System and method for supplying a fluid for use in dialysis therapy

Abstract

An arrangement is provided for supplying a fluid for use in dialysis therapy. The arrangement comprises a vessel (10) for holding the fluid, an inlet line (L1) for directing the fluid to an inlet port (10a) on the vessel, an electrical heating device (12) for heating the fluid in the vessel, and a supply line (L2) for directing the fluid from an outlet port (10b) of the vessel. A fluid pump (P1) is arranged to achieve a flow of the fluid along the inlet line, through the vessel, and along the supply line. A heat exchanger (14) is arranged to transfer heat between the inlet line and the supply line, and a heat pump (15), for example thermoelectric, is operable to transfer heat between the inlet line and the supply line. A control device (30) operates the heat pump so as to achieve a target temperature of the fluid in the supply line, downstream of the heat exchanger and the second location.

Description

[0001] SYSTEM AND METHOD FOR SUPPLYING A FLUID FOR USE IN DIALYSIS

[0002] THERAPY

[0003] Technical Field

[0004] The present disclosure relates generally to dialysis therapy, and in particular to a technique of supplying a fluid at a target temperature for use in dialysis therapy.

[0005] Background Art

[0006] Dialysis therapy is undertaken to replace or supplement the normal blood-filtering function of the kidneys. It is used when the kidneys are not working well, which is known as kidney failure and includes acute kidney injury (AKI) and chronic kidney disease (CKD). Dialysis therapy involves removal of water from the body of the patient suffering from kidney failure, as well as exchange of solutes with the patient's blood. One example of dialysis therapy is extracorporeal (EC) blood therapy, in which blood is circulated outside of the patient and interfaced with one or more treatment fluids through a dialyzer membrane. Modalities of extracorporeal blood therapy include hemodialysis (HD), hemofiltration (HF) and hemodiafiltration (HDF). Another example of dialysis therapy is peritoneal dialysis (PD), in which a treatment fluid is infused into the peritoneal cavity of the patient to interface with the blood of the patient through the peritoneal membrane.

[0007] Treatment fluids used in HD and PD are commonly known as dialysis fluids. In HF, the treatment fluid is known as replacement fluid, since it is infused into the blood of the patient to replace fluid removed during therapy. In HDF, both dialysis fluid and replacement fluid are used.

[0008] Treatment fluid may be supplied from a pre-filled bag attached to a dialysis system or be generated in the dialysis system by mixing water with one or more concentrates. Such water needs to be purified, which may be made centrally or locally in the dialysis system.

[0009] Fluids in the dialysis system may contain gases. For example, the water used to initially prepare a treatment fluid may contain a significant amount of entrained gases, such as nitrogen and oxygen. Further, gases such as carbon dioxide may be formed during the mixing of water and concentrate. It is desirable to remove such gases to avoid the formation of gas bubbles, which may interfere with the pumping of the fluid and cause errors in sensor readings. In EC blood therapy, gas bubbles may also reduce diffusive clearance across the dialyzer membrane, and may even present a dangerous condition for a patient if the gas crosses the dialyzer membrane into the EC blood circuit and causes gas bubbles in the blood returning to the patient.

[0010] Dialysis systems therefore include one or more degassing devices. Conventionally, such a degassing device operates by pressure reduction, in which a degassing pump is operated to lower the partial pressure of the fluid to be degassed so that gas bubbles are formed, which are evacuated by the degassing pump. This technique requires many components and is complex to implement into a safe and functional system.

[0011] The prior art comprises US3738382, which proposes to heat the water to achieve degassing upstream of a mixing device. As the temperature of the water is increased, the solubility of gases in the water decreases. By increasing the temperature of the water within a vessel by use of an electrical heater upstream of the vessel, entrained gas in the water will form bubbles, accumulate above the water and flow out of the vessel. This technique obviates the need for a degassing pump and control thereof. To limit power consumption, US3738382 proposes to arrange a heat changer to pre-heat the incoming water to the vessel, by transfer of heat to the incoming water from the heated water leaving the vessel. A further heat exchanger is arranged downstream of the temperature regulator to transfer heat from the degassed water to a liquid concentrate before the water and the liquid concentrate are mixed in a mixing device to form a dialysis fluid. A temperature regulator with an associated heater may be disposed in the flow path between the heat exchanger and the further heat exchanger. A similar technique is disclosed in EP0228968.

[0012] In view of growing environmental concerns, it is generally desirable to reduce the consumption of electrical power when using thermal regulation for degassing of a fluid.

[0013] The prior art discussed hereinabove has a specific short-coming. In US3738382, it is noted that the temperature of the dialysis fluid should be about 37°C, i.e., approximately at body temperature. The use of heat exchangers in US3738382 presumes that the temperature of the incoming water does not exceed a limit value. If the limit value is exceeded, the resulting dialysis fluid will have a temperature above body temperature. In warmer climates, and also under other circumstances, it is possible that the temperature of the incoming water is quite high, for example 20-25°C. To accommodate for these temperatures, the heat exchangers may be designed with a reduced heat transfer capacity, which will result in an undesirably high electrical power consumption when the system is used with incoming water at normal (lower) temperatures. Alternatively, the flow rate of the water may be increased with increasing temperature of the incoming water, to reduce the heat transfer in the heat exchangers. However, this adds complexity to the system. It may also be undesirable from a therapy perspective to change the flow rate of the dialysis fluid.

[0014] The foregoing description of desires and short-comings is not limited to degassing of fluid, but is generally applicable to all situations in which a fluid for use in dialysis therapy is heated while flowing through a vessel, which is configured to contain a portion of the heated fluid.

[0015] Summary

[0016] It is an objective to at least partly overcome one or more limitations of the prior art.

[0017] One objective is to provide, in the context of dialysis therapy, a power-efficient technique of achieving a target temperature of a fluid downstream of a heating arrangement that includes an electrical heating device for heating the fluid and a vessel for holding the fluid at an elevated temperature.

[0018] A further objective is to provide such a technique that is simple, robust and capable of handling different temperatures of the fluid entering the heating arrangement.

[0019] Another objective is to provide a power-efficient technique of degassing a fluid for use in dialysis therapy.

[0020] One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by a system for supplying a fluid for use in dialysis therapy, and a computer-implemented method according to the independent claims, embodiments thereof being defined by the dependent claims.

[0021] A first aspect is a system for supplying a fluid for use in dialysis therapy. The system comprises: a vessel for holding the fluid; an inlet line arranged to direct the fluid to an inlet port on the vessel; an electrical heating device arranged for heating the fluid in the vessel; a supply line arranged to direct the fluid from an outlet port of the vessel; at least one fluid pump for achieving a flow of the fluid along the inlet line, through the vessel, and along the supply line; a heat exchanger, which comprises one or more first fluid channels and one or more second fluid channels and is configured to transfer heat between the one or more first fluid channels and the one or more second fluid channels, wherein the one or more first fluid channels are fluidly interposed in the inlet line, and the one or more second fluid channels are fluidly interposed in the supply line; a heat pump, which is operable to transfer heat between a first location in the inlet line and a second location in the supply line; and a control device configured to operate the heat pump so as to achieve a target temperature of the fluid in the supply line downstream of the heat exchanger and the second location.

[0022] Below, embodiments of the system of the first aspect are recited. In some embodiments, the heat pump is a thermoelectric heat pump.

[0023] In some embodiments, the second location is downstream of the one or more second fluid channels in the supply line.

[0024] In some embodiments, the first location is upstream or downstream of the one or more first fluid channels in the inlet line.

[0025] In some embodiments, the system further comprises a temperature sensor arranged to provide a sensor signal indicative of fluid temperature in the supply line downstream of the heat exchanger and the second location, and the control device is configured to control the heat pump by feedback control based on the sensor signal.

[0026] In some embodiments, the control device is configured to operate the at least one fluid pump to achieve a predefined flow rate of the fluid through the supply line while the heat pump is operated to achieve the target temperature of the fluid.

[0027] In some embodiments, the electrical heating device comprises a heating element arranged within the vessel to be submerged in the fluid.

[0028] In some embodiments, the control device is configured to operate the electrical heating device, during a degassing procedure, to achieve a predefined fluid temperature within the vessel so as to release entrained gases from the fluid within the vessel.

[0029] In some embodiments, the vessel comprises a gas outlet, which is open to surrounding atmosphere during the degassing procedure.

[0030] In some embodiments, the predefined temperature is in a range of 50-99°C, preferably in a range of 60-97°C.

[0031] In some embodiments, the control device is configured to operate a valve arrangement in the system to define a production flow path from an intake inlet on the inlet line via the vessel to a supply outlet on the supply line, and to operate the at least one fluid pump to pump the fluid along the production flow path so as to supply the fluid at the supply outlet.

