GB2060864A

GB2060864A - Method and plant for heat recovery from sewage water

Info

Publication number: GB2060864A
Application number: GB8034208A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-10-24
Filing date: 1980-10-23
Publication date: 1981-05-07
Also published as: SE430184B; DE3039505A1; SE7908805L; GB2060864B

Abstract

A method and plant for the recovery of heat from sewage water is characterized in that the sewage water from the upper part of a collecting cistern (9) is led to a heat exchanger unit (14) and therefrom again to the lower part of the cistern (9). A heat exchange medium such as water is circulated (20, 21) through the heat exchanger unit in a counterflow relative to the sewage water, whereby the heat absorbed in the heat exchange medium from the sewage water is recovered in the evaporator (23) of a heat pump (22). The heat exchange unit (14) comprises pipe coils (15) through which the heat exchange medium flows and which are located in annular chambers through which the sewage water flows. The pipe coils are cleaned by brushes on a rotating arm (Fig. 3). <IMAGE>

Description

SPECIFICATION Method and plant for heat recovery from sewage water This invention relates to a method of recovering heat from sewage water and to a plant for performing this method.

Large amounts of heat energy are lost with sewage water. This heat energy primarily originates from hot water supplied by tap (bath, washing, dish-washing, cleaning) but also from cold water, which is heated owing to the cold water pipes being laid in warmed rooms.

It also originates from cooking activities (drain) and from human beings (faeces and urine). This applies to residential buildings as well as to industrial premises, public baths and hospitals.

No practically applied solution has heretofore been developed for recovering this heat energy. The reasons for this are primarily, that the sewage water is heavily contaminated, has a relatively low temperature, and that its flow varies widely in time, the variations ranging from substantially zero to a maximum value during the day.

In accordance with the present invention there is proposed a method of recovering heat from sewage water, characterized in that the sewage water is led upwardly into a collecting vessel, from the upper part of which it is discharged to a heat exchanger unit, from which the cooled sewage water again is led in return into the lower part of the collecting vessel, from which lower part the sewage water is discharged, a heat medium circulating in the heat exchanger unit and heated by the sewage water being led to the evaporator of a heat pump and thereafter returned to the heat exchanger unit.Also in accordance with the present invention there is proposed a plant for heat recovery from sewage water, comprising a cistern with a supply pipe for sewage water and an outlet at the bottom of the cistern for connecting the sewage water to a discharge pipe, a heat exchanger unit, a pipe connecting the heat exchanger unit with the upper part of the cistern for the transport of hot sewage water to the heat exchanger unit, and a pipe connecting the heat exchanger unit with the cistern for transporting the sewage water from the heat exchanger unit to the cistern, the heat exchanger unit having coils for a heat medium circulating in said coils and absorbing the heat in the sewage water, piping leading a heat medium heated by the sewage water to an evaporator, and piping connecting the evaporator with the coils for leading the heat medium cooled in the evaporator, which evaporator is located in a heat pump.

The invention is described in greater detail by reference to the accompanying drawings which illustrate a preferred embodiment of plant and in which: Figure 1 shows how a plant according to the invention can be coupled to a sewer, Figure 2 is a schematic side view of the plant, Figure 3 is a section of the heat exchanger comprised in the plant, Figure 4 is a plan view of the heat exchanger in Fig. 3, Figure 5 shows a portion of a detail comprised in the heat exchanger, and Figure 6 shows a part of the plant with four heat exchangers connected in series.

In Fig. 1 there is shown a building 1, for example a hospital, and a sewer 2 extending from the building. The sewer 2 has a branch pipe 3 coupled to a pumping station 4, which, via a pipe 5 pumps the sewage water to a heat recovery plant 6 constructed according to the invention. From the heat recovery plant 6 the sewage water, from which heat has been recovered, is re-cycled to the sewer 2 via a pipe 7. That portion of the sewer 2 which is located between the branch pipes 3 and 7, acts as a shunt pipe and has a valve, which normally is closed when the plant is in operation. The heat energy recovered from the sewage water, for example in the form of hot water, is transported to the consumer, i.e. the hospital building 1, via pipes 8.

