EP4370472A1

EP4370472A1 - Method for treating a fluid comprising salts and system for implementing the method

Info

Publication number: EP4370472A1
Application number: EP22748356.7A
Authority: EP
Inventors: Frédéric Garcia; Georges Vial; Marie-Noëlle DESBOUCHE-JANNY
Original assignee: Hydromecanique et Frottement SAS
Current assignee: Hydromecanique et Frottement SAS
Priority date: 2021-07-16
Filing date: 2022-07-13
Publication date: 2024-05-22
Also published as: CN115812067A; CA3220980A1; BR112023026168A2; US20240278147A1; WO2023285515A1; KR20240037947A; EP4119505A1; MX2024000706A; JP2024525676A

Abstract

The invention relates to a method for treating a fluid, which comprises: a step (S31) of introducing the fluid to be treated into an enclosure (225) of a dryer (220); and a step (S32) of drying the fluid in the enclosure (225), including a first phase (B) during which a weight of the enclosure decreases and, when the weight of the enclosure reaches a low threshold or when a rate of variation of the weight of the enclosure is less than a first predefined value, the drying step comprises a complementary step of refilling the enclosure until the weight of the enclosure reaches a high threshold, and a second phase (C) during which the weight of the enclosure decreases and, when the rate of variation of the weight is less than a second predefined value, the method comprises a step (S33) of extracting a solid residue in powder form. The invention also relates to a system for implementing the method.

Description

Method for treating a fluid comprising salts and installation for carrying out the method

The invention relates to a method for treating a fluid, in particular a fluid containing salts, called "saline solution", in particular at a low or medium salt concentration, that is to say having for example a salts less than 500 g/L, or even 300 g/L.

It aims in particular to recover fluid waste, such as that generated by a salt bath treatment line.

The invention also relates to an installation making it possible to implement such a method.

By way of illustration in the field of nitriding, parts, for example made of steel, are generally treated in batches of several parts, also called by batch, on a nitriding line.

For this, the parts to be treated are degreased, then rinsed and dried in an oven.

The dry parts are then immersed in a nitriding bath, in a tank (also called crucible), at high temperature (for example around 500-650°C). Such a nitriding bath is generally composed mainly of molten nitriding salts.

The purpose of nitriding, for example, is to give parts a higher surface hardness and to improve their mechanical properties, for example by diffusing nitrogen into the steel of steel parts.

After nitriding, the parts are optionally immersed in an oxidation bath, in a tank (also called a crucible), for example at around 450°C. Such an oxidation bath is generally composed mainly of molten oxidizing salts. The purpose of oxidation is, for example, to improve the corrosion resistance of parts. It generally gives them a uniform black appearance.

After nitriding, or oxidation if applicable, the parts undergo a quenching operation, for example in a tank of water at a temperature much lower than that of the bath, i.e. relatively cold.

However, over successive passages, the various baths become polluted.

The water in the rinsing or quenching tanks (also called “breakdown water”) is also enriched in oxidation and/or nitriding salts, for example in nitrates and nitrites. These quenching waters, as hazardous liquid waste, need to be treated by companies specializing in the treatment of such waste. In general, the treatment consists of incineration.

In addition, it is necessary to store these quenching waters before sending them for such treatment.

At the same time, passing successive batches through the nitriding and/or oxidation baths generates sludge, which also contains nitriding and/or oxidation salts.

These different types of waste therefore need to be stored before being sent for treatment.

Storage and treatment not only generate significant costs, but also have a harmful ecological impact.

A certain need has therefore appeared to be able to treat this waste, in particular to at least recover the salts it contains. The particle size of the reclaimed salt should not be too fine in order to avoid the problem of volatility of the powder, nor too large (for example greater than 1 cm) because a larger grain retains residual water more easily. It can then be dangerous to use such a salt for example for treatments in a molten salt bath, because the instantaneous evaporation of the water during the fusion of the salt can give rise to projections of molten salt.

For this purpose of salt recovery, drying technologies have been tested, here on nitriding and/or oxidizing quench waters, on a "semi-industrial" scale, in particular, an evapo-concentration process, or even a process spray atomization. Tests were carried out with a vacuum evaporator-concentrator with scraper. The process made it possible to obtain a concentrate with approximately 30% humidity, which cannot be used as it is for application to a nitriding/oxidation line. An additional drying step is then necessary to obtain a powder with a dryness of at least 95%, or even if possible at least 98%. A centrifugation test did not achieve the required dryness. This two-step approach was therefore not adopted.

Atomization consists of drying a solution introduced through a nozzle, by a stream of hot air in an atomization tower; the droplets are instantly dried and the powder is collected in a cyclone. Tests with a single-effect atomizer produced powders with a characteristic size of between 30 μm and 50 μm, that is to say much too fine for the intended purposes of use.

Other tests with a "multi-effect" atomizer made it possible to obtain a powder with a higher particle size, but which did not however correspond to the objectives set: in fact, the target dryness for certain salts was not reached. and the particle size profile of other salts obtained did not correspond to the required profile.

