WO2023105085A1

WO2023105085A1 - Heat exchanger arrangement for wastewater

Info

Publication number: WO2023105085A1
Application number: PCT/EP2022/085388
Authority: WO
Inventors: Kent SAMUELSSON; John-Andreas PETTERSSON
Original assignee: Samster AB
Current assignee: Samster AB
Priority date: 2021-12-10
Filing date: 2022-12-12
Publication date: 2023-06-15
Anticipated expiration: 2024-06-10

Abstract

A heat exchanger arrangement for harvesting energy from wastewater, which arrangement comprises a container (1, 101, 201) having a wastewater inlet (2, 102, 201) and a wastewater outlet (3, 103, 203 ). Abed (7, 107, 207) comprising tire derived aggregate (TDA) is contained in said container (1, 101, 201). At least one heat absorbing conduit (8, 10, 108, 110, 208, 210) arranged to conduct a heat absorbing medium is embedded in said bed (7, 107, 207).

Description

HEAT EXCHANGER ARRANGEMENT FOR WASTEWATER

TECHNICAL FIELD

[0001] The present disclosure relates to the field of energy harvesting and in particular to a heat exchanger arrangement for harvesting energy from wastewater. The arrangement may find applications for harvesting energy from e.g. greywater emanating from households, wastewater generated at industries or process water used at breweries and other foodstuff industries.

BACKGROUND

[0002] There are many applications at which it is desirable to recover energy carried as heat in wastewater emanating from for example households and industries. In the past, such energy has been lost by discharging the heated wastewater without any energy recovery at all. However, increasing demands on preservation of the environment and reduction of energy consumption has resulted in the development of arrangements for harvesting energy from such wastewater.

[0003] Such known arrangements typically comprise a traditional heat exchanger where heat carried by the wastewater is transferred to a heat absorbing medium. The heated medium is then conducted to another device at which the absorbed energy is converted into usable energy. The energy absorbed from the wastewater may e.g. be used for heating the air or the domestic water of a building. The heat exchanger may e.g. be a concentric tube heat exchanger where a flow of wastewater is conducted to flow in parallel with a flow of a heat absorbing medium in respective concentrically arranged tubes separated by a heat conducting wall. Alternatively, a plate heat exchanger may be used. In such cases, the heat absorbing medium typically flows inside the heat exchanger in internal spaces formed by the plates. The plate heat exchanger may be immersed in a tank containing the wastewater or may be arranged in a tube or the like where the wastewater is conducted to flow passed the outside of the plate heat exchanger.

[0004] The known wastewater energy harvesting arrangements however, often exhibit a comparatively low energy transfer efficiency. Additionally, at many applications the wastewater contains organic substances which may cause biological growth on the heat exchanger. Such biological growth further reduces the energy transfer efficiency and causes the requirement of periodical cleaning of the heat exchangers.

SUMMARY

[0005] An object of the present disclosure is to provide an enhanced heat exchanger arrangement for harvesting energy from wastewater.

[0006] Another object is to provide such an arrangement which exhibits a comparatively high heat transfer efficiency.

[0007] An additional object is to provide such an arrangement which has a long service life and requires comparatively low maintenance.

[0008] A further object is to provide such an arrangement which may easily be installed at existing wastewater systems an integrated with auxiliary energy systems at the site of installation.

[0009] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0010] The term “wastewater” is used to signify any type of water-containing liquid which has been used in an activity or process in a household, in public service, in industry or in other businesses.

[0011] The term “greywater” is used to signify lightly polluted domestic wastewater generated in households, office buildings, public baths and the like from streams without faecal contamination, i.e., all streams except for the wastewater from toilets. Sources of greywater typically emanates from sinks, showers, baths, washing machines and/or dishwashers.

[0012] The term “tire derived aggregate” and its abbreviation “TDA” is used to signify a bulk material made of recycled tires, which have been shredded into pieces of varying sizes and geometries. ASTM D6270-17 referred to herein is an internationally recognized standard practice for use of scrap tires in civil engineering applications.

