Production of sulfuric acid and mineralization of carbon dioxide

Abstract

The present invention relates to a method for producing sulfuric acid from industrial gases and for the mineralization of CO2, comprising: continuously passing a CO2-containing gas through an aqueous ammonia solution in a first reactor, or continuously passing a CO2-containing gas and ammonia gas through water to produce a [(NH4)2CO3 / NH4HCO3] solution; continuously withdrawing the [(NH4)2CO3 / NH4HCO3] solution from the first reactor, optionally cooling the [(NH4)2CO3 / NH4HCO3] solution, and supplying it to a second reactor; supplying the second reactor to a gas stream containing NH3 and CO2 discharged from the first reactor, thereby producing (NH4) in the second reactor. The present invention relates to a method comprising: a CO2 absorption step, which includes generating an aqueous solution of (NH4)2CO3 and releasing a gas that is essentially free of NH3 and CO2 from a second reactor; a CO2 mineralization step, which includes reacting (NH4)2CO3 in water with calcium sulfate [CaSO4] to produce a solution of ammonium sulfate [(NH4)2SO4], precipitating solid calcium carbonate [CaCO3], separating CaCO3 from the solution, and recovering ammonium sulfate crystals from the solution; and an H2SO4 production step, which includes thermally decomposing (NH4)2SO4 to produce sulfuric acid and supplying the ammonia stream released from the thermally decomposed (NH4)2SO4 to the CO2 absorption step.

Description

[Technical Field]

[0001] Sulfuric acid (H2SO4) is one of the most important chemical substances. Sulfuric acid is primarily produced by the catalytic oxidation of sulfur dioxide to obtain sulfur trioxide, which is then bubbling into sulfuric acid, thereby absorbing the sulfur trioxide into the solution. Water is then added at an appropriate rate to obtain an acid with approximately 98% purity.

[0002] H2SO4 can be recovered from ammonium sulfate [(NH4)2SO4] by thermal decomposition accompanied by the release of ammonia, as described, for example, in German Patent No. 1151492, European Patent No. 83831, and International Publication No. 03 / 27018. International Publication No. 96 / 09248 describes a multi-step method for producing sulfuric acid, which begins with producing ammonium sulfate by reacting carbon dioxide, ammonia, and gypsum (calcium sulfate) in water, as follows. CO2+2NH3+CaSO4+H2O→(NH4)2SO4+CaCO3

[0003] Fine-grained calcium carbonate suitable for use in the paper industry was obtained. In the next step, described in International Publication No. 96 / 09248, ammonium sulfate was thermally decomposed to obtain sulfuric acid and ammonia. Figure 1 is a reproduction of the corresponding block diagram of the method in International Publication No. 96 / 09248. It can be seen that the stream of ammonia gas released from the thermally decomposed (NH4)2SO4 is supplied to the (NH4)2SO4 / CaCO3 production reaction.

[0004] A process that can simultaneously generate H2SO4 and mineralize CO2 into a stable and environmentally acceptable form, namely calcium carbonate, is highly advantageous. The proposed method for producing H2SO4, namely, capturing CO2 from the atmosphere using ammonia and converting it into calcium carbonate, offers significant environmental benefits.

[0005] The experimental results reported below show that the above chemical reaction, in which NH3 and CO2 react with a CaSO4 slurry in water, is difficult to complete according to International Publication No. 96 / 09248. The inventors have found that the efficiency of this method is improved by dividing the above chemical reaction into steps carried out in separate reactors. Specifically, the reaction between ammonia and carbon dioxide in water to produce an aqueous ammonium carbonate solution is completed first, as follows. 2NH3 + CO2 + H2O → (NH4)2CO 3(aq) (1)

[0006] Next, an aqueous solution of ammonium carbonate is reacted with gypsum to produce a solution of ammonium sulfate and water-insoluble calcium carbonate as follows: (NH4)2CO 3(aq) +CaSO 4(S) →(NH4)2SO 4(aq) +CaCO 3(S) (2)

[0007] The final step is the thermal decomposition of ammonium sulfate, yielding sulfuric acid products as follows: (NH4)2SO 4(s) →H2SO 4(l) +2NH 3(g) (3) The released ammonia gas can then be supplied to the reaction of equation (1).

[0008] However, the reaction of Equation (1) is not without difficulties. The NH3-CO2-H2O system is sensitive to temperature, and when the ratio of reactants changes, various ammonium salts may be formed. A review article titled "amine versus ammonia absorption of CO2 as a measure of reducing GHG emission: a critical analysis" [Bandyopadhyay, Clean Tech Environ Policy (2011) 13:269-284] discusses the reaction between NH3 and CO2 and shows multiple reactions occurring in the NH3-CO2-H2O system. Equations (5)-(12) in the Bandyopadhyay article indicate the formation of various salts such as (NH4)2CO3, NH4HCO3, and NH4COONH2. NH 3 / When the NH / CO2 ratio is low, ammonium bicarbonate [NH4HCO3] is likely to form. However, ammonium bicarbonate has a much lower solubility than ammonium carbonate, so it is necessary to consider the solubility limit. On the other hand, NH 3 / When the NH / CO2 ratio is high, ammonia loss may occur. The reason is that when flue gas or other CO2-containing industrial gas passes through the ammonia solution in the absorption tower, some ammonia is inevitably carried away by the effluent gas stream discharged from the reactor. In large-scale facilities, ammonia loss becomes very significant.

