Self-heating shaft furnace and method for preparing phosphoric acid by using self-heating shaft furnace through kiln method

Abstract

The invention provides a self-heating shaft furnace and a method for preparing phosphoric acid by using the self-heating shaft furnace through a kiln method.The shaft furnace comprises a furnace body and a phosphorus gas pipeline, the furnace body comprises an overflow chamber, a combustion chamber and a reduction chamber, and the method for preparing the phosphoric acid comprises the steps that green pellets with the P2O5 content larger than or equal to 5% and an external reducing agent are mixed and then continuously added into the reduction chamber; during operation from top to bottom, indirect heat exchange is carried out between the flue gas and high-temperature flue gas reversely flowing from bottom to top outside the partition wall, and phosphorus-containing coal gas and residual tailings are formed after carbon thermal reduction reaction; the phosphorus-containing coal gas returns to the combustion chamber for combustion to provide heat for the reaction process; the discharged P2O5-containing flue gas is subjected to heat recovery, washing and condensation to generate phosphoric acid and tail gas; and residual tailings are discharged out of the reduction chamber after being cooled, and the residual reducing agent is recycled. The method not only realizes complete isolation of the reduction zone and the oxidation zone, solves the problem of direct utilization of medium-low-grade phosphorite, but also effectively recycles the heat energy of the phosphorus-containing coal gas, the prepared phosphoric acid is good in quality, and compared with an electric furnace phosphoric acid process, the external heat supply energy consumption can be reduced by 20-50%.

Description

Technical Field

[0001] The invention relates to the technical field of kiln-process phosphoric acid, and in particular to a self-heating vertical furnace and a method for preparing phosphoric acid by a kiln process using the self-heating vertical furnace. Background Art

[0002] With the high-intensity exploitation of phosphate resources, high-grade phosphate resources are becoming increasingly scarce. The full development and utilization of medium and low-grade phosphate resources is of great significance to the sustainable development of the phosphorus chemical industry.

[0003] The mature phosphoric acid production process is mainly divided into wet process and thermal process. The wet phosphoric acid process has high requirements on the grade of phosphate ore, and the produced phosphoric acid has many impurities, which is mainly used for the production of phosphate fertilizers; due to the large amount of by-product phosphogypsum, it not only causes a waste of sulfur resources, but also brings serious environmental problems. The thermal phosphoric acid process requires that the P2O5 content of the phosphate ore entering the furnace is not less than 25%, and the average power consumption per ton of yellow phosphorus is about 14,000 to 15,000 kWh; for every 1% decrease in the mass fraction of P2O5 in the reaction material, the power consumption for producing 1 t of yellow phosphorus will increase by 300 to 350 kWh, and the recovery rate of phosphorus will decrease by about 0.5%; although the quality of the prepared phosphoric acid is good, the heat energy of yellow phosphorus combustion, CO combustion and high-temperature slag is difficult to effectively utilize, which causes the energy consumption of the electric furnace to remain high.

[0004] The kiln phosphoric acid process is an unconventional thermal phosphoric acid production method based on the principle of thermal phosphoric acid reaction, with the goal of reducing energy consumption. Its design idea is: phosphate ore reduction and yellow phosphorus oxidation are completed in one step in the reactor, and the heat of yellow phosphorus oxidation is directly used for phosphate ore reduction to achieve the goal of reducing energy consumption. This process does not require acid to produce phosphoric acid, has low energy consumption, and can directly use medium and low-grade phosphate ore, which is in line with the characteristics of my country's phosphate ore resources, so it has broad application prospects.

[0005] At present, the reactors used in the kiln phosphoric acid process mainly include rotary kilns and tunnel kilns. Through the verification of the pilot plant, the problem of direct application of low- and medium-grade phosphate ore has been solved, but it cannot operate stably for a long period of time. The main reason is that the reduction zone and the oxidation zone cannot be effectively isolated, which makes it difficult to control the reaction process and the temperature in the kiln, resulting in problems such as material adhesion, carbon loss of reducing agent and P2O5 reabsorption.

[0006] In view of the shortcomings of the existing kiln-based phosphoric acid process reactor, relevant improvement measures are mainly concentrated in two aspects: pellet preparation and reactor improvement.

[0007] In terms of pellet preparation: Patent CN 117776127 A proposes to use a coating agent mixed with β-gypsum powder, coal powder and residue to wrap the reaction balls to prevent carbon loss and adhesion; Patent CN 116768169A proposes to control the comprehensive alkalinity of the mixture to achieve the purpose of preventing the reaction balls from bonding themselves; and patents CN116902935A and CN115159481A propose a double-layer ball idea, which is isolated by an external high-melting-point inert material layer to solve the P2O5 back-absorption problem. Although the above measures can alleviate the oxidation and reduction isolation problem in rotary kilns and tunnel kilns to a certain extent, they have not completely solved the defect that the reactor is essentially unable to achieve oxidation and reduction isolation.

