METHOD FOR TREATING A FLUID COMPRISING SALTS AND SYSTEM FOR IMPLEMENTING THE METHOD

Abstract

A process for treating a fluid includes: a step of introducing fluid to treat into a chamber of a dryer, a step of drying the fluid in the chamber including a first phase during which a weight of the chamber reduces and when the weight of the chamber reaches a lower threshold or a rate of variation of the weight of the chamber is less than a first predefined value, the drying step includes a step of complementary filling of the chamber until the weight of the chamber reaches an upper threshold and a second phase during which the weight of the chamber decreases and when the rate of variation of the weight is less than a second predefined value, the process includes a step of extracting a solid residue in powder form. The invention also concerns an installation for implementing the process.

Claims

1. Process for treating a fluid, comprising: A step of introducing fluid to treat into a chamber of a dryer; A step of drying the fluid in the chamber by putting at a temperature comprised between 30? C. and 90? C. and at a pressure comprised between 10 mbars and 900 mbars, the drying step comprising a sub-step of evaporating at least some of the fluid, producing at least water vapor, and a sub-step of increasing salt concentration of the fluid contained in the chamber, the drying step comprising: a first phase during which a weight of the chamber reduces and when the weight of the chamber reaches a lower threshold or a rate of variation of the weight of the chamber is less than a first predefined value, the drying step comprises a step of complementary filling of the chamber until the weight of the chamber reaches an upper threshold; and a second phase during which the weight of the chamber decreases and when the rate of variation of the weight is less than a second predefined value, the process comprises A step of extracting a solid residue in powder form.

2. The process according to claim 1, comprising a step of checking a weight of the chamber, and when the weight reaches the lower threshold or when the rate of variation of the weight of the chamber is less than the first predefined value, the process comprises a step of opening a filling valve and the step of complementary filling is implemented, and when the weight of the chamber reaches an upper threshold, the process comprises a step of closing the filling valve.

3. The process according to claim 1, wherein the drying step is configured to produced the solid residue with a moisture content comprised between 0.5% and 5%, by weight.

4. The process according to claim 1, wherein the drying step is configured to produced the solid residue in powder form of particle size comprised between 100 ?m and 1000 ?m on average.

5. The process according to claim 1, comprising a step of condensing vapor coming from the dryer, producing a condensate.

6. The process according to claim 5, comprising a step of introducing the condensate into a tank of rinsing water.

7. Installation configured to implement a process according to claim 1, the installation comprising at least one dryer which comprises at least one chamber, in particular a non rotary chamber, and at least one inlet for fluid to dry, an outlet for discharging solid residue, and a vapor outlet, wherein the dryer comprises a load cell system configured for weighing the chamber.

8. The installation according to claim 7, wherein the dryer comprises a mixer configured to turn in the chamber at a speed comprised between 1 rpm and 100 rpm.

9. The installation according to claim 7, wherein the dryer chamber comprises a lump-breaker configured to limit a formation of lumps in the fluid treated in the chamber, the lump-breaker being configured to turn up to a speed of 1500 rpm.

10. The installation according to claim 9, wherein the dryer comprises at least one filling valve; the filling valve being configured to be open when a weight of the chamber reaches a lower threshold or when a rate of variation of the weight of the chamber is less than a first predefined value, and to be closed when the weight of the chamber reaches an upper threshold.

11. The installation according to claim 10, further comprising a control system configured to control an opening or a closing of the at least one filling valve according to a weight of the chamber measured by the load cell system.

12. The installation according to claim 7, wherein the chamber comprises a wall formed by a double jacket, and in that the double jacket is configured of cause a heat-conveying fluid to circulate therein.

13. The installation according to claim 12, wherein the heat-conveying fluid is configured to maintain a temperature between 30? C. and 90? C. in the chamber where the fluid is treated.

14. The installation according to claim 7, characterized in that it claim 7, further comprising a vacuum module configured to produce a pressure in the chamber of the dryer comprised between 10 mbars and 900 mbars.

