RU2420452C1 - Method of producing thermal phosphoric acid and apparatus for realising said method - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to chemical industry. The method of producing thermal phosphoric acid involves preliminary thermal treatment of phosphorite, quartzite and coke, preparation of a mixture from said components at given ratio, where said mixture has acidity index of 0.76-1.0, and loading said mixture into furnace bins and then feeding through pipes into the bath of a phosphorus furnace, in which there are self-sintering electrodes. The completeness of the process of reducing phosphorus from the mixture is controlled by feeding fine coke and/or phosphorite into the reaction zone through the inner cavity of the self-sintering tubular electrodes, tapping slag and ferrophosphorus. Partial burning of the furnace gas containing phosphorus and carbon oxide in an air current is carried out under the furnace roof by feeding air. The remaining furnace gas is then fed for after-burning through loading pipes by creating optimum discharge in the gas passage. Pre-cooled phosphorus pentaoxide obtained during burning is fed for hydration to obtain phosphoric acid. Phosphoric acid is cooled. The gas is cleaned from acid mist in an electrofilter and then released into the atmosphere. ^ EFFECT: method and device enable to obtain cheap phosphoric acid without using high-quality phosphate raw material. ^ 4 cl, 4 dwg, 1 ex

Description

The invention relates to a method for producing phosphoric acid by the electrothermal method, which consists in the fact that phosphorus-containing gases are cleaned of dust and extinguished in a stream of air upon leaving the furnaces. At the same time, not only phosphorus and phosphorous hydrogen present in small amounts are burned, but also carbon monoxide, as well as hydrogen and hydrogen sulfide.

The development of electrothermal methods for the production of phosphoric acid from the very first years of the occurrence of this problem was carried out in several directions. Comparatively quickly, methods were developed for the complete combustion of gases (single-stage) and the combustion of liquid phosphorus (two-stage).

The two-stage method for the production of thermal acid is more advanced, has several advantages compared to the single-stage method, and therefore has become the main one in the production of phosphoric acid.

This method of phosphoric acid production is based on the reduction of phosphates (NN Postnikov Thermal Phosphoric Acid, Khimiya Publishing House M., 1970) to elemental phosphorus, its subsequent oxidation to phosphorus oxide (V) and hydration of the oxide to phosphoric acid: Ca ₅ (PO ₄ ) ₃ F> P _n > P ₂ O ₅ > H ₃ PO _4.

The restoration of phosphorus from natural phosphates is a complex multi-stage heterogeneous process that proceeds through the stages:

- preparation of the charge for electric sublimation;

- heating the components of the charge,

- entry into the melt of calcium phosphate and silicon oxide,

- dissociation of tricalcium phosphate,

- diffusion of the products of dissociation to the surface of carbon particles,

- the interaction of tricalcium phosphate with carbon and the formation of phosphorus, carbon monoxide (II) and calcium oxide,

- removal of calcium oxide from the reaction zone in the form of calcium silicates.

In the absence of fluxes, the reduction reaction proceeds at 1400 ° C for 20 minutes. To reduce the process temperature and shift the reaction equilibrium to the right, silica, alumina, or aluminosilicates are introduced into the system, which bind the resulting calcium oxide in the form of easily removed slag:

2Ca ₅ (PO ₄ ) ₃ F ₂ + 15С + 6SiO ₂ = 3P ₂ + 15CO + 3 (3CaO · 2SiO ₂ ) + 2CaF ₂ + H, where H = 1730 kJ.

In the presence of fluxes, the reduction reaction proceeds in the diffusion region at a rather high rate even at a temperature of ~ 1300 ° C and is accelerated by factors that enhance diffusion in the solid phase and in the melt — an increase in the dispersion of charge components, the formation of low-melting polyelectic systems, etc. To increase the mobility of the melt and facilitate the discharge of slag, the recovery process is carried out in practice at 1350-1500 ° C.

Phosphorus combustion - a heterogeneous exothermic process - proceeds according to the equation: P _{4 liquid} + 5O _{2 gas} = P ₄ O _{10 TV} -H, where H = 753 kJ.

The degree of oxidation of phosphorus depends on the temperature in the combustion zone and on the rate of diffusion of oxygen to the surface of liquid phosphorus. To ensure complete combustion and to exclude the possibility of the formation of lower phosphorus oxides, the process is carried out at a temperature of 1000-1400 ° C and a twofold excess of air.

Hydration of phosphorus oxide (V) proceeds through a series of stages. At the first stage of the process, due to the high temperature in the system, the interaction of phosphorus oxide vapors with water gives metaphosphoric acid: P ₄ H ₁₀ + 2H ₂ O = 4HPO ₃ -H.

With decreasing temperature, metaphosphoric acid through polyphosphoric acid is converted into phosphoric (orthophosphoric) acid: HPO ₃ + H ₂ O = H ₃ PO ₄ -H.

During the oxidation of phosphorus and hydration of phosphorus (V) oxide, a large amount of heat is released, which must be removed from the system to maintain the optimal thermal regime of the process. The most common circulation-evaporation schemes, in which the cooling of gases occurs due to heat exchange with circulating phosphoric acid and as a result of the evaporation of water from it.

