Method and system for processing organic waste

Abstract

The method can include circulating the organic waste in liquid form sequentially along a liquid passage of a heat exchanger and into an evaporator; the evaporator evaporating the organic waste from the liquid form to a gaseous form; circulating the organic waste in the gaseous form along a gas passage of the heat exchanger, including transferring heat from the organic waste in gaseous form to the organic waste in liquid form, thereby condensing water contained in the organic waste in gaseous form against the at least one shared wall and reducing a mass flow rate of the organic waste in gaseous form, said reducing the mass flow rate having a decompressing effect on the organic waste in gaseous form; and compressing the organic waste in gaseous form within the gas passage in a manner to at least partially compensate for the decompressing effect.

Description

METHOD AND SYSTEM FOR PROCESSING ORGANIC WASTEBACKGROUND

[0001] There are very large volumes of organic waste which are generated by human activity across the globe, and they can come from different sources including agricultural sources such as porcine manure, bovine manure, duck manure, other animal production manure, biomethanizer digestate, and other sources such as municipal sludge, fluids from carcasses, septic tank residue, etc. Such organic waste may be in a liquid form, including slurries of various rheological or viscous traits, and including more or less solid particulate matter content. While organic waste may contain significant quantities of molecules of interest, such as water and fertilizers, it may also include contaminants, and may therefore need to be processed before it can suitably be used in agriculture or otherwise released to the environment. For instance, organic waste may contain significant quantities of nitrogen in the form of ammonia, and while nitrogen is a valuable fertilizer, ammonia is a contaminant which may need to be transformed before a more valuable form of nitrogen may be obtained.

[0002] Various systems and methods have been developed over the years to process organic waste. While many such systems and methods have been useful to a certain degree, there always remains room for improvement. Indeed, several factors may affect the commercial feasibility of a system or method to process organic waste, such as costs, effectiveness, and the value (nature and quantity) of the molecules which can be extracted. There thus remained room for improvement.SUMMARY

[0003] In accordance with one aspect, there is provided a method of processing organic waste, the method comprising : circulating the organic waste in liquid form sequentially along a liquid passage of a heat exchanger and into an evaporator; the evaporator evaporating the organic waste from the liquid form to a gaseous form; circulating the organic waste in the gaseous form along a gas passage of the heat exchanger, including transferring heat from the organic waste in gaseous form to the organic waste in liquid form across at least one shared wall of the gas passage and of the liquid passage, thereby condensing water contained in the organic waste in gaseous form against the at least one shared wall and reducing a mass flowrate of the organic waste in gaseous form, said reducing the mass flow rate having a decompressing effect on the organic waste in gaseous form; and compressing the organic waste in gaseous form within the gas passage in a manner to at least partially compensate for the decompressing effect.

[0004] In accordance with another aspect, there is provided a system for processing organic waste, comprising : an evaporator having an evaporator inlet and an evaporator outlet; a heat exchanger having a liquid inlet configured to receive said organic waste, one or more liquid passage extending from the liquid inlet to a liquid outlet, the liquid outlet fluidly connecting the evaporator inlet, the heat exchanger further having a gas inlet fluidly connecting the evaporator outlet, one or more gas passage extending from the gas inlet to a gas outlet and to a water outlet, the one or more gas passage sharing at least one heat transfer wall with the one or more liquid passage; the one or more gas passage having a length extending in a flow direction from the gas inlet to the gas outlet, and a cross-sectional area, the cross-sectional area reducing along the length.

[0005] In accordance with another aspect, there is provided a system for processing organic waste, comprising : an evaporator having an evaporator inlet and an evaporator outlet; a heat exchanger having a liquid inlet configured to receive said organic waste, a liquid passage extending from the liquid inlet to a liquid outlet, the liquid outlet fluidly connecting the evaporator inlet, the heat exchanger further having a gas inlet fluidly connecting the evaporator outlet, a gas passage extending from the gas inlet to a gas outlet and to a water outlet, the gas passage sharing at least one heat transfer wall with the one or more liquid passage, and a compressor located at an intermediary location along a length of the gas passage, between the gas inlet and the gas outlet.

