WO2024159639A1 - System and method for accelerating direct mineralization of flue gas carbon dioxide with desulfurized gypsum - Google Patents

Abstract

Provided in the present application are a system and a method for accelerating direct mineralization of flue gas carbon dioxide with desulfurized gypsum. The method comprises: absorbing carbon dioxide from a desulfurized flue gas by using ammonia water as an absorbent, so as to obtain an ammonium carbonate absorption liquid; heating a desulfurized gypsum to obtain a semi-hydrated gypsum; hydrating the semi-hydrated gypsum to obtain a hydrated solution of the semi-hydrated gypsum; and subjecting the ammonium carbonate absorption liquid, the hydrated solution of the semi-hydrated gypsum and the ammonia water to a mineralization reaction, so as to obtain a mixture of solid calcium carbonate and ammonium sulfate.

Description

A system and method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum Technical Field

The present application relates to the technical field of flue gas treatment, and in particular to a system and method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum.

Background Art

Ammonia (NH ₃ ) and gypsum (CaSO ₄ ) are used to react with CO ₂ in flue gas to produce ammonium sulfate (fertilizer) and calcium carbonate (see Formula 1), thereby achieving flue gas decarbonization and mineralization.
CO ₂ +2NH ₃ +CaSO ₄ ·2H ₂ O→(NH ₄ ) ₂ SO ₄ +CaCO ₃ ↓+2H ₂ O (1)

This technology combines the capture and utilization of _CO2 into one. The whole process does not involve high temperature and organic solvents, avoiding the problems of high cost and secondary pollution. The mineralization product is calcium carbonate, which has a stable form and does not have environmental risks such as leakage, saving monitoring costs and can be reused for flue gas desulfurization or permanently and safely sealed. The reaction product ammonium sulfate is a high-value-added industrial product (fertilizer) used in agricultural production. The whole set of technologies can significantly reduce the cost of decarbonization while obtaining benefits, and has high technical and economic efficiency. The decarbonization of this technology also involves the disposal of gypsum, an industrial waste, which can effectively reuse industrial solid waste and generate huge social and economic benefits.

At present, the raw materials for direct mineralization are mostly phosphogypsum and desulfurized gypsum. The content of calcium sulfate dihydrate in phosphogypsum is greater than 85% (first-grade product), and the content of calcium sulfate dihydrate in desulfurized gypsum is greater than 95% (first-grade product, the content of calcium sulfate hemihydrate is less than 0.5%). The rate-controlling step of the direct mineralization reaction of flue gas _CO2 with industrial solid waste gypsum to produce calcium carbonate and ammonium sulfate is the dissolution of gypsum. The solubility of calcium sulfate dihydrate is low (20°C, 2.05g/L solubility), and the dissolution rate is slow, resulting in a slow reaction rate. In order to maintain sufficient time for gypsum to dissolve during the engineering application process, the reaction equipment is bulky, resulting in high investment cost, low system efficiency, and high decarbonization cost.

Summary of the invention

In view of this, one purpose of the present application is to provide a method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum, wherein the desulfurized dihydrate gypsum is heated to be converted into hemihydrate gypsum, and then the high solubility of the hemihydrate gypsum is utilized to first dissolve the hemihydrate gypsum to form a high calcium ion concentration solution, and then immediately undergo a liquid-liquid reaction with ammonium carbonate. The mineralization reaction speed is very fast and the mineralization efficiency is high, which can significantly reduce the cost of removing and fixing _CO2 .

Another object of the present application is to provide a system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum.

To achieve the above object, the first embodiment of the present application proposes a method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum, comprising:

Ammonia water is used as an absorbent to absorb carbon dioxide in the flue gas after desulfurization to obtain ammonium carbonate absorption liquid;

heating the desulfurized gypsum to obtain hemihydrate gypsum;

Hydrate the hemihydrate gypsum to obtain a hydrated hemihydrate gypsum solution;

The ammonium carbonate absorption liquid, the hydrated solution of the hemihydrate gypsum and aqueous ammonia are subjected to a mineralization reaction to obtain a mixture of solid calcium carbonate and ammonium sulfate.

In some embodiments, the residence time of the hemihydrate gypsum hydration is 5-20 min.

In some embodiments, the hemihydrate gypsum is hydrated in pure water or an aqueous solution containing ammonium sulfate, and the added amount of the hemihydrate gypsum is 5-30 wt % of the pure water or the aqueous solution containing ammonium sulfate.