The sewage water is pumped to the heat recovery plant, shown schematically in Fig. 2, via the pumping station 4 through the pipe 5 upwardly into a sewage water cistern 9 (Fig.

2), which is connected at the bottom to a pipe 7 for draining the cooled sewage water off through the sewer 2. Towards the bottom of the cistern 9 there is connected a level pipe 10, which is connected to the pipe 7. A valve 11 is located in the pipe 7 between the cistern and the level pipe. When this valve 11 is closed the sewage water in the cistern is on the same level (37) as the bend of the level pipe 1 0. From the upper part of the cistern 9, the "hot" sewage water which has entered and which may have a temperature of about 30-40"C during the day, is tapped via a pipe 1 2 to a heat exchanger 14, which will be described later.The heat energy in the sewage water is emitted in the heat exchanger 1 4 to pipe coils 1 5 arranged therein, whereafter the sewage water flows back from the heat exchanger to the cistern 9 through a pipe 13, which opens into the bottom part of the cistern, as shown in Fig. 2. In order to prevent solid impurities from being passed to the heat exchanger 14, a sieve is connected ahead of the pipe 1 2. This sieve 1 6 has the form of a cylindrical basket, in which the cylinder surface consists of a sieve network extending upwardly above the liquid level 37.

The upper part of cistern 9 contains arms 1 7 which have nozzles and are intended to rotate about a central shaft. For cleaning the sieve network, the liquid level in the cistern 9 is lowered by opening the valve 11 whereafter the sieve network is flushed clean by means of the rotating nozzles, which are supplied with flusing water via the pipe 1 8. The impurities which have adhered on the outside of the sieve network are thereby released and sink to the bottom of the cistern 9. The sieve network preferably is flushed clean at regular intervals, of for example 24 hours, whereby simultaneously sludge collected on the cistern bottom is discharged via the valve 11.

In the present instance water is used as the heat absorbing medium in the pipe coils 1 5 of the heat exchanger 14, this water being stored in a water reservoir 1 9. Cold water is led from the bottom region of the reservoir via the pipe 20 to the heat exchanger 14, in which the water is heated by the sewage water and returned to the upper region of the reservoir 19 via the pipe 21. Also coupled to the water reservoir 19, is a heat pump 22 with evaporator 23 and condenser 24, so that the hot water at the top of the reservoir emits its heat energy via the pipe 25 to the evaporator 23, from where it is recycled to the bottom region of the reservoir, in which the cooled water is stored.Also shown is a circulation pump 43, an electric motor 26 with compressor, and outgoing and ingoing pipes 27 to the circulation circuit for the heat carrier of the heat pump, i.e. for the medium, which is heated by the sewage water (and by the energy supplied to the compressor) and to be used for consumption and/or heating purposes. This medium, for example, may be water.

In order not to interfere with the layer formation between cold bottom water and hot surface water occurring in the cistern and reservoir, the outlets from the pipes 15, 21 and 26 are extended by diffusers 28, as shown in Fig. 2, through which the speed of the liquid flowing out can so far as possible be reduced.

The reservoir 1 9 serves as a buffer during the period of low energy supply through the sewage water, for example during the night, in that the reservoir has a volume for storing so much hot water that the heat pump during this period can be supplied with hot water.

The principle of the plant according to the invention having been described, from which description also the mode of operation of the plant should be apparent, the heat exchanger 14 is hereafter described in greater detail.

Without a satisfactorily operating heat exchanger, the plant would not operate satisfactorily. The heat exchanger, therefore, must be deemed to be a critical part of the entire system.

The heat exchanger 14 which is shown comprises a housing 29 with a central passage 30. A plurality of heat exchanging surfaces are arranged concentrically in the hous ing and in relation to each other. Each surface consists of a plurality of pipe coils coupled in parallel (in Fig. 3 and 5 twenty coils are shown). The ends of the pipes 1 5 are comprised in a "surface package" are connected to a common distributor 32, by which the head medium, in this case the water, is led into the pipe coils 15, and to a common recipient 33, by meand of which the water is collected and discharged from the package.

