WO2008029023A1

WO2008029023A1 - Effluent treatment method and treatment plant employing such a method

Info

Publication number: WO2008029023A1
Application number: PCT/FR2007/001434
Authority: WO
Inventors: Patrick Delaine
Original assignee: Nexter Munitions
Priority date: 2006-09-06
Filing date: 2007-09-05
Publication date: 2008-03-13
Also published as: FR2905372A1; EP2066591A1; FR2905372B1

Abstract

The subject of the invention is an effluent treatment method comprising a step of dehydrating/drying the effluent inside at least one drying oven (2) supplied with hot gas by at least one burner (9) using a fuel. This method is characterized in that it comprises an additional step of separately treating a fatty fraction of the effluent, this step consisting in partial dehydration of a fatty fraction of the effluent and supplying combustible fats used to supply at least one burner (9). The invention is also aimed at a treatment plant employing such a method.

Description

PROCESSING METHOD AND ¹ WASTE TREATMENT FACILITY IMPLEMENTING SUCH A METHOD

The technical field of the invention is that of processes and installations for the treatment of effluents.

Known methods of treatment generally comprise means ensuring dehydration or drying of solid residues. These means generally comprise at least one drying oven which is supplied with hot gas by at least one burner using a fuel.

Today there is the problem of limiting greenhouse gas emissions. It is therefore desirable to minimize the use of fossil fuels. The effluents of the treatment plants always include a more or less significant fat fraction which poses problems for its treatment. It must be separated from the water in order to allow the treatment of the latter and its return to the distribution circuits. Generally separation is ensured by filtering upstream of the effluent treatment plants collected. The treatment of concentrated fats being generally carried out by biological treatment in so-called grease trays. The biological treatment of these fats is slow and it strongly depends on the climatic conditions. Changes in temperature and pH affect the performance of the treatment.

Means have been proposed, however, to facilitate the separation of water and fat. These means generally include filtering steps and distillation or evaporation of water. The patents DE4212456 and FR-2833938 thus describe installations combining filtration and fractional distillation or evaporation.

However, the treatments are slow and use a lot of energy. Fatty sludge must always be reprocessed.

It is the object of the invention to provide a method and an effluent treatment plant that allow save energy and limit the use of fossil fuels or from bio mass.

Thus, the subject of the invention is an effluent treatment process comprising a step of dehydration / drying of the effluents inside at least one drying oven supplied with hot gas by at least one burner using a fuel, characterized in that it comprises a complementary step of treating separately a fatty fraction of the effluents, a step consisting in the partial dehydration of a fatty fraction of the effluents and supplying combustible fats used to supply at least one burner.

The partial dehydration step may advantageously be preceded by at least one step of filtration and heating of the fatty fraction of the effluents.

The partial dehydration step will preferably be followed by a step of storing the dehydrated fat in a heated buffer tank. The invention also relates to an effluent treatment plant implementing this method, installation comprising a means for dewatering / drying the effluents and comprising at least one burner supplying hot gas at least one drying oven, installation characterized in that it also comprises means for treating a fatty fraction of the effluents separately to partially dehydrate them, the fats thus extracted being then used by at least one burner. The effluent treatment plant may comprise at least one multi-fuel burner that can use grease or another fuel.

The means for treating the fatty fraction of the effluents may comprise at least one stage for filtering and heating the fat fraction.

The treatment means may comprise at least one dehydration stage of the fat fraction downstream of the filtration stage or stages. The installation may comprise a heated reservoir constituting a storage buffer for dehydrated grease, a tank located downstream of the dehydration stage and connected to the burner. Advantageously, the hot water extracted at the level of the dehydration stage will be used to heat the filter stage (s) and / or the reservoir through a reheating circuit.

The heating circuit can be opened, the overflow of water produced by the dehydration stage being discharged after passing through the heating circuit.

The heating circuit may be coupled to a heat exchanger heated by the burner, so as to form with this exchanger a closed circuit to ensure an initial heating of the filter stages and / or tank-.

The heat exchanger of the dehydration stage may comprise at least two separate circuits, a first circuit that will use the water vapor extracted from the dehydration stage and a second closed circuit that will be connected to a heat exchanger heated by the burner.

The second circuit may include a valve that will regulate the temperature of the exchanger of the dehydration stage. The invention will be better understood on reading the following description of particular embodiments, a description given with reference to the accompanying drawings and in which:

FIG. 1 schematizes an effluent treatment installation according to a first embodiment of the invention,

- Figure 2 schematically an alternative embodiment of such an effluent treatment plant.