In some embodiments, during the mineralization reaction, the ammonium carbonate absorption solution and the hydrated solution of the hemihydrate gypsum are added to the reaction system at the same time.

In some embodiments, the molar ratio of hemihydrate gypsum to ammonium carbonate participating in the mineralization reaction is 1:(1-1.1).

In some embodiments, the pH of the mineralization reaction is 9-12.

In some embodiments, the temperature of the mineralization reaction is 25-60° C., the time of the mineralization reaction is 5-20 min, and the mineralization reaction is carried out under stirring.

In some embodiments, the temperature at which the desulfurized gypsum is heated is 120-180°C.

In some embodiments, the heating is performed in a flowing dry air atmosphere.

In some embodiments, the desulfurized gypsum is desulfurized gypsum after vacuum dehydration.

In some embodiments, the desulfurized gypsum is heated by the flue gas after the air preheater of a thermal power plant.

In some embodiments, the method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum further includes:

separating the mixture of solid calcium carbonate and ammonium sulfate into solid-liquid state to obtain solid calcium carbonate and a filtrate containing ammonium sulfate;

A part of the filtrate containing ammonium sulfate is used for crystallization to obtain ammonium sulfate, and the other part is used for hydrating the hemihydrate gypsum.

To achieve the above-mentioned purpose, the second embodiment of the present application proposes a system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum, comprising:

A heat exchange unit, wherein the heat exchange unit is used to heat the desulfurized gypsum;

A first reactor, wherein the inlet of the first reactor is connected to the material outlet of the heat exchange unit;

a second reactor, wherein the inlet of the second reactor is connected to the outlet of the first reactor;

The decarbonization unit has a flue gas inlet, a first ammonia water inlet and a slurry outlet, the first ammonia water inlet is connected to an ammonia tank, and the outlet of the ammonia tank and the slurry outlet are both connected to the second reactor.

In some embodiments, the system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum also includes a filtration unit, the inlet of the filtration unit is connected to the outlet of the second reactor; the filtrate outlet of the filtration unit is divided into two paths, one is connected to the ammonium sulfate concentration and crystallization system, and the other is connected to the first reactor.

In some embodiments, the material channel of the heat exchange unit is connected to a dry air pipeline or a flue gas pipeline after an air preheater of a thermal power plant, and the heat exchange unit has a gas outlet.

In some embodiments, the heat exchange unit is a rotary dryer or a drying oven.

In some embodiments, the first reactor and the second reactor are both tank reactors.

In some embodiments, the decarbonization unit is a tower reactor.

In some embodiments, the filtration unit is a filter press.

In some embodiments, the system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum further includes a desulfurization belt conveyor, which is connected to the material inlet of the heat exchange unit.

The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum in the embodiment of the present application can bring the following beneficial effects:

(1) Fast dissolution rate, high calcium ion content, and fast mineralization reaction rate.

Conventional mineralization reactions directly use dihydrate gypsum slurry as raw material, while in the present application, the desulfurized dihydrate gypsum is first decomposed into hemihydrate gypsum by heating. The solubility of hemihydrate gypsum is about 4 times that of dihydrate gypsum, and the dissolution rate is also very fast. The hemihydrate gypsum is hydrated into a solution and then reacted with the decarbonized ammonium carbonate absorption liquid. This is a liquid-liquid reaction. The concentration of calcium ions in the solution is high, the reaction speed is fast, and the efficiency is high.

(2) The waste heat of flue gas is used to convert dihydrate gypsum into hemihydrate gypsum, and the process is simple.

There are five crystal forms of calcium sulfate, namely calcium sulfate dihydrate (CaSO ₄ ·2H ₂ O), α-type and β-type calcium sulfate hemihydrate (α-CaSO ₄ ·1/2H ₂ O, β-CaSO ₄ ·1/2H ₂ O), α-type and β-type anhydrous calcium sulfate I (α-CaSO ₄ Ⅰ, β-CaSO ₄ Ⅰ), α-type and β-type anhydrous calcium sulfate II (α-CaSO ₄ Ⅱ, β-CaSO ₄ Ⅱ), anhydrous calcium sulfate II (CaSO ₄ Ⅱ), and anhydrous calcium sulfate I (CaSO ₄ Ⅰ). Dihydrate gypsum can be decomposed into β-type hemihydrate calcium sulfate by being heated to 120-180°C under dry air conditions for dehydration. The present application utilizes the low-temperature flue gas after the air preheater of a thermal power plant to directly exchange heat with the desulfurized gypsum after vacuum dehydration to convert the dihydrate gypsum into hemihydrate gypsum, and then conducts hydration and mineralization reactions. The process is simple, has high efficiency in utilizing flue gas waste heat, and is conducive to engineering applications.