15. The installation according to claim 7, further comprising a condenser, connected to the vapor outlet of the dryer, the condenser being configured to condense the vapors coming from the dryer by the vapor outlet and produce a condensate, and wherein the installation comprises a condensate supply pipe configured to extract the condensate from the condenser and introduce the condensate back into a tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0147] The invention, according to an example embodiment, will be properly understood and its advantages will be clearer on reading the following detailed description, given by way of illustrative example that is in no way limiting, with reference to the accompanying drawings in which:

[0148] FIG. 1 is a diagrammatic representation of a conventional nitriding line.

[0149] FIG. 2 illustrates a treatment installation according to an example embodiment of the invention, set up in parallel with a nitriding line such as shown in FIG. 1;

[0150] FIG. 3 is a diagram of a dryer according to an example embodiment;

[0151] FIG. 4 shows a diagram illustrating a treatment process according to an embodiment of the invention; and

[0152] FIG. 5 presents a graph illustrating the fluid treatment in the chamber 225 of the dryer 220 by semi-continuous filling.

DETAILED DESCRIPTION

[0153] FIG. 1 shows an example of a nitriding line 10.

[0154] Parts, for example of steel, are arranged in a cage 11 in order to be treated in batches of several parts, also called batch processing.

[0155] For this, the cage 11 is for example immersed in a first tank 12 containing a degreasing bath.

[0156] They are next rinsed, for example by immersing the cage 11 successively in a rising water bath 13, or even several rinsing water baths in a series 13a, 13b, 13c.

[0157] They are next dried in an oven 14.

[0158] The cage 11 is next immersed in at least one nitriding bath 15, or even two successive baths 15a, 15b as shown diagrammatically here. Such a nitriding bath 15 is generally mainly composed of molten nitriding salts, at a temperature of approximately 500-650? C. After nitriding, the parts are optionally immersed in an oxidizing bath 16. Such an oxidizing bath 16 is generally mainly composed of molten oxidizing salts, at a temperature of approximately 450? C.

[0159] After the nitriding, or the oxidation as the case may be, the parts undergo a quenching step, for example in a quenching water tank 17, at a temperature very much lower than that of the bath, i.e. relatively cool.

[0160] Next, the parts are rinsed in a post-treatment rinsing tank 18, or several tanks 18a, 18b, 18c in series.

[0161] Possibly, other treatment operations may be applied, for example such as impregnation. The cage may then be immersed in an impregnation bath 19 for example.

[0162] However, the various baths become polluted in the course of successive passes through. For example, sludge gets secreted into the nitriding and/or oxidizing baths 15, 16, which contain nitriding and/or oxidizing salts.

[0163] The water of the post-treatment rinsing or quenching tanks 18, 17 (also referred to as expend water) is also enriched in oxidizing and/or nitriding salts, for example nitrates and nitrites.

[0164] This quenching water 17, being dangerous liquid waste, requires to be treated by companies specialized in the treatment of such waste.

[0165] These different forms of waste thus require storage before being sent for treatment.

[0166] FIG. 2 shows an example of an installation 200 making it possible to treat at least part of this waste by recycling the salts it contains.

[0167] In this example, a fluid containing salts is extracted from the quenching tank 17, but it could of course be any other tank containing a fluid constituting a salt solution.

[0168] For this, the installation 200 mainly comprises a dryer 220, shown in more detail diagrammatically in FIG. 3.

[0169] To convey the fluid to treat from a tank (here the quenching tank 17)) to the dryer 220, the installation here first of all comprises an extraction system 201.

[0170] Here the extraction system 201 comprises for example a buffer tank 203, and at least one upstream pipe 202, leading from the tank from where the fluid to treat is extracted to the buffer tank 203.

[0171] The upstream pipe 202 here for example comprises a filtration system 205.

[0172] The filtration system 205 comprises for example a screen of mesh size less than or equal to 50 ?m, for example comprised between 2 ?m and 50 ?m, or possibly for example between 5 ?m and 10 ?m.

[0173] Here, the filtration system 205 further comprises a magnetic bar, which is for example configured to eliminate magnetic particles that may be contained in the particles to treat. 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 221 of the dryer 220 for fluid to dry.

[0174] The dryer 220 here comprises at least two outlets 222, 223: an outlet for discharge of solid residue 222 and a vapor outlet 223.

[0175] The vapor outlet 223 is provided with two parallel paths which are connected to a vacuum module 207.

