Preparation method of phosphoric acid

Abstract

The invention discloses a preparation method of phosphoric acid. The preparation method comprises the following steps: grinding and drying phosphorite and silica, and separating to obtain tail gas and materials; preheating step by step by a four-stage preheater, removing free water in the material, and feeding the material into a melting furnace; heating and melting the material into a molten material through a melting furnace heater in the melting furnace; the molten material automatically flows into a reduction area of the liquid-solid phase reaction tank through a channel at the bottom of the melting furnace, and phosphorus steam and CO gas are generated; the phosphorus steam and the CO gas escape from a molten liquid interface layer and enter a carbon solid carbon particle layer above a reduction zone of the liquid-solid reaction tank and an oxidation zone to generate phosphoric anhydride steam and CO2 gas, and the phosphoric anhydride steam is cooled and absorbed by a phosphoric acid hydration tower to prepare phosphoric acid. The invention has the advantages that: the reduction reaction of the molten material is carried out at the lower part of the reduction area of the liquid-solid reaction tank; the oxidation reaction of phosphorus steam and CO is carried out in the oxidation zone above the reduction zone of the liquid-solid reaction tank, the combustion reaction of carbon particles can be controlled by controlling the oxygen adding amount, additional heat can be provided for the reaction, and the reduction rate of phosphate ore and the thermal efficiency of a production system are improved.

Description

Technical Field

[0001] The invention relates to the technical field of thermal phosphoric acid production in phosphorus chemical industry, and in particular to a method for preparing phosphoric acid. Background Art

[0002] Phosphorus pentoxide is the anhydride of phosphoric acid, and its hydrate phosphoric acid is an important intermediate in the phosphorus chemical industry. There are currently two mature industrialized methods for producing phosphoric acid in the world: one is to decompose phosphate ore with sulfuric acid to obtain wet-process phosphoric acid; the other is to reduce phosphate ore, silica, and coke into yellow phosphorus in an electric furnace, and then oxidize the yellow phosphorus into phosphorus pentoxide in another set of equipment and hydrate it to obtain thermal phosphoric acid. Kiln-process phosphoric acid is to mix phosphate ore, silica, and coke in a certain proportion, granulate or shape them and wrap them, and send them into a rotary kiln or tunnel kiln for solid-state reduction and oxidation reaction to produce a combustible mixed gas of phosphorus vapor and CO. The mixed gas directly undergoes oxidation reaction with air to generate phosphoric anhydride and carbon dioxide gas and release a large amount of heat. The reaction heat is provided to the mixed material for reduction reaction, and the phosphoric anhydride gas produced by oxidation is hydrated to produce phosphoric acid. Due to the high technical difficulty, this method has only built a small-scale industrial test device and has not been effectively promoted and applied in industry.

[0003] Wet phosphoric acid consumes a large amount of sulfuric acid and can only use medium- and high-grade phosphate ore. It also produces a large amount of phosphogypsum as a by-product. Because it is acidic, the disposal cost is high. my country lacks sulfur resources, and medium- and high-grade phosphate ore accounts for a small proportion. Thermal phosphoric acid consumes a lot of electricity. It takes 14,000 kwh to produce one ton of yellow phosphorus. Most companies do not use the generated CO. In addition, the phosphoric acid production and yellow phosphorus equipment are separated, and the heat released by the phosphorus oxidation reaction is not well utilized and wasted. Kiln-process phosphoric acid can effectively utilize the heat released by CO and phosphorus oxidation reactions. Industrial tests have shown that the cost of granulation or molding packaging is high. The ring formation of the rotary kiln caused by various factors is difficult to solve, and it cannot be continuously and stably operated for a long period of time. The tunnel kiln car has a short life and high cost, the material block is large in size, and the heat transfer efficiency is low. There is no industrial application device for kiln-process phosphoric acid that can be continuously operated so far.