In addition, the equipment which appeared necessary for the implementation of the aforementioned methods is relatively bulky and sophisticated, and also requires ancillary equipment (evapoconcentration and vibrofluidizer), which makes them relatively expensive.

A "hybrid" version (flash atomizer) was also tested on pilot equipment.

Flash atomization is based on the same principle as an atomization tower but is characterized by a toroidal drying chamber allowing to accelerate the drying of the particles, with a more compact equipment.

However, tests carried out have not been conclusive because the powder agglomerates prematurely in the toroidal chamber.

There are also crystallization processes with controlled particle size, implemented in a crystallizer, but they have proven to be difficult to use or insufficiently effective for multi-component solutions or very soluble salts.

The known processes therefore produce powders that are too fine, or at too high a humidity level, or are too expensive, or are not suitable for treating multi-component salts. It therefore appeared necessary to develop another treatment method for recovering and recycling residual salts in a saline solution, in particular at least for fluid waste containing nitriding and/or oxidation salts.

The present invention thus aims to overcome, at least in part, the aforementioned drawbacks, further leading to other advantages. For this purpose, according to a first aspect of the invention, a process for treating a fluid comprising salts, in particular nitriding and/or oxidation salts, is proposed, the process comprising:

A step of introducing the fluid to be treated into an enclosure of a dryer;

A step of drying the fluid in the enclosure by bringing it to a temperature between 30°C and 90°C and at a pressure between 10 mbar and 900 mbar, the drying step comprising a sub-step of evaporation of at least part of the fluid, producing at least one water vapour, and a sub-step of increasing the concentration of salts in the fluid contained in the enclosure, the drying step comprising: o a first phase during which a weight of the enclosure decreases and when the weight of the enclosure reaches a low threshold or when a rate of variation of the weight of the enclosure is less than a first predefined value, the drying step comprises a step of additional filling of the enclosure until the weight of the enclosure reaches a high threshold; and o a second phase during which the weight of the enclosure decreases and when the rate of variation of the weight is less than a second predefined value, the method comprises a step of extracting a solid residue in powder form. Such a process thus makes it possible to recover nitriding and/or oxidation salts, but also salts resulting from heat treatment, or even desalination of seawater. The fluid to be dried can, for example, come from a solution aqueous saline from a tank of a nitriding production line, for example a quench tank. Furthermore, the fluid to be treated, the saline solution, can be multi-component and include very soluble salts.

For example, the fluid to be dried initially has a salt concentration of less than 500 g/L, for example between 50 g/L and 500 g/L, or even for example between 300 g/L and 400 g/L.

Such a process thus makes it possible to recover the salts contained in the fluids resulting from a nitriding line, for example in the quenching waters and/or the sludges, and thus reduce the waste; Incidentally, certain treatment costs are thus controlled.

Such a method makes it possible to eliminate quantities of fluid waste since these are recycled, at least in part, or even entirely as far as possible, to extract the salts contained in these fluids following the successive passages of parts in at least a vat from which they come.

It also allows a limitation of the waste of non-renewable resources and a recovery of raw materials.

For example on oxidizing and/or nitriding quench waters, such a process makes it possible in particular to obtain a particle size, composition and dryness of the salts desired recovered, in a possibly relatively short drying time, and in a single drying step.

For example, the dryer enclosure is kept under vacuum.

The vacuum denotes for example here a pressure of between about 10 mbar and 900 mbar (millibar), for example between 20 mbar and 500 mbar, or even between 20 mbar and 100 mbar.

Such a vacuum allows water to evaporate from the saline solution at relatively low temperatures, for example between 35°C and 90°C. It can also be used to suck up the fluid to be treated. The additional filling during the drying step thus allows a semi-continuous filling of the enclosure, that is to say a filling such that the fluid to be treated is added to the enclosure of the dryer while the enclosure is void due to processing. Thus, the first phase of the drying step comprises at least one cycle in which the fluid is concentrated while vapors are evaporated, until the weight of the enclosure reaches a low threshold or its rate of variation is less than a first predefined value, then additional filling is performed.

Indeed, during the treatment, i.e. during the drying step and in particular during the concentration phase, part of the fluid, in particular the water in the fluid, evaporates, and consequently, the weight of the content of the pregnant decreases. At the same time, the concentration of salts in the fluid contained in the enclosure increases. For example, the dryer comprises a system of load cells configured to control a weight of fluid contained in the enclosure.

During the first phase of the drying step, when the weight of the enclosure reaches for example a certain threshold, called low threshold, or when a rate of variation of the weight of the enclosure is lower than a first predefined value ( ie the variation in weight decreases over a given time interval), then the valve is opened to introduce the fluid to be treated. As long as the weight is greater than this threshold, or varies more than the first predefined value, then the enclosure is considered sufficiently filled, and the evaporation follows its course. The low threshold is chosen so that the addition of fluid has a low impact on the temperature of the contents of the enclosure (for example, the temperature varies less than 20%, even 15%, even less than 10% or even 5%, or even less than 3% relative to the average temperature of the contents of the enclosure before addition); for example, the low threshold is chosen to represent approximately 85% of the maximum volume of the enclosure. The thresholds are for example determined for each additional filling so as to represent a substantially constant filling volume. Indeed, as the drying step progresses, the fluid concentrates in salt in the enclosure. The same volume therefore weighs more and more. Therefore, the threshold value may vary from one additional filling to another.

