FR2490329A1 - Heat recovery from polluted hot water - uses two heat exchangers of spiral tubes to heat cold water feed - Google Patents

Abstract

The circuit recuperates heat contained in dirty hot water. The dirty water is sent successively into two receptacles each with a separate heat exchanger. The cold water running across these exchangers is heated, by conduction, slowly in one and quickly in the other. The water then passes separately towards the hot water tank and drain tanks. The heat exchanging process is completely static. The dirty water circulates near the cold water circuit as a counter flow before separately heated. The waste water circulates in a small container and the exchangers are spiral and tubular.

Description

 The present invention relates to a process for recovering calories from waste water, as well as a device for implementing this process.

 It finds its place in the context of the fight against wasted energy.

 Hot water, both domestic and industrial, is usually discharged into the sewer. The heat energy they contain is thus permanently lost.

 The present invention allows the permanent recycling of a large part of this energy, and therefore achieves a significant saving.

 Certainly, the idea of recovering calories from wastewater is not new.

 In known methods and devices of this kind, an attempt has been made to solve the problem by using sophisticated equipment, using probes, solenoid valves, pump, electronic regulator, etc. Such complexity, reliability and hypothetical unrtdement, to which comes add a high cost price, condemned such systems.

 The present invention does not have these drawbacks. It does not call upon any mechanics; simple in its organization, easy to install1, low cost, certain reliability since its operation is static, it guarantees an indisputable economy.

 The subject of the invention is a process for recovering heat energy from hot waste water, characterized in that this waste water statically and permanently loses a significant part of the calories which it contains in drinking water, this thanks to a double exchanger.

 The first exchanger is contained in a small tank where the wastewater circulates. Arranged in the form of a coil, it instantly torises.

 The second exchanger plunges into a large tank where the wastewater is stored. Its tubular cylindrical shape which characterizes it allows an exchange by accumulation.

 Drinking water benefits, we see two superimposed exchanges, in communication with each other, which are counted or supplement each other.

 The explanations which follow will show us this.

 The invention also relates to a process for the flow of drinking water, characterized by the fact that it borrows successively, as we have just seen, the two exchangers, and then separates, to be consumed directly, on the one hand, and replenish the hot water tank, on the other hand.

These processes, which are closely linked to each other, using two separate exchangers and a particular path, constitute the device which is the subject of the present invention.
This will be well understood thanks to the light of the following description, made with reference to the appended drawings, of which Figures 1 to 4 represent the various functions of the device.

Referring first to FIG. 1, it can be seen that the installation consists of:
1. A small waste water receiver 1 in which a submersible exchanger 2 supplied with drinking water dives.

 2. A storage tank 3 receiving the water from the receiver I thanks to an overflow 4 and in which there is a cylindrical exchanger 5 where the drinking water also circulates.

3. A distribution circuit for said consumption water, punctuated in 6 - 7 - 8 - 9 v 10 and 11
Figure 2 shows in detail the receiver washes its exchanger 2
1 o The receiver first, consists of a plastic envelope 1 whose dimensions may be, but not limited to, depending on the areas of application, twenty centimeters in diameter for a height of sixty centimeters. This cylindrical envelope, closed in the lower part, receives a removable cover 12 allowing maintenance visits to the device.

 This envelope is equipped with: a) a collector 13 infected with the collection and guiding of waste water. It opens into the upper part of the tank.

 b) an overflow 4 originating at the bottom of the tank in order to favor the phenomenon of thermosyphonage and to preserve as much as possible the hottest waters contained in the upper part of the tank.

 c) a depletion valve 14 allowing the complete emptying of the device.

 d) thermal insulation 15.

 2. The exchanger 2 is a coil made of spiral copper tube over the total height of the receiver, in a direction which allows exchange against the current.

 Easy disassembly of the device allows complete cleaning.

 FIG. 3 shows in detail the storage tank 3 with the cylindrical exchanger 5.

 1. The tank is made of plastic. Its dimensions can be, but are not limited to, depending on the areas of call cation; one hundred and twenty five centimeters in height for a diameter of sixty centimeters; that is to say a capacity of three hundred and fifty liters.

 It is equipped with: a) an overflow 16, a collector 17 and a depletion valve 18 identical to those which are fitted to the receiver 1 and operating in the same way.

b) a stratification plate 19 placed halfway up the tank and crossed by the exchanger
A certain clearance allows a slower circulation of worn batten between the two upper and lower compartments which it delimits.

 c) a safety overflow 20.

d) insulation 21
2. The tubular cylindrical exchanger 5 is made of copper. Its dimensions may be (without limitation for the same reasons as above), eighty centimeters in height for a diameter of twenty eight centimeters, its content then being about fifty liters.

 It is arranged in the tank 3, so that its upper part is always submerged; its lower part is provided with feet, in order to keep it raised and out of contact with the coolest water located at the bottom of the tank.

