Scrubber apparatus for removing carbon dioxide and controlled atmosphere operating method

Abstract

The present disclosure relates to an activated carbon scrubber apparatus 300 for carbon dioxide (CO2) removal from a controlled environment and a method of operating the same. The scrubber apparatus is configured to switch between an adsorption configuration in which the scrubber apparatus is configured to provide a CO2-rich gas from a controlled environment to a sorbent bed (302) containing activated carbon for CO2 adsorption and return a treated gas to the controlled environment, and a regeneration configuration in which the scrubber apparatus is configured to provide a regeneration gas from outside the controlled environment to the sorbent bed to desorb CO2 and regenerate the activated carbon and discharge a CO2-rich gas to outside the controlled environment. The method includes operating the scrubber apparatus alternately in the adsorption and regeneration configurations in a plurality of cycles, wherein the scrubber apparatus is operated at a cycle frequency between 4 and 30 cycles per hour. A heater (303) is controlled to heat the sorbent bed in the regeneration configuration.

Description

TECHNICAL FIELD

[0001] The present invention relates to an activated carbon scrubber apparatus for removing carbon dioxide (CO2) from a controlled environment, and a method of operating a scrubber apparatus for controlled atmosphere applications. In particular, although not exclusively, the invention relates to such a scrubber apparatus and method for use with transport refrigeration systems, such as for refrigerated trucks and sea containers. BACKGROUND

[0002] Controlled atmosphere is a term used in the art to indicate control over the gas mixture within an enclosed space. Controlled atmosphere is of particular relevance to the transport of products, such as fruit and vegetables. For example, it can be desirable to control the relative proportions of carbon dioxide, oxygen and other constituent gases within an environment in which a product store is stored. The term "controlled atmosphere" is used herein to indicate the class of products, i.e. products configured to control the gas mixture in an enclosed space, whereas the expression "controlled environment" is used to denote the gas volume within such an enclosed space itself.

[0003] It is known to use regenerative scrubber apparatuses to remove carbon dioxide from controlled atmospheres. Typical adsorbents for use with such systems include zeolites (aluminosilicate minerals), such as zeolite 13x.

[0004] Activated carbon is known to be provided in gas filtration and control systems, in particular for the removal of volatile organic compounds. However, due to its relatively low adsorption efficiency and high temperature regeneration process, no practical solution has been considered for providing regenerative adsorption. SUMMARY

[0005] According to a first aspect of the present disclosure, there is provided a method of operating an activated carbon scrubber apparatus to remove carbon dioxide (CO2) from a controlled environment;

[0006] wherein the scrubber apparatus is configured to switch between an adsorption configuration and a regeneration configuration,

[0007] the scrubber apparatus is configured, in the adsorption configuration, to provide a CO2-rich gas to an adsorbent bed from the controlled environment, and to return treated gas to the controlled environment, wherein the adsorbent bed comprises activated carbon for CO2 adsorption;

[0008] the scrubber apparatus is configured, in the regeneration configuration, to provide a regeneration gas to the adsorbent bed from outside the controlled environment to desorb CO2 and regenerate the activated carbon, and to discharge CO2-rich gas to outside the controlled environment;

[0009] the method comprises:

[0010] operating the scrubber apparatus in the adsorption configuration and the regeneration configuration alternately in a plurality of cycles, each cycle comprising a single period in the adsorption configuration and a single period in the regeneration configuration;

[0011] wherein the scrubber apparatus is operated at a cycle frequency of between 4 and 30 cycles per hour;

[0012] controlling a heater to heat the adsorbent bed in the regeneration configuration.

[0013] The adsorbent bed can be heated by indirect heating of the adsorbent bed by heating a regeneration gas upstream of the adsorbent bed. The adsorbent bed can be heated directly by transferring heat from a heat transfer element to the adsorbent bed. For example, the heat transfer element can be a heating element of an electric heater or can be a heat exchange element of a heat pump.

[0014] The adsorbent bed can comprise predominantly activated carbon. For example, the adsorbent bed can be not less than 70 wt.% activated carbon, or not less than 80 wt.%, or not less than 90 wt.%, or not less than 95 wt.%, or not less than 99 wt.% of the adsorbent bed can be activated carbon. The adsorbent bed can consist of activated carbon.

[0015] The cycle frequency can be between 10 and 20 cycles per hour.

[0016] For each cycle, the scrubber apparatus can be operated at a cycle ratio of between 1 : 1 and 5: 1, the cycle ratio being defined as the ratio between the period in the adsorption configuration and the period in the regeneration configuration. The cycle ratio can be between 2: 1 and 4: 1.

[0017] For each cycle, the scrubber apparatus can be operated in the regeneration configuration for at least 45 seconds, for example 1 minute or more.

[0018] During each cycle, the adsorbent bed can be heated to a maximum average temperature of no more than 75 °C, for example no more than 50 °C, no more than 40 °C, or no more than 30 °C. The maximum average temperature can be no less than 15 °C, for example no less than 20 °C.

[0019] The expression "maximum average temperature" relates to the highest average temperature to which the adsorbent bed is heated. Thus, the maximum average temperature is not a temperature limit above which the bed cannot be heated, but is the actual highest average temperature to which the adsorbent bed is heated during a cycle (and heating is performed during operation in the regeneration configuration such that the highest average temperature is typically reached at the end of the period in the regeneration configuration).

[0020] During each cycle, the heating can be performed so that the discharged CO2-rich gas has a maximum temperature of no more than 75°C (e.g., no more than 50°C, no more than 40°C, or no more than 30°C) when discharged from the adsorbent bed. During each cycle, the heating can be performed so that the discharged CO2-rich gas has a maximum temperature of no less than 15°C (e.g., no less than 20°C) when discharged from the adsorbent bed.

[0021] The heater can be controlled to transfer heat to the adsorbent bed during the regeneration configuration at a maximum specific heat transfer rate of no more than 5 kW / kg (e.g., no more than 3 kW / kg) relative to the weight of the adsorbent material in the adsorbent bed.

[0022] The scrubber apparatus can be operated so that the volumetric flow rate of gas through the adsorbent bed during operation in the regeneration configuration is higher than the volumetric flow rate of gas through the adsorbent bed during operation in the adsorption configuration.

[0023] The volumetric flow rate during operation in the regeneration configuration can be at least 50% greater than the volumetric flow rate during operation in the adsorption configuration.

[0024] The adsorbent bed can be configured so that the average flow velocity through the adsorbent bed is less than 0.5 m / s in the adsorption configuration and greater than 0.5 m / s in the regeneration configuration.