Thus, for example, the method comprises a step of controlling a weight of the enclosure, and when the weight reaches the low threshold or the rate of variation of the weight of the enclosure is less than the first predefined value, the method comprises a step of opening a filling valve and the step of additional filling of fluid to be treated in the enclosure is implemented.

And for example, when the weight of the enclosure reaches a high threshold, the process includes a step of closing the filling valve.

For example, the load cell system is also configured to detect the end of drying, at the end of the second phase. For example, when the weight of the loudspeaker remains relatively constant over time (that is to say that the variation in the weight of the loudspeaker over time becomes less than a second predefined value), it is then considered that any the water has been evaporated and the product is “dry” (has reached a target dryness level).

The first predefined value and the second predefined value can be equal or different, for example the second predefined value can be lower than the first predefined value; for example the second predefined value can be close to zero. For example, after a predefined number of additional fillings, or the enclosure reaches a certain weight, then the second phase is implemented.

For example, the additional fillings of the first phase are repeated until a salt concentration in the fluid contained in the containment reaches a target value; for example at least 400 g/L, preferably at least 500 g/L for oxidation and/or nitriding salts, but the target value obviously depends on the nature of the salts and/or the applications considered.

In an exemplary implementation, the drying step is configured to produce the solid residue having a moisture content of between 0.5% and 5%, by weight, or even between 0.5% and 3%, or even between 1% at 2%.

The humidity level is for example monitored by a thermal balance, for example on a sample of solid residue taken.

In an exemplary implementation, the drying step is configured to produce the solid residue having a specific particle size. For example, the solid residue is in the form of a powder with a grain diameter of between 100 μm and 1000 μm, for example between 200 μm and 500 μm, on average. The particle size should not be too fine in order to avoid the problem of volatility of the powder, nor too large (for example greater than 1 cm) because a larger grain retains residual water more easily.

Thanks to such a drying process, by means of a dryer as described below in the context of the present invention, it is possible to obtain the desired particle size.

In an exemplary implementation, the drying step includes a breaking-up step. Such a step aims to limit, or even avoid, the formation of a clod in the containment.

In an exemplary implementation, the method includes a step of condensing the steam from the dryer, producing a condensate.

The process then also allows a reduction in water consumption by reusing the condensate. For example, the method then comprises a step of injecting the condensate into a tank, for example a tank of rinsing water.

For example, the condensate obtained can thus be used as rinsing water.

The vapor condensation step is for example implemented in a condenser. According to one implementation option, the process includes a gas absorption-neutralization step generated during the vapor condensation step by an absorber-neutralizer, also known as a scrubber.

In an interesting embodiment, the method comprises a step of extracting fluid to be treated from a tank of a nitriding line, or even for example from a storage tank.

For example, the process includes a stage of filtration of the fluid to be treated before the stage of introduction into the enclosure of the dryer.

The filtration step comprises for example a step of passing the fluid through a sieve with a mesh size of less than or equal to 50 μm, for example between 2 μm and 50 μm. The filtration step includes, for example, a particle removal step using a magnetic bar.

For example, such a magnetic bar picks up magnetic particles, in particular for example iron oxides.

The invention also relates to an installation configured to implement a method comprising at least some of the steps described previously. For this, the installation comprises at least one dryer, which is configured to implement at least the drying step.

The dryer mainly comprises an enclosure.

The enclosure is for example generally cylindrical in shape. The enclosure is for example a non-rotating enclosure.

For example, the enclosure includes at least one fluid inlet to be dried, configured to introduce fluid to be dried into the enclosure.

For example, the enclosure includes at least one solid residue discharge outlet. For example, the enclosure has at least one steam outlet. In an interesting embodiment, the dryer comprises a mixer, in particular a helical mixer heated, for example by circulation of a heat transfer fluid.

For example, the mixer is configured to rotate in the enclosure, for example at a moderate speed, for example up to 100 rpm, for example between 1 rpm and 100 rpm (revolutions per minute), by example between 1 and 25 rpm, which makes it possible to mix, in a sufficiently homogeneous manner here, the fluid to be dried and to improve its contact with a wall of the enclosure.

The mixer passes for example at a distance from the wall of the enclosure in order to avoid scraping the wall and thus limit wear of the mixer. In other words, the helical agitator is heated and extends close to the wall of the enclosure in order to guarantee a homogeneity of the mixture and a uniformity of the temperature in the enclosure.

In an interesting embodiment, the enclosure has a conical bottom.

Such a conical bottom facilitates the unloading of the solid residue obtained. For example, the solid residue (e.g. in powder form) is discharged from the dryer enclosure by gravity.

For example, the conical bottom has the solid residue unloading outlet.

In addition, a traditional dryer is usually designed for batch operation, to dry dry pasty products, with a filling rate of 60% to 100% of a volume of the enclosure.