[0032] In some embodiments, the control device is configured to perform a heat disinfection procedure, said heat disinfection procedure comprising: operating the valve arrangement to define a disinfection flow path, in which the supply line is fluidly connected, at a location downstream of the heat exchanger, to the inlet line, at a location upstream of the heat exchanger, and fluid flow through the supply outlet is blocked; and operating, while the fluid in the vessel has a heat disinfection temperature, the at least one fluid pump to achieve a circulating flow of the fluid along the disinfection flow path until a heat disinfection criterion is fulfilled.

[0033] In some embodiments, the system further comprises a return line, which extends from a return inlet to a return outlet, and the heat exchanger or a further heat exchanger is arranged to transfer heat between the inlet line and the return line, and the heat disinfection procedure comprises: operating the valve arrangement to define a further disinfection flow path, which is fluidly separated from the disinfection flow path and includes the return path, and operating a fluid pump in the further disinfection flow path to achieve a circulating flow of the fluid along the further disinfection flow path.

[0034] In some embodiments, the heat disinfection procedure further comprises: operating the at least one fluid pump, during at least part of the heat disinfection procedure, to pump the fluid in a direction from the vessel into the inlet line.

[0035] In some embodiments, the system further comprises a return line, which extends from a return inlet to a return outlet, and the disinfection flow path includes at least part of the return line.

[0036] In some embodiments, the heat disinfection procedure further comprises: operating, at start of the heat disinfection procedure, the valve arrangement to establish fluid communication between the supply line and a drain, close the inlet line upstream of the heat exchanger , and operate the at least one fluid pump to pump a portion of the fluid in the vessel into the supply line towards the drain.

[0037] In some embodiments, the heat disinfection procedure further comprises: operating, when said portion of the fluid in the vessel has been pumped, the valve arrangement to open the inlet line to achieve a throughflow of the fluid from the intake inlet via the inlet line through the vessel; and operating the electrical heating device to attain the heat disinfection temperature of the fluid in the vessel while the at least one fluid pump is operated to achieve the throughflow.

[0038] In some embodiments, the heat disinfection temperature is in a range of 80-105°C.

[0039] In some embodiments, the outlet port is located above the inlet port to retain a volume of the fluid in the vessel as the fluid flows through the vessel.

[0040] In some embodiments, the system further comprises a mixing sub-system, which is fluidly interposed in the supply line and operable to mix the fluid with one or more concentrates for generation of a treatment fluid for use in dialysis therapy.

[0041] In some embodiments, the system further comprises a water purification subsystem, which is fluidly interposed in the supply line and operable to process the fluid for removal of impurities to generate water suitable for use in dialysis therapy.

[0042] A second aspect is a computer-implemented method of supplying a fluid for use in dialysis therapy. The method comprises: operating at least one fluid pump to convey the fluid from a fluid source through an inlet line into a vessel and from the vessel through a supply line, while directing the fluid in the inlet line through one or more first fluid channels of a heat exchanger and while directing the fluid in the supply line through one or more second fluid channels of the heat exchanger, wherein the heat exchanger is configured for heat transfer between the one or more first fluid channels and the one or more second fluid channels; operating an electrical heating device to heat the fluid in the vessel; and operating a heat pump to transfer heat between a first location in the inlet line and a second location in the supply line, to achieve a target temperature of the fluid in the supply line downstream of the heat exchanger and the second location.

[0043] In some embodiments of the second aspect, the electrical heating device is operated, during a degassing procedure, to achieve a predefined fluid temperature within the vessel so as to release gases from the fluid within the vessel.

[0044] In some embodiments of the second aspect, the method comprises: operating a valve arrangement, during the degassing procedure, to define a production flow path from an intake inlet on the inlet line via the vessel to a supply outlet on the supply line, and operating the at least one fluid pump to pump the fluid along the production flow path so as to supply the fluid at the supply outlet.

[0045] In some embodiments of the second aspect, the method comprises a heat disinfection procedure comprising: operating the valve arrangement to define a disinfection flow path, in which the supply line is fluidly connected, at a location downstream of the heat exchanger, to the inlet line, at a location upstream of the heat exchanger, and in which fluid flow through the supply outlet is blocked; and operating, while the fluid in the vessel has a heat disinfection temperature, the at least one fluid pump to achieve a circulating flow of the fluid along the disinfection flow path until a heat disinfection criterion is fulfilled.

[0046] In some embodiments of the second aspect, the valve arrangement is operated to include at least part of a return line, which extends from a return inlet to a return outlet, in the disinfection flow path.

[0047] In some embodiments of the second aspect, the heat disinfection procedure further comprises: operating the valve arrangement to define a further disinfection flow path, which is fluidly separated from the disinfection flow path and includes a return path, which extends from a return inlet to a return outlet; and operating a fluid pump in the further disinfection flow path to achieve a circulating flow of the fluid along the further disinfection flow path.

[0048] In some embodiments of the second aspect, the method further comprises: operating the at least one fluid pump, during at least part of the heat disinfection procedure, to pump the fluid in a direction from the vessel into the inlet line.

[0049] In some embodiments of the second aspect, the heat disinfection procedure further comprises: operating, at start of the heat disinfection procedure, the valve arrangement to establish fluid communication between the supply line and a drain, and to close the inlet line upstream of the heat exchanger; and operating the at least one fluid pump to pump a portion of the fluid in the vessel into the supply line towards the drain.

[0050] In some embodiments of the second aspect, the heat disinfection procedure further comprises: operating, when said portion of the fluid in the vessel has been pumped, the valve arrangement to open the inlet line to achieve a throughflow of the fluid from the intake inlet via the inlet line through the vessel; and operating the electrical heating device to attain the heat disinfection temperature of the fluid in the vessel while the at least one fluid pump is operated to achieve the throughflow.

[0051] A third aspect is a computer-readable medium comprising program instructions, which when executed by processing circuitry, causes the processing circuitry to perform the method of the second aspect or any of its embodiments.

[0052] The second and third aspects share technical effects with the first aspect.

[0053] Still other objectives, aspects, embodiments, as well as technical effects, features and advantages may appear from the following detailed description, from the attached claims as well as from the drawings.

[0054] Brief Description of the Drawings

[0055] FIGS 1 A-1B are schematic views of example dialysis systems connected to a patient.

[0056] FIG. 2 is a block diagram of a system including an example arrangement for thermal degassing of water and generation of treatment fluid.

[0057] FIG. 3 is a flow chart of an example method of operating a system for degassing of incoming fluid.

[0058] FIG. 4 is a graph of measured oxygen level of water as a function of water temperature.

[0059] FIGS 5 A-5B are a flow charts of example methods of operating the system in FIG. 2 for heat disinfection.

[0060] FIG. 6A is a block diagram of an example variant of the system in FIG. 2, FIG. 6B is a flow chart of an example method of operating the system in FIG. 6A for degassing of incoming fluid, and FIGS 6C-6D are a flow charts of example methods of operating the system in FIG. 6A for heat disinfection.

[0061] FIG. 7 is a block diagram of an example arrangement for thermal degassing of water in accordance with a variant.

[0062] FIG. 8 is a section view of an example thermoelectric heat pump for use in the arrangements in FIGS 2, 6 A and 7.

[0063] Detailed Description of Example Embodiments Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments are shown. Indeed, the subject of the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure may satisfy applicable legal requirements.

[0064] Also, it will be understood that, where possible, any of the advantages, features, functions, devices, and / or operational aspects of any of the embodiments described and / or contemplated herein may be included in any of the other embodiments described and / or contemplated herein, and / or vice versa. In addition, where possible, any terms expressed in the singular form herein are meant to also include the plural form and / or vice versa, unless explicitly stated otherwise. As used herein, "at least one" shall mean "one or more" and these phrases are intended to be interchangeable. Accordingly, the terms "a" and / or "an" shall mean "at least one" or "one or more", even though the phrase "one or more" or "at least one" is also used herein. As used herein, except where the context requires otherwise owing to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, that is, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments.

[0065] As used herein, the terms "multiple", "plural" and "plurality" are intended to imply provision of two or more elements. The term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0066] It will furthermore be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing the scope of the present disclosure.

[0067] Well-known functions or constructions may not be described in detail for brevity and / or clarity. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0068] As used herein, "dialysis therapy" refers to any therapy that replaces or supplements the renal function of a patient by use of a medical fluid. Dialysis therapy includes, without limitation, extracorporeal (EC) blood therapy and peritoneal dialysis (PD) therapy.

[0069] As used herein, "treatment fluid" refers to any fluid that is consumed as a result of dialysis therapy. Treatment fluid includes, without limitation, dialysis fluid for infusion into the peritoneal cavity during PD therapy, dialysis fluid for supply to a dialyzer during EC blood therapy, and replacement fluid and substitution fluid for infusion into blood during EC blood therapy.

