A production system and process for coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum

Abstract

The present invention provides a production system and process for coupling sulfur reduction of phosphogypsum and carbon reduction of phosphogypsum. The production system includes a plurality of suspension preheaters, which are sequentially connected to a pre-calciner and a first gas-solid separator through pipelines. The first gas-solid separator is sequentially connected to a reduction decomposition furnace, a second gas-solid separator, and a weak oxidation furnace through pipelines. The bottom discharge port of the second gas-solid separator is connected to a rotary kiln through a pipeline, and the flue gas channel of the rotary kiln is connected to the reduction decomposition furnace. The present invention can reasonably select the corresponding reduction route according to the sulfur and coal prices at that time, solve the economic problem, reduce the worries of enterprises, and accelerate the enthusiasm for the comprehensive utilization construction of phosphogypsum. Coupling sulfur reduction of phosphogypsum in carbon reduction can significantly increase the SO2 gas concentration of the product, reduce the manufacturing and operation costs of sulfuric acid plants, and also reduce carbon emissions.

Description

Technical Field

[0001] The present invention belongs to the fields of chemical engineering technology and building materials technology, relates to the field of comprehensive utilization of phosphogypsum, and specifically relates to a production process for coupling sulfur reduction of phosphogypsum and carbon reduction of phosphogypsum, a technical route selection for phosphogypsum reduction in the production of sulfuric acid from phosphogypsum, and a production method for increasing the SO2 gas concentration in a sulfuric acid production device using phosphogypsum. Background Art

[0002] Phosphogypsum is a solid waste generated during the wet process of producing phosphoric acid, and about 4.8 - 5.5 tons of phosphogypsum are produced per ton of wet-process phosphoric acid. With the continuous development of the phosphate fertilizer industry, the discharge of phosphogypsum is increasing day by day, and the comprehensive utilization of phosphogypsum is a worldwide problem. At present, policies formulated in various regions of the country are, firstly, to encourage the comprehensive utilization of phosphogypsum, and secondly, to force enterprises to act based on the principle of determining production based on the consumption of phosphogypsum. There are many phosphogypsum products, but considering the large production volume of phosphogypsum, the largest market for end products that can digest phosphogypsum is the cement branch in building materials. The production of sulfuric acid from phosphogypsum and co-producing cement clinker has received a great deal of attention as the only route in the current market that can consume a large amount of phosphogypsum products, and it is one of the best choices to achieve the consumption of solid waste phosphogypsum and the recycling of sulfur and calcium resources.

[0003] However, economically speaking, carbon reduction still has a profit margin when the price of sulfur is at a high level, but the losses are obvious when the price of sulfur drops. The historical price fluctuation cycle of sulfur is three drops and two rises, which means that most of the time it is at a loss. Sulfur reduction has more advantages than carbon reduction when the price of sulfur is low and the price of coal is high. Currently, the problems with sulfur reduction are as follows: 1. It is easy to generate sublimated sulfur, which clogs the suspension preheater and the equipment in the sulfuric acid production section; 2. The core equipment of sulfur reduction, such as the sulfur vaporizer or sulfur heat exchanger, has high requirements for equipment, is highly corrosive at high temperatures, and the equipment is easily damaged. The main reason for the lack of large-scale devices at present is that the industrial stability of the core equipment, the sulfur vaporizer and sulfur heat exchanger, cannot be guaranteed. There have been cases where the sulfur heat exchanger in a pilot plant was frequently blocked. The problems with carbon reduction are as follows: 1. Using carbon as a reducing agent has a high cost, the product is CO2, and the carbon emissions are large, which is not environmentally friendly; 2. The SO2 gas concentration in the flue gas produced is low, the investment in the sulfuric acid plant is large, and the operating cost is high; 3. The moisture content of the flue gas at the kiln tail is high, the dew point temperature of the flue gas before entering the sulfuric acid plant is high, and it is easy to corrode the pipeline if the heat is not controlled well. Summary of the Invention

[0004] The present invention provides a production process for coupling sulfur reduction of phosphogypsum and carbon reduction of phosphogypsum to solve the problem of excessive losses in carbon reduction for sulfuric acid production from phosphogypsum when the price of sulfur is low, and to solve the problem of treating solid waste sulfur slag in the sulfuric acid industry. The amount of reducing agent added can be flexibly adjusted according to the prices of sulfur and coke powder. Moreover, when using sulfur and sulfur slag, the SO2 gas concentration can be increased, solving the drawback of low SO2 gas concentration in the traditional carbon reduction process of phosphogypsum. By reasonably selecting the reduction route based on the sulfur and coal prices at that time, the economic problem is solved, opening up a new path for large-scale production of enterprises. In addition, the problem of solid waste sulfur slag is solved, making this technical route have better selectivity.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The raw meal prepared by mixing phosphogypsum and auxiliary materials enters the suspension preheater. The heat generated by combustion in the pre-calciner enters the suspension preheater to heat the raw meal to 750°C - 1000°C, so as to meet the reaction temperature required for sulfur reduction and carbon reduction of phosphogypsum. One or more reducing agents such as reduced carbon, sulfur slag, gaseous or liquid sulfur are added into the reduction furnace. The heat provided by the kiln tail flue gas entering the reduction furnace is used to heat sulfur to gasify to 750°C and to provide the reaction heat required for the reduction reaction to be absorbed. Inside the reduction furnace, the reducing agent and phosphogypsum complete the pre-decomposition reaction (CaS04 + 2C → CaS + 2CO2, CaS04 + 2S → CaS + 2SO2). The generated gaseous SO2 and the kiln gas are treated together and then enter the flue gas sulfuric acid production section (SO2 + 1 / 202 → SO3↑, SO3 + H2O → H2SO4). The generated solid phase goes to the rotary kiln for subsequent reactions to produce cement clinker (3CaSO4 + CaS = 4CaO + 4SO2, 2CaO + SiO2 = C2S, 3CaO + SiO2 = C3S, 3CaO + AlO3 = C3A, 4CaO + Al2O3 + Fe2O3 = C4AF, etc.).