Here, given the fluid to be treated, such operation in batch mode would greatly limit the productivity and yield of the process. For example, the dry residue obtained after drying 2000 L of fluid would occupy only about 20% of the volume of the dryer enclosure as considered here. The dryer considered here then makes it possible to work in “semi-continuous” mode. For this, it comprises for example a system of load cells.

Such a system of weigh cells is configured to weigh the enclosure, possibly continuously, and incidentally to weigh the contents of the enclosure.

For example, the weighing system comprises at least one weighing sensor. In order to correctly measure the weight of the enclosure, it is preferably mechanically decoupled from the rest of the installation, for example by using flexible conduits on the inputs and outputs.

A loss in weight of the contents of the enclosure, in particular due to evaporation of water from the treated fluid, can then be compensated for by adding the fluid to be treated. This also makes it possible to increase a salt concentration of the fluid contained in the enclosure as the drying operation progresses.

The volume of the dry residue thus obtained in the end is of the order of 50% to 75% of the volume of the enclosure, even greater than 80% and ideally greater than 90%.

This "semi-continuous" filling operation can be fully automated: the number of additions and the quantity of fluid per addition can, for example, be configurable. The additions of fluid are made during drying: the fluid is "sucked up", for example by pressure difference from a tank, for example a storage tank or buffer tank, connected to the dryer, without breaking the vacuum of the enclosure .

For this, for example, the dryer has at least one filling valve. For example, the filling valve is configured to be opened when a weight of the enclosure reaches a low threshold or when a rate of variation of the weight of the enclosure is lower than a first predefined value, and to be closed when the enclosure weight reaches a high threshold or when enclosure filling reaches its maximum level. The weight, measured by the system of weigh cells, is for example correlated to the degree of filling of the enclosure.

For example, the installation comprises a control system configured to control an opening or a closing of the at least one filling valve as a function of a weight of the enclosure measured by the weighing system. In an interesting exemplary embodiment, the enclosure comprises a wall formed by a double envelope.

The double envelope is for example configured to cause a heat transfer fluid to circulate therein.

The heat transfer fluid is for example configured to maintain a temperature of between 30° C. and 90° C. in the enclosure where the fluid is treated. For example, the same heat transfer fluid circulates in the wall of the enclosure and in the helical mixer.

For example, the dryer is a vacuum agitated vertical mixer dryer.

In an exemplary embodiment, the enclosure of the dryer comprises a lump breaker configured to limit the formation of a clod in the fluid treated in the enclosure.

This lump breaker is for example a knife lump breaker, placed at the bottom of the enclosure. Such a lump breaker is for example configured to rotate up to a speed of 1500 rpm.

In an exemplary embodiment, the installation comprises an extraction system configured to convey the fluid to be treated from a reservoir, for example a tank of a nitriding line, to the dryer.

For example, the extraction system includes a filtration system.

The filtration system comprises for example a sieve with a mesh of less than or equal to 50 μm, for example between 2 μm and 50 μm, or even for example between 5 μm and 10 μm.

For example, the filtration system further comprises a magnetic bar, which is for example configured to eliminate magnetic particles which would be contained in the fluid to be treated.

For example, the steam outlet of the dryer is equipped with a filter. The filter is for example configured to filter vapors. For this, the filter comprises for example a filter cartridge, for example with unclogging with compressed air.

The filter retains, for example, ultra-fine powders. Unclogging removes these powders and thus restores the filter's efficiency.

According to an exemplary embodiment, the unclogged powders fall back by gravity into the enclosure of the dryer.

According to an example of implementation, the installation comprises a boiler configured to maintain the enclosure of the dryer at the desired temperature.

For example, the boiler is configured to heat up to around 130°C the heat transfer fluid circulating in the double jacket of the containment, as well as in the helical mixer.

The boiler is configured to have a heating mode and a cooling mode to reduce the temperature of the solid residue produced.

In an exemplary embodiment, the installation includes a vacuum module. For example, the vacuum module is configured to produce a moderate vacuum in the enclosure of the dryer, that is to say a pressure of between 10 mbar and 900 mbar, for example between 20 mbar and 500 mbar, or even between 20 mbar and 100 mbar.

For example, the vacuum module is configured to produce a pressure of approximately 10 mbar in a drying configuration.

For example, the vacuum module is configured to produce a pressure of approximately 50 mbar in an evaporation configuration.

Such a pressure, assimilated to a vacuum, thus makes it possible to evaporate water from the fluid at low temperature, that is to say at a temperature between 30°C and 90°C. The vacuum module is for example connected to the steam outlet of the dryer.

For example, the vacuum module includes at least one vacuum pump.

In an exemplary embodiment, the installation further comprises a condenser.

The condenser is for example configured to condense the vapors coming from the dryer via the vapor outlet and to produce a condensate. The condenser is for example connected to a steam outlet of the dryer.

The condenser is for example a tube bundle condenser.

The installation thus makes it possible to recover water, which can be reused.

In an exemplary embodiment, the installation comprises a chiller.

For example, a tubular heat exchanger is connected to the chiller. For example, the installation includes a condensate tank configured to collect condensed vapours.

In an exemplary embodiment, the installation comprises a condensate supply pipe configured to extract the condensate from the condenser and possibly reinject it into a tank, for example a tank of rinsing water. As an interesting option, the condensate supply line includes a filter.