[0008] Reactor improvement: Patent CN201952232U proposes that the combustion chamber and material channel of the grate tube structure be used in the upper part of the vertical kiln to achieve effective isolation of the reduction zone and the oxidation zone; Patent CN101556108B proposes that the metal gas duct be used at the top of the vertical kiln to recover the heat generated by the combustion of phosphorus-containing coal gas, and heat the purified tail gas, which is passed into the furnace as a heat source to provide heat for the reduction reaction of the material; and Patent CN201096450Y proposes to set up multiple groups and rows of preheating chambers and reduction chambers in series in the main working section, surrounded by oxidation combustion zones and multiple groups of heat tubes, to achieve effective isolation of oxidation and reduction zones and uniform temperature control. The above-mentioned design improvements made to address the essential defects of rotary kilns and tunnel kilns are mostly complex in structure, and the reliability and maturity of the devices are insufficient, making it difficult to adapt to the needs of industrial production. Summary of the invention

[0009] In view of the deficiencies in the prior art, the present invention proposes a self-heating vertical furnace and a method for preparing phosphoric acid by a kiln method using the self-heating vertical furnace. The self-heating vertical furnace is designed with independent overflow chambers, combustion chambers, reduction chambers and phosphorus coal gas pipelines to achieve complete isolation of the combustion chamber from the overflow chamber and the reduction chamber, and the respective reducing atmospheres and oxidizing atmospheres do not interfere with each other, which completely eliminates the design defects of the existing reactor; the method for preparing phosphoric acid: the phosphorus-containing pellets are treated with an external reducing agent to effectively reduce the adhesion of the pellets and reduce the carbon loss of the pellets; the recycling of the external reducing agent and the effective recycling of the phosphorus-containing coal gas help to reduce the carbon consumption of the system and reduce the energy consumption of the vertical furnace.

[0010] The technical solution of the present invention is:

[0011] A self-heating vertical furnace, comprising a furnace body and a phosphorus coal gas pipeline, wherein the furnace body comprises an overflow chamber, a combustion chamber, and a reduction chamber, and is characterized in that:

[0012] The overflow chamber has a circular or square cross-sectional shape, is built of refractory materials, is placed above the combustion chamber, and is separated from the combustion chamber by a sealing plate. The overflow chamber is also provided with a phosphorus coal gas outlet;

[0013] The cross-sectional shape of the combustion chamber is consistent with that of the overflow chamber, and is built of refractory materials. It is divided from top to bottom by multiple layers of choke plates according to temperature ranges into: a preheating section connected to the flue gas outlet, a high-temperature section I connected to the phosphorus coal gas inlet, and a high-temperature section II connected to the combustion chambers on both sides; one or more air guide holes are also provided on each layer of the choke plates of each section; the flue gas outlet connected to the preheating section of the combustion chamber is connected to the external heat recovery device and the washing and condensing device in turn;

[0014] The reduction chamber has a circular or rectangular cross-sectional shape and is built of a high thermal conductivity composite material; one or more reduction chambers are placed in the same overflow chamber and combustion chamber; the reduction chamber placed in the overflow chamber is also provided with one or more overflow ports; the reduction chamber inlet is connected to the nitrogen sealed silo at the top of the furnace body, and the outlet is connected to the cooling device and the discharge device at the bottom of the furnace body in turn;

[0015] The front end of the phosphorus gas pipeline is connected to the gas outlet of the overflow chamber, and the rear end is connected to the phosphorus gas inlet of the high-temperature section I; the interface pipe connected to the phosphorus gas pipeline is provided with a regulating valve and a shut-off valve, and is also connected to the external air pipeline; the connected air pipeline branches are all provided with regulating valves and shut-off valves.

[0016] Furthermore, the sealing plate is a refractory masonry with a labyrinth structure; the choke plate is a thermal shock resistant, low creep refractory masonry and is provided with air guide holes.

[0017] Furthermore, the rear end of the phosphorus coal gas pipeline is also connected to a combustion chamber on one side of the high temperature II section.

[0018] Furthermore, the combustion chamber connected to the high temperature stage II is provided with an external burner with a calorific value higher than 700 kcal / m 3 The gas is used as fuel for the early stage of furnace baking and regulating the temperature in the combustion chamber.