[0013] According to a first aspect, the present disclosure provides heat exchanger arrangement as set out in appended claim 1. The heat exchanger arrangement is intended for harvesting energy from wastewater. The heat exchanger arrangement comprises; a container having a wastewater inlet and a wastewater outlet, a bed comprising tire derived aggregate (TDA), which bed is contained in said container, and at least one heat absorbing conduit, arranged to conduct a heat absorbing medium, which heat absorbing conduit is embedded in said bed.

[0014] The heat exchanger arrangement is thus based on the basic principle of arranging a conduit conducting a heat absorbing media in a container or tank where the conduit is immersed in the wastewater which passes through the container from the inlet to the outlet. As the wastewater passes the conduit, heat from the wastewater is transferred through the conduit wall and is absorbed by the heat absorbing media flowing through the conduit.

[0015] According to the present disclosure this basic principle has been greatly enhanced by arranging the heat absorbing conduit in a bed of TDA in the container and to pass the wastewater through the TDA bed when it flows from the inlet to the outlet. By this means several particularly advantageous properties of TDA is utilized for enhancing the heat transfer from the wastewater to the heat absorbing medium.

[0016] Firstly, the geometrical shape of the pieces of shredded tires causes turbulence in the wastewater flow as it passes the heat conducting conduit. Due to the original annular shape with generally U-shaped cross-section of the tires, the shredded TDA pieces exhibit single or double curved geometries such that the TDA bed will contain a comparatively high amount of voids between individual TDA pieces. When the wastewater flows through the porous TDA bed, turbulence is induced to the flow, which turbulence increases the heat transfer through the conduit wall as the wastewater passes the conduit.

[0017] Secondly, the rubber material often with embedded steel reinforcing wires forming the TDA pieces has a specific heat capacity suitable for absorbing and temporarily storing excessive heat of the wastewater. At may applications, the temperature of the wastewater supplied to the heat exchanger arrangement varies greatly over time. At greywater applications for example, the temperature of the wastewater will be considerably higher after certain activities in the household, such as after cooking and linen washing than after other activities such as rinsing of vegetables and dishes. From an overall energy efficiency perspective, it is preferable if the temperature gradient between the wastewater and the heat absorbing media in the conduit may be kept to fluctuate as little as possible over time. The heat capacity of the TDA allows the TDA to absorb heat from the wastewater at periods of high temperature wastewater supply and to dissipate heat to the wastewater in the container at periods of no or low temperature wastewater supply. By this means the fluctuations of the temperature gradient at the heat transfer through the conduit wall are reduced and the gradient is kept at a suitable value over longer periods of times, such that the overall heat transfer to the heat absorbing media is increased.

[0018] Thirdly, at certain applications, such as at greywater applications, the wastewater comprises organic substances. The rubber material of the TDA has the ability to react chemically with such organic substances in exothermic chemical reactions. Hence, at such applications, the chemical energy stored in the organic substances and in the TDA rubber is converted to heat by the exothermic reactions and transferred to the greywater and further to the heat absorbing medium. By this means the total energy supplied to the absorbing media comprises, in addition to the heat energy carried by the supplied greywater also the chemical energy caried by the organic substances in the greywater.

[0019] Fourthly, the organic substances comprised in greywater and other types of wastewater often comprise phosphates which are harmful to the environment. At the exothermic reactions mentioned above and at other chemical reactions involving the organic substances and the TDA, such phosphates are adhered and bound to the surfaces of the TDA pieces. Thereby the amount of phosphates which reaches the greywater outlet from the container is reduced to thereby reduce the risk of such phosphates reaching and harming the environment.

[0020] Additionally, the tendency of the organic substances contained in the greywater to be bounded to the TDA pieces by chemical reactions counteracts corresponding reactions involving the outer wall of the heat absorbing conduit. Hereby, the formation of so-called biofilms on the heat absorbing conduit is reduced. This is highly advantageous since otherwise, such biofilm formation on the conduit acts as a thermal insulation which reduces the desired heat transfer from the greywater to the heat absorbing medium.