According to an interesting option, the installation here also includes an absorber-neutralizer, commonly called a scrubber.

For example, the scrubber is connected to the condenser and makes it possible to reduce or even eliminate any presence of toxic or corrosive gases, possibly contained in the condensate (for example ammonia for nitriding).

The invention, according to an exemplary embodiment, will be well understood and its advantages will appear better on reading the detailed description which follows, given by way of indication and in no way limiting, with reference to the appended drawings in which: - figure 1 schematically represents a traditional nitriding line; FIG. 2 illustrates a treatment installation according to an exemplary embodiment of the invention, placed in parallel with a nitriding line as represented in FIG. 1; FIG. 3 schematically shows a dryer according to an exemplary embodiment; - Figure 4 shows a diagram illustrating a processing method according to an embodiment of the invention; and

FIG. 5 presents a graph illustrating the treatment of the fluid in the enclosure 225 of the dryer 220 by semi-continuous filling.

Figure 1 shows an example of a nitriding line 10. Parts, for example steel, are arranged in a cage 11 in order to be treated in batches of several parts, also called by batch.

For this, the cage 11 is for example immersed in a first tank 12 containing a degreasing bath.

They are then rinsed, for example by immersing the cage 11 successively in a bath of rinsing water 13, or even several baths of rinsing water in cascade 13a, 13b, 13c.

Then, they are dried in an oven 14.

Cage 11 is then immersed in at least one nitriding bath 15, or even two successive baths 15a, 15b as shown here. Such a nitriding bath 15 is generally composed mainly of molten nitriding salts, at a temperature of approximately 500-650°C.

After nitriding, the parts are optionally immersed in an oxidation bath 16. Such an oxidation bath 16 is generally composed mainly of molten oxidizing salts, at a temperature of around 450°C. After nitriding, or oxidation where appropriate, the parts undergo a quenching operation, for example in a quenching water tank 17, at a temperature much lower than that of the bath, i.e. relatively cold.

Then, the parts are rinsed in a post-treatment rinsing tank 18, or several tanks 18a, 18b, 18c in cascade. Optionally, other treatments can be applied, such as impregnation. The cage can then be then immersed in an impregnation bath 19 for example.

However, over successive passages, the various baths become polluted.

For example, sludge is secreted into the nitriding 15 and/or oxidation 16 baths, which contain nitriding and/or oxidation salts. The water in the post-treatment rinsing 18 or quenching 17 tanks (also called “breakdown water”) is also enriched in oxidation and/or nitriding salts, for example in nitrates and nitrites.

These quenching waters 17, as hazardous liquid waste, need to be treated by companies specializing in the treatment of such waste.

FIG. 2 shows an example of an installation 200 making it possible to treat at least part of this waste and to recycle the salts which it contains. In this example, a fluid containing salts is extracted from the quench tank 17, but it could of course be any other tank containing a fluid corresponding to a saline solution.

For this, the installation 200 mainly comprises a dryer 220, shown schematically in more detail in Figure 3. To route the fluid to be treated from a tank (here the quenching tank 17) to the dryer 220, the installation here comprises first an extraction system 201.

Here, the extraction system 201 comprises for example a buffer tank 203, and at least one upstream pipe 202, leading from the tank from which the fluid to be treated is extracted to the buffer tank 203. The upstream pipe 202 comprises here by example a 205 filtration system.

The filtration system 205 comprises for example a sieve with a mesh of less than or equal to 50 μm, for example between 2 μm and 50 μm, or even for example between 5 μm and 10 μm.

Here, the filtration system 205 further comprises a magnetic bar, which is for example configured to eliminate magnetic particles which would be contained in the fluid to be treated.

Downstream of the buffer tank 203, the extraction system 201 comprises for example at least one downstream pipe 204, leading from the buffer tank 203 to the dryer 220, in particular to an inlet of fluid to be dried 221 of the dryer 220. The dryer 220 here comprises at least two outlets 222, 223: a solid residue discharge outlet 222 and a steam outlet 223.

The steam outlet 223 has two parallel paths which are connected to a vacuum module 207.

A first of the two paths from the steam outlet 223 is for example provided with a filter 224. The filter 224 is for example configured to filter vapors. For this, the filter 224 comprises for example a filter cartridge, for example with unclogging with compressed air.

For example, as long as the content of the dryer is liquid enough, the vapors are condensed directly without passing through the filter 224, that is to say passing through a second of the two paths coming from the vapor outlet 223 and leading to the vacuum model 207.

But when the content is relatively dry, for example during a phase C of the process as described below, there may then be dust entrained by the vapors and it is then preferable to pass through the filter 224, c i.e. via the first of the two paths from the steam outlet 223.

The filter 224 is therefore for example activated during phase C of the method.

The installation also includes, for example, a boiler 206 configured to maintain an enclosure of the dryer at the desired temperature. The boiler 206 is for example configured to heat up to approximately 130° C. a heat transfer fluid configured to maintain an interior of the enclosure at a desired temperature.

