阅读说明：本技术 一种以脱硫石膏制备硫酸铵和碳酸钙的方法 (Method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum ) 是由 陈锡炯 项飞鹏 刘毅 刘春红 杜凯敏 王伟健 于 2019-11-05 设计创作，主要内容包括：本发明涉及一种以脱硫石膏制备硫酸铵和碳酸钙的方法,以固体碳酸氢铵和高浓度脱硫石膏浆液作为反应物料,经过两步反应可以得到碳酸钙含量较高的固相产物以及硫酸铵晶体。本发明的有益效果是：本发明将电厂脱硫石膏直接转化为含量93％以上的碳酸钙,可回收用于电厂脱硫使用,从而实现钙元素的循环利用,另一产物硫酸铵可以作为农业化肥外销,适合电厂脱硫石膏的大规模处理,有效解决了火电厂脱硫石膏难以回收利用的问题。对比其他类似原理制备方法,本发明的反应物料简化,只有两种反应物；工艺参数温和,常压中低温反应；反应时间较短,有较优的生产效率。(The invention relates to a method for preparing ammonium sulfate and calcium carbonate by using desulfurized gypsum, which takes solid ammonium bicarbonate and high-concentration desulfurized gypsum slurry as reaction materials and can obtain a solid-phase product with higher calcium carbonate content and ammonium sulfate crystals through two-step reaction. The invention has the beneficial effects that: the method directly converts the power plant desulfurization gypsum into calcium carbonate with the content of more than 93 percent, and can be recycled for power plant desulfurization, so that the recycling of calcium element is realized, the other product ammonium sulfate can be used as an agricultural chemical fertilizer for export sales, the method is suitable for large-scale treatment of the power plant desulfurization gypsum, and the problem that the desulfurization gypsum of a thermal power plant is difficult to recycle is effectively solved. Compared with other preparation methods based on similar principles, the method has the advantages that the reaction materials are simplified, and only two reactants are needed; the technological parameters are mild, and the reaction is carried out at normal pressure and low temperature; the reaction time is short, and the production efficiency is better.)

1. The method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum is characterized by comprising the following steps:

step 1, drying wet desulfurized gypsum in hot air at 40-80 ℃;

step 2, treating the dried gypsum by a grinder, and controlling the particle size of the dried gypsum to be 100-500 meshes;

step 3, preparing the dry gypsum and water into suspension slurry with the gypsum mass fraction of 40-70% under the stirring state, and heating the suspension slurry to 30-60 ℃ in a water bath or oil bath environment;

step 4, adding solid ammonium bicarbonate with a certain proportion into the gypsum slurry for multiple times, reacting under the stirring condition, and heating in a water bath or oil bath environment at the temperature of 30-60 ℃ to serve as a first-stage reaction;

step 5, filtering the mixed solution after reaction by a centrifugal machine or vacuumizing to separate a solid product taking calcium carbonate as a main component and a liquid taking ammonium sulfate as a main component to serve as a first-stage reaction product;

step 6, preparing a solid product which takes calcium carbonate as a main component in the first-stage reaction product into a suspension slurry with the solid mass fraction of 30-60% again, and adding solid ammonium bicarbonate to react to obtain a second-stage reaction;

step 7, filtering the second-stage reaction mixed solution by a centrifuge or vacuum to separate a solid product taking calcium carbonate as a main component and a liquid taking ammonium sulfate as a main component, wherein the liquid in the second-stage reaction product is merged into the liquid in the first-stage reaction product to be used as an ammonium sulfate liquid;

step 8, evaporating and crystallizing ammonium sulfate liquid by taking power plant flue gas or low-quality steam as a heat source to obtain ammonium sulfate crystals;

and 9, drying the second-stage reaction product solid at 100-110 ℃ for later use or directly putting the second-stage reaction product solid as limestone into a power plant desulfurization system for use.

2. The method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum according to claim 1, wherein: step 1, the moisture content of the wet desulfurization gypsum is not more than 30 percent; the main component CaSO of the desulfurized gypsum is dehumidified in a dry state₄·2H₂The other solids content than 0 is less than 15%.