[0006] In accordance with another aspect, there is provided a method of processing organic waste, the method comprising : circulating the organic waste in liquid form sequentially along a liquid passage of a heat exchanger and into an evaporator; the evaporator evaporating the organic waste from the liquid form to a gaseous form; circulating the organic waste in the gaseous form along a gas passage of the heat exchanger, including transferring heat from the organic waste in gaseous form to the organic waste in liquid form across at least one shared wall of the gas passage and of the liquid passage, thereby progressively condensing watercontained in the organic waste in gaseous form against the at least one shared wall, a cross- sectional area of the gas passage narrowing along a length of the gas passage, in a flow direction of the organic waste in gaseous form.

[0007] In accordance with another aspect there is provided a method of processing organic waste, the method comprising : circulating the organic waste in liquid form sequentially along a liquid passage of a heat exchanger and into an evaporator; the evaporator evaporating the organic waste from the liquid form to a gaseous form; circulating the organic waste in the gaseous form along a gas passage of the heat exchanger, including transferring heat from the organic waste in gaseous form to the organic waste in liquid form across at least one shared wall of the gas passage and of the liquid passage, thereby progressively condensing water contained in the organic waste in gaseous form against the at least one shared wall; and compressing the organic waste in gaseous form at at least one intermediary position along a length of the gas passage.

[0008] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.DESCRIPTION OF THE FIGURES

[0009] In the figures,

[0010] Fig. 1 is a schematic view of an example of a system for processing organic waste;

[0011] Fig. 2 is a schematic view of a heat exchanger;

[0012] Fig. 3 is a schematic view of a heat exchanger;

[0013] Fig. 4 is a schematic view of a heat exchanger;

[0014] Fig. 5 is a schematic view of an alternate example of a system for processing organic waste; and

[0015] Fig. 6 is a flow chart of an example method of processing organic waste.DETAILED DESCRIPTION

[0016] Fig. 1 shows an example of a system 10 for processing organic waste. The organic waste can contain substantial quantities of ammonia, or of molecules which may degrade to ammonia. The organic waste may be liquid manure from the porcine industry, to name one possible example, or another form of organic waste such as those presented above. In this example, the system includes a heat exchanger 12 of the gas-to-liquid type, and an evaporator 14. The heat exchanger 12 can be referred to as the gas-to-liquid heat exchanger, or as the first heat exchanger, for example, and may be referred to simply as the heat exchanger 12 in contexts where it may be the only heat exchanger 12 in the system. The heat exchanger 12 can have an inlet and an outlet associated to the liquid form (e.g., liquid phase) of the organic waste, and which can thus be labelled herein the liquid inlet 16 and liquid outlet 18 for ease of reference. The heat exchanger 12 can have an inlet and an outlet associated to the gaseous form (e.g., gaseous phase) of the organic waste, and which can thus be labelled herein the gas inlet 20 and the gas outlet 22 for ease of reference. The evaporator 14 can have an evaporator inlet 24 and an evaporator outlet 26. The liquid inlet 16 of the heat exchanger 12 can be fluidly connected to a source of organic waste, and be operable to receive a flow rate of the organic waste in liquid form. The liquid outlet 18 of the heat exchanger 12 can be fluidly connected to the evaporator inlet 24. The evaporator outlet 26 can be fluidly connected to the gas inlet 20 either directly, or via an optional compressor 28, depending on the embodiment.

[0017] Various types of heat exchangers exist both in principle (e.g., cross-flow, counterflow) and in construction (plates, tubes, etc.), and many different types or constructions of heat exchangers may be used as the heat exchanger 12, only a few examples of which will be presented below. In general, heat exchangers can be said to have two different fluid passages which both convey fluid between a respective inlet and a respective outlet, are fluidly partitioned from one another, while being configured for heat exchange with one another across one or more shared wall. The different fluid passages may be unitary, or manifold from a plenum into a plurality of conduits to then manifold back into another plenum, for instance. The one or more shared wall are typically made of a material which promotes heat transfer, such as a metal or other material which has a high thermal conductivity coefficient (e.g., more than 10W / (m.K), or more than 100W / (m.K)). The fluids can both be liquids, both be gasses, or can be a liquid and a gas, and the shapes and configurations of the passages are typicallyengineered in a manner to optimize heat transfer or otherwise achieve certain specifications of heat transfer performance. In a heat exchanger 12 of the gas-to-liquid heat exchanger type, such as the example heat exchanger 12 presented in Fig. 2, the passages are configured to favor flow rate and heat exchange between a gas and a liquid.