[0025] The cycle ratio can be variable. The controller can cause the cycle ratio to vary between a relatively lower ratio and a relatively higher ratio in response to determining a low power condition and a high power condition, respectively, of a controlled atmosphere system in which the scrubber apparatus is installed. The low power condition can correspond to the controlled atmosphere system being supplied with power from a local power source without access to shore power, and the high power condition corresponds to the controlled atmosphere system being supplied with power from a shore power source.

[0026] The scrubber apparatus can be installed in a controlled atmosphere system, such as a transport refrigeration system for a marine shipping container, a trailer, or a truck.

[0027] The controlled atmosphere system can be operated to regulate a level of carbon dioxide within a controlled environment. The regulation can include determining a requirement to reduce the level of carbon dioxide to a threshold or below. In response to determining the requirement to reduce the level of carbon dioxide, the scrubber apparatus can be operated (i.e., controlled to operate) in a CO2 reduction mode to remove carbon dioxide from the controlled environment until the carbon dioxide is reduced to the threshold or below. During operation in the CO2 reduction mode, the scrubber apparatus can be alternately operated (i.e., controlled to operate) in the adsorption configuration and the regeneration configuration.

[0028] Accordingly, despite operating in the CO2 reduction mode, the scrubber apparatus is periodically operated such that the scrubber apparatus does not perform adsorption of carbon dioxide (i.e. in a regeneration configuration). If there are multiple scrubber apparatuses, each of the scrubber apparatuses can be operated in the regeneration configuration simultaneously during operation in the CO2 reduction mode such that no scrubber apparatus performs adsorption despite the scrubber apparatuses operating in the CO2 reduction mode.

[0029] The adjustment can comprise determining that the level of carbon dioxide is reduced to a threshold or below. The determination can comprise determining that the level of carbon dioxide is within a target range. In response to the determination, the scrubber apparatus can be placed in a standby mode in which the scrubber apparatus is deactivated or operated (i.e. controlled to operate) at a relatively lower CO2 removal rate than in the CO2 reduction mode. The scrubber apparatus can be deactivated by turning off the heater and / or the blower. When deactivated, the scrubber can be placed in the regeneration configuration. There can be passive (i.e. non-forced) flow of regeneration gas to regenerate the adsorbent bed even when deactivated and in the regeneration configuration.

[0030] According to a second aspect, there is disclosed a scrubber apparatus for removing carbon dioxide from a controlled environment, the scrubber apparatus comprising:

[0031] an adsorbent bed comprising activated carbon for CO2 adsorption;

[0032] a gas exchange mechanism configured to switch between an adsorption configuration and a regeneration configuration,

[0033] in the adsorption configuration, the adsorbent bed is in fluid communication with a controlled environment inlet to receive CO2 rich gas from the controlled environment for adsorption, and in the adsorption configuration, the adsorbent bed is in fluid communication with a controlled environment outlet to return treated gas to the controlled environment;

[0034] in the regeneration configuration, the adsorbent bed is in fluid communication with a regeneration gas inlet to receive regeneration gas from outside of the controlled environment for desorption, and in the regeneration configuration, the adsorbent bed is in fluid communication with an external outlet to discharge CO2 rich gas to outside of the controlled environment;

[0035] a heater configured to heat the adsorbent bed in the regeneration configuration;

[0036] a controller configured to cause the scrubber apparatus to operate alternately in the adsorption configuration and the regeneration configuration in a plurality of cycles, each cycle comprising a single period in the adsorption configuration and a single period in the regeneration configuration;

[0037] wherein the controller is configured to cause the scrubber apparatus to operate at a cycle frequency of between 4 and 30 cycles per hour, for example between 10 and 20 cycles per hour;

[0038] wherein the controller is configured to control the heater to heat the adsorbent bed in the regeneration configuration.

[0039] The scrubber apparatus can comprise one or more blowers for directing gas through the adsorbent bed. The controller can be configured to control the one or more blowers such that the volumetric flow rate of gas through the adsorbent bed during operation in the regeneration configuration is higher than the volumetric flow rate of gas through the adsorbent bed during operation in the adsorption configuration. The volumetric flow rate during operation in the regeneration configuration can be at least 50% greater than the volumetric flow rate during operation in the adsorption configuration.

[0040] The heater can have a maximum specific heat transfer rate for heating the adsorbent bed of no more than 5 kW / kg relative to the weight of adsorbent material in the adsorbent bed, for example no more than 3 kW / kg.

[0041] The controller can be configured to cause the scrubber apparatus to operate at a cycle ratio of between 1 : 1 and 5: 1, the cycle ratio being defined as the ratio between the period in the adsorption configuration and the period in the regeneration configuration, for example between 2: 1 and 4: 1.

[0042] According to a third aspect, there is disclosed a controlled atmosphere system, for example a transport refrigeration system, comprising a scrubber apparatus according to the second aspect.

[0043] The controlled atmosphere system can be configured to regulate the level of carbon dioxide within a controlled environment, and can be configured to determine a requirement to reduce the level of carbon dioxide to a threshold or below. The controlled atmosphere system can be configured to operate the scrubber apparatus in a CO2 reduction mode in response to determining the requirement to reduce the level of carbon dioxide. The scrubber apparatus can be configured to operate alternately in the adsorption configuration and the regeneration configuration during operation in the CO2 reduction mode.

[0044] The disclosure extends to any combination of the features of the methods and apparatus described above in relation to the first to third aspects of the disclosure and elsewhere herein, other than where such combinations are mutually exclusive. BRIEF DESCRIPTION OF DRAWINGS

[0045] The application will now be described by way of example with reference to the accompanying drawings in which:

[0046] Figure 1is a partial schematic cross-sectional side view of an exemplary refrigerated transport container including a scrubber apparatus;

[0047] Figure 2 is a simplified cross-sectional view of an exemplary scrubber apparatus;

[0048] Figure 3 is a simplified cross-sectional view of another exemplary scrubber apparatus;

[0049] Figures 4 to 6 is a graph of test results for carbon dioxide removal at different frequencies of a cyclic scrubber operation; and

[0050] Figure 7 is a flowchart of an exemplary method of operating a scrubber apparatus. DETAILED DESCRIPTION

[0051] The present invention relates to the operation of a scrubber apparatus for CO2 removal, wherein the adsorbent material of the scrubber apparatus is activated carbon.

[0052] The present invention will be described by way of example only with reference to examples for use in a refrigeration module of a refrigerated transport system, in particular a refrigerated transport container. However, it will be appreciated that the present disclosure is primarily directed to a scrubber apparatus and a method of operating the same, which is equally applicable to other types of installations and environments.