(3) The solution after dissolving hemihydrate gypsum is used for mineralization reaction, which is highly efficient and low-cost.

The hydration process of hemihydrate gypsum is to first form a saturated hemihydrate gypsum solution and then precipitate dihydrate gypsum crystals. Therefore, reasonable control of the time of hemihydrate gypsum is the key to ensuring a high calcium ion concentration in the solution. The present application utilizes the high solubility of hemihydrate gypsum to first dissolve the hemihydrate gypsum to form a high calcium ion concentration solution, and then immediately reacts with ammonium carbonate in a liquid-liquid manner. The mineralization reaction is very fast and the mineralization efficiency is high, which can significantly reduce the cost of removing and fixing _CO2 .

Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

FIG1 is a flow chart showing a method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to an exemplary embodiment of the present application.

FIG2 is a flow chart showing a method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to another exemplary embodiment of the present application.

FIG3 is a schematic diagram of a system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to an exemplary embodiment of the present application.

FIG. 4 is a particle size analysis diagram of the desulfurized gypsum in Example 1.

FIG5 is a scanning electron microscope (SEM) characterization image of the desulfurized gypsum in Example 1 at a scale of 30 μm.

FIG6 is a scanning electron microscope (SEM) characterization image of the desulfurized gypsum in Example 1 at a scale of 10 μm.

Reference numerals:
1-heat exchange unit; 2-first reactor; 3-second reactor; 4-decarbonization unit; 5-ammonia tank; 6-filtration unit; 7-desulfurization belt conveyor.

DETAILED DESCRIPTION

The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but cannot be understood as limiting the present application.

Throughout the application, the disclosure of numerical ranges includes all values within the entire range and disclosure of further subdivided ranges, including endpoints and sub-ranges given within those ranges.

In the application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be made through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

The following describes a method and system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to an embodiment of the present application with reference to the accompanying drawings.

Figure 1 is a flow chart of a method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to an exemplary embodiment of the present application. As shown in Figure 1, the method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum includes the following steps:

S101. Using ammonia water as an absorbent, absorbing carbon dioxide in the flue gas after desulfurization to obtain ammonium carbonate absorption liquid.

In the present application, ammonia water is used as an absorbent to absorb carbon dioxide in flue gas to obtain ammonium carbonate absorption liquid, which is an existing ammonia decarbonization technology in the art and will not be described in detail here.

S102, heating the desulfurized gypsum to obtain hemihydrate gypsum.

The solubility of β-type calcium sulfate hemihydrate is about 4 times that of calcium sulfate dihydrate (20°C, 8.16 g/L solubility). Now, the use of β-type hemihydrate calcium sulfate (also known as hemihydrate gypsum in this application) as the raw material for the mineralization reaction significantly increases the content of dissolved calcium sulfate in the solution, and the limiting factors of the reaction are solved to increase the rate of the mineralization reaction, shorten the reaction time, improve the reaction efficiency, and reduce the system cost of the direct mineralization reaction. Therefore, it is very important to convert the existing desulfurized dihydrate gypsum into the hemihydrate gypsum of this application.

In some embodiments, the desulfurized gypsum is desulfurized gypsum after vacuum dehydration, which is dihydrate gypsum.

In some embodiments, the temperature of heating the desulfurized gypsum is 120-180° C. As non-limiting examples, the heating temperature includes but is not limited to 120° C., 130° C., 140° C., 150° C., 160° C., 170° C., or 180° C., etc.

In some embodiments, heating is performed in a flowing dry air atmosphere. It should be noted that dihydrate gypsum can be decomposed into β-type hemihydrate calcium sulfate by heating to 120-180°C under flowing dry air conditions for dehydration; if heating is performed in a closed space or non-dry environment, water vapor is easily generated during heating, causing the dihydrate gypsum to decompose into α-type hemihydrate calcium sulfate.