[0021] The heat exchanger arrangement with a heat absorbing conduit embedded in a TDA bed, which bed is passed by the wastewater thus entails several advantages comprising increased heat transfer efficiency, reduced need for maintenance and reduced environmental harm.

[0022] According to embodiments of said first aspect, the porosity of the bed may be 50 - 80 %, preferably 60 - 70 %.

[0023] The TDA comprised in said bed may be Type A TDA according to ASTM

D6270 - 17.

[0024] The mean size of the TDA particles may be 20 - 125 mm.

[0025] The TDA may constitute at least 90 % of the dry weight of the bed.

[0026] The wastewater inlet may be arranged at or above an upper portion of the bed.

[0027] A separator for separating solids from the wastewater may be arranged between the wastewater inlet and the bed.

[0028] At least on heat absorbing conduit may form an upwardly tapering helix embedded in the bed. By this means the heat carried by the downwardly flowing wastewater is evenly distributed over the length of the heat absorbing conduit.

[0029] The heat exchanger arrangement may comprise a first and a second heat absorbing conduit embedded in the bed, wherein the first heat absorbing conduit is arranged at a vertical level above the second head absorbing conduit.

[0030] According to particular embodiments the heat exchanger arrangement may be arranged for harvesting energy from household generated grey water. At such embodiments the volume of the TDA bed may be between 1 and 6 m3 and preferably between 2 and 4 m3.

[0031] At such embodiments the heat exchanger arrangement may comprise two first heat absorbing conduits each having a length of between 15 and 25 m and two second heat absorbing conduits each having a length of 25 and 35 m. [0032] The wastewater outlet may comprise a bypass opening arranged to expel wastewater from the container at excessive incoming wastewater flows through the inlet.

[0033] Further objects and advantages will be apparent from the following description of exemplifying embodiments and from the appended claims

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

[0035] Fig 1 is a sketch schematically illustrating a heat exchanger arrangement according to one embodiment.

[0036] Fig 2 is a sketch schematically illustrating a heat exchanger arrangement according to another embodiment.

[0037] Fig. 3 is a diagram schematically illustrating a heat exchanger arrangement according to another embodiment when used together with a ground source heat pump

DETAILED DESCRIPTION

[0038] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

[0039] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0040] Fig. 1 illustrates schematically a heat exchanger arrangement according to one embodiment. The heat exchanger arrangement is intended harvesting of energy from greywater supplied from a residential building comprising one or several households. The heat exchanger arrangement comprises tank or container 1 having a greywater inlet 2 arranged at the top of the container 1. The container 1 is sealed from the surrounding such that it may be buried in the ground without risking intrusion of foreign matter into the container 1. In the schematically illustrated example, the interior volume of the container is approx. 3,75 m3.

[0041] A greywater supply conduit 4 is connected to the greywater inlet 2. Typically, the upstream end (not shown) of the supply conduit 4 is connected to an arrangement (not shown) for collecting greywater from drain gutters, wash basins, kitchen-sinks and washing machines in the building.

[0042] The arrangement also comprises a greywater outlet 3 which comprises an outlet tube 12 which extends vertically from a lower mouth 13 arranged in proximity to the bottom of the container 1 to an upper outlet arrangement situated generally in level with the upper surface of a TDA bed 7 contained in the container 1. The outlet arrangement comprises a first outlet conduit 14 which communicates with the outlet tube 12 and is arranged in level with the normal level of the greywater surface in the container 1, i.e. approximately at the upper surface of the TDA bed 7. A second outlet conduit 15 is arranged above the first outlet conduit at a level situated above the normal level of the greywater surface in the container 1. Also the second outlet conduit 15 communicates with the outlet tube 12. A bypass opening 16 is arranged in the outlet tube 12, above the normal level of the greywater surface, i.e. above the TDA bed 7. The first 14 and second 15 outlet conduits are connected to a common greywater drainage conduit 5. The drainage conduit 5 may be connected to the municipal or a private sewage. However, from an environmental point of view it may be advantageous to recirculate the greywater from the heat exchanger arrangement to the building as technical water or even as drinking water. In such instances, the drainage conduit 5 may be connected to one or several filtration and/or water purification arrangements (not shown) for making the water usable as technical or drinking water.