[0009] The inventors have found a process design that enhances the selectivity of the reaction in which ammonia reacts with carbon dioxide in water to produce (NH4)2CO3, while minimizing the loss of unabsorbed ammonia. A CO2-containing gas stream (from flue gas) is continuously introduced into an ammonium hydroxide solution packed in a first reactor using a diffuser, sparger, or membrane (these terms are used interchangeably herein) to generate a large number of slow-moving CO2 bubbles or microbubbles in the first reactor. Note that the ammonium hydroxide solution can be pre-prepared in a concentrated form in another tank and continuously supplied to the reactor in the form of an aqueous stream, or it can be generated in situ by continuously injecting ammonia gas released by the thermal decomposition of ammonium sulfate according to the reaction of formula (4) into the water or dilute ammonia solution in the first reactor, i.e., into a sparger immersed in water, in parallel with the carbon dioxide stream. The reaction mixture, consisting of an aqueous solution of (NH4)2CO3 / NH4HCO3, produced in the first reactor, is continuously drawn, optionally passed through a condenser, and supplied to the second reactor as a feed stream. The gas stream leaving the first reactor contains unreacted ammonia and / or unreacted CO2; this gas stream is supplied to the second reactor, where it is absorbed by the (NH4)2CO3 / NH4HCO3 solution, which is continuously supplied to the second reactor. The experimental results shown below demonstrate that the process design of the present invention enables minimizing NH3 loss and achieving high conversion rates of CO2 to (NH4)2CO3 (>95%, >96%, and >99%). The exhaust air stream released from the second reactor into the atmosphere is essentially free of CO2 and residual NH3.

[0010] Therefore, the present invention mainly relates to a method for producing sulfuric acid from industrial gases (e.g., flue gas) and for the mineralization of CO2, CO2 absorption step comprising: continuously sparging a CO2-containing gas through an aqueous ammonia solution in a first reactor, or continuously sparging a CO2-containing gas and ammonia gas through water to produce a [(NH4)2CO3 / NH4HCO3] solution; continuously withdrawing the [(NH4)2CO3 / NH4HCO3] solution from the first reactor, optionally cooling the [(NH4)2CO3 / NH4HCO3] solution, supplying it to a second reactor, supplying the gas stream containing NH3 and CO2 discharged from the first reactor to the second reactor, thereby producing an aqueous (NH4)2CO3 solution in the second reactor, and releasing a gas that is essentially free of NH3 and CO2 from the second reactor; A CO2 mineralization step comprising reacting (NH4)2CO3 in water with calcium sulfate [CaSO4] to produce a solution of ammonium sulfate [(NH4)2SO4], precipitating solid calcium carbonate [CaCO3], separating CaCO3 from the above solution, and recovering ammonium sulfate crystals from the above solution; and H2SO4 production step, which includes thermally decomposing (NH4)2SO4 to produce sulfuric acid and supplying the ammonia stream released from the thermally decomposed (NH4)2SO4 to a CO2 absorption step. Regarding methods including

[0011] The effluent from the first reactor consists of a mixed salt [(NH4)2CO3 / NH4HCO3] solution in a ratio of at least 3:1, for example, 4:1 to 10:1 (by weight). The effluent from the second reactor consists essentially of a (NH4)2CO3 solution; the amount of bicarbonate is, for example, <1.0% by weight, <0.5% by weight, or <0.1% by weight. "Gas essentially free of NH3 and CO2" usually means NH3 at 100 ppm or less and CO2 at 100 ppm or less.

[0012] Figure 2 is a flowchart showing one preferred process design for carrying out a CO2 absorption step using ammonia, using two series-connected reactors labeled Reactor 1 and Reactor 2, respectively. The subsequent steps, namely the CO2 mineralization step and the H2SO4 production step, carried out in a stirred batch reactor labeled Reactor 3 and Reactor 4, respectively, are also shown in Figure 2.

[0013] The CO2 absorption process is described in detail here using Figures 2 and 3 (the latter also describes the specific experimental setup used in the tests reported below; elements identified in capital letters refer to Figure 2, and elements identified in bold numbers in parentheses refer to Figure 3).

[0014] Starting with the CO2 absorption process, the reactants supplied to reactor 1 consist of CO2-containing gas (indicated as "flue gas inlet"), ammonia (5) (either an aqueous NH4OH solution or NH3 gas), and water. The effluent (6) from reactor 1, consisting of a [(NH4)2CO3 / NH4HCO3] solution, is drawn out of reactor 1 by a pump (P1) and enters reactor 2.

[0015] One variation of the present invention, shown in Figure 3, involves the circulation of the reaction mixture in reactor (1), for example, the majority of the effluent (6) is circulated and returned to reactor (1) via a process line (6ret). A small portion of the effluent (6) is branched off from the circulation loop (7), and the branched flow (7) enters reactor (2). Optionally, the flow (6ret) or flow (7) passes through a heat exchanger (not shown) to remove heat. However, circulation and cooling of the effluent from reactor 1 are not essential and are not shown in Figure 2.

[0016] The gas discharge line (8) connects the gas outlet of reactor 1 (1) to the gas inlet of reactor 2 (2). As a result, the gas discharged from reactor 1 (1), along with the remaining unreacted NH3 and CO2, flows into reactor 2 (2). The reaction is completed in reactor 2 (2).