[0176] A first of the two paths coming from the vapor outlet 223 is for example provided with a filter 224.

[0177] The filter 224 is for example configured to filter vapors. For this, the filter 224 for example comprises a filtering cartridge, for example having unclogging by compressed air.

[0178] For example, so long as the content of the dryer is sufficiently liquid, the vapors are condensed directly without passing by the filter 224, that is to say by passing via a second of the two paths coming from the vapor outlet 223 and leading to the vacuum module 207.

[0179] However, 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 vapor and it is then preferable to pass via the filter 224, that is to say via the first of the two paths coming from the vapor outlet 223.

[0180] The filter 224 is thus for example activated during phase C of the process.

[0181] The installation for example also comprises a boiler 206 configured to keep a chamber of the dryer at a desired temperature.

[0182] The boiler 206 is for example configured to heat, to approximately 130? C., a heat-conveying fluid configured to keep an interior of the chamber at a desired temperature.

[0183] The heater 206 may be switched to heating or cooling mode to reduce the temperature of the solid residue produced in the chamber during a discharging phase, via the outlet 222 for discharging solid residue.

[0184] Downstream of the dryer, the installation next comprises the vacuum module 207 to which is connected the vapor outlet 223.

[0185] The vacuum module comprises for example at least one vacuum pump configured to produce a moderate vacuum in a chamber of the dryer 220, that is to say a pressure comprised between 10 mbars and 900 mbars.

[0186] The vacuum module for example comprises two pumps which may be used in series or individually (according to the application and effectiveness required), for example a Roots pump, and a liquid ring pump.

[0187] The installation may further comprise a condenser 208 configured to condense the vapor coming from the dryer 220 by the vapor outlet 223. The condenser is for example a tubular condenser. The condenser 208 for example comprises a tubular heat exchanger. For this, the installation may further comprise a cooler 209.

[0188] For example, the tubular heat exchanger 208 is connected to the cooler 209.

[0189] The condensed vapors may be collected in a condensate reservoir.

[0190] Here, downstream of the condenser 208, the installation comprises a condensate supply pipe 210 configured to extract the condensate from the condenser and possibly introduce it back into a rinsing water tank, for example here the rinsing tank 18c.

[0191] It is to be noted that here, the condensate for example comprises liquid water, produced by the condensation of the water vapor coming from the dryer.

[0192] In the present example embodiment, the condensate supply pipe 210 optionally comprises a filter 211.

[0193] According to an advantageous option, the installation also here 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 a possible presence of toxic or corrosive gases.

[0194] Such gases, for example ammonia, may possibly be contained in the condensate.

[0195] The dryer 220 is illustrated in more detail in FIG. 3.

[0196] The dryer 220 is configured to dry fluids containing salts, whether they be liquids or sludges, in a vacuum. These fluids are also designated salt solutions.

[0197] The dryer 220 is a vacuum dryer, in particular a heated vertical mixer, turning at a moderate speed to obtain a rising perimeter flow of product and renewal of the product in contact with the heated walls of the chamber.

[0198] For this, the dryer mainly comprises a chamber 225, which is provided with the inlet 221 for fluid to dry, the outlet 222 for discharging solid residue and the vapor outlet 223.

[0199] The chamber 225 is fixed here, in that it is not rotary, and is held by a mounting 228.

[0200] The chamber 225 here comprises a conical bottom which facilitates discharging of the solid residue obtained.

[0201] The outlet 222 for discharging solid residue is thus preferably formed at an end of the conical bottom, at the bottom of the chamber.

[0202] The outlet 222 for discharging solid residue comprises for example a spherical valve with metal-to-metal contact.

[0203] According to a favored feature, the chamber 225 comprises a double jacket, that is to say an outside wall and an inside wall delimiting between them a space enabling circulation of a heat-conveying fluid.

[0204] The heat-conveying fluid is for example heated by electric heating such as the boiler 206 to heat it to 130? C. for example.

[0205] For example, the heat-conveying liquid comprises an oil.

[0206] In the present example embodiment, the inside wall thus forms an internal tank, which is for example of Hastelloy C22, or any equivalent material.

[0207] In the chamber 225, the dryer here comprises a mixer 226 configured to mix and dry the content of the chamber, i.e. the fluid to treat.

