FR2648128A1 - Method and installation for manufacturing fertilizers from compost or other waste (residual) products - Google Patents

Abstract

According to the method, a waste product is treated with sulphuric acid to dissolve the organic materials, the solution thus obtained is filtered to remove the undesirable materials not dissolved by the sulphuric acid, the filtered solution is mixed with tribasic calcium phosphate (tricalcium phosphate) and/or dolomite to obtain a homogeneous mixture (slip), this slip is placed in contact with recycling products and granulates are formed, then drying is carried out so as to cause evaporation of the water and concentration of the acid until a sufficient concentration is reached in the granulates to allow a rapid neutralisation reaction of the phosphate and/or of the dolomite, then the drying of the granulates is continued until a determined moisture level is reached and the marketable product is separated from the excessively coarse or fine products, as is known per se. Application, especially to upgrading of urban waste composts.

Description

 The present invention relates to the recycling of composts essentially originating from the treatment of household waste, and of other wastes such as sewage sludge and effluents produced by fermentation digesters.

 These composts and these wastes can be defined as being a mixture of solid products, in a more or less humid environment, which has been subjected to, this is particularly the case for household waste, mechanical grinding and sorting operations, and in all cases, biological transformation operations of organic matter by fermentation, heating and aerobic or anaerobic bio-degradation.

As an indication, an urban compost can have the following composition
- Fertilizers
N: 0.6 to 1.5E
P205:: '0.5 to 2.55
K20: 0.2 to 2e.

- Organic materials
20 to 309
- Water
30 to 35eus
- Mineral elements and trace elements
These elements such as Mg, S, Cu, Na, Ca, Mo,
B can be in very variable quantity but are very interesting by their agronomic value.

- Annoying elements
Glass, plastic, rubber, metals.

 These troublesome elements are found in variable quantities and in a more or less well-ground form, depending on the process used and the quality and efficiency of the equipment in the processing and sorting workshops.

 These composts as well as the sludges are used in agriculture because they make it possible to carry out an organic amendment and to carry out a contribution of trace elements as well as fertilizing elements.

Such use, however, offers significant drawbacks, namely
- Handling and transport of tonnages and large volumes of material for a low supply of fertilizing elements;
- Slow and incomplete assimilation by plants of the nutrients found in composts and sludge in the form of non-soluble and poorly assimilable chemical combinations;
- Risk of soiling the soil with composts too rich in glass, plastic, rubber and non-biodegradable materials.

 It is also known in the art to dissolve certain relatively noble organic materials, such as soaps or leathers, in relatively concentrated and hot sulfuric acid.

 Sulfuric acid containing these dissolved materials can be used to manufacture simple superphosphate or monocalcium phosphate, provided that it has a concentration greater than 70-s, for example between 70 and 75. For this purpose, l acid and tricalcium phosphate to obtain a fluid slurry which is introduced into an apparatus called "cellar" in which is carried out the exothermic reaction of transformation of tricalcium phosphate into monocalcic phosphate, with production of lime sulfate, from which results a passage of the mixture from the fluid state to the solid state as well as an evaporation of water. On leaving the cellar, superphosphate can be stored before granulation or granulated immediately.

 Such a process cannot be transposed to composts or sludge, because the slurry which would be obtained by dissolving the composts in sulfuric acid would be very diluted due to the water provided by the compost and would no longer have the optimum concentration sufficient to rapidly neutralize the phosphate, according to the known process.

 It is precisely the objective that the invention sets itself, that of proposing a process and a Latin plant making it possible to recover, under interesting industrial and economic conditions, products such as composts originating from the treatment of household waste and other similar waste. .

 To this end, the subject of the invention is a process for manufacturing fertilizers from a residual product such as compost, sludge or other waste, characterized in that the residual product is treated with l sulfuric acid to dissolve organic matter, the dissolution product thus obtained is filtered to remove undesirable materials not dissolved by sulfuric acid, the filtered dissolution product is mixed with neutralizing agent chosen from tricalcium phosphate and / or dolomite or any other raw material containing one or more fertilizing elements capable of neutralizing sulfuric acid, to obtain a homogeneous slurry, this slurry is brought into contact with recycling products and granules are formed, then drying is carried out so as to cause evaporation of the water and the concentration of the acid, until a sufficient concentration is reached within the granules to allow a rapid reaction of the acid with the neutralizing agent, then the drying of the granules is continued until a predetermined humidity level is reached and, as known per se, the commercial product is separated from the products which are too large or too fine .