The boiler 206 can be switched to heating or cooling mode to reduce the temperature of the solid residue produced in the enclosure during a discharge phase, via the solid residue discharge output 222.

Downstream of the dryer, the installation then includes the vacuum module 207 to which the steam outlet 223 is connected.

The vacuum module comprises for example at least one vacuum pump configured to produce a moderate vacuum in an enclosure of the dryer 220, that is to say a pressure of between 10 mbar and 900 mbar.

The vacuum module comprises for example two pumps which can be used in series or individually (depending on the application and the efficiency required): for example a Roots pump, and a liquid ring pump.

The installation can also comprise a condenser 208 configured to condense the vapors coming from the dryer 220 via the vapor outlet 223. The condenser is for example a tube bundle condenser. The condenser 208 comprises for example a tubular heat exchanger.

For this, the installation may also include a cooler 209.

For example, the tubular heat exchanger of the condenser 208 is connected to the chiller 209. Condensed vapors can be collected in a condensate tank.

Here, downstream of the condenser 208, the installation comprises a condensate supply pipe 210 configured to extract the condensate from the condenser and possibly reinject it into a tank of rinsing water, for example here the rinsing tank 18c. It should be noted that here, the condensate includes, for example, liquid water, produced by the condensation of water vapor from the dryer.

In this exemplary embodiment, the condensate supply line 210 optionally includes a filter 211.

According to an interesting option, the installation here also comprises an absorber-neutralizer 212, commonly called a scrubber 212. Here, the scrubber 212 is connected to the condenser 208 and makes it possible to reduce or even eliminate any presence of toxic or corrosive gases.

Such gases, for example ammonia, are possibly contained in the condensate. The dryer 220 is shown in more detail in Figure 3.

The 220 dryer is configured to dry fluids containing salts, whether liquid or slurry, under vacuum. These fluids are also referred to as saline solutions.

The 220 dryer is a vacuum dryer, in particular with a heated vertical mixer, rotating at a moderate speed to obtain an upward flow of perimeter product and renewal of the product in contact with the heated walls of the enclosure.

For this, the dryer mainly comprises an enclosure 225, which is provided with the fluid inlet to be dried 221, the solid residue discharge outlet 222 and the steam outlet 223.

The enclosure 225 is here fixed, in the sense that it is not rotatable, and is held by a support 228.

The enclosure 225 here has a conical bottom which facilitates the unloading of the solid residue obtained.

The solid residue discharge outlet 222 is therefore preferably formed at one end of the conical bottom, at the bottom of the enclosure. The solid residue unloading outlet 222 comprises for example a spherical valve with metal-metal contact.

According to a preferred characteristic, the enclosure 225 comprises a double envelope, that is to say an outer wall and an inner wall delimiting between them a space allowing circulation of a heat transfer fluid. The heat transfer fluid is for example heated by an electric heater such as the boiler 206 to heat it up to 130° C. for example.

For example, the heat transfer fluid comprises an oil.

In the present exemplary embodiment, the inner wall thus forms an inner tank, which is for example made of Hastelloy C22, or any equivalent material.

In enclosure 225, the dryer here comprises a mixer 226 configured to mix and dry the contents of the enclosure, i.e. the fluid to be treated.

The mixer comprises for example a helical blade heated by the circulation of a heat transfer fluid. The mixer 226 is for example configured to rotate at a variable speed depending on the needs, for example up to 100 rpm.

The mixer 226 passes here at a distance from the interior wall of the enclosure 225 in order to avoid scraping the wall and thus limit wear of the mixer 226.

According to an interesting option present here, the dryer comprises a lump breaker (chopper) 230 in the enclosure 225; such a lump breaker 230 is for example configured to rotate at a speed of up to 1500 rpm to break up any clods.

To achieve semi-continuous filling, the dryer includes a filling valve 227.

In this exemplary embodiment, the filling valve 227 is connected to the fluid inlet to be dried 221 of the dryer.

For example, the filling valve 227 is placed between the fluid tank to be treated and the dryer.

The filling valve 227 is opened or closed depending on a weight of the enclosure. When it is open, it then allows an introduction of fluid to be treated into the enclosure, via the fluid inlet to be dried 221, by suction of the fluid thanks to the vacuum module 207.

To know the weight of the enclosure, the dryer comprises a system of load cells 229. This makes it possible to know the state of filling of the enclosure and, in function, to introduce the fluid to be treated. In the present embodiment, the load cell system 229 comprises at least two, preferably three, weight sensors regularly spaced around the enclosure. Their measurement values are then for example averaged (or added) to determine a weight of the enclosure, and therefore know its filling state. A weight sensor is here schematically arranged between a shoulder of the enclosure and a support part 228.

Figure 4 illustrates the main steps of a process for treating a fluid comprising salts according to an exemplary implementation of the invention, for example in the context of an installation as illustrated in Figure 2.

The method includes, for example, a sequence of steps as follows.

The method first comprises a step S1 of extracting fluid to be treated from a tank, here a quenching tank 17 of a nitriding line.

