METHOD AND APPARATUS FOR RECOVERING HEAT FROM WASTEWATER

Abstract: A method of recovering heat from wastewater, sewage and other similar, not 100% pure liquid for utilization in a heat pump or the like, in which air is utilized as a heat transferring medium between wastewater and circulation medium in the heat pump. The novelty is that the wastewater, the sewage or the like is retained in the holding compartment (5) before being discharged in wastewater conduits or the like, that air is blown into the water by means of at least one nozzle (14, 14') extending down under the wastewater surface, and that the air above the water surface, which will thereby be saturated with aqueous steam, is caught and led through a heat exchanger apparatus (17) for emission of heat to the circulation medium of the heat pump (2) before being blown down again into the wastewater.

Description: METHOD AND APPARATUS FOR RECOVERING HEAT FROM WASTEWATER The present invention relates to a method of re¬ covering heat from wastewater, sewage and other simi¬ lar, not 100% pure liquid for utilization in a heat pump or the like, in which air is used as a heat-trans- 5 ferring medium between wastewater and circulation me¬ dium in the heat pump. Several attempts have Rarlier been made to recover heat in wastewater, sewage and the like. According to Swedish printed Application 410,764 use is made of the 10 ventilation air in the sewer system, which air has been heated during the passage through said system by the sewage passing on therein in a heat pump. In this prior art apparatus air is supplied to the sewer system di¬ rectly from the atmosphere and follows the sewage con- 15 duits up to a building where the heated air is branched off and is allowed to pass the heat exchanger to a heat pump. In this prior art apparatus one starts, so to speak, from atmospheric air, which means that during the winter season, when the heat demand is the greatest, 20 the temperature of the incoming air often is consider¬ ably below the freezing point. This means that much en-, ergy will get lost exclusively for the purpose of heating the air to such a temperature that the heat pump can give some economic yield. In the application of prior 25 art technique the fact is that the heat yield will be inferior the greater the water flow is. As the part of the conduit area occupied by water increases, the area available to throughflowing air will become less. The heat exchange between water and air xvill also be 30 very bad since transfer will take place only in the boundary layer between water and air. The object of this invention is to provide an apparatus permitting a far better recovery of the heat content in wastewater. PR/BP The essential characteristic of the method accord- ing to the invention resides in: retaining in a holding compartment the wastewater, the sewage or other similar liquid, before being discharged in wastewater conduits or the like; blowing air into the water by means of at least one nozzle opening under or above the wastewater surface; and catching the air, which during said blowing is caused to pass the water and become saturated with aqueous steam, and leading it through a heat exchanger for emission of heat to the circulation medium of the heat pump before being blown down again in the waste¬ water. The invention and an apparatus for carrying out the method according to it will be described more fully be- low with reference to examples of embodiment illustra¬ ted in the accompanying drawings, in which: . Fig. 1 shows schematically how the apparatus can be installed in a residential building; Fig. 2 shows a flow diagram for the apparatus; Fig. 3 is sectional side view of an embodiment of the invention; Fig. 4 is a top view showing the same embodiment; and Fig. 5 is a side view of another embodiment of the invention. Fig. 1 illustrates how the apparatus of the inven- .tion can be installed. The wastewater or sewage conduits from the building are designated by 1. A heat pump 2 which may be of conventional design is connected in the usual way with a water heater 3. According to the in¬ vention a device 4 for recovery of heat from the waste¬ water is intercalated in the sewage conduit 1 so that effluent water will pass it before the water, deprived of its heat content, is discharged in the discharge net. ' In order to obtain the required holding time for the wastewater or sewage in a container or tank 5 in¬ cluded in the apparatus, said container or tank is con- structed so as to retain a certain amount of water. The two embodiments of. the apparatus according to the invention are different as far as the design of the tank 5 is concerned. In both the embodiments the container or tank 5 is closed also upwardly. In the embodiment according to Figs. 2 - 4 the tank 5 has an inlet 6 and an outlet 7. The inlet 6 is placed at the top of the tank and the outlet 6 is placed at a vertical distance from the bottom 8 of the tank. This makes that a predetermined amount will always be in the tank and that when water is supplied a corresponding quantity will leave the tank through the outlet. In the embodiment of Fig. 5 a pump conduit 9 from a submersible pump 10 arranged adjacent the bottom of the tank is connected to the outlet 7' which is spaced from the tank bottom and serves only as an overflow outlet. The pump 10 may of course be replaced by a suc¬ tion tube from a pump mounted at another suitable point and the pressure tube of which is allowed to open into the outlet 7*. The pump is controlled by a floating body 11 which senses the water level in the tank 5 and starts the pump when an upper level has been reached and stops it when a predetermined lower level has been reached. In both the embodiments a fan means 12 is arranged adjacent the tank 5. This may consist of one or, as shown in Fig. 2, two or more fans. The pressure tubes of the fans 13 has blow nozzles 14 which, in the embo- diments shown, open under the water surface 15 in the tank 5. If the air is given high speed they may open above the water surface. The suction channel 16 to the fan extends from the closed upper part of the tank 5 where the air saturated .with aqueous steem is collected. Arranged in the air circulation circuit between the suction side and the pressure tubes is an air/liquid heat exchanger 17. The liquid side of this exchanger is coupled to a heat pump 2 in Fig. 1 via conduits 18 . *» In the embodiment according to Figs. 2, 3 and 4 the pressure tubes 13 and nozzles 14 of the fans 12 are stationary and open at a predetermined distance under the water surface 15. In this embodiment the water sur¬ face remains constant because the in- and outlets 6, 7 are situated at a predetermined distance from the bottom 8 of the tank. In the embodiment according to Fig. 5, where the water level may vary, the nozzle 14' of the pressure tube 13 is adapted to be movable and connected with the floats 11 so that the nozzle can be displaced up¬ wards and downwards by the floats according as the wa¬ ter surface changes. The nozzle will thereby be situa- ted at the intended distance from the water surface, under said surface or, alternatively, above it. In operation, when there is wastewater in the tank, air is pressed by means of the fan 12 through the pres¬ sure tubes or tube 13 down into the wastewater. During the passage through the water the air will be heated and absorb aqueous steam. The air-steam mixture will thereupon, under the influence of the fan, be sucked through the suction channel 16 and pass through the heat exchanger 17 where heat is emitted to the circu- lation medium of the heat pump for passing on to the pump. The apparatus of the invention utilizes as heat transferring medium not only the air heated by the waste¬ water but also, and to a higher degree, the aqueous steam which is released during the passage of the air through the water. The aqueous steam is condensed in the heat exchanger, which gives a substantially increased heat yield. Calculations and tests taken have proved that it is possible without any difficulties to reach a constant and high efficiency of about 80%. With the use of normal heat pump technique this in- invention makes it possible to utilize those great amounts of energy which normally get lost with waste¬ water and sewage. The apparatus according to the in¬ vention will not require any accumulator or other ex- pensive and bulky accessory units. The main reason therefor is that hot water consumption and the demand of hot water production will coincide in time. The ap¬ paratus of the invention may have a very wide power range with maintained efficiency. This applies especial* ly to the embodiment according to Fig. 5 where the treatment may take place batchwise. The apparatus of the invention permits simple mounting in practically any building since, especially if the embodiment of Fig. 5 is applied, no regard has to be paid to drops in the discharge conduit. The invention should not be considered restricted to that described above and shown in the drawings but may be modified in various ways within the scope of the appended claims.

