CN114620753B - Low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat - Google Patents
Low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/18—Carbonates
- C01F11/181—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by control of the carbonation conditions
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2/00—Lime, magnesia or dolomite
- C04B2/02—Lime
- C04B2/04—Slaking
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- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2/00—Lime, magnesia or dolomite
- C04B2/10—Preheating, burning calcining or cooling
- C04B2/12—Preheating, burning calcining or cooling in shaft or vertical furnaces
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Abstract
The invention discloses a low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat, which comprises the following steps: A. calcining limestone, and separating solid and gas of the calcined product to obtain calcium oxide and heat Q 1 Is a kiln gas; B. performing dry digestion by taking the calcium oxide obtained in the step A as a raw material to obtain digestion reaction heat Q 2 And calcium hydroxide powder; C. b, adding the calcium hydroxide powder obtained in the step B into warm water to prepare calcium hydroxide slurry, and performing tempering and impurity removal to obtain calcium hydroxide slurry with concentration and temperature meeting carbonization requirements; D. reacting the calcium hydroxide slurry obtained in the step C with kiln gas obtained in the step A to obtain carbonization reaction heat Q 3 Light calcium carbonate slurry and carbonized tail gas; E. dehydrating the light calcium carbonate slurry generated in the step D to form light calcium carbonate wet powder, and using Q 1 、Q 2 、Q 3 Drying the wet light calcium carbonate powder, and crushing and grading to obtain the light calcium carbonate product. The invention can save energy, reduce consumption and reduce tail gas.
Description
Technical Field
The invention relates to the field of inorganic chemistry, in particular to a low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat.
Background
Light calcium carbonate is called light calcium carbonate (containing nano-grade calcium carbonate for short), is one of the most widely used inorganic nonmetallic products at present, and is widely used in the industries of rubber, paper making, plastics, paint, printing ink, printing, cables, food, medicine, daily necessities, feed, lubricating oil and the like due to the advantages of innocuity, environmental friendliness, high cost performance and the like. Light weightThe main production process of calcium is carbonization, mainly based on Ca (OH) 2 With CO 2 Acid-base neutralization reaction between them generates CaCO in liquid phase 3 Precipitation (carbonization for short in the industry) generally comprises the procedures of calcination, digestion, slurry impurity removal, carbonization, surface treatment, solid-liquid separation, drying, crushing and grading, and the like, and is a typical high-energy consumption and high-emission process.
In the prior art, a great deal of heat energy is consumed for calcining limestone to prepare calcium oxide; when calcium oxide reacts with water to generate calcium hydroxide, a large amount of heat energy is generated; the calcium hydroxide also releases heat energy in the process of reacting with carbon dioxide gas to produce calcium carbonate. The utilization rate of the heat energy is extremely low, the heat energy is naturally discharged into the atmosphere, and the heat energy is occasionally utilized, and only auxiliary water for production and living is heated. On the other hand, if the digestion reaction of calcium oxide adopts wet digestion, the temperature of the digestion liquid at normal temperature needs to be raised to about 45 ℃, and a process of energy-consuming and heating is also needed; before the calcium hydroxide slurry reacts with carbon dioxide, the calcium hydroxide slurry needs to be forcedly cooled to be produced, and a process of energy consumption and temperature reduction is needed; drying and dewatering the light calcium slurry after solid-liquid separation also requires energy-consuming heating. As described above, the traditional light calcium production process has long flow, large intermediate liquid phase conveying capacity, repeated heating and cooling phenomena, and meanwhile, a large amount of chemical reaction heat cannot be effectively extracted and utilized to be wasted, so that the energy consumption is high and the carbon dioxide tail gas is seriously discharged.
Chinese patent document CN102958843a discloses "slaked lime particles, light calcium carbonate, paper and coated paper using the same, and a method for producing light calcium carbonate" on 3/6 2013, wherein: a slaked lime particle having a volume particle size distribution wherein the cumulative volume of particles having a particle diameter of 1.0 [ mu ] m or less is 20% or less and the cumulative volume of particles having a particle diameter of 100 [ mu ] m or less is 95% or more. In the step of obtaining the slaked lime particles, it is preferable to add and mix slaked water to the quicklime in a molar ratio to the quicklime of 2.5 or less. The slaked lime particles are slurried, and the slaked lime slurry at 20-70 ℃ is carbonated by blowing a carbon dioxide-containing gas into light calcium carbonate. The light calcium carbonate obtained can be used as a filler for paper or as a pigment for coated paper. The method solves the problem of large liquid phase conveying capacity in the traditional process based on wet digestion to a certain extent, simplifies the light calcium production process flow, but does not relate to the problems of recovery and utilization of chemical reaction heat and process waste heat, reduction of carbon emission and the like.