The fluid to be treated, then the quench water containing salts originating from the previous nitriding and oxidation baths, is conveyed by the extraction system 201. The method comprises for example a step S2 of filtration of the fluid to be treated, for example by the filtration system 205. The filtration step S2 here comprises both a step S21 of passing the fluid through the sieve of the filtration system 205 and a step S22 of eliminating magnetic particles, such as iron oxides , by the magnetic bar.

The method then comprises a fluid treatment step S3, namely:

A step S31 of introducing fluid to be treated into the enclosure 225 of the dryer 220, via the fluid inlet to be dried 221;

A step S32 of drying the fluid in the enclosure 225 by placing it at a temperature of between 30° C. and 90° C. and at a pressure of between

10 mbar and 900 mbar; and

A step S33 for extracting a solid residue in powder form, which is for example recovered by the solid residue discharge outlet 222. The drying step S32 comprises two sub-steps, which take place concomitantly: o a sub-step S321 of evaporation of at least part of the fluid, producing at least one water vapor which is extracted from the enclosure 225 through the vapor outlet 223, and o a sub-step S322 of increasing the concentration in salts of the fluid contained in the enclosure 225 As described in more detail in connection with FIG. 5, the drying step here comprises two phases: o a first phase (indicated “B” in FIG. 5) during which a weight of the enclosure decreases and when the weight of the enclosure reaches a low threshold or when a rate of variation of the weight of the enclosure is less than a first predefined value, the drying step comprises a step of additional filling of the enclosure until the weight of the enclosure reaches a high threshold; and o a second phase (indicated "C" in FIG. 5) during which the weight of the enclosure decreases and when the rate of variation of the weight is less than a second predefined value, the step S33 of extracting the solid residue is implemented.

To carry out the semi-continuous filling, the method here comprises a step S4 of controlling a weight of the enclosure 225, for example by the system of load cells 229, and when the weight reaches a low threshold (corresponding to a threshold filling bottom) or that a rate of variation of the weight of the enclosure is less than a second predefined value, the method comprises a step S51 of opening the filling valve 227 and the step of additional filling of fluid to be treated in enclosure 225 is implemented. When the weight of the enclosure reaches a high threshold (corresponding to a high filling threshold), the method includes a step S52 of closing the filling valve 227.

At the same time, the interior of the enclosure is maintained under vacuum, which allows suction of fluid to be treated in the enclosure when the filling valve 227 is open.

The method here also comprises a step S6 of condensing the steam coming from the dryer 220 through the steam outlet 223 by means of the condenser 208, thus producing a condensate.

According to an option represented here, the method comprises a step S7 of absorption-neutralization of the vapor, by the absorber-neutralizer 212.

The condensate is for example then routed through the condensate supply line 210. According to another option shown here, the method includes a step S8 of filtering the condensate through the filter 211 of the condensate supply line 210.

Then the method includes a step S9 of injecting the condensate into the rinsing tank 18c.

This graph more precisely shows a change in the degree of filling of the enclosure (in %), in ordinates, as a function of time according to an arbitrary unit here, in abscissas. This graph here highlights four phases over time: a phase "A" corresponding to step S31 of introducing fluid to be treated into the enclosure 225 of the initially empty dryer 220, a phase "B" corresponding to the first stage of the drying step S32, during which the contents of the enclosure are mainly concentrated in salts, a "C" phase corresponding to the second phase of the drying step S32, and finally a "D" phase which corresponds to the step S33 for extracting the solid residue, for example via the solid residue unloading outlet 222. Filling is usually done with a lift pump (not shown). The end of filling can be detected by weighing or by volumetry.

The enclosure is placed under vacuum after the filling of step S31 for introducing the fluid to be treated, for example by the vacuum module 207.

During the first phase "B", the weight of the enclosure is monitored, for example continuously; reaching a low threshold, or slowing down to reach the first predefined value, triggers the opening of the filling valve 227, the fluid is then sucked up by the vacuum; reaching the high threshold triggers the closing of the filling valve 227. As fluid is added, the salt content in the enclosure increases. The high and low thresholds can change over fillings, in particular to maintain a constant volume filling rate. Indeed, the density of salt can differ from the density of water and the weight depends on the salt content.

The number of fillings and the variation of the thresholds can be programmed in advance or be controlled entirely by weight, flow rate or salt content measurements. When the desired content is reached, the first phase “B” is finished. Then begins the second phase "C" during which there is no more fluid supply.

In this stage, the pumping can be reinforced, for example by using a rotary compressor (Roots pump) upstream of the vacuum pump of the vacuum module, which makes it possible to achieve higher dryness rates. In this stage, the weight is also constantly monitored. The loss of weight per unit of time (equivalent to the rate of evaporation) then makes it possible to estimate the rate of remaining humidity and to determine the end of the drying.

It is preferably during the second phase "C" that the lump breaker is started, either from the start, or when a certain humidity level is reached.

Finally, the dryer is emptied.

By way of example, a drying operation was carried out on oxidation quench waters from a nitriding chain. The solution to be treated had an average concentration of 255 g/L. An initial weight of 2324 kg (corresponding to a volume of 1857 L) was introduced into the enclosure of the dryer. The enclosure was put under vacuum (ie under approximately 50 mbar) by means of a liquid ring pump. The solution was brought to a temperature of 38°C.