3. The method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum according to claim 1, wherein: dividing the solid ammonium bicarbonate into 10-15 parts by equivalent, and sequentially adding gypsum slurry; the mixing proportion condition of the solid ammonium bicarbonate and the gypsum slurry is that the reactant CaSO₄·2H₂0 and NH₄HCO₃The molar ratio of the ammonium bicarbonate to the gypsum slurry is 0.35-0.45, and the reaction time of the solid ammonium bicarbonate and the gypsum slurry under the stirring condition is 40-80 min; the stirring speed during the reaction is 400-700 r/min; adding the mixture for one section every 3min, and reacting for about 5-20 min after the last addition.

4. The method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum according to claim 1, wherein the conditions of the two-stage reaction in step 6 are as follows: maintenance of the reactant CaSO₄·2H₂0 and NH₄HCO₃The overall molar ratio of (a) to (b) is 0.35-0.45; the stirring speed during the reaction is 400-700 r/min; the reaction temperature is 30-60 ℃, the reaction time is 40-80 min, and the heating is carried out in a water bath or oil bath environment; the second-stage reaction comprises the following specific steps: feeding solid ammonium bicarbonate once or in multiple times according to the mass of the solid ammonium bicarbonate30 to 60 percent of suspension slurry, the reaction temperature is 40 to 60 ℃, and the suspension slurry is heated by a water bath or an oil bath.

5. The method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum according to claim 1, wherein CaSO is contained in the reaction system of the two-stage reaction in step 6₄·2H₂0 and NH₄HCO₃The overall molar ratio of (A) is 0.35 to 0.45.

6. The method for preparing ammonium sulfate and calcium carbonate from desulfurized gypsum according to claim 1, wherein the ammonium sulfate crystals obtained in step 8 are separated by a centrifuge after evaporation crystallization and dried by hot air at 100-110 ℃.

Technical Field

The invention relates to a resource utilization technology of gypsum which is a desulfurization byproduct of a thermal power plant, in particular to a method for preparing ammonium sulfate and calcium carbonate by using desulfurization gypsum.

Background

Thermal power is still the main power generation form in China, and by the end of 2017, the thermal power utilization ratio in the power generation utilization capacity in China reaches 62.2%; in order to meet the national emission standard, the tail end of the common boiler of the thermal power generating unit adopts a flue gas desulfurization process to reduce the main pollutant SO₂The discharge amount of (c); the limestone wet process is the most mature and widely used flue gas desulfurization technology at present, a desulfurization byproduct, namely gypsum, is generated by the process, and the power plant desulfurization gypsum generated in China every year is estimated to be more than 8000 million tons. Although the yield of the desulfurized gypsum is extremely high, the comprehensive utilization rate of the desulfurized gypsum is low due to the reasons of quality, market demand and the like, most of the gypsum can be only stockpiled or discarded, so that the land is occupied, the environmental problem is caused, and the value of the gypsum is not exerted. On the other hand, the thermal power plant has huge demand for calcium carbonate-containing substances such as limestone due to the desulfurization requirement, and the use cost of the limestone of the power plant will gradually increase along with the gradual increase of the requirement on the mining environment of the limestone in the future, so that a process route which takes desulfurized gypsum as a raw material and converts the desulfurized gypsum into calcium carbonate is developed, which is not only beneficial to the treatment of a large amount of currently accumulated gypsum, but also can bring considerable economic benefits to the thermal power plant in the future.