Known two-stage method for producing thermal phosphoric acid, described in the book "Electrothermal processes of chemical technology", ed. V.A. Ershova. - L .: Chemistry, 1984. A three-phase electric furnace RKZ-72 F (ore-thermal, round, closed, 72 MB · A, phosphoric) with self-sintering electrodes comes from a furnace bunker, a mixture consisting of phosphate, silicon oxide (quartzite ) and coke, where it is melted and phosphorus is reduced. The gas leaving the furnace, containing 6-10% phosphorus, passes through a gas cutter to an electrostatic precipitator, where dust is extracted from it. The purified gas is sent to the condenser-washers - hot and cold, cooled by the water sprayed in them, which circulates in a closed circuit. Condensed liquid phosphorus is collected in tanks and from there it enters the sump, where phosphorus is separated from the sludge and enters the phosphorus tank. The degree of condensation of phosphorus from the gas reaches 0.995. Gas leaving condensers containing up to 85% vol. carbon monoxide, used as fuel or burned. Slag accumulating in the lower part of the furnace is continuously poured and used in the production of cement and other building materials. From the sump, the molten phosphorus is fed into the combustion tower, where it is sprayed by nozzles in a stream of air. Circulating phosphoric acid, pre-cooled in the refrigerator, is fed into the cooling tower, part of it in the form of 73% phosphoric acid is discharged as production acid and is delivered to the warehouse. For replenishment, the required amount of water is introduced into the system. At a temperature of 100 ° C, gas from the combustion tower enters the hydration-cooling tower irrigated with phosphoric acid, where the hydration process ends. Due to irrigation, the temperature of phosphoric acid at the outlet is reduced to 40-45 ° C. The acid circulating in the hydration tower is cooled in the refrigerator. Gas is sent from the hydration tower to the electrostatic precipitator, the phosphoric acid condensed from it in the mist enters the collector, and the exhaust gases are released into the atmosphere.

Phosphoric acid obtained by the electrothermal method has universal application and is used in the production of mineral fertilizers, feed and industrial phosphates, as well as in the food industry.

Another advantage of the electrothermal method is the possibility of obtaining high-quality phosphoric acid from low-grade phosphate raw materials with a low content of P ₂ O ₅ through various methods of preparing the charge for electric sublimation of phosphorus (agglomeration, pelletizing, briquetting, etc.) and conducting the recovery process itself.

The main disadvantage of this method is the high energy intensity due to the large heat loss in the process of obtaining yellow phosphorus, which was not used, and additional energy was required to cool it before being fed to acid systems.

Recently, in connection with the closure of ore-thermal furnaces for the production of phosphorus in a number of countries (USA, Russia, etc.), one of the main methods for the production of phosphoric acid is the extraction method.

The extraction method is based on the decomposition of phosphate raw materials by acids (mainly sulfuric and to a lesser extent nitric and hydrochloric). The main methods for its preparation are given in the book "Technology of phosphate and complex fertilizers", ed. S.D. Evenchik and A.A. Brodsky, M. Chemistry, 1987), and the improvements to the process of obtaining are protected by many patents of foreign countries and patents of the Russian Federation, for example, sulfuric acid extraction - No. 2102999, 2145571, 2174491, 2356833 and other

Thus, a method for producing extraction phosphoric acid (RF patent No. 2356833) involves the decomposition of phosphate feed in a multi-zone extractor of phosphoric and sulfuric acids in the presence of recirculated pulp to produce calcium sulfate pulp in phosphoric acid, ripening it, cooling the pulp with air in foam mode, and separating the product from the precipitation of calcium sulfate by filtration, washing the precipitate in countercurrent mode with water to obtain reverse phosphoric acid and returning it to the decomposition stage. The pulp obtained at the decomposition stage, taken in an amount of 30-100% of the recirculated at this stage, is fed for cooling, and the cooling is carried out in the mode of blowing air under the grate with a volumetric ratio of air to pulp in the cooler 2.5-18.0 and irrigation density cooler lattices 800-2800 m ³ / (m ² · h), and the obtained gas-solid-liquid dispersion is discharged into the free volume under the extractor cover. Pulp with a temperature of 89-96 ° C and 80-90 ° C, respectively, is used for cooling, respectively, when the hemihydrate and dihydrate modes of EPA production are implemented. Cooling is carried out at a temperature gradient between the pulp supplied for cooling and the cooled pulp of 1.0-4.5 ° C. The method allows to reduce air consumption and the amount of exhaust gases from the reactor during air cooling of the pulp in the foam mode, as well as to ensure high efficiency of extraction of P ₂ O ₅ from phosphate raw materials.

Methods for producing EPA by extraction with a solution of hydrochloric acid are described in patents of the Russian Federation, for example, No. 2295421, 2300496, 2326814, 2353577, etc.

The essence of the method of processing phosphate ore (RF patent No. 2353577) is that it includes a one-step countercurrent process for the decomposition of phosphate ore, characterized by a P ₂ O ₅ content exceeding 20% by weight, treatment with an aqueous hydrochloric acid solution having an HCl concentration below 10% by weight, with the formation of a treatment solution consisting of an aqueous phase in which calcium phosphate is in dissolved form, and from a solid phase containing impurities; preliminary neutralization of the treatment solution containing calcium phosphate in the solution to a first pH value that is less than the pH value at which a substantial portion of this dissolved calcium phosphate precipitates as calcium monohydrogen phosphate (DCP), with precipitation of impurities; the first separation of the insoluble solid phase and the aqueous phase of the treatment solution; re-neutralizing the aqueous phase obtained during the first separation to a second pH above the indicated first pH with precipitation of DCP; and a second separation of the re-neutralized aqueous medium, which is an aqueous solution of calcium chloride and precipitated DCP. The method allows to optimize the ratio between the yield of dissolved P ₂ O ₅ and the degree of purity of the final product and to ensure an economically viable process,

The main disadvantage of EPC is its limited use, because it has a lot of impurities, a relatively low concentration (49-54% P ₂ O ₅ ), therefore it is used mainly for fertilizers,

In addition, when it is received, a huge amount of phosphogypsum, nepheline and other harmful waste is formed.