[0070] As used herein, "heat disinfection" refers to a technique of deactivating bacteria and viruses by subjecting them to a fluid at a required temperature for a required time period. The fluid may be water, optionally in combination with a cleaning agent.

[0071] As used herein, "AO concept" refers to an established technique of quantifying the effect of heat disinfection on deactivation of microorganisms. An AO value may be calculated according to: .40 = io( _80) / z■ At , where T is the fluid temperature (in °C), z is a bacteria coefficient, and At is the exposure time at the fluid temperature. By use of this equation, a value of the microbial deactivation may be calculated, by summation or integration, during heat-up, holding, and cooling of any moist heat disinfection process. For example, a condition for sufficient heat disinfection may be that the AO value is at least 500, 600, 700, 800 or 900.

[0072] Like reference signs refer to like elements throughout.

[0073] The present disclosure relates to a technique of supplying a fluid for use in dialysis therapy. The technique is applicable to both peritoneal dialysis (PD) therapy and extracorporeal (EC) blood therapy. For context only, systems for PD therapy and EC blood therapy will be briefly discussed with reference to FIGS 1 A-1B.

[0074] FIG. 1 A is a generic overview of a dialysis system 1 for EC blood therapy. The dialysis system 1 is fluidly connected to the vascular system of a patient P on a fluid path. In the illustrated example, the fluid path is defined by tubing 2a for blood extraction and tubing 2b for blood return. As indicated by arrows, the dialysis system 1 is operable to draw blood from the patient P through tubing 2a, process the blood, and return the processed blood to the patient through tubing 2b. The respective tubing 2a, 2b is connected to an access device (for example a catheter, graph or fistula, not shown) in fluid communication with the vascular system of the patient P. The dialysis system 1 may be configured to process the blood by any form of EC blood therapy, such as HD, HF or HDF. In HD and HDF, a continuous flow of treatment fluid is interfaced with the blood of the patient in a filtration unit ("dialyzer"), resulting in a continuous flow of spent treatment fluid. In HF, fluid ("ultrafiltrate") is drawn from the blood via the dialyzer. In HF and HDF, treatment fluid may be supplied to the blood upstream and / or downstream of the dialyzer. A drain line 3 is connected to the dialysis system 1 for conveying the spent treatment fluid or ultrafiltrate to a drain 4.

[0075] The dialysis system 1 may comprise one or more electrically controlled machines and may be implemented to provide different levels of functionality. In a first implementation, the dialysis system 1 includes a therapy system, which is operable to control the flows of treatment fluid and blood, as well as a fluid preparation system that is configured to generate the treatment fluid for the therapy system by mixing one or more concentrates with purified water, which is received from a source 5 on fluid line 6. In a second implementation, the dialysis system 1 includes the therapy system, the fluid preparation system and a water purification system that is configured to generate the purified water based on source water, which is received from the source 5.

[0076] FIG. IB is a generic overview of a dialysis system 1 for PD therapy. The dialysis system 1 is fluidly connected to the peritoneal cavity PC of a patient P. As indicated by a double-ended arrow, the dialysis system 1 is operable to convey fresh dialysis fluid into PC and to receive spent dialysis fluid from PC on a fluid path 2. The fluid path 2 may be defined by tubing that connects to an implanted catheter (not shown) in fluid communication with the peritoneal cavity PC. A drain line 3 is connected to the dialysis system 1 for conveying the spent dialysis fluid to a drain 4. PD therapy is typically implemented as daily treatment sessions, each comprising a number of fluid exchange cycles. The respective fluid exchange cycle may include a fill phase, a dwell phase and a drain phase, performed in sequence. In the fill phase, fresh dialysis fluid is supplied to PC on fluid path 2. In the dwell phase, the dialysis fluid resides in PC. In the drain phase, spent dialysis fluid is extracted from PC on fluid path 2.

[0077] Like in FIG. 1 A, the dialysis system 1 may comprise one or more electrically controlled machines and may be implemented to provide different levels of functionality. The first and second implementation examples are equally applicable to the dialysis system 1 for PD therapy.

[0078] FIG. 2 is a block diagram of a system for supplying a fluid for use in dialysis therapy. The system will be used for describing a technique of achieving a target temperature of the fluid downstream a heat-and-hold arrangement including an electrical heating device and a vessel. In FIG. 2, the fluid is purified water (product water), and the vessel is arranged for use in degassing of the product water before it is mixed with one or more concentrates to form a treatment fluid for dialysis therapy. The system in FIG. 2 is thus an example of a fluid preparation system.

[0079] The system in FIG. 2 is at least partly located within a machine having an outer casing 19 that defines a supply port or outlet 19a for output of fresh treatment fluid, and a return port or inlet 19b for input of waste fluid. In the illustrated example, which is highly schematic, a fluid line 21a is connected in fluid communication with the supply port 19a by a terminal connector 20a on the fluid line 21a, and a fluid line 21b is connected in fluid communication with the return port 19b by a terminal connector 20b on the fluid line 21b. The fluid lines 21a, 21b are connected in fluid communication with a subject 22 of dialysis therapy. In the example of PD therapy, the subject 22 comprises the peritoneal cavity of the patient (cf. PC in FIG. IB), and the waste fluid is spent dialysis fluid. In the example of EC blood therapy, the subject 22 comprises a dialyzer and an EC blood circuit connected to the dialyzer. The waste fluid may be spent treatment fluid if HD or HDF is performed, or ultrafiltrate if HF is performed. As is well-known in the art, the fluid lines 21a, 21b may be disposable components which are arranged to interface with pumps, sensors, clamps, etc., of the machine.

[0080] The system in FIG. 2 is operated by a control device 30 through control signals Cj, which are generated in accordance with a predefined logic and based on sensor signals Si. In the illustrated example, the control signals Cj include signals Cl-Cl l, and the sensor signals Si include signals SI -S3. These signals will be described below. As noted, FIG. 2 is schematic and further control signals and sensor signals may be used in a real-world implementation.

[0081] The predefined logic of the control device 30 may be implemented by hardware, or a combination of hardware and software. In the example of FIG. 2, the control device

[0082] 30 comprises processor circuitry 31 and computer memory 32. The processor circuitry

[0083] 31 may comprise one or more processors, such as a CPU, DSP, ASIC, FPGA, etc. A control program may be stored in the memory 32 and executed by the processor circuitry 31 to perform any of the methods, procedures, or functions as described herein. The control program may be supplied to the control device 30 on a computer-readable medium, which may be a tangible (non-transitory) product (e.g., magnetic medium, optical disk, read-only memory, flash memory, etc.) or a propagating signal.

[0084] Starting from the left in FIG. 2, the system includes an intake inlet 7a for receiving product water from a source (cf. 5 in FIGS 1 A-1B), and a return outlet 7b for discharging waste fluid, for example into a drain (cf. 4 in FIGS 1 A-1B) or into a fluid line extending to a drain. The inlet and outlet 7a, 7b may or may not be provided with a respective connector, as shown. An inlet line LI extends from the inlet 7a to an inlet port 10a on a vessel 10, and a supply line L2 extends from an outlet port 10b on the vessel 10 to the supply port 19a. A first fluid pump Pl is arranged in the supply line L2 to draw product water through the inlet line LI, via the vessel 10 and through the supply line L2. In the illustrated example, the fluid pump Pl is operated based on a control signal C5, which sets the flow rate in the supply line L2.

[0085] A mixing sub-system 16 is fluidly interposed in the supply line L2 and operable, based on a control signal C4, to mix one or more concentrates with the product water to produce the treatment fluid. The mixing sub-system 16 is configured to generate the treatment fluid on the fly, by mixing the concentrate(s) into the product water as it flows through the mixing sub-system 16. Such in-line mixing sub-systems are well-known in the art and need no further description. Downstream of the mixing sub-system 16, a conductivity sensor 17 is arranged to provide a sensor signal S2 representing the electrical conductivity of the treatment fluid, and a temperature sensor 18 is arranged to provide a sensor signal S3 representing the temperature of the treatment fluid ("fluid temperature"). The sensors 17, 18 may be separate devices, as shown, or be integrated into a unitary device.

[0086] As used herein, a device being "fluidly interposed" in a fluid line implies that the device is inserted into the fluid line to pass, and optionally process, a fluid flowing along the fluid line. In other words, the device defines one or more fluid paths from a first end of the device to a second end of the device, and the first and second ends are connected in fluid communication with the fluid line.