[0017] The effluent (9) from reactor 2(2), consisting of a high-concentration [(NH4)2CO3] solution (e.g., 100 g / l or more by weight, e.g., 150-300 g / l), is sent to a storage tank (labeled "storage tank" (10)). The treated gas is discharged from reactor 2(2) through line (11) and passes through an absorption column (labeled "ammonia scrubber") or similar apparatus, where residual NH3 reacts with sulfuric acid to produce (NH4)2SO4, which is then treated as described below.

[0018] The reactors and piping are made of stainless steel or suitable plastic such as PVC or HDPE. The wetted parts of the pump supplying the liquid flow are made of stainless steel, for example. As shown in Figure 3, arrays of CO2 and NH3 sensors can be installed in different locations to monitor the progress of the reaction. Specifically, CO2 sensors (12a, 12b, 12c) can be installed upstream of reactor (1), downstream of reactor (1), and downstream of reactor (2), respectively, and NH3 sensors (13a, 13b) can be installed downstream of reactor (1) and downstream of reactor (2), respectively. These sensors are part of an automatic control system that regulates the supply rate of the reactant / product flow in the process.

[0019] CO2-containing gases from various sources can be used as feedstocks for the process. In addition to typical flue gases and industrial CO2-containing gases, the stream produced in a steam methane reforming (SMR) plant is notable in that it contains a relatively high percentage of CO2 (about 17%). In the case of flue gases discharged from fossil fuel power plants, the CO2 levels in the incoming gas stream typically range from 10,000 to 200,000 ppm (1 to 20%, e.g., 1 to 18%, e.g., 1 to 15%, e.g., 7 to 14% CO2). Before entering the reactor (1), the flue gas typically passes through a series of conventional treatments (not shown) consisting of particulate removal (e.g., by filtration or electrostatic precipitation), a denitrification unit (conversion of nitrogen oxides), and wet scrubbing (for the selective removal of SO2) to produce a CO2-containing gas essentially free of other acidic components (the gas temperature at this stage is generally 100 to 200 °C). The flue gas free of NOx and SOx passes through a heat exchanger (labeled "inlet gas heat exchanger") to cool the gas stream to about 40 to 50 °C. The heat released from the flue gas can be recovered using a stream of fresh air and directed to serve downstream operations. The CO2-containing gas is drawn by a first blower / fan (not shown) generating a gas stream of 50,000 to 100,000 m 3 / h and enters the reactor 1(1), where a CO2 absorption reaction with ammonia occurs (CO2 / air is bubbled in the reactor 1(1) at about 0.5 bar).

[0020] Reactor 1(1) is a gas-liquid contactor. One of the features of this process is that when the incoming air / CO2 gas stream (4) is injected into the liquid in the reactor 1(1) through one or more sparging devices (14) installed below the liquid level in the reactor 1(1), CO2 microbubbles are formed. Depending on the configuration of the reactor 1(1), different-shaped sparging devices can be used to generate finely dispersed and uniform CO2 microbubbles.

[0021] For example, a flat or tubular sparger (14) made of a chemical-resistant plastic such as HDPE, polypropylene, or stainless steel (e.g., a fine bubble air disk diffuser) can be installed in the reactor 1(1). The orifice size of the gas sparger ranges from 3 to 500 μm, for example, 3 to 100 μm, for example, 3 to 20 μm, for example, 3 to 10 μm. The reactor 1(1) may be cylindrical or cuboid, and one or more flat spargers or one or more tubular spargers are horizontally attached to the bottom of the reactor. Alternatively, some shapes allow the sparger to be arranged parallel to the longitudinal axis of the reactor 1(1). The configuration of the reactor for the absorption of CO2 using ammonia will be described below together with a specific sparger shape.

[0022] There are multiple ways to supply ammonia to the reactor 1(1): A) Continuously supply a concentrated ammonium hydroxide (NH4OH) solution to the reactor 1(1) (such a solution is prepared in advance by injecting ammonia gas generated in the thermal decomposition reaction of (NH4)2SO4 into water; the NH4OH solution thus produced is held in a tank (5) at an ammonia concentration in the range of, for example, 10 - 30%). A centrifugal pump delivers the NH4OH solution to the reactor (1) through a lateral liquid inlet or by injection into the return line (6ret). The injected ammonia is diluted by a suitable volume of water pre-filled in the reactor 1(1).

[0023] B) Continuously aerate NH3 gas into the aqueous medium in the reactor 1(1) (i.e., as described later, the ammonia gas generated by the thermal decomposition of (NH4)2SO4 is cooled / compressed and stored in a liquid state or cooled and stored as a gas under pressure in an ammonia cylinder labeled "ammonia tank" in Figure 2).

[0024] Regarding option B), the CO2 and NH3 gas flows can be passed through the liquid separately (i.e., separate flows enter reactor 1(1) through different sparging devices and inlets at different locations, or these flows are mixed upstream of reactor 1(1) and the combined (CO2+NH3) flow is passed through the liquid). There are several techniques to generate a mixed flow, for example, by injecting pressurized ammonia into the CO2 gas flow or by venturi injection.

[0025] For example, in a cylindrical reactor, CO2 microbubbles are formed using a sparger as described above, but NH3 microbubbles are dispersed in water using an L-shaped sparger tube. The shorter part of the L-shaped sparger receives the NH3 flow from the side inlet of the reactor. The longer part is immersed in the liquid parallel to the longitudinal axis of the cylindrical reactor. Since the longer part is perforated, ammonia flows out through the orifice and dissolves well in the solution.