The method takes ammonium carbonate or ammonium bicarbonate as a raw material to generate calcium carbonate and ammonium sulfate with calcium sulfate dihydrate, and a great deal of research has been carried out before, and a part of process patents are generated. For example: in patent CN103910371A, solid ammonium bicarbonate, ammonia water and calcium sulfate dihydrate slurry with solid-liquid mass ratio of 10% -30% are used as reactants, and calcium carbonate solid and ammonium sulfate solution are obtained by reaction; CN102583443A, solid phosphogypsum reacts with ammonium carbonate solution with certain concentration to prepare ammonium sulfate solution and obtain calcium carbonate solid; CN109250743A, waste alkali and by-product of caprolactamPreparing light calcium carbonate and sodium sulfate by reacting phosphogypsum; CN108439451A, converting calcium sulfate dihydrate crystals into calcium sulfate hemihydrate crystals in phosphogypsum in a mixed acid system of concentrated sulfuric acid and diluted phosphoric acid to obtain purified phosphogypsum, then obtaining crude calcium carbonate through a first-stage conversion reaction, dissolving the crude calcium carbonate in a hydrochloric acid solution, filtering to obtain a calcium chloride solution, and finally obtaining a calcium carbonate product through a second-stage conversion reaction of the calcium chloride solution; CN108408751A, mixing the phosphogypsum and the deionized water uniformly, then adding ammonia A, and introducing CO at constant speed under the conditions of normal temperature and stirring₂Reacting, and preparing the high-purity calcium carbonate through other intermediate reactions. The methods have the characteristics of special reaction substances and reaction conditions, but at present, a process route for preparing calcium carbonate and ammonium sulfate by directly reacting solid ammonium bicarbonate and high-concentration desulfurized gypsum slurry serving as reaction raw materials does not exist.

The total stability of ammonium carbonate is worse than that of ammonium bicarbonate, and the economic value is much higher than that of ammonium bicarbonate, so that the economic efficiency is better when the ammonium bicarbonate is used as a reaction raw material than when the ammonium carbonate is used as a reaction raw material. In the actual use process, ammonium carbonate is less directly adopted as a reaction raw material, and ammonium bicarbonate, ammonia water and carbon dioxide are adopted as raw materials to synthesize ammonium carbonate, and then the ammonium carbonate reacts with calcium sulfate dihydrate, so that the complexity of equipment is increased. The ammonium bicarbonate also has thermal sensitivity and poor stability at high temperature, so the reaction temperature cannot be too high, and meanwhile, the pretreatment of the ammonium bicarbonate is carried out at normal and low temperature as much as possible, so the heating operation of the ammonium bicarbonate is avoided, and the decomposition of the ammonium bicarbonate by heating is prevented. During the reaction, the ammonium bicarbonate is dissolved in water to absorb a great deal of heat, so that the temperature is obviously reduced, and the ammonium bicarbonate is reasonably added in batches to avoid the violent fluctuation of the reaction temperature.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a method for preparing ammonium sulfate and calcium carbonate by using desulfurized gypsum. The method takes solid ammonium bicarbonate and high-concentration desulfurized gypsum slurry as reaction materials, the reaction materials are simple, and a solid-phase product with higher calcium carbonate content and ammonium sulfate crystals can be obtained through two-step reaction.

The method for preparing ammonium sulfate and calcium carbonate by using desulfurized gypsum specifically comprises the following steps:

step 1, drying wet desulfurized gypsum in hot air at 40-80 ℃;

step 2, treating the dried gypsum by a grinder, and controlling the particle size of the dried gypsum to be 100-500 meshes;

step 3, preparing the dry gypsum and water into suspension slurry with the gypsum mass fraction of 40-70% under the stirring state, and heating the suspension slurry to 30-60 ℃ in a water bath or oil bath environment;

step 4, adding solid ammonium bicarbonate with a certain proportion into the gypsum slurry for multiple times, reacting under the stirring condition, and heating in a water bath or oil bath environment at the temperature of 30-60 ℃ to serve as a first-stage reaction;

step 5, filtering the mixed solution after reaction by a centrifugal machine or vacuumizing to separate a solid product taking calcium carbonate as a main component and a liquid taking ammonium sulfate as a main component to serve as a first-stage reaction product;

step 6, preparing a solid product which takes calcium carbonate as a main component in the first-stage reaction product into a suspension slurry with the solid mass fraction of 30-60% again, and adding solid ammonium bicarbonate to react to obtain a second-stage reaction;

step 7, filtering the second-stage reaction mixed solution by a centrifuge or vacuum to separate a solid product taking calcium carbonate as a main component and a liquid taking ammonium sulfate as a main component, wherein the liquid in the second-stage reaction product is merged into the liquid in the first-stage reaction product to be used as an ammonium sulfate liquid;

step 8, evaporating and crystallizing ammonium sulfate liquid by taking power plant flue gas or low-quality steam as a heat source to obtain ammonium sulfate crystals;

and 9, drying the second-stage reaction product solid at 100-110 ℃ for later use or directly putting the second-stage reaction product solid as limestone into a power plant desulfurization system for use.