[0007] A production system for coupling sulfur reduction of phosphogypsum and carbon reduction of phosphogypsum, the production system includes a plurality of suspension preheaters, the suspension preheaters are sequentially connected to a pre-calciner and a first gas-solid separator through pipelines, the first gas-solid separator is sequentially connected to a reduction decomposition furnace, a second gas-solid separator and a weak oxidation furnace through pipelines, the bottom discharge ports of the second gas-solid separator are respectively connected to the rotary kiln through pipelines, and the flue gas channel of the rotary kiln is connected to the reduction decomposition furnace.

[0008] Preferably, the first gas-solid separator is connected to the flue gas pipeline of the rotary kiln through a pipeline; the raw meal prepared by mixing phosphogypsum and auxiliary materials enters the suspension preheater, and a fuel coal inlet pipeline c is provided below the pre-calciner d.

[0009] Preferably, a first reducing carbon inlet and a sulfur inlet are provided outside the lower part of the furnace body of the reduction decomposer, and an air or oxygen inlet is provided for the weak oxidizer. The substances at the sulfur inlet include gaseous sulfur or liquid sulfur.

[0010] Preferably, a second reducing carbon inlet and a sulfur slag inlet are provided on the upward flue gas pipeline between the rotary kiln h and the reduction decomposer e.

[0011] More preferably, the second reducing carbon inlet is located above the sulfur slag inlet. Near the flue gas pipeline of the rotary kiln, sulfur slag is fed in, and near the reduction furnace, raw meal and reducing carbon are fed in. The main consideration is that the sulfuric acid slag is quickly gasified when heated in the upward flue gas duct. After gasification, it travels forward together with phosphogypsum, avoiding separate sublimated sulfur that does not come into contact with phosphogypsum. This not only ensures the gasification time of the sulfur slag but also ensures that the sulfur slag reacts with CaSO4 immediately after gasification and no sublimated sulfur is generated subsequently.

[0012] Preferably, a plurality of suspension preheaters are connected in series, and the gas phase of the next-stage suspension preheater is refluxed to the previous-stage suspension preheater.

[0013] The described production system is used to couple the production processes of sulfur-reducing phosphogypsum and carbon-reducing phosphogypsum. The production process includes the following steps:

[0014] S1: The raw meal enters the suspension preheater, and hot air enters the suspension preheater to dry the raw meal;

[0015] S2: Coal and hot air enter the precalciner as the heat source for raw meal drying and temperature increase;

[0016] S3: After the raw meal is dried and heated up by the suspension preheater and then enters the precalciner, it enters the first gas-solid separator for gas-solid separation. The solid enters the reduction decomposer, and the gas enters the suspension preheater;

[0017] S4: Reducing carbon enters the reduction decomposer from the first reducing carbon inlet or the second reducing carbon inlet, sulfur enters from the sulfur inlet, and sulfur slag enters from the sulfur slag inlet;

[0018] S5: The flue gas at the kiln tail of the rotary kiln enters the reduction decomposer to provide heat for the reduction reaction;

[0019] S6: Sulfur or sulfur slag or reducing carbon and phosphogypsum undergo a pre-reduction decomposition reaction in the reduction decomposer and then enter the second gas-solid separator for gas-solid separation;

[0020] S7: After the flue gas passes through the second gas-solid separator, air or oxygen is supplemented to remove unreacted sublimated sulfur and CO;

[0021] S8: The solid phase of the second gas-solid separator enters the rotary kiln; thus completing the production process of coupling sulfur-reducing phosphogypsum and carbon-reducing phosphogypsum.

[0022] Preferably, in step S4, the molar ratio of (reducing carbon + sulfur) to calcium sulfate is 0.55 - 0.75, where sulfur is the total molar amount of sulfur in sulfur slag + liquid sulfur or gaseous sulfur, and calcium sulfate refers to the calcium sulfate obtained after dehydration of phosphogypsum in raw materials. Phosphogypsum (calcium sulfate dihydrate) becomes hemihydrate gypsum at 100°C and above, and loses its crystal water to become anhydrous phosphogypsum, i.e., calcium sulfate, after 500°C. Reducing carbon refers to the carbon used in the reduction reaction. In actual production, coke fines (coal with a high carbon content, 77% - 85%) are used, and CaS04 + 2C → CaS + 2CO2.

[0023] Preferably, in step S3, the pre - calcination furnace heats the raw materials to above 900°C, and after gas - solid separation by the first gas - solid separator, the materials enter the reduction decomposition furnace.

[0024] Preferably, in step S5, the temperature of the flue gas at the tail of the rotary kiln is 800°C - 1100°C.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The purpose of the present invention is a production method that couples the sulfur - reduction technology of phosphogypsum and the carbon - reduction technology of phosphogypsum. First, it reasonably selects the corresponding reduction route according to the prices of sulfur and coal at that time, solves the economic problem, reduces the concerns of enterprises, and accelerates the enthusiasm for the comprehensive utilization construction of phosphogypsum. Second, coupling sulfur - reduction of phosphogypsum in carbon - reduction can significantly increase the SO2 gas concentration of the product, reduce the manufacturing and operating costs of sulfuric acid plants, and also reduce carbon emissions. Third, it solves the solid waste sulfur slag generated by sulfur - based sulfuric acid production, reduces the enterprise's solid waste disposal costs and increases the SO2 gas concentration of this technical route.

[0027] 2. The process of the present invention belongs to a fully - enclosed circulation process system. The discharged substances and the heat energy contained therein are all recycled and utilized by subsequent production units. No new three - wastes are generated, and solid waste phosphogypsum and solid waste sulfur slag are eliminated, which conforms to the concept of green chemistry.

[0028] 3. The production process of the present invention is simple, easy to operate, has low production costs, and good economic benefits.

[0029] 4. There are a second inlet for reducing carbon and an inlet for sulfur slag on the upward flue gas pipeline between the rotary kiln and the reduction decomposition furnace. When coming out of the flue and entering the reduction decomposition furnace, they are carried by the flue gas and are evenly distributed in the reduction decomposition furnace. Liquid sulfur is sprayed in multiple points through a ring pipe to ensure uniformity. In actual production, because it operates continuously, as long as the phosphogypsum is evenly distributed, sulfur will inevitably react with phosphogypsum during its upward movement after vaporization. The addition point of sulfur slag can also be added to the upward flue between the rotary kiln and the reduction decomposition furnace, where it is dispersed by the flue gas and is evenly distributed before entering the reduction decomposition furnace.