To expand its application in the production of feed, technical and food phosphates, EPA must be cleaned of various impurities and increase its concentration.

A known method of purification of extraction phosphoric acid (EPA) from impurities (RF patent No. 2301198). A method for purifying extraction phosphoric acid involves the stepwise extraction of phosphoric acid with tributyl phosphate, aqueous phosphoric acid stripping from the organic phase, which is carried out in a pulsation mode, separation of the aqueous and organic phases after the extraction and stripping stages, returning the regenerated extractant to the extraction step. Step extraction is carried out in two stages. At the first stage, the starting EPA and the extractant containing 5-12% phosphoric acid from the second extraction stage are fed. The process in the first stage is carried out until the extraction of 0.5-0.75 wt.h. H ₃ PO ₄ from the starting acid to the extract, which is sent for re-extraction, and the raffinate obtained at this stage is fed to the second extraction stage, and it is carried out in the presence of sulfuric acid at a mass ratio of H ₃ PO ₄ : H ₂ SO ₄ equal to (1.5-10.5): 1. The technical result consists in increasing the yield of purified acid.

All these operations require the use of additional equipment, energy consumption and worsen the technical and economic indicators of the process of obtaining phosphoric acid.

Of interest, still theoretical, is the problem of producing phosphorus (V) oxide directly from phosphates by thermal dissociation of tricalcium phosphate:

Ca ₃ (PO ₄ ) ₂ = 3CaO + P ₂ O ₅ + H

by analogy with the industrial process of dissociation of calcium carbonate:

CaCO ₃ = CaO + CO ₂ + H, where H = 178 kJ.

However, the practical implementation of this method is limited by the extremely high value of the thermal effect for practical use and is associated with the need to ensure high temperatures and high energy consumption.

It should be recognized that N. N. Postnikov It turned out to be right, predicting that over time, given the development of technology, it is possible to return to a single-stage method for producing thermal phosphoric acid, since it has relative simplicity in hardware design.

According to a single-stage method, the furnace phosphorus-containing gas obtained in an ore-thermal electric furnace was removed through a gas duct from under the furnace vault, it was burned in combustion chambers and afterburned with atmospheric oxygen entering these chambers. In this case, the phosphorus contained in the furnace gas was oxidized to phosphorus pentoxide, and carbon monoxide to carbon dioxide. The resulting gases were cooled using an additional air supply and water. Due to the hydration of pentoxide, phosphoric acid was released from the gases. The heat released as a result of exothermic oxidation of phosphorus and carbon monoxide was not utilized.

However, with the development of a single-stage process for the production of phosphoric acid, its serious shortcomings were revealed, the main drawback being the need for strict synchronization of the operation of the electric furnace and acid systems. Forced shutdown of an electric furnace or one of the units of the acid system led to a shutdown of the entire production.

It is known that in the USA there have been numerous attempts to obtain phosphoric acid from phosphate feed in rotating drums, so this acid is called drum acid. Patents are known, the authors of which were: Laple, Megi, Park, Sayeman and Hard, but all of them were realized only at the stage of pilot installations, but then, for economic reasons, they were abandoned. The main disadvantages of the production of drum phosphoric acid were that the high temperature and partial oxidation of carbon in the solid phase led to the release of fluorine, sodium, potassium and sulfur into the exhaust gases, the formation of deposits at the end of the drum and flues, contamination of production acid and additional sanitary costs post-treatment of acid flue gases.

Known US patent No. 7378070, published May 27, 2008, "Method for producing phosphorus pentoxide", which includes the formation in the drum of a layer of agglomerate with a molar ratio of calcium to silicon (M _to ) less than 1.0 and maintaining a temperature of 1180 ° C in the layer or higher over at least 50% of the length of the layer without exceeding a temperature of 1380 ° C over the entire length of the layer. Less than 10% of the phosphate introduced with the agglomerate remains in the slag, while the product of time by the ratio of the surface of the layer to its volume for the layer heated above 1180 ° C was less than 50 (min · ft ² ) / ft ³ . Hot slag from the drum is removed through the shutter into a rotating cooler and then onto a conveyor belt to a dump.

Hot gases containing production P ₄ O ₁₀ oxide leave the drum at a temperature of 1100 ° C, pass through a cyclone to separate dust and are fed to a spray tower, where they come in contact with recirculating cooled strong phosphoric acid, which absorbs half of the total P ₄ O ₁₀ oxide tower and cools the exhaust gases to ~ 260 ° C. Production phosphoric acid (76% P ₂ O _{5 is} diluted with recirculating water vapor. The remaining phosphoric acid is removed from the gases, for which it is sent from the tower to a pressurized Venturi pipe into which circulating cold weak phosphoric acid is fed as a scrubbing liquid. The tail fan draws gases through the drum and scrubber system After the fan, the gases are treated in a desulfurization scrubber to clean them of acid components before releasing them into the atmosphere.

This invention has reduced carbon burnout, but cannot completely eliminate the disadvantages of the method for producing drum acid, in particular the full utilization of the heat generated during phosphorus reduction. In addition, it can be carried out while strictly maintaining the thickness and temperature of the sinter layer or pellets along the entire length of the drum, and the carbon consumption increases by 30%.