Chinese patent document CN109666187a discloses "a method for preparing light calcium carbonate based on slaked lime" in 2019, 1, 17, comprising: firstly, preparing calcium hydroxide slurry by using slaked lime powder; then, the calcium hydroxide slurry is led into a first reaction cavity through a first water inlet, a second discharge port is closed, and high-pressure carbon dioxide gas is led into the reaction cavity through the first air inlet; a first stirrer is arranged in the first reaction cavity; then detecting the pH value of the calcium hydroxide slurry, and if the pH value meets the preset pH value, obtaining a calcium carbonate suspension; then heating the calcium carbonate suspension to 45-95 ℃ and adding a coating agent; and finally, filtering, washing, drying and crushing the calcium carbonate suspension to obtain the light calcium carbonate. According to the invention, the high-pressure carbon dioxide is introduced and the first stirrer is arranged in the first reaction cavity, so that the conversion of calcium hydroxide slurry into calcium carbonate suspension is accelerated, and the production efficiency of calcium carbonate is improved; the quality of the calcium carbonate is improved by adding the coating agent. The method can be regarded as an extension of patent CN102958843a, changing carbonization conditions and adding surface treatment processes, and also does not pay attention to the problems of reducing energy consumption and carbon emission.
Chinese patent document CN109879304a discloses "a nano/submicron calcium carbonate efficient carbonization process" in 2019, 6, 14 days, comprising the steps of: calcining a limestone raw material to generate quicklime, adding water to digest the lime to generate lime milk, and preparing the lime milk into calcium hydroxide quickslurry with 20-50% of solid content; mechanically reducing the granularity of calcium hydroxide in the suspension to below 2 microns, then putting the obtained superfine raw slurry into a carbonization tower, introducing kiln gas for carbonization reaction until the pH value of the reaction slurry is 6.5-7, and stopping carbonization to obtain nano/submicron calcium carbonate slurry; carrying out wet surface treatment on the slurry by using a surface modifier, and carrying out filter pressing dehydration, drying and crushing to obtain nano/submicron calcium carbonate; according to the invention, the solid particles in the raw slurry are reduced to below 2 microns from original 5-10 microns, so that the carbonization time of the raw slurry is greatly shortened, the agglomeration of products is reduced, and the production efficiency is improved. The method only focuses on carbonization links in the production of the light calcium carbonate, aims at improving the carbonization reaction speed and efficiency by thinning calcium hydroxide particles, but has limited effects of shortening carbonization time on energy conservation, consumption reduction and emission reduction from the whole process of the production of the light calcium carbonate.
In summary, the existing light calcium production process cannot adapt to the aims of energy conservation, consumption reduction and emission reduction of modern industrial production, and especially does not meet the national development strategy of carbon reaching peak and carbon neutralization, so that the energy conservation transformation of the light calcium production process is quickened, and the development of a new process with more environmental protection, energy conservation and low carbon is urgent.
Disclosure of Invention
Based on the problems, the invention provides a low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat, and the process of combining a dry method and a wet method is adopted to produce the light calcium carbonate, so that the liquid phase volume and the conveying energy consumption of a procedure before carbonization are greatly reduced, meanwhile, the heat energy generated in each production link is effectively extracted and utilized, the energy-saving and consumption-reducing effects are obvious, kiln gas generated by absorbing and calcining limestone is fully utilized, and the problem of carbon dioxide tail gas emission is greatly solved.