The effluent treatment plant 1 according to the invention comprises an effluent dewatering / drying means which is constituted by a drying oven 2 connected to a hot gas generator 3 by a pipe 4.

The effluents 6 are introduced (ES) into the furnace 2 by a hopper 5. They are evacuated via a hatch 7. A carpet motorized rolling mill may be placed at the bottom of the furnace 2 to drive the dried effluents towards the escape hatch 7.

The hot gases are discharged out of the furnace 2 by the pipe 8. The heat can be recovered using an exchanger (not shown) for example to warm the premises or to preheat the effluents.

The heated gas may be air. This gas is heated by a burner 9 which is supplied with fuel by pipes 10a, 10b. The pipe 10a is connected to a tank 11, for example a fuel tank. A valve 12 is interposed on the tubing to isolate the tank 11 of the burner 9.

The tubing 10b is also connected to a second reservoir 13 (or buffer tank) which contains partially dehydrated fats 15.

This tank can be isolated from the burner 9 by a valve 14.

The burner 9 is a multi-fuel burner that can use both fats 15 and another fuel (fuel or gas). Such burners are well known to those skilled in the art. They generally associate for each type of fuel means of specific injection of the fuel in question and which are coupled to ignition means also specific. Fats of organic origin (animal or vegetable) have satisfactory combustibility characteristics. However, it is necessary to thin them for use in a burner. This is why the tank 13 comprises a heating means 16, such as tubes which surround the tank and which are traversed by a fluid having a temperature of the order of 50 ° C so as to keep the fat partially dehydrated at a temperature of the order of 40 ^° C.

It is of course possible to implement a burner using other types of fuel than fuel or gas in addition to the grease (eg wood). According to the invention, the greases used by the burner are supplied directly by the effluent treatment plant.

Thus, the installation 1 thus comprises means making it possible to treat a fatty fraction of the effluents separately in order to partially dehydrate them and thus supply the reservoir 13.

The means for treating the fatty fraction of the effluents thus comprise at least one stage 17 for filtering and heating this fat fraction EG.

Depending on the type of installation considered, it will be possible to treat specific fatty effluents (residues of collection of cooking oils for example) independent of aqueous effluents from collection networks. It may also be provided a stage (not shown) providing a simple separation (for example by decantation) of the fatty part of the effluents arriving from a collection network. The non-fat part will then be treated, for example by the conventional biological processes of the purification plants.

The installation here comprises two filter stages 17a, 17b. Each stage comprises one or more filter screens 18 whose mesh size are chosen decreasing from upstream to downstream. These sieves retain solid impurities. They are periodically cleaned and the impurities removed are baked 2.

An example of a cleaning filter that can be used is given by the patent FR2833855.

Line 19 makes it possible to conduct the filtered grease from the first filtering stage 17a to the second stage 17b.

A pump (not shown) may be disposed on this pipe to accelerate the conduct of the filtered grease.

In order to facilitate the filtering and the conducting of the fatty effluents, each filtering stage 17 is heated by means of a heating means 20a, 20b, such tubes which surround each filtering stage and which are traversed by a fluid having a temperature of the order of 90 ^° C. After filtering, the fatty effluents are conducted via line 21 to a dehydration stage 22.

This stage comprises a heat exchanger 23 which comprises a hot cylindrical wall 24 on which the fatty effluent is sprayed or spread. Moreover the enclosure of the stage 22 is in slight depression (of the order of 5.10 ^{~ 2} Mega

Pascals). This depression is obtained thanks to a pump 28.

The combination of the dispersion of the effluent in a thin layer on a hot wall with the depression leads to the vaporization of the water contained in the effluent. This water in the form of steam is collected by the pipe 25 at an upper part of the tank of the stage 22.

The dehydration stage is not described here in detail. Patent FR2833853 describes an example of a dehydrator that can be used.

A valve 36 is disposed on the pipe 21 and regulates the flow of the fatty effluents to the dehydrator 22. The opening of this valve 36 will be controlled by the flow of vapor collected by the pipe 25 (flow measured by a suitable means). The goal is to avoid a clogging of the stage 22 by the fatty effluents. Dehydration should indeed be ensured by ^continuous avoiding an accumulation of non dehydrated effluent tank bottom of the dehydrator 22. When the steam flow is low the flow of effluent is also reduced. As the flow of steam increases, the flow of effluents can also be increased. The skilled person will size the servo according to the dimensional characteristics of the floor 22.