The closest technical solution to the claimed method is a method for producing phosphoric acid, implemented at the factory of the company TVA in Wilson Dam (USA). A charge consisting of crushed phosphorite, coke and quartzite in a ratio of 100: 16.2: 36 was loaded into a three-phase electric furnace with a capacity of 6 MVA with a triangular arrangement of electrodes. Gases from the furnace, after cleaning from dust, entered the combustion chamber. The air needed to burn the gases was supplied to the chamber by a blower. An additional amount of cold air, supplied by a second blower, was mixed with the gases leaving the combustion chamber. Along the walls of the combustion chamber were suspended metal pipes through which cooling water flowed. A significant part of the heat of combustion of gases was transferred to water. Hot water flowing from the combustion chamber entered the collector, from where it was pumped into the spray tower. Chilled water was again supplied to the pipes of the combustion chamber. To replenish the evaporated water, fresh water was introduced into the system. Thus, significant cooling of the gases was achieved. Gases entered the hydration tower at a temperature of 480 ° C, were cooled here to 150 ° C in contact with sprayed water, and sent to an electrostatic precipitator. From here, the gases were aspirated into the scrubber for washing and then removed through the chimney from the system. Acid from the hydration tower and the electrostatic precipitator drained into the collection tank and then pumped into the storage (NN Postnikov “Thermal Phosphoric Acid”, Khimiya Publishing House M., 1970, p. 241-243).

The described scheme is characterized by a number of unjustified difficulties and does not provide useful heat recovery, because it was transmitted to water, which again cooled. The increased additional air supply supplied by the additional blower led to an increase in the volume of gases and an increase in the size of the electrostatic precipitator.

The technical task of the invention is to improve the one-step method for producing thermal phosphoric acid by achieving the use of heat from the reaction gases in the process of restoring phosphorus and the heat released during their combustion, which will significantly improve the technical and economic indicators of phosphoric acid production.

The technical result is achieved due to the fact that in the well-known one-step process for the production of thermal phosphoric acid, including preliminary heat treatment of phosphorite, quartzite and coke, the preparation of them, in a predetermined ratio, of a charge with an acidity module of 0.76-1.0, loading it into the furnace hopper, followed by feeding through the tubes into the bath of a phosphoric electric furnace, in which self-sintering electrodes are located, monitoring and control of the electric and technological operation of the furnace, the discharge of slag and ferrophosphorus, forming which is stored in the furnace during phosphorus reduction, burning and burning the furnace gas containing phosphorus and carbon monoxide generated in an electric furnace in a stream of air, followed by supplying a gas containing phosphorus pentoxide to hydrate to produce phosphoric acid, cooling it, and cleaning gases in an electrostatic precipitator from acid fog and gas emissions into the atmosphere, changes have been made, namely:

- in the reaction zone of the restoration of phosphorus from the mixture additionally served fines of coke and / or phosphorite;

- air is dosed under the furnace arch for partial burning of the resulting furnace gas and maintaining the optimum temperature under the furnace arch;

- the afterburning of the furnace gas generated during the reduction of phosphorus is carried out in the afterburner, where it enters through the tubes;

- before supplying the gas containing phosphorus pentoxide to the hydration tower, it is cooled to a certain temperature in the recuperator;

- before discharging gas into the atmosphere, it is subjected to sanitary cleaning.

In addition, air is supplied under the furnace arch in such a way that the combustion of furnace gas containing phosphorus and carbon monoxide is not more than 35% vol., Oxygen enriched air is supplied to the afterburner with an excess of oxygen (K = 1.5-2.0), “vacuum is created along the entire technological path from the furnace to the release of gas into the atmosphere. The air heated in the recuperator is sent to a waste heat boiler, where superheated steam is formed, which is used to produce secondary electricity.

Drying of each charge component is carried out in drying drums at a temperature of ~ 500 ° C and up to a humidity of 1%. Separate processing of the components of the charge allows you to sift the fines from the conditional pieces and use it for other purposes, in particular coke and phosphorite can be used to control the temperature under the roof of the furnace and the oxidation of phosphorus and carbon.

The supply of the correcting components of the charge through the tubular electrodes directly to the reaction zone of phosphorus reduction allows a more rapid influence on the oxidation of phosphorus and carbon, ensuring the completeness of the reaction.

The dosed air supply under the arch of the phosphoric furnace allows maintaining the temperature in the subwater space of the furnace within 1300-1700 ° C and partial (up to 35% vol.) Oxidation of the furnace gas containing phosphorus and carbon monoxide.

Maintenance of rarefaction in a phosphoric furnace within minus 5 minus 50 mm of water. Art. allows you to ensure the removal of furnace gases through the mixture in the ducts and their entry into the afterburner.

The afterburning of the furnace gas with oxygen enriched air with its excess (α = 1.5-2.5), allows for the complete oxidation of phosphorus and carbon monoxide.

The creation of rarefaction along the entire path from the phosphorus furnace to the release of gases into the atmosphere ensures the transportation of gases throughout the path.

The cooling of phosphorus pentoxide in the recuperator (up to 600 ° C) allows the use of the heat released for this purpose for useful purposes and the reduction of energy consumption in the production of phosphoric acid.

Sanitary cleaning of gases before releasing them into the atmosphere allows you not to violate the ecology of the environment.