As appears from the Figures, the water is pumped by the circulation pump 34 via the pipe 20 and distributor 32 into the pipe coils of the first package 1 5. The water is led via the recipient 33 from the first package through a connecting pipe 35 to the distributor 32' of the package located inside of said first package (Fig. 4). From the recipient 33' of this package the water is led to the third package via a pipe 35' and distributor 32".

From the recipient 33" of this third package the water is led to the fourth package via the pipe 35" and distributor 32"'. From the recipient 33"' of the fourth package the water is led via the pipe 21 to the upper portion of the reservoir 1 9.

Between the concentrically arranged heat exchanger packages 15, concentrically arranged partition walls 36 are located. These walls downwardly abut the bottom of the heat exchanger housing and upwardly extend over the level 37 of the sewage water in the heat exchanger. The pipe 1 2 from the cistern 9 opens into the inner compartment of the heat exchanger, i.e. between the inner wall of the housing (passage wall 30) and the innermost partition wall 36. The sewage water is discharged from the heat exchanger via the pipe 13, which is connected to the outermost compartment of the heat exchanger, as appears from Figs. 3 and 4. Near the bottom of the partition walls 36 there are openings 37 and these, in the embodiment shown, extend along a radius to the outlet 1 3.It will be apparent from the foregoing that the heat absorbing water flows through the heat exchanger coils connected in series from the outermost package to the innermost one, while the sewage water, the heat of which is to be recovered, flows from the innermost chamber to the outermost one via the open ings 37. The energy exchange thus occurs according to the counterflow principle, in such a manner that the sewage water temperature drops by steps from compartment to compart ment, while the water temperature in the coils increases after a bent curve.

Upwardly in the heat exchanger there is a rotary arm 38, which is driven by a motor 39 via a shaft 40 extending through the central passage 30 of the housing 29. This arm and shaft are mounted in a conventional manner (not shown). The arm 38 has vertically di rected brushes 41, (Fig. 3), which upon rotation of the arm sweep the pipe coils 1 5 and thereby keep the surfaces of the pipe coils clean. As clearly appears from Fig. 2, the plant shown is entirely "open", and the surface of the sewage water in the cistern 9 and in the heat exchanger 14 will be at the same level 37. The pump effect required for circulating the sewage water through the heat exchanger 14 is obtained by rotation of the arm and therewith the movement of the brushes in the chambers. In principle, the pump is a very slowly operating circulation pump.The flow rate of the sewage water through the heat exchanger can be controlled by the speed of the arm 38 and/or a valve 42 in the outlet from the heat exchanger, (Fig. 4).

The brushes 41 are exchangeable and easily accessible from the upper side of the heat exchanger.

Fig. 2 shows a simple plant layout i.e. with a cistern 9, a heat exchanger 14 and a reservoir 1 9. It is, of course, possible to connect in series several such systems or instead of one to provide several heat exchangers coupled to a cistern and a reservoir.

In order to reduce the size of the heat exchanger, several smaller heat exchangers can be connected in series to each other, the counterflow principle still being maintained.

In Fig. 6 four heat exchangers are shown, each one being in principle similar to the one described. The heat exchanging surfaces of the respective heat exchangers 43 are connected in series to each other via conduits 45, to the supply pipe 20 for the heat medium and to the discharge pipe 21. The sewage water flows from the cistern 9 via the pipe 1 2 in a counterflow through the heat exchangers which, thus, are connected to each other via the pipes 46 for the sewage water.

In the cases of continuous sewage water flows, it is not necessary to use the reservoir 19, but the heat absorbing water can be coupled directly to the evaporator of the heat pump. Instead of using water as the heat medium other media occurring in the field of art and generally used can be applied.

Claims

1. A method of recovering heat from sewage water, characterized in that the sewage water is led upwardly into a collecting vessel, from the upper part of which it is discharged to a heat exchanger unit, from which the cooled sewage water again is led in return into the lower part of the collecting vessel, from which lower part the sewage water is discharged, a heat medium circulating in the heat exchanger unit and heated by the sewage water being led to the evaporator of a heat pump and thereafter returned to the heat exchanger unit.