[0018] One way to favor heat exchange between a gas and a liquid is to use a plurality of conduits which each have a cross-sectional area and length selected taking into account the viscosity of the gas and the expected pressure, velocity and temperature conditions. It may be desired to configure the conduits for the flow to be relatively turbulent along the individual conduits while allowing a satisfactory flow rate across. Indeed, if the cross-sectional area of a given conduit is too large, the flow may become relatively laminar along the conduit, and the central portion of the flow may not mix efficiently, and therefore remain substantially insulated from the periphery of the gas passage which makes it less efficient to exchange heat between the gas and the liquid, across the shared walls, potentially requiring longer passages and making the heat exchanger more expensive. If the cross-sectional area is too small, heat transfer favoring turbulence may occur, but the gas may generate too much difficulty to proceed across the passage, potentially requiring more passages and making the heat exchanger more expensive.

[0019] Accordingly, there can be a preferred range of values of conduit length and cross- sectional area to achieve good heat transfer efficiency for given values of pressure, temperature and velocity of the gas circulating in the gas passage. However, in the case of some organic waste vapors, when the gas circulates along the length of the gas passages, between the gas inlet and the gas outlet, and transfers heat to the liquid circulating in the liquid passages across the shared heat transfer walls, some water vapor contained in the organic waste vapors may condense into liquid water on the shared heat transfer walls. In addition to having an effect on the heat transfer coefficient between the organic waste vapors and the liquid organic waste, the condensing of water vapor into liquid water can have a significant effect on the gas characteristics along the length of the gas passages. Indeed, liquid water is a lot denser than water vapor, and the condensing of liquid water thus reduces the mass flow rate of gas in favor of an increase in the mass flow rate or liquid water, thereby having a decompressive effect on the remaining mas flow rate of gas circulating in the conduit, loweringthe pressure when the conduit has a constant cross-sectional area. The lowering of the pressure has an effect on the flow characteristics of the gas circulating in the conduit, and further has an effect on the liquid transition temperature, since water vapor has a tendency to condense at a higher temperature when the pressure is higher. Accordingly, the condensing of water vapor into liquid water on the shared heat transfer walls may significantly affect the fluid flow dynamics and / or heat transfer dynamics, potentially rendering the cross-sectional area of the conduit no longer adapted to promote efficient heat transfer.

[0020] It was found that at least in some embodiments, imparting a compressing effect to the organic waste in gaseous form along the length of the gas passage could partially or perhaps even fully, compensate for the decompressing effect stemming from the condensing of water vapor into liquid water. There are different ways of compressing the organic waste in a manner to impart such a compressing effect. Two example ways of compressing the organic waste will be presented below, in relation with example embodiments which will be described and illustrated. More specifically, a first one is to reduce, progressively or via one or more stages, the cross-sectional area of the gas passage along the length thereof. Reducing the cross-sectional area of the gas passage forces the same mass flow rate of gas through a smaller cross-sectional area, thereby compressing the mass flow rate of gas. A first example where the cross-sectional area of the gas passage is reduced progressively is presented in Fig. 2, and a second example where the cross-sectional area of the gas passage is reduced by stages is presented in Fig. 3. A second way of compressing the organic waste in gaseous form in a manner to impart such a compressing effect is to compress the organic waste vapors using one or more compressor at one or more intermediary locations along the length of the gas passage. An example embodying this second way of addressing the issue is presented below with reference to Fig. 4.