In addition, an increase in temperature under the furnace roof from 1000 to 1300-1700 ° C allowed, due to the counterflow of the furnace gas, to heat the mixture at the outlet of the ducts to 500-600 ° C, and before it enters the furnace top to 800-900 ° C and the furnace gas passing through the charge is cleaned of dust and other impurities.

As a result of the application of these solutions, it is possible to utilize a significant part of the heat obtained in the phosphorus furnace and in the afterburner of the furnace gas, which reduces the energy consumption for sublimating phosphorus by 30–50%.

The composition of the equipment for the production of thermal phosphoric acid by the two-stage method was described above and from it we can conclude that in production, and these are actually three workshops: preparation of the charge, the furnace shop and the workshop for thermal phosphoric acid, the following main equipment is used. In the charge preparation workshop: receivers of each of the components (receiving hoppers), crushers equipped with classifiers, drying drums for heat treatment of the charge with a given acidity module, and a hopper for storing the charge. The furnace shop contains: one or several phosphoric three-phase electric furnaces containing a closed bath with three self-sintering electrodes located at the vertices of a regular triangle, the water-cooled electric holders of which are connected to the corresponding single-phase transformer equipped with a voltage stage selector. The furnace bath is equipped with slots for draining slag and ferrophosphorus, a water cooling system consisting of pipelines with shutoff valves. The batch feed system from the batch preparation shop comprises charge conveyors for loading the bunkers into the furnace bins, which are equipped with estruses for supplying the batch to the furnace bath.

Monitoring the operation of the furnace is carried out by a control system that includes a system for bypassing the electrodes of the furnace, regulating the electrical regime and monitoring process parameters (temperature, P ₂ O ₅ content in slag, etc.). Gas ducts connected to electrostatic precipitators equipped with a system for shaking off the corona and precipitation electrodes, the exits of electrostatic precipitators are connected to condensers of hot and cold condensation, as well as to collectors of phosphorus, sludge and boiler milk equipped with submersible pumps.

The thermal phosphoric acid workshop includes a phosphorus combustion tower, a hydration tower, a cooling tower, an electrostatic precipitator, fans, production acid collectors.

For a one-step method, a furnace electrostatic precipitator, capacitors, a tower for burning elemental phosphorus and some other equipment are not needed.

The closest device that implements a single-stage process for the production of thermal phosphoric acid according to the claimed method is a device for implementing the method, selected as a prototype.

The scheme for the production of thermal phosphoric acid by the single-stage method (Fig. 117, p.242, NN Postnikov “Thermal phosphoric acid”, “Chemistry” Publishing House M., 1970) contains a three-phase electric furnace with a triangular arrangement of self-sintering electrodes in bath furnace, which is equipped with slots for draining slag and ferrophosphorus. The scheme contains (conditionally) furnace bunkers with a mixture containing phosphorite, quartzite and coke mixed in a certain ratio, which are fed through the tubes to the furnace bath, a device for cleaning furnace gases from dust, connected to the combustion chamber of the furnace gas, equipped with water-cooled pipes, a chamber afterburning, cooling-hydration tower, electrostatic precipitator, scrubber, cooling tower, collectors of hot and flushing water, production acid, pumps and fans.

It should be noted that in this diagram there is no equipment of the batch preparation shop, but it is similar to the previously described in the two-stage process. In addition, the diagram does not include furnace transformers and other electrical elements, does not mention the bypass and control systems of the electric mode, without which it is impossible to realize the operation of a phosphoric electric furnace, but they are in principle traditional and do not differ from the one-stage or two-stage method for producing thermal phosphoric acid is being implemented.

The main disadvantage of the given technological scheme is that it cannot provide sufficient utilization of the heat of exothermic reactions occurring in the phosphorus furnace and combustion chambers, despite the fact that there is an attempt to utilize it, but, as it is implemented, it only led to a complication and increase in the quantity equipment, which significantly reduces the technical and economic indicators of the production of thermal phosphoric acid.

In order to eliminate these shortcomings in a known device containing receiving hoppers of phosphorite, quartzite and coke, crushers, drying drums, conveyors for mixing the components of the charge and feeding it into the furnace hoppers, which are connected via a feed chute to the bathtub of a closed three-phase electric furnace with a triangular arrangement in self-sintering electrodes equipped with slots for draining slag and ferrophosphorus, a furnace gas afterburner, one of the inputs of which is connected to an air supply device into it, and the outlet with an inlet audio-cooling hydration coupled to the collector productional phosphoric acid and electrostatic precipitator, the outputs of which are connected to the collector of phosphoric acid and a fan, changes in both the composition of equipment, and the design of the individual elements necessary to implement the claimed method, namely:

- to obtain the correcting components introduced, after rotating the drums, a coke grinder and screening of fines of phosphorite;

- additionally introduced correction bins of phosphorite and coke connected to the internal cavity of the corresponding self-sintering electrode made of tubular;

- charging chutes are made of two parts, the upper part being connected to the inlet of the afterburner, and the lower part being connected to its outlet and entrances to the furnace bath;

- the phosphoric furnace is equipped with an air input device for the vault of the furnace bath;

- a recuperator is placed between the combustion chamber and the cooling-hydration tower,

one of the outputs of which is connected to a recovery boiler, which is connected to an electric generator;

- an absorber is placed between the electrostatic precipitator and the gas exhaust fan into the atmosphere for sanitary cleaning of the gas.

The invention is a method for producing thermal phosphoric acid and a device for its implementation is illustrated by the following description and drawings, which depict the following:

Figure 1 shows the technological scheme of a one-stage process for the production of thermal phosphoric acid.