[0043] At normal flow rates of the incoming greywater supplied to the greywater inlet 2, the surface level of the greywater contained in the container 1 will lie generally in level with the upper surface of the TDA bed 7. At such conditions the greywater will exit the container through the lower mouth 13, the outlet tube 12 and the first outlet conduit 14 as indicated by the flow arrow Fl shown in fig. 1. At excessive incoming flow rates however, the limited flow capacity of the first outlet conduit 14 will limit the outlet flow such that the surface level of the greywater will rise in the container. When the greywater surface reaches the level of the bypass opening 16, the excessive incoming greywater will be expelled from the container via the bypass opening 16 and the second outlet conduit 15 as indicated by flow arrow F2. The outlet arrangement described above assures that the surface level of the greywater does not rise above the intended level.

[0044] A separator 6 for separating solids from the incoming greywater is arranged inside the container 1, in proximity to and downstream of the greywater inlet 2. At the shown example, the separator 6 comprises a strainer plate which extends horizontally over essentially the entire cross-sectional area of the container 1. The exemplifying strainer has a mesh size of 3 mm. However, any mesh size in the range of 2-5 mm has proven useful for greywater applications.

[0045] The container further contains a bed 7 of tire derived aggregate (TDA). In the shown example, the TDA is a TDA denominated CLR LF-001, provided by Wieder Tech incorporated association. The TDA comprises vulcanised cross-linked rubber with steel and textile reinforcements obtained by shredding rubber tires. The TDA has further been cleaned for eliminating small loose particles and any zinc oxide present after the shredding process. The particle size of the cleaned TDA is 20 - 125 mm, the non-compacted porosity is 65-67 % and the bulk density is approx. 360 kg / m3.

[0046] Due to the double curved three-dimensional geometry of the tires from which the TDA is obtained, the individual TDA pieces or particles exhibit single or double curved three-dimensional geometries. By this means, the bed 7 of TDA received in the container exhibits voids in-between the individual TDA pieces and the porosity remains comparatively high when the TDA has been filled into the container 1 to form the bed 7. The bed 7 of TDA occupies the interior space of the container 1 from the bottom up to the separator 6. In the shown example the TDA bed 7 also supports the separator 6, which rests on the upper surface of the TDA bed 7.

[0047] A first heat absorbing conduit 8 is embedded in an upper portion of the bed 7. In the schematic illustration shown in fig. 1, the first heat absorbing conduit extends back and forth one turn between two opposing walls of the container 1. However, in reality the first heat absorbing conduit typically extends back and forth several turns which are arranged such that the total active length of the conduit 8 is distributed over essentially the entire cross-sectional area of the container, at the level of the first conduit 8. In the vertical direction of the bed, the turns are distributed over the upper half portion of the bed 7.

[0048] The ends of the first conduit 8 extends through respective bushings 9 arranged in a container wall. Outside of the container 1, the two ends of the first heat absorbing conduit 8 is connected to a utility device (not shown in fig. 1) for converting the heat energy carried by the conduit into usable energy. In the shown example, the diameter of the first heat absorbing conduit 1, is typically chosen between 15 and 32 mm. At such diameters, the active length of the first heat absorbing conduit, which active length is the length of the conduit that extends through the bed inside the container, is approx. 25 - 50 m.