[0021] Referring now to Fig. 2, a first example of a heat exchanger 112 is presented. The heat exchanger 112 is of the gas-to-liquid type. The heat exchanger 112 has a liquid inlet 116 configured to receive the organic waste in liquid form (liquid organic waste), and a liquid passage 130 extending between the liquid inlet 116 and the liquid outlet 118. The heat exchanger 112 further has a gas inlet 120 configured to receive the organic waste in gaseous form (organic waste vapors), and a gas passage 132 having a conduit formed by two flat metalplates which are inclined in a manner to taper towards one another in the direction of the gas outlet 122. Accordingly, the cross-sectional area of the gas passage 132 along the conduit, taken normal to the orientation of the gas flow, progressively reduces along the length of the conduit, taken in the direction of the gas flow, between the inlet and the outlet. The tapering of the flat metal plates is the source of the progressive reduction in cross-sectional area of the gas passage along the conduit and can impart a compressive effect to the organic waste vapors which may, partially or fully, compensate for the decompressive effect stemming from the condensing of water vapor contained in the organic waste vapors into liquid water against the flat metal plates. In this embodiment, the liquid water can be collected by gravity and evacuated from a water outlet 134 such as a drain.

[0022] Referring now to Fig. 3, a second example of a heat exchanger 212 is presented. The heat exchanger 212 is of the gas-to-liquid type. The heat exchanger has a liquid inlet 216 configured to receive the organic waste in liquid form (liquid organic waste), and a liquid passage 230 extending between the liquid inlet 216 and the liquid outlet 218. The heat exchanger 212 further has a gas inlet 220 configured to receive the organic waste in gaseous form (organic waste vapors), and a gas passage 232. In this example, the gas passage 232 includes a sequence of a plurality of sets of tubes 240, 242, 244, 246 intercalated by plenums 248, 250, 252, 254. The number of tubes decreases from one set to the next along the sequence. In this embodiment, the tubes extend within a vessel. The space around the tubes within the vessel constitutes the liquid passage, which extends around the tubes. Two opposite ends of the vessel are partitioned from the liquid passage and is used to form the plenums.

[0023] In this embodiment, the sets of tubes 240, 242, 244, 246 extend in sequence between plenums 250, 252, 254 on alternating sides, forming a number of gas passage stages corresponding to the number of sets of tubes 240, 242, 244, 246. In this embodiment, all the tubes are identical, and have same diameter and of the same length, but the number of tubes is reduced from one stage to the next, thereby reducing the gas passage cross-sectional area from one stage to the next. Accordingly, the cross-sectional area of the gas passage 232 along the conduit, taken normal to the orientation of the gas flow, progressively reduces along the serpentine length of the gas passage 232, relative the local direction of the gas flow, betweenthe inlet 220 and the outlet 222. The reduction in the number of tubes from one stage / set to the next in the sequence is the source of the progressive reduction in cross-sectional area of the gas passage along the conduit and can impart a compressive effect to the organic waste vapors which are forced in to a smaller and smaller cross-sectional area at each stage along the way. The compressive effect may, partially or fully, compensate for the decompressive effect stemming from the condensing of water vapor contained in the organic waste vapors into liquid water against the internal faces of the tubes. In this embodiment, the liquid water can be collected by gravity and evacuated from a water outlet 234 such as one or more drain.

[0024] In one mode of operation, the entirety of the organic waste vapors enters a first plenum 248 through the gas inlet 220. From the first plenum 248, the organic waste vapors manifold into the tubes of the first set 240, shown here in the number of 8 to provide one potential example. As the gas circulates along the first set of 8 tubes 240, it transfers heat into the cooler, liquid organic waste circulating in the liquid passage 230, across the high thermal conductivity material from which the tubes are made of (e.g., metal). In a first portion of the length of the first set of tubes 240, the flow conditions may be ideal for balancing considerations such as condensing rate of water, heat transfer, and mass flow rate. As the organic waste vapors loses some of its heat in the first portion of the length of the first set of tubes 240, its temperature decreases, leading to some condensing of water vapor contained in the organic waste vapors into liquid water, on the internal face of the tubes of the first set / stage 240.

[0025] The condensing of water transforms a portion of the gaseous mass flow rate into liquid mass flow rate. The liquid mass flow rate is much denser than the gaseous mass flow rate, leaving significantly less gas occupying the same cross-sectional area, thereby reducing gaseous pressure in the tubes. In the latter portion of the length of the first set of tubes 240, the flow conditions may no longer satisfactorily balance considerations such as condensing rate of water, heat transfer, and / or mass flow rate. For instance, the flow may have become more laminar and / or the boundary layer may have increased, or the water liquid / vapor transition temperature may have changed due to reduction in pressure. At this point, the flow exits the first set of tubes into a second plenum 250. The second plenum 250 also acts here as a portion of the gas passage 232 fluidly connecting the outlets of the first set of tubes 240to inlets of a second set of tubes 242. In the first plenum 248, the mass flow rate of the organic waste vapors may be 100% gaseous. In the second plenum 250, given the condensing of water vapor into liquid water which took place along the first set of tubes 240, a portion of the mass flow rate may now be liquid, say 15% liquid and 85% gaseous for instance.