2. A method as defined in claim 1, characterized in that the heat medium from the heat exchanger unit is led to the upper part of a reservoir, and that the heat medium after the evaporator of the heat pump is led to the lower part of the reservoir.

3. A method as defined in claim 1 or claim 2, characterized, in that the heat medium is led into substantially cylindrical heat exchange surfaces located concentrically inside each other in the heat exchanger unit, commencing from the outer surface, that the heat medium is led from the innermost surface to the evaporator, that the sewage water is led to flow about the heat exchange surfaces, commencing from the innermost surface, and that the sewage water is led from the region for the outer surface to the collecting vessel part.

4. A plant for heat recovery from sewage water, comprising a cistern with a supply pipe for sewage water and an outlet at the bottom of the cistern for connecting the sewage water to a discharge pipe, a heat exchanger unit, a pipe connecting the heat exchanger unit with the upper part of the cistern for the transport of hot sewage water to the heat exchanger unit, and a pipe connecting the heat exchanger unit with the cistern for transporting the sewage water from the heat exchanger unit to the cistern, the heat exchanger unit having coils for a heat medium circulating in said coils and absorbing the heat in the sewage water, piping leading a heat medium heated by the sewage water to an evaporator, and piping connecting the evaporator with the coils for leading the heat medium cooled in the evaporator, which evaporator is located in a heat pump.

5. A plant as defined in claim 4, characterized in that the heat exchanger unit consists of a cylindrical housing comprising at least one heat exchanger, in which housing cylindrical formed heat exchanging surfaces are concentrically arranged in spaced relationship and communicating with each other, and walls located concentrically between said surfaces, a pipe for the transport of hot sewage water to the heat exchanger opening in the region for the innermost heat exchange surface in the housing, and a pipe for the transport of the sewage water to the cistern joining to the radially outer part of the housing, piping for heated heat medium connected to the innermost heat exchange surface, and piping for cooled heat medium being connected to the outer heat exchange surface.

6. A plant as defined in claim 5, characterized in that the cylindrical housing is arranged with it's axis vertical, and that cleaning members sweeping the heat exchange surfaces are arranged to extend in that axial direction of the housing from a carrying means rotatable about the axis.

7. A plant as defined in claim 6, characterized in that the cistern and the heat exchanger unit form with each other communicating vessels, and that circulation of the sewage water through the heat exchanger unit is effected by movement of the cleaning members.

8. A plant as defined in any one of the claims 4 to 7, characterized in that the outlet of the cistern is connected to a level pipe which opens into a discharge pipe, which forms a shunt pipe with a valve between the level pipe and the cistern bottom.

9. A plant as defined in any one of the claims 4 to 8, characterized in that the piping for heated heat medium comprises a first pipe which opens into the upper part of a reservoir, from which upper part a second pipe leads to the evaporator. and that the piping for cooled heat medium comprises a third pipe, which from the evaporator opens into the lower part of the reservoir, from which lower part a fourth pipe leads to the heat exchanger unit.

10. A plant as defined in claim 9, characterized in that the first and the second pipe open into a first common upwardly directed diffusor, the opening of which is located in the vicinity of the liquid level in the reservoir, and that the third and the fourth pipe open into a second common downwardly directed diffusor, the opening of which is located in the vicinity of the bottom of the reservoir.

11. A plant as defined in any of claims 4 to 10, characterized in that the pipe for hot sewage water is connected to a sieve basket located in the upper part of the cistern and extending above the sewage water surface, and that the pipe for transporting the sewage water from the heat exchanger unit to the cistern opens into a downwardly directed diffusor, the opening of which is located in the vicinity of the cistern bottom.

1 2. A plant as defined in any of claims 5 to 11, characterized in that the heat exchanger comprises two or more heat exchangers, the heat exchange surfaces of which are connected in series with each other, the heat exchangers being connected in series with respect to the flow of sewage water through the heat exchangers.

1 3. A method for recovering heat from sewage water substantially as hereinbefore described with reference to the accompanying drawings.

14. A plant for recovering heat from sewage water and constructed substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.