[0049] A second heat absorbing conduit 10 is also embedded in the TDA bed 7. The second heat absorbing conduit is arranged below the first conduit 8 and in a lower portion of the TDA bed 7. Just as the first conduit, the second heat absorbing conduit 10 extends back and forth several turns which are arranged such that the total active length of the second conduit 10 is distributed over essentially the entire cross-sectional area of the container, at the level of the second conduit 10. In the vertical direction of the bed, the turns of the second heat absorbing conduit 10 are distributed over the lower half portion of the bed 7.

[0050] As for the first conduit, the ends of the second heat absorbing conduit 10 extends through respective bushings 11 arranged in a container wall. Outside of the container 1, the two ends of the second heat absorbing conduit 10 is connected to a utility device (not shown in fig. 1) for converting the heat energy carried by the conduit into usable energy. The first 8 and second 10 heat absorbing conduits may be connected to one and the same utility device or to respective devices. In the shown example, the diameter of the second heat absorbing conduits is between 15 and 32 mm and its active length is approx. 25 - 50 m.

[0051] Both the first 8 and the second 10 heat absorbing conduits carry a heat absorbing medium which is circulated through the respective heat absorbing conduit 8, 10. In the shown example the heat absorbing medium carried in the first conduit 8 is water and the heat absorbing medium carried in the second conduit 10 is a mixture of water and bio ethanol comprising 20-30% of bio ethanol by weight.. In both the first and second heat absorbing conduits, temperature of the heat absorbing medium is kept to approx, between o and 10 °C at the entry into the container 1. This may readily be accomplished in a well-known manner by regulating the utility device (not shown) to which the first and second heat absorbing conduits are connected outside of the container 1.

[0052] In the shown example the heat exchanger arrangement comprises one first and one second heat absorbing conduit. The arrangement may however comprise two or several first heat absorbing conduits and/or two or several second heat absorbing conduits. When dimensioning the heat exchanger arrangement, it is the combined active length of the first and second heat absorbing conduits respectively which are taken into consideration.

[0053] At not shown embodiments of the heat exchanger arrangement, the second heat absorbing conduit is eliminated such that only one, two or several first heat absorbing conduits are embedded in the TDA bed. At such embodiments, the first heat absorbing conduit or conduits may preferably extend vertically over a major vertical portion of the TDA bed.

[0054] Fig. 2 schematically illustrates a heat exchanger arrangement according to a second embodiment. Just as at the embodiments shown in fig. 1 this heat exchanger arrangement also comprises a container 201, with a greywater inlet 202 and a greywater outlet 203. The greywater outlet 203 is designed essentially as the greywater outlet described above with reference to fig. 1 and this description is not repeated here. The container further holds a TDA bed 207 which extends vertically from the bottom of the container 201 up to a separator 206 which is supported by the upper surface of the bed 201. Also at this embodiment, a first 208 and a second 210 heat absorbing conduit are embedded in the TDA bed 207. The first heat absorbing conduit 207 is arranged vertically above the second heat absorbing conduit 210. However, at this embodiment both the first 208 and the second 210 heat absorbing conduits are formed as a respective upwardly tapering helix. By this means, the heat carried by the greywater is evenly distributed over the entire active length of the respective heat absorbing conduit, as the greywater flows downwardly through the TDA bed 207.

[0055] The volume of the container and the TDA bed received therein as well as the active length of the first and, when applicable, the second heat absorbing conduit may vary depending on the wastewater load. At greywater applications, the following values has been proven suitable for an efficient energy harvesting when the heat exchanger arrangement is arranged to receive the grey water produced in a residential building comprising up to 50 apartments, typically housing up to approx. 200 persons:

Interior container volume 3-4 m3

TDA particle size 25-125 mm

TDA bed porosity 60-70 %

TDA bed volume 2,5-3,75 m3

Active length of first heat absorbing conduit 25-50 m

Active length of second heat absorbing conduit 25-50 m

Media flow through first and second heat absorbing 0.5 - 1,5 1/s conduit

Conduit diameter 15 - 32 mm

Harvested power up to 80 kW

[0056] Again referring to fig. 1, in use, greywater is intermittently supplied through the supply conduit 4 to the greywater inlet 2, depending on the instant usage of showers, bathtubs, bathroom and kitchen faucets, dishwashers, washing machines etc. Typically, the temperature of the greywater supplied to the greywater inlet varies between 25 and 80 °C. The greywater flow through the inlet typically varies between 0.3 and 3601/min and the maximum flow may reach 36201/min.