In order to achieve the aim of the invention, the invention adopts the following technical scheme: a low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat comprises the following steps:
A. calcining limestone, and separating solid and gas of the calcined product to obtain calcium oxide and heat Q 1 Is a kiln gas;
B. performing dry digestion by taking the calcium oxide obtained in the step A as a raw material to obtain digestion reaction heat Q 2 And calcium hydroxide powder;
C. b, adding the calcium hydroxide powder obtained in the step B into warm water to prepare calcium hydroxide slurry, and performing tempering and impurity removal to obtain calcium hydroxide slurry with concentration and temperature meeting carbonization requirements;
D. hydrogen obtained in step CAnd C, reacting the calcium oxide raw slurry with kiln gas obtained in the step A to obtain carbonization reaction heat Q 3 Light calcium carbonate slurry and carbonized tail gas;
E. dehydrating the light calcium carbonate slurry generated in the step D to form light calcium carbonate wet powder, and using Q 1 、Q 2 、Q 3 Drying the wet light calcium carbonate powder, and crushing and grading to obtain the light calcium carbonate product.
Preferably, the kiln gas obtained in the step A is high-temperature kiln gas, the light calcium carbonate wet powder obtained in the step E is firstly used as a heat source to carry out primary drying heat exchange to obtain medium-temperature kiln gas, the medium-temperature kiln gas is sequentially subjected to primary heat exchange and secondary heat exchange, the digestion steam and the process backwater are sequentially heated, the heat exchange and the temperature reduction are carried out to obtain low-temperature kiln gas, and the low-temperature kiln gas is further used for carbonization reaction of calcium hydroxide slurry in the step D.
Preferably, in step B, the heat of digestion Q generated by dry digestion of calcium oxide 2 And E, taking steam as a carrier, heating the carrier into superheated steam by using medium-temperature kiln gas, and performing secondary drying on the light calcium carbonate wet powder obtained in the step E as a heat source.
Preferably, in the step D, the carbonization reaction heat Q generated by the carbonization reaction of the calcium hydroxide slurry and the low-temperature kiln gas 3 And E, performing tertiary drying on the light calcium carbonate wet powder obtained in the step E as a heat source.
Preferably, in step E, a multi-heat source synergistic distributed multi-stage drying mode is adopted for the light calcium carbonate wet powder: using high temperature kiln gas as heat source Q 1 And working medium, carrying out primary drying in an air flow dryer, and reducing the water content of the light calcium carbonate wet powder to 35%; by using the heat of digestion Q 2 And the primary drying waste heat generates high-temperature steam, and the high-temperature steam is used as a heat source and working medium to carry out secondary drying in a steam drum dryer, so that the water content of the light calcium carbonate wet powder is further reduced to 25%; by using the heat of carbonization Q 3 And secondary drying waste heat, heating circulating air by a high-efficiency heat converter to generate high-temperature air, performing tertiary drying in a belt type through-flow dryer as a heat source and working medium, finally reducing the water content of the light calcium carbonate wet powder to below 0.5%, and finally obtaining the light calcium carbonate wet powder through crushing and gradingTo a light calcium carbonate product.
Preferably, in the step A, the kiln temperature is 240-300 ℃; in the step D, the light calcium carbonate wet powder is dried by adopting an air flow dryer, wherein the average temperature of the air inlet end of the air flow dryer is 260+/-5 ℃, and the average temperature of the air outlet end of the air flow dryer is 160+/-5 ℃.
Preferably, in the step B, dry digestion is carried out in a closed heat-insulating reactor, wherein the solid-liquid mass ratio of calcium oxide to water is 1:1.0-1.2, the digestion is immediately carried out when the temperature of the calcium oxide is not lower than 80 ℃ after the calcium oxide is discharged from a kiln, the digestion water is preheated by medium-temperature kiln gas, the temperature is not lower than 60 ℃, dynamic digestion is firstly adopted in the digestion process, and the digestion is converted into static digestion after the liquid phase disappears.
Preferably, the temperature of the calcium hydroxide slurry obtained in step C is not higher than 35 ℃ and the concentration is not higher than 15%.
Preferably, in the step D, the carbonization reaction adopts a two-stage serial bubbling carbonization process, and the carbonization reactor is provided with a water circulation jacket to extract the carbonization reaction heat Q 3 The initial carbonization temperature is not higher than 35 ℃ and the final carbonization temperature is not higher than 75 ℃.
Preferably, the CO in the kiln gas produced in step A 2 The concentration is 32-37%, CO 2 Performing two-stage serial bubbling carbonization reaction in the step D as a carbon source, absorbing the carbon source by calcium hydroxide, and carbonizing residual CO in tail gas 2 The concentration is 5% -7%; after the heat energy carried in kiln gas is recovered, the heat energy is led into the light calcium carbonate cooked pulp at a low flow rate to further absorb CO 2 Final evacuation of CO from exhaust 2 The concentration is lower than 3%.