Preferably, the moisture content of the wet desulfurized gypsum in the step 1 is not more than 30 percent; the main component CaSO of the desulfurized gypsum is dehumidified in a dry state₄·2H₂The other solids content than 0 is less than 15%.

Preferably, the solid of step 4Dividing the ammonium bicarbonate into 10-15 parts by equivalent, and sequentially adding gypsum slurry; the mixing proportion condition of the solid ammonium bicarbonate and the gypsum slurry is that the reactant CaSO₄·2H₂0 and NH₄HCO₃The molar ratio of the ammonium bicarbonate to the gypsum slurry is 0.35-0.45, and the reaction time of the solid ammonium bicarbonate and the gypsum slurry under the stirring condition is 40-80 min; the stirring speed during the reaction is 400-700 r/min; adding the mixture for one section every 3min, and reacting for about 5-20 min after the last addition.

Preferably, the conditions of the second-stage reaction in step 6 are as follows: maintenance of the reactant CaSO₄·2H₂0 and NH₄HCO₃The overall molar ratio of (a) to (b) is 0.35-0.45; the stirring speed during the reaction is 400-700 r/min; the reaction temperature is 30-60 ℃, the reaction time is 40-80 min, and the heating is carried out in a water bath or oil bath environment; the second-stage reaction comprises the following specific steps: feeding solid ammonium bicarbonate once or in several times into suspension slurry with the solid mass fraction of 30-60%, wherein the reaction temperature is 40-60 ℃; heating with a water bath or oil bath.

Preferably, CaSO is present in the reaction system of the two-stage reaction described in step 6₄·2H₂0 and NH₄HCO₃The overall molar ratio of (A) is 0.35 to 0.45.

Preferably, the ammonium sulfate crystal in the step 8 is obtained by separating the ammonium sulfate crystal by a centrifuge after evaporation crystallization and drying the ammonium sulfate crystal by hot air at the temperature of 100-110 ℃.

The invention has the beneficial effects that:

(1) the method directly converts the power plant desulfurization gypsum into calcium carbonate with the content of more than 93 percent, and can be recycled for power plant desulfurization, so that the recycling of calcium element is realized, the other product ammonium sulfate can be used as an agricultural chemical fertilizer for export sales, the method is suitable for large-scale treatment of the power plant desulfurization gypsum, and the problem that the desulfurization gypsum of a thermal power plant is difficult to recycle is effectively solved. Compared with other preparation methods based on similar principles, the method has the advantages that the reaction materials are simplified, and only two reactants are needed; the technological parameters are mild, and the reaction is carried out at normal pressure and low temperature; the reaction time is short, and the production efficiency is better.

(2) The reaction temperature is a core factor influencing the conversion efficiency of the reaction, the decomposition of ammonium bicarbonate can be carried out at high temperature to reduce the conversion rate of the reaction, and the reaction is not facilitated at low temperature, so that a proper reaction temperature range exists, but the dissolution of solid ammonium bicarbonate can absorb a large amount of heat to influence the temperature stability. The invention can avoid the decomposition of ammonium bicarbonate in large quantity by accurately controlling the steps and temperature of the reaction process, thereby obtaining higher conversion rate, and can obtain a solid-phase product with the effective content of calcium carbonate more than 93 percent by adding further two-stage reaction, and the solid-phase product can be used for desulfurization recycling of a thermal power plant or other application scenes of limestone.

Detailed Description

The present invention will be further described with reference to the following examples. The following examples are set forth merely to aid in the understanding of the invention. It should be noted that, for a person skilled in the art, several modifications can be made to the invention without departing from the principle of the invention, and these modifications and modifications also fall within the protection scope of the claims of the present invention.