Lime production process and system with reduced carbon emissions

Abstract

The present invention relates to the chemical industry and provides a process and system for producing quicklime with reduced carbon emissions. The solution uses industrial coal gas or natural gas to provide the energy required for calcination, and adjusts the amount of circulating flue gas to control the reactive atmosphere. After dry preheating, gypsum is reduced and calcined using a hydrogen-containing reducing gas, achieving a decomposition rate approaching 100%. The calcined product undergoes CaO upgrading depending on its CaO content, with the yield of upgraded CaO also approaching 100%. The hydrogen atom content in the reducing gas determines the amount of CO2 emissions reduced during the process. This process not only provides a new, sustainable, and pollution-free treatment method for currently difficult-to-treat industrial gypsum, but also alleviates China's current sulfur resource shortage and reduces its dependence on external sources. The calcined product, quicklime, can be used as a desulfurization and denitrification agent instead of natural limestone. Furthermore, CO2 emissions during the quicklime production process are significantly reduced, which is of great significance for reducing carbon emissions and achieving carbon neutrality in the industrial process.

Description

[Technical field]

[0001] The present invention relates to the chemical engineering field, and in particular to a process and system for producing quicklime with reduced carbon emissions. [Background technology]

[0002] The information disclosed in this Background section merely enhances the understanding of the overall background of the present invention, but is not necessarily acknowledged as an admission or in any manner implying that the information constitutes prior art known to those skilled in the art.

[0003] China has abundant reserves of gypsum resources, with reserves of about 57 billion tons. Gypsum is also a by-product of the chemical fertilizer industry and various pollution control systems. Phosphogypsum is a solid waste discharged during the production of phosphorus fertilizer and phosphoric acid. China's annual discharge of phosphogypsum is about 55 million tons, with a comprehensive utilization rate of only about 10 million tons and an accumulated deposition of about 300 million tons. Desulfurized gypsum is a solid waste generated in industrial flue gas desulfurization systems, and China's annual production of desulfurized gypsum is about 100 million tons.

[0004] At present, the total amount of industrial by-product gypsum in the world is small, and 90% is used at a low level and low added value. The utilization rate of phosphogypsum in Europe and the United States is generally less than 10%, and most of it is stored. At present, the world's accumulation of phosphogypsum is about 6 billion tons, with an average annual increase of 150 million tons. The utilization rate of desulfurized gypsum is significantly higher than that of phosphogypsum, which is basically maintained at about 50% in Europe and China, and most of it is used in basic building materials such as gypsum boards. In Japan, the utilization rates of phosphogypsum and desulfurized gypsum both reach more than 90% (Japan has serious shortages of natural gypsum sources), but the amount is relatively small and is in fields with low-level science and technology and low content, such as building materials.

[0005] Currently, the pollutant SO2 in flue gas can be recycled to produce sulfuric acid, sulfur, and liquid SO2. However, the prerequisite for the SO2 in flue gas to be captured is that the SO2 in the flue gas must reach a certain concentration, and the higher the concentration, the easier it is to capture and the lower the capture cost.