[0030] 5. Control the degree of the reduction reaction by controlling the molar ratio of (carbon + sulfur) to calcium sulfate at 0.55 - 0.75 to avoid the appearance of sublimated sulfur. Since a small amount of oxygen is introduced into the reduction decomposition furnace at the kiln tail, the ratio we control is 0.55 - 0.75.

[0031] 6. Since the reaction temperature required for sulfur reduction of the materials is above 750 °C, while the temperature of phosphogypsum entering the kiln is generally only over 700 °C, the flue gas at the kiln tail for sulfur reduction not only serves as heat supplement in the reduction reaction furnace but also as the heat source required to heat phosphogypsum from 25 °C to 700 °C. Therefore, the heat in the reduction decomposition furnace is insufficient, and it is necessary to heat sulfur to above 750 °C to supplement part of the heat source. This requires a dedicated sulfur vaporizer and a dedicated sulfur heat exchanger. This invention does not adopt this method. Instead, we choose to heat the raw meal containing phosphogypsum from 25 °C to above 900 °C with a calciner and then enter the reduction decomposition furnace. The flue gas at the kiln tail provides the heat for sulfur vaporization and the heat required for the endothermic reaction. After the reaction, there is still surplus heat in the flue gas, and waste heat recovery is adopted to produce steam. Moreover, since the moisture in the flue gas is separated from another flue gas and does not enter the acid-making system, the flue gas dew point is more than 70 °C lower than that of the flue gas for sulfur reduction and carbon reduction, and more heat can be recovered.

[0032] 7. Using carbon and sulfur coupled reduction of sulfur in phosphogypsum as a reducing agent, the product is SO2, which is a beneficial product for this system, reducing carbon emissions and increasing sulfuric acid production.

[0033] 8. Using carbon and sulfur coupled reduction of sulfur in phosphogypsum as a reducing agent, the product is SO2, which solves the problem of low gas concentration, can reduce the investment in sulfuric acid plants, and the sulfuric acid plants can also be equipped with a low-temperature waste heat recovery system to produce steam, saving energy consumption.

[0034] 9. The moisture content of the flue gas at the kiln tail is low, and the flue gas dew point temperature is low before entering the sulfuric acid plant, making it easier to control and protecting the pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic process flow diagram of the present invention.

[0036] Wherein: suspension preheater a, first suspension preheater a1, second suspension preheater a2, third suspension preheater a3, first gas-solid separator b, fuel coal inlet pipe c, precalciner d, reduction decomposition furnace e, weak oxidation furnace f, second gas-solid separator g, rotary kiln h, second reduction carbon inlet i, sulfur inlet j, sulfur slag inlet k, air or oxygen inlet m, first reduction carbon inlet n. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, so that the technical solutions and beneficial effects of the present invention are clearer. It can be understood that the embodiments and the drawings only provide reference and explanation, and are used to better explain the present invention rather than limit the present invention. Unless otherwise specified, the technical terms described in the present invention have the same meanings and rights as those generally understood by those skilled in the relevant art.

[0038] Example 1

[0039] A production system for coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum. The production system includes a number of suspension preheaters a, and the suspension preheater a is sequentially connected to a pre-calciner d and a first gas-solid separator b through pipelines. The first gas-solid separator b is sequentially connected to a reduction decomposition furnace e, a second gas-solid separator g, and a weak oxidation furnace f through pipelines. The bottom discharge port of the second gas-solid separator g is respectively connected to a rotary kiln h through pipelines, and the flue gas channel of the rotary kiln h is connected to the reduction decomposition furnace e.

[0040] Preferably, the first gas-solid separator b is connected to the flue gas pipeline of the rotary kiln h through a pipeline; the raw meal configured with phosphogypsum and auxiliary materials enters the suspension preheater a, and a fuel coal inlet pipeline c is provided below the pre-calciner d.

[0041] Preferably, a first reduction carbon inlet n and a sulfur inlet j are provided outside the lower part of the furnace body of the reduction decomposition furnace e, and an air or oxygen inlet m is provided in the weak oxidation furnace f. The substances at the sulfur inlet j include gaseous sulfur or liquid sulfur.

[0042] Preferably, a second reduction carbon inlet i and a sulfur slag inlet k are provided on the upward flue gas pipeline between the rotary kiln h and the reduction decomposition furnace e.

[0043] Further preferably, the second reduction carbon inlet i is located above the sulfur slag inlet k. Near the flue gas pipeline of the rotary kiln is the inlet of sulfur slag, and near the reduction furnace is the inlet of raw meal and reduction carbon. The main consideration is that the sulfuric acid slag is heated and quickly gasified in the upward flue gas duct. After gasification, it meets the phosphogypsum and moves forward together, avoiding the situation where there is separate sublimated sulfur that does not contact the phosphogypsum. This not only ensures the gasification time of the sulfur slag (for example, the annual addition amount of sulfur slag is 10,000 tons, the actual addition amount is 1.3 t / h, and the flue gas is 70,000 m³ / h, and the flue gas temperature is about 1000 °C, and sulfur will quickly gasify), but also ensures that the sulfur slag reacts with CaSO4 immediately after gasification and no sublimated sulfur will be generated subsequently.

[0044] Preferably, the suspension preheater a has 3 connected in series: the first suspension preheater a1, the second suspension preheater a2, and the third suspension preheater a3. The gas phase of the third suspension preheater a3 flows back to the second suspension preheater a2, and the gas phase of the second suspension preheater a2 flows back to the first suspension preheater a1.