Figure 2 shows a part of a device that implements the proposed method, in terms of electric sublimation of yellow phosphorus, combustion and afterburning of furnace gas, heat recovery from furnace gas.

Figure 3 shows a part of a device that implements the proposed method, in part related to the production of phosphoric acid from phosphorus pentoxide.

Figure 4 shows the cooling circuit of the electric holders, furnace transformers.

Figure 1 shows the sequence of operations of the proposed method, which are carried out in the respective devices, namely: crushing of each component 1-3; drying each component 4-6; grinding part of coke 7 and feeding into the correction hopper 8; classification of phosphorite 9 and its supply to the adjustment hopper 10; mixing the components of the charge (phosphorite, quartzite and coke) in a predetermined ratio on the conveyor 11, feeding it into the furnace bunker 12; afterburning furnace gas 13, through which the mixture enters the bath of the phosphor furnace 14; a recuperator 15 for air cooling of the furnace gas containing phosphorus pentoxide; phosphoric acid hydration and cooling tower 16; a collection of 17 production acids; an electrostatic precipitator 18 for purifying gases from phosphoric acid mist; a high-pressure fan 19 for discharging purified gas into the atmosphere; a waste heat boiler 20 for utilizing the heat of the air heated in the recuperator and using the resulting superheated steam to produce secondary electricity.

Figure 2 shows: conveyors 11 for feeding the mixture into furnace bins 12; adjustment bunkers of coke 8 and phosphorite 10; charging chutes 21 connected to the afterburners 13 and charging chutes 22 for supplying the charge to the electric furnace bath 25 lined with blocks 26. Electric current is supplied to the electric furnace 14 from the furnace transformers 24 via self-sintering tubular electrodes 23. The furnace bath is provided through corresponding channels with a shaft discharge 28 and receivers of molten ferrophosphorus 29 and molten slag 30. Air is supplied under the furnace arch and into the afterburner via pipelines 31 and 32. Correction coke and / or phosphorite is fed into the tubular electrode I am a device 33. In addition, figure 2 shows a recuperator 15, a waste heat boiler 20, and an electric generator 49.

Figure 3 shows: a gas duct 35, 36 from recuperators 15 to a hydration tower 37 connected to a phosphoric acid collector 38 having a submersible pump 39, a cooling tower 40, an electrostatic precipitator 41 for purifying gas from a phosphoric acid mist, a gas duct 42 connected to an adsorber 43 gas purification connected to the pulp collector 44 and high-pressure fan 45 for the release of purified gas into the atmosphere. Figure 3 also shows the heat exchangers 50 of circulating water (labels), which in the process of obtaining phosphoric acid are auxiliary equipment.

Figure 4 shows a part of a furnace cooling installation, in particular cooling of electric holders, comprising heat exchangers 46, a water softening tank 47, pumps 48 and associated pipelines. The equipment for cooling the furnace bath, the let of the furnace lid includes similar equipment (not shown in Fig. 4).

The principle of the implementation of a single-stage method for producing thermal phosphoric acid was discussed above. Consider some of its features on the example of work on the proposed embodiment of the proposed method for producing thermal phosphoric acid.

The starting raw materials for the production of thermal phosphoric acid are: phosphate, siliceous materials and metallurgical coke, which respectively should contain at least 18% P ₂ O ₅ , 90% SiO ₂ , 85% C.

In the batch compartment, preparations are made for the batching of materials and the preparation of a batch intended for feeding into a phosphorus furnace. The bulk material coming from the bunkers is crushed if necessary (pos. 1-3). The requirements for particle size distribution are determined depending on the component of the charge, so for phosphorite and siliceous raw materials - 10-70 mm, and for coke - 5-25 mm. The raw material enters the drying drums (pos. 4-6) for heat treatment. The charge components are dried at 500 ° C to a moisture content of 1%. After drying, the components previously screened from the fine fractions are fed to the preparation of the mixture (item 11).

In the start-up period, at low capacities of the electric furnace, the mixture is prepared in the calculated ratio of phosphorite and quartzite based on the acidity modulus of 0.76 1.0, and coke to ensure recovery reactions, basic and secondary. This ratio is the same as in the prototype, i.e. phosphorite: coke: quartzite = 100: 16.2: 36, and in terms of the charge - 66: 10.5: 23.5. The acidity modulus is M _k = SiO ₂ + Al ₂ O ₃ / CaO + MgO = 0.80.

Under steady state conditions at optimal electric furnace capacities, the coke content in the charge decreases and can be from 80% to 0% of the calculated one, the rest of the coke is fed through a system of tubular electrodes (pos. 8, 10, 33), which prevents coke burning in the oxidizing medium under the roof ovens.

To ensure good gas permeability of the mixture passing through the electric furnace, it is prepared with the following particle size distribution - phosphate feedstock - 10-70 mm, quartzite - 10-70 mm, coke - 5-25 mm.

Coke entering the system of tubular electrodes (pos. 8, 33) is crushed to a class of 0-5 mm (pos. 7). Corrective phosphorite entering the system of tubular electrodes (pos. 10, 33) of a class of 0-10 mm is a screening when classifying phosphorite when composing a charge (pos. 11).

