FR2499426A1 - METHOD AND DEVICE FOR THE RECOVERY OF AMINES FROM EXHAUST-CONTAINING AIR - Google Patents

Abstract

The invention relates to a method and a device for recovering the amines from the exhaust air. IN A FIRST STAGE, THE AMINES IN THE EXHAUST AIR ARE CONVERTED, USING A WASHING SOLUTION CONTAINING PHOSPHORIC ACID, INTO AMMONIUM PHOSPHATE, WHICH IS MIXED WITH OXIDE OR CALCIUM HYDROXIDE, WITH DISCHARGE OF THE AMINES FORMED AND SEPARATION OF THE CALCIUM PHOSPHATE OBTAINED, THE AMINES BEING CONDENSED IN A THIRD STAGE OF THE PROCESS. THE INVENTION FINDS ITS MAIN APPLICATION IN FOUNDRIES.

Description

The invention relates to a recovery process

  of amines from exhaust air, originating in par-.

  foundries, containing amines and washed in exhaust air purification systems with washing solutions, as well

  for carrying out this process.

  One of the subdivisions of the foundry operations

  stone-making workshops, o sand,

  accelerate the hardening of the structure, are introduced

  at the same time as catalysts, in particular amines, in kernel pulling machines. These

  amines are sent to the atmosphere with the air of evacuation

  and pollute the environment. The official requirements

  decreed because of this defined state of affairs.

  There are limit concentrations in the emissions, which no longer make it possible to evacuate the air without treatment. Exhaust air cleaning facilities are

absolutely necessary.

  Air purification facilities of this type are already known. They consist for example of washing towers in which a washing solution, coming from a nozzle device installed at a great height, is sent, via an absorption unit, against the flow of air. evacuation containing amines and produced in

  foundry workshops. The exhaust air is dis-

  sated pollutants by purging against the current, which is accompanied by a strong transfer of material. The amines are then in the wash water, which, up to

  now, was sent, diluted, into the

  areas. The disadvantages are the water pollution associated with this operation and, in addition, the loss of large quantities of amines, which are lost as

raw materials.

  The object of the invention is to create a method and a dis-

  positive, instead of losing them irreparably, to recover by recycling the necessary amines in a foundry, and thus save raw materials and reduce pollution of waste water. To this end, the invention relates to a process in which the exhaust air, containing amines, is converted to ammonium phosphate by the use of a washing solution containing phosphoric acid, in which the solution of ammonium phosphate is mixed

  under agitation with calcium oxide and / or hydrogen

  calcium hydroxide, with evacuation of free gaseous amines

  and separation and drying of calcium phosphate

  product, the gaseous amines being finally condensed.

  It is thus possible to recover as raw material for foundries the amines used and to simultaneously produce calcium phosphate for further use as fertilizer, and this in a globally economical way. We can then do

  large savings in raw material, and in particular

  bind, treat by-products and avoid polluting the environment. This results in a considerable decrease

  operating costs in foundries.

  Advantageously, the ammonium phosphate, produced in the first stage of the process, is first stored, then sent, after a preliminary purification, in concentrated form to the second stage of the process, in which the mixing takes place with calcium oxide and / or calcium hydroxide. In this way, it is possible to prevent the mixing of different types of amines

  with each other, and to carry out the separate treatment

  in batches. The mixture of the ammonium phosphate solution with fumarum oxide and / or calcium hydroxide is advantageously reduced to the exclusion of air to give vapors to the vapors. high concentration

of amines.

  In particular! it is advantageous to treat in the

  second stage of the process the ammonium phosphate solution

  mixed with alkali metal and / or hydroxide

  calcium, with a heat input in the initial phase

  and then, using the heat of reaction of the exothermic processes, possibly by evacuation of heat, in a temperature range between 85 and 105 ° C. Preferably, the working temperature should be 90 ° C in this stage of the process. The amine-containing vapors removed by this process can be pre-cooled to about 450 ° C to separate the water, the amine-containing water and thus separated back to the number two stage of the process. The vapors containing amines and thus concentrated are then, according to an advantageous embodiment of

  invention, and after passing through a stage of dehydration

  on silica gel in the third floor of the

  process, cooled to a temperature below the temperature

  boiling point of the amines, and condensed. The condensed amines are dehydrated to a

  less than 0.2%, and they can thus be used

  again as a raw material for foundries. The calcium phosphate formed in stage 2 and in the form of a suspension is preferably neutralized with phosphoric acid and separated from the solution by a decantation process. Filtration is then carried out, and further treatment is carried out by drying the filter cake. The final product thus obtained can be used as a fertilizer, or for the manufacture of fertilizers. This gives a globally economic utility of the proposed recycling process, saving raw materials and avoiding the elimination, necessary until now and polluting

for the environment of waste.

  The device according to the invention for executing

  The process described above is based on an upstream wet scrubber, which uses a wash solution containing phosphoric acid, and is characterized by reactor intended to form gaseous amines and a

  suspension of calcium phosphate, a column of

  tillation to condense the amines and a device for filtering and drying the calcium phosphate suspension. This treatment plant takes the washing solution formed at the wet scrubber operators, which allows, as desired, to eliminate pollutants without equipment internal to the company.