[0087] As noted above, the system includes a heat-and-hold arrangement, which is operated to achieve a degassing of the product water. Specifically, the heat-and-hold arrangement is operable to increase the temperature of the product water and increase the residence time of the flowing water, so as to allow gases in the product water to form bubbles and escape from the fluid. To this end, the heat-and hold arrangement includes an electrical heating device 12 and a vessel, reservoir or tank 10. To increase the residence time of the fluid, the vessel 10 is arranged to contain fluid within the vessel 10 while fluid flows through the vessel 10. In FIG. 2, this is simply achieved by arranging the outlet port 10b above the inlet port 10a, as seen in the vertical direction (direction of gravity). The vessel 10 may include any number of inlet and outlet ports 10a, 10b. It is realized that the vertical location of the lowest outlet port 10b determines the amount of fluid that is contained in the vessel 10 during fluid throughflow. The residence time of the fluid in the vessel 10 is in turn given by the amount of fluid that is contained in the vessel 10, as well as the flow rate of fluid through the vessel 10.

[0088] In a variant, not shown, the fluid level in the vessel 10 is controlled by a float switch, which is configured to mechanically and automatically close the inlet port 10a when the fluid level reaches a maximum level in the vessel 10. In another variant, not shown, the control device 30 is configured to selectively open and close the valve VI based on signals from one or more level sensors that are arranged to sense two or more fluid levels in the vessel 10. Both of these variants allow the outlet port 10b to have any placement on the vessel 10.

[0089] The vessel 10 comprises one or more gas outlets or vents 11 (one shown), which fluidly connect the interior of the vessel 10 to the surrounding atmosphere. Thus, in FIG. 2, the vessel 10 is open to ambient. In a variant, the gas vent 11 may be selectively opened and closed by the control device 30, for example via an on / off valve on the gas vent 11. The electrical heating device 12 comprises a heating element 12a, which is configured to operate by resistive heating, and a supply unit 12b, which is configured to supply an electrical current through the heating element 12a to generate thermal energy (heat). The heating element 12a is arranged in the vessel 10 to be submerged in the fluid therein. In other words, the heating element 12a is suitably arranged beneath the lowest fluid level that can be attained in the vessel 10 during operation of the system. Any number of heating elements 12a may be used. The operation of the heating device 12 is controlled via a control signal C3 to the supply unit 12b. In the illustrated example, a temperature sensor 13 is associated with the vessel 10 to provide a sensor signal SI that represents the temperature of the fluid in the vessel 10. The temperature sensor may be of any type, including an infrared sensor, a thermocouple, a resistance thermometer, a thermistor, a pyrometer, etc. In a variant, the temperature sensor 13 is omitted.

[0090] In a variant, the heating element 12a is instead arranged in the inlet line LI, i.e., located upstream of the vessel 10. It is currently believed that a more efficient and well- controlled heating of the product water is achieved by arranging the heating element 12a inside the vessel 10. Further, compared to arranging the heating element 12a in the inlet line LI, the risk that the heating element 12a is damaged by being inadvertently powered in a dry environment is reduced by arranging the heating element 12a inside the vessel 10. The heating element 12a is likely to rapidly burn up if powered in a dry environment. This risk is significantly smaller in the vessel 10 than in the inlet line LI, where even a short interruption in the flow of product water may expose the heating element 12a to a dry environment.

[0091] A heat exchanger (HX) 14 is fluidly interposed in the inlet line LI and the supply line L2 to transfer thermal energy from the heated product water that leaves the vessel 10 to the incoming product water. HX 14 defines at least one first fluid channel 14a, which is fluidly interposed in the inlet line LI to receive and pass incoming product water, and at least one second fluid channel 14b, which is fluidly interposed in the supply line L2 to receive and pass the heated product water from the vessel 10. HX 14 is a passive device which is designed to transfer a nominal amount of heat Hl for a given fluid and a given flow rate from the fluid in the second fluid channel(s) 14b to the fluid in the first fluid channel(s) 14a. The transfer of Hl reduces the required power consumption of the heating device 12 to heat the product water within the vessel 10 to a given temperature and maintain the product water at this temperature. HX 14 may be of any type, such as a plate heat exchanger, a tube heat exchanger or a spiral heat exchanger, and HX 14 may be arranged in a counter flow configuration (as shown) or a parallel flow configuration. The fluid temperature at four locations within the system are designated by T1-T4 in FIG. 2. T1 is the temperature of the product water that enters the system via the inlet line LI . T2 is the temperature of the product water in the supply line L2 between the vessel 10 and the HX 14. T2 corresponds to the fluid temperature in the vessel. T3 is the temperature of the product water in the supply line L2 at the outlet of the second fluid channel(s) 14b. T4 is the temperature of the treatment fluid that is provided by the system. T4 corresponds to the temperature measured by the temperature sensor 18. For a fixed T2 and a fixed flow rate of product water through the system, T3 will increase with increasing T1 and decrease with decreasing Tl. If unattended, variations in T3 will result in variations in T4, which will have an impact on the patient. It is generally desirable for T4 to be well-controlled. For example, T4 may be set to body temperature, for example 35-37°C, to minimize the impact on the patient. In some situations, it may be desirable to heat or cool the patient, which may be achieved by increasing T4 or decreasing T4, respectively.

[0092] To enable T4 to be well-controlled, the system includes a thermoelectric heat pump (THP) 15, which is operable to transfer thermal energy (heat) between a first location 15a in the inlet line LI intermediate HX 14 and the vessel 10, and a second location 15b in the supply line L2 downstream of HX 14. The THP 15 is an active device, which is electrically operable to control the amount of heat that is transferred. Also the direction of heat transfer by the THP 15 is controllable. As shown, the THP 15 may be operated to transfer a controlled amount H2 of heat from 15a to 15b, or to transfer a controlled amount H2' of heat from 15b to 15a. The amounts H2, H2' are "controlled" in the sense that they are selectively adjustable. The operation of the THP 15 is controlled by a control signal C2.

[0093] Typically, HX 14 is designed and installed in the system to render a nominal T4, which is equal to a body temperature, for a nominal Tl, which is an average or "common" temperature of the incoming product water. Maximum deviations in Tl, over time and / or between different installations, are typically within ±10°C, which means that the THP 15 needs to be operable to correct for similar deviations in T3.

[0094] A THP 15 utilizes the Peltier effect to create a heat flux at the junction of two different types of materials. Generally, the THP 15 is a solid-state device that transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. A THP is also known as a Peltier device or a Peltier heat pump. An example of a THP is described further below with reference to FIG. 8.

[0095] The THP 15 provides a power-efficient and simple device for stabilizing and controlling the downstream temperature of the treatment fluid that is generated from the product water by the mixing sub-system 16. It may be noted that the THP 15 is more power efficient for increasing the temperature at 15b compared to decreasing the temperature at 15b, since it is easier to transfer heat from a warmer side to a colder side than the other way around. Even more power-efficient operation may be achieved by replacing the THP 15 for a conventional heat pump that operates to transfer thermal energy using a refrigeration cycle. However, compared to a conventional heat pump, the THP 15 has the advantages of being small and silent, operating without moving parts, having long operative life, and requiring little or no service and maintenance.

[0096] A technical advantage of using the THP 15 (or a conventional heat pump) lies in its ability of being switched between adding thermal energy and removing thermal energy at 15b. This is a significant technical advantage that expands the utility of the system in FIG. 2, for example by allowing for a wider range of product water temperatures.

[0097] The system of FIG. 2 includes a return line L3 that extends from the return port 19b to the outlet 7b for discharge of waste fluid. In the illustrated example, a fluid pump P2 is arranged in the return line 3 and operated based on a control signal C9, which sets the flow rate of waste fluid into the return port 19b.

[0098] In the illustrated example, the system further includes a first connecting line L4, which fluidly connects the supply line L2 to the return line L3 near the ports 19a, 19b. The first connecting line L4 may thus be seen to extend between a location at the port 19a and a location at the port 19b. A set of on / off valves V2, V3, V4 form a first valve device, which is operable to be switched between a normal state and a bypass state. In the normal (first) state, the connecting line L4 is closed, and the supply and return lines L2, L3 are open to the ports 19a, 19b. In the bypass (second) state, the connecting line L4 is open, and fluid flow through the ports 19a, 19b is blocked. In the illustrated example, the valves V2-V4 are operated by control signals C6-C8. The skilled person realizes that the first valve device may be configured in many ways to be switchable between the first and second states.