 It is crossed by a bundle of copper tubes 22 with a preferential diameter of 34/36. Open at their two ends, their function is to increase the exchange potential of the device and to give it better resistance to pressure. However, their lower opening 23 is constricted. This constriction associates its effect with that which is.

obtained by the stratification plate 19 to slow the wise passage of waste water between the upper and lower parts of the tank.

 The water in the cold water circuit enters and arrives at the bottom of the exchanger, after having crossed it from top to bottom in the current flow thanks to a tube which ends in a tee 24. It comes out through another copper tube which originates at the top 25.

The operation of the device which has just been described is as follows:
During a call for hot water on a station 10, the waste water from this drawing is sent to the receiver l in which it gives up a significant part of its calories to the drinking water which circulates in the exchanger at serpentine 2.

After having been freed of these calories, the waste water travels through the overflow 4 until it reaches the storage tank 3. The excess calories which it has not lacked in the receiver i will replace those which have have been absorbed by the consumption strip which was contained in the exchanger 5 during the dead time between the present drawing and the previous
Here is a description of the wastewater route.

Let’s analyze the one borrowed by drinking water
At the same time, the stress exerted on the drawing station 10 causes an appEl on the cold water inlet 6
The water contained in the exchanger 5 is set in motion and rises to pass through the exchanger 2
This water has benefited from a first exchange of temperature in the storage tank 3. This first exchange can be described as long or "by accumulation"; the drinking water contained in the tubulated cylinder 5 having had the interval between two withdrawals to gradually raise its temperature as a function of that of the wastewater in which it is bathed.

We will give it the qualifier "temperate water" when it arrives in 7
The second exchange, short or "instant", occurs in
the coil exchanger 2 where the drinking water, already tem perée sssenrichiL new calories, especially as the
temperature of the water withdrawn, then used, which passes through the receiver
1, is high
We will give it the qualifier "lukewarm water" when
she arrives in 8
This is when this lukewarm water breaks up into arr
in 9 to take two directions; one towards the ball
hot water 11 where it is called in place of water
hot drawn;; the other, to the draw-off station 10.

This double path allows a double economy, direct and indirect, or rather two complementary savings
In fact, the water first tempered, then lukewarm then comes to benefit directly from the drawing, by slowing down the flow of the hot water circuit coming from the tank (first saving); and; indirectly to the balloon itself, which benefits from a preheated water inlet, will consume less energy to raise its temperature (second economy)
They are complementary, because the division into 9 is done in proportions which arithmetically complement each other
We said, on page - 1-, lines 37 - 38 - 39 -, that the two exchangers, too, complement or replace each other.

They complement each other, indeed, when racking and emptying are
This is not the case when drawing a bath for example. Because the bath emptying is closed, the coil exchanger 2 becomes inoperative. It is at this time that the accumulation exchanger 5 supplements to the failure of the first.

This is the main reason which led to the adoption of two two associated exchangers
It is not the only one
The solution of a coil exchanger immersed in the
storage tank 3 had the disadvantage of a risk of fouling, leading to a drop in yield.

In addition, the tank 3 receiving wastewater at different
temperatures, some cold since the system is not
selective, the exchanger, under these conditions, would have lost its ef
while, immersed in a receiver 1 located immediately
tely under the fall of the wastewater, it takes advantage, without waiting for the calories they offer. The voluntarily reduced dimension of this receiver allowing the residual water it contains permanently to offer only a low inertia, viX defeated by the new contributions. In this way it ensures a profitable modular function
By way of nonlimiting example, an installation carried out as a prototype in an existing individual building will be described below.
This building lent itself particularly well to the experiential; indeed, the hot and cold water pipes, as well as the outlets and the hot water tank, were united in a zone of the ground floor. floor located vertically under the bathroom.

This is how the installation work of the system and its removal at the end of the experiment did not last more than four hours.
The prototype was in all respects in accordance with the description and the drawings attached to this request
Initially, the tank 3 was loaded, that is to say filled with lukewarm water so as to prime the cessus, simulating plausible conditions of use.

The temperature of the cold water supply was twelve degrees
proves experience: it is carried out empty, i.e. by switching off heat exchangers 2 and 5. However, the wastewater is collected in the tank 3
We draw 96 liters of water at 40 degrees in the bathtub simultaneously drained
It can be seen that: a) the temperature of the waste water around the overflow 16 varies from approximately 22 to 24 degrees
b) the temperature of the waste water stored in the upper part of the tank 3 reaches 35 degrees
A first analysis of these results shows that the position of the overflow 16 whose orifice is located in the lower part of the tank 3, as well as the separating partition 19
played their role in promoting stratification
The expense for this experiment is 2,800 w.