[0026] In this example, the tubes of the second set 242 are in a smaller number, let us say 4 for example. While the tubes of the second set 242 may have the same length and diameter as the tubes of the first set 240, their smaller number can reduce the overall cross-sectional area of the second stage, forcing here the lesser amount of gaseous mass flow rate into a correspondingly smaller cross-sectional area. The second set of tubes 242 can thus be configured in a manner to achieve, again, conditions which balance considerations such as condensing rate of water, heat transfer, and / or mass flow rate, at least along the first portion of the length. Here again, the transfer of heat from the organic waste vapors circulating in the gas passages of the second stage to the liquid organic waste circulating in the liquid passage may decrease the temperature of the organic waste vapors and lead to further condensation of water vapor contained therein into liquid water against the internal faces of the tubes. Here again, the condensation of liquid water may decrease the gaseous pressure and in the latter portion of the length of the tubes of the second stage, and the flow conditions may no longer suitably balance considerations such as condensing rate of water, heat transfer, and / or mass flow rate. At the ends of the tubes of the second stage, only a portion, say 70% for example, of the original gaseous flow rate may remain in gaseous form, and the gas may recombine in a third plenum 252 also serving as a portion of the gas passage 232 connecting inlets of a third set of tubes 244.

[0027] The number of tubes of the third set may again be reduced, let us say 2 for example, compared to the previous set, again reducing the cross sectional area of the gas passage 232 along its length and compressing the lesser mass flow rate of gas into a correspondingly smaller surface area, and so forth, until the final set of tubes 246 is reached, which is the fourth set of tubes following a fourth plenum in this example and which only has one tube in this example. It will be noted that a flow restrictor may be used at the gas outlet 222, and / or at any intermediary location along the gas passage 232, to sustain a desired level of pressure within a corresponding area, or the entirety, of the gas passage 232.

[0028] It will be noted that in alternate embodiments, the number of stages, and the number and shape of tubes or conduits corresponding to different ones of the stages can vary. In another example, there may be by only two sets of tubes for instance. In yet another example, there may be more than four sets of tubes for instance. The progressive reduction in number of tubes / total cross-sectional area may be more or less aggressive than the 1 reduction per stage presented in the example above, and can be constant (linear) or not constant (nonlinear) from one stage to the next. Experience led to believe that using more than two stages was preferable in some embodiments.

[0029] Referring now to Fig. 4, a third example of a heat exchanger 312 is presented, in accordance with a second way of compressing the organic waste in gaseous form. The heat exchanger 312 is of the gas-to-liquid type. The heat exchanger 312 has a liquid inlet 316 configured to receive the organic waste in liquid form (liquid organic waste), and a liquid passage 330 extending between the liquid inlet 316 and the liquid outlet 318. The heat exchanger 312 further has a gas inlet 320 configured to receive the organic waste in gaseous form (organic waste vapors), and a gas passage 332. In this example, the gas passage 332 includes a sequence of a plurality of sets of tubes 340, 342, 344, 346 intercalated by compressors 360, 362, 364, and the sets of tubes 340, 342, 344, 346 are fluidly connected to corresponding compressors 360, 362, 364 via corresponding plenums.