[0045] Example 2

[0046] The production system described in Example 1 is used for the production process of coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum. The production process includes the following steps:

[0047] S1: The raw meal enters the suspension preheater a, and hot air enters the suspension preheater a to dry the raw meal;

[0048] S2: Coal and hot air enter the pre-calciner d as the heat source for drying and heating up the raw meal;

[0049] S3: After the raw meal is dried and heated up by the suspension preheater a and then enters the pre-calciner d, it then enters the first gas-solid separator b for gas-solid separation. The solid enters the reduction decomposition furnace e, and the gas enters the suspension preheater a;

[0050] S4: Reducing carbon enters the reduction decomposition furnace e from the first reducing carbon inlet n or the second reducing carbon inlet i, sulfur in gaseous or liquid form enters from the gaseous or liquid sulfur inlet j of sulfur, and sulfur slag enters from the sulfur slag inlet k;

[0051] S5: The tail gas of the rotary kiln h enters the reduction decomposition furnace e to provide heat for the reduction reaction;

[0052] S6: Sulfur or sulfur slag or gaseous sulfur or liquid sulfur or sulfur slag or reducing carbon and phosphogypsum in the reduction decomposition furnace e undergo a pre-reduction decomposition reaction and then enter the second gas-solid separator g for gas-solid separation;

[0053] S7: The flue gas passes through the second gas-solid separator g to supplement oxygen and remove unreacted sublimated sulfur and CO;

[0054] S8: The solid phase of the second gas-solid separator g enters the rotary kiln; thus completing the production process of coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum.

[0055] Preferably, in step S4, the molar ratio of (reducing carbon + sulfur) to calcium sulfate is 0.6, where sulfur is the total molar amount of sulfur in sulfur slag + liquid sulfur or gaseous sulfur, and calcium sulfate refers to the calcium sulfate obtained after dehydration of phosphogypsum in the raw meal. Phosphogypsum (calcium sulfate dihydrate) becomes hemihydrate gypsum at 100°C and above, and loses its crystal water to become anhydrous phosphogypsum, i.e., calcium sulfate, after 500°C. Reducing carbon refers to the carbon used for the reduction reaction. In actual production, coke fines (simply understood as coal with a high carbon content, 77% - 85%) are used, CaS04 + 2C → CaS + 2CO2.

[0056] Preferably, in step S3, the pre-calciner d heats up the raw meal to above 950°C, and after gas-solid separation by the first gas-solid separator b, it enters the reduction decomposition furnace e.

[0057] Preferably, in the step S5, the temperature of the flue gas at the tail of the rotary kiln h is 1000 °C.

[0058] During the experiment, on average, 79 t / h of phosphogypsum after water washing, flotation and pressure filtration (containing 15% free water before entering the phosphogypsum dryer), 4.8 t / h of clay, and 2.9 t / h of sandstone were used. 34.7 t / h of 98% sulfuric acid was produced, the consumption of physical coal was 13.32 t / h, the consumption of reducing coal (coke containing 77%-82% carbon) was 3.27 t / h, and the consumption of sulfur slag (sulfur content close to 70%) was 0.96 t / h. The comprehensive energy consumption of the conversion system was 329 kg of standard coal per ton of sulfuric acid, including 312.78 kg of standard coal per ton of sulfuric acid for fuel coal, 73.47 kg of standard coal per ton of sulfuric acid for reducing coal, 19 kg of sulfur slag per ton of sulfuric acid, the SO2 gas concentration at the outlet of the weak oxidation furnace was 14.05%, the SO2 gas concentration before the converter was 8.84%, the by-product steam was 0.85 t / t of sulfuric acid, the waste heat power generation was 1350 KWH, and the decomposition rate of phosphogypsum was 98.3%.

[0059] Example 3

[0060] Example 3-1: Based on Example 2, the difference is that in the step S4, the molar ratio of (reducing carbon + sulfur) to calcium sulfate is 0.7, where sulfur is the total molar amount of sulfur in sulfur slag + liquid sulfur or gaseous sulfur, and calcium sulfate refers to the raw material phosphogypsum, and the calcium sulfate obtained after mixing auxiliary materials and calcining into cement clinker.

[0061] During the experiment, the raw materials and the amount of acid production were basically the same as in Experiment 2. Due to the increase in the molar ratio, the usage of reducing carbon and fuel coal changed slightly. On average, the consumption of reducing coal (coke containing 77%-82% carbon) was 3.81 / h, and the consumption of physical coal was 12.81 t / h. The comprehensive energy consumption of the conversion system was 329 kg of standard coal per ton of sulfuric acid, including 300.54 kg of standard coal per ton of sulfuric acid for fuel coal, 85.71 kg of standard coal per ton of sulfuric acid for reducing coal, 19 kg of sulfur slag per ton of sulfuric acid, the SO2 gas concentration at the outlet of the weak oxidation furnace was 14.08%, the SO2 gas concentration before the converter was 8.85%, the by-product steam was 0.9 t / t of sulfuric acid, the waste heat power generation was 1355 KWH, and the decomposition rate of phosphogypsum was 98.3%. Compared with Example 2, the increase in the (C+S) / S ratio did not result in an obvious increase in the decomposition rate of phosphogypsum. The SO3 content in the clinker decreased, but the CaS content increased, indicating that the proportion of CaS generated in the first reduction reaction exceeded 1 / 4 of the total proportion of CaSO4, and the dosage of the reducing agent was already on the high side. In terms of economic cost, the arrival price of steam coal is 1200 yuan / ton, and the arrival price of reducing carbon is 2700 yuan / ton. The cost increase of adopting Example 3-1 is (0.08571 - 0.07347) / 0.78 * 34.7 * 310 * 24 * 2700 - (0.31278 - 0.30054) * 7 / 5.7 * 1200 * 34.7 * 310 * 24 * 1200 = 6.2816 million yuan / year.

[0062] Considering the finished product quality and economic benefits comprehensively, it is important to select an appropriate value for the molar ratio of (reducing carbon + sulfur) to calcium sulfate.

[0063] Example 3-2: Based on Example 2, the difference is that in step S4, the molar ratio of (reducing carbon + sulfur) to calcium sulfate is 0.5, where sulfur is the total molar amount of sulfur in sulfur slag + liquid sulfur or gaseous sulfur, and calcium sulfate refers to the raw material phosphogypsum, which is calcined into cement clinker after adding auxiliary materials to obtain calcium sulfate.

[0064] The SO3 content in the clinker is 3.5%, which is greater than the 1.5% allowed by the national standard "GB / T 21372-2008", and the quality of the clinker is unqualified. Although the theoretical C / S ratio of 0.5 can complete the reaction, in fact, due to the residual oxygen in the reduction furnace and other side reactions consuming the reducing carbon, the decomposition of phosphogypsum is incomplete and the SO3 exceeds the standard.