[0099] In the illustrated example, the system further includes a second connecting line L5, which fluidly connects the return line L3 to the inlet line LI near the inlet 7a and the outlet 7b. The second connecting line L5 may thus be seen to extend between a location at the inlet 7a and a location at the outlet 7b. A set of on / off valves VI, V5, V6 form a second valve device, which is operable to be switched between a normal state and a bypass state. In the normal (first) state, the connecting line L5 is closed, the inlet line LI is open to the inlet 7a, and the return line L3 open to the outlet 7b. In the bypass (second) state, the connecting line L5 is open, and fluid flow through the inlet port 7a and the outlet port 7b is blocked. In the illustrated example, the valves VI, V5 and V6 are operated by control signals Cl, CIO and Cl 1. Alternative configurations of the second valve device are apparent to the skilled person.

[0100] Although not shown in FIG. 2, the system may include a further heat exchanger, which is arranged to transfer heat between the return line L3 and the inlet line LI upstream of HX 14. Such a further heat exchanger is useful to reduce the power consumption of the system when there are concurrent flows in the inlet and return lines LI, L3, by transferring heat from the waste fluid to the product water.

[0101] FIG. 3 is a flow chart of an example method 100 of operating the system in FIG. 2 to generate a flow of treatment fluid via the supply port 19a. The method 100 is performed by the control device 30 being operated to generate control signals Cl-Cl 1.

[0102] By step 101, a drain flow path is defined through the system. For the system in FIG. 2, this is achieved by setting the first valve device in the bypass state, and the second valve device in the normal state. Thereby, valves VI, V3, V5 are open, and valves V2, V4, V6 are closed.

[0103] In step 102, the fluid pump Pl is operated to generate a flow of product water into and through the system. The fluid pump P2 may or may not be operated.

[0104] In step 103, the electrical heating device 12 is operated to achieve a designated degassing temperature of the product water in the vessel 10. Step 103 may be started when the heating element 12a is submerged in product water, which may be given by a predefined time from start of step 102, a level sensor (not shown) in the vessel 10, a flow sensor (not shown) in the supply line L2, etc. The control signal C3 for the heating device 12 may be generated by open-loop control or closed-loop control, or a combination thereof. Closed-loop control may use signal SI as a feedback signal. Alternatively, the feedback signal may be based on estimations of the fluid temperature in the vessel 10, for example based on the signal S3 from the temperature sensor 18.

[0105] The degassing temperature in step 103 may be set in view of the desired degassing performance. FIG. 4 shows measurement data of oxygen solubility in water as a function of water temperature. As seen, after a plateau at about 50°C, the oxygen solubility decreases rapidly with increasing water temperature. A similar behavior is seen for nitrogen gas. It is currently believed that the degassing temperature should be at least 50°C for adequate performance, and below 100°C to prevent boiling. In some embodiments, the degassing temperature is in the range of 60-97°C, such as 70-95°C.

[0106] In step 104, the mixing sub-system 16 is operated to start mixing the product water with the concentrate(s) at predefined proportions, thereby converting the inflow of product water into a corresponding outflow of treatment fluid. The electrical conductivity of the treatment fluid may be monitored via the signal S2 from the conductivity sensor 17, and the dosing of the respective concentrate may be adjusted (via control signal C4) to maintain a target conductivity of the treatment fluid.

[0107] In step 105, the THP 15 is operated to achieve a target temperature of the resulting treatment fluid (cf. T4 in FIG. 2). In some embodiments, step 105 generates the control signal C2 for the THP 15 by open-loop control, for example based on a look-up table that maps an operating state of the system (flow rate, inlet temperature, etc.) to a THP setting. Thus, in these embodiments, the THP 15 is controlled without temperature feedback from temperature sensors in the system. In other embodiments, for more precise temperature control, feedback control (closed-loop control) is used in step 105. In FIG. 2, the signal S3 may be used as a feedback signal to represent the temperature of the treatment fluid, and the control device 30 may generate the control signal C2 to minimize the difference between the signal S3 and the target temperature. Any type of control algorithm may be used, including P, PI or PID, as well as model-based approaches such as Model Predictive Control (MPC), Linear-Quadratic-Gaussian (LQG), etc. A model-based approach may be implemented to counteract the impact of the thermal inertia of components located between the THP 15 and the temperature sensor 18 on the temperature adjustment of the treatment fluid. Components with potentially high thermal inertia include the heat exchanger 14, the vessel 10, and the mixing system 16.

[0108] In a variant, the temperature adjustment of step 105 is performed before the start of mixing in step 104. In this variant, the THP 15 is operated to achieve the target temperature of the product water at the temperature sensor 18 according to step 105, by open-loop control or closed-loop control, whereupon the dosing of concentrate(s) into the product water according to step 104 is started. If the addition of a concentrate is endothermic, to cause a slight decrease in temperature, the THP 15 may be operated to increase the fluid temperature at position 15b to compensate for the temperature decrease. One reason for performing temperature adjustment before the start of mixing is that the conductivity signal S2 is highly temperature dependent, so conductivity control will be more accurate if the target temperature is achieved before start of mixing.

[0109] By step 106, a production flow path is defined through the system. Step 106 is performed when the treatment fluid fulfils a predefined criterion, for example in terms of conductivity (given by signal S2) and / or temperature (given by signal S3). In step 106, the first valve device may be switched to the normal (first state) so that treatment fluid is supplied via the supply port 19a and waste fluid is received via the return port 19b. The fluid pump P2 is operated to convey the waste fluid along the return line L3 through the outlet 7b. In an alternative, if no waste fluid is generated, only valve V2 is opened in step 106, whereas valve V4 remains closed and valve V3 is closed.

[0110] In step 107, dialysis therapy is performed in accordance with a treatment schedule, which may be predefined or set by medical staff, as is well-known in the art. When the dialysis therapy is completed, the method 100 may proceed to perform a heat disinfection procedure 200, which will be described below with reference to FIGS 5 A- 5B.

[0111] It may be noted that the flow rate of treatment fluid may be determined by the dialysis therapy. In EC blood therapy, the flow rate of treatment fluid is defined by the treatment schedule, since it directly affects the efficacy of the therapy. The flow rate need not be fixed throughout dialysis therapy, but it is well-defined over time. In some forms of PD therapy, the flow rate may also be given by the treatment schedule, for example in Continuous Flow PD (CFPD). As noted above, this is one reason why it is undesirable to control the target temperature by adjusting the fluid flow rate through the system. Thus, it is generally desirable that the fluid pump Pl is operated to generate a predefined flow rate during the dialysis therapy in step 107.

[0112] FIG. 5A is a flow chart of an example method 200 of performing a heat disinfection of the system in FIG. 2. It may be beneficial to perform the method directly after the dialysis therapy (step 107 in FIG. 3), to make use of the heated product water in the vessel 10. The method 200 is performed by the control device 30.

[0113] By step 201, a drain flow path is defined through the system. For the system in FIG. 2, this is achieved by setting the first valve device in the bypass state, and the second valve device in the normal state. Thereby, valves VI, V3, V5 are open, and valves V2, V4, V6 are closed. In step 202, the mixing sub-system 16 is operated to stop adding concentrate(s) to the product water. In step 203, the fluid pump Pl is operated to generate a flow of product water into and through the system. The fluid pump P2 may or may not be operated in step 203. By step 201, the fluid flow generated by step 203 will be directed from the supply line L2 to the return line L3 via the connecting line L4.

[0114] In step 204, the electrical heating device 12 is operated to achieve a designated heat disinfection temperature of the product water in the vessel 10. Experiments indicate that the heat disinfection temperature may be in the range of 80-99°C. Step 204 may be performed by analogy with step 103. By step 204, the fluid temperature in the vessel 10 is increased while there is a continuous flow of product water into and through the system, from inlet 7a to outlet 7b. The flow of product water through the system will push remaining treatment fluid and any remaining concentrate through the outlet 7b, to thereby flush the system. It is to be noted that the product water that flushes the system is well below the heat disinfection temperature, typically below 40-60°C, as a result of the continuous inflow of cold product water and the operation of HX 14. This may be advantageous if the treatment fluid and / or a concentrate is sensitive to excessive temperatures. For example, some acid (A) concentrates and glucose concentrates may be subject to caramelization at high temperatures. The THP 15 may or may not be operated during step 204.

[0115] By step 205, a heat disinfection path is defined through the system. In the example of FIG. 2, the second valve device is switched to the bypass state. This corresponds to valve V6 being open, and valves VI, V5 being closed. By step 205, the fluid flow will be directed from the return line L3 to the inlet line LI via the connecting line L5. In some embodiments, step 205 is triggered when the heat disinfection temperature has been reached in the vessel 10. Alternatively or additionally, step 205 may be triggered when conductivity of the fluid, given by signal S2, is below a predefined limit. The predefined limit may be set to ensure that the system is properly flushed. By step 205, the intake of product water is terminated and the existing product water in the system is circulated in the system, along line LI, vessel 10, lines L2, L4, L3, L5 and back to line LI. Thus, the heat disinfection path is a circulation path, which will be exposed to an elevated fluid temperature. The heating device 12 may or may not be operated to achieve and maintain the heat disinfection temperature in the vessel 10 during step 205. Step 205 is continued until a heat disinfection criterion is fulfilled, whereupon the fluid pump Pl is stopped (and P2, if operating) in step 206. Step 206 may also involve stopping the operation of the heating device 12, if operated in step 205. In one example, the A0 value is monitored, and the method proceeds to step 206 when the A0 value reaches a predefined target. The A0 value may be calculated based on the fluid temperature, for example given by signal SI or S3. In another example, the method 200 proceeds to step 206 when the fluid temperature has exceeded a predefined value for a predefined time. After step 206, the system is again ready to perform the method 100 in FIG. 3.