In the present application, the method of heating the desulfurized gypsum is direct contact heating. In some embodiments, the flue gas after the air preheater of a thermal power plant is used to heat the desulfurized gypsum. In this way, the flue gas after the air preheater of a thermal power plant can be used as a heating atmosphere to replace the dry air atmosphere, and as a heat exchange medium, so that: on the one hand, the flue gas exchanges heat with the desulfurized gypsum after vacuum dehydration, and the waste heat of the flue gas is used to decompose the dihydrate gypsum into hemihydrate gypsum, and the high solubility of the hemihydrate gypsum is used to form a solution containing a high calcium ion concentration, and then the mineralization reaction is immediately carried out, which increases the mineralization reaction speed and simplifies the process; on the other hand, the waste heat utilization rate of the flue gas can be improved, which is conducive to engineering applications.

S103, hydrating the hemihydrate gypsum to obtain a hydrated hemihydrate gypsum solution.

The hydration process of hemihydrate gypsum is as follows: when hemihydrate gypsum is dissolved in water, the saturated solubility of hemihydrate gypsum is reached first. Since the solubility of hemihydrate gypsum is greater than that of dihydrate gypsum, dihydrate gypsum in the solution will spontaneously precipitate crystals. Due to the precipitation of dihydrate gypsum, the dissolution equilibrium of hemihydrate gypsum is destroyed, causing the hemihydrate gypsum to further dissolve, compensating for the calcium ions and sulfate ions consumed by the crystallization of dihydrate gypsum, until the hemihydrate gypsum is completely dissolved to form dihydrate gypsum. Therefore, it is key to control the addition amount and dissolution time in the dissolution process of hemihydrate gypsum to prevent the hemihydrate gypsum from being converted into dihydrate gypsum crystals. The control of dissolution time is to ensure that the concentration of calcium ions in the solution is the highest before dihydrate gypsum crystals are formed, which is conducive to the mineralization reaction.

In some embodiments, the semi-hydrated gypsum is hydrated in pure water or an aqueous solution containing ammonium sulfate, and the amount of the semi-hydrated gypsum added includes but is not limited to 5-30wt% of the pure water or the aqueous solution containing ammonium sulfate. It should be noted that the mass content of ammonium sulfate in the aqueous solution containing ammonium sulfate is preferably not more than 30wt%. As a non-limiting example, the amount of the semi-hydrated gypsum added includes but is not limited to 5wt%, 10wt%, 15wt%, 20wt% or 30wt% of the pure water or the aqueous solution containing ammonium sulfate. The amount of the semi-hydrated gypsum added within the above range can prevent the semi-hydrated gypsum from being converted into dihydrated gypsum crystals; when it is greater than 30wt%, the reaction rate of the semi-hydrated gypsum is limited; when it is less than 5wt%, the solution concentration is low, which is not conducive to the concentration and crystallization of ammonium sulfate.

In some embodiments, the residence time (i.e., hydration time) of the hemihydrate gypsum hydration is 5-20 minutes. As a non-limiting example, the residence time of the hemihydrate gypsum hydration includes but is not limited to 5 minutes, 10 minutes, 15 minutes, or 20 minutes. When the hydration residence time is within the above range, the highest concentration of calcium ions in the solution can be ensured before dihydrate gypsum crystals are formed, which is beneficial to the mineralization reaction; if it is greater than 20 minutes, dihydrate gypsum crystals will precipitate; if it is less than 5 minutes, the hydration effect of hemihydrate gypsum will be poor.

S104, subjecting the ammonium carbonate absorption liquid, the hydrated solution of hemihydrate gypsum and aqueous ammonia to a mineralization reaction to obtain a mixture of solid calcium carbonate and ammonium sulfate.

In some embodiments, during the mineralization reaction, the ammonium carbonate absorption liquid and the solution after the hemihydrate gypsum is hydrated are added to the reaction system at the same time. In this way, the calcium ion concentration in the initial reactants can be increased, which is conducive to accelerating the reaction; if the ammonium carbonate absorption liquid and the solution after the hemihydrate gypsum is hydrated are not added at the same time, it will cause the precipitation of dihydrate gypsum or the product calcium carbonate to be coated on the surface of gypsum, reducing the reaction speed and conversion rate.