[0006] Quicklime is widely used in metallurgy, environmental protection, fine chemicals, food and other industries. China's annual demand for lime is about 250 million tons, of which the demand for high-quality, high-activity, high-calcium lime is about 100 million tons. The main source of industrial quicklime is calcined limestone. China has abundant limestone reserves, but excessive development has caused serious damage to surface vegetation and the ecological environment. In addition, the process of calcining limestone to produce quicklime generates a large amount of CO2, and about 1.79 tons of limestone are required to produce 1 ton of quicklime, generating about 0.79 tons of CO2. Such a large amount of CO2 emission greatly hinders the reduction of carbon emissions and the progress of carbon neutrality, so there is an urgent need to find a quicklime production process with low or zero CO2 emissions. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes a quicklime production process with reduced carbon emissions by combining the gypsum reduction decomposition process, CaS CaO production technology, and sulfur production technology by coupling high-concentration SO2 with reducing gas. The energy required for calcination is provided by using industrial coal gas or natural gas, and the amount of circulating flue gas is adjusted to adjust the nature of the reactive atmosphere. As for gypsum (natural gypsum or industrial by-product gypsum), the main component is CaSO4·2H2O. After drying and preheating, CaSO4 or CaSO4·0.5H2O is obtained. After reduction and calcination by hydrogen-containing reducing gas, the decomposition rate reaches nearly 100%. For the calcined product, whether to perform CaO upgrading is determined according to the CaO content ratio, and the yield of upgraded CaO is also close to 100%. The hydrogen atom content in the reducing gas determines the amount of CO2 emission reduction during the process. The high-concentration SO2 produced during the process is then reacted with reducing gas under the action of a catalyst to produce sulfur. The sulfur obtained by reducing SO2 with a gas reducing agent has higher purity and higher quality.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0009] In a first aspect of the present invention, there is provided a process for producing quicklime with reduced carbon emissions, comprising: The preheated gypsum is contacted with hydrogen-containing reducing gas at 700-1200°C to generate CaO, CaS and SO2 flue gas, then the SO2 flue gas is separated into gas and solid, and the solid material and SO2 flue gas I are collected; if the CaO% in the calcined solid material is < 95%, the solid material is upgraded with CaO so that the CaO% in the solid material is ≥ 95%, then the gas and solid separation is performed, the solid CaO is collected, and the solid CaO is stored after cooling, and the SO2 flue gas II is collected; Alternatively, the preheated gypsum is contacted with a hydrogen-containing reducing gas at 700 to 1200 ° C., the concentration of the reducing agent M is controlled to 10% or less, and the CO2 concentration is controlled to 8 times or more the concentration of the reducing agent M, CaSO4 is completely decomposed into CaO, and the gypsum is cooled and then stored. The SO2 flue gas I is first used to preheat gypsum, and then mixed with the SO2 flue gas II, and reduced to elemental sulfur vapor in the presence of a catalyst, and then recovered to obtain and store sulfur; The flue gas after sulfur recovery is divided into three parts; one part is returned to the reduced calciner to adjust the reactive atmosphere, another part is used for CaO upgrading in the upgrader, and the last part is burned and purified in the system boiler before being discharged.

[0010] The present invention provides a quicklime production process with reduced carbon emissions that uses hydrogen-containing reducing gas to reduce and decompose gypsum (natural gypsum or industrial by-product gypsum), not only alleviating the problem of Chinese industrial gypsum (mainly calcium sulfate dihydrate) being difficult to treat, but also utilizing it as a resource, recovering sulfur resources and quicklime, alleviating the current situation of China's sulfur resource shortage, and reducing external dependency on sulfur resources. Quicklime can be used as a desulfurization agent for wet desulfurization and an additive for blast furnace iron sintering materials instead of natural limestone, reducing the mining of natural limestone resources. In addition, the CO2 emissions in the quicklime production process can be significantly reduced, which is of great significance for reducing carbon emissions in industrial processes and achieving carbon neutrality.

[0011] Research has shown that the main component of gypsum is calcium sulfate dihydrate, and that the decomposition route of calcium sulfate changes when it comes into contact with hydrogen-containing reducing gases such as hydrogen, methane, and coal gas. In the temperature range of 700℃ to 1200℃, two reactions occur simultaneously in gypsum. First, JPEG0007627470000001.jpg66170

[0012] In many cases, two types of reactions exist simultaneously and compete with each other. The distribution of products differs depending on the reduction potential. CaS reacts with CO2 at 500-1200°C to produce CaO, high-concentration SO2, and high-concentration CO (CaS+3CO2→CaO+SO2+3CO), and CaS reacts with water vapor at 500-1200°C to produce CaO, high-concentration SO2, and high-concentration H2 (CaS+3H2O→CaO+SO2+3H2). In the reaction temperature range of 700-1200℃, regardless of whether the reactive atmosphere is CO, H2, CH4, natural gas, coal gas, etc., by controlling the concentration of reducing agent M to 10% or less and adding 8 times more CO2, CaSO4 can be completely decomposed and decomposed into CaO, and the yield of CaO is more than 99.5%. The SO2 and CO / H2 in the combustion flue gas act as a catalyst to cause an oxidation-reduction reaction in the temperature range of 400-1000℃ to generate elemental sulfur vapor, which can be recovered by dust removal and cooling.

[0013] A second aspect of the present invention provides a system for producing quicklime with reduced carbon emissions, comprising a reduction calciner, a CaO upgrader, a quicklime storage silo, a SO2 reduction tower, a sulfur recovery device, a sulfur storage tank, a boiler, and a flue gas cleaning system, the reduction calciner being provided with a gypsum inlet and a hydrogen-containing reducing gas inlet, the material outlet of the reduction calciner being connected to each of the CaO upgrader and the quicklime storage silo, the gas outlet of the reduction calciner being connected to the SO2 reduction tower, the material outlet of the SO2 reduction tower being connected to the sulfur recovery device and the sulfur storage tank, in that order, and the SO2 reduction tower being further connected to the boiler and the flue gas cleaning system, in that order.