Claims: CLAIMS 1. A method of recovering heat from wastewater, sewage and other similar, not 100% pure liquid for uti¬ lization in a heat pump or the like, said liquid being retained in a holding compartment (5) before it is dis- charged in wastewater conduits or the like, and in which air is utilized as a heat transferring medium between liquid and circulation medium in the heat pump, c h a r a c t e r i z e d by: - circulating the air in a closed system while causing the air by means of at least one nozzle (14, 14') to be brought into in¬ timate contact with the liquid in the holding compart¬ ment whereby it will be saturated with aqueous steam; and catching this air and leading it through a heat ex¬ changer apparatus (17) for emission of heat to the cir- culation medium of the heat pump (2) prior to being brought in contact again with the liquid. 2. Apparatus for carrying out the method as claimed in claim 1, in which air is used as heat transferring medium between the liuid and a circulation medium in a heat pump (2), c h a r a c t e r i z e d in that the air circulates in a closed system, that at least one nozzle (14) connected with the pressure side of at least one fan or the like (2) is adapted to open under or above the water surface of a liquid thus retained in order to blow down air into it, that the otherwise closed compartment (5) has at least one exhaust opening (16) situated above the water surface and connected with the suction side of said fan, and that there is arranged in the channel, provided with the fan, between said exhaust opening (16) and the nozzle (14), a heat exchanger (17) which is adapted to be passed by circu¬ lation air which flows through said channel and which under its contact with the liquid has been heated and mixed with aqueous steam in order to emit heat to the circulation medium of the heat pump. 3. Apparatus as claimed in claim 2, c h a ¬ r a c t e r i z e d in that the compartment, in which the liquid is temporarily retained, consists of a con- tainer with an outlet (7) spaced from the bottom thereof. 4. Apparatus as claimed in claim 3, c h a ¬ r a c t e r i z e d in that the mouth of a suction tube for a pump, a submersible pump or the like (10) is arranged at the bottom (8) of the container (5) , and that the container (5) includes a floating means (11) sensing the liquid level therein and actuating a switch for the pump in order to keep the liquid level in the container within predetermined limits. 5. Apparatus as claimed in claim 4, c h a - r a c t e r i z e d in that the nozzle (14') connected with the pressure side of the fan (12) is movable and connected with the floating means (11) sensing the liq¬ uid level, so that the nozzle (14) will be kept at a predetermined distance from the liquid surface inde- pendently of the liquid level.

Inventors: WALLIN LENNART, WALLIN, LENNART
Applicants: WALLIN LENNART, WALLIN, LENNART
Application year: 1985
Main classification: F24J3
IPC codes: F24D17