[0116] FIG. 5B shows another embodiment of the method 200. In step 201', a drain flow path is defined through the system. For the system in FIG. 2, this is achieved by setting the first valve device in the bypass state, and the second valve device in the normal state. Further, VI is closed in step 201'. The embodiment in FIG. 5B presumes that the vessel 10 already contains heated water when the method 200 is started. For example, the vessel 10 is likely to contain heated water when a dialysis therapy has just been completed (cf. method 100 in FIG. 3). By using the existing heated water in the vessel 10, the total duration of the method 200 may be reduced. In the embodiment of FIG. 5B, step 203 is performed to cause the heated water to be drawn from the vessel 10 into the supply line L2, the connecting line L4, and the return line L3, without new water entering the system (since VI is closed). As the heated water is directed along the return line L3 into the outlet 7b, the fluid level in the vessel 10 will decrease. Such a gradual depletion of the vessel 10 is facilitated when the vessel 10 is open to the surrounding atmosphere (cf. vent 11). The electrical heating device 12 may or may not be operated during step 203 to maintain the temperature of the heated water in the vessel 10. Like in FIG. 5A, step 202 may be performed before step 203 to stop the operation of the mixing sub-system 16. In step 205, a circulation path is established, by switching the second valve device to the bypass state. This corresponds to valve V6 being open, and valves VI, V5 being closed. Step 205 may be initiated when a portion of the heated water in the vessel 10 has been drawn from the vessel 10, for example when the fluid level in the vessel 10 reaches a predefined level. By step 205, since the fluid pump Pl is running (and, optionally, also P2), the heated water is circulated on the circulation path. Optionally, valve VI may be opened in step 205 so that new water is admitted into and flows through the vessel 10. If so, step 204 is performed to heat the water in the vessel 10 to the heat disinfection temperature. The flow of heated water on the circulation path is maintained until the heat disinfection criterion is fulfilled in step 206.

[0117] In a variant of the system in FIG. 2, a further heat exchanger (not shown) is arranged to transfer heat from the outgoing fluid in the return line L3 to the incoming fluid in the inlet line LI upstream of HX 14. This will reduce the power consumption of the system.

[0118] In all examples given herein, it is conceivable that the vent 11 is selectively closed during at least part of the heat disinfection procedure. This allows the water to be heated to a temperature of 100°C or more, for example in the range of 100-105°C, which will reduce the total duration of the method 200.

[0119] It may be desirable to avoid conveying fluid from the return line L3 to the inlet line LI during the heat disinfection. This may be avoided in an example system shown in FIG. 6A. For brevity of presentation, the description of the system in FIG. 6A will be limited to differences over the system in FIG. 2. In the following, all valves in the system are collectively referred to as a "valve arrangement" to facilitate the description.

[0120] The system in FIG. 6A has a first recirculation line L4', which fluidly connects the supply line L2 to the inlet line LI near the ports 19a, 7a. The first recirculation line L4' may thus be seen to extend from an end of the supply line L2 to a beginning of the inlet line LI. An on / off valve V2' is arranged in the first recirculation line L4'. The system in FIG. 6A has a second recirculation line L3', which is fluidly connected to and extends between the ends of the return line L3, at the ports 19b, 7b. An on / off valve V4' is arranged in the second recirculation line L3'. Like in FIG. 2, a connecting line L4 fluidly connects the supply line L2 to the return line L3. The connecting line L5 in FIG. 2 has been replaced for a further heat exchanger (HX) 30, which is arranged to transfer heat between the inlet line LI, at a location upstream of HX 14, and the return line L3. HX 30 defines at least one first fluid channel 30a, which is fluidly interposed in the inlet line LI, and at least one second fluid channel 30b, which is fluidly interposed in the return line L3. Like HX 14, HX 30 is a passive device which is designed to transfer heat from a hotter fluid to a colder fluid. As will be described below, thermal energy (heat) H3 may be transferred from the inlet line LI to the return line L3 during heat disinfection.

[0121] In the illustrated example, the valve arrangement includes an on / off valve V7, which is arranged on the vent 11 and is operable to selectively open and close the vent 11. Further, the fluid pump Pl is capable of being operated in two directions and is thus capable of generating a flow directed from the vessel 10 into the supply line L2 (forward direction), or a flow directed from the vessel 10 into the inlet line LI (reverse direction). When the fluid pump Pl is operated in the reverse direction, the valve V7 is closed to cause a flow of heated water from the vessel 10 into the inlet line LI.

[0122] FIG. 6B is a flow chart of an example method 100 of operating the system in FIG. 6A to generate treatment fluid. Some steps will differ from FIG. 3 and will be described in additional detail. In step 101, like in FIG. 3, a drain flow path is established. The drain flow path includes the inlet line LI, the vessel 10, the supply line L2, the connecting line L4, and the return line L3. In the system of FIG. 6 A, the drain flow path is defined by valves VI, V3, V5 being open, and valves V2', V2, V4, V4' being closed. Thereby, the drain flow path is open to the inlet 7a, closed to the outlet 19a, closed to the first and second recirculation lines L3', L4' and open to drain (via the outlet 7b). Steps 102-105 and 107 are identical to the method in FIG. 3. In step 106, like in FIG. 3, a production flow path is established to extend from the inlet 7a along the inlet line LI, through the vessel 10, and along the supply line L2 to the outlet 19a. In the system of FIG. 6A, the production flow path is defined by valves VI, V2 being open, and V2', V3 being closed. Thereby, the production flow path is open to the inlet 7a, open to the outlet 19a, closed to the first and second recirculation lines L3', L4' and closed to the connecting line L4. Optionally, like in FIG. 3, valves V4, V5 may be open, and the fluid pump P2 may be operated to convey waste fluid along the return line L3 through the outlet 7b to drain. It is understood that valve V4' may be closed to enable the fluid pump P2 to pump the waste fluid along the return line L2.

[0123] FIG. 6C is a flow chart of an example method 200 of performing a heat disinfection of the system in FIG. 6A. The method in FIG. 6C corresponds to the method in FIG. 5 A. Some steps will differ from FIG. 5 A and will be described in additional detail. In step 201, like in FIG. 5A, a drain flow path is established. The drain flow path may be identical to the drain flow path established by step 101 in FIG. 6B. Optionally, valve V4' may be open in step 201 so that both L3 and L3' are flushed with product water in step 201. Steps 202-204 and 206 may be identical to the method in FIG. 5 A. As noted with reference to FIG. 5 A, the THP 15 may or may not be operated during step 204. In step 205, like in FIG. 5A, the valve arrangement is operated to establish a heat disinfection path which is a circulation path. In contrast to FIG. 5A, the circulation path does not include the return line L3. Instead, the circulation path is established by use of the first recirculation line L4'. The circulation path includes the inlet line LI, the vessel 10, the supply line L2, and the first recirculation line L4'. In the following, this circulation path is denoted "first circulation path". In the system of FIG. 6 A, the first circulation path is defined by valve V2' being open, and valves VI, V2, V3 being closed. Thereby, the first circulation path is closed to the inlet 7a, closed to the outlet 19a, open to the first recirculation line L4' and closed to the connecting line L4. By step 205, heated product water is circulated through the first circulation path for heat disinfection. To heat disinfect the return line L3, the valve arrangement may be operated to establish a further heat disinfection path that is fluidly separated from the heat disinfection path. The further heat disinfection path is a second circulation path that includes the return line L3 and the second recirculation line L3'. In the system of FIG. 6A, the second circulation path is defined by valve V4' being open, and valves V3, V4, V5 being closed. The fluid pump P2 is operated to circulate fluid in the second circulation path. By HX 30, heat H3 is transferred from the heated product water in the first circulation path to the fluid in the second circulation fluid. The fluid temperature in the first circulation path and the heat transfer capacity of HX 30 may be adapted so that the fluid in the second circulation path is heated to a temperature suitable for heat disinfection.