[0065] Example 3-3: Based on Example 2, the difference is that in step S4, the molar ratio of (reducing carbon + sulfur) to calcium sulfate is 0.8, where sulfur is the total molar amount of sulfur in sulfur slag + liquid sulfur or gaseous sulfur, and calcium sulfate refers to the raw material phosphogypsum, which is calcined into cement clinker after adding auxiliary materials to obtain calcium sulfate.

[0066] The CaS content in the clinker is 4.8%. First, the decomposition rate of phosphogypsum is too low, and 4.8% of the S is not decomposed and utilized in CaS. Second, it is greater than the allowed 2%, and the quality of the clinker is unqualified. CaS releases H2S during the cement hydration stage to produce Ca(OH)2. The quality is already unqualified, and economically, it is the same as 3-1. The higher the molar ratio of (reducing carbon + sulfur) to calcium sulfate, the less cost-effective it is.

[0067] Example 4

[0068] Example 4-1: Based on Example 2, the difference is that in step S4, the pre-calcination furnace d heats the phosphogypsum to 950 °C.

[0069] During the experiment, on average, 79 t / h of phosphogypsum (containing 15% free water before entering the phosphogypsum dryer), 4.8 t / h of clay, and 2.9 t / h of sandstone were used in the washing, flotation, and pressure filtration process. 34.7 t / h of 98% sulfuric acid was produced, with a physical coal consumption of 13.32 t / h, a reduction coal (coke containing 77%-82% carbon) consumption of 3.27 t / h, and a sulfur slag (sulfur content close to 70%) consumption of 0.96 t / h. The comprehensive energy consumption of the conversion system was 329 kg of standard coal per ton of sulfuric acid. Among them, the fuel coal consumption was 312.78 kg of standard coal per ton of sulfuric acid, the reduction coal consumption was 73.47 kg of standard coal per ton of sulfuric acid, the sulfur slag consumption was 19 kg per ton of sulfuric acid, the SO2 gas concentration at the outlet of the weak oxidation furnace was 14.00%, the SO2 gas concentration before the converter was 8.8%, the by-product steam was 0.83 t per ton of sulfuric acid, the waste heat power generation was 1300 KWH, and the decomposition rate of phosphogypsum was 98.3%. The low temperature of the pre-calcination furnace led to the need for more heat in the rotary kiln. The rotary kiln needed to consume more coal and air. Although the total heat remained unchanged, the decomposition rate and total coal consumption were not affected, but the SO2 gas concentration and the amount of by-product steam decreased slightly, making the overall energy consumption less cost-effective.

[0070] Example 4-2: Based on Example 2, the difference is that in step S4, the pre-calcination furnace d heats the phosphogypsum to 700 °C. Previously, the temperature of the kiln gas discharged from the pre-calcination kiln was high, and the excess heat energy (about 480 °C at the outlet of the previous suspension preheater) could be used to dry the phosphogypsum. Now the temperature is low (the temperature corresponding to 700 °C at the outlet of the suspension preheater is 240-300 °C), so an additional independent heat source for supplementary coal combustion needs to be added to dry the phosphogypsum. The coal consumption of the pre-calcination kiln decreases, and the temperature of the raw material entering the rotary kiln is low. The rotary kiln needs to use more coal, resulting in a significant decrease in the SO2 gas concentration, a reduction in the output of medium-pressure steam and low-pressure steam, and an increase in the comprehensive energy consumption of the system. Moreover, too much heat needs to be transferred through the kiln, resulting in an inability to increase the phosphogypsum treatment production capacity.

[0071] Example 6

[0072] Based on Example 2, in the process system, the reduction carbon inlet i and the connection between the first gas-solid separator b and the flue gas pipeline of the rotary kiln h are located below the sulfur slag inlet k.

[0073] When the addition point is above, the second gas-solid separator scales quickly and there is sulfur adhesion. It is suspected that when the sulfur state changes and touches the phosphogypsum, the viscosity increases during the liquefaction process of solid sulfur, and the surrounding phosphogypsum is adhered and agglomerated. Later, the solid sulfur slag was changed to be sprayed from below, and the liquid sulfur injection port was changed to multi-point injection.

[0074] Comparative Example 1:

[0075] Traditional carbon reduction process mode:

[0076] S1: The dried phosphogypsum, clay, and sandstone are proportionally configured into raw materials and enter the raw material homogenization silo;

[0077] S2: The reduced carbon after drying and crushing by the vertical mill is added to the raw material homogenizing silo in proportion, and the homogenized raw material enters the suspension preheater a through the belt.

[0078] S3: The flue gas at the kiln tail of the rotary kiln h is used as the heat source for raw material drying and temperature increase.

[0079] S4: After drying and increasing the temperature of the raw material, the flue gas enters the sulfuric acid production section from flue gas.

[0080] S5: After drying and increasing the temperature by the suspension preheater a, the raw material enters the rotary kiln h.

[0081] S6: After completing the three stages of preheating, reduction decomposition, and calcination mineralization in the rotary kiln, the raw material enters the grate cooler for cooling.

[0082] During the experiment, on average, 79 t / h of phosphogypsum washed, floated, and filtered (containing 15% free water before entering the phosphogypsum dryer), 4.8 t / h of clay, and 2.9 t / h of sandstone were used, 34.6 t / h of 98% sulfuric acid was produced, 16.36 t / h of physical coal was consumed, and 3.64 t / h of reduced coal (coke containing 77%-82% carbon) was consumed. The comprehensive energy consumption of this system is 492.8 kg of standard coal per ton of sulfuric acid, including 385 kg of standard coal per ton of sulfuric acid for fuel coal consumption, 82 kg of standard coal per ton of sulfuric acid for reduced coal consumption, the SO2 gas concentration at the outlet of the suspension preheater is 9.47%, the SO2 gas concentration before the converter is 6.42%, there is no by-product steam, no waste heat power generation, the power consumption for production is 210 KWH per ton of sulfuric acid, and the decomposition rate of phosphogypsum is 98%.