[0026] Regarding alternative designs for gas-liquid contactors housing tubular spaggers, Figures 1-5 of the joint application, International Publication No. 2022 / 130380, show that such designs are adaptable to applications where ammonia absorbs CO2 to produce ammonium carbonate. The gas-liquid contactor comprises a longitudinal horizontal housing enclosed by a bottom, top, and side, An array of tunnel-shaped sparging devices arranged horizontally and parallel to each other inside a housing, wherein the sparging devices are surrounded by an upward-curving surface, and orifices are distributed on the curved surface; One or more gas inlet manifolds connected to an array of tunnel-shaped sparging devices, suitable for introducing individual gas flows into the tunnel-shaped sparging devices, A gas outlet opening located on the upper surface and connected to a gas discharge line, the gas discharge line having a gas outlet opening connected to a second gas-liquid contact device, A first liquid supply line configured to supply a liquid flow of an aqueous ammonium hydroxide solution into the housing through one or more liquid inlet openings, A discharge opening to which an effluent discharge line is connected for removing reaction products from the gas-liquid contact device, wherein the effluent discharge line is connected to a discharge opening to a second gas-liquid contact device. Includes.

[0027] Regarding the conditions of reactor 1(1), the amount of ammonia supplied to reactor 1(1) is adjusted to meet stoichiometric requirements (an NH3 / CO2 molar ratio of approximately 2:1) by adjusting the supply rate of either the NH4OH aqueous solution stream or the ammonia gas. For example, CO2 is measured in the inflow gas stream, and unabsorbed NH3 is measured in the outflow gas stream (by NH3 sensors 13a and 13b located at the outlets of the first and second reactors). Based on the measured level of CO2 entering reactor 1, the automatic control system can change the flow rate of aqueous ammonia by controlling the pump supplying aqueous ammonia from tank (5), or by using a mass flow controller / pressure regulator located in the line supplying ammonia gas from the ammonia tank. A reaction temperature in the range of approximately 10 to 40°C is preferred, and a temperature of 10 to 30°C is particularly preferred. The pH inside reactor 1(1) is weakly alkaline.

[0028] Gas (8) is discharged from reactor 1(1) and is usually drawn into reactor 2(2) using a second blower / fan as shown in Figure 2, and enters reactor (2) through the bottom or side inlet of the reactor, preferably through a sparging device (14), where it is bubbling at approximately 0.5 bar. The liquid effluent consisting of the [(NH4)2CO3 / NH4HCO3] solution leaving reactor 1(1) is optionally supplied to reactor 2(2) after passing through a heat exchanger (not shown) that cools the solution to 20-30°C, and the cooled solution then enters reactor 2(2). For example, the heat exchanger is based on a cooling coil through which a coolant passes, or any other type of heat exchanger. The residual NH3 / CO2 in gas (8) mixes with the [(NH4)2CO3 / NH4HCO3] solution in reactor 2(2).

[0029] Typically, reactor 2(2) is a replica of reactor (1). However, other configurations are possible, namely, the aeration of gas (8) through reactor 2(2) is beneficial but not essential, and alternative gas / liquid contact patterns may be considered for reactor 2(2).

[0030] The reported experimental results indicate that the level of unabsorbed ammonia measured downstream of reactor 2(2) was at least twice, at least three times, and even at least five times lower than the level measured downstream of reactor 1(1), and that the CO2 conversion rate exceeded 90%, and even exceeded 95% (99%).

[0031] The CO2-mineralization step occurs when calcium sulfate is suspended in a pre-prepared ammonium carbonate solution. The two inorganic salts undergo ion exchange, producing an insoluble precipitate, calcium carbonate, and ammonium sulfate dissolved in the solution. As shown in Figure 2, this reaction proceeds in a batch reactor (labeled reactor 3) under stirring. Any source of calcium sulfate can be used, but gypsum (i.e., CaSO4·2H2O, the naturally occurring mineral form of calcium sulfate; gypsum is also readily available as a byproduct of phosphoric acid production, known as gypsum phosphate) is the primary source. However, the hemihydrate CaSO4· 1 / 2 H2O and anhydrous CaSO4 can also be used as starting materials for the reaction.

[0032] For example, gypsum is added to a stirred batch reactor 3 (e.g., with an external jacket) that has been pre-filled with an aqueous solution of (NH4)2CO3 received from a storage tank. The concentration of (NH4)2CO3 in the solution is preferably at least 150 g / l. The gypsum supplied to the reaction may be pre-ground to obtain fine gypsum having a particle size of, for example, 50 mesh (maximum 300 μm) or 60 mesh (maximum 250 μm). The finer the particle size of the gypsum, the more efficient the reaction. The ground calcium sulfate is added little by little, either as a solid or as a slurry in water. The progress of the reaction in reactor 3 can be monitored by sampling the reaction mixture and measuring the concentration of dissolved carbonate. This is due to the reaction and the release of CO3 2- (aq) This is because it is gradually consumed and separated from the solution in the form of water-insoluble calcium carbonate. The reaction proceeds effectively at temperatures in the range of 15–40°C.

[0033] After the reaction is complete (on an industrial scale, the reaction is expected to last 0.5 to 5 hours), the effluent (in the form of a suspension) exiting reactor 3 is separated into an aqueous phase and a solid phase by, for example, filtration, centrifugation, or any other acceptable technique (separation by centrifugation is shown in Figure 2).

