorbent solution; a heating step that includes heating the loaded absorbent solution before the loaded absorbent enters the desorber stage; and a flashing step that includes flashing the loaded absorbent solution to produce a liquid phase and a gas phase; wherein heating step includes heating the liquid phase from the flash step to produce a hot loaded absorbent solution that can be fed to the desorbed.

46. The process according to claim 45, wherein the flashing step is carried out after the heating step.

47. The process according to claim 46, wherein the heating step includes heating the liquid phase from the flashing step prior to enters the liquid phase entering the desorbing step.

48. The process according to claim any one of claims 45 to 47, wherein the flashing step is operated at a pressure such that the vapour pressure of the loaded absorbent solution is reduced to the operating pressure of the desorbing step.

49. The process according to any one of claims 45 to 48, wherein the absorbent solution is a non-precipitating MEA absorbent of 25 to 35 wt% concentration, and suitably 30wt% concentration, and the loading of the loaded absorbent solution is 42% or greater, the temperature of the absorbent solution is 100 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step.

50. The process according to any one of claims 45 to 48, wherein the absorbent solution is a precipitating absorbent where the concentration is 40 to 50 wt% carbonate, and suitably 45wt % carbonate, and the loading of the loaded absorbent solution is 65% or greater, the temperature of the absorbent solution is 110 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step.

51. The process according to any one of claims 45 to 48, wherein the absorbent solution is a precipitating absorbent where the concentration is 40 to 50 wt% carbonate, and suitably 45wt % carbonate, and the loading of the loaded absorbent solution is 80% or greater, the temperature of the absorbent solution is 100 Deg C or greater, and the flashing step reduces the pressure of the loaded absorbent solution from a pressure above the bubble point pressure to an operating pressure of the desorbing step.

52. A plant of treating an absorbent solution that is recirculating between an absorber stage and a desorber stage, wherein the plant includes: the absorber stage in which the absorbent solution contacts an acid gas feed to provide a loaded absorbent solution discharged from the absorber stage and a product gas lean in acid gas; the desorber stage receives the loaded absorbent solution and in which acid gas is desorbed to provide a lean absorbent and a rich acid gas product, in which the desorber stage has an operating temperature profile;a first heater in which at least a portion of the loaded absorbent solution is heated to a first temperature which is less than the operating temperature of the desorber stage; a second heater in which the at least portion of the loaded absorbent solution is heated from the first temperature to a second temperature, wherein the second heater is configured to transfer heat from the lean absorbent solution to the loaded absorbent solution; and wherein the first heater is configured to transfer heat from a heat source of the plant other than the lean absorber solution.

53. The plant according to claim 52, wherein the first heater is configured to transfer heat to the at least a portion of the loaded absorbent solution by any one or a combination of: a recuperative heat exchanger that is configured to transfer heat from the feed gas to the loaded absorbent solution, such as the first substream; a condenser heat exchanger that is configured to transfer sensible and / or latent heat from the rich acid gas stream discharged from the desorber stage to the loaded absorbent solution, such as the first substream rich acid gas discharged from the disorber stage after one or more compression stage; an intercooler heat exchanger that is configured to transfer heat from the rich acid gas stream, after one or more of compression stages to the loaded absorbent solution, such as the first substream; and a recovery heat exchanger that is configured for transferring heat from a hot fluid discharged from a reboiler of the disrober stage, to the load absorbent solution, such as the first substream saturated output of a reboiler of the desorber stage.

54. The plant according to claim 52 or 53, wherein the first heater is configured to transfer heat to the at least a portion of the loaded absorbent solution from a hot stream discharged from the desorber stage other than the lean absorbent solution.

55. The plant according to any one of claims 52 to 54, wherein the first heater is configured to transfer heat to the at least portion of the loaded absorbent solution by at least one of the following: a condenser heat exchanger that is configured to transfer sensible and / or latent heat from the rich acid gas stream discharged from the desorber stage to the loaded absorbent solution, such as the first substream, andthe recovery heat exchanger that is configured for transferring heat from a hot fluid discharged from a reboiler of a desorber stage to the load absorbent solution, such as the first substream.