[0057] From the inlet 2, the greywater pours down by gravity onto the separator 6 where the greywater is distributed over the upper surface of the separator 6 and pours down through perforations in the strainer plate. Solids, such as hair, foodstuff and the like are separated from the greywater by remaining on the upper surface of the separator 6. The separated solids may be periodically removed from the separator 6 e.g. by means of a sludge suction device arranged a truck or by manual removal. At an application of the heat exchanger arrangement servicing a residential building with 50 apartments housing approx. 200 persons, it is expected that approx. 1001 of solids is separated per year. This implies that a suitable maintenance interval of approx, twice per year for removing the separated solids is suitable. [0058] After passing the separator 6, the greywater flows through the TDA bed 7 towards the greywater outlet 3. On its way through the bed 7, the greywater first passes the first 8 heat absorbing conduit and thereafter the second 10 heat absorbing conduit. At instances when greywater of comparatively high temperatures is supplied to the container 1, TDA in the upper region of the bed 7 will absorb heat from the greywater as it passes down to the first heat absorbing conduit 8. Correspondingly, when greywater of lower temperatures is supplied to the container 1, heat absorbed by the TDA in the upper portion of the bead 7 will be transferred to the greywater on its passage to the first heat absorbing conduit. By this means the temperature of the greywater passing by the first heat absorbing conduit 8 will typically be maintained at 20-40 °C.

[0059] During the greywater’s passage of the first heat absorbing conduit 8, heat is transferred from the greywater through the conduit wall to the heat absorbing medium circulating through the first conduit 8. The temperature of the heat absorbing medium exiting from the container 1 will thus be higher than the 0-10 °C it has when entering to the container 1. Typically, when exiting the from the container 1, the heat absorbing medium in the first conduit 8 has a temperature of approx. 30 °C.

[0060] Since heat is transferred from the greywater during its passage of the first heat conducting conduit 8, the temperature of the greywater will be lower when it reaches the portion of the bed where the second heat absorbing conduit 10 is embedded. As in the upper portion of the bed 7 the temperature of the greywater is here maintained at a comparatively constant level due to the ability of the TDA in this portion of the bed 7 to absorb and emit heat from and to the greywater. Typically, the temperature of the greywater passing the lower portion of the bed where the second heat absorbing conduit is embedded is maintained at 10-30 °C. When passing the second heat absorbing conduit 10 heat will be transferred from the greywater to the heat absorbing medium in the second conduit 10, such that the temperature of the heat absorbing medium when exiting from the container is approx. 20 °C.

[0061] By arranging the heat absorbing conduits embedded in a bed of TDA the advantages specified in the summary above are achieved. The combined effect of the turbulence inducing geometry, the specific heat capacity and the ability to react exothermically has proven to greatly enhance the energy efficiency of the heat exchanger arrangement as compared to conventional heat exchangers used for harvesting energy from greywater. At installations where the heat exchanger arrangement described above is supplied with greywater from residential buildings comprising 50 apartments housing approx. 200 persons the heat exchanger arrangement may, harvest up to 200 MWh per year. This may be compared to conventional heat exchanger arrangements comprising plate and pipe heat exchangers submersed in a greywater tank where the year average energy harvesting typically is around 70 MWh up to maximum 100 MWh per year.

[0062] In addition to the enhanced energy harvesting efficiency, the heat exchanger arrangement described above also exhibits the advantages of greatly reducing the need for maintenance. This is accomplished due to the ability of the TDA to promote biological growth on the TDA particles, whereby such growth on the heat transferring walls between the greywater and the heat absorbing medium is reduced. By this means the need of rinsing or cleaning of the heat transferring walls may be heavily reduced or even completely eliminated.