Then the evaporation/concentration cycles started. In total, 3397 kg of quench water were added in ten steps (i.e. an average of 377 kg at each addition) for 2421 minutes (corresponding to the duration of phase B) until a mass concentration by 52%.

The final drying phase (phase C) was then initiated until the observation of the liquid-solid phase transition after 21 hours of drying for a dry residue analyzed at 91.67% (dryness rate). The changeover to vapor filtration mode was made, the lump breaker was activated and a vacuum of 10 mbar was reached after the Roots pump was activated.

After 6 hours of drying at 85°C, 1217 kg of a powder with a solids content of 99.09% were extracted from the dryer, then reused on the nitriding line with no quality impact. The drying operation also generated 4335 kg of condensate which was reused in the rinsing of the nitriding line.

Claims

CLAIMS 1. Process for treating a fluid, in particular comprising salts, the process comprising:

A step (S31) of introducing fluid to be treated into an enclosure (225) of a dryer (220);

A step (S32) of drying the fluid in the enclosure (225) by placing it at a temperature of between 30° C. and 90° C. and at a pressure of between

10 mbars and 900 mbars, the drying step comprising a sub-step (S321) of evaporation of at least part of the fluid, producing at least one water vapour, and a sub-step (S322) of increasing concentration of salts in the fluid contained in the enclosure (225), the drying step comprising: o a first phase (B) during which the weight of the enclosure decreases and when the weight of the enclosure reaches a low threshold or that a rate of variation of the weight of the enclosure is less than a first predefined value, the drying step comprises a step of additional filling of the enclosure until the weight of the enclosure reaches a high threshold ; and o a second phase (C) during which the weight of the enclosure decreases and when the speed of variation of the weight is less than a second predefined value, the method comprises a step (S33) of extracting a solid residue under powder form.

2. Method according to claim 1, comprising a step (S4) of controlling a weight of the enclosure (225), and when the weight reaches the low threshold or the speed of variation of the weight of the enclosure is lower at the first predefined value, the method comprises a step (S51) of opening a filling valve (227) and the complementary filling step is implemented, and when the weight of the enclosure reaches a high threshold , the method includes a step (S52) of closing the filling valve (227).

3. Process according to any one of claims 1 or 2, in which the drying step is configured to produce the solid residue having a moisture content of between 0.5% and 5%, by weight.

4. Method according to any one of claims 1 to 3, in which the drying step (S32) is configured to produce the solid residue in the form of a powder with a grain diameter of between 100 μm and 1000 μm on average.

5. Method according to any one of claims 1 to 4, comprising a step (S6) of condensing the steam from the dryer (220), producing a condensate.

6. Method according to claim 5, comprising a step (S9) of injecting the condensate into a tank of rinsing water (18).

7. Installation (200) configured to implement a method according to any one of the preceding claims, the installation (200) comprising at least one dryer (220) which comprises at least one enclosure (225), in particular an enclosure not rotary, and at least one fluid inlet to be dried (221), a solid residue unloading outlet (222), and a steam outlet (223), in that the dryer (220) comprises a system of load cells (229 ) configured to weigh the enclosure (225).

8. Installation (200) according to claim 7, characterized in that the dryer (220) comprises a mixer (226), in particular a heated helical mixer, configured to rotate in the enclosure (225) at a speed of between 1 rpm and 100 rpm.

9. Installation (200) according to any one of claims 7 or 8, characterized in that the enclosure of the dryer comprises a lump breaker (230) configured to limit clod formation in the fluid treated in the enclosure, the lump breaker being configured to rotate up to a speed of 1500 rpm.

10. Installation (200) according to any one of claims 7 to 9, characterized in that the dryer (220) comprises at least one filling valve (227); the filling valve (227) being configured to be opened when a weight of the enclosure reaches a low threshold or a rate of variation of the weight of the enclosure is less than a first predefined value, and closed when the weight of the loudspeaker reaches a high threshold.

11. Installation (200) according to claims 9 and 10, characterized in that it comprises a control system configured to control an opening or a closing of the at least one filling valve (227) according to a weight of the enclosure (225) measured by the load cell system.

12. Installation (200) according to any one of claims 7 to 11, characterized in that the enclosure (225) comprises a wall formed of a double envelope, and in that the double envelope is configured to circulate therein a heat transfer fluid.

13. Installation (200) according to claim 12, characterized in that the heat transfer fluid is configured to maintain a temperature between 30°C and

90°C in the enclosure (225) where the fluid is treated.

14. Installation (200) according to any one of claims 7 to 13, characterized in that it comprises a vacuum module (207) configured to produce a pressure in the enclosure (225) of the dryer (220) of between 10 mbar and 900 mbar.

15. Installation (200) according to any one of claims 7 to 14, characterized in that it comprises a condenser (208), connected to the steam outlet (223) of the dryer (220), the condenser (208) being configured to condense the vapors from the dryer (220) through the vapor outlet (223) and produce a condensate, and in that the installation (200) comprises a condensate feed line (210) configured to extract the condensate from the condenser (208) and reinjecting it into a tank (18).