The low-carbon process method for producing the light calcium carbonate by comprehensively utilizing chemical reaction heat is designed by the technical scheme, and mainly comprises the following steps of:
(1) Limestone with uniform granularity is sent into a lime kiln to be burned into lime, and high-temperature kiln gas generated in the calcination process is led into an air flow dryer after two-stage dust removal, so that clean heat Q is obtained 1 The high-temperature kiln gas is used for primary drying of light calcium carbonate to obtain medium-temperature kiln gas; the intermediate-temperature kiln gas is subjected to primary and secondary heat exchange to obtain low-temperature kiln gas which is used as CO 2 Source for subsequent carbonation of calcium oxide(abbreviated as carbonization);
(2) Preparing calcium hydroxide powder by taking lime burned in the step (1) as a raw material through a dry digestion process, and extracting reaction heat Q of calcium oxide and hydration reaction in the process in a steam mode 2 Heating the water vapor through primary heat exchange to obtain about 130 ℃ superheated steam, and performing secondary drying on the light calcium carbonate by using the superheated steam as a heat source through a steam drum dryer; the superheated steam brings out the saturated steam with the water content of the material cooled to about 120 ℃;
(3) After slaking and heat exchange in the step (2), calcium hydroxide powder with the temperature lower than 80 ℃ is split, 50% of the calcium hydroxide powder is directly processed into calcium hydroxide products, and the other 50% of the calcium hydroxide powder is added with water to prepare calcium hydroxide slurry, and the calcium hydroxide slurry with the concentration and the temperature meeting carbonization requirements is obtained through tempering and impurity removal; it is to be noted that if no split flow is made in this step, the heat generated by the existing heat and the subsequent chemical reaction is less than the heat required by all calcium hydroxide powder through wet digestion and the subsequent process. From the viewpoints of comprehensively utilizing heat energy and reducing exhaust emission, the calcium hydroxide powder diversion in the step is recommended; however, the diversion means can never influence the implementation effect of energy conservation and emission reduction; the split ratio can meet the drying requirement of the light calcium carbonate product generated by converting residual calcium hydroxide according to the long-term actual measurement of the inventor, and the split ratio is 50% or more of calcium hydroxide, and the process waste heat and the chemical reaction heat do not need external heat supply. The person skilled in the art can make proper proportion adjustment according to the process characteristics and the product requirements of the factory;
(4) Pumping the calcium hydroxide slurry into a carbonization tower, adding a required crystal form control agent, a dispersing agent and the like, and carrying out two-stage carbonization reaction with low-temperature kiln gas at the temperature lower than 60 ℃ in a liquid phase to generate light calcium carbonate (slurry) with certain crystal form and granularity; at the same time, the carbonization reaction heat Q is extracted in the form of hot water at about 60 ℃ and carbonized tail gas at 70 ℃ through a water circulation jacket of the carbonization tower 3 Heating hot water to about 80 ℃ by an absorption heat pump, heating circulating air by a high-efficiency heat converter together with the saturated steam at 120 ℃ obtained in the step (2) to obtain high-temperature air, and carrying out three-phase treatment on light calcium carbonate serving as a heat source and working medium in a belt type through-flow dryerStage drying;
(5) The light calcium slurry is subjected to sedimentation and densification, surface treatment is performed after the solid content reaches more than 25%, good dispersion of oleic acid in a water phase is realized at a lower temperature by adding an emulsifying agent, and surface treatment of calcium carbonate particles is finished under the high shearing action by 15% of oleic acid water emulsion, so that the light calcium finished slurry is obtained. (note: no surface treatment is required if it is ordinary light calcium);
(6) The light calcium finished product slurry is subjected to solid-liquid separation by a plate-frame filter press to obtain a filter cake with solid content of more than 63%, and filtrate is returned to a digestion system for recycling after being treated by a water treatment system;
(7) Adopts a multi-heat source cooperative distributed multi-stage drying mode to obtain the Q 1 、Q 2 、Q 3 And (3) drying the filter cake in the step (6) as a main heat source, and then crushing, grading and packaging to obtain a light calcium carbonate product.