[0208] The mixer for example comprises a helical blade heated by the circulation of a heat-conveying fluid.

[0209] The mixer 226 is for example configured to turn at a variable speed according to need, for example up to 100 rpm.

[0210] The mixer 226 here passes at a distance from the inside wall of the chamber 225 in order to avoid scraping the wall and thus limiting wear of the mixer.

[0211] According to an advantageous option present here, the dryer comprises a lump-breaker (chopper) 230 in the chamber 225, such a lump-breaker 230 is for example configured to turn at a speed up to 1500 rpm to break possible lumps.

[0212] To perform semi-continuous filling, the dryer comprises a filling valve 227.

[0213] In the present example embodiment, the filling valve 227 is connected to the dryer inlet 221 for fluid to dry.

[0214] For example, the filling valve 227 is placed between the reservoir for fluid to treat and the dryer.

[0215] The filling valve 227 is open or closed according to a weight of the chamber.

[0216] When it is open, it enables introduction of fluid to treat into the chamber, via the inlet 221 for fluid to dry, through suction of fluid by virtue of the vacuum module 207.

[0217] To know the weight of the chamber, the dryer comprises a load cell system 229.

[0218] This makes it possible to know the state of filling of the chamber, and, accordingly, to introduce fluid to treat.

[0219] In the present example embodiment, the load cell system 229 comprises at least two, preferably three, weighing sensors regularly spaced around the chamber. Their measurement values are then for example averaged (or added together) to determine a weight of the chamber, and thus to know its filling state.

[0220] A weighing sensor is diagrammatically disposed here between a shoulder of the chamber and a mounting part 228.

[0221] FIG. 4 illustrates the main steps of a process for treating a fluid comprising salts according to an example of implementation of the invention, for example in the context of an installation as illustrated in FIG. 2.

[0222] The process for example comprises a sequence of steps as follows.

[0223] The process first of all comprises a step S1 of extracting fluid to treat from a tank, here a quenching tank 17 of a nitriding line.

[0224] The fluid to treat, which is then quenching water containing salts coming from earlier baths for nitriding and oxidizing, is conveyed by the extraction system 201.

[0225] The process for example comprises a step S2 for filtering the fluid to treat, for example by the filtering system 205. The filtering step S2 here comprises at the same time a step S21 for passing the fluid through the screen of the filtering system 205 and a step S22 of eliminating magnetic particles, such as iron oxides, by the magnetic bar.

[0226] The process next comprises a step S3 of treating the fluid, i.e.: [0227] A step S31 of introducing fluid to treat into the chamber 225 of the dryer 220, via the inlet 221 for fluid to dry; [0228] A step S32 of drying the fluid in the chamber 225 by placing at a temperature comprised between 30? C. and 90? C. and at a pressure comprised between 10 mbars and 900 mbars; and [0229] A step S33 of extracting a solid residue in powder form, which is for example recovered via the outlet 222 for discharging solid residue.

[0230] The drying step S32 comprises two steps, which take place concomitantly: [0231] A sub-step S321 of evaporating at least some of the fluid, producing at least water vapor which is extracted from the chamber 225 by the vapor outlet 223, and [0232] a sub-step S322 of increasing salt concentration of the fluid contained in the chamber 225

[0233] As described in more detail in connection with FIG. 5, the drying step here comprises two phases: [0234] a first phase (indicated as B in FIG. 5) during which a weight of the chamber reduces and when the weight of the chamber reaches a lower threshold or a rate of variation of the weight of the chamber is less than a first predefined value, the drying step comprises a step of complementary filling of the chamber until the weight of the chamber reaches an upper threshold; and [0235] a second phase (indicated as C in FIG. 5) during which the weight of the chamber reduces 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.

[0236] To perform the filling semi-continuously, the process here comprises a step S4 of checking a weight of the chamber 225, for example by the load cell system 229, and when the weight reaches a lower threshold (corresponding to a lower filling threshold) or when a rate of variation of the weight of the chamber is less than a second predefined value, the process comprises a step S51 of opening the filling valve 227 and the step of complementary filling of fluid to treat in the chamber 225 is implemented. When the weight of the chamber reaches an upper threshold (corresponding to an upper filling threshold), the process comprises a step S52 of closing the filling valve 227.