In some embodiments, the molar ratio of hemihydrate gypsum and ammonium carbonate participating in the mineralization reaction is 1:(1-1.1). As a non-limiting example, the molar ratio of hemihydrate gypsum and ammonium carbonate participating in the mineralization reaction includes but is not limited to 1:1, 1:1.05 or 1:1.1, etc. The molar ratio of hemihydrate gypsum and ammonium carbonate participating in the mineralization reaction within the above range can increase the reaction rate and the utilization rate of the reactants; if it is less than 1:1, the reaction is incomplete; if it is greater than 1:1.1, the ammonium carbonate reacts incompletely and enters the ammonium sulfate crystallization system, the decomposition of ammonium carbonate and the reduction of the purity of ammonium sulfate will occur.

In some embodiments, the pH of the mineralization reaction is 9-12. As a non-limiting example, the pH of the mineralization reaction includes but is not limited to 9, 10, 11 or 12. The pH of the mineralization reaction is within the above range and can be 10.5; if it is less than 9, the mineralization reaction speed is slow; if it is greater than 12, it will lead to alkali solution waste and ammonia escape.

In some embodiments, the temperature of the mineralization reaction is 25-60°C, the time of the mineralization reaction is 5-20 min, and the mineralization reaction is carried out under stirring. As a non-limiting example, the temperature of the mineralization reaction includes but is not limited to 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, etc., and the time of the mineralization reaction includes but is not limited to 5 min, 10 min, 15 min or 20 min, etc.

FIG2 is a flow chart of a method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to another exemplary embodiment of the present application. The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum comprises the following steps:

S201, using ammonia water as an absorbent to absorb carbon dioxide in the flue gas after desulfurization to obtain ammonium carbonate absorption liquid.

S202, heating the desulfurized gypsum to obtain hemihydrate gypsum.

S203, hydrating the hemihydrate gypsum to obtain a hydrated hemihydrate gypsum solution.

S204, subjecting the ammonium carbonate absorption liquid, the hydrated solution of hemihydrate gypsum and aqueous ammonia to a mineralization reaction to obtain a mixture of solid calcium carbonate and ammonium sulfate.

Among them, steps S201-S204 are the same as the aforementioned steps S101-S104 and will not be repeated here.

S205, separating the solid-liquid mixture of solid calcium carbonate and ammonium sulfate to obtain solid calcium carbonate and a filtrate containing ammonium sulfate.

In the present application, a mixture of solid calcium carbonate and ammonium sulfate is separated into solid and liquid to obtain solid calcium carbonate and a filtrate containing ammonium sulfate, wherein the filtrate containing ammonium sulfate can be subjected to crystallization treatment to obtain ammonium sulfate, thereby realizing resource utilization. In the present application, the method of solid-liquid separation is not limited, specifically: in some embodiments, solid-liquid separation can be carried out by centrifugal separation; in other embodiments, solid-liquid separation can be carried out by suction filtration; in some embodiments, solid-liquid separation can also be carried out by filter press.

S206. A portion of the filtrate containing ammonium sulfate is used for crystallization to obtain ammonium sulfate, and the other portion is used for hydrating hemihydrate gypsum.

In the present application, after filtering the absorption liquid after the mineralization reaction, a part of the absorption liquid is recycled for hydrating hemihydrate gypsum and dissolving dihydrate gypsum, which can further increase the concentration of ammonium sulfate in the absorption liquid, save water, and reduce the operating cost of the system.

It should be noted that, in the present application, the step of obtaining the ammonium carbonate absorption solution and the step of obtaining the hemihydrate gypsum can be performed in any order, or can be performed simultaneously.

The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum in the embodiment of the present application heats the desulfurized dihydrate gypsum to convert it into hemihydrate gypsum, and then utilizes the high solubility of the hemihydrate gypsum to first dissolve the hemihydrate gypsum to form a high calcium ion concentration solution, and then immediately reacts it with ammonium carbonate in a liquid-liquid reaction. The mineralization reaction speed is very fast and the mineralization efficiency is high, which can significantly reduce the cost of removing and fixing _CO2 .

The difference between the method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum in the embodiment of the present application and the existing principle method is that the existing mineralization process is a gas-liquid-solid three-phase reaction of gypsum, ammonia water and _CO2. The solid gypsum needs to pass through the liquid membrane and then enter the liquid phase, and the gaseous _CO2 also needs to pass through the liquid membrane to enter the liquid phase. The three-phase reaction has large resistance, slow reaction speed and low efficiency. The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum in the embodiment of the present application adopts dihydrate gypsum-hemihydrate gypsum-calcium sulfate solution to react with the decarbonization reaction liquid ammonium carbonate, which is a liquid-liquid direct reaction with fast reaction speed and high efficiency.