[0124] In some embodiments, the heat disinfection is terminated (step 206) when the heat disinfection criterion is fulfilled for the first circulation path. In other embodiments, the heat disinfection is terminated when the heat disinfection criterion is fulfilled for both the first circulation path and the second circulation path. The fluid temperature in the second circulation path may be estimated based on the fluid temperature in the first circulation path, or may be given by a temperature sensor (not shown) in the second circulation path.

[0125] In some embodiments of the method 200 in FIG. 6C, the fluid pump Pl may be operated in the reverse direction at least during an initial phase of step 205. This may speed up the heat disinfection of the second circulation path, by increasing the fluid temperature in the fluid channel(s) 30a of HX 30 at the beginning of step 205 and thereby speeding up the increase in fluid temperature in the second circulation path.

[0126] FIG. 6D is a flow chart of an alternative for performing a heat disinfection of the system in FIG. 6 A. The method 200 in FIG. 6D corresponds to the method in FIG. 5B. Some steps will differ from FIG. 5B and will be described in additional detail. In step 201', like in FIG. 5B, a drain flow path is established. The drain flow path includes the inlet line LI, the vessel 10, the supply line L2, the connecting line L4, and the return line L3. In the system of FIG. 6A, the drain flow path is defined by valves V3, V5 being open, and valves VI, V2', V2, V4, V4' being closed. Thereby, the drain flow path is closed to the inlet 7a, closed to the outlet 19a, closed to the first and second recirculation lines L3', L4' and open to drain (via the outlet 7b). Steps 202-203 are identical to the method in FIG. 5B. Like in FIG. 5B, step 203 causes the heated water to be drawn from the vessel 10 into the supply line L2, the connecting line L4, and the return line L3, without new water entering the system (since VI is closed). If necessary, a step 205' may be performed to refill the vessel 10 with heated fluid. In step 205' of FIG. 6D, the valve arrangement may be operated to define a circulation path, which corresponds to the first circulation path but with valve VI open. During and / or after step 205', step 204 may be performed to heat the water in the vessel 10 to a heat disinfection temperature. The THP 15 may or may not be operated during step 204. The method in FIG. 6D further includes step 205, which may be performed as described with reference to FIG. 6C. If step 205' is performed, the system may be simply switched from step 205' to step 205 by closing the inlet valve VI. Like in FIG. 6C, the valve arrangement may be further operated to establish the second circulation path during step 205, and the fluid pump P2 may be operated to circulate fluid in the second circulation path, so that heat H3 is transferred by HX 30. As noted with reference to FIG. 6C, the fluid pump Pl may be operated in the reverse direction at least during an initial phase of step 205. The flow of heated water through the vessel 10 is maintained until the heat disinfection criterion is fulfilled (step 206).

[0127] In a variant of the system in FIG. 6A, HX 30 is omitted and HX 14 is configured as a three-fluid heat exchanger, which is thus fluidly interposed in the inlet line LI, the supply line L2 and the return line L3. Three-fluid heat exchangers are commercially available and need no further description. In some embodiments, HX 14 is fluidly interposed in the return line L3 only during heat disinfection. This may be achieved by a bypass arrangement that is operable to direct any waste fluid that is pumped from the inlet 19b to the outlet 7b, for example during production of treatment fluid, on a flow path outside of HX 14. FIG. 7 shows a variant of the heat-and-hold arrangement in FIG. 2 (and FIG. 6A). In relation to FIG. 2, the first location 15a is shifted from downstream to upstream of HX 14 in the inlet line LI. This will increase the temperature difference between the first and second locations 15a, 15b, which may improve the ability of the THP 15 to transfer heat H2' from 15b to 15a, for example when there is a need to reduce the fluid temperature at 15b. The configuration of the THP 15 in FIG. 2 is likely to be more power efficient for increasing the temperature at 15b compared to decreasing the temperature at 15b. In a further alternative, not shown, the second location 15b may instead be located upstream of HX 14 in the supply line L2. However, the adjustment of the temperature of the treatment fluid (T4) by the THP 15 will be rendered less direct since the intervening heat exchanger. HX 14 has a thermal inertia that will cause dampening and delay between a change of temperature by the THP 15 at 15b and a corresponding temperature change downstream of HX 14.

[0128] In a variant, the system is operable to switch the location 15a between being upstream and being downstream of the HX 14 in the inlet line LI. For example, one side of the THP 15 may be connected by fluid lines (not shown) to the inlet line LI both at a location upstream of the HX 14 and at a location downstream of the HX 14, and one or more valves (not shown) in the fluid lines may be operable to fluidly connect this side of the THP 15 either to the upstream or the downstream location. The one or more valves may be operated manually or by the control device 30. In view of powerefficiency, the downstream location (cf. 15a in FIG. 2) may be preferable when heat is likely to be added to the location 15b, and the upstream location (cf. 15a in FIG. 7) may be preferable when heat is likely to be removed from the location 15b. Thus, by switching the location 15a depending on the actual or expected temperature of the incoming water, the system may be adjusted to maximize its power efficiency.

[0129] FIG. 8 is a section view of an example THP 15. FIG. 8 is given for the purpose of illustration and is not intended to be limiting. The THP 15 comprises a thermoelectric element 50, which is formed by an alternating arrangement of p-type semiconductor blocks 52a and n-type semiconductor blocks 52b. As is well-known, a majority of charge carriers move from low potential to high potential in an n-type semiconductor, and from high potential to low potential in a p-type semiconductor. The blocks 52a, 52b are connected in series by electrodes 53, and are sandwiched between sheets 54 of electrically insulating material. Contact ends of the electrodes 53 are connected by electric conductors 51a, 51b to a power source 51, which is operable to apply a voltage over the thermoelectric element 50 to cause a parallel heat flux through the blocks 52a, 52b, as indicated by block arrows. The heat flux is reversed by reversing the applied voltage. The opposing sides of the thermoelectric element 50 are interfaced with fluid flows Al, A2 in fluid channels 55a, 55b. Optionally, the opposing sides of the thermoelectric element 50 may be provided with surface structures to increase the surface area and thereby increase the heat transfer per unit time. In FIGS 2, 6A and 7, the fluid channels 55a, 55b correspond to the inlet line LI at the first location 15a and the supply line L2 at the second location 15b.

[0130] In the foregoing, the system in FIG. 2 (and FIG. 6A) is operated to generate treatment fluid on-demand for use in dialysis therapy. However, the system may alternatively be configured to generate the treatment fluid off-line, for example for storage in a reservoir. In such a scenario, it may still be relevant to achieve a target temperature of the treatment fluid in the supply line L2, for example to avoid that temperature variations affect the operation of the mixing sub-system 16 or to avoid that temperature variations affect the accuracy of the conductivity sensor 17 (if not temperature-compensated).

[0131] The heat-and-hold arrangement comprising HX 14, vessel 10 and THP 15 is not only applicable for degassing of product water in a fluid preparation system, as shown in FIG. 2 and FIG. 6 A. In an alternative, the heat-and-hold arrangement is included in a water purification system for generating product water from source water, for example tap water. The heat-and hold arrangement may be installed in the water purification system for degassing of the source water upstream of a purification sub-system. In FIG. 2 and FIG. 6 A, the block 16 may represent such a water purification sub-system, which may perform purification by sedimentation, filtering, reverse osmosis, ion exchange, etc. Alternatively or additionally, the heat-and-hold arrangement may be installed in the water purification system for degassing of the product water.

[0132] The technique described hereinabove is not limited to degassing, but is generally applicable to all situations in which a fluid for use in dialysis therapy is heated while flowing through a vessel, which is configured to contain a portion of the heated fluid, and where it is relevant to achieve a target temperature of the fluid downstream of the vessel. For example, fluid in the vessel 10 may be used as a buffer to ensure access to heated fluid in the event of an intermediate power loss.

[0133] While the subject of the present disclosure has been described in connection with what is presently considered to be the most practical embodiments, it is to be understood that the subject of the present disclosure is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the appended claims.

[0134] Further, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the parti- cular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

Claims

CLAIMS1. A system for supplying a fluid for use in dialysis therapy, said system comprising: a vessel (10) for holding the fluid, an inlet line (LI) arranged to direct the fluid to an inlet port (10a) on the vessel (10), an electrical heating device (12) arranged for heating the fluid in the vessel (10), a supply line (L2) arranged to direct the fluid from an outlet port (10b) of the vessel (10), at least one fluid pump (Pl, P2) for achieving a flow of the fluid along the inlet line (LI), through the vessel (10), and along the supply line (L2), a heat exchanger (14), which comprises one or more first fluid channels (14a) and one or more second fluid channels (14b) and is configured to transfer heat between the one or more first fluid channels (14a) and the one or more second fluid channels (14b), wherein the one or more first fluid channels (14a) are fluidly interposed in the inlet line (LI), and the one or more second fluid channels (14b) are fluidly interposed in the supply line (L2), a heat pump (15), which is operable to transfer heat between a first location (15a) in the inlet line (LI) and a second location (15b) in the supply line (L2), and a control device (30) configured to operate the heat pump (15) so as to achieve a target temperature of the fluid in the supply line (L2) downstream of the heat exchanger (14) and the second location (15b).