[0014] A third aspect of the present invention provides an application of the above-mentioned quicklime production system in reducing carbon emissions and achieving carbon neutrality.

[0015] Beneficial effects of the present invention include: The present invention provides a quicklime production process with reduced carbon emissions. The CO2 concentration is controlled to be more than 8 times the concentration of the reducing agent M, and the gypsum can be directly decomposed into quicklime by reacting gypsum with hydrogen-containing reducing gas at high temperature to produce two substances, CaO and CaS, at the same time. CaS reacts with CO2 or steam at high temperature to produce CaO. By using calciner, CaO upgrader, high-temperature separator, SO2 gas-phase reduction technology, sulfur recovery equipment and various heat exchangers, the reaction conditions are precisely controlled to produce quicklime using solid industrial waste gypsum that is difficult to treat, and sulfur is also produced as a by-product. Quicklime can be used as a desulfurization and denitrification agent instead of natural limestone, and sulfur is an important industrial raw material with a very high market value. In addition, the present invention reduces and decomposes gypsum with hydrogen-containing reducing gas to produce quicklime, which can reduce the CO2 emission in the quicklime production process, and the amount of CO2 emission reduction is related to the content of hydrogen atoms in the reducing gas. By using pure H2 to reduce and calcinate gypsum to produce quicklime, the quicklime production process can achieve zero CO2 emissions. This invention is of great significance to the reduction of carbon emissions and carbon neutrality in the chemical industry.

[0016] The beneficial effects of this process are: 1. The hydrogen-containing reducing gas is used to reduce and decompose gypsum to produce quicklime and sulfur products, providing a brand new quicklime production process and reducing the amount of CO2 emissions during quicklime production, which is of great significance to reducing carbon emissions and achieving carbon neutrality. 2. The production of quicklime and sulfur products from industrial by-product gypsum not only solves the problem of industrial by-product gypsum being difficult to process, but also realizes high-value utilization of industrial solid waste, thereby increasing the added value of the process and improving its economic efficiency. 3. The reduction and decomposition of gypsum using a hydrogen-containing reducing agent not only significantly reduces the decomposition temperature of gypsum, but also significantly shortens the reaction time and greatly reduces the energy consumption of the process. 4. This process solves the current situation that a small amount of CaS is inevitably generated during the conventional gypsum calcination. The presence of CaS is an unfavorable factor for the product produced by calcining gypsum to produce quicklime. If CaS is present during the use of quicklime, it will have a significant impact on the activity and quality of the quicklime, and may produce sulfur pollutants such as H2S. The quicklime product calcined by this process has a higher content of effective components (CaO), higher purity, higher activity, higher corresponding utility value, and wider range of uses. 5. When the concentration of the reducing agent M is controlled to 10% or less and the CO2 concentration is controlled to 8 times or more than the concentration of the reducing agent M, CaSO4 can be completely decomposed and decomposed into CaO, and the yield of CaO is more than 99.5%. According to this discovery, the range of reducing gases is broadened, and it is not limited to using CO as a reducing agent, and gypsum can be directly reduced and decomposed into quicklime (CaO%≧95%). Even if other reducing agents, such as hydrogen-containing reducing agents such as H2, CH4, C2H4, H2S, natural gas, coal gas, etc. are used, gypsum can be reduced and decomposed into quicklime (CaO%≧95%). This discovery provides a theoretical basis for a quicklime production process with low or no CO2 emissions.

[0017] This process provides a brand new, sustainable and non-polluting treatment method for industrial gypsum, which is currently difficult to treat, and not only realizes the recycling of gypsum, but also alleviates China's current sulfur resource shortage and reduces its external dependency on sulfur resources. The calcined product, quicklime, can be used as a desulfurization and denitrification agent instead of natural limestone, reducing limestone mining and protecting the ecological environment. In addition, it can significantly reduce CO2 emissions in the quicklime production process, which is of great significance for reducing carbon emissions in the industrial process and achieving carbon neutrality. Therefore, this process has a broad market prospect. [Brief description of the drawings]

[0018] The specification drawings which form a part of the present invention are intended to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their explanations are intended to interpret the present invention and are not intended to unduly limit the present invention.

[0019] [Figure 1] FIG. 1 is a schematic diagram of a quicklime production process and system with reduced carbon emissions in Example 1 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0021] It should be noted that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form, and it should be understood that when the terms "comprise" and / or "comprise" are used herein, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] For ease of explanation, when the characters "up", "down", "left" and "right" are described in the present invention, they only indicate that they correspond to the up, down, left and right directions of the drawings themselves, and are not intended to limit the structure, but are merely intended to simplify and simplify the explanation of the present invention, and are not intended to indicate or imply that the designated device or element has a specific orientation or is required to be constructed and operated in a specific orientation, and should not be understood as limiting the present invention.