[0034] The calcium carbonate separated from the suspension in the first centrifuge is stored in a tank (labeled "limestone tank"). In fact, since calcium carbonate may still contain some residual ammonium sulfate, it may be desirable to carry out a second separation step to recover a second harvest of ammonium sulfate. For this purpose, the calcium carbonate is transported to a reactor (labeled "limestone washing reactor"), where water is supplied to extract the ammonium sulfate into the aqueous phase. Solid / liquid separation, e.g., centrifugation or any other suitable filtration device, provides solid calcium carbonate that is essentially free of ammonium sulfate. The calcium carbonate may be disposed of in a landfill (through the "limestone outlet"), as carbon dioxide in this mineral form is environmentally acceptable. Alternatively, industrially acceptable grades of CaCO3 can be recovered by further processing steps, e.g., by drying the reaction products.

[0035] The clear supernatant / filtrate stream obtained after removing insoluble calcium carbonate in the first and second centrifuges (and optionally, the solution produced by the reaction of unabsorbed ammonia with sulfuric acid in an ammonium scrubber located downstream of reactor 2) is delivered to and held in a storage tank (labeled "ammonium sulfate tank" in Figure 2). The stored solution consists, for example, of an aqueous solution of ammonium sulfate with a concentration of at least 150 g / l.

[0036] Ammonium sulfate is recovered from the solution by conventional methods, namely concentration by evaporation, for example, thin-film evaporation (the corresponding apparatus is labeled "thin-film dryer" in Figure 2), or concentration in a spray dryer, thereby crystallizing the ammonium sulfate. The moisture content of the wet crystals is usually 5-10% by weight, and residual moisture can be removed in a fluidized bed dryer. The dried (NH4)2SO4 crystals thus formed are used to produce sulfuric acid while simultaneously releasing ammonia.

[0037] The H2SO4 production process, i.e., the thermal decomposition of the previously formed ammonium sulfate crystals, is carried out by methods known in the art, as described, for example, in German Patent No. 1151492, European Patent No. 83831, and International Publication No. 03 / 27018. Perhaps the most sophisticated approach, shown in the latter publication, is based on the melting of ammonium sulfate added to concentrated sulfuric acid (95-97%). Ammonium sulfate melts at 235°C and decomposes above 250°C. The boiling point of concentrated sulfuric acid is above 300°C. Therefore, there exists a temperature "window" that allows the acid to remain in a liquid state (kipping) while enabling the melting / decomposition of ammonium sulfate.

[0038] As shown in Figure 2, the thermal decomposition takes place in reactor 4, which is filled with sulfuric acid heated to approximately 275-285°C, for example, 280°C. Next, ammonium sulfate crystals are added to the hot sulfuric acid. The weight ratio of (NH4)2SO4 / H2SO4 is in the range of 1:10-1:20. When ammonium sulfate reacts with the hot acid, it decomposes into ammonia gas and sulfuric acid. The resulting NH3 gas is exhausted, cooled (the corresponding heat exchanger is labeled "ammonia heat exchanger" in Figure 2), and stored in gaseous form under pressure, or compressed and stored as liquid ammonia (labeled "ammonia tank" in Figure 2) for use in the CO2 absorption reaction. The H2SO4 produced intrinsically, i.e., the H2SO4 produced by the decomposition of ammonium sulfate, mixes readily with the pre-filled concentrated sulfuric acid. To maintain a constant liquid level in the reactor, the H2SO4 is continuously withdrawn from the reactor. In this way, concentrated sulfuric acid (approximately 98%) is produced and can be diluted with water as needed.

[0039] Figure 2 shows a preferred scheme for recycling process heat and process flow to effectively meet process needs with minimal energy cost. As the high-temperature sulfuric acid product is continuously drawn from reactor 4, it passes through a heat exchanger (referred to as the “steam heat exchanger,” also referred to herein as the “third heat exchanger”), where the acid transfers heat to steam discharged from the evaporator (i.e., from the “film dryer”). The steam is recompressed by an electrically operated compressor (the mechanical steam recompressor is referred to as the “MVR”) and then reused to heat the evaporator. The acid discharged from the third heat exchanger is still very hot, and its temperature may be in the range of 150–200°C. In the first heat exchanger (referred to as the “sulfuric acid heat exchanger”), heat is transferred from sulfuric acid to ammonium sulfate solution as it flows from the storage tank to the evaporator (i.e., through the process line connecting the “ammonium sulfate tank” and the “film dryer”). Next, the cooled sulfuric acid is stored and diluted as appropriate (labeled "sulfuric acid"). Before the ammonium sulfate flow enters the evaporator, it is further heated as it passes through a second heat exchanger (labeled "heat exchanger for condensed acid") supplied by steam discharged from the evaporator. The water produced by condensation is stored in a reservoir (labeled "condensation tank") and supplied to reactor 1 by the process line, where calcium carbonate can be treated, for example, in the stage of extracting a second harvest of ammonium sulfate in the "limestone washing reactor".