The main charge through the conveyor 11 is loaded into the furnace hoppers 12, of which through the charging chutes 21 through the afterburning chamber 13 and then the charging chutes 22 enter the phosphor furnace 14. The phosphor furnace is a round steel bath, the bottom and lower part of which are lined with coal blocks 26, and the upper part of the side walls with chamotte brick 25. The furnace is equipped with three tubular self-sintering electrodes 23. The furnace is supplied with electric energy from three single-phase transformers 24 equipped with stage switches voltage. The current from the transformers via a short network is supplied to the self-sintering electrodes. The furnace bath is closed by a reinforced concrete arch and a steel lid with holes for electrodes and charge loading. The furnace has a tap hole for discharging ferrophosphorus into the shaft 28 and further into the pit 29 and tap holes for discharging slag 30, which is fed to crushed stone (not shown). The phosphor furnace has autonomous water cooling systems. The parts of the electric holders, a short network, a metal furnace body, a furnace lid and slag doors are cooled by water. Cooling systems, as a rule, include the following equipment (see Fig. 4): heat exchangers 46, softened water tanks 47, pumps 48 and pipelines equipped with the necessary shutoff valves (valves, valves, etc.). Water circulates in a closed cycle with heat exchangers, where it is cooled from 40 to 35 ° C.

To utilize the physical and potential heat of the furnace gas, air 31 is supplied under the bath for partial combustion of the furnace gases, and oxygen enriched air 32 is supplied to the afterburner to completely burn the residual phosphorus and carbon monoxide. The mixture is heated in estrus 22 to a temperature of 500-700 ° C due to contact with the furnace gas coming from the underwater space, having a temperature in the range 1300-1700 ° C, enters the underwater space, where it also additionally heats the furnace gas in the charge cones before entering the furnace top. The temperature of the charge entering the furnace top (the surface of the charge forming the lower boundary of the underwater space) is 800-900 ° C. The mixture, moving in the furnace bath from the top to the lower layers, warms up due to the physical heat of the reaction gases (furnace gas) and the heat released during the conversion of electrical energy into heat. With increasing temperature, solid-phase reactions between the formed CaO and SiO _{2 take place} . The area of solid-phase processes can be distinguished into an independent zone (zone 1). Its lower level is determined by the beginning of the melting of the mineral part of the charge. In the melting zone 2, a liquid phase forms and interacts with solid quartzite. The result is a phosphate-silicon melt, which flows into the lower zones of the furnace. Coke, having a lower density, floats in the resulting liquid phase. In addition, with the lowering charge new portions of coke come in, it accumulates, and a third - carbon zone forms. Coke entering the melt from the system of tubular electrodes also floats into the third carbon zone. Zones 1 and 2 are preparatory, necessary for the main reaction - reduction of phosphate, which occurs in the carbon zone. The size of the carbon zone and the conditions existing in it determine the operating mode of the furnace as a whole. In zone 3, the conductivity reaches its maximum value, since it has a high coke content and the contact between its particles is provided by the conductive melt. Through the carbon zone, contact is made between the electrodes and the hearth of the furnace, so the ends of the electrodes should be at or in this zone. The electric power of the furnace, the temperature of the exhaust gases, and the thermal and electric efficiency of the furnace depend on the position of the ends of the electrodes.

The phosphorus reduction reaction in this zone is described by the equation:

2Ca ₅ (PO ₄ ) ₃ F ₂ + 15C + (x + y) SiO ₂ -3P ₂ + 15CO + (9 + 2y) CaO · xSiO ₂ + ySiF ₄ + (1-2y) CaF

2Ca ₃ P ₂ O ₈ → 6CaO + P ₄ O ₁₀

In this case, the effect of SiO ₂ on the reduction process consists in the binding of CaO and thereby enhancing the thermal dissociation of Ca ₃ P ₂ O ₈ . It follows from this that ensuring the normal operation of the carbon zone is decisive from the point of view of the technological thermal, electrical regime of the furnace. The specified electric power of the furnace is supported by the electric mode controller, in particular, for example, the most famous is the FosKar automatic control system, which is protected by a whole range of inventions, including RF patent No. 2081818 "Method for controlling the process of producing phosphorus in an electrothermal furnace", and it is ensured and control over such technological parameters as the position of the electrode (electrode distance - under), the temperature of the exhaust gases, the content of P ₂ O ₅ , etc., by maintaining as an electrode and / or by switching the voltage levels of the transformer. Additional adjustment can also be carried out by feeding fine coke and corrective phosphorite through a system of tubular electrodes. As the self-sintering electrodes are burned, they are bypassed. The bypass per shift is 8-12 cm, depending on the working capacity of the electric furnace. The kiln gas formed during reduction, containing phosphorus of 6-8% and CO 80-85%, passes through the layers of the charge and enters the underwater space. At the same time, air is metered into the subswater space through a pipe 31 in such a quantity that up to 35% of the furnace gas is burned in the subswater space of the electric furnace. In this case, the temperature of the furnace gas increases from 1000 ° C (physical heat) to 1500-1700 ° C due to the partial combustion of phosphorus and carbon monoxide. This gas from the underwater space due to the vacuum created by the fans 45, is sucked through the heat, through which the main charge is constantly loaded into the furnace. During the operation of the furnace, the composition of the main charge can be adjusted, because the use of tube self-sintering electrodes allows a portion of coke or phosphorite to be added directly to the phosphate reduction zone, thereby controlling the completeness of reduction and the temperature under the furnace arch, as well as the size of the carbon zone. This is carried out according to the results of the operation of control devices for the content of P ₂ O ₅ in the slag, acidity modulus (M _k ) as follows. Coke on the conveyor 33 from the correction hoppers 8 is loaded into the internal cavity of the electrode. The supply of phosphorite is carried out similarly from the bins 10.