  The subclaims contain forms of

  advantageous realization of treatment facilities

according to the invention.

  The invention will be better understood with regard to the

  description and the accompanying drawings, which represent

  Embodiments of the invention are illustrated in which: Figure 1 is a schematic diagram of the process for recovering amines from exhaust air; Figure 2 is a block diagram of the preferred amine recovery process; Figure 3 shows schematically the installation corresponding to the block diagram of Figure 2 of the drawings. The exhaust air containing amines and formed in the foundries is treated, in an evacuation air washer known and not shown in the drawings, with washing solutions containing phosphoric acid, so that a solution of ammonium phosphate is removed from the scrubber, which is first stored and then transported in concentrated form, using transport tanks, to the treatment plant. The recovery of the useful substances from the washing solution can be carried out according to the block diagram of FIG. 1. For this purpose, a reactor 1, from a transport tank, is charged with a washing solution B in the form an ammonium phosphate solution. The reactor 1 is made with a double wall, and is equipped, for the control of temperature, with a combined heating and cooling system, which is fed with water vapor or cooling water . An agitator 12, which can be driven by an engine

  outside 13, is inside the reactor 1.

  In the reactor 1, via the supply line 14, quicklime A is introduced, which

  is mixed with slow stirring solution phos

  Ammonium lighthouse, protected from the air.

  To initiate the reaction, heat is sent through the double wall of reactor 1. Gaseous amines and calcium phosphate are formed, which is

  in the form of a suspension. The reaction is exothermi-

  that, as soon as the operating temperature of the reactor has reached a value between 85 and 1050C, the cooling circuit using

  where the temperature is maintained within the indicated range.

  The continuation of the treatment of the vapors containing amines and escaped from the reactor 1 on the one hand, and the suspension containing calcium phosphate on the other hand, is shown in the block diagram of FIG. the right and left production sequence. It emerges that the vapors containing amines in gaseous form are sent to a distillation column 3 with three trays, possibly after pre-cooling in a coolant, not shown,

  to then be condensed in a post-coolant 4.

  When performing a pre-cooling, there is

  separation of water, which is reintroduced into the reaction

  1 by recycling, because this water is still

amines.

  The product obtained at this stage still has a water content of about 2%. To ensure additional dehydration, it is pumped through a molecular sieve, and then sent as a finished product with practically no water (less than about 0.2%) to a container.

collector 11.

  The suspension obtained in the reactor 1 is first concentrated, in order to produce pure calcium phosphate, in a decanter 15, the supernatant solution of which is either introduced again into the reactor 1, or purified on a molecular sieve 16 and rejected in the form of wastewaterF. The wad C thus concentrated is filtered in a filter 8, then dried in the dryer 9, and it can, after a preparation carried out in a

  equipment 10 and meeting the specifications of the

  fertilizer industry, be used as a phosphate raw material. The filtrate D can ,. after a treatment

  in the molecular sieve 16, be sent to the resident water

  duaire. or again to reactor 1, in which case a condensation

  7 is inserted in the circuit.

  The exemplary embodiment of an amine recovery unit shown in Figures 2 and 3 is based on the same principle. The latter consists of reacting, in an alkaline solution, the amine attached to phosphoric acid, according to the following formula: ## STR2 ## The Scheme ## STR2 ## The Scheme of principle of Figure 2 represents an example with indication of quantities and temperatures. It emerges that 250 kg of a spent solution G of trialkylacryl phosphate washing are attacked by 179 kg of Ca (OH) 2, indicated in H, in the reactor 1. 56.8 kg of a mixture are obtained. Steam

  of amine and water vapor, which crosses the distillation column

  3 and then refrigerant 4. This gives 56.8 kg of condensate

  sat with about 2% s of IH20. The amine thus obtained is dehydrated using the molecular sieve 5, the initial temperature of the vapors, which was between 85 and 105 C, lowering to a value below 35 C. To suppress a possible attr-ition of molecular sieve, the amine is subjected to filtration in the filter 17

  before introduction into the collecting tank 11.

  It is intended to regulate molecular sieve 5

  air heater 6 with hot air blower (temperature

  air temperature greater than 130 ° C.) and a condenser 7.

  1,372.19 kg of a suspension is obtained in the reactor.

  I containing calcium phosphate, which is first of all

  neutralized in a neutralizer.

  18 with a motor 19 is installed in the neutralizer.

  The latter produces 159.46 kg of wastewater K less

0.1% ammonium phosphate.

  The filtration already described above in the filter 8 is then carried out at about 90.degree. C., followed by the drying of the filter cake E in the dryer 9 at about 120.degree.

  finally, the processing of 212.73 kg of calcium phosphate

obtained in the equipment 10.