 According to another characteristic, organic or chemical raw materials constituting additives are introduced at the same time as the products for recycling, chosen for example from the group comprising: oil cakes, meat, fish or leather meal, salts nitrogen, salts containing P205 and salts containing K20.

 The invention also relates to an installation allowing the implementation of the process defined above and comprising a tank for mixing the residual product and sulfuric acid, at least one sieving or filtration station to separate the slurry obtained in the mixing tank of the insoluble materials, means for washing these insoluble materials with sulfuric acid, means for washing the insoluble materials with water, a kneader in which the acid mixture is mixed filtered with the neutralizing agent such as tricalcium phosphate and / or dolomite, a mixer-granulator provided with means for supplying recycled dry product and into which the slurry from the mixer is introduced, a dryer-reactor apparatus in which are introduced the granules from the mixer-granulator, as well as sieving means, grinding and recycling refuse.

 The invention will be described in more detail below with reference to the accompanying drawing, the single figure of which is a diagram of an installation according to the invention.

We have represented on this diagram
- a homogenizing tank 1 equipped with an agitator 2;
- a filtration or sieving device 3;
- a station 4 for washing with sulfuric acid;
- a station 5 for washing with water;
Tray 1 is supplied with compost or other waste, in 20, as well as more or less dilute sulfuric acid, by pipes shown diagrammatically in 21, 22, 23, coming from washing stations 4 and 5. A separate acid supply can also be provided.

 The washing stations 4 and 5 are supplied with acid and water respectively by pipes 24, 25.

 - A first mixer 6 which can be of conventional construction and which will not be described in detail, into which are introduced, on the one hand, the slurry coming from the filter 3 through a line 26 and, on the other hand, the agent neutralizing agent such as tricalcium phosphate or dolomite, at 27.

- A second mixer 7 also constituting a granulator, arranged in series with the first and into which can be introduced at 28 dry recycling products as well as possibly, at 29, other addition products; this mixer granulator is also preferably provided with propellers 8 rotating at high speed (1000 to 3000 revolutions / minute);
- A dryer 9 which can on the whole be of conventional construction and which it will be indicated, simply that it is constituted by a rotating cylinder, equipped in a first zone of entry of rapidly advancing turns 10, followed by a smooth zone 11 then a third zone comprising lifting shovels 12.

 - the installation is completed by a sieving device 13, 14 making it possible to separate the merchant product from the too fine granules as well as from the too large granules which are ground in a grinder 15, the fine products and the coarse products thus ground then being recycled to the granulator mixer.

The merchant product is evacuated in 30 to be stored or shipped.

 The drying cylinder is also connected at 31 to a suction device, not shown, equipped with purification means.

The different phases of the process according to the invention are as follows:
First of all, the compost or the residual sludge containing organic products is dissolved in sulfuric acid, by mixing the compost and an acid solution in the tank 1 equipped with the agitator 2.

 The retention time in this tank can be of the order of 10 to 15 minutes, for example.

 The supply of compost, acid and water is continuous and is controlled in a known manner by dosimeters and flow meters (not shown).

 The temperature of the slurry in this tank must be of the order of at least 90 to 95 "C. If this temperature is not reached, for example due to the use of an acid that is too diluted, it is necessary to reheat the mixture and to equip the tank with reheating means such as a coil in which a heated fluid circulates.

 Extraction from the tank 1 is also carried out continuously, for example by overflow.

 The liquid slurry leaving the homogenization tank is filtered in 3, to separate from this slurry insoluble materials (glass, plastic, metals, etc.) having a size for example greater than 1.5 mm. The insoluble materials are then washed successively with sulfuric acid (in 4) and with water (in 5), the washing solutions then being recycled into tank 1.

 After filtration, the acidic slurry containing dissolved organic matter is introduced continuously into the mixer 6, to be mixed there with tricalcium phosphate in powder form, with the aim of making monocalcium phosphate.

 Alternatively, in this mixer, the organic acidic slurry can be mixed with dolomite, to make a product containing magnesium sulfate.

 A mixture of tricalcium phosphate and dolomite can also be introduced into the mixer.

 Obtained at the outlet of the first mixer a thickened homogeneous slurry which is transferred to the second mixer 7 to be transformed into wet and acid granules. To this end, recycling products and, where appropriate, additives consisting of organic or mineral fertilizing raw materials are added to the second mixer, in order to optionally make a binary or ternary fertilizer.