[0019] A method for preparing phosphoric acid by a kiln process using a self-heating shaft furnace, characterized in that it comprises the following steps:

[0020] (1) Preparation of green pellets: After mixing phosphate rock powder and additives, they are pelletized and dried in sequence to prepare green pellets with a moisture content of less than 2%;

[0021] (2) Mixing before entering the furnace: Mixing the green pellets and the external reducing agent in a mass ratio of 50-80% to 20-50%;

[0022] (3) Phosphorus reduction in the furnace: the mixture of the green pellets and the external reducing agent is continuously placed in the reduction chamber, and the green pellets run from top to bottom in the reduction chamber; the heated flue gas flows countercurrently from bottom to top in the combustion chamber; the heat is indirectly transferred to the material through the large wall of the reduction chamber; the green pellets pass through the preheating section, high temperature section I and high temperature section II in sequence, and then carbon thermal reduction reaction occurs to form phosphorus-containing coal gas (containing P4 and CO) and residual tailings; the phosphorus-containing coal gas runs from bottom to top, passes through the material layer and is discharged into the overflow chamber from the overflow hole at the top of the reduction chamber;

[0023] Overall reaction formula: 2Ca 10 (PO4)6F2+30C+21SiO2=20CaSiO3+30CO+3P4+SiF4;

[0024] (4) Combustion of phosphorus gas: The phosphorus-containing gas is introduced from the overflow chamber through the phosphorus gas pipeline into the high-temperature I section and high-temperature II section combustion chambers of the combustion chamber; the phosphorus-containing gas and air diffuse and burn in the high-temperature I section, and the rising high-temperature flue gas heats the materials in the reduction chamber of this section; the phosphorus-containing gas and air mix and burn in the combustion chamber on one side connected to the high-temperature II section, and the flue gas heats the materials in the reduction chamber of this section from bottom to top after passing through the nozzle; the rising high-temperature flue gas heats the materials in the reduction chamber in the preheating section and is discharged from the flue gas outlet;

[0025] Main reaction formula 1: P4+5O2=2P2O5; Main reaction formula 2: 2CO+O2=2CO2

[0026] (5) Flue gas post-treatment: The P2O5-containing flue gas is connected to an external heat recovery device from the flue gas outlet, and after the temperature is reduced to 50-300° C., it is connected to a washing and condensing device to separate the phosphoric acid solution and tail gas;

[0027] (6) Tailings post-treatment: The residual tailings are cooled to 50-150° C. by a cooling device and then continuously discharged from the reduction chamber by a discharging device; after physical separation, the recovered residual reducing agent is recycled.

[0028] Preferably, the additive is compounded by a binder, silica and coal powder in a mass ratio of 1-10%, 40-70% and 29-50%; the coal powder has a fixed carbon content of 80-95% and an ash content of 2-10%.

[0029] Preferably, the P2O5 content in the green pellets is 5-24%, and the pellet size is 5-50 mm; the reducing agent has a particle size of 5-50 mm and is one or more of biochar, crushed coke, lignite, bituminous coal, and anthracite.

[0030] Preferably, the control temperature of the overflow chamber is 150-350°C, the control temperature of the combustion chamber preheating section is 600-1150°C, the control temperature of the high temperature section I is 1150-1250°C, and the control temperature of the high temperature section II is 1200-1350°C; the flue gas outlet temperature of the combustion chamber preheating section is 600-800°C.

[0031] Preferably, the gas pressure in the overflow chamber is 0 to 5 kPa, and the gas pressure in the high temperature section I and high temperature section II of the combustion chamber is -5 to 0 kPa.

[0032] Preferably, the controlled material speed of the green pellets in the reduction chamber is 7.5-25 mm / min, and the total residence time in the reduction chamber is 10-20 h.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The overflow chamber of the vertical furnace is fully isolated from the combustion chamber, and the combustion chamber is completely independent from the reduction chamber. The respective reducing atmospheres and oxidizing atmospheres do not interfere with each other, thus achieving complete isolation of the reduction zone and the oxidation zone; the design defects of the existing reactor are completely eliminated.

[0035] (2) The vertical furnace is provided with an overflow chamber and a combustion chamber and one or more reduction chambers. The reduction chambers are placed inside the overflow chamber and the combustion chamber. By increasing the number of reduction chambers through modular combination, the needs of large-scale production can be met, overcoming the current single electric furnace maximum output of 13,000 tons / year capacity limitation.

[0036] (3) By controlling the pressure of each section in the combustion chamber, it is ensured that the phosphorus-containing coal gas in the overflow chamber smoothly enters the combustion chamber for oxidation combustion reaction; the high-temperature flue gas generated indirectly heats the materials in the reduction chamber, which not only avoids the back absorption of P2O5 by the material balls, but also realizes the effective recovery and utilization of the chemical heat of the phosphorus-containing coal gas.