Figure 3 is a schematic diagram of a system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to an exemplary embodiment of the present application. As shown in Figure 3, the system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to an exemplary embodiment of the present application includes a heat exchange unit 1, a first reactor 2, a second reactor 3 and a decarbonization unit 4. Among them: the heat exchange unit 1 is used to heat the desulfurized gypsum; the inlet of the first reactor 2 is connected to the material outlet of the heat exchange unit 1; the inlet of the second reactor 3 is connected to the outlet of the first reactor 2; the decarbonization unit 4 has a flue gas inlet, a flue gas outlet, a first ammonia water inlet and a slurry outlet, the first ammonia water inlet is connected to the ammonia tank 5, and the outlet of the ammonia tank 5 and the slurry outlet of the decarbonization unit 4 are both connected to the second reactor 3.

In some embodiments, the system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum of the present application further includes a filter unit 6, the inlet of the filter unit 6 is connected to the outlet of the second reactor 3; the filtrate outlet of the filter unit 6 is divided into two paths, one path is connected to the ammonium sulfate concentration and crystallization system, and the other path is connected to the first reactor 2. The ammonium sulfate concentration and crystallization system is a prior art and will not be described in detail here.

In some embodiments, the material channel of the heat exchange unit 1 is connected to the dry air pipeline or the flue gas pipeline after the air preheater of the thermal power plant, and the heat exchange unit 1 has a gas outlet.

In some embodiments, the heat exchange unit 1 is a rotary dryer or a drying furnace, wherein the heat exchanger can be a tubular heat exchanger or a plate heat exchanger.

In some embodiments, the first reactor 2 and the second reactor 3 are both kettle reactors, including but not limited to stainless steel reactors, hydrothermal reactors, etc. These reactors are equipped with stirring devices, and the structures are prior art and will not be described in detail here.

In some embodiments, the decarbonization unit 4 is a tower reactor, including but not limited to a bubble tower reactor, a spray tower reactor, a plate tower reactor, a decarbonization tower, and the like.

In some embodiments, the filtration unit 6 includes but is not limited to a filter press, a centrifugal separator, and the like.

In some embodiments, the system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum of the present application further includes a desulfurization belt conveyor 7 , which is connected to the material inlet of the heat exchange unit 1 .

Taking the case where the heat exchange unit adopts a rotary dryer and the filter unit 6 adopts a filter press as an example, the method for mineralizing carbon dioxide in flue gas by using the system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum of this embodiment is as follows:

The desulfurized gypsum is added into a rotary dryer, and the hot flue gas of the power plant is directly contacted with the desulfurized gypsum for drying to obtain hemihydrated gypsum; the hemihydrated gypsum is then added into the first reactor, and is stirred by a stirring device in the first reactor to obtain hemihydrated gypsum slurry; the desulfurized flue gas then enters a decarbonization tower, is decarbonized by ammonia method, and is then discharged; the hemihydrated gypsum slurry and the ammonium carbonate absorption liquid at the bottom of the decarbonization tower are simultaneously pumped into the second reactor; the slurry at the bottom of the second reactor is extracted and filtered through a filter press to obtain solid calcium carbonate, and a part of the filtrate enters the ammonium sulfate crystallization system, and the other part enters the first reactor.

The method and system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to the embodiments of the present application are explained below with reference to specific embodiments.

Example 1

The system of accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum in this embodiment comprises a heat exchange unit 1, a first reactor 2, a second reactor 3, a decarbonization unit 4, an ammonia tank 5, a filtration unit 6 and a desulfurization belt conveyor 7, wherein: the heat exchange unit 1 is a rotary dryer, the decarbonization unit 4 is a decarbonization tower, the first reactor 2 and the second reactor 3 are both stainless steel reactors, the filtration unit is a plate and frame filter press, the solid outlet of the desulfurization system vacuum belt conveyor 7 is connected to the material inlet of the heat exchange unit 1, the material outlet of the heat exchange unit 1 is connected to the material inlet of the first reactor 2, and the heat exchange unit 1 is connected to the material inlet of the first reactor 2. The medium inlet is connected to the flue after the air preheater of the power plant, the hot medium outlet of the heat exchange unit 1 is connected to the flue before the bag filter, the bottom outlet of the first reactor 2 is connected to the top inlet of the second reactor 3, the bottom slurry outlet of the second reactor 3 is connected to the filter unit 6, the outlet liquid of the filter unit 6 is connected to the ammonium sulfate crystallization system on one path, and connected to the top liquid inlet of the first reactor 2 on the other path; the flue gas pipeline after desulfurization is connected to the flue gas inlet of the decarbonization unit 4, and the outlet of the ammonia tank 5 is connected to the first ammonia water inlet at the bottom of the decarbonization unit 4 on one path, and connected to the second ammonia water inlet of the second reactor 3 on the other path.