2. The system of claim 1, wherein the heat pump (15) is a thermoelectric heat pump.

3. The system of claim 1 or 2, wherein the second location (15b) is downstream of the one or more second fluid channels (14b) in the supply line (L2).

4. The system of any preceding claim, wherein the first location (15a) is upstream or downstream of the one or more first fluid channels (14a) in the inlet line (LI).

5. The system of any preceding claim, further comprising a temperature sensor (18) arranged to provide a sensor signal (S3) indicative of fluid temperature in the supply line (L2) downstream of the heat exchanger (14) and the second location (15b),and wherein the control device (30) is configured to control the heat pump (15) by feedback control based on the sensor signal (S3).

6. The system of any preceding claim, wherein the control device (30) is configured to operate the at least one fluid pump (Pl, P2) to achieve a predefined flow rate of the fluid through the supply line (L2) while the heat pump (15) is operated to achieve the target temperature of the fluid.

7. The system of any preceding claim, wherein the electrical heating device (12) comprises a heating element (12a) arranged within the vessel (10) to be submerged in the fluid.

8. The system of any preceding claim, wherein the control device (30) is configured to operate the electrical heating device (12), during a degassing procedure (100), to achieve a predefined fluid temperature within the vessel (10) so as to release entrained gases from the fluid within the vessel.

9. The system of claim 8, wherein the vessel (10) comprises a gas outlet (11), which is open to surrounding atmosphere during the degassing procedure (100).

10. The system of claim 8 or 9, wherein the predefined temperature is in a range of 50-99°C, preferably in a range of 60-97°C.

11. The system of any preceding claim, wherein the control device (30) is configured to operate a valve arrangement in the system to define a production flow path from an intake inlet (7a) on the inlet line (LI) via the vessel (10) to a supply outlet (19a) on the supply line (L2), and to operate the at least one fluid pump (Pl, P2) to pump the fluid along the production flow path so as to supply the fluid at the supply outlet (19a).

12. The system of claim 11, wherein the control device (30) is configured to perform a heat disinfection procedure, said heat disinfection procedure (200) comprising: operating the valve arrangement to define a disinfection flow path, in which the supply line (L2) is fluidly connected, at a location downstream of the heat exchanger (14), to the inlet line (LI), at a location upstream of the heat exchanger (14), and fluid flow through the supply outlet (19a) is blocked, andoperating, while the fluid in the vessel (10) has a heat disinfection temperature, the at least one fluid pump (Pl, P2) to achieve a circulating flow of the fluid along the disinfection flow path until a heat disinfection criterion is fulfilled.

13. The system of claim 12, which further comprises a return line (L3), which extends from a return inlet (19b) to a return outlet (7b), wherein the heat exchanger (14) or a further heat exchanger (30) is arranged to transfer heat between the inlet line (LI) and the return line (L3), and wherein the heat disinfection procedure (200) comprises: operating the valve arrangement to define a further disinfection flow path, which is fluidly separated from the disinfection flow path and includes the return path (L3), and operating a fluid pump (P2) in the further disinfection flow path to achieve a circulating flow of the fluid along the further disinfection flow path.

14. The system of claim 13, wherein the heat disinfection procedure (200) further comprises: operating the at least one fluid pump (Pl, P2), during at least part of the heat disinfection procedure, to pump the fluid in a direction from the vessel (10) into the inlet line (LI).

15. The system of claim 12, which further comprises a return line (L3), which extends from a return inlet (19b) to a return outlet (7b), and wherein the disinfection flow path includes at least part of the return line (L3).

16. The system of any one of claims 12-15, wherein the heat disinfection procedure (200) further comprises: operating, at start of the heat disinfection procedure, the valve arrangement to establish fluid communication between the supply line (L2) and a drain (4), close the inlet line (LI) upstream of the heat exchanger (14), and operate the at least one fluid pump (Pl, P2) to pump a portion of the fluid in the vessel (10) into the supply line (L2) towards the drain (4).

17. The system of claim 16, wherein the heat disinfection procedure (200) further comprises: operating, when said portion of the fluid in the vessel (10) has been pumped, the valve arrangement to open the inlet line (LI) to achieve a throughflow of the fluid from the intake inlet (7a) via the inlet line (LI) through the vessel (10); and operating the electrical heating device (12) to attain the heat disinfection temperature of the fluid in the vessel (10) while the at least one fluid pump (Pl, P2) is operated to achieve the throughflow.

18. The system of any one of claims 12-17, wherein the heat disinfection temperature is in a range of 80-105°C.

19. The system of any preceding claim, wherein the outlet port (10b) is located above the inlet port (10a) to retain a volume of the fluid in the vessel (10) as the fluid flows through the vessel (10)20. The system of any preceding claim, further comprising a mixing sub-system (16), which is fluidly interposed in the supply line (L2) and operable to mix the fluid with one or more concentrates for generation of a treatment fluid for use in dialysis therapy.

21. The system of any one of claims 1-19, further comprising a water purification sub-system (16), which is fluidly interposed in the supply line (L2) and operable to process the fluid for removal of impurities to generate water suitable for use in dialysis therapy.

22. A computer-implemented method of supplying a fluid for use in dialysis therapy, said method comprising: operating (102) at least one fluid pump to convey the fluid from a fluid source through an inlet line into a vessel and from the vessel through a supply line, while directing the fluid in the inlet line through one or more first fluid channels of a heat exchanger and while directing the fluid in the supply line through one or more second fluid channels of the heat exchanger, wherein the heat exchanger is configured for heat transfer between the one or more first fluid channels and the one or more second fluid channels; operating (103) an electrical heating device to heat the fluid in the vessel; and operating (105) a heat pump to transfer heat between a first location in the inlet line and a second location in the supply line, to achieve a target temperature of the fluid in the supply line downstream of the heat exchanger and the second location.

23. The method of claim 22, wherein the electrical heating device is operated, during a degassing procedure (100), to achieve a predefined fluid temperature within the vessel so as to release gases from the fluid within the vessel.

24. The method of claim 22 or 23, further comprising: operating (101) a valve arrangement to define a production flow path from an intake inlet on the inlet line viathe vessel to a supply outlet on the supply line, and operating (102) the at least one fluid pump to pump the fluid along the production flow path so as to supply the fluid at the supply outlet.

25. The method of any one of claim 24, which comprises a heat disinfection procedure (200) comprising: operating (205) the valve arrangement to define a disinfection flow path, in which the supply line is fluidly connected, at a location downstream of the heat exchanger, to the inlet line, at a location upstream of the heat exchanger, and in which fluid flow through the supply outlet is blocked, and operating (203), while the fluid in the vessel has a heat disinfection temperature, the at least one fluid pump to achieve a circulating flow of the fluid along the disinfection flow path until a heat disinfection criterion is fulfilled.

26. The method of claim 25, wherein the heat disinfection procedure (200) further comprises: operating (205) the valve arrangement to define a further disinfection flow path, which is fluidly separated from the disinfection flow path and includes a return path, which extends from a return inlet to a return outlet, and operating (203) a fluid pump in the further disinfection flow path to achieve a circulating flow of the fluid along the further disinfection flow path.

27. The method of claim 26, further comprising: operating (205) the at least one fluid pump, during at least part of the heat disinfection procedure, to pump the fluid in a direction from the vessel into the inlet line.

28. The method of claim 25, wherein the valve arrangement is operated to include at least part of a return line, which extends from a return inlet to a return outlet, in the disinfection flow path.

29. The method of claim 25-28, wherein the heat disinfection procedure (200) further comprises: operating (20 T), at start of the heat disinfection procedure, the valve arrangement to establish fluid communication between the supply line and a drain, and to close the inlet line upstream of the heat exchanger, and operating (203) the at least one fluid pump to pump a portion of the fluid in the vessel into the supply line towards the drain.

30. The method of claim 29, wherein the heat disinfection procedure (200) further comprises: operating (205’), when said portion of the fluid in the vessel has been pumped, the valve arrangement to open the inlet line to achieve a throughflow of the fluid from the intake inlet via the inlet line through the vessel; and operating (204) the electrical heating device to attain the heat disinfection temperature of the fluid in the vessel while the at least one fluid pump is operated to achieve the throughflow.

31. A computer-readable medium comprising computer instructions, which when executed by processor circuitry (31), causes the processor circuitry (31) to perform the method of any one of claims 22-30.

Images