2nd experiment: it is carried out 4 hours after the end of the first. We proceed to a new racking, identical to the first, that is to say 96 liters at 40 degrees, while the exchanger 5 is put into service (excluding of the exchanger 2)
It can be seen that the temperatures of the waste water at the top and bottom of the tank are roughly the same as in the first experiment.
Throughout the duration of the experiment, the temperature of the cold water circuit at the outlet of the exchanger was measured at point 7, that is to say water qualified as detem perated in our description. following results are saved
During the drawing of the first ten liters 34 to 32 degrees
"""""next 32 to 29
Then 29 to 27
And 27 to 25 "
So 25 to 23
From 23 to 21 'I
Suite 21 9 19
For 19 to 18
Finish 18 to 17
During the drawing of the last six liters 17 to 16.5 n
If we add the calories thus recovered, taking into account the temperature of the cold water inlet at 12 degrees we get the average result per liter of 12 degrees taken from the wastewater. This result, modest in appearance, however, translates into an economy greater than forty percent that the graph in Figure 4 shows
This is confirmed by the expense which comes out at 1,600 W.

about instead of 2,800 the previous time
3rd experiment: It took place under the same conditions as the second, except that the evacuation of the dry water is deferred. The water drawn is collected in the bathtub and is not evacuated until the end of filling
The savings achieved under these conditions are practically the same as in the previous case.

It should be noted that these experiments were carried out under deliberately unfavorable conditions: long racking (equivalent to that of a bath) which gradually depletes the capacity of the exchanger 5
For a shorter drawing (30 liters for a shower for example), the calculations taken from the second experiment give the following results: 18 degrees taken from each liter of waste water. The savings then exceed sixty percent.

4th experiment: Exchanger 2 has been put into service, i.e. coupled with exchanger 5
Prior to the experiment Xon registers a temperature of 31 degrees at the top of the storage tank 3
We support, in the same way as before, 96 liters of water at 40 degrees with immediate drainage.

 It is noted that, during the drawing off, the temperature, at the outlet of the overflow 16 does not exceed 22 degrees, that recorded on the cold water circuit, at the outlet of the exchangers, at point 8 (this is to say that which is qualified as lukewarm in our description), varies as follows as the water is drawn, and for each ten liters: 30 -30 -29 -28 -27 -27.5 -27 -26 5- 26 5-26 5.

 Compared with the second experiment, the yield has improved considerably. The drop in temperatures which ranged from 34 to 16.5 degrees is only this time from 30 to 26.5 degrees. this thanks to the instant exchange effect produced by exchanger 2. It has stabilized above all to a much higher degree.

 The combination of the effect of the two exchangers made it possible to obtain a saving which the calculations put at sixty percent.

 The expenditure recorded during this experience confirms this.

5th experiment: withdrawal of 30 liters of cold water;
It is found that this cold water does not appreciably affect the temperature at the top of the tank.

 6th experiment: racking of 30 liters using only the cold water circuit which crosses the two exchangers.

We therefore closed the arrival of the hot water circuit.

 Beforehand the temperature recorded at the top of the tank is 33 degrees.

 During the experiment the temperature drops only from 32 to 29.5 degrees. This would have made it possible to take a shower for free, for example.

 It follows from this experience that it will be in the lion's interest to plan a separate circuit to obtain fresh batten.

 The system may include a purifying filter and a decasser.

The device, object of the invention, can be used in
all the cases where hot water has its reason to be. It finds its place in the industrial and domestic fields (dairies, laundry, bathrooms) The co-activities (schools, municipal showers) offer a particularly interesting field of application .

 The graph in FIG. 4 shows the percentages of savings that can be hoped for as a function of the temperatures reached by lukewarm water coming from the cold water circuit, after it has passed through the exchangers.

 The calculations were made taking into account a 12 degree cold water inlet.

 If we take the example of the representative curve of lukewarm water having reached 26 degrees, we can read that the economy is 50% for a demand for hot water at 40 degrees. This economy reaches 61 S; when the demand is 35 degrees.

 The range of current use of hot water (in gray on the graph) which can be estimated to be between 340 and 46 for the needs of a bathroom for example, shows a saving spreading out from 30 to 100%, for lukewarm water varying between 22 and 36 degrees a

Claims (5)

 1. Method for recovering the calories contained in hot wastewater, characterized by the fact that consists in sending this wastewater successively in two containers each containing a separate heat exchanger, while the cold water circuit traverses these exchangers against current, by preheating by conduction, slowly in one and quickly in the other, before going separately to the hot water tank and to the draw-off station.  2. Method according to claim 1, characterized in that the temperature exchange between 11 waste water and the consounatqon water stops statically, crest to say without any intervention r1veanlque.  3. Method according to claim 1, characterized by the fact that consists of making a strip coming from the cold water circuit against the current in the exchangers before it separates to take advantage of its preheating, and the balloon hot water, and the draw-off station in service.  4. Device according to claim 1, characterized in that the waste water circulates in a container of small capacity in which plunges a coil exchanger spiral in the direction of the link, said waste water then passing through an overflow originating in the lower part of the container, to be conducted in a gran capacity tank where a tubular cylindrical exchanger is immersed, the latter tank itself being provided with an overflow arranged in the same way as the previous one.  5. Device according to claim 1, characterized in that the cold water circuit is preheated by slow conduction, staying between two withdrawals, in the tubular cylindrical echaflower, and, by rapid conduction, during a withdrawal, in the coil exchanger, the two exchanges complementing or replacing each other.