[0237] In parallel, the interior of the chamber is kept under a vacuum, which enables fluid to treat to be sucked into the chamber when the filling valve 227 is open.

[0238] The process here also comprises a step S6 of condensing vapor coming from the dryer 220 by the vapor outlet 223 by means of the condenser 208, thereby producing a condensate.

[0239] According to an option represented here, the process comprises a step S7 of vapor scrubbing, by the scrubber 212.

[0240] The condensate is for example next conveyed by the condensate supply pipe 210.

[0241] According to another option shown here, the process comprises a step S8 of filtering the condensate by the filter 211 of the condensate supply pipe 210.

[0242] Next the process comprises a step S9 of injecting the condensate into the rinsing tank 18c.

[0243] FIG. 5 presents a graph illustrating the fluid treatment in the chamber 225 of the dryer 220 by semi-continuous filling.

[0244] This graph shows more specifically a change in the filling ratio of the chamber (in %), along the y-axis, according to time that has an arbitrary unit here, along the x-axis.

[0245] This graph here shows four phases over time: a phase A corresponding to step S31 of introducing fluid to treat into the chamber 225 of the dryer 220 which is initially empty, a phase B corresponding to the first phase of drying step S32, during which the content of the chamber is mainly concentrated in salts, a phase C corresponding to the second phase of drying step S32, and lastly a phase D which corresponds to the step S33 of extracting solid residue, for example by the outlet for discharging solid residue 222.

[0246] Filling is usually made with a lift pump (not shown). The end of filling may be detected by weighing or volume measurement.

[0247] The chamber is placed under a vacuum after the filling of step S31 of introducing fluid to treat, for example by the vacuum module 207.

[0248] During the first phase B, the weight of the chamber is monitored, for example continuously; reaching a lower threshold, or a slowing until the first predefined value is reached, triggers the opening of the filling valve 227, the fluid is then sucked by the vacuum; reaching the upper threshold triggers the closing of the filling valve 227 again. With the additions of fluid, the salt content in the chamber increases progressively. The upper and lower thresholds may change in the course of the filling operations, in particular to maintain a constant filling ratio in terms of volume. As a matter of fact, the density of the salt may differ from the density of water and the weight depends on the salt content.

[0249] The number of filling operations and the variation of the thresholds may be programmed in advance or be entirely governed by the measurements of weight, flow rates or salt content.

[0250] When the desired content is reached, the first phase B is terminated. The second phase C then begins, during which there is no further addition of fluid.

[0251] In this step, pumping may be strengthened, for example using a rotary compressor (Roots pump) upstream of the vacuum pump of the vacuum module, which makes it possible to attain higher degrees of dryness. In this step, the weight is also monitored constantly. The weight loss per unit time (equivalent to an evaporation rate) then makes it possible to estimate the remaining moisture content and to determine the end of drying. It is preferably during the second phase C that the lump-breaker is set to work, either right from the start, or when a certain moisture content has been reached.

[0252] Lastly, the dryer is emptied.

[0253] By way of example, a drying operation was carried out on oxidation quenching water coming from a nitriding production line. The solution to treat had an average concentration of 255 g/L. An initial weight of 2324 kg (for a volume of 1857 L) was introduced into the dryer chamber. The chamber was placed under a vacuum (i.e. under approximately 50 mbars) by means of a liquid ring pump. The solution was brought to a temperature of 38? C.

[0254] Next the evaporation/concentration cycles were commenced. In total, 3397 kg of quenching water were added in ten steps (i.e. on average 377 kg per addition) for 2421 minutes (constituting the duration of phase B), until a concentration by mass of 52% was attained.

[0255] The final drying phase (phase C) was then triggered until the liquid-solid phase transition was observed after 21 hours of drying for a dry residue analyzed at 91.67% (degree of dryness). Switching to vapor filtering mode was carried out, the lump-breaker was triggered and a vacuum of 10 mbars was attained after triggering the Roots pump.

[0256] After 6 hours of drying at 85? C., 1217 kg of a powder were extracted from the dryer, having a 99.09% dry extract, then re-used on the nitriding production line without impacting quality. The operation of drying generated in parallel 4335 kg of condensates which were reused in the rinsing operations of the nitriding production line.