[0063] Fig. 3 schematically illustrates a heat exchanger arrangement according to a second embodiment installed in in connection with a ground source heat pump.

[0064] According to this embodiment, the heat exchanger arrangement comprises a container 101 having a greywater inlet 102 connected to a greywater supply conduit 104. A separator 106 for separating solids from the incoming greywater is arranged below the greywater inlet 102. As in the embodiment shown in fig. 1 the arrangement also comprises a greywater outlet 103, comprising an outlet tube 111 which extends vertically from a lower mouth 112 to an upper outlet arrangement. The outlet arrangement comprises a first outlet conduit 113, a second outlet conduit 114 arranged above the normal level of the greywater surface and a bypass opening 115 arranged in the outlet tube 111, above the normal level of the greywater surface.

[0065] A TDA bed 107 is received in the container 101. A first heat absorbing conduit is embedded in the upper half portion of the TDA bed 107 and a second heat absorbing conduit 110 is embedded in the lower half of the bed.

[0066] Fig. 3 further schematically illustrates how the heat exchanger arrangement may be connected to a ground source heat pump arrangement. The heat pump arrangement 300 comprises a ground loop 301 circulating a brine for collecting heat from the ground. Heat collected from the ground is transferred to a refrigerant circulating in a heat pump loop 302 via an evaporator 303. The refrigerant is further circulated through a compressor 304 to a condenser 305, where heat is transferred from the refrigerant to a heat carrying medium circulating in a utility loop 306 . From the condenser 305 the refrigerant is circulated back to the evaporator 303 via an expansion valve 307. The utility loop 306 circulates the heated heat carrying medium to the devices 308, 309 to be heated such as radiators, floor heating circuits, and the like and thereafter back to the condenser 307. Such ground source heat pump arrangements are all known in the art and not described further in detail here.

[0067] Now, the heat exchanger arrangement of this disclosure may be connected to the heat pump arrangement 200 in order to efficiently use the energy harvested from the greywater to thereby decrease the energy consumption of the heat pump arrangement. Typically, the first 108 and second 110 heat absorbing conduits of the heat exchanger arrangement may be connected to the ground source heat pump arrangement 300 in the following manner. The first heat absorbing conduit 108 is connected to a water accumulator tank 310 such that water acting as a heat absorbing medium is circulated from the accumulator tank 310 to the lower end of the heat absorbing conduit 108 in the TDA bed 107 and back from the upper end of the heat absorbing conduit to the accumulator tank 310. Water from the accumulator tank 310 s also circulated from the tank 310 through the warm side of a first heat exchanger 312 and back to the tank 310. The cold side of the first heat exchanger 312 receives cold fresh water from the facility’s cold water supply CW such that this water is initially heated during passage of the first heat exchanger 312. The so initially heated fresh water is conducted from the first heat exchanger 312 to the cold side of a second heat exchanger 314, the hot side of which is integrated in the heat pump loop 3012, between the compressor 204 and the condenser 305. By this means, heat carried by the hot gas in the heat pump loop 302, downstream of the compressor 304, is transferred to the initially heated fresh water in the second heat exchanger 214, such that the fresh water reaches the desired hot water HW temperature to be supplied to utility installations such as sanitary mixers of the facility. Typically, the fresh water reaches a hot water temperature of approx. 45- 60 ⁰ when passing the second heat exchanger 314 for being provided as hot fresh water to in the facility.

[0068] The second heat absorbing conduit 110 of the heat exchanger arrangement is connected to the ground loop 201 of the heat pump arrangement. For this purpose, a shunt valve 316 is arranged in the ground loop 301, such that an adjustable portion of the brine flow, when returning from the bore hole or the like, where the brine absorbs heat from the ground, is branched off to the lower end of the second heat absorbing conduit 110 embedded in the TDA bed 107. The upper end of the second heat absorbing conduit 110 is connected to the shunt valve 316.