[0040] Another aspect of the present invention is an apparatus for producing sulfuric acid from industrial gases and for mineralizing CO2, A first reactor and a second reactor connected in series, wherein one or more spaggers are installed in the first reactor, preferably also in the second reactor, and a supply line supplied by a CO2-containing gas source is connected to the spaggers in the first reactor; the effluent outlet of the first reactor is connected to the liquid inlet of the second reactor by a first piping line; the gas outlet of the first reactor is connected to the gas inlet of the second reactor by a first gas discharge line; the effluent outlet of the second reactor is connected to one or more storage tanks by a second piping line; the gas leaving the second reactor is released into the atmosphere by a second gas discharge line; a CO2 sensor is located upstream of the first reactor, and an NH3 sensor is located downstream of the first reactor. A third reactor (e.g., a stirred batch reactor) supplied by one or more storage tanks, wherein the outlet of the third reactor is connected to a first solid / liquid separator by a third piping line, the first solid / liquid separator discharges to a liquid storage tank and a solid storage tank, the liquid storage tank is connected to an evaporator by a process line, a first heat exchanger and a second heat exchanger are arranged on the process line leading into the evaporator, the evaporator is provided with a solid discharge line and a steam recirculation loop, a third heat exchanger and optionally mechanical evaporative recompression means are arranged along the steam recirculation loop, and the third reactor is supplied by one or more storage tanks, A fourth reactor connected to the evaporator described above, which receives solid material from there, having a gas discharge line that exits the fourth reactor and enters an ammonia tank, a cooler and / or compressor arranged along the gas discharge line, the ammonia tank being connected by a process line to the first reactor or to a container supplying to the first reactor, and the effluent outlet of the fourth reactor being connected by a fourth piping line to the third heat exchanger and the first heat exchanger, Blower and pump for supplying and recovering gaseous and liquid process flows It is a device that includes this. [Brief explanation of the drawing]

[0041] [Figure 1] Figure 1 shows a conventional process design (International Publication No. 96 / 09248) for bubbling NH3 and CO2 through a CaSO4 slurry in water. [Figure 2] Figure 2 is a preferred process flow diagram of the present invention, comprising three main parts: a CO2 absorption step in which ammonia is used to obtain ammonium carbonate, which takes place in two series-connected reactors; a CO2 mineralization step in which ammonium carbonate reacts with gypsum to obtain ammonium sulfate and calcium carbonate; and a step in which sulfuric acid and ammonia are obtained by thermal decomposition of ammonium sulfate. [Figure 3] Figure 3 shows the experimental apparatus used in the example. [Figure 4] Figure 4 shows the CO2 conversion rate versus time plot for the experiment in Example 3. [Figure 5] Figure 5 shows the CO2 conversion rate versus time plot for the experiment in Example 6.

[0042] Examples Examples 1 and 2 Production of ammonium carbonate from ammonia and carbon dioxide: The effect of two reactors connected in series A series of experiments were conducted to investigate the reaction of ammonia and carbon dioxide in water to produce ammonium carbonate.

[0043] Experimental apparatus The experimental apparatus is shown in Figure 3. Reactors (1) and (2) have the same configuration. Each reactor consisted of a rectangular tank with the following dimensions: length = 50 cm; width = 25 cm; height = 50 cm. A tubular spagger (length = approximately 50 cm, diameter = 60 mm, made of EPDM or stainless steel) was horizontally installed in each reactor. The orifice diameter of the spagger was approximately 10 μm.

[0044] The liquid discharge line of reactor (1) was connected to the side inlet of reactor (2). A centrifugal dosing pump P1 was installed to draw out the liquid effluent from reactor (1). Most of the effluent (6) was recirculated and returned to reactor (1) via pipe (6ret). A small amount of effluent (6) was branched off from the circulation loop (7), and the branched flow (7) entered reactor (2). The product solution was drawn from reactor (2) via a conduit to a storage tank (10) (9) and recovered there.

[0045] The CO2 source was commercially available 100% CO2 filled in a gas cylinder. The CO2 and air streams were fed into a gas mixer and mixed to produce a CO2 / air (6%) mixed flow (4), which was then introduced to reactor (1) by a blower at various flow rates as shown in Table 1 (a gas flow meter was placed along the line). A second blower was installed to draw the outflow gas stream (8) from reactor (1) into reactor (2) through a tubular spagger attached to the bottom of reactor (2). The gas stream (11) discharged from the top of reactor (2) was passed through an acid trap (consisting of a 6% H2SO4 solution).

[0046] An aqueous solution of NH4OH (28% by weight) was held in a tank (5) connected to reactor (1) by a polypropylene pipe. The flow of the NH4OH solution from tank (5) to reactor (1) was driven by a peristaltic pump.

[0047] An array of sensors was placed within the system: two CO2 sensors and three NH3 sensors. One CO2 sensor was placed at the inlet of reactor (1) (to measure the CO2 concentration in the incoming air / CO2 mixed stream), and the other sensor was placed downstream of the acid trap (to measure the CO2 level in the purified gas). Three NH3 sensors were placed downstream of reactor (1), reactor (2), and the acid trap, respectively, to measure the percentage of unreacted ammonia flowing out of the first and second reactors and the trap. A pH electrode was immersed in reactor (1).

[0048] Experimental protocol Each experiment was initiated by filling reactors (1) and (2) with 20 liters of deionized water. A tubular spagger was submerged approximately 10–20 cm below the surface level of the solution.

[0049] An air / CO2 mixed gas stream was drawn into reactor (1) through a side opening by a first blower (0.5 bar) and passed through a sparger at the flow rates shown in Table 1 below to generate microbubbles. A second blower operated at 0.5 bar to send the gas stream leaving reactor (1) to a sparger installed in reactor (2). A pump supplied an aqueous NH4OH solution at a flow rate adjusted to meet the stoichiometric requirement of approximately 2:1, the reactor temperature was 15°C to 25°C, and the pH was weakly alkaline. The flow rate of the liquid stream pumped from the first reactor to the second reactor was 4 L / min, and the residence time was several minutes.