 Depending on the humidity of the thickened slurry and the composition of the product to be obtained, the ratio between the weight of the solid materials introduced into the mixer 7 and the weight of the slurry, can vary between 1 and 3 approximately. In this second mixer, the materials present are not only mixed to obtain a homogeneous product, but are also mixed by the propellers 8 so as to divide the dough progressively thickened by solid materials, into particles of diameter between 1 and 5 mm and to keep them suspended in the mixer.

 To obtain good formation and good resistance of the granulated particles, the temperature in the second mixer must be at least about 60 ° C. If due to the use of too dilute acid or the incorporation of too large quantities of cold additives this temperature is not reached, the mixture should be reheated with steam and / or fitted the mixer of a heating jacket.

At the outlet of this device, the granulated particles are preferably introduced by gravity into the drying cylinder 9 arranged to fulfill the following three functions
- rounding the granulated particles leaving the mixer 7;
- Concentrate the acid solution impregnating the granules to accelerate the neutralization reactions;
- Dry the granules to give them the characteristics of mechanical resistance and non-mass recovery essential to the qualities required for the merchant product.

 In the first zone 10, the granules advance rapidly, then in the smooth zone 11 these granulated particles are rounded on the walls of the cylinder, compact and see their density when lying by rolling on each other.

 In the third zone 12, the granules are taken up by the lifting shovels arranged to carry out a mixing of the granules and especially a total and homogeneous filling of the section of the cylinder where the granules fall in rain and are brought into contact with the circulating hot air in the same direction as the product, in order to obtain the best heat exchange yield.

 From a certain level of drying, the free acid included in each granule reaches the optimum concentration to quickly neutralize the phosphate and / or dolomite used in the composition of the complex to be manufactured.

 After this neutralization reaction, the granules continue in the last part of the cylinder the drying operation necessary to obtain a good quality fertilizer.

 By way of example, the main characteristics of the drying cylinder can be given below, which can of course vary depending on the composition of the products which it is desired to obtain.

- Residence time in the drying cylinder
approximately 30 to 45 minutes.

- Gas temperature
- at the cylinder entrance: from 300 to 400 'C
- at the cylinder outlet: from 80 to 100. C
- Peripheral rotation speed: from 25 to
32 m per minute approximately,
- Humidity of the granules at the outlet: from 1 to
4a according to the compositions.

 At the outlet of the drying cylinder 9, the coming granules undergo the conventional and well-known sieving operations at 13 and 14, recycling and cooling with regard to the merchant product. The excessively large granules are ground at 15 and mixed with products that are too fine, to feed the mixer 7.

 Of course, if this is necessary to maintain a correct supply rate of the mixer 7 with recycling product, it is possible to take at 32 from the commercial product the essential complement.

 The process and the installation which have just been described make it possible to use residual acids of concentration lower than 70-s, which at the present time and in known techniques must be mixed with noble acid with concentration high. The method according to the invention is therefore particularly advantageous from an economic point of view, since the cost of the drying evaporation operation carried out in the drying cylinder 9 is less than the cost represented by acid at high concentration.

 It is particularly advantageous in fact to reach a sufficient acid concentration during the drying operation, by evaporation of the excess water.

 This process makes it possible to recover, under satisfactory industrial and economic conditions, composts or other sludges and residues having a certain value for soil enrichment.

 The following examples illustrate the present invention.

EXAMPLE 1
Manufacture of an organic superphoshate dosing 16 \ of P205.

Raw materials used for the production of 1000 kg of finished product - 75% recovery sulfuric acid. . 438 kg
(waste acid common on the market) - 33% water compost. . 300 kg - phosphate 33.5 P205. 485 kg - washing water. . .... 50 kg
Total. . 1.273 kg
Water content of the mixture.

- 438 x 0.25 acid. +. ,,., 109.5 kg - compost 300 x 0.33. .... 99.0 kg 99.0 kg - from washing. 50.0 kg
258.5 kg
Sulfuric acid content 100 s.

438 x 0.75 ... . . 328.5 kg
Concentration of the acid in the mixture. 55.9 '.

 The operating conditions are collated in Table I.

EXAMPLE 2
Manufacture of organic magnesia dosing 9% MgO.

Raw materials used for the production of 1000 kg of finished product - 75% recovery sulfuric acid. 610 kg - 33% water compost. 407 kg - dolomite dosing 21% MgO. 429 kg - washing water. 50 kg
1.496 kg
Water content of the mixture - acid 610 x 0.25. 252.5kg - compost 407 x 0.33 ... ....... 134.3 kg - washing water. .......... zoukg
336.8 kg
Sulfuric acid content 100 t 610 x 0.75 ... . . 457.5 kg
Concentration of the acid in the mixture 57.59 5.