[0004] The smelting reduction method is a method of using carbon and other reducing agents to carry out a reduction reaction with metal oxides in a molten state. Smelting reduction technology is mainly used in the field of ironmaking. With the widespread development of smelting reduction ironmaking technology, people's understanding of smelting phosphorus smelting technology has also improved. The Institute of Chemical Metallurgy of the Chinese Academy of Sciences conducted exploratory experimental research on the smelting reduction of coal powder and phosphate rock powder in the early 1980s, and proposed the idea of ​​smelting reduction phosphorus smelting in a reverberatory furnace. Its invention patent for the process of preparing phosphoric acid by smelting reduction heat (ZL97100773.X) has been authorized. This patent has the process of stopping coal, stopping materials and switching to nitrogen injection, and the operation and control are complicated.

[0005] A method for producing phosphorus pentoxide by melting phosphate ore (ZL200710050248.9) is an improvement on ZL97100773.X. It requires adding two types of materials, carbon-free and carbon-containing, to the reactor. Since cold materials are added, the reaction temperature varies greatly, production cannot be carried out continuously and stably, and operation control is also very complicated. The temperature range of the molten material reduction reaction in the reactor is 1200℃-1900℃. When the temperature of the molten material is greater than 1500℃, side reactions such as the generation of SiC and SiO will occur, consuming silicon and carbon raw materials and increasing production costs.

[0006] In both methods, the reduction reaction zone and the oxidation reaction zone are isolated by gas phase, and the isolation reliability is poor, and the reduction rate of phosphate ore is difficult to guarantee.

[0007] The melting kiln phosphoric acid production process (202210053138.2) intends to use high-magnesium phosphate ore and add potassium feldspar to achieve low melting point batching, so as to control the slag temperature flowing out of the kiln to 1200℃~1400℃, and the temperature of the P2O5 and C02 mixed gas discharged from the kiln to 1200℃~1400℃. And use the appropriate amount of excess carbon layer at the interface of the molten flow reduction layer to isolate the reduction zone from the oxidation zone to avoid the problem of low phosphorus yield and serious carbon loss caused by phosphorus reversion. However, the amount of excess carbon is difficult to control, the thickness of the excess carbon layer is difficult to ensure, and the isolation effect cannot be guaranteed. As a result, the phosphorus yield of phosphoric acid in its embodiment is only 84.8%, and a large amount of phosphorus is still present in the slag. The slag can only be used as phosphorus-containing silicon, calcium, potassium and magnesium fertilizer, and its output is three times that of phosphoric acid. In order to ensure the temperature of the kiln, it is also necessary to mix the supplementary fuel with the preheated excess oxygen-containing air and burn it to obtain flue gas containing excess oxygen, and the flue gas enters the kiln from the upper part of the kiln. The phosphate rock used must also be high-magnesium phosphate rock, which will decompose more CO2 and cause higher kiln energy consumption.

[0008] In the above methods, material heating, reduction and oxidation reactions are all carried out in the same furnace. The organic matter, calcium carbonate and magnesium carbonate in the raw materials cannot be removed in advance, and the moisture cannot be completely removed, which will inevitably increase the energy consumption of the reactor and affect the product quality. The reactor is mainly based on radiation heat transfer. The gas phase temperature of the reactor is high, the gas phase space volume is large, the requirements for the furnace lining material are high, and the masonry cost is high. In the melting kiln phosphoric acid production process, in order to reduce the amount of KPO3 generated by the volatilization of K2O in potassium feldspar, the reduction reaction temperature is controlled at a low level, the slag temperature is 1200-1400℃, the flow rate is slow, the required reaction time is long, and the production capacity is limited. In order to solve the problems of long reaction time of the mixture, insufficient reaction, and poor isolation effect of the appropriate excess carbon layer, the same inventor made improvements in a phosphoric acid production process (202410729794.9), set up a stirring mechanism in the reactor, and set up a heat exchange plate to separate the reduction zone and the oxidation zone. However, since the reaction temperature is above 1250°C, the material requirements for the stirring mechanism and the heat exchange plate are relatively high, and it is more difficult to select the heat exchange plate with both heat conduction and heat transfer functions, and the equipment manufacturing cost is high. The outlet gas temperature is also very high, and no subsequent utilization device is set up, and there is still much room for improvement in thermal efficiency. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a method for preparing phosphoric acid.