[0050] The experiment was conducted according to two programs: operating only reactor (1); and operating both reactors (1) and (2). CO2 and NH3 levels in the inflow and outflow gas streams were continuously recorded throughout the test period using sensors placed at various locations. Each operation lasted for 8 to 12 hours.

[0051] result The results are shown in Table 1. The CO2 level in the inflow air / CO2 gas stream measured throughout the experiment was 6%. [Table 1]

[0052] Examples 1A and 2A correspond to experiments conducted using a single reactor, while Examples 1B and 2B are parallel experiments conducted under the same conditions but using a pair of reactors. The results demonstrate the advantages of conducting the reaction using two reactors in series. Specifically, switching to an experimental design utilizing two reactors minimizes ammonia loss and increases the conversion rate by approximately 10%.

[0053] Examples 3 and 4 Preparation of ammonium carbonate from ammonia and carbon dioxide in two reactors connected in series. Further experiments were conducted to study the reaction between ammonia and carbon dioxide in water to produce ammonium carbonate, using the same experimental setup and protocol as described in Examples 1 and 2. This time, all experiments were performed using a pair of reactors. The reaction conditions and results are shown in Table 2. The experiments were conducted for 5 hours. [Table 2]

[0054] The results shown in Table 2 demonstrate that the process design of the present invention can achieve a high conversion rate, for example, 99%. The proportion of ammonia effluent from the second reactor was considerably lower than the unabsorbed ammonia carried away by the exhaust gas from the first reactor. These results are also shown graphically in Figure 4 as a CO2 conversion rate versus time plot for Example 3. The average CO2 conversion rate measured over 5 hours was approximately 99%.

[0055] Example 5 Preparation of calcium carbonate and ammonium sulfate from ammonium carbonate and calcium sulfate One liter of ammonium carbonate solution with a concentration of 150 g / l was placed in a reaction vessel, followed by the addition of gypsum (210 g; particle size 60 mesh). The mixture was stirred with a standard stirrer for 2 hours. The progress of the reaction was monitored by collecting samples at 30-minute intervals, and the dissolved carbonate anion (CO3) was detected. 2- The concentration change of ) was measured. The dissolved carbonate anions "disappear" from the solution due to the precipitation of CaCO3.

[0056] CO3 in the aqueous phase 2-To measure the concentration, a sample of the reaction mixture was filtered through Whatman 41 filter paper, and the suspended solid was separated from the aqueous phase. The clear filtrate was collected, and the sample was taken from it and added to a sealed container with one outlet connected to a measuring tube. A 6% sulfuric acid solution was added to this container. The carbon dioxide gas produced by the reaction between the sulfuric acid and the dissolved carbonate was collected in the measuring tube. (NH4)2CO3+H2SO4→(NH4)2SO4+CO2+H2O (5)

[0057] The results are shown in Table 3 below. The changes measured during the 120-minute test period are shown for CO3 at t=0. 2- It is expressed as a percentage of the initial concentration. [Table 3]

[0058] Example 6 (Comparative; International Publication No. 96 / 09248) One-step reaction: CO2 + 2NH3 + CaSO4 + H2O → (NH4)2SO4 + CaCO3 Using a stirred reactor, the efficiency of a one-step conversion from CO2, ammonia, and aqueous gypsum slurry to ammonium sulfate and calcium carbonate was tested.

[0059] A reactor was filled with 30 liters of 25% NH4OH. An air / CO2 (6%) mixed gas stream was continuously supplied to the reactor via a sparger at a feed rate of 8 L / min. Simultaneously, a 25% NH4OH solution was supplied at a flow rate that met the molar ratio requirement of approximately 2:1 throughout the experiment. After a few minutes, gypsum (250 g; particle size 60 mesh) was added to the reactor, resulting in vigorous foaming. The experiment continued for 6 hours; the effluent from the reactor was continuously discharged into a storage tank (the reactor volume was approximately 60% during the reaction). The CO2 level in the gas discharged from the reactor was continuously recorded. The results are shown in Figure 5 as a CO2 conversion rate versus time plot. The average CO2 conversion rate measured over 6 hours was approximately 95%.

[0060] At the end of the experiment, the solid was removed from the reaction mixture and the filtrate was collected. Dissolved carbonate anions (CO3) in the filtrate 2- The concentration of CO2 was measured using the technique described above, namely by determining the volume of CO2 bubbles produced by the reaction of unreacted ammonium carbonate with sulfuric acid. The concentration of unreacted ammonium carbonate was found to be 61 g / L. This result indicates that the process design, which relies on supplying ammonia water to a reactor filled with crushed gypsum suspended in water and allowing microbubbles of CO2 to flow continuously through this mixture, is inefficient. CO2 is absorbed by ammonia in the system, and the resulting ammonium carbonate then reacts with calcium sulfate to give ammonium sulfate and calcium carbonate, but a fairly large proportion of ammonium carbonate in the solution remains unreacted, so the overall one-step reaction (CO2 + 2NH3 + CaSO4 + H2O → (NH4)2SO4 + CaCO3) is not completed.