Compared with the traditional process, the method mainly improves the following steps:
firstly, fully recovering and utilizing heat energy of high-temperature kiln gas generated during limestone calcination, extracting heat by an airflow dryer, primary heat exchange and secondary heat exchange respectively according to the temperature characteristics of the kiln gas, and heating digested steam and process backwater, wherein the kiln gas temperature is reduced from about 260 ℃ to 60 ℃ to obtain low-temperature kiln gas. At the same time, utilize the rich CO 2 The high-temperature kiln gas directly dries the light calcium carbonate, can effectively neutralize free base generated by the light calcium at high temperature, inhibits the alkali return of the product and reduces the pH value of the product.
And secondly, calcium hydroxide powder is obtained by digesting calcium oxide by a dry method, compared with the process of calcium hydroxide slurry obtained by wet digestion, the digestion reaction efficiency is greatly improved, the volume and weight of intermediate products are remarkably reduced (about 80% of water can be reduced according to the actual measurement of the inventor), thereby reducing a large number of transfer storage tanks and supporting facilities for storing the slurry, reducing the energy consumption for transporting materials and simplifying the process.
Thirdly, a large amount of digestion reaction heat Q generated during dry digestion is fully extracted and utilized by high-temperature steam 2 And the tail gas waste heat of the air flow dryer is used for carrying out secondary drying on the light calcium by taking the superheated steam as a working medium through a steam rotary dryer, and the superheated steam carries moisture to form saturated steam, so that the heat energy can be further extracted. Compared with saturated steam, the superheated steam drying has the outstanding advantages of small heat transfer resistance, high moisture migration speed, high drying efficiency and high heat energy utilization rate (up to about 90%).
And fourthly, calcium hydroxide powder generated by the dry digestion reaction can be prepared into calcium hydroxide slurry with lower temperature by adding warm water, the initial temperature condition of carbonization can be met without forced cooling, and the energy consumption is reduced.
Fifthly, low-temperature kiln gas is obtained after heat extraction and is used as a carbon source for carbonization of calcium hydroxide raw slurry, and carbonization reaction heat Q is fully extracted and utilized through cyclic heat exchange and heat pump heating 3 And heating the circulating air through a heat energy converter to form circulating hot air, and performing tertiary drying on the light calcium product in a belt type through-flow dryer as a working medium.
Sixthly, adopting a two-stage serial carbonization process, and fully absorbing CO in the low-temperature kiln gas by taking calcium hydroxide slurry as a continuous phase 2 And the carbonized tail gas is led into the light calcium carbonate cooked pulp at a low flow rate to further absorb CO after heat exchange 2 Compared with the traditional carbonization process, the method can be used for preparing CO in kiln gas 2 The absorptivity of the catalyst is improved from about 76% to more than 90%, and the total carbon emission is reduced.
Seventhly, carrying out surface treatment on the calcium carbonate slurry obtained by carbonization at a lower temperature, and then thickening the slurry, and dehydrating the slurry until the calcium carbonate content in the slurry is increased to more than 25%, thereby shortening the dehydration time; and the concentrated slurry is subjected to filter pressing dehydration by adopting a filter press, the water content of a filter cake is controlled to be lower than 40%, and the drying energy consumption is reduced.
And eighth, a multi-heat source cooperative distributed multi-stage drying mode is adopted. Using high temperature kiln gas as heat source Q 1 And working medium, carrying out primary drying in an air flow dryer; by using the heat of digestion Q 2 And the primary drying waste heat generates high-temperature steam which is used as a heat source and working medium to carry out secondary drying in a steam drum dryer; by using the heat of carbonization Q 3 And two (II)The waste heat of the stage drying (the external heat source Q can be supplemented according to the requirement) Outer part ) And heating circulating air through a high-efficiency heat converter to generate high-temperature air, and performing three-stage drying in a belt type through-flow dryer as a heat source and working medium. It can be seen that the calcination heat energy (high temperature kiln gas) and the digestion heat energy (water vapor) are respectively extracted and utilized by the upper stage and then flow to the lower stage, and finally are recycled at the high-efficiency heat converter, and a small amount of heat loss of a system pipeline is removed, and the system heat energy is almost continuously and circularly extracted and utilized, so that the comprehensive heat energy utilization rate of the process can be up to more than 90%, the requirement of the light calcium drying process on external heat energy is greatly reduced, and the energy-saving and emission-reducing effects are remarkable.