[0030] In this embodiment, the tubes extend within a vessel. The space around the tubes within the vessel constitutes the liquid passage 330, which extends around the tubes. Two opposite ends of the vessel are partitioned from the liquid passage and is used to form the plenums. Sets of tubes extend in sequence between plenums and compressors on alternating sides, forming a number of gas passage stages corresponding to the number of sets of tubes 340, 342, 344, 346. In this embodiment, all the tubes are identical, and have same diameter and the same length, and are provided in the same number of tubes from one stage to the next, leading to a gas passage having a cross-sectional area which is constant between each condensing stage. The compressors 360, 362, 364 are used to increase the pressure of the organic waste in gaseous form between the stages. The compressors 360, 362, 364 are disposed at a number of intermediary locations along the length of the gas passage 332, between corresponding pairs of stages. The compressors 360, 362, 364 may be of varioustypes, such as rotary screw compressors, centrifugal compressors, scroll compressors, reciprocating compressors, etc. The compressors 360, 362, 364 can impart a compressive effect to the organic waste vapors. The compressive effect may, partially or fully, compensate for the decompressive effect stemming from the condensing of water vapor contained in the organic waste vapors into liquid water against the internal faces of the tubes. In this embodiment, the liquid water can be collected by gravity and evacuated from a water outlet 334 such as one or more drain.

[0031] In one mode of operation, the entirety of the organic waste vapors enters a first plenum through the gas inlet 320. From the first plenum, the organic waste vapors manifold into the tubes of the first set 340, shown here in the number of 4 to provide one potential example. As the gas circulates along the first set of 4 tubes, it transfers heat into the cooler, liquid organic waste circulating in the liquid passage 330, across the high thermal conductivity material from which the tubes are made of (e.g., metal). In a first portion of the length of the first set of tubes 340, the flow conditions may be ideal for balancing considerations such as condensing rate of water, heat transfer, and mass flow rate. As the organic waste vapors looses some of its heat in the first portion of the length of the first set of tubes 340, its temperature decreases, leading to some condensing of water vapor contained in the organic waste vapors into liquid water, on the internal face of the tubes of the first set / stage.

[0032] The condensing of water transforms a portion of the gaseous mass flow rate into liquid mass flow rate. The liquid mass flow rate is much denser than the gaseous mass flow rate, leaving significantly less gas occupying the same cross-sectional area, thereby reducing gaseous pressure in the tubes. In the latter portion of the length of the first set of tubes, the flow conditions may no longer satisfactorily balance considerations such as condensing rate of water, heat transfer, and / or mass flow rate. For instance, the flow may have become more laminar and / or the boundary layer may have increased, or the water liquid / vapor transition temperature may have changed due to reduction in pressure. At this point, the flow exits the first set of tubes 340 into a second plenum. The second plenum also acts here as a portion of the gas passage fluidly connecting the outlets of the first set of tubes 340 to an inlet of the first compressor 360.

[0033] In the first plenum, the mass flow rate of the organic waste vapors may be 100% gaseous. In the second plenum, given the condensing of water vapor into liquid water which took place along the first set of tubes, a portion of the mass flow rate may now be liquid, say 15% liquid and 85% gaseous for instance. The compressor 360 can restore the pressure which the organic waste vapors had in the first plenum, in which case the second set of tubes 342, even if in the same dimensions, configuration, and number than the first set of tubes 340, can now be configured in a manner to achieve, again, conditions which balance considerations such as condensing rate of water, heat transfer, and / or mass flow rate, at least along the first portion of the length. Here again, the transfer of heat from the organic waste vapors circulating in the gas passages of the second stage to the liquid organic waste circulating in the liquid passage may decrease the temperature of the organic waste vapors and lead to further condensation of water vapor contained therein into liquid water against the internal faces of the tubes. Here again, the condensation of liquid water may decrease the gaseous pressure and in the latter portion of the length of the tubes of the second stage, and the flow conditions may no longer suitably balance considerations such as condensing rate of water, heat transfer, and / or mass flow rate. At the ends of the tubes of the second stage, only a certain portion, say 70% for example, of the original gaseous flow rate may remain in gaseous form for instance, and the gas may recombine in a corresponding plenum also serving as a passage connecting an inlet of the second compressor 362.

[0034] The second compressor 362 can restore the pressure, in which case the second set of tubes 342, even in the same dimensions, configuration, and number than the first set of tubes 340, can now be configured in a manner to achieve, again, conditions which balance considerations such as condensing rate of water, heat transfer, and / or mass flow rate, at least along the first portion of the length. The effect can be repeated along the third set of tubes 344, third compressor 364, and so forth, until the final set of tubes 346 is reached, which is the fourth set of tubes in this example. It will be noted that a flow restrictor may be used at the gas outlet 322, and / or at any intermediary location along the gas passage 332 such as between the outlets of a given set of tubes and the inlet of the corresponding compressor, to sustain a desired level of pressure within a corresponding area of the gas passage.