 The operating conditions are collated in Table I.

EXAMPLE 3
Production of an organochemical fertilizer 2.7.10 + 3 MgO.

Raw materials used for the production of 1000 kg of finished product - 75% sulfuric acid. 387 kg - water compost 33 263 kg - dolomite 21 5. MgO 143 kg - phosphate 33.5. P205. 212 kg - ammonium sulphate 21 t. 195 kg - potassium chloride 61 t 170 kg - washing water 50 kg
1.420 kg
Water content of the mixture - acid 387 x 0.25 96.75 kg - du.compost 263 x 0.33 86.75 kg - washing water 50.00 kg
233.54 kg
Acid content 100% 387 x 0.75. . -. . . . 290.25 kg
Concentration of acid in the mixture ... 55.41.

 The operating conditions are collated in Table I.

TABLE I - OPERATING CONDITIONS
Mixing in tank 1 Example 1 Example 2 Example 3 - Temperature in CC 90 90 90 - Residence time in
minutes 10 10 15
Washing water on sieve 5 - Quantity in liters 50 50 50
Mixer 6 - Temperature in C 90 90 95 - Residence time in
minutes 3 4 3
Mixer 7 - Temperature in C 80 75 60
Dryer 9 - Gas temperature
entry in "C 320 350 300 - Gas temperature
outlet at C 90 90 90 - Product temperature
entering "C 80 75 60 - Product temperature
outgoing C 90 90 85 - Residence time in
minutes 30 30 84'0
Recycling rate required for granulation 2 3 2
Humidity of marketable product has water 3 to 4 3 to 4 4
These examples illustrate the manufacture with a known residual acid available on the market.

These same fabrications can be made with a more dilute acid, the essential difference from the point of view of implementation consisting in increasing the recycling rate.

Claims (7)

 1. A method of manufacturing fertilizer from a residual product such as compost, sludge or other waste, characterized in that the residual product is treated with sulfuric acid to dissolve the organic materials , the dissolution product thus obtained is filtered to remove undesirable materials not dissolved by sulfuric acid, the filtered dissolution product is mixed with a neutralizing agent chosen from tricalcium phosphate and / or dolomite or any other raw material containing one or more fertilizing elements capable of neutralizing sulfuric acid, to obtain a homogeneous slurry, this slurry is brought into contact with recycling products and granules are formed, then drying is carried out so as to cause the evaporation of the water and the concentration of the acid, until a sufficient concentration is reached within the granules to allow a rapid reaction of the acid with the neutralizing agent, then the drying of the granules is continued until a predetermined humidity level is reached and the commercial product is separated, as known per se, from products that are too large or too fine.  2. Method according to claim 1, characterized in that at least one additive is added to the recycling products comprising at least one organic or chemical raw material having a fertilizing or soil-improving power.  3. Method according to claim 2, characterized in that the additive comprises at least one material chosen from the group comprising oil cakes, meat, fish or leather meal, nitrogen salts, salts containing P205 or K20.  4. Method according to any one of claims 1 to 3, characterized in that sulfuric acid having a concentration of less than 70- .. is used.  5. Installation for implementing the method according to any one of claims 1 to 4, characterized in that it comprises a tank (1) for mixing the residual product and sulfuric acid, at least one station for sieving or filtration (3) to separate insoluble materials from the slurry obtained in the mixing tank, means (4) for washing these insoluble materials with sulfuric acid, means (5) for washing insoluble materials by water, a kneader (6) in which the filtered acid slurry is mixed with the neutralizing agent, a granulator kneader (7) provided with means (26) for supplying dry recycled product and in which is introduced the slurry from the mixer, a dryer-reactor (9) into which are introduced the granules from the mixer-granulator (7), as well as means (13, 14, 15) of sieving, grinding and recycling refusals.  6. Installation according to claim 5, characterized in that it comprises means (27) for introducing into the kneader-granulator (7) at least one additive comprising at least one organic or chemical material with fertilizing power or for amending soils.  7. Installation according to any one of claims 5 to 7, characterized in that the dryer-reactor (9) is a cylinder which comprises at least three zones: a zone (10) of rapid advance, a zone t11) substantially smooth where the granules are watering and an area where the cylinder has lifting scoops (12) and where the neutralization reaction takes place followed by additional drying.