  The quantities involved in the example above are the following: 1. Loads Used washing solution G 250 1 / h Lime Hsèlon the concentration of the washing solution 2. Reactor 450 1 Total volume 500 1 Temperature 85-1050C Quantity Steam 50 m3 (perfect gas) 3. Distillation column Quantity overhead 25 m3 (perfect gas) Overhead temperature 37-450C Number of trays 3 4. Refrigerant Amount Quantity 25 ml (gas), 112 1 (liquid) Temperature 37-450C Input temperature max. 20'C 5. Neutralization tank Filling volume 450 1 Total volume 500 1 6. Filtration Input 450 kg Sludge I (10% H20) 250 kg Sludge from the neutralization tank

are very fine.

7. Molecular sieve column

3 columns, alternate beds.

  The different equipment of the installation possesses

  The following features: 1. Reactor Double-walled tank, made of V4A steel, with the following features: agitator, drain valve

  sludge, outlet pipe for amine vapors.

  Filling neck for Ca (OH) 2 and the solution of

used wash.

  2. Column 3 trays, temperature regulation at the head of

  column (t max = 40 C). Material: glass.

  3. Refrigerant Refrigerant against glass current. Fluid of

cooling: water.

4. Dehydration

  4 A molecular sieve, glass tube.

  5. Neutralization Stainless steel container with supply line,

stirrer and pH regulation.

6. Filtration

See point 6 above.

  7. Dryer Dryer with racks, or other 8. Regeneration of the molecular sieve

  Blower with hot air (approx 200 C) and condenser.

  In FIG. 3, the following is indicated in: L the used solution; M the cooling water circuit; N the cooling water return circuit; Water vapor at a pressure of 300 kPa; Condensate at a pressure of 300 kPa; Q dry air; R vape-r water at a pressure of 2 MPa; and

  S the condensate at a pressure of 2 MPa.

  Of course, the invention is not limited to the embodiments described above and shown, from which we can provide other modes and other embodiments, without it coming out of

framework of the invention.

Claims (17)

claims   1. Process for recovering amines from air   with amines, in particular from   of smelters, and which is washed with washing solutions in exhaust air cleaning plants, characterized in that, in a first stage of the process, the exhaust air containing amines is   converted, using a washing solution containing   phosphoric acid, in ammonium phosphate, in a second stage of the process, the solution of ammonium phosphate. is mixed with stirring and slow heating to calcium oxide and / or calcium hydroxide, with release of gaseous amines released and separation and drying of calcium phosphate product, and   in a third stage of the process, the gaseous amines its are finally condensed.   2. Method according to claim 1, characterized in that the ammonium phosphate produced in the first   first stage of the process is first stored and then, after   preliminary submission, sent in concentrated form to xth stage of the process.   3. Method according to one of the claims   1 and 2, characterized in that the mixture of the solution of   ammonium phosphate and calcium oxide and / or   Calcium oxide is made safe from air.   4. Method according to any one of the claims   1 to 3, characterized in that, in the second stage of the process, the ammonium phosphate solution, mixed with calcium oxide and / or with calcium hydroxide, is maintained at a temperature between 85 and 1050C, by supply of heat in the initial phase and then by the use of process heat of reaction   exothermic, possibly by elimination of heat.   5. Method according to claim 4, characterized in   which maintains a working temperature of 900C.   6. Process according to any one of the claims   1 to 5, characterized in that the amine-containing vapors are pre-cooled to about 450 ° C, and the water droplets produced containing amines are   separated and returned to the second stage of the process.   7. Process according to any one of the claims   1 to 6, characterized in that the vapors containing amines are, after passing through a dehydration stage in the third stage of the process, cooled to a temperature below the boiling point of the amines, and condensed.   8. Process according to any one of the claims   1 to 7, characterized in that the condensed amine is dehydrated   to a water content of less than 0.2%.   9. Process according to any one of the claims   1 to 8, characterized in that the calcium phosphate formed in the second stage of the process and in the form of an alkaline suspension is neutralized with acid   phosphoric and separated from the solution by decantation.   The method of claim 9, characterized in   what is followed by filtration, the filter cake   undergoing further processing by drying, grinding, sieving, etc. 11. Device for carrying out the process according to   any one of claims 1 to 10, with a scrubber   discharge air, wet, installed upstream, characterized in that it comprises a reactor (1) intended   to prepare the gaseous amines and a suspension of phos-   calcium pellet, a distillation column (3) for condensing the amines and a device (8, 9) for filtering   and drying the calcium phosphate suspension.   12. Method according to claim 10, characterized in that the reactor (1) is lined with a double wall and   a device for regulating the temperature.   13. Device according to one of the claims   11 and 12, characterized in that the reactor (1) has an agitator (12).   14. Device according to any one of the claims   11 to 13, characterized in that the distillation column   lation (3) has three trays, one refrigerant (4) being mounted downstream.   15. Device according to any one of the claims   11 to 14, characterized in that one or more sieve units are provided for residual dewatering. molecular (5).   16. Device according to any one of the claims   11 to 15, characterized in that the dryer (9) is a fluidized bed dryer.   17. Device according to any one of the claims   11 to 16, characterized in that there is provided a   divertor (2) with an agitator (18).