[0053] Figure 1 A transport container 100 is schematically illustrated including an outer wall 102 separating an interior controlled environment of interior gas from an exterior atmosphere of exterior gas. By way of example, cargo 104 is disposed in a cargo space 105 of the container, such as loaded with fresh fruits and vegetables, and the controlled environment is a volume of gas filling the enclosed cargo space 105. Figure 1 is a partial view showing a first end of a container including a refrigeration module 200. For simplicity of the drawing, an end of the container and cargo 104 facing away from the first end of the container is not shown, as indicated by continuation line 106.

[0054] The refrigeration module 200 is installed in the transport container to provide a refrigerated transport container. The refrigeration module 200 is typically disposed at one end of the container adjacent to the wall 102 of the transport container 100.

[0055] The refrigeration module 200 includes a structural frame 202 that, when installed in the container 100, is located within the container and is open so as to allow the return air 108 flow to be directed to components of the refrigeration module 200 (as will be described below) and to deliver the supply air 110 flow to the cargo space.

[0056] The refrigeration module 200 includes an outer wall 204 which can serve as the outer wall of the transport container 100 separating the interior environment of the container from the outside atmosphere.

[0057] The exemplary refrigeration module 200 includes a refrigeration circuit including an evaporator 206 disposed on the interior of the outer wall 204 and a condenser 208 disposed on the exterior of the outer wall 204. The refrigeration circuit can include a compressor, an expansion valve, and flow lines connecting the components of the circuit, as is known in the art, the evaporator is configured such that, in use, heat is transferred from the interior atmosphere to the circulating refrigerant, and the condenser is configured to transfer heat from the refrigerant to the outside atmosphere.

[0058] In the present example, an evaporator fan 210 is disposed to direct the return air 108 flow through the evaporator 206 to be cooled, and then as the supply air 110 to the cargo space. In this particular example, the refrigeration module is configured such that the return air flows downward through the refrigeration module, and the evaporator fan 210 is disposed upstream, and thus generally above the evaporator 206. However, in other examples, the evaporator fan 210 can be disposed upstream or downstream relative to the evaporator, and the specific orientation and direction of flow through the evaporator fan 210 can be different.

[0059] The refrigeration module further includes a carbon dioxide removal apparatus 300 ("scrubber apparatus"), a gas sensor 224 for monitoring parameters related to the composition of the interior atmosphere, and a controller 226. As Figure 1 shown, in the present example, the controller 226 is disposed on the exterior of the outer wall 204 of the refrigeration module, while the carbon dioxide removal apparatus 300 and the gas sensor 224 are disposed on the interior of the outer wall 204.

[0060] In this particular example, the carbon dioxide removal apparatus 300 and the gas sensor 224 are disposed between the evaporator fan 210 and the evaporator 206, such that the evaporator fan 210 is configured to direct the return air 108 flow toward the carbon dioxide removal apparatus and past the sensor 224. However, other relative positions can be employed in other examples, and the return air flow can be conveyed through the carbon dioxide removal apparatus by an integrated blower of the apparatus 300 or by a blower upstream or downstream of the apparatus.

[0061] As Figure 1 shown, the refrigeration module 200 further includes a fresh air vent 212 which is configured to be selectively opened and closed to allow a flow of fresh air into the cargo space 105, as is known in the art.

[0062] In a variant of the above example, additional equipment for controlling the gas mixture in the controlled environment can be provided, whether as part of the refrigeration module 200 or another module to be installed in the container 100. Controlled atmosphere systems can generally be classified as passive and active. Passive systems tend to rely on the natural adsorption of constituent gases at high concentrations by a sorbent or passage through a selectively permeable membrane or molecular sieve. Active systems generally involve a system that controls the composition of an inlet gas stream that displaces (i.e., flushes out) the internal gas within the controlled environment to adjust the overall composition of the controlled environment. For example, some active systems use a compressor and a selectively permeable membrane or molecular sieve in order to generate, adjust the composition of an inlet gas stream to provide a relatively reduced amount of oxygen and a relatively increased amount of one or more other constituent gases, such as nitrogen. It is contemplated that the scrubber equipment described herein, whether incorporated in a refrigeration module or some other installation of a transport refrigeration system, can be used in conjunction with all manner of passive and active systems, fresh air vents, and the like.

[0063] Figure 2 An example configuration of a carbon dioxide removal equipment 300 (also referred to herein as a scrubber equipment) is shown. In this example, the scrubber equipment includes a sorbent bed 302 containing activated carbon. In this particular example, the sorbent bed 302 consists of activated carbon. In other examples, the sorbent bed can predominantly contain activated carbon, for example the sorbent bed can be not less than 70 wt.% activated carbon, or not less than 80 wt.%, or not less than 90 wt.%, or not less than 95 wt.%, or not less than 99 wt.% of the sorbent bed is activated carbon.

[0064] The specific form of activated carbon provided can vary, such that the present disclosure is equally applicable to sorbent beds that differ from one another in terms of particle size, surface area to weight ratio, porosity, and the like. An example of a suitable type of activated carbon is granular activated carbon available from Silcarbon Aktivkohle GmbH, Germany under the trade name Silcon SIL-40-3s, which has a characteristic diameter of 3 mm.

[0065] In the present example, the sorbent bed 302 is provided with a heater 303 having heating coils extending through the sorbent bed 302 for direct heating. In this particular example, the heater 303 is configured to transfer heat to the sorbent bed at a rate of up to 2 kW per kg of sorbent material, although in other examples the heater 303 can be configured to transfer more or less heat energy. Other forms of heating are contemplated in the present disclosure, which will be described below with reference to FIG. 4. Figure 3 A brief description is made.

[0066] In this example, the adsorbent bed 302 is disposed within a conduit 304 having an inlet portion and an outlet portion connected to an inlet switching manifold 306 and an outlet switching manifold 308, respectively. The inlet switching manifold 306 is configured to selectively provide gas to the inlet portion of the conduit 304 from one of two ports, including an inlet interior gas port 318 configured to receive a flow of interior gas from the controlled environment for removal of carbon dioxide at the adsorbent bed, and an exterior gas inlet port 320 configured to receive a flow of regeneration gas (e.g., an exterior gas such as ambient air) from outside of the controlled environment for desorption of carbon dioxide from the adsorbent bed. The outlet switching manifold 308 is configured to selectively provide gas from the outlet portion of the conduit 304 to one of two ports, including an outlet interior gas port 338 configured to return treated gas from the adsorbent bed to the controlled environment, and an outlet exterior gas port 340 configured to vent CO2-rich gas to outside of the controlled environment. A blower 305, such as a fan, is disposed within the conduit 304 to controllably convey gas along the conduit 304. In this example, the blower 305 is disposed upstream of the adsorbent bed 302, but in other examples one or more blowers 305 can be disposed at any suitable location for driving gas through the conduit 304.