The method of accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum in this embodiment comprises the following steps:

Desulfurized gypsum from a power plant is used as a raw material for mineralization reaction. The main components of the desulfurized gypsum are shown in Table 1. The particle size of the desulfurized gypsum is mainly concentrated in 10-100 nm. The particle size distribution diagram is shown in Figure 4. The SEM characterization of the desulfurized gypsum is shown in Figures 5 and 6.

10 kg of the desulfurized gypsum was added to the heat exchange unit and dried with the flue gas after the air preheater of the power plant at 150°C for 60 minutes to obtain 9.23 kg of hemihydrated gypsum powder. The hemihydrated gypsum powder was then added to the first reactor containing 100 L of water and hydrated at 30°C for 10 minutes to obtain the absorption liquid. The speed of the agitator in the first reactor during the hydration process was 500 r/min. The flue gas after desulfurization of the power plant (the volume content of carbon dioxide is 12.5%) enters the decarbonization unit for ammonia decarbonization, and the flue gas after decarbonization is discharged from the flue gas outlet of the decarbonization unit (the volume content of carbon dioxide is 0.8%). The decarbonization absorption liquid at the bottom of the decarbonization unit and the absorption liquid in the first reactor are simultaneously pumped into the second reactor, so that the molar ratio of the hemihydrate gypsum and ammonium carbonate entering the second reactor is 1:1.05. At the same time, ammonia water is pumped into the second reactor, and the pH of the mixed solution in the second reactor is adjusted to 10. After stirring at 30°C for 10 minutes for mineralization reaction, it is discharged to the filtration unit for filtration. A part of the filtrate (ammonium sulfate content is 5wt%) is recycled into the first reactor as absorption liquid for hydration and dissolution of dihydrate gypsum, and the other part is discharged to the ammonium sulfate concentration and crystallization system for filtration to obtain calcium carbonate.

Table 1 Main components of desulfurized gypsum in Example 1

The conversion rate calculation formula of desulfurized gypsum in this embodiment is:

Conversion rate of desulfurized gypsum = molar amount of calcium ions in the obtained calcium carbonate/molar amount of calcium ions in the desulfurized gypsum*100%;

The mass fraction of calcium carbonate obtained in this embodiment is tested according to the flue gas desulfurization gypsum chemical analysis method of industry standard JC/T 2437-2018, and then the molar amount of calcium ions in the generated calcium carbonate is calculated. The conversion rate of gypsum in this embodiment is calculated according to the above formula to be 98.8%; in addition, it is tested that the purity of calcium carbonate is 98wt%.

The calculation formula for the removal rate of carbon dioxide in this embodiment is:

Carbon dioxide removal rate = (the volume content of carbon dioxide in the flue gas after desulfurization of the power plant - the volume content of carbon dioxide in the flue gas at the flue gas outlet of the decarbonization unit) / the volume content of carbon dioxide in the flue gas after desulfurization of the power plant * 100%;

Through testing and calculation, the removal rate of carbon dioxide in this embodiment is 93.6%.

Embodiment 2-10

Example 2-10 is basically the same as Example 1, except that in the method of accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum, some design process parameters, gypsum conversion rate, calcium carbonate purity, and carbon dioxide removal rate are different, as shown in Table 2.

Comparative Examples 1-6

Comparative Examples 1-6 are basically the same as Example 1, except that in the method of mineralizing flue gas carbon dioxide with desulfurized gypsum, some design process parameters and gypsum conversion rates are different, as shown in Table 2.

Table 2 Partial design process parameters and effects of Examples 1-10 and Comparative Examples 1-6

As can be seen from Table 1, after hot flue gas drying, the desulfurized gypsum is converted into hemihydrate gypsum, the mineralization reaction rate is accelerated, the conversion rate of gypsum is significantly improved, and the purity of calcium carbonate is also improved accordingly; the hydration time of hemihydrate gypsum is also beneficial to improve the conversion rate of gypsum and the purity of calcium carbonate within a suitable range; the heating temperature of gypsum also affects the conversion rate of hemihydrate gypsum.