Claims

1. Production of sulfuric acid from industrial gases and CO ２ A method for the mineralization of, CO ２ Continuously aerate the gas containing CO through an aqueous ammonia solution in the first reactor, or ２ continuously aerate the gas containing CO and ammonia gas through water to produce a [(NH ４ ) ２ CO ３ / NH ４ HCO ３ solution; draw the [(NH ４ ) ２ CO ３ / NH ４ HCO ３ solution continuously from the first reactor, optionally cool the [(NH ４ ) ２ CO ３ / NH ４ HCO ３ solution, and then supply it to the second reactor. Supply a gas stream containing NH ３ and CO ２ discharged from the first reactor to the second reactor, whereby an aqueous solution of (NH ４ ) ２ CO ３ is produced in the second reactor, and a gas essentially free of NH ３ and CO ２ is released from the second reactor. This includes a CO ２ absorption process;​​​​ (NH ４ ) ２ CO ３ calcium sulfate [CaSO4] ４ ] reacts with ammonium sulfate [(NH ４ ) ２ SO ４ [A solution is produced, and solid calcium carbonate [CaCO3] is formed. ３ ] precipitates, CaCO ３ CO2 includes separating CO2 from the solution and recovering ammonium sulfate crystals from the solution. ２ Mineralization process; and Said (NH ４ ) ２ SO ４ It is thermally decomposed to produce sulfuric acid, and the thermally decomposed (NH ４ ) ２ SO ４ CO2 ２ H ２ SO ４ Generation process A method that includes this.

2. The NH discharged from the first reactor ３ and CO ２ The method according to claim 1, wherein a gas stream containing is passed through the solution in the second reactor.

3. The method according to claim 1 or 2, wherein the ventilation is performed through a gas spagger having an orifice size in the range of 3 to 500 μm.

4. The method according to claim 3, wherein the orifice size of the gas sparger is in the range of 3 to 20 μm.

5. The method according to claim 1 or 4, wherein the level of unabsorbed ammonia measured downstream of the second reactor is at least three times lower than the level measured downstream of the first reactor.

6. (NH) produced in the second reactor ４ ) ２ CO ３ The method according to any one of claims 1 to 5, wherein the solution contains 0.5% by weight or less of ammonium bicarbonate.

7. The aforementioned CO ２ The method according to any one of claims 1 to 6, wherein the inorganicization step is carried out in a third reactor, and the generated ammonium sulfate solution is evaporated to recover ammonium sulfate crystals.

8. The method according to claim 7, wherein, upstream of the evaporation, the ammonium sulfate solution is heated in the first heat exchanger by heat transferred from the high-temperature sulfuric acid produced by the thermal decomposition of the ammonium sulfate in the fourth reactor.

9. Before the flow of ammonium sulfate enters the evaporator, it is further heated in a second heat exchanger by the steam discharged from the evaporator, and the water produced by the condensation of the steam is the CO ２ The CO2 for the absorption process and / or for processing the resulting calcium carbonate ２ The method according to claim 8, wherein in the inorganicization step, the material is supplied to the first reactor by a process line.

10. The method according to claim 8 or 9, comprising the steps of: evaporating the ammonium sulfate solution in a thin-film evaporator; transporting the ammonium sulfate crystals to the fourth reactor; continuously drawing high-temperature sulfuric acid from the fourth reactor; transferring heat to the steam discharged from the evaporator by passing the high-temperature sulfuric acid through a third heat exchanger; recompressing the steam; and guiding the steam to heat the evaporator.

11. The method according to claim 10, wherein, as the ammonium sulfate solution flows from the storage tank to the evaporator, the sulfuric acid discharged from the third heat exchanger is passed through the first heat exchanger to transfer heat to the ammonium sulfate solution upstream of evaporation.

12. Sulfuric acid is produced from industrial gases, CO ２ A device for mineralizing, - At least a first reactor and a second reactor connected in series, wherein one or more spargers are installed in the first reactor, preferably also in the second reactor, and CO2 is supplied to the sparger in the first reactor. ２ A supply line is connected to a source of contained gas; the effluent outlet of the first reactor is connected to the liquid inlet of the second reactor by a first piping line; the gas outlet of the first reactor is connected to the gas inlet of the second reactor by a first gas discharge line; the effluent outlet of the second reactor is connected to one or more storage tanks by a second piping line; the gas leaving the second reactor is released into the atmosphere by a second gas discharge line; CO ２ The sensor is located upstream of the first reactor, and NH ３ The sensor is located downstream of the first reactor, between the first reactor and the second reactor, - A third reactor supplied by one or more storage tanks, wherein the outlet of the third reactor is connected to a first solid / liquid separator by a third piping line, the first solid / liquid separator discharges to a liquid storage tank and a solid storage tank, the liquid storage tank is connected to an evaporator by a process line, a first heat exchanger and a second heat exchanger are arranged on the process line leading into the evaporator, the evaporator is provided with a solid discharge line and a steam recirculation loop, a third heat exchanger and optionally mechanical evaporative recompression means are arranged along the steam recirculation loop, the third reactor, - A fourth reactor connected to the evaporator, from which it receives solid material, having a gas discharge line that exits the fourth reactor and enters an ammonia tank, with a cooler and / or compressor positioned along the gas discharge line, the ammonia tank being connected by a process line to the first reactor or to a container supplying the first reactor, and the effluent outlet of the fourth reactor being connected by a fourth piping line to the third heat exchanger and the first heat exchanger, - Blowers and pumps for supplying and recovering process flows of gases and liquids A device that includes this.

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