[0023] Regarding the interpretation of terms, the terms "attached", "connected", "connected", "fixed" and the like in the present invention should be understood in a broad sense, for example, they may be fixedly connected, detachably connected, or integral, they may be mechanically connected, electrically connected, directly connected, indirectly connected via an intermediate medium, an internal connection of two elements, or an interactive relationship between two elements. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0024] The present invention will be described in more detail with reference to the following specific examples. It will be pointed out that the specific examples are not intended to limit the present invention, but should be construed as such. Example 1:

[0025] A quicklime production process with reduced carbon emissions, mainly comprising: The gypsum is stored in the gypsum storage silo, and the amount of the material is precisely controlled by the feeding machine and sent to the gypsum preheating dryer for preheating and drying. The high temperature heat source is the high temperature flue gas discharged from the calcination section. The temperature of the gypsum after preheating and drying is 600-1000°C. It first enters the calciner, where the reaction temperature is 700-1200°C. The amount of hydrogen-containing reducing gas and circulating flue gas is controlled, and the relatively high temperature, JPEG0007627470000002.jpg57170 is generated to generate CaS. Alternatively, by controlling the concentration of the reducing agent M to be 10% or less and the CO2 concentration to be 8 times or more than the concentration of the reducing agent M, CaSO4 can be completely decomposed and decomposed into CaO, and the yield of CaO is more than 99.5%. The high-concentration SO2 flue gas generated by the reduced calciner enters the high-temperature separator 1 with the calcined material, and the separated solid material is determined to be upgraded to CaO according to its CaO content ratio. If the CaO% in the calcined solid material is ≥ 95%, it can be directly stored in the quicklime storage silo after cooling. If the CaO% in the calcined solid material is < 95%, it needs to enter the CaO upgrader for upgrading. In the upgrader, the CaS in the calcined solid material reacts with the water vapor in the circulating flue gas at 500.~1200℃ to produce CaO, high concentration SO2 and high concentration H2 (CaS+3H2O→CaO+SO2+3H2), or the CaO in the circulating flue gas can be used as a substitute for CaO. It reacts with the CO2 in the gas to produce CaO, high-concentration SO2 and high-concentration CO (CaS+3CO2→CaO+SO2+3CO), and the CaO% in the upgraded solid material is ≧95%. It is separated into gas and solid by high-temperature separator 2, cooled and then sent to the quicklime storage silo. The high-concentration SO2 flue gas separated by high-temperature separator 1 is a reducing atmosphere. It first enters the gypsum preheating and drying system, and the residual heat of the flue gas is used to preheat and dry the gypsum. The flue gas after utilizing the residual heat enters the SO2 reduction tower.The high-concentration SO2 gas separated by the high-temperature separator 2 is also a reducing atmosphere, and is mixed with the flue gas separated by the high-temperature separator 1 and then sent to the SO2 reduction tower. In the SO2 reduction tower, at a temperature range of 400-1000°C, the SO2 in the flue gas can be reduced to elemental sulfur vapor by the reducing gas through the action of catalyst. The elemental sulfur vapor is recovered in the sulfur recovery device to obtain sulfur, which is then stored in the sulfur storage tank. The exhaust gas after sulfur recovery is divided into three parts. One part returns to the reducing calciner to adjust the reactive atmosphere, the other part enters the CaO upgrader to participate in the reaction, and the last part enters the boiler to burn the unreacted CO or hydrogen generated during the reaction, and then enters the flue gas purification system together with the boiler flue gas for purification before being discharged.