[0083] Example 7

[0084] 79 t / h of phosphogypsum (15% free water) enters the phosphogypsum drying section from the homogenization silo via a belt, and is dried to 120 °C - 130 °C by an independent heat source calciner, removing the free water and converting part of CaSO4·2H2O into CaSO4·1 / 2H2O. The dried phosphogypsum enters the hemihydrate gypsum homogenization silo for homogenization. The auxiliary materials enter the auxiliary material homogenization silo after drying and crushing, and the raw coal and reducing coal enter the fuel coal bin and reducing coal bin after being dried by a vertical mill. The auxiliary materials and hemihydrate gypsum are discharged onto the belt, proportionally configured, and then enter the raw meal homogenization silo. The raw meal coming out after homogenization at 34 °C and the reducing coal at 70 °C are proportioned on the belt according to the C / S ratio of 0.65 - 0.75 and then sent to the suspension preheater by the belt. The raw meal enters the kiln tail of the rotary kiln via the suspension preheaters a1, a2, and a3, and the temperature in the suspension preheater rises from 35 °C to 780 °C. In the preheating section and decomposition section of the rotary kiln, the temperature first rises from 780 °C to 1170 °C, and the material undergoes a reduction reaction to generate CaO and enters the firing section, i.e., 2C + CaSO4 → CaS + 2CO2, CaS + 3CaSO4 → 4CaO + 4SO2. In the firing section, the solid phase temperature rises from 1170 °C to 1450 °C to undergo a mineralization reaction to generate C3S, C2S, C3A, and C4AF, i.e., 2CaO + SiO2 = C2S, 3CaO + SiO2 = C3S, 3CaO + Al2O3 = C3A, 4CaO + Al2O3 + Fe2O3 = C4AF. Then it exits the kiln head of the rotary kiln, is cooled by a grate cooler, and enters the clinker silo. The gas phase enters the suspension preheater from 1600 °C at the kiln head of the rotary kiln to 1010 °C at the kiln tail of the rotary kiln, exchanges heat with the raw meal in the suspension preheater, and then enters the gas-solid separator through the fuel coal into pipeline c. When exiting the gas-solid separator, the temperature is 326 °C and the SO2 gas concentration is 9.47%. The gas phase enters the conversion section of the sulfuric acid workshop after passing through a bag filter, a primary dynamic wave, a packed tower, two-stage electric demisters, and a drying tower. After oxygen is added according to the O / S ratio of 1:1, the SO2 gas concentration is 6.42%. In the conversion section, it can barely operate without turning on the electric furnace and cannot produce steam. Once the decomposition condition in the kiln is abnormal and the SO2 gas concentration drops, the conversion heat fluctuates and the electric furnace has to be prepared to be turned on. During normal operation, the average amount of phosphogypsum processed is 79 t / h, the sulfuric acid produced is 35 t / h, the reducing coal (coke, containing 77% - 82% residual carbon) is 3.86 t / h, and the total standard coal equivalent of the fuel coal and calcining coal is 13.5 t / h.

[0085] Example 8

[0086] 79 t / h of phosphogypsum (15% free water) enters the phosphogypsum drying section from the homogenization silo via a belt, and is dried from 510 °C of the waste heat of the pre-calciner flue gas to 120 °C - 150 °C, removing the free water and partially converting CaSO4·2H2O into CaSO4·1 / 2H2O. The flue gas after heat exchange at 150 °C enters the tail washing section to treat the dust and SO2 carried in the flue gas. The dried phosphogypsum enters the hemihydrate gypsum homogenization silo for homogenization. The auxiliary materials enter the auxiliary material homogenization silo after drying and crushing, and the raw coal and reducing coal enter the fuel coal bin and reducing coal bin after being dried by a vertical mill. The auxiliary materials (3.01 t / h of clay and 5.31 t / h of sandstone after drying), and the hemihydrate gypsum are discharged onto the belt, proportionally configured and then enter the raw material homogenization silo. The raw material coming out of the homogenization at 34 °C is sent to the suspension preheater by a belt. The raw material passes through the suspension preheaters a1, a2, a3, the pre-calciner d, and the gas-solid separator b and enters the reduction decomposition furnace, and the temperature rises from 34 °C to 920 °C - 970 °C. 70 °C reducing coal is added to the solid-phase pipeline from b to the reduction decomposition furnace. After being proportioned according to the C / S ratio of 0.65 - 0.75, it follows the flue gas rising in the rotary kiln and enters the reduction decomposition furnace, and part of the reduction reaction is completed in the reduction decomposition furnace, that is, 2C + CaSO4 → CaS + 2CO2. Then it enters the gas-solid separator g, and the separated solid phase enters the tail of the rotary kiln. In the decomposition section of the rotary kiln, the temperature first rises from 970 °C to 1170 °C, and the materials that are not completely reacted in the reduction furnace continue to undergo reduction reactions to generate CaO and enter the firing section, that is, 2C + CaSO4 → CaS + 2CO2, CaS + 3CaSO4 → 4CaO + 4SO2. In the firing section, the solid-phase temperature rises from 1170 °C to 1450 °C to undergo mineralization reactions to generate C3S, C2S, C3A, and C4AF, that is, 2CaO + SiO2 = C2S, 3CaO + SiO2 = C3S, 3CaO + Al2O3 = C3A, 4CaO + Al2O3 + Fe2O3 = C4AF. Then it exits the head of the rotary kiln, is cooled by a grate cooler and enters the clinker silo. The gas phase of the rotary kiln enters the pre-reduction furnace from 1600 °C at the kiln head to 1010 °C at the tail of the rotary kiln to provide heat for the reduction reaction. Then it is separated by a gas-solid separator and enters the weak oxidation furnace to supply hot air to react with the participating CO and sublimated sulfur. Then it undergoes heat recovery through air heat exchange and boiler heat exchange and then bag dust removal. The temperature after exiting the bag filter is 250 °C and the SO2 gas concentration is 12.20%. After passing through the first-stage dynamic wave, packed tower, two-stage electric demister, and drying tower, it enters the conversion section of the sulfuric acid workshop. After oxygen is supplied according to the O / S ratio of 1:1, the SO2 gas concentration is 8.16%. The conversion section can be equipped with a low-temperature waste heat recovery system to by-product low-pressure steam. During startup, the average treatment of phosphogypsum is 79 t / h, the production of sulfuric acid is 35 t / h, the reducing coal (coke, containing 77% - 82% residual carbon) is 3.2 t / h, the total of fuel coal and calcining coal is equivalent to 12 t / h of standard coal, and the by-product of 0.7 MPa steam is 30 t / h.