It can be seen in the figure that the various heat exchangers 20a, 20b, 23 and 16 are all connected in series with each other. The high temperature water vapor produced by the stage 22 first circulates in the exchanger 23 and then it is led through a pipe 27 to the exchanger 20b. It is then led to the exchanger 20a via line 37 and finally a line 38 leads it to the exchanger 16 from which it exits via line 34. A three-way valve 26 is interposed between the steam recovery pipe 25 and the inlet of the first heat exchanger 23.

In steady state the valve 26 is opened so as to conduct the recovered hot vapors directly to the exchanger 23.

The flow of steam can be accelerated using the pump 28.

The hot water (in the form of water vapor) which is extracted at the level of the dehydration stage is thus used to heat the filter stage or stages through a heating circuit comprising the pipes 27, 37, 38, 34 and the different exchangers. The invention therefore saves energy. Water vapor at a temperature of about 110 ⁰ C is conducted to the various exchangers where it allows to fluidize the effluents upstream of the dehydration stage. Downstream, the steam also makes it possible to maintain in a fluid state the fats in the tank 13.

The decrease in the pressure of the steam leads to its condensation in the pipes. The temperature in the circuit remains close to 90 ° C which is sufficient to ensure the desired fluidifications. In steady state, the volume of water constantly increases due to the continuous dewatering of the effluents. The circuit 27, 37, 38, 34 is therefore an open heating circuit. The pipe 34 is connected to a water collection tank 29 via a three-way valve 30. The recovered water can be conducted periodically or continuously to a conventional biological purification station.

Thus, the overflow of water that is produced by the dehydration stage is removed continuously after extraction of useful calories through the different exchangers.

It is however necessary to be able to start the installation. For this purpose a specific heat exchanger 31 is arranged in the hot gas generator 3 so that it can be heated by the burner 9.

This exchanger can be coupled to the heating circuit 27, 37, 38, 34 through a valve 32 and the three-way valve 30.

At the start of the installation, the valve 32 is opened and the three-way valve 26 is connected in parallel so as to connect the exchanger 31 directly to the exchanger 23 of the dehydration stage 22. Furthermore, the valve is positioned three channels 30 so as to connect the pipe 34 to the heat exchanger 31 and no longer to the tank 29.

Thus, the various heat exchangers 20a, 20b, 23 and 16 of the heating circuit are all supplied by the heat exchanger 31 which is heated by the burner 9 and constitute, with this heat exchanger, a closed circuit making it possible to provide initial heating for the various stages of heating. installation. Of course, during the start-up phase, the burner 9 is fed from the tank 11. When the production of the water vapor by the dehydrator 22 reaches a certain level (determined by a measurement of the pressure at the level of the collection pipe 25 ) the valve 32 is closed, the valve 30 is tilted towards the tank 29 and the valve 26 is also tilted so as to connect the exchanger 23 directly to the pipe 25 for sampling steam.

Reheating of the different units is then provided directly by the dehydration plant 22.

The temperature of the exchanger 23 however decreases over time and it is therefore necessary to periodically provide additional calories.

For this purpose the exchanger 23 will comprise two separate circuits: a first circuit which has already been described uses the water vapor extracted from the dehydrator 22. A second circuit is connected by the pipes 39a and 39b to the exchanger 31 which is heated by the burner 9. This circuit is closed and comprises a valve 40 which makes it possible to regulate the flow of fluid in this circuit, therefore the calories driven to the exchanger 23.

A slaving (not shown) will regulate the opening of the valve 40 as a function of the temperature of the wall 24 of the dehydrator 22. This completes the calorie intake necessary for the dehydration step and the device can therefore operate continuously in saving as much energy as possible. When, moreover, the level of fat contained in the reservoir 13 reaches a sufficient level (determined by a level or mass measurement), the valve 12 is closed and the valve 14 is opened and the burner 9 is supplied from the reservoir 13 Of course, the temperature levels required for each exchanger (20a, 20b, 23 and 16) are adjusted using thermostatic valves 35 arranged at the hot inlet of each exchanger.

It is of course possible to use also the second circuit of the exchanger 23 for starting the installation.