[0026] The gypsum may be a calcium sulfate product having a particle size of 60 μm to 3 mm and a moisture content of 5 to 20%, such as wet desulfurized gypsum, semi-dry desulfurized ash, phosphorus gypsum, or natural gypsum; The high concentration SO2 flue gas produced by the calciner has a SO2% of 2-10%, a CO% of 4-20%, a temperature of 700-1200°C, and main components of SO2, CO, N2, CO2, etc. The high-concentration SO2 gas produced by the CaO upgrader has a SO2 content of 2-10%, an O2 content of 4-10%, a temperature of 500°C to 1200°C, and main components of SO2, CO, N2, CO2, etc. The hydrogen-containing reducing gas has main components of H2, CH4, C2H4, H2S, natural gas, coal gas, etc., and the content may be a combination of some or all of the above components according to the origin of the reducing gas; The main components of the exhaust gas are N2, CO, CO2, etc., with CO2% being 10 to 80% and H2O% being 10 to 80%; The gypsum preheater may be a gas-solid heat exchanger of various types, such as a multi-stage cyclone, a shell-and-tube heat exchanger, a plate-and-shell heat exchanger, or a plate heat exchanger; The feeder may be of various types, such as a screw feeder, an airlock feeder, etc. The external heat source may be a burner, the fuel of which may be of various types such as coal, natural gas, diesel, coal gas, etc., or may be a microwave reactor or an electrically heated reactor; The high-temperature separator may be a high-temperature cyclone separator, a high-temperature axial flow separator, or other types of separators; The calciner and CaO upgrader can be of various types, such as moving bed, rotary kiln, fixed bed, turbulent bed, bubbling bed, micro-fluidized bed, spouted bed, etc. The reduced calciner and the CaO upgrader may be two independent reactors, or may be in different positions in the same reactor if different reactive atmospheres are separated; The gas transport process is powered by an induction fan or blower; The reduced high-concentration SO2 flue gas discharged from the reduced calciner is separated by a high-temperature separator, and then secondary dust removal is performed by a high-temperature filter, after which the sulfur is condensed by a sulfur condenser to recover the sulfur. The purity of the recovered sulfur reaches 99.7% or more, complying with the first-class standard for industrial sulfur.

[0027] Finally, it should be explained that the above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art may still modify the technical solutions described in the above embodiments, or may equivalently replace some of them. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention. Although the above describes a specific embodiment of the present invention, it does not limit the protection scope of the present invention, and those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the technical solutions of the present invention without the need for creative work are still within the protection scope of the present invention.

Claims

1. A process for producing quicklime with reduced carbon emissions, comprising: Step (1) Gypsum preheated in a gypsum preheating dryer is placed in a reduction calciner and contacted with a hydrogen-containing reducing gas at 700 to 1200°C to produce CaO, CaS, and SO ２ generating a flue gas I containing Step (2): The product obtained in step (1) is subjected to gas-solid separation to obtain the solid material produced by the reduced calciner and SO ２ collecting flue gas I containing Step (3) The SO collected in step (2) ２ The flue gas I containing ２ The SO is reduced to sulfur vapor in a reduction tower under catalytic conditions, and the recovered sulfur is obtained. ２ The flue gas I containing ２ The exhaust gas is then desulfurized in the reduction tower. Step (4): If the CaO content in the solid material collected in step (2) is CaO%<95%, perform CaO upgrading on the solid material in a CaO upgrading machine so that the CaO content in the solid material is CaO%≧95%, and then perform gas-solid separation. Collect the solid CaO, cool it, and store it. The SO produced by the CaO upgrading machine is ２ and collecting flue gas II containing Step (5) The SO collected in step (4) ２ The flue gas II containing the SO ２ Send to reduction tower and SO ２ The SO ２ and mixing the flue gas I containing sulfur to obtain a sulfur-recovered exhaust gas; The above steps (1) to (5) are carried out in sequence, The specific method of CaO upgrading is that CaS reacts with water vapor in flue gas at 500-1200°C to produce CaO, SO ２ and H ２ is produced or CO in the flue gas ２ Reacts with CaO, SO ２ and CO are produced, The exhaust gas from which sulfur has been recovered is divided into three parts. One part is returned to the reduced calciner to adjust the reactive atmosphere, the other part is used for CaO upgrading in the upgrader, and the remaining part is burned and purified in the system boiler before being discharged. The exhaust gas contains N ２ , CO, CO ２ , H ２ O and CO ２ % is 10-80%, H ２ A quicklime production process with reduced carbon emissions, with O% being 10-80%.

2. 2. The process for producing quicklime with reduced carbon emissions according to claim 1, characterized in that the gypsum has a particle size of 60 μm to 3 mm and a moisture content of 5 to 20%, and is at least one type of gypsum selected from the group consisting of wet desulfurized gypsum, semi-dry desulfurized ash, phosphogypsum, and natural gypsum.

3. The SO ２ The flue gas I containing ２ The main components are: 2-10%, CO% 4-20%, and temperature 700-1200°C. ２ , C.O., N ２ , CO ２ The process for producing quicklime with reduced carbon emissions according to claim 1, further comprising:

4. The main component of the hydrogen-containing reducing gas is H ２ , C.H. ４ , C ２ H ４ , H ２ 2. The process for producing quicklime with reduced carbon emissions according to claim 1, characterized in that the carbon dioxide emitted is a combination of some or all of the following components: S, natural gas, and coal gas.

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