The method is used for the industrialized production of the light calcium carbonate, has the outstanding advantages of simple process, small liquid phase conveying capacity of intermediate products, high utilization rate of chemical reaction heat and waste heat, less discharge of three wastes and low carbon and environmental protection, and compared with the light calcium carbonate product obtained by the prior art, the method has the advantages of obviously reducing the production cost and fully releasing the profit capability on the premise of basically consistent main technical indexes, and has market competitiveness. More importantly, under the large trend of carbon reaching peak and carbon neutralization, the traditional high-energy consumption and high-pollution light calcium carbonate production mode is difficult to succeed, and the process method conforming to the green chemistry and low-carbon economic principle provided by the method has great and profound significance for breaking the development dilemma of the light calcium carbonate industry.
The relevant data are calculated below using a light calcium carbonate producer on the scale of one hundred thousand tons per year:
and firstly, three major liquid phase temperature control energy consumption can be saved by comprehensively recovering and utilizing heat energy through the system:
digestion and heating: heating from about 23 ℃ to about 45 ℃ at room temperature requires about heat
36×10000×1000Kg×4.2Kj/Kg.℃×(45-23)＝3.33×10 10 Kj
Cooling and carbonizing: the average temperature is 50 ℃ and is cooled to 35 ℃ required by carbonization, and the heat quantity required for cooling and neutralization is about
57×10000×1000Kg×4.2Kj/Kg.℃×(50-35)＝3.59×10 10 Kj
And (3) heating surface treatment: heating from an average temperature of 55 ℃ to 65 ℃ requires about heat
60×10000×1000Kg×4.2Kj/Kg.℃×(65-55)＝2.52×10 10 Kj
The total of the three heat amounts to about 9.44×10 10 Kj, according to standard coal 2.93×10 7 Kj/ton calculation can save about 3221.8 tons/year of standard coal. The average coal consumption (heat value 6500 Kcal/Kg) of the current active light calcium products in industry is about 135 Kg/ton, and the saved coal is used for drying the light calcium and can be used for drying about 2.57 ten thousand tons of active light calcium products.
Combining or reducing intermediate processes, reducing the conveying amount of an intermediate liquid phase and saving power consumption:
table 1: comparing the liquid phase conveying capacity of the process with that of the traditional process
As shown in table 1, the total liquid phase quantity required to be delivered by the traditional process is about 262 ten thousand cubic meters calculated according to the annual energy production of one hundred thousand tons of light calcium of the company; the total process of the invention is about 153 kilo-cubic, the liquid phase conveying capacity of 109 kilo-cubic is reduced by 41.6 percent, the electricity consumption can be saved by about 60 kilo-watt-hour only by one process (calculated by a 100-cubic/hour, 55KW and a mortar pump), the electricity consumption can be saved by about 6 kilo-watt-hours per ton of product on average, and the electricity consumption of 180 degrees is based on the average ton of product in the calcium carbonate industry, and the electricity consumption can be saved by about 3.3 percent only by one process.
Thirdly, the light calcium is dried and utilizes the waste heat and the reaction heat of a production system, and external energy consumption is not needed under the condition of the invention.
At present, the utilization of high-temperature flue gas and dry tail gas of a shaft kiln in the industry is relatively more, and the utilization of digestion reaction heat is still blank. Similarly, the energy production accounting of light calcium with hundred thousand tons/year is carried out, and the theoretical requirement of the intermediate raw material calcium hydroxide is about 7.4 ten thousand tons, but the invention is based on the characteristics of the calcium carbonate industry (the calcium hydroxide and the light calcium are produced simultaneously) and the characteristics of the factory carry out 50 percent split on the intermediate product calcium hydroxide, namely 14.8 ten thousand tons of calcium hydroxide are required. In other words, the amount of calcium oxide available for extraction of heat of digestion reaction is 11.3 ten thousand tons, and 7.64 ten thousand tons of water is converted into 120 ℃ water vapor by dry pressurized digestion, and the available amount of drying heat is about:
7.64×10000×1000Kg×2201Kj/Kg＝16.81×10 10 kj corresponds to 5737 tons of standard coal.