[0087] Example 9

[0088] 79 t / h of phosphogypsum (15% free water) enters the phosphogypsum drying section from the homogenization silo via a belt, and is dried from 510 °C by the waste heat of the pre-calciner flue gas to 120 °C - 150 °C, removing free water and partially converting CaSO4·2H2O to CaSO4·1 / 2H2O. The flue gas after heat exchange enters the tail washing section at 150 °C to treat the dust and SO2 entrained in the flue gas. The dried phosphogypsum enters the hemihydrate gypsum homogenization silo for homogenization. The auxiliary materials enter the auxiliary material homogenization silo after drying and crushing, and the raw coal and reducing coal enter the fuel coal bin and reducing coal bin after being dried by a vertical mill. The auxiliary materials (2.76 t / h of clay and 4.38 t / h of sandstone after drying) and hemihydrate gypsum are discharged onto the belt and proportioned before entering the raw material homogenization silo. The raw material coming out of the homogenization is at 34 °C and is sent to the suspension preheater by a belt. The raw material passes through the suspension preheaters a1, a2, a3, the pre-calciner d, and the gas-solid separator b and enters the reduction decomposition furnace, where the temperature rises from 34 °C to 920 °C - 970 °C. 70 °C reducing coal is added to the solid-phase pipeline from b to the reduction decomposition furnace, and 0.7 t / h of sulfur slag (69.3% sulfur, 5.63% sulfate radical, 8.31% calcium oxide, 2.37% silicon dioxide, etc.) is added to the gas-phase flue duct from the rotary kiln to the reduction decomposition furnace, and is proportioned according to the (C / S + S / S) ratio of 0.65 - 0.75. Then the flue gas following the upward movement of the rotary kiln enters the reduction decomposition furnace, and partial reduction reactions are completed in the reduction decomposition furnace, i.e., 2C + CaSO4 → CaS + 2CO2, 2S + CaSO4 → CaS + 2SO2. Then it enters the gas-solid separator g, and the separated solid phase enters the tail of the rotary kiln. In the decomposition section of the rotary kiln, the temperature first rises from 970 °C to 1170 °C, and the materials that are not completely reacted in the reduction furnace continue to undergo reduction reactions to generate CaO and enter the firing section, i.e., 2C + CaSO4 → CaS + CO2, CaS + 3CaSO4 → 4CaO + 4SO2. In the firing section, the solid-phase temperature rises from 1170 °C to 1450 °C to undergo mineralization reactions to generate C3S, C2S, C3A, and C4AF, i.e., 2CaO + SiO2 = C2S, 3CaO + SiO2 = C3S, 3CaO + Al2O3 = C3A, 4CaO + Al2O3 + Fe2O3 = C4AF. Then it exits the head of the rotary kiln, is cooled by a grate cooler, and enters the clinker silo. The gas phase of the rotary kiln enters the pre-reduction furnace from 1600 °C at the kiln head to 1010 °C at the tail of the rotary kiln to provide heat for the reduction reaction. Then it is separated by the gas-solid separator and enters the weak oxidation furnace to supply hot air to react with the participating CO and sublimated sulfur. Then, after heat recovery through air heat exchange and boiler heat exchange, it undergoes bag dust removal. The temperature after exiting the bag dust collector is 250 °C and the SO2 gas concentration is 14.06%. After passing through the first-stage dynamic wave, packed tower, two-stage electric demister, and drying tower, it enters the conversion section of the sulfuric acid workshop. After oxygen is supplied according to the O / S ratio of 1:1, the SO2 gas concentration is 8.84%. The conversion section can be equipped with a low-temperature waste heat recovery system to by-product low-pressure steam.During operation, the average amount of phosphogypsum processed is 79 t / h, sulfuric acid produced is 36.48 t / h, reduced coal (coke, with residual carbon of 77% - 82%) is 3 t / h, digestion of sulfuric acid residue is 0.7 t / h, the total standard coal equivalent of fuel coal and calcined coal is 12 t / h, and by-product steam of 0.7 MPa is 32 t / h.