[0035] It will be noted that in alternate embodiments, the number of stages, and the number and shape of tubes or conduits corresponding to different ones of the stages can vary. In another example, there may be by only two sets of tubes and a single compressor for instance. In yet another example, there may be more than four sets of tubes for instance. The pressure increase imparted by the successive compressors can be constant from one compressor to the next, or non constant.

[0036] It will be noted that the second way of compressing the organic waste vapors, which involves the use of compressors, can be combined with the first way of compressing the organic waste vapors, such as the reduction in cross-sectional area of the gas passage, in some embodiments. For instance, compressors could alternately be used at an intermediary location along the second plenum 250, third plenum 252, or fourth plenum 254 of the heat exchanger 212 of Fig. 3.

[0037] Returning to Fig. 1 , it will be noted that the system for processing organic waste may have additional elements than the heat exchanger 12 and the evaporator 14. For instance, in some embodiments, it may be preferable to compress the organic waste in the gaseous form upstream of the heat exchanger 12. This may be achieved by a compressor 28 fluidly connected between the evaporator outlet 26 and the gas inlet 20. In some embodiments, it may be desired to collect some or all of the gas from the gas outlet 22. For instance, in some embodiments, the gas from the gas outlet 22 may have a certain concentration of nitrogen, and it may be desired to retrieve the gas to retrieve the nitrogen. In some embodiments, the gas may be collected directly from the gas outlet 22. In other embodiments, a concentrating device 70 may be used to increase the concentration of one or more molecule of interest in the gas prior to collection. Various forms of concentrating devices exist, such as columns for instance.

[0038] In some embodiments, it may be desired to further recover heat from the water received from the water outlet 34 of the heat exchanger 12. In one example, the water received from the water outlet 34 of the heat exchanger 12 can be conveyed to a second heat exchanger 72. The second heat exchanger 72 can be of the liquid-to-liquid type, and have a hot passage in which the water received from the water outlet 34 of the heat exchanger 12 is conveyed, and a cold passage along which the organic waste in liquid form is conveyedupstream of the gas-to-liquid heat exchanger 12. In the second heat exchanger 72, the liquid flow of water and of organic waste in liquid form may remain separated, but be placed in heat exchange contact with one another across one or more shared wall for instance, as known in the art. The water received from the gas-to-liquid heat exchanger may still, in some embodiments, contain a significant amount of impurities. In some embodiments, the level of impurities may render the water improper for release to the environment or improper for another intended use. In such embodiments, it may be desired to perform stripping of the water from the impurities, in a manner to yield purer water. The stripping may be performed before or after the liquid-to-liquid heat exchanger 72 in embodiments where a liquid-to-liquid heat exchanger 72 is used. The stripping may be performed by a vapor stripping device 74, for instance. A vapor stripping device 74 may be of the co-current or countercurrent flow type, and be provided in the form of a packed or trayed column, for instance.

[0039] Another example embodiment of a system to process organic waste is presented in Fig. 5. In this embodiment, the system may include only a heat exchanger HX1 of the liquid- to-liquid type and an evaporator. There may be a source of a heat-carrying liquid other than the organic waste. The heat-carrying liquid can be placed in thermal exchange contact with a flow of the organic waste in the heat exchanger HX1 to preheat the organic waste upstream of the evaporator. Optionally, a second, gas-to-liquid type heat exchanger HX2 may be used to place the organic waste in vapor form in thermal exchange contact with the organic waste in liquid form, in a manner to recover heat from the evaporation in heating the organic waste in liquid form upstream of the evaporator. Optional compressor, vapor stripping device, and / or concentrating device may also be used.