[0067] Each of the switching manifolds 306, 308 includes appropriate means of gas valves for switching between a plurality of positions, which are exclusively connected in fluid communication the conduit 304 with a respective one of the gas ports 318, 320, 338, 340.

[0068] The scrubber apparatus further includes a controller 360, which in this example is operably coupled to each of the switching manifolds 306, 308, to the heater 303, and to the blower 305.

[0069] The switching manifolds 306, 308 together form a gas exchange mechanism configured to switch between an adsorption configuration and a regeneration configuration. In the adsorption configuration, the adsorbent bed 302 is in fluid communication with the controlled environment inlet (i.e. the inlet internal gas port 318) to receive CO2-rich gas from the controlled environment for adsorption, and the adsorbent bed 302 is in fluid communication with the controlled environment outlet (i.e. the outlet internal gas port 338) to return treated gas to the controlled environment. Fluid communication with the inlet external gas port 338 and the outlet external gas port 340 can be prevented. In the regeneration configuration, the adsorbent bed 302 is in fluid communication with the regeneration gas inlet (i.e. the inlet external gas port 320) to receive regeneration gas from outside of the controlled environment for desorption, and the adsorbent bed 302 is in fluid communication with the external outlet (i.e. the outlet external gas port 340) to discharge CO2-rich gas to outside of the controlled environment. Fluid communication with the inlet internal gas port 318 and the outlet internal gas port 320 can be prevented.

[0070] The controller 360 is configured to control the gas exchange mechanism to switch between the adsorption configuration and the regeneration configuration. The controller 360 is further configured to cause the heater 303 to heat the adsorbent bed 302 when in the regeneration configuration. The controller 360 is further configured to control the blower 305, for example to turn the blower 305 on and off. The controller 306 is operable to vary the speed of the blower 305, and thereby vary the speed (or volumetric flow rate) of the flow through the conduit 304, as will be described below. In this example, the scrubber apparatus is configured for one-way flow through the adsorbent bed 302, since there is an inlet manifold at one end and an outlet manifold at the other end. However, it will be appreciated that the scrubber apparatus can have any suitable configuration, and indeed can be configured to cause gas to pass through the adsorbent bed in different directions when operating in the adsorption configuration and the regeneration configuration, respectively.

[0071] In this example, the controller 360 is further configured to monitor signals received from the temperature sensor 362 for monitoring the operating temperature of the scrubber apparatus 300. The temperature sensor 362 can be provided at any suitable location, depending on what quantity is to be measured and what form of control, if any, is to be implemented. It is envisaged that the heater 303 can be controlled by the controller 360 based on the operating temperature, for example to ensure that the operating temperature is within an operating range during operation in the regeneration configuration.

[0072] As is known in the art, a relevant factor in terms of regenerative performance is the temperature of the adsorbent bed (i.e. the temperature of the adsorbent material within the bed). As the regenerative gas passes through the adsorbent bed, the temperature of the gas as it is discharged from the adsorbent bed can be equal to the temperature of the adsorbent bed or at least a function of the temperature of the adsorbent bed (e.g. the average temperature of the adsorbent material within the adsorbent bed).

[0073] In this example, the operating temperature corresponding to the temperature of the adsorbent bed is monitored, in particular by providing a temperature sensor 362 within conduit 304 downstream of the adsorbent bed. In other examples, one or more temperature sensors can be located at other positions for monitoring the temperature of the adsorbent bed, for example one or more can be distributed within the adsorbent bed 302 to enable the average temperature of the adsorbent bed to be estimated.

[0074] As Figure 2 shown, the controller 360 of the scrubber apparatus 300 is operably coupled to the controller 226 of the chiller module 200, such that the controller 226 of the chiller module 200 can instruct the controller 360 of the scrubber apparatus 300 to change the operating mode of said scrubber apparatus 300, as will be described in further detail below.

[0075] In brief summary, Figure 3 A scrubber apparatus 300’ is shown, which has a similar configuration to the scrubber apparatus 300 described above with reference to Figure 2 the difference being only in the form and arrangement of the heater. In this example, the heater 303’ is provided upstream of the adsorbent bed 302, so as to heat the gas stream provided to the adsorbent bed 302 in the regenerative configuration. Thus, in this embodiment, the adsorbent bed 302 is indirectly heated by heating the gas (which then heats the adsorbent bed). The following description applies equally to the scrubber apparatus 300 and the scrubber apparatus 300’ described above. Figure 2 Figure 3 For the sake of brevity of the following description, reference can be made to the “scrubber apparatus 300”, but it is to be considered that this applies equally to either example.

[0076] Before discussing the operation of the scrubber apparatus 300 and the associated advantages, a brief description of the prior art with respect to the use of activated carbon for the removal of CO2 is provided.

[0077] Whilst activated carbon is a known adsorbent material for adsorbing CO2, activated carbon has not been considered a practical choice for a regenerative adsorption system for a controlled atmosphere.

[0078] ​In particular, published technical information from activated carbon manufacturers indicates that activated carbon has a low adsorption efficiency (about 3% by weight - i.e. the amount of carbon dioxide is equal to 3% of the weight of the activated carbon). Further, this published technical information indicates that activated carbon will be regenerated at high temperatures (e.g. 250°C or higher). Further still, this published technical information indicates that for CO2 removal applications, a type of activated carbon known as impregnated activated carbon should be used (i.e. impregnated with additional chemicals to enhance the adsorption of specific gases and molecules). However, this impregnated activated carbon is understood to be single use and is not suitable for regeneration.

[0079] An example of this technical information on activated carbon has been published by Cabot Corporation of the United States. An information sheet on reactivation services for activated carbon indicates thermal reactivation temperatures in excess of 900°C. A copy of the information sheet published prior to the priority date of the present application is available on the “Internet Archive” (“Wayback Machine”) at: web.archive.org / web / 20200421162405 / https: / / www.cabotcorp.com / solutions / products-plus / activated-carbon / reactivation-services

[0080] A further example of this technical information has been published by TROX KS Filter a.s of the Czech Republic in reference to an activated carbon reactivation process at temperatures up to 830° for 30 minutes. The reactivation process is described as having considerable quality advantages compared to other technologies (specific reference is made to other technologies such as thermal desorption in the range of 250 to 350°C) and states that lower temperatures do not lead to the restoration of the activated surface. A copy of the information sheet published prior to the priority date of the present application is available on the “Internet Archive” (“Wayback Machine”) at: web.archive.org / web / 20200421162554 / https: / / www.ksklimaservice.cz / en / reactivation-of-activated-carbon-servicing-and-disposal-of-filters