The heat which can be extracted from the high-temperature kiln gas of the vertical kiln is as follows:
8500m 3 /h×270Kj/m 3 /3600＝1912.5Kw
total heat is 1912.5kw×360×24×3600 Kj/h=5.95×10 10 Kj
Equivalent to 2030 tons of standard coal.
The heat extractable for the carbonation reaction is:
7.4×10000×1000×118×1000Kj/74＝11.8×10 10 kj corresponds to 4027 tons of standard coal.
The three heat components are (16.81+5.95+11.8). Times.10 in total 10 Kj＝34.56 10 Kj is equivalent to 11650 tons of standard coal, according to the heat energy utilization scheme of the invention, the heat energy recovery and utilization rate can reach 91 percent, the actual available heat energy is equivalent to about 11650 multiplied by 0.91=10601 tons of standard coal, the available heat energy can be converted into 10601 multiplied by 1.07 multiplied by 1000/113= 100381 tons of dry light calcium products, the heat requirement of 10 ten thousand tons of dry light calcium is completely met, namely the self-sufficiency of heat required by drying is realized, and external heat supply is not needed.
Considering the scheme of splitting 50% calcium hydroxide, if accounting is performed without splitting, the total available heat energy is about (16.81/2+5.95+11.8) ×10 10 Kj＝26.15×10 10 Kj can be used for converting heat energy into about 8032 tons of standard coal under the technical conditions, and 8032 multiplied by 1.07 multiplied by 1000/113= 76055 tons of light calcium carbonate can be dried, namely 76% of the drying heat energy of 10 ten thousand tons of light calcium carbonate is solved by internal circulation, only 24% of external heat supply is needed, and the energy-saving effect of the process method is still very remarkable.
Fourth, pollutant emission is reduced:
the absorption rate of the carbon dioxide in the kiln gas is improved from 76% to more than 90% by two-stage carbonization absorption of the carbon dioxide kiln gas in the carbonization process and reabsorption of the residual carbon dioxide in the carbonized tail gas by utilizing calcium carbonate slurry, 10 ten thousand tons of light calcium is produced, and the emission of the carbon dioxide gas can be reduced by about 0.9 ten thousand tons.
By combining the above, the process and flow of the invention can reduce the power consumption of invalid liquid phase conveying power by about 60 kilowatts and reduce the emission of carbon dioxide by 600 tons when the 10 kilotons of light calcium carbonate is produced; the drying saves the coal consumption by 10601 tons and reduces the emission of 26428 tons of carbon dioxide; the absorption of kiln gas reduces the carbon dioxide emission by about 9000 tons, the total emission reduction of carbon dioxide is 36028 tons, the carbon emission is 9825.8 tons, the carbon emission of light calcium ton products is reduced by about 98.258Kg, compared with the current 160 Kg/ton carbon emission level of the common light calcium industry, the carbon emission reduction of more than 61% is realized, and the social and ecological benefits are remarkable.
Drawings
FIG. 1 is a flow chart of a conventional process for producing light calcium carbonate;
FIG. 2 is a flow chart of the process for producing the light calcium carbonate according to the invention;
FIG. 3 is a diagram of the comprehensive utilization of heat energy of the light calcium carbonate production system according to the present invention;
Detailed Description
The invention is further described below with reference to the drawings and detailed description.
Comparative example
(1) Lime stone with uniform granularity is sent into a lime kiln to be burned into lime, and high-temperature kiln gas generated in the calcination process is subjected to two-stage dust removal and water spray purification; the temperature is reduced to below 80 ℃, and then the mixture is pressurized to 0.08Mpa by an air compressor to be used as CO 2 The source is used for the carbonation reaction (abbreviated as carbonization) of the following calcium oxide;
(2) Taking the lime burned in the step (1) as a raw material, adding process water which is 5 times of the mass of the lime and is preheated to more than 45 ℃ for wet digestion, preparing calcium hydroxide slurry, and directly exhausting water vapor;
(3) The calcium hydroxide slurry in the step (2) is subjected to three-stage refining and impurity removal to obtain calcium hydroxide raw slurry with the temperature of about 50 ℃ and the solid content of about 14.5%;
(4) The calcium hydroxide is producedCooling the slurry to below 35deg.C by a refrigerator, pumping into a carbonization tower, adding required crystal form control agent and dispersant, etc., and mixing with CO at about 80deg.C 2 The kiln gas with the content of about 34 percent is subjected to carbonization reaction in a bubbling carbonization tower to generate light calcium carbonate (slurry) with certain crystal form and granularity; CO in kiln gas 2 About 76% of the absorption and utilization rate of (C), about 70 ℃ of the carbonized tail gas and CO 2 The content is about 8.1 percent, and the mixture is directly emptied;
(5) The solid content of the light calcium carbonate slurry is about 18%, after curing for 12 hours, the temperature is reduced from about 70 ℃ to 50 ℃, the light calcium carbonate slurry is heated to more than 57 ℃ by the drying waste heat for surface treatment, saponified liquid of about 3.0% oleic acid (relative to the dry weight of the calcium carbonate) is added, and the surface treatment of the calcium carbonate particles is completed by continuously stirring for 50 minutes, so that the light calcium carbonate finished product slurry is obtained.