[0040] With reference to Fig. 6, in accordance with one embodiment, there is provided a method 400 of processing organic waste. The method 400 can include circulating 410 the organic waste in liquid form sequentially along a liquid passage of a heat exchanger and into an evaporator. The method can include the evaporator evaporating 420 the organic waste from the liquid form to a gaseous form. The method can include circulating 414 the organic waste in the gaseous form along a gas passage of the heat exchanger, including transferring heat from the organic waste in gaseous form to the organic waste in liquid form across at least one shared wall of the gas passage and of the liquid passage, thereby progressivelycondensing water contained in the organic waste in gaseous form against the at least one shared wall and reducing a mass flow rate of the organic waste in gaseous form, said reducing the mass flow rate having a decompressing effect on the organic waste in gaseous form. The method can include compressing 416 the organic waste in gaseous form along a length of the gas passage in a manner to at least partially compensate for the decompressing effect.

[0041] As can be understood, the examples described above and illustrated are intended to be exemplary only. Many variants are possible, as will be understood from the reading of this specification by persons having common general knowledge and ordinary skill in the art. In particular, it will be understood that the expression heat exchanger is intended to be construed in a broad sense, as including a heat exchanger including one or more than one heat exchanger unit. In the case of a heat exchanger composed of more than one heat exchanger unit, the heat exchanger units may be connected in series or in parallel, for instance. The scope is indicated by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method of processing organic waste, the method comprising : circulating the organic waste in liquid form sequentially along a liquid passage of a heat exchanger and into an evaporator; the evaporator evaporating the organic waste from the liquid form to a gaseous form; circulating the organic waste in the gaseous form along a gas passage of the heat exchanger, including transferring heat from the organic waste in gaseous form to the organic waste in liquid form across at least one shared wall of the gas passage and of the liquid passage, thereby condensing water contained in the organic waste in gaseous form against the at least one shared wall and reducing a mass flow rate of the organic waste in gaseous form, said reducing the mass flow rate having a decompressing effect on the organic waste in gaseous form; and compressing the organic waste in gaseous form within the gas passage in a manner to at least partially compensate for the decompressing effect.

2. The method of claim 1 , wherein said compressing includes reducing the cross- sectional area of the gas passage.

3. The method of claim 1 wherein said compressing includes compressing the organic waste in gaseous form with a compressor at at least one intermediary position along a length of the gas passage.

4. The method of claim 1 wherein the heat exchanger is a first heat exchanger, further comprising circulating the organic waste in the liquid form in a cold passage of a second heat exchanger upstream of the first heat exchanger, circulating condensed water collected from the first heat exchanger in a hot passage of the second heat exchanger, and transferring heat from the condensed water to the organic waste in liquid form across at least one shared wall of the hot passage and of the cold passage.

5. The method of claim 1 further comprising collecting the organic waste in gaseous form downstream of the heat exchanger.

6. The method of claim 5 further comprising concentrating at least one molecule of interest in the organic waste in gaseous form subsequently to said condensing and prior to said collecting.

7. The method of claim 5 wherein the organic waste in gaseous form downstream of the heat exchanger includes nitrogen.

8. The method of claim 1 further comprising stripping condensed water collected from the heat exchanger.

9. A system for processing organic waste, comprising : an evaporator having an evaporator inlet and an evaporator outlet; a heat exchanger having a liquid inlet configured to receive said organic waste, one or more liquid passage extending from the liquid inlet to a liquid outlet, the liquid outlet fluidly connecting the evaporator inlet, the heat exchanger further having a gas inlet fluidly connecting the evaporator outlet, one or more gas passage extending from the gas inlet to a gas outlet and to a water outlet, the one or more gas passage sharing at least one heat transfer wall with the one or more liquid passage; the one or more gas passage having a length extending in a flow direction from the gas inlet to the gas outlet, and a cross-sectional area, the cross-sectional area reducing along the length.

10. A system for processing organic waste, comprising : an evaporator having an evaporator inlet and an evaporator outlet; a heat exchanger having a liquid inlet configured to receive said organic waste, a liquid passage extending from the liquid inlet to a liquid outlet, the liquid outlet fluidly connecting the evaporator inlet, the heat exchanger further having a gas inlet fluidly connecting the evaporator outlet, a gas passage extending from the gas inlet to a gas outlet and to a water outlet, the gas passage sharing at least one heat transfer wall with the one or more liquid passage, and a compressor located at an intermediary location along a length of the gas passage, between the gas inlet and the gas outlet.

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