In summary, the method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum in the embodiments of the present application aims to address the problem in the prior art that "the controlling step of the direct mineralization reaction of gypsum and flue gas _CO2 to produce calcium carbonate and ammonium sulfate is the dissolution of gypsum, which seriously restricts the mineralization reaction rate and affects the conversion rate of gypsum". The waste heat of flue gas from a thermal power plant is used to convert desulfurized gypsum into β-type calcium sulfate hemihydrate with higher solubility and faster dissolution rate, thereby increasing the rate of the mineralization reaction and the purity of calcium carbonate, while increasing the production capacity of the system and reducing the cost of mineralizing _CO2 .

In the present application, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may refer to the description of the present invention in any suitable manner without contradiction. The different embodiments or examples described in the book as well as the features of the different embodiments or examples are combined and combined.

Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims (10)

A method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum, comprising: Ammonia water is used as an absorbent to absorb carbon dioxide in the flue gas after desulfurization to obtain ammonium carbonate absorption liquid; heating the desulfurized gypsum to obtain hemihydrate gypsum; Hydrate the hemihydrate gypsum to obtain a hydrated hemihydrate gypsum solution; The ammonium carbonate absorption liquid, the hydrated solution of the hemihydrate gypsum and aqueous ammonia are subjected to a mineralization reaction to obtain a mixture of solid calcium carbonate and ammonium sulfate. The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to claim 1, wherein the residence time of the hemihydrate gypsum hydration is 5-20 min; And/or, the semi-hydrated gypsum is hydrated in pure water or an aqueous solution containing ammonium sulfate, and the addition amount of the semi-hydrated gypsum is 5-30wt% of the pure water or the aqueous solution containing ammonium sulfate. The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to claim 1, wherein In the mineralization reaction, the ammonium carbonate absorption solution and the hydrated solution of the hemihydrate gypsum are added to the reaction system at the same time; and/or, the molar ratio of hemihydrate gypsum and ammonium carbonate involved in the mineralization reaction is 1:(1-1.1); And/or, the pH of the mineralization reaction is 9-12; And/or, the temperature of the mineralization reaction is 25-60° C., the time of the mineralization reaction is 5-20 min, and the mineralization reaction is carried out under stirring. The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to claim 1, wherein the temperature at which the desulfurized gypsum is heated is 120-180°C; And/or, the heating is performed in a flowing dry air atmosphere. The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to claim 1, wherein the desulfurized gypsum is desulfurized gypsum after vacuum dehydration; And/or, the desulfurized gypsum is heated by using flue gas after the air preheater of a thermal power plant. The method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to claim 1, wherein the method for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum further comprises: separating the mixture of solid calcium carbonate and ammonium sulfate into solid-liquid state to obtain solid calcium carbonate and a filtrate containing ammonium sulfate; A part of the filtrate containing ammonium sulfate is used for crystallization to obtain ammonium sulfate, and the other part is used for hydrating the hemihydrate gypsum. A system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum, comprising: A heat exchange unit, wherein the heat exchange unit is used to heat the desulfurized gypsum; A first reactor, wherein the inlet of the first reactor is connected to the material outlet of the heat exchange unit; a second reactor, wherein the inlet of the second reactor is connected to the outlet of the first reactor; The decarbonization unit has a flue gas inlet, a first ammonia water inlet and a slurry outlet, the first ammonia water inlet is connected to an ammonia tank, and the outlet of the ammonia tank and the slurry outlet are both connected to the second reactor. The system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to claim 7 further includes a filtration unit, the inlet of which is connected to the outlet of the second reactor; the filtrate outlet of the filtration unit is divided into two paths, one of which is connected to the ammonium sulfate concentration and crystallization system, and the other is connected to the first reactor. The system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurized gypsum according to claim 8, wherein the material channel of the heat exchange unit is connected to the dry air pipeline or the flue gas pipeline after the air preheater of a thermal power plant, and the heat exchange unit has a gas outlet; And/or, the heat exchange unit is a rotary dryer or a drying furnace; And/or, both the first reactor and the second reactor are kettle reactors; And/or, the decarbonization unit is a tower reactor; And/or, the filtration unit is a filter press. The system for accelerating the direct mineralization of flue gas carbon dioxide by desulfurization gypsum according to claim 7 further includes a desulfurization belt conveyor, which is connected to the material inlet of the heat exchange unit.