[0010] In order to solve the above technical problems, the technical solution of the present invention is:

[0011] A method for preparing phosphoric acid comprises the following steps:

[0012] S1: Phosphate rock and silica are added to a roller press through a feed port and crushed, and then sent to a drying mill for grinding and drying, and then separated into tail gas and material through a first preheater;

[0013] S2: The material is preheated step by step in the four-stage preheater and free water in the material is removed before entering the melting furnace;

[0014] S3: Add fuel to the melting furnace through the melting furnace heater or use electrodes to heat the material into a molten material, and at the same time heat the organic matter in the molten material to burn out and make the mass fraction of the molten material 3%. ～ 5% of carbonates completely decompose to release CO2;

[0015] S4: The molten material flows by gravity into the reduction zone of the liquid-solid phase reaction tank through the bottom channel of the melting furnace, and undergoes a reduction reaction with the carbon solid particles in the reduction zone of the liquid-solid phase reaction tank to generate phosphorus vapor and CO gas;

[0016] S5: Phosphorus vapor and CO gas escape from the molten liquid interface layer and enter the carbon solid carbon particle layer and oxidation zone above the reduction zone of the liquid-solid phase reaction tank, and dry hot air and / or oxygen are added through the oxygenation pipe to make the phosphorus vapor and CO undergo oxidation reaction to generate phosphoric anhydride vapor and CO2 gas, and the released heat is transferred to the carbon solid particles. The temperature of the reduction zone of the liquid-solid phase reaction tank is ensured to be 1400°C to 1500°C by controlling the amount of dry hot air and / or oxygen introduced;

[0017] S6: The phosphoanhydride vapor and CO2 gas are collected through the gas collection pipeline and enter the boiler to exchange heat with soft water for cooling, and then enter the heat exchanger to exchange heat with dry air or / and oxygen for indirect heat recovery, and then the hot air or / and oxygen are transported to the oxidation zone through the oxygenation pipe;

[0018] S7: Phosphoric anhydride vapor is cooled and absorbed in a phosphoric acid hydration tower to produce phosphoric acid.

[0019] Preferably, the tail gas obtained in step S1 is discharged into a purification device for treatment via a tail gas blower.

[0020] Preferably, the fuel used by the melting furnace heater 4 in step S2 is composed of one or more of pulverized coal, natural gas, CO and heavy oil.

[0021] Preferably, the drying mill is a vertical mill, a Raymond mill or a ball mill.

[0022] Preferably, a slag tank for recovering phosphorus and carbon in the molten liquid slag that has reacted with the carbon solid particles is provided at the tail of the reduction zone of the liquid-solid phase reaction tank.

[0023] Preferably, the gas discharged from the phosphoric acid hydration tower in step S7 is sent to the outlet of the four-stage preheater through a scrubber and an induced draft fan to burn the CO gas and absorb trace amounts of P2O5.

[0024] Preferably, the phosphoric anhydride vapor in step S7 can also be condensed by a phosphoric anhydride condenser and collected by a high-temperature bag filter to obtain phosphoric anhydride. The gas discharged from the high-temperature bag filter is sent to the outlet of the four-stage preheater by an induced draft fan to burn CO gas and absorb trace amounts of P2O5.

[0025] Preferably, the phosphoric acid can be produced by cooling and absorbing the gas discharged from the high-temperature bag filter through the phosphoric acid hydration tower, and the gas discharged from the phosphoric acid hydration tower is sent to the outlet of the fourth-stage preheater by the induced draft fan through the scrubber to burn the CO gas and absorb trace amounts of P2O5.

[0026] Preferably, the temperature of the reduction zone of the liquid-solid phase reaction tank is 1430°C to 1480°C.

[0027] Beneficial effects of the present invention:

[0028] The raw material heating and melting process and the molten material liquid reduction reaction of the present invention are respectively carried out in different reactors; the raw material is preheated and melted by a mature and reliable cyclone preheater; the reduction reaction is carried out in the reduction zone at the lower part of the liquid-solid phase reaction tank; the phosphorus vapor and CO oxidation reaction are carried out in the carbon solid carbon particle layer and the oxidation zone above the reduction zone of the liquid-solid phase reaction tank, and the combustion reaction of the carbon particles can be controlled by controlling the amount of oxygen added, which can provide additional heat for the reaction; the reaction heat is directly transferred to the carbon solid particles, and the carbon solid particle layer is used to isolate the reduction reaction zone from the oxidation reaction zone, thereby preventing the occurrence of phosphoric anhydride back-absorption reaction, thereby improving the reduction rate of phosphate ore and the thermal efficiency of the production system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the process flow of the first embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the process flow of the second embodiment of the present invention;

[0031] Figure 3 Schematic diagram of the process flow of the third embodiment of the present invention.

[0032] In the figure,

[0033] 1- tail gas fan, 2- roller press, 3- drying mill, 4- melting furnace heater, 5- melting furnace, 6- carbon solid particle feeding pipe, 7- gas collection pipeline, 8- carbon solid carbon particle layer and oxidation zone, 10- liquid-solid phase reaction tank reduction zone, 11- ferrophosphorus discharge port, 12- oxygenation pipe, 13- boiler, 14- heat exchanger, 15- phosphorus anhydride condenser, 16- high temperature bag dust collector, 17- induced draft fan, 18- phosphoric acid hydration tower, 19- four-stage preheater, 20- scrubber, 21- first preheater. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Reference Figure 1 As shown, a method for preparing phosphoric acid comprises the following steps:

[0036] S1: Phosphate rock and silica are added to the roller press 2 through the feed port, crushed, and then sent to the drying mill 3 for grinding and drying, and then separated into tail gas and material in the first preheater 21;

[0037] S2: The material is preheated step by step in the four-stage preheater 19 and free water in the material is removed before entering the melting furnace 5;

[0038] S3: In the melting furnace 5, fuel is added through the melting furnace heater 4 or electrodes are used to heat the material to melt it into a molten material, and at the same time, the organic matter in the molten material is burned by heating, and the carbonate with a mass fraction of 3% to 5% in the molten material is completely decomposed to release CO2;

[0039] S4: The molten material flows by gravity through the bottom channel of the melting furnace 5 into the liquid-solid phase reaction tank reduction zone 10, and undergoes a reduction reaction with the carbon solid particles in the liquid-solid phase reaction tank reduction zone 10 to generate phosphorus vapor and CO gas;

[0040] S5: Phosphorus vapor and CO gas escape from the molten liquid interface layer and enter the carbon solid carbon particle layer and oxidation zone 8 above the liquid-solid phase reaction tank reduction zone 10, and add dry hot air and / or oxygen through the oxygenation pipe 12 to make the phosphorus vapor and CO undergo oxidation reaction to generate phosphoric anhydride vapor and CO2 gas, and transfer the released heat to the carbon solid particles. The temperature of the liquid-solid phase reaction tank reduction zone 10 is ensured to be 1400℃~1500℃ by controlling the amount of dry hot air and / or oxygen introduced;

[0041] S6: The phosphoric anhydride vapor and CO2 gas are collected through the gas collection pipe 7 and enter the boiler 13 for heat exchange with soft water to reduce the temperature, and then enter the heat exchanger 14 for indirect heat exchange with dry air or / and oxygen to recover heat, and then the hot air or / and oxygen enter the oxygenation pipe 12;

[0042] S7: The phosphoric anhydride vapor is cooled and absorbed in a phosphoric acid hydration tower 18 to produce phosphoric acid.

[0043] It should be noted that the mixed powder of phosphate rock and silica is first melted into liquid before being mixed with solid carbon particles for reaction. Solid carbon particles are not only reaction raw materials, but also heat carriers and heat supply bodies, and also physical isolation entities between the reduction zone and the oxidation zone of the chemical reaction. Phosphorus vapor and CO gas escaping from the molten liquid interface pass through a solid carbon particle layer of a certain thickness to form a reducing atmosphere isolation zone, so that the reduction reaction and oxidation reaction can proceed smoothly in different areas. The oxidation reaction can be carried out in the solid carbon particle layer or in the gas phase space without a solid carbon particle layer. The solid carbon particle layer uses coke, anthracite, blue carbon, graphite or a mixture thereof. The carbon particles are not only reducing agents, but also have the functions of heat supplement fuel, heat carrier, and isolation entity between the reduction zone and the oxidation zone of the chemical reaction.

[0044] The first preheater and the fourth preheater are cyclone preheaters commonly used in cement production. The first preheater and the fourth preheater and the melting furnace 5 can provide molten materials for multiple liquid-solid reaction tanks. The dry air and / or oxygen fed into the melting furnace 5 are preheated dry air and / or oxygen. The liquid-solid phase reaction tank reduction zone 10 is a polygonal reaction tank, and the length is determined according to the reaction time being greater than 45 minutes.

[0045] In order to treat the tail gas, the tail gas obtained in step S1 is discharged into the purification device through the tail gas fan 1 for treatment.

[0046] Specifically, the fuel used by the melting furnace heater (4) in step S2 is composed of one or more of pulverized coal, natural gas, CO and heavy oil.

[0047] Specifically, the drying mill 3 is a vertical mill, a Raymond mill or a ball mill.

[0048] In order to recover phosphorus and excess carbon in the molten liquid slag and discharge the liquid-solid phase reaction tank in layers according to slag and ferrophosphorus, a slag tank 11 for recovering phosphorus and carbon in the molten liquid slag that has reacted with carbon solid particles is provided at the tail of the reduction zone 10 of the liquid-solid phase reaction tank. The slag tank 11 contains only molten material and does not contain coke solid particles. The present application discharges ferrophosphorus through the ferrophosphorus discharge port 11; the carbon solid particle feeding pipe 6 is used to add carbon solid particles. The following reactions occur in the slag tank:

[0049] 2[P]+[C]+6O2=2P2O5+CO2

[0050] FeP+O2=Fe2O3+P2O5

[0051] Reference Figure 1 As shown, in order to burn out the CO gas, the gas discharged from the phosphoric acid hydration tower 18 in step S7 is sent to the outlet of the four-stage preheater 19 by the induced draft fan 17 through the scrubber 20 to burn out the CO gas and absorb trace amounts of P2O5.

[0052] As another embodiment, refer to Figure 2 As shown, the phosphoric anhydride vapor in step S7 can also be condensed by the phosphoric anhydride condenser 15 and collected by the high-temperature bag filter 16 to obtain phosphoric anhydride. The gas discharged from the high-temperature bag filter 16 is sent to the outlet of the four-stage preheater 19 by the induced draft fan 17 to burn the CO gas and absorb trace amounts of P2O5.

[0053] As another embodiment, refer to Figure 3 As shown, the gas discharged from the high-temperature bag filter 16 can also be cooled and absorbed by the phosphoric acid hydration tower 18 to produce phosphoric acid. The gas discharged from the phosphoric acid hydration tower 18 is sent to the outlet of the four-stage preheater 19 by the induced draft fan 17 through the scrubber 20 to burn the CO gas and absorb trace amounts of P2O5.

[0054] The temperature of the reduction zone 10 of the liquid-solid phase reaction tank is 1430°C to 1480°C, preferably 1430°C, 1440°C, 1450°C, 1460°C, 1470°C and 1480°C to ensure that the reduction zone 10 of the liquid-solid phase reaction tank reaches a suitable temperature.

[0055] The powder material can also be melted into a molten material by the electrode. The phosphate ore in the present application can be low-grade phosphate ore or medium-grade phosphate ore.

[0056] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the scope of protection of the present invention.

Claims

1. A method for preparing phosphoric acid, characterized in that: The following steps are involved: S1: Phosphate ore and silica are added to a roller press (2) through a feed port for crushing and then sent to a drying mill (3) for grinding and drying. The tail gas and the material are then separated in a first preheater (21); S2: the material is preheated step by step in the four-stage preheater (19) and free water in the material is removed before entering the melting furnace (5); S3: heating the material in the melting furnace (5) by means of the melting furnace heater (4) or by using electrodes to melt the material into a molten material, and simultaneously heating the material so that organic matter in the molten material is burned out, and carbonates with a mass fraction of 3% to 5% in the molten material are completely decomposed to release CO2; S4: the molten material flows by gravity through the bottom channel of the melting furnace (5) into the liquid-solid phase reaction tank reduction zone (10), undergoes a reduction reaction with the carbon solid particles in the liquid-solid phase reaction tank reduction zone (10), and generates phosphorus vapor and CO gas; S5: Phosphorus vapor and CO gas escape from the molten liquid interface layer and enter the carbon solid carbon particle layer and oxidation zone (8) above the reduction zone (10) of the liquid-solid phase reaction tank, and dry hot air and / or oxygen are added through the oxygenation pipe (12) to cause an oxidation reaction between the phosphorus vapor and CO to generate phosphoric anhydride vapor and CO2 gas, and the released heat is transferred to the carbon solid particles. By controlling the amount of dry hot air and / or oxygen introduced, the temperature of the reduction zone (10) of the liquid-solid phase reaction tank is ensured to be 1400°C to 1500°C. S6: The phosphoric anhydride vapor and CO2 gas are collected through the gas collection pipe (7) and enter the boiler (13) to exchange heat with soft water for cooling, and then enter the heat exchanger (14) to indirectly exchange heat with dry air and / or oxygen to recover heat, and the hot air and / or oxygen enter the oxygenation pipe (12); S7: The phosphoric anhydride vapor is cooled and absorbed in a phosphoric acid hydration tower (18) to produce phosphoric acid.

2. The method for preparing phosphoric acid according to claim 1, characterized in that: The tail gas obtained in step S1 is discharged into a purification device for treatment via a tail gas blower (1).

3. The method for preparing phosphoric acid according to claim 1, characterized in that: The fuel used by the melting furnace heater (4) in step S2 is composed of one or more of pulverized coal, natural gas, CO and heavy oil.

4. The method for preparing phosphoric acid according to claim 1, characterized in that: The drying mill (3) is a vertical mill, a Raymond mill or a ball mill.

5. The method for preparing phosphoric acid according to claim 1, characterized in that: The tail of the liquid-solid phase reaction tank reduction zone (10) is provided with a slag tank (9) for recovering phosphorus and carbon in the molten liquid slag that has completed the reaction with the carbon solid particles.

6. The method for preparing phosphoric acid according to claim 1, characterized in that: In step S7, the gas discharged from the phosphoric acid hydration tower (18) is sent to the outlet of the fourth-stage preheater (19) through the scrubber (20) and the induced draft fan (17) to burn the CO gas and absorb trace amounts of P2O5.

7. The method for preparing phosphoric acid according to claim 1, characterized in that: The phosphoric anhydride vapor in step S7 can also be condensed by a phosphoric anhydride condenser (15) and collected by a high-temperature bag filter (16) to obtain phosphoric anhydride. The gas discharged from the high-temperature bag filter (16) is sent to the outlet of the fourth-stage preheater (19) by an induced draft fan (17) to burn CO gas and absorb trace amounts of P2O5.

8. The method for preparing phosphoric acid according to claim 7, characterized in that: The phosphoric acid hydration tower (18) can also be used to cool and absorb the gas discharged from the high-temperature bag filter (16) to produce phosphoric acid. The gas discharged from the phosphoric acid hydration tower (18) is sent to the outlet of the fourth-stage preheater (19) through the scrubber (20) and the induced draft fan (17) to burn CO gas and absorb trace amounts of P2O5.

9. The method for preparing phosphoric acid according to any one of claims 1 to 8, characterized in that: The temperature of the reduction zone (10) of the liquid-solid phase reaction tank is 1430°C to 1480°C.

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