Such a variant is shown in FIG. 2. In this case, the heating circuit 25, 27, 37, 38, 34 is always an open circuit. The pipe 25 for extracting water vapor is connected directly to the first circuit of the exchanger 23 via the thermostatic valve 35.

The duct 34 is connected to the tank 29 with the possible interposition of a stopcock 30. The second circuit of the exchanger 23 is connected by the ducts 39a and 39b to the exchanger 31 which is heated by the burner 9.

This second circuit is used on the one hand during startup and on the other hand to provide the extra calories needed during continuous operation. At the start, the fluidification of the effluents in the filters 17a, 17b may be ensured by a bypass (not shown) of the second circuit coming from the exchanger 31. This branch will be connected to specific exchanger circuits surrounding the filters 17a and 17b. These heating circuits (not shown) will be distinct from the exchangers 20a, 20b used during the continuous operation of the installation.

Different variants are possible without departing from the scope of the invention.

For example, the multi-fuel burner may be replaced by two separate burners connected in parallel with the inlet of the same gas generator 3. A burner will conventionally use an external energy source (gas, fuel oil, wood). other burner will use the fat.

The choice of a single burner or several burners will depend on the volume of grease produced by the installation and therefore the particular operating conditions.

It will also be possible to provide several gas generators and several furnaces 2. Some gas generators are powered by a burner using the grease of other generators fed by conventional burners. In all cases, at least one conventional burner coupled to a start-up exchanger circuit 31 will be provided.

Claims

A method for treating effluents comprising a step of dewatering / drying the effluents inside at least one drying oven (2) supplied with hot gas by at least one burner (9) using a fuel, characterized in that it comprises a complementary step of treatment separately from a fatty fraction of the effluents, a step consisting in the partial dehydration of a fatty fraction of the effluents and supplying combustible fats used to supply at least one burner (9) .

2. Effluent treatment process according to claim 1, characterized in that the partial dehydration step is preceded by at least one step of filtration and heating of the fatty fraction of the effluents.

3. Effluent treatment process according to one of claims 1 or 2, characterized in that the partial dehydration step is followed by a step of storing dehydrated fat in a heated buffer tank (13).

4. effluent treatment plant implementing the method according to one of the preceding claims and comprising an effluent dewatering / drying means and comprising at least one burner (9) supplying hot gas at least one drying oven (2). , characterized in that the installation also comprises means (17, 22) for treating a fatty fraction of the effluents separately to partially dehydrate them, the fats thus extracted being then used by at least one burner ( 9).

5. effluent treatment plant according to claim 4, characterized in that it comprises at least one multi-fuel burner (9) that can use greases or other fuel.

6. Effluent treatment plant according to one of claims 4 or 5, characterized in that the means for treating the fatty fraction of the effluents comprise at least one at least one stage (17a, 17b) for filtering and heating the fat fraction.

7. effluent treatment plant according to claim 6, characterized in that the processing means comprise at least one stage (22) of dehydration of the fat fraction downstream of the filtering stage or stages (17a, 17b).

8. effluent treatment plant according to claim 7, characterized in that it comprises a reservoir (13) heated constituting a dehydrated fat storage buffer (15), reservoir disposed downstream of the stage (22) of dehydration and connected to the burner (9).

9. effluent treatment installation according to _one of Claims 7 or 8, characterized in that the hot water extracted at the stage (22) of dehydration is used to heat the stage or stages (17a, 17b) filter and / or the tank (13) through a heating circuit (27, 37, 38, 34).

10. effluent treatment plant according to claim 9, characterized in that the heating circuit (27, 37, 38, 34) is open, the overflow of water produced by the dehydration stage (22) being evacuated after passage through the heating circuit.

11. effluent treatment plant according to one of claims 9 or 10, characterized in that the heating circuit (27, 37, 38, 34) can be coupled to a heat exchanger (31) heated by the burner (9). , so as to form with this exchanger a closed circuit for providing initial heating of the filter stages (17a, 17b) and / or the tank (13).

12. Effluent treatment plant according to one of claims 9 to 11, characterized in that the heat exchanger (23) of the dehydration stage (22) comprises at least two separate circuits, a first circuit which uses the steam water extracted from the dehydration stage (22) and a second closed circuit (39a, 39b) which is connected to a heat exchanger (31) which is heated by the burner (9).

13. effluent treatment plant according to claim 12, characterized in that the second circuit (39a, 39b) comprises a valve (40) for regulating the temperature of the exchanger (23) of the dehydration stage .