(common light calcium carbonate does not require surface treatment);
(6) The light calcium finished product slurry is squeezed and dehydrated by a plate-frame filter press to obtain a filter cake with solid content of more than 60%, and filtrate is directly returned to a digestion system for recycling after being treated by a water treatment system;
(7) And (3) drying the filter cake in a disc dryer at a temperature of 240-150 ℃ by taking high-temperature heat conduction oil generated by a heat conduction oil furnace as working medium to obtain a light calcium semi-finished product with the water content lower than 0.5%, and then crushing, grading and packaging to obtain a light calcium carbonate product, wherein the sampling number is SF-PCC-1. The production process flow diagram of this comparative example is shown in fig. 1.
Examples
(1) Limestone with uniform granularity is sent into a lime kiln to be burned into lime, and high-temperature kiln gas generated in the calcination process is led into an air flow dryer after two-stage dust removal, so that clean heat Q is obtained 1 The high-temperature kiln gas (average about 265 ℃) is used for primary drying of light calcium carbonate to obtain medium-temperature kiln gas (average about 161 ℃); the intermediate-temperature kiln gas is subjected to primary heat exchange and secondary heat exchange successively to obtain low-temperature kiln gas (average about 67 ℃) which is used as CO 2 The source is used for the carbonation reaction (abbreviated as carbonization) of the following calcium oxide;
(2) Adopting a dry digestion process, taking lime (average about 85 ℃) burned in the step (1) as a raw material, adding equal mass of digestion water at 60 ℃, preparing calcium hydroxide powder in a heat insulation reactor, extracting reaction heat Q2 of calcium oxide and hydration reaction in the process in a water vapor form, heating the water vapor through primary heat exchange to obtain 130 ℃ superheated steam, and carrying out secondary drying on light calcium carbonate by a steam drum dryer as a heat source; the superheated steam brings out the water content of the material and reduces the temperature to 120 ℃ saturated steam;
(3) After slaking and heat exchange in the step (2), calcium hydroxide powder with the temperature lower than 80 ℃ is split, 50% of the calcium hydroxide powder is directly processed into calcium hydroxide products, the other 50% of the calcium hydroxide powder is prepared into calcium hydroxide slurry by adding warm water, and the calcium hydroxide slurry with the concentration of 14.3% and the temperature of 33.7 ℃ is obtained through tempering and impurity removal, so that the calcium hydroxide slurry meeting the carbonization requirement is obtained;
(4) Pumping the calcium hydroxide slurry into a carbonization tower, adding a required crystal form control agent, a dispersing agent and the like, and carrying out two-stage carbonization reaction with low-temperature kiln gas at the temperature lower than 60 ℃ in a liquid phase to generate light calcium carbonate (slurry) with certain crystal form and granularity; at the same time, the carbonization reaction heat Q is extracted in the form of hot water at about 60 ℃ and carbonized tail gas at 70 ℃ through a water circulation jacket of the carbonization tower 3 Heating hot water to about 80 ℃ through an absorption heat pump, heating circulating air through a high-efficiency heat converter together with saturated steam at 120 ℃ obtained in the step (2) to obtain high-temperature air, and performing three-stage drying on light calcium carbonate in a belt type through-flow dryer as a heat source and working medium;
(5) The light calcium slurry is subjected to sedimentation and densification, surface treatment is carried out after the solid content reaches more than 25%, good dispersion of oleic acid in a water phase is realized at a lower temperature by adding an emulsifying agent, and the surface treatment of calcium carbonate particles is finished by