[0069] Thus, at the above-described installation example, heat absorbed by the second heat absorbing conduit 110 embedded in the TDA bed 107 is used for raising the temperature of the brine in the ground loop 301 before reaching the evaporator 203. Additionally, heat absorbed by the first heat absorbing conduit 108 embedded in the TDA bed 107 is used for preheating the cold fresh-water CW of the facility before the final conventional heating in the second heat exchanger 314 to the desired hot water supply temperature of the facility. By this means the use of the heat exchanger arrangement efficiently reduces the overall energy consumption of the facility.

[0070] The aspects of the present disclosure have mainly been described above with reference to a few embodiments and examples thereof. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. For example, in the embodiments and examples described above, the heat exchanger arrangement is used for harvesting of energy from household generated greywater. As readily understood, the heat exchanger arrangement may also be used for harvesting of energy from wastewater generated by other means such as wastewater generated in industries or process water generated at breweries and other foodstuff industries. In the description above, CLR LF-001 has been given as an example of TDA which is usable at the heat exchanger arrangement. However, may other types and brands of TDA may be equally suitable.

Claims

1. A heat exchanger arrangement for harvesting energy from wastewater, which arrangement comprises;

- a container (1, 101, 201) having a wastewater inlet (2, 102, 202) and a wastewater outlet (3, 103, 203),

- a bed (7, 107, 207) comprising tire derived aggregate (TDA), which bed is contained in said container (1, 101, 201), and

- at least one heat absorbing conduit (8, 10, 108, 110, 208, 210), arranged to conduct a heat absorbing medium, which heat absorbing conduit is embedded in said bed (7, 107, 207).

2. A heat exchanger arrangement according to claim 1, wherein the porosity of the bed (7, 107, 207) is 50 - 80 %, preferably 60 - 70 %.

3. A heat exchanger arrangement according to claim 1 or 2, wherein the TDA comprised in said bed (7, 107, 207) is Type A TDA according to ASTM D6270 - 17.

4. A heat exchanger arrangement according to any of claims 1-3, wherein the mean size of the TDA particles is 20 - 125 mm.

5. A heat exchanger arrangement according to any of claims 1-4, wherein the TDA constitutes at least 90 % of the dry weight of the bed.

6. A heat exchanger arrangement according to any of claims 1-5, wherein the wastewater inlet (2, 102, 202) is arranged at or above an upper portion of the bed (7, 107, 207).

7. A heat exchanger arrangement according to any of claims 1-6, wherein a separator (6, 106, 206) arranged to separate solids from the wastewater is arranged between the wastewater inlet (2, 102, 202) and the bed (7, 107, 207).

8. A heat exchanger arrangement according to any of claims 1-7, wherein at least one heat absorbing conduit (208, 210) forms an upwardly tapering helix embedded in the bed (207).

9. A heat exchanger arrangement according to any of claims 1-8, comprising at least one first (8, 108, 208) and at least one second (10, 110, 210) heat absorbing conduit embedded in the bed (7, 107, 207), wherein the at least one first heat absorbing conduit (8, 108, 208) is arranged at a vertical level above the at least one second head absorbing conduit (10, 110, 210).

10. A heat exchanger arrangement according to claim 9, comprising two first heat absorbing conduits and two second heat absorbing conduits.

11. A heat exchanger arrangement according to any of claims 1-10, arranged for harvesting energy from household generated greywater, wherein the volume of the TDA bed (7, 107, 207) is between 1 and 6 m3, preferably between 2 and 4 m3.

12. A heat exchanger arrangement according to claim 10 and 11, comprising two first heat absorbing conduits each having a length of between 15 and 25 m and two second heat absorbing conduits each having a length of between 25 and 35 m.

13. A heat exchanger arrangement according to any of claims 1-12, wherein the wastewater outlet (3, 103) comprises a bypass opening (16, 116) arranged to expel wastewater from the container (1, 101) at excessive incoming wastewater flows through the inlet (2, 102).