[0081] Further, the activated carbon entry on the public encyclopedia Wikipedia states that the most common regeneration technique employed in industrial processes is thermal reactivation, which generally follows three steps including (i) drying of the adsorbent at about 105 °C; (ii) high temperature desorption and decomposition (500 to 900 °C) under inert atmosphere; and (iii) residual organic gasification at high temperature (800 °C) by non-oxidizing gases (steam or carbon dioxide). A copy of the information disclosed in the encyclopedia prior to the priority date of the present application is available on the “Internet Archive” (“Wayback Machine”) at: web.archive.org / web / 20200421162750 / https: / / en.wikipedia.org / wiki / Activated_carbon

[0082] Accordingly, activated carbon is typically only found in actual controlled atmosphere systems for purposes other than CO2 removal, such as removal of volatile organic compounds (VOCs) or other gases and particles for which activated carbon has been published to have relatively high removal efficiency. While it has been previously suggested to use activated carbon in a regenerative scrubber for removal of CO2, these suggestions envision continuous use in adsorption mode until CO2 is below a threshold before switching to regeneration mode. Given the low adsorption efficiency of activated carbon, it is believed that these suggestions, if implemented in practice, would require a relatively large adsorbent bed in order to provide sufficient CO2 removal capacity.

[0083] However, the inventors have surprisingly discovered that activated carbon can be used for efficient removal of carbon dioxide if a scrubber apparatus is alternately operated between an adsorption configuration and a regeneration configuration at a relatively fast cycling rate. This enables the size of the activated carbon adsorbent bed to be reduced and opens up the use of activated carbon as a practical option for removal of CO2.

[0084] Some of the terminology used in the following description includes the terms “cycle”, “cycle frequency” and “cycle ratio”. A cycle includes a single period of operating the scrubber apparatus in the adsorption configuration and a single period of operating the scrubber apparatus in the regeneration configuration. The term “cycle frequency” relates to the number of cycles in a period of time, where the cycle frequency is defined in cycles / hour in the present disclosure. The term “cycle ratio” relates to the ratio of the period in the adsorption configuration and the period in the regeneration configuration for each cycle.

[0085] The inventors have surprisingly found that by operating the scrubber apparatus within a short cycle, the CO2 removal efficiency per cycle is reduced (as expected), but the total CO2 removal efficiency per unit of time can be increased. In particular, it is believed that activated carbon adsorbent has a relatively high initial rate of adsorbing carbon dioxide, which rapidly decreases.

[0086] The inventors have surprisingly found that an adsorbent bed comprising activated carbon can in fact be regenerated sufficiently well at relatively low temperatures and during relatively short regeneration periods to repeatedly provide a relatively high initial adsorption rate (as obtainable after regeneration). This is said to be surprising because of the conventional wisdom about activated carbon that regeneration is at relatively high temperatures, i.e. repeated regeneration within a short time frame (i.e. at a relatively high cycle frequency) is clearly an impractical process. This is at least because adsorption is conventionally believed to occur at relatively low temperatures (known as Le-Chatelier's principle), while regeneration occurs at relatively high temperatures (e.g. above 250°C, as discussed above), such that there are inherent practical difficulties in heating and cooling to switch between these operating conditions within a short time, and of course there would be high energy costs associated with doing so.

[0087] The inventors have conducted tests showing that with only moderate heating during regeneration conditions, sufficient regeneration occurs within a relatively short regeneration period such that the scrubber apparatus can be operated at a relatively high frequency to repeatedly obtain a relatively high initial rate of carbon dioxide adsorption. In particular, the inventors have found that sufficient regeneration occurs even when the adsorbent bed is heated to no more than 30°C, although there is improved performance at higher temperatures, e.g. up to 40°C, up to 50°C or up to 75°C.

[0088] The inventors have tested CO2 removal while varying a number of factors, including:

[0089] cycle frequency; and

[0090] cycle ratio.

[0091] Figure 4 is a graph showing carbon dioxide removal per cycle versus cycle frequency. As can be seen, the amount of carbon dioxide removed per cycle generally decreases as the cycle frequency (e.g. per hour) increases.

[0092] However, the inventors have found that at a suitable cycle ratio, the carbon dioxide removal rate per unit of time actually increases as the cycle frequency increases, as Figure 5The graph shows the removal rate (grams / kilogram of adsorbent / hour) versus the cycle frequency. With the benefit of hindsight having analysed the data, it is considered that, within the range of frequency cycling, the benefit of returning more frequently to the relatively higher initial adsorption relationship outweighs the disadvantage of adsorbing less carbon dioxide per cycle and regenerating the activated carbon more frequently. Figure 5 The incremental benefit of indicating further increases in cycle frequency decreases with increasing cycle frequency, such that there is an optimum cycle frequency for the peak removal rate. Figure 5 A particularly advantageous range between 4 and 30 cycles per hour is shown. Depending on the operating conditions and configuration, the advantageous range can extend to higher cycle frequencies, for example up to 50 cycles per hour.

[0093] This trend is observed whilst testing at what is considered to be a reasonable range of cycle ratios (i.e. ratios between 5:1 and 1 :1, adsorb:regen).

[0094] However, the inventors deduce that, for any given cycle frequency, there will be an optimum cycle ratio. In particular, if the extreme conditions of high cycle ratio and low cycle ratio are considered, it is clear that a very high cycle ratio will not provide an improvement over long term operation in the adsorption configuration alone, because there is insufficient time to usefully regenerate the activated carbon in the regeneration configuration. Conversely, it is clear that a very low cycle ratio means that the activated carbon can be well regenerated, but there is insufficient time allocated to actually perform adsorption in an efficient manner.

[0095] Accordingly, the inventors have determined that the cycle ratio can be optimised to find, for a given cycle frequency, the cycle ratio which provides the highest amount of carbon dioxide removal per unit of time (i.e. over a number of consecutive cycles). Testing does show that, for the same cycle frequency, two different cycle ratios can achieve the same CO2 removal rate per unit of time, and it is considered that the two such cycle ratios will lie either side of the optimum cycle ratio at this cycle frequency, and that the plot of removal rate (in units of time) against cycle ratio can take the shape of a bell curve.

[0096] Since the heater is active during operation in the regeneration configuration, the energy consumption is directly proportional to the amount of time spent in the regeneration configuration, and is therefore largely a function of the cycle ratio, and independent of the cycle frequency (particularly if the heating is applied at a constant rate). However, the total energy consumption is influenced to some extent by the cycle frequency, due to the energy consumed in operating the gas exchange mechanism to move between the adsorption and regeneration configurations.

[0097] The inventors have found that, when designing practical implementations of scrubber apparatus, the CO2 removal rate is one of many factors to be considered. It is believed that high cycle frequencies would fatigue the scrubber apparatus itself, since high frequency operation of any means for switching between the adsorption configuration and the regeneration configuration can lead to early component failure. Thus, from the perspective of component resilience and system reliability, lower cycle frequencies are advantageous.

[0098] Further, in recognition that each regeneration period begins with a transition period in which the temperature is gradually ramped up towards the temperature for effective regeneration, it is believed that higher cycle frequencies tend to spend more cumulative time in the transition period. Thus, it is believed that as cycle frequency is increased, the optimal cycle ratio tends to decrease (i.e. spend more time in the regeneration configuration).

[0099] Thus, the inventors have determined that, while higher cycle rates tend to provide better CO2 removal rates (to a point), higher cycle rates are associated with reduced component lifetime (or, alternatively, higher manufacturing costs for resilience) and higher energy consumption.

[0100] Figure 6 is a bi-axial plot of CO2 removal rate per unit time and energy consumption versus cycle frequency. This again illustrates the trend of removal rate with increasing cycle frequency, but also illustrates that the actual choice of cycle ratio (i.e. where one is believed to be approaching the optimum for operation at this cycle frequency) tends to increase towards higher ranges of cycle frequency.

[0101] By selecting a moderate cycle frequency, a particularly good balance between CO2 removal efficiency, component wear / reliability and energy consumption can be achieved, where the advantages associated with improved CO2 removal performance (per unit time) have been achieved to a point, but are diminishing. For example, considering Figures 4 to 6 In light of the data presented in

[0102] It will be appreciated that the particular frequency that can be selected will depend on many factors. For example, various trade-offs can be influenced by the power rating of the heater (where a low power heater naturally requires longer to heat the adsorbent bed to the target temperature), the temperature of the gas received from the controlled environment, the CO2 concentration of the gas, the humidity and other factors. However, Figures 4 to 6The data presented in the above table show that the cyclical operation is in principle advantageous and that operation in the range of 4 to 30 cycles per hour offers significant advantages over continuous operation in the conventional adsorption configuration of the art (i.e. where regeneration only occurs after the CO2removal target has been reached and adsorption is stopped). For the reasons set out above, the range of 10 to 20 cycles per hour is considered to be particularly advantageous.

[0103] The inventors have found that it can be advantageous to adjust the velocity of the gas stream through the adsorbent bed depending on whether the scrubber apparatus is operating in the adsorption configuration or the regeneration configuration. Without wishing to be bound by theory, it is believed that the relatively lower velocity during adsorption improves the adsorption performance because the residence time of the molecules in the adsorbent bed is greater and there is less inertia for the carbon dioxide molecules to settle and remain on the adsorbent. Conversely, in regeneration, it is believed that the higher velocity of the regeneration gas can provide increased energy to help entrain the carbon dioxide molecules. Further, when a heater heats the regeneration gas in order to heat the adsorbent bed, the higher velocity facilitates heat transfer to the adsorbent bed. For example, tests have shown improved cycle efficiency (i.e. carbon dioxide removal rate per hour) under conditions where the average velocity through the adsorbent bed during adsorption is less than 0.5 m / s and the average velocity through the adsorbent bed during regeneration is greater than 0.5 m / s. The optimum flow rate for each configuration is believed to depend on the specific configuration of the adsorbent bed and any cartridge in which the adsorbent bed is provided.

[0104] The above has discussed the principles of high frequency operation, the following description relates to further reference to Figure 7 The flowchart operation of an example of a scrubber apparatus 300 as described above, wherein the scrubber apparatus 300 is as part of a refrigeration module 200 as described above.

[0105] Figure 7 The example method 700 relates to a method in which a scrubber apparatus is controlled to operate in a CO2reduction mode or in a standby mode. In the CO2reduction mode, CO2is removed from a controlled environment at a relatively high rate to achieve an overall reduction in the CO2level (i.e. concentration) in the controlled environment, whereas in the standby mode, the CO2level in the controlled environment can be within an acceptable target range such that the scrubber apparatus is either deactivated or operated at a relatively low CO2removal rate. For example, if cargo such as fruit and vegetable produce is breathing and thereby generating CO2at a relatively high rate, operation at a relatively low CO2removal rate can not result in an overall reduction in the CO2level in the controlled environment. As will be described below, other methods of operating a scrubber apparatus are envisaged within the present disclosure.

[0106] In block 702, the scrubber apparatus is controlled to operate in a CO2reduction mode or in a standby mode. Figure 7), the controller 360 of the scrubber device operates in standby mode when instructed by the controller 226 of the refrigeration module 200, which monitors the CO2level using the sensor 224. In this particular example, when in standby mode, the gas exchange mechanism (provided by the manifolds 306, 308) is in the regeneration configuration, the heater 303 is deactivated, and the blower 305 is deactivated. Thus, in standby mode, the scrubber device 300 effectively consumes no power, but remains open to receive regenerating gas, thereby passively regenerating at low temperature. In other examples, the operation in standby mode can be different, as will be discussed in further detail at the end of the specification.

[0107] In block 704, the controller 226 of the refrigeration module 200 determines that the requirement for the CO2level in the controlled environment to be reduced, e.g. has determined that the CO2level has exceeded a threshold. For example, the controller 226 can monitor the CO2level in the controlled environment in order to maintain the CO2level within a target range, or target a setpoint concentration. In other examples, the controller can be the controller 360 of the scrubber device, which performs such control, and can be coupled to a sensor (e.g. the sensor 224) for monitoring the CO2level in the controlled environment.

[0108] In block 706, in response to determining that the CO2level is to be reduced, the controller 226 instructs the controller 360 of the scrubber device to operate in a CO2reduction mode until the CO2level is reduced to the target or below. The threshold CO2level at which the CO2reduction mode is initiated can be higher than the target CO2level, such that in use, the CO2level is allowed to gradually rise before being periodically reduced. This control method can reduce the amount of time required for the scrubber device to operate in the CO2reduction mode, while still allowing relatively good control to maintain the CO2level within the target range. As mentioned above, in other examples, the controller can be the controller 360 of the scrubber device which determines to initiate the CO2reduction mode.

[0109] In blocks 708 and 710, the controller 360 alternately operates the scrubber device in the adsorption configuration (block 708) and the regeneration configuration (block 710), while controlling the heater 303 in a plurality of cycles to heat the adsorbent bed 302 in the regeneration configuration until it is determined that the CO2target is met (block 712).

[0110] In this particular example, the controller 360 causes the scrubber device to operate at a cycle frequency of 15 cycles per hour, and at a cycle ratio of 3: 1. This corresponds to 3 minutes of operation in the adsorption configuration, followed by 1 minute of operation in the regeneration configuration.

[0111] The controller 360 causes the blower 305 to operate at a higher speed in the regeneration configuration than in the adsorption configuration, such that the volumetric flow rate of gas through the adsorbent bed 302 during operation in the regeneration configuration is higher (e.g., 50% higher) than the volumetric flow rate of gas through the adsorbent bed 302 during operation in the adsorption configuration. In other examples, the speed can be equal between the two configurations.

[0112] The scrubber apparatus is configured such that the adsorbent bed 302 is exposed to the respective gas flow (i.e., gas from the controlled environment and gas from outside the controlled environment, depending on the configuration) at approximately the same total pressure (sum of static and dynamic pressure) as the source location of the respective gas. For example, when the regeneration gas is ambient air sourced from outside the controlled environment, the scrubber apparatus is configured to provide the regeneration gas to the adsorbent bed at approximately atmospheric pressure. Any increase in total pressure due to operation of the blower 205 can be minimal, such as 5 to 50 Pa, in order to allow it to be driven through the adsorbent bed. Similarly, the scrubber apparatus is configured to provide gas from the controlled environment to the adsorbent bed at approximately the same pressure as the controlled environment within the cargo space, and any increase in total pressure due to operation of the blower 205 is minimal, such as 5 to 50 Pa. In other words, the scrubber apparatus 300 is operated such that the blower 205 drives the respective gas flow through the adsorbent bed 302 with a minimal pressure drop through the adsorbent bed, e.g., no more than 100 Pa, e.g., no more than 50 Pa.

[0113] In this particular example, the heater 303 is controlled to apply heat at a maximum rated power of 2 kW / kg of adsorbent material throughout the regeneration configuration, such that the temperature of the adsorbent material is raised during operation of the regeneration configuration. Heaters with greater or lesser specific power can be used. In some examples, the heater can initially be run at high power in order to bring the adsorbent bed up to a target temperature, and then the power can be reduced once the target temperature is reached. Feedback can be provided using the monitored operating temperature (as described above) to control the heater.

[0114] In this example, the adsorbent material reaches a maximum average temperature of approximately 30°C during operation in the regeneration configuration in each cycle. Similarly, the regeneration gas is heated to a maximum discharge temperature of approximately 30°C when passing through the adsorbent bed that is directly heated Figure 2 ), or transfers heat to the adsorbent bed Figure 3), such that the regenerating gas exits with a maximum discharge temperature of about 30°C. In other examples, these temperatures can be higher or lower. The inventors believe that a suitable maximum temperature (e.g., the highest average temperature of the adsorbent bed, or the highest average temperature of the regenerating gas as it discharges through the adsorbent bed) that allows for sufficient regeneration while minimizing energy consumption is no more than 75°C, such as no more than 50°C, no more than 40°C, or no more than 30°C; and no less than 15°C, such as no less than 20°C. The controller can be configured to ensure that the temperature reaches a value within a range defined between any permutation of these limits, and likewise the present disclosure contemplates methods of operation in which the temperature lies within a range defined between any permutation of these limits.

[0115] Once the controller 226 determines that the CO2 target is satisfied, the controller 226 instructs the controller 360 of the scrubber apparatus 300 to return to the standby mode (block 712). As discussed above, this control can be performed by the controller 360 of the scrubber apparatus 300 itself.

[0116] It is contemplated that the period of operation in the CO2 reduction mode extends over multiple cycles. For example, the scrubber apparatus can be operated in the CO2 reduction mode for at least 5 cycles, at least 10 cycles, or at least 20 cycles before the CO2 reduction mode ends. The controller 360 can be configured to operate in the CO2 reduction mode for a predetermined minimum number of cycles (e.g., at least 5 cycles, at least 10 cycles, or at least 20 cycles). Thus, unlike conventional modes of operating a regenerative scrubber, the scrubber apparatus is alternately operated in the adsorption configuration and the regeneration configuration while continuously seeking to reduce the overall CO2 level in the controlled environment.

[0117] As discussed above, other modes of operation are contemplated in the present disclosure. In a variation of the above example, the scrubber apparatus can be operated in the standby mode but cycled (i.e., alternated between the adsorption configuration and the regeneration configuration) in a manner that achieves a relatively lower CO2 removal rate per unit time and optionally with lower power consumption. For example, the operating parameters of the scrubber apparatus can be adjusted such as (i) increasing the cycle ratio (thereby decreasing the proportion of time spent in the regeneration configuration with the heater on); (ii) decreasing the heater power, or disabling the heater; and / or (iii) decreasing the speed of the blower 305, or disabling the blower.

[0118] Further, in some examples, the scrubber apparatus can be continuously operated in the cycled mode of operation, rather than being continuously operated in a mode that alternates between the CO2 reduction mode and the standby mode. For example, the scrubber apparatus can be controlled to achieve a variable CO2 removal rate by adjusting one or more control parameters, such as selected from the group consisting of:

[0119] An operating parameter of the blower, for example, the power supplied to the blower during adsorption and / or regeneration, or the rotational speed of the fan during adsorption and / or regeneration;

[0120] The cycle ratio;

[0121] The cycle frequency;

[0122] An operating parameter of the heater, such as the heater power, or a target operating temperature as described elsewhere herein.

[0123] In response to monitoring of the variable CO2 level within the controlled environment, a variable CO2 removal rate can be requested. For example, the controller (e.g., the controller of the refrigeration module or the controller of the scrubber apparatus) can monitor the respiration rate of the cargo and request a variable CO2 removal rate accordingly, or can request a variable CO2 removal rate in accordance with any suitable control strategy for controlling the CO2 level in the controlled environment.

[0124] As described above, in order to reduce power consumption, the scrubber apparatus can be operated at a cycle ratio that is higher than the theoretically optimal cycle ratio (CO2 removal rate) for the selected cycle frequency. However, the controller can be configured to switch from such a non-optimal cycle ratio to a relatively lower cycle ratio (e.g., close to or at the optimal cycle ratio) when it is determined (e.g., by the controller or another controller of the corresponding installation) that mains electricity (i.e., utility power) is available instead of a local power source (such as a generator or a battery).

Claims

1. A method of operating an activated carbon scrubber apparatus of a transport refrigeration system to remove carbon dioxide (CO2) from a controlled environment; wherein the scrubber apparatus is configured to switch between an adsorption configuration and a regeneration configuration, the scrubber apparatus is configured to provide, in the adsorption configuration, CO2-rich gas to a sorbent bed from the controlled environment, the sorbent bed comprising activated carbon for adsorption of CO2, and to return treated gas to the controlled environment, the scrubber apparatus is configured to provide, in the regeneration configuration, regeneration gas to the sorbent bed from outside the controlled environment to desorb CO2 and regenerate the activated carbon, and to discharge CO2-rich gas to outside the controlled environment; the method comprises: operating the scrubber apparatus alternately in the adsorption configuration and the regeneration configuration in a plurality of cycles, each cycle comprising a single period in the adsorption configuration and a single period in the regeneration configuration; wherein the scrubber apparatus is operated at a cycle frequency of between 4 and 30 cycles per hour; controlling a heater to heat the sorbent bed in the regeneration configuration.

2. The method of claim 1, wherein, the cycle frequency is between 10 and 20 cycles per hour.

3. The method of claim 1 or 2, wherein, for each cycle, the scrubber apparatus is operated at a cycle ratio of between 1 : 1 and 5: 1, the cycle ratio being defined as the ratio between the period in the adsorption configuration and the period in the regeneration configuration.

4. The method of any preceding claim, wherein, during each cycle, the sorbent bed is heated to a maximum average temperature of no more than 75°C.

5. The method of any preceding claim, wherein, during each cycle, the heating is performed such that the discharged CO2-rich gas has a maximum temperature of no more than 75°C when discharged from the sorbent bed.

6. The method of any preceding claim, wherein, the heater is controlled to transfer heat to the sorbent bed during the regeneration configuration at a maximum specific heat transfer rate of no more than 5 kW / kg relative to the weight of sorbent material in the sorbent bed.

7. The method of any preceding claim, wherein, the scrubber apparatus is operated such that the volumetric flow rate of gas through the sorbent bed during operation in the regeneration configuration is higher than the volumetric flow rate of gas through the sorbent bed during operation in the adsorption configuration; optionally, wherein the volumetric flow rate during operation in the regeneration configuration is at least 50% greater than the volumetric flow rate during operation in the adsorption configuration.

8. The method of any preceding claim, wherein, the scrubber apparatus of the transport refrigeration system is for a marine shipping container, a trailer, or a truck.

9. The method of claim 8, wherein, the transport refrigeration system is operated to regulate a level of carbon dioxide within a controlled environment; wherein the regulation comprises determining a requirement to reduce the level of carbon dioxide to a threshold value or below; wherein, in response to determining the requirement to reduce the level of carbon dioxide, the scrubber apparatus is operated in a CO2 reduction mode to remove carbon dioxide from the controlled environment until the carbon dioxide is reduced to the threshold value or below; and wherein, during operation in the CO2 reduction mode, the scrubber apparatus is operated alternately in the adsorption configuration and the regeneration configuration.

10. The method of claim 3, wherein the cycle ratio is between 2: 1 and 4:

1.

11. The method of claim 4, wherein, the maximum average temperature is no more than 50°C.

12. The method of claim 4, wherein, the maximum average temperature is no more than 40°C.

13. The method of claim 4, wherein, the maximum average temperature is no more than 30°C.

14. The method of claim 4, wherein, the maximum average temperature is no less than 15°C.

15. The method of claim 4, wherein, the maximum average temperature is no less than 20°C.

16. The method of claim 5, wherein, the maximum temperature is no more than 50°C.

17. The method of claim 5, wherein, the maximum temperature is no more than 40°C.

18. The method of claim 5, wherein, the maximum temperature is no more than 30°C.

19. The method of claim 5, wherein, during each cycle, the heating is performed such that the discharged CO2-rich gas has a maximum temperature of no less than 15°C when discharged from the adsorbent bed.

20. The method of claim 5, wherein, during each cycle, the heating is performed such that the discharged CO2-rich gas has a maximum temperature of no less than 20°C when discharged from the adsorbent bed.

21. The method of claim 6, wherein, the maximum specific heat conductivity is no more than 3 kW / kg.

22. A transport refrigeration system comprising a scrubber apparatus for removing carbon dioxide from a controlled environment, the scrubber apparatus comprising: an adsorbent bed comprising activated carbon for CO2 adsorption; a gas exchange mechanism configured to switch between an adsorption configuration and a regeneration configuration, in the adsorption configuration, the adsorbent bed is in fluid communication with a controlled environment inlet to receive CO2-rich gas from the controlled environment for adsorption, and in the adsorption configuration, the adsorbent bed is in fluid communication with a controlled environment outlet to return treated gas to the controlled environment; in the regeneration configuration, the adsorbent bed is in fluid communication with a regeneration gas inlet to receive regeneration gas from outside of the controlled environment for desorption, and in the regeneration configuration, the adsorbent bed is in fluid communication with an outside outlet to discharge CO2-rich gas to outside of the controlled environment; a heater configured to heat the adsorbent bed in the regeneration configuration; a controller configured to cause the scrubber apparatus to operate alternately in the adsorption configuration and the regeneration configuration in a plurality of cycles, each cycle comprising a single period in the adsorption configuration and a single period in the regeneration configuration; wherein the controller is configured to cause the scrubber apparatus to operate at a cycle frequency of between 4 and 30 cycles per hour; wherein the controller is configured to control the heater to heat the adsorbent bed in the regeneration configuration.

23. The transport refrigeration system of claim 22, wherein, the cycle frequency is between 10 and 20 cycles per hour.

24. The transport refrigeration system of claim 22 or 23, comprising one or more blowers for directing gas through the adsorbent bed, wherein the controller is configured to control the one or more blowers such that a volumetric flow rate of gas through the adsorbent bed during operation in the regeneration configuration is higher than a volumetric flow rate of gas through the adsorbent bed during operation in the adsorption configuration; optionally, wherein the volumetric flow rate during operation in the regeneration configuration is at least 50% greater than the volumetric flow rate during operation in the adsorption configuration.

25. The transport refrigeration system of any of claims 22-24, wherein, The heater has a maximum specific heat conduction rate for heating the adsorbent bed of no more than 5 kW / kg relative to the weight of adsorbent material in the adsorbent bed.

26. The transport refrigeration system of any of claims 22-25, wherein, The controller is configured to cause the scrubber apparatus to operate at a cycle ratio between 1:1 and 5:1, the cycle ratio being defined as the ratio between the period in the adsorption configuration and the period in the regeneration configuration.

27. The transport refrigeration system of claim 25, wherein, The maximum specific heat conduction rate for heating the adsorbent bed is no more than 3 kW / kg.

28. The transport refrigeration system of claim 26, wherein, The cycle ratio is between 2:1 and 4:

1.

29. The transport refrigeration system of claim 28, wherein, The transport refrigeration system is configured to regulate a level of carbon dioxide within a controlled environment, and is configured to determine a requirement to reduce the level of carbon dioxide to a threshold or below; wherein the transport refrigeration system is configured to operate the scrubber apparatus in a CO2 reduction mode in response to determining the requirement to reduce the level of carbon dioxide; and wherein the scrubber apparatus is configured to alternately operate in the adsorption configuration and the regeneration configuration during operation in the CO2 reduction mode.

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