[0089] Example 10

[0090] 79 t / h of phosphogypsum (15% free water) enters the phosphogypsum drying section from the homogenization silo via a belt, and is dried from 510 °C of the waste heat of the pre-calciner flue gas to 120 °C - 150 °C, removing the free water and converting part of CaSO4·2H2O into CaSO4·1 / 2H2O. The flue gas after heat exchange at 150 °C enters the tail washing section to treat the dust and SO2 carried in the flue gas. The dried phosphogypsum enters the hemihydrate gypsum homogenization silo for homogenization. The auxiliary materials enter the auxiliary material homogenization silo after drying and crushing, and the raw coal and reducing coal enter the fuel coal bunker and reducing coal bunker after being dried by a vertical mill. The auxiliary materials (2.76 t / h of clay and 4.38 t / h of sandstone after drying), and the hemihydrate gypsum are discharged onto the belt, proportionally configured, and then enter the raw meal homogenization silo. The raw meal coming out after homogenization at 34 °C is sent to the suspension preheater by a belt. The raw meal passes through the suspension preheaters a1, a2, a3, the pre-calciner d, and the gas-solid separator b and enters the reduction decomposition furnace, where the temperature rises from 34 °C to 920 °C - 970 °C. 70 °C reducing coal is added to the solid-phase pipeline from b to the reduction decomposition furnace, and 0.5 t / h of liquid sulfur at 125 °C is sprayed into the reduction decomposition furnace at multiple points, and is proportioned according to the (C / S + S / S) ratio of 0.65 - 0.75. Then, part of the reduction reaction is completed in the reduction decomposition furnace, that is, 2C + CaSO4 → CaS + 2CO2, 2S + CaSO4 → CaS + 2SO2. Then it enters the gas-solid separator g, and after separation, the solid phase enters the tail of the rotary kiln. In the decomposition section of the rotary kiln, the temperature first rises from 970 °C to 1170 °C, and the materials that are not completely reacted in the reduction furnace continue to undergo reduction reactions to generate CaO and enter the firing section, that is, 2C + CaSO4 → CaS + CO2, CaS + 3CaSO4 → 4CaO + 4SO2. In the firing section, the solid-phase temperature rises from 1170 °C to 1450 °C to undergo mineralization reactions to generate C3S, C2S, C3A, and C4AF, that is, 2CaO + SiO2 = C2S, 3CaO + SiO2 = C3S, 3CaO + Al2O3 = C3A, 4CaO + Al2O3 + Fe2O3 = C4AF. Then it exits the head of the rotary kiln, is cooled by a grate cooler, and enters the clinker silo. The gas phase of the rotary kiln enters the pre-reduction furnace from 1600 °C at the kiln head to 1010 °C at the tail of the rotary kiln to provide heat for the reduction reaction. Then, after being separated by the gas-solid separator, it enters the weak oxidation furnace to supply hot air to react with the participating CO and sublimated sulfur. Then, after heat recovery through air heat exchange and boiler heat exchange, it undergoes bag dust removal. The temperature after exiting the bag filter is 250 °C, and the SO2 gas concentration is 14.06%. After passing through the first-stage dynamic wave, packing tower, two-stage electric demister, and drying tower, it enters the conversion section of the sulfuric acid workshop. After oxygen is supplied according to the O / S ratio of 1:1, the SO2 gas concentration is 8.84%. The conversion section can be equipped with a low-temperature waste heat recovery system to by-product low-pressure steam. During startup, the average treatment of phosphogypsum is 79 t / h, the production of sulfuric acid is 36.48 t / h, the reducing coal (coke, containing 77% - 82% residual carbon) is 3 t / h, the liquid sulfur is 0.5 t / h, the total of fuel coal and calcining coal is equivalent to 12 t / h of standard coal, and the by-product 0.7 MPa steam is 32 t / h.

[0091] The above embodiments are only the preferred technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. The embodiments in this application and the features in the embodiments can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. Any changes, substitutions or improvements that can be easily conceived by any person skilled in the art within the technical scope disclosed by the present invention are also covered by the protection scope of the present invention.

Claims

1. A production system for coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum, characterized in that, The production system includes several suspension preheaters (a). The suspension preheaters (a) are sequentially connected to a precalciner (d) and a first gas-solid separator (b) through pipelines. The first gas-solid separator (b) is sequentially connected to a reduction decomposition furnace (e), a second gas-solid separator (g), and a weak oxidation furnace (f) through pipelines. The bottom discharge port of the second gas-solid separator (g) is connected to a rotary kiln (h) through a pipeline. The flue gas channel of the rotary kiln (h) is connected to the reduction decomposition furnace (e). The first gas-solid separator (b) is connected to the flue gas pipeline of the rotary kiln (h) through a pipeline. The raw meal prepared by mixing phosphogypsum and auxiliary materials enters the suspension preheater (a). A fuel coal inlet pipeline (c) is provided below the precalciner (d). An inlet (n) for the first reduction carbon and a sulfur inlet (j) are provided outside the lower part of the furnace body of the reduction decomposition furnace (e). The weak oxidation furnace (f) is provided with an air or oxygen inlet (m). The substance at the sulfur inlet (j) includes gaseous sulfur or liquid sulfur. A second inlet (i) for reduction carbon and a sulfur slag inlet (k) are provided on the upward flue gas pipeline between the rotary kiln (h) and the reduction decomposition furnace (e). The production process of the production system for coupling sulfur reduction of phosphogypsum and carbon reduction of phosphogypsum includes the following steps: S1: The raw meal enters the suspension preheater (a), and hot air enters the suspension preheater (a) to dry the raw meal. S2: Coal and hot air enter the precalciner (d) as the heat source for drying and heating the raw meal. S3: After the raw meal is dried and heated in the suspension preheater (a) and then enters the precalciner (d), it then enters the first gas-solid separator (b) for gas-solid separation. The solid enters the reduction decomposition furnace (e), and the gas enters the suspension preheater (a). S4: Reduction carbon enters the reduction decomposition furnace (e) from the first inlet (n) for reduction carbon or the second inlet (i) for reduction carbon, gaseous sulfur or liquid sulfur enters from the sulfur inlet (j), and sulfur slag enters from the sulfur slag inlet (k). The molar ratio of (reduction carbon + sulfur) to calcium sulfate is 0.55 - 0.75, where sulfur is the total molar amount of sulfur in sulfur slag + liquid sulfur or gaseous sulfur, and calcium sulfate refers to the calcium sulfate obtained after dehydration of phosphogypsum in the raw meal. S5: The flue gas at the kiln tail of the rotary kiln (h) enters the reduction decomposition furnace (e) to provide heat for the reduction reaction. S6: Gaseous sulfur or liquid sulfur or sulfur slag or reduction carbon and phosphogypsum undergo a pre-reduction decomposition reaction in the reduction decomposition furnace (e) and then enter the second gas-solid separator (g) for gas-solid separation. S7: After the flue gas passes through the second gas-solid separator (g), oxygen is supplemented to remove unreacted sublimated sulfur and CO. S8: The solid phase of the second gas-solid separator (g) enters the rotary kiln, completing the production process of coupling sulfur reduction of phosphogypsum and carbon reduction of phosphogypsum.

2. The production system for coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum according to claim 1, wherein The second inlet (i) for reduction carbon is located above the sulfur slag inlet (k).

3. The production system for coupling sulfur reduction of phosphogypsum and carbon reduction of phosphogypsum according to claim 1, characterized in that, Several suspension preheaters (a) are connected in series, and the gas phase of the lower-stage suspension preheater flows back to the upper-stage suspension preheater.

4. The production system for coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum according to claim 1, wherein: In step S3, the precalciner (d) heats the raw meal to above 900 °C, and after gas-solid separation by the first gas-solid separator (b), it enters the reduction decomposition furnace (e).

5. The production system for coupling sulfur-reduced phosphogypsum and carbon-reduced phosphogypsum according to claim 1, wherein: In the step S5, the temperature of the flue gas at the tail of the rotary kiln (h) is 800°C - 1100°C.

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