56. The plant according to any one of claims 52 to 55, wherein the plant includes a splitter that splits the loaded absorbent stream in the first and second substreams in which the first substream is heated in the first heater and the second heater, and a second substream of the loaded absorbent is heated in the second heater without being heated in the first heater.

57. The plant according to claim 56, wherein the second substream is initially heated using heat energy from the regenerated lean absorbent solution and the plant include a combiner in which the second substream is combined with the first substream after the first substream has been heated in the first heater.

58. The plant according to any one of claims 52 to 54, wherein the plant includes a splitter that splits the loaded absorbent stream into the first and second substreams in which the first substream is heated in the first heater by heat transferred from the acid gas discharged from the desorber, without heat being transferred from the saturated output of a reboiler.

59. The plant according to any one of claims 52 to 54, wherein the plant includes a splitter that splits the loaded absorbent stream into the first and second substreams in which the first substream is heated in the first heater by heat being transferred from the saturated stream, without heat being transferred from an acid gas discharged from the desorber stage.

60. The plant according to any one of claims 52 to 59, wherein the plant includes a third heater in which the loaded absorbent is heated using steam after the second heating step.

61. The plant according to any one of claim 52 to 60, wherein the plant includes a pump that pressurises the loaded absorbent solution to suppress the vaporisation of gas from the loaded absorbent in the first and second heaters.

62. The plant according to claim 61, wherein the plant includes a controller that controls the pressure of the loaded absorbent solution based on maintaining the loaded absorbent solution above the bubble point pressure at a maximum temperature of the loaded absorbent solution.

63. The plant according to any one of claims 52 to 62, wherein the plant includes a flash vessel that is arranged to receive the loaded absorbent solution after being heated in either the first heater or after the second heaters, the flashing vessel discharges a liquid phase and a gas phase.

64. The plant according to any one of claims 42 to 63, wherein the flash vessel is operated at a pressure such that the vapour pressure of the loaded absorbent solution approximates the operating pressure of the desorbing step.

65. A plant of treating an absorbent solution that is recirculating between an absorber stage and a desorber stage, wherein the plant includes: the absorber stage in which the absorbent solution contacts an acid gas feed to provide a loaded absorbent solution discharged from the absorber stage and a product gas lean in acid gas; the desorber stage receives the loaded absorbent solution and in which acid gas is desorbed to provide a lean absorbent and a rich acid gas product, in which the desorber stage has an operating temperature profile; a heater for heating the loaded absorbent solution before the loaded absorbent enters the desorber stage; and a pump for pressurising the loaded absorbent solution during the heating step to suppress the vaporisation of the acid gas from the loaded absorbent. wherein the pump pressurises the loaded absorbent to a pressure greater than the operating pressure of the absorber stage and desorber stage.

66. The plant according to claim 65, wherein plant includes a controller that controls pressurisation of the loaded absorbent based on maintaining the solution above the bubble point pressure of the maximum temperature of the heating step.

67. A plant of treating an absorbent solution that is recirculating between an absorber stage and a desorber stage, wherein the plant includes: the absorber stage in which the absorbent solution contacts an acid gas feed to provide a loaded absorbent solution discharged from the absorber stage and a product gas lean in acid gas; the desorber stage receives the loaded absorbent solution and in which acid gas is desorbed to provide a lean absorbent and a rich acid gas product, in which the desorber stage has an operating temperature profile;flashing vessel into which the loaded absorbent solution is fed to flash the loaded absorbent solution to produce a liquid phase and a gas phase that are discharged from the flash vessel; a heater that heats the liquid phase from the flash vessel to produce a hot loaded absorbent solution that can be fed to the desorber stage.

68. The plant according to claim 67, wherein the plant includes: a first preliminary heater for heating at least a portion of the loaded absorbent solution to a first temperature which is less than the operating temperature of the desorber stage; a second heater in which the at least portion of the loaded absorbent solution is heated from the first temperature to a second temperature, wherein the second heater is configured to transfer heat from the lean absorbent solution to the loaded absorbent solution; and wherein the first heater is configured to transfer heat from a heat source of the plant other than the lean absorber solution.

69. The plant according to claim 70 or 71, wherein the flashing vessel is operated at a pressure such that the vapour pressure of the loaded absorbent solution in the flashing vessel is reduced to the operating pressure of the desorber stage.

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