The furnace gas, passing through the charge, heats it to 500-900 ° C, thereby reducing the time of its complete melting. In the direction of the furnace gas through the charge to the afterburner 13, it gives its heat to it, while being cleared of some impurities, and at the inlet to the chamber its temperature is 300-600 ° C. The supply of oxygen-enriched air to the afterburner with an excess of α = 1.5-2.5 is due to the fact that P ₄ and CO are completely burned, and the temperature at the outlet of the afterburner is maintained at least 1200 ° C. In the afterburner, vacuum is maintained. To ensure the normal process of obtaining thermal acid, it is provided that in the event of clogging of the loading leaks or a decrease in the amount entering the afterburner of the furnace gas (judged by the increase in pressure in the furnace), the furnace gas enters the afterburner, bypassing the tubes, through the duct 34, in which a gate is installed that is closed during normal flow of furnace gas through estrus.

The flue gas from the afterburner enters the ceramic recuperator 15, where it is cooled to a temperature of not more than 700 ° C, giving off heat to the air, which is heated to a temperature of more than 600 ° C. Heated air enters from the recuperator 15 into the waste heat boiler and is then used to generate electricity by means of an electric generator 49.

The cooled phosphorus pentoxide enters the cooling-hydration tower 37, where it is in contact with water and phosphoric acid is formed, which enters the collector 38 with a submersible pump 39 and then to the warehouse. In the cooling tower 40, the pentoxide contacts the circulating phosphoric acid and 73% phosphoric acid is obtained, which also enters a collection similar to the previous one. Due to irrigation, the temperature of phosphoric acid at the outlet is reduced to 40-45 ° C. From the cooling tower 40, gas is sent to an electrostatic precipitator 41, from where phosphoric acid condensed from it from the mist enters the collector, and the offgases through the duct 42 are sent to the absorber 48 for purification and then released into the atmosphere.

The specific indicators of the process for producing thermal phosphoric acid will depend on the quality of heat treatment of the mixture, its type (piece or agglomerates) and other factors.

The proposed method for the production of thermal phosphoric acid eliminates the disadvantages inherent in both single-stage and two-stage methods for the production of thermal phosphoric acid, because when it is implemented, it maximizes the use of physical and potential heat obtained from the combustion of furnace gas.

All this allows you to get phosphoric acid, the cost of which is comparable to purified extraction acid, but without the use of high-quality phosphate raw materials, such as apatite.

Currently, a working draft of the production of the proposed method is being completed, and its implementation is possible using well-known equipment in 2011-12.

Claims (4)

1. A method of producing thermal phosphoric acid, including preliminary heat treatment of phosphorite, quartzite and coke, preparation of a charge with an acid modulus of 0.76-1.0 at a given ratio of components, and loading it into furnace bunkers, followed by feeding a phosphor furnace through tubules in which self-sintering electrodes are located, monitoring and control of the electric and technological operating conditions of the furnace, discharge of slag and ferrophosphorus, burning and afterburning of the furnace gas formed during the recovery process containing phosphorus and carbon monoxide in a stream of air, followed by feeding the obtained phosphorus pentoxide to hydrate to produce phosphoric acid, cooling it, purifying the gas in the electrostatic precipitator from an acid mist and emitting gases into the atmosphere, characterized in that it controls the completeness of phosphorus reduction from the charge is carried out by supplying fines of coke and / or phosphorite to the reaction zone through the internal cavity of self-sintering tubular electrodes, partial combustion of the furnace gas is carried out under the arch of the furnace by feeding air, then the remaining furnace gas is fed for afterburning through the loading tubes by creating an optimal vacuum in the gas path, it is pre-cooled before being fed phosphorus pentoxide for hydration, and the gases are sanitized before being released to the atmosphere. 2. The method according to claim 1, characterized in that the temperature in the underwater space of the furnace is maintained within 1300-1700 ° C due to the dosed air supply in an amount sufficient to burn at least 35% of the produced furnace gas. 3. The method according to claim 1, characterized in that the afterburning of the furnace gas is carried out in excess of air enriched with oxygen at α = 1.5-2.5. 4. The device for implementing the method according to claim 1, containing receiving bins of phosphorite, quartzite and coke, crushers, drying drums for their heat treatment, conveyors for mixing the components of the charge and feeding it into the furnace bunkers, which are connected through a loading tube to a closed three-phase electric bathtub phosphor furnace with self-sintering electrodes located in it, as well as equipped with slots for draining slag and ferrophosphorus, control devices and a control system for electric and technological mode, an afterburner gas, the inlets of which are connected to an air supply device and an electric furnace gas duct, and the outlet is connected to a cooling-hydration tower connected to a production phosphoric acid collector and an electrostatic precipitator, the outputs of which are connected to a phosphoric acid collector and a fan, characterized in that it is additionally introduced coke shredder, coke adjustment bins and phosphorite fines, mechanisms for feeding them into the internal cavity of tubular self-sintering electrodes, the furnace bath is equipped with a device for introducing air ha under the furnace arch, loading tubes are made integral, with their upper part in the direction of the charge being connected to the entrances of the afterburner, and the lower part to the exits of the afterburner, a recuperator for cooling phosphorus pentoxide is introduced between the afterburner and the hydration tower, one of the exits it is connected to a recovery boiler, and between the electrostatic precipitator and high-pressure fan there is an absorber for sanitary gas treatment.

Images