[0037] (4) The reduction chamber uses a high thermal conductivity composite material with the characteristics of high thermal conductivity, low porosity, high temperature resistance, wear resistance and acid corrosion resistance. It not only helps to improve the heating efficiency of the material and reduce the flue gas outlet temperature, but also helps to enhance the long-term production stability of the vertical furnace.

[0038] (5) The material balls move from top to bottom in the reduction chamber, and the smoke flows from bottom to top in the combustion chamber, so the heat is fully utilized and the reduction efficiency is high; the material feeding speed is slow and the material reacts fully; the isolation effect of the external reducing agent not only effectively avoids the adhesion between materials and between materials and walls, but also greatly reduces the carbon loss of materials.

[0039] (6) The use of the vertical furnace to prepare phosphoric acid by the kiln process solves the problem of direct utilization of medium- and low-grade phosphate ore, effectively utilizes the chemical heat of phosphorus-containing coal gas, and produces phosphoric acid of better quality; the recycling of non-coking coal reducing agents reduces production costs; and compared with the electric furnace phosphoric acid process, external energy consumption can be reduced by 20 to 50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a schematic structural diagram of a self-heating vertical furnace device according to an embodiment of the present invention.

[0041] Figure 2 This is a schematic structural diagram of a self-heating vertical furnace device according to Embodiment 2 of the present invention.

[0042] Figure 3 The present invention is a flow chart of a method for preparing phosphoric acid by a kiln method using a self-heating vertical furnace.

[0043] Figure markings: 1-nitrogen sealed silo; 2-overflow chamber; 3-combustion chamber; 4-reduction chamber; 5-sealing plate; 6-choke plate; 7-cooling device; 8-discharging device; 9-phosphorus coal gas pipeline; 10-air pipeline; 31-preheating section; 32-high temperature section I; 33-high temperature section II; 34-combustion chamber; 35-burner; 36-combustion chamber phosphorus coal gas inlet; 37-nozzle; 38-high temperature section I phosphorus coal gas inlet; 39-smoke outlet; 41-reduction chamber overflow; 61-choke plate air guide hole; 91-phosphorus steam pipeline regulating valve; 101-air pipeline valve group. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. The devices further described in the present invention are all existing structures.

[0045] Embodiment 1:

[0046] like Figure 1As shown, a self-heating vertical furnace includes a furnace body and a phosphorus coal gas pipeline 9. The furnace body includes: an overflow chamber 2, a combustion chamber 3, and a reduction chamber 4. The characteristics are: the cross-sectional shape of the overflow chamber 2 is square or circular, and is built of refractory materials, is placed above the combustion chamber 3, and is separated from the combustion chamber 3 by a sealing plate 5. The overflow chamber 2 is also provided with a phosphorus coal gas outlet 21; the cross-sectional shape of the combustion chamber 3 is consistent with that of the overflow chamber 2, and is built of refractory materials, and is divided into temperature zones from top to bottom by multi-layer choke plates 6. : a preheating section 31 connected to a flue gas outlet 39, a high temperature section I 32 connected to a phosphorus coal gas inlet 38, and a high temperature section II 33 connected to combustion chambers 34 on both sides; the separated sections are connected through one or more air guide holes 61 on each layer of the choke plate 6; the flue gas outlet 39 connected to the combustion chamber preheating section 31 is connected to the external heat recovery device and the washing and condensing device in turn; the cross-sectional shape of the reduction chamber 4 is rectangular or circular, and is built of a high thermal conductivity composite material; one or more reduction chambers 4 are placed in the same The overflow chamber 2 is connected to the combustion chamber 3; the reduction chamber 4 placed in the overflow chamber 2 is also provided with one or more overflow ports 41; the inlet of the reduction chamber 4 is connected to the nitrogen sealed silo 1 at the top of the furnace body, and the outlet is connected to the cooling device 7 and the discharge device 8 at the bottom of the furnace body in sequence; the front section of the phosphorus coal gas pipeline 9 is connected to the gas outlet 21 of the overflow chamber, and the rear end is connected to the phosphorus coal gas inlet 38 of the high temperature section I; the interface pipe connected to the phosphorus coal gas pipeline 9 is provided with a valve group 91 of a regulating valve and a cut-off valve, and is also connected to the external air pipeline 1 0; the connected air duct branches are all provided with valve groups 101 of regulating valves and shut-off valves; further, the sealing plate 5 is a refractory masonry with a labyrinth structure; the choke plate 6 is a refractory masonry with thermal shock resistance and low creep, and is provided with air guide holes 61; further, the combustion chamber 34 connected with the high temperature section II is provided with an external burner 35, which uses natural gas as fuel and is used for early furnace baking and supplementing the temperature in the combustion chamber; further, the combustion chamber 24 is connected with the high temperature section II 33 by a nozzle 37.

[0047] A method for preparing phosphoric acid by a kiln process using a self-heating vertical furnace, the process is as follows Figure 3 As shown:

[0048] (1) Using low- to medium-grade phosphate rock powder with a P2O5 content of 17.8% as a raw material and a mixture of 10% methyl cellulose, 55% silica and 35% anthracite as an additive; the phosphate rock powder and the additive are mixed in a mass ratio of 68%:32% to obtain a mixture with a P2O5 content of 12.1%, a SiO2 / CaO molar ratio of 1.2, and a C / P molar ratio of 4.5; the mixture is successively pelletized and dried to prepare green pellets with a moisture content of 1.5% and a strength of ≥500N.

[0049] (2) Blue coke with an external particle size of 5 to 20 mm and green pellets are mixed in a mass ratio of 30% to 70%, and after being mixed, they are sent to the nitrogen-sealed silo at the top of the vertical furnace by the feeding and distribution device; the mixed material is continuously added to the reduction chamber of the vertical furnace through the feeding device under the silo; the material surface in the reduction chamber is controlled to be 0.5m below the overflow hole to maintain the overflow chamber temperature between 150 and 350°C, while also reserving a certain operating space for the overflow gas.

[0050] (3) The green pellets and the externally prepared lignite in the reduction chamber run from top to bottom; the high-temperature flue gas in the combustion chamber flows countercurrently from bottom to top; the heat of the flue gas is continuously transferred to the pellets in the reduction chamber through the high-thermal conductivity refractory material of the partition wall; the green pellets undergo corresponding carbon thermal reduction reactions in the high-temperature stage I and high-temperature stage II, and form phosphorus-containing coal gas (containing P4 and CO) and residual tailings; the phosphorus-containing coal gas runs from bottom to top, passes through the material layer and is discharged into the overflow chamber from the overflow hole at the top of the reduction chamber.

[0051] (4) The phosphorus-containing coal gas with a temperature of about 200°C is introduced from the overflow chamber into the high-temperature I and high-temperature II combustion chambers of the combustion chamber through a pipeline; and burns in the combustion chamber with the injected air; the temperature in the combustion chamber is controlled by the regulating valves on the phosphorus coal gas pipeline and the air pipeline, and is supplemented by the combustion of natural gas by the burner; the phosphorus coal gas is burned to produce flue gas containing P2O5, and the flue gas continuously changes its running direction in the preheating section, high-temperature I and high-temperature II sections under the intervention of the choke plate in the combustion chamber, and the heat is continuously transferred to the reduction chamber partition wall during the process, and the material balls in the reduction chamber are continuously heated indirectly.

[0052] (5) The flue gas containing P2O5 at about 700°C is connected to an external heat recovery device through a flue gas duct and then its temperature is reduced to 120°C. After washing and condensation, phosphoric acid with a concentration of 85-90% and tail gas with a temperature of 50°C are formed.

[0053] (6) The residual tailings from the carbon thermal reduction reaction are discharged into the cooling device through the bottom of the reduction chamber. After being cooled to 100-120°C, they are sent to the screening chamber by a conveyor belt for separation. The recovered residual reducing agent is re-incorporated into the raw pelletizing ingredients.

[0054] During the implementation process, the cross-section of the vertical furnace reduction chamber is rectangular, with a width of 400mm, a length of 1500mm, and an effective height of approximately 10000mm; the temperatures of each section are: 300°C in the overflow chamber, 600-1150°C in the preheating section, 1150-1250°C in the high-temperature section I, and 1200-1350°C in the high-temperature section II; the pressure in the overflow chamber is 1kPa, the pressure in the high-temperature section I of the combustion chamber is 0kPa, and the pressure in the high-temperature section II is -2kPa; the controlled material speed in the reduction chamber is 10mm / min, and the total residence time of the green pellets in the reduction chamber is approximately 16h.

[0055] The implementation results are: the removal rate of P2O5 is about 90%. For every ton of green pellets with a P2O5 content of 12.1%, about 109.3 kg of P2O5 can be obtained, and the phosphorus-containing coal gas generated is about 256 Nm 3 ; It can provide about 51% of the total heat for each ton of green pellets with a P2O5 content of 12.1% processed by the vertical furnace, and the amount of external natural gas consumed is about 66Nm 3 , calculated based on the external heat consumption per ton of P2O5, it is approximately 19GJ. Compared with the external electrical energy of 30.7GJ per ton of P2O5 in the electric furnace process, the external energy consumption is reduced by approximately 32.5%.

[0056] Embodiment 2:

[0057] like Figure 2 As shown, a self-heating vertical furnace includes a furnace body and a phosphorus coal gas pipeline 9, the furnace body includes: an overflow chamber 2, a combustion chamber 3, and a reduction chamber 4, characterized in that: the cross-sectional shape of the overflow chamber 2 is square, or circular, and is built of refractory materials, is placed above the combustion chamber 3, and is separated from the combustion chamber 3 by a sealing plate 5, and the overflow chamber 2 is also provided with a phosphorus coal gas outlet 21; the cross-sectional shape of the combustion chamber 3 is consistent with that of the overflow chamber 2, and is built of refractory materials, and is divided from top to bottom by a multi-layer choke plate 6 into: The preheating section 31 connected to the combustion chamber port 39, the high temperature section I 32 connected to the phosphorus coal gas inlet 38 and the high temperature section II 33 connected to the combustion chambers 34 on both sides; the separated sections are connected through one or more air guide holes 61 on each layer of the choke plate 6; the flue gas outlet 39 connected to the combustion chamber preheating section 31 is connected to the external heat recovery device and the washing and condensing device in turn; the cross-sectional shape of the reduction chamber 4 is rectangular or circular, and is built of high thermal conductivity composite materials; one or more reduction chambers 4 are placed in the same overflow chamber 2 and the combustion chamber 3; the reduction chamber 4 placed in the overflow chamber 2 is also provided with one or more overflow ports 41; the inlet of the reduction chamber 4 is connected to the nitrogen sealed silo 1 at the top of the furnace body, and the outlet is connected to the cooling device 7 and the discharge device 8 at the bottom of the furnace body in turn; the front section of the phosphorus coal gas pipeline 9 is connected to the gas outlet 21 of the overflow chamber, and the rear end is connected to the phosphorus coal gas inlet 38 of the high temperature section I and the inlet 36 of the combustion chamber 34 on one side of the high temperature section II; the interface pipe connected to the phosphorus coal gas pipeline 9 is provided with a valve group 91 of a regulating valve and a cut-off valve, and is also connected to the external air Pipeline connection 10; the connected air pipeline branches are all provided with valve groups 101 of regulating valves and shut-off valves; further, the sealing plate 5 is a refractory masonry with a labyrinth structure; the choke plate 6 is a thermal shock-resistant, low-creep refractory masonry, and is provided with air guide holes 61; further, the combustion chamber 34 connected to the high-temperature II section is provided with an external burner 35, which uses natural gas as fuel and is used for early furnace baking and supplementing the temperature in the combustion chamber; further, the combustion chamber 34 is connected to the high-temperature II section 33 by a nozzle 37.

[0058] A method for preparing phosphoric acid by a kiln process using a self-heating vertical furnace, the process is as follows Figure 3 As shown:

[0059] (1) using medium-grade phosphate rock powder with a P2O5 content of 24% as a raw material and a mixture of 10% methyl cellulose, 48% silica and 42% blue carbon as an additive; the phosphate rock powder and the additive are mixed in a mass ratio of 68%:32% to obtain a mixture with a P2O5 content of 16%, a SiO2 / CaO molar ratio of 1.0, and a C / P molar ratio of 4.5; the mixture is successively pelletized and dried to prepare green pellets with a moisture content of 1.5% and a strength of ≥500N;

[0060] (2) Blue coke with an external particle size of 5 to 20 mm and green pellets are mixed in a mass ratio of 50% to 50%, and then sent to the nitrogen sealed silo at the top of the vertical furnace by the feeding and distribution device after mixing; the mixed material is continuously added to the reduction chamber of the vertical furnace through the feeding device under the silo; the material surface in the reduction chamber is controlled to be 0.5m below the overflow hole to maintain the overflow chamber temperature between 150 and 350°C, and at the same time, a certain running space is reserved for the overflow gas;

[0061] (3) The green pellets and the external blue carbon in the reduction chamber run from top to bottom; the high-temperature flue gas in the combustion chamber flows countercurrently from bottom to top, and the heat of the flue gas is continuously transferred to the pellets in the reduction chamber through the high-thermal conductivity refractory material of the partition wall; the green pellets undergo corresponding carbon thermal reduction reactions in the high-temperature stage I and high-temperature stage II, and form phosphorus-containing coal gas (containing P4 and CO) and residual tailings; the phosphorus-containing coal gas runs from bottom to top, passes through the material layer and is discharged into the overflow chamber from the overflow hole at the top of the reduction chamber;

[0062] (4) The phosphorus-containing coal gas with a temperature of about 300°C is introduced from the overflow chamber into the high-temperature I and II combustion chambers of the combustion chamber through a pipeline; and burns in the combustion chamber with the injected air; the temperature in the combustion chamber is controlled by the regulating valves on the phosphorus coal gas pipeline and the air pipeline, and is supplemented by the burner burning natural gas; after the phosphorus coal gas is burned, flue gas containing P2O5 is generated. Under the intervention of the choke plate in the combustion chamber, the flue gas continuously changes its running direction in the preheating section, high-temperature I and high-temperature II sections, and in the process, the heat is continuously transferred to the reduction chamber partition wall, and the pellets in the reduction chamber are continuously heated indirectly;

[0063] (5) The flue gas containing P2O5 at a temperature of about 750°C is connected to the heat recovery device through the flue gas duct from the flue gas outlet to a temperature of 150°C. After washing and condensation, phosphoric acid with a concentration of 85-90% and tail gas with a temperature of 50°C are formed;

[0064] (6) The residual tailings from the carbon thermal reduction reaction are discharged into the cooling device through the bottom of the reduction chamber. After being cooled to 100-120°C, they are sent to the screening chamber by a conveyor belt for separation. The recovered residual reducing agent is re-incorporated into the raw pelletizing ingredients.

[0065] During the implementation process, the cross-section of the vertical furnace reduction chamber is rectangular, with a width of 400mm, a length of 1500mm and a height of about 10000mm; the temperatures of each section are: 300℃ in the overflow chamber, 600-1150℃ in the preheating section, 1150-1250℃ in the high-temperature section I, and 1200-1350℃ in the high-temperature section II; the pressure in the overflow chamber is 1kPa, the pressure in the high-temperature section I of the combustion chamber is 0kPa, and the pressure in the high-temperature section II is -2kPa; the controlled material speed in the reduction chamber is 8mm / min, and the total residence time of the green pellets in the reduction chamber is 18h.

[0066] The implementation results are: the removal rate of P2O5 is about 92%. When treating one ton of green pellets with a P2O5 content of 16.32%, about 150kg of P2O5 can be obtained, and the phosphorus-containing coal gas generated is about 305Nm 3 ; It can provide about 58.6% of the total heat for each ton of green pellets with a P2O5 content of 16.68% processed by the vertical furnace, and the amount of external natural gas consumed is about 63.5Nm 3 , calculated based on the external heat consumption per ton of P2O5, it is approximately 14GJ. Compared with the external electrical energy of 28.2GJ per ton of P2O5 in the electric furnace process, the external energy consumption is reduced by approximately 48.5%.

[0067] The above is a clear and complete description of the technical solutions in the embodiments of the present invention in combination with the drawings in the embodiments of the present invention; it should be noted that the embodiments described herein are only some embodiments of the present invention, rather than all implementations of the present invention, and the embodiments are only exemplary, and their role is only to provide the public with a more intuitive and clear way to understand the content of the present invention, rather than to limit the technical solutions of the present invention. Without departing from the concept of the technical solution of the present invention, all other implementation plans that can be thought of by ordinary technicians in this field without making creative work, and other simple replacements and various changes to the technical solution of the present invention, all belong to the protection scope of the present invention.

Claims

1. A self-heating vertical furnace, comprising a furnace body and a phosphorus coal gas pipeline, wherein the furnace body comprises an overflow chamber, a combustion chamber, and a reduction chamber, and is characterized in that: The overflow chamber has a circular or square cross-sectional shape, is built of refractory materials, is placed above the combustion chamber, and is separated from the combustion chamber by a sealing plate. The overflow chamber is also provided with a phosphorus coal gas outlet; The cross-sectional shape of the combustion chamber is consistent with that of the overflow chamber, and is built of refractory materials. It is divided from top to bottom by multiple layers of choke plates according to temperature ranges into: a preheating section connected to the flue gas outlet, a high-temperature section I connected to the phosphorus coal gas inlet, and a high-temperature section II connected to the combustion chambers on both sides; one or more air guide holes are also provided on each layer of the choke plates of each section; the flue gas outlet connected to the preheating section of the combustion chamber is connected to the external heat recovery device and the washing and condensing device in turn; The reduction chamber has a circular or rectangular cross-sectional shape and is built of a high thermal conductivity composite material; one or more reduction chambers are placed in the same overflow chamber and combustion chamber; the reduction chamber placed in the overflow chamber is also provided with one or more overflow ports; the reduction chamber inlet is connected to the nitrogen sealed silo at the top of the furnace body, and the outlet is connected to the cooling device and the discharge device at the bottom of the furnace body in turn; The front end of the phosphorus gas pipeline is connected to the gas outlet of the overflow chamber, and the rear end is connected to the phosphorus gas inlet of the high-temperature section I and the combustion chamber on one side of the high-temperature section II; the interface pipe connected to the phosphorus gas pipeline is provided with a regulating valve and a shut-off valve, and is also connected to the external air pipeline; the connected air pipeline branches are all provided with regulating valves and shut-off valves.

2. The self-heating vertical furnace according to claim 1, characterized in that: The sealing plate is a refractory masonry with a labyrinth structure; the choke plate is a refractory masonry with a thermal shock resistance and low creep and is provided with air guide holes.

3. The self-heating vertical furnace according to claim 1, characterized in that: The rear end of the phosphorus coal gas pipeline is also connected to a combustion chamber on one side of the high temperature II section.

4. The self-heating vertical furnace according to claim 1, characterized in that: The combustion chamber communicated with the high temperature II stage is provided with an external burner.

5. A method for preparing phosphoric acid by a kiln process using the self-heating vertical furnace according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Preparation of green pellets: After mixing phosphate rock powder and additives, they are pelletized and dried in sequence to prepare green pellets with a moisture content of less than 2%; (2) Mixing before entering the furnace: Mixing the green pellets and the external reducing agent in a mass ratio of 50-80% to 20-50%; (3) Phosphorus reduction in the furnace: the mixture of the green pellets and the external reducing agent is continuously placed in the reduction chamber, and the green pellets run from top to bottom in the reduction chamber; the heated flue gas flows countercurrently from bottom to top in the combustion chamber; the heat is indirectly transferred to the material through the large wall of the reduction chamber; the green pellets pass through the preheating section, high temperature section I and high temperature section II in sequence, and then carbon thermal reduction reaction occurs to form phosphorus-containing coal gas and residual tailings; the phosphorus-containing coal gas runs from bottom to top, passes through the material layer, and is discharged into the overflow chamber from the overflow hole at the top of the reduction chamber; (4) Combustion of phosphorus gas: The phosphorus-containing gas is introduced into the high-temperature I and II combustion chambers of the combustion chamber from the overflow chamber through the phosphorus-containing gas pipeline; the phosphorus-containing gas and air diffuse and burn in the high-temperature I section, and the rising high-temperature flue gas heats the materials in the reduction chamber of this section; the phosphorus-containing gas and air mix and burn in the combustion chamber on one side connected to the high-temperature II section, and the flue gas heats the materials in the reduction chamber of this section from bottom to top after passing through the nozzle; the rising high-temperature flue gas heats the materials in the reduction chamber in the preheating section and is discharged from the flue gas outlet; (5) Flue gas post-treatment: The flue gas containing P2O5 is connected to an external heat recovery device from the flue gas outlet. After the temperature is reduced to 50-300°C, it is connected to a washing and condensing device to separate the phosphoric acid solution and tail gas; (6) Tailings post-treatment: The residual tailings are cooled to 50-150° C. by a cooling device and then continuously discharged from the reduction chamber by a discharging device; After physical separation, the recovered residual reducing agent is recycled.

6. The method for preparing phosphoric acid by a kiln process using a self-heating shaft furnace according to claim 5, characterized in that: The additive is compounded by a binder, silica and coal powder according to the mass ratios of 1-10%, 40-70% and 29-50%; the fixed carbon content of the coal powder is 80-95%, and the ash content is 2-10%.

7. The method for preparing phosphoric acid by a kiln process using a self-heating shaft furnace according to claim 5, characterized in that: The P2O5 content in the green pellets is 5-24%, and the pellet size is 5-50mm; the reducing agent has a particle size of 5-50mm and is one or more of biochar, crushed coke, semi-coke, lignite, bituminous coal, and anthracite.

8. The method for preparing phosphoric acid by a kiln process using a self-heating shaft furnace according to claim 5, characterized in that: The control temperature of the overflow chamber is 150-350°C, the control temperature of the combustion chamber preheating section is 600-1150°C, the control temperature of the high temperature section I is 1150-1250°C, and the control temperature of the high temperature section II is 1200-1350°C; the flue gas outlet temperature of the combustion chamber preheating section is 600-800°C.

9. The method for preparing phosphoric acid by a kiln process using a self-heating shaft furnace according to claim 5, characterized in that: The pressure in the overflow chamber is 0 to 5 kPa, and the pressure in the high temperature section I and high temperature section II of the combustion chamber is -5 to 0 kPa.

10. The method for preparing phosphoric acid by using a self-heating shaft furnace in a kiln process according to claim 5, characterized in that: The material speed of the green pellets in the reduction chamber is 7.5-25 mm / min, and the total residence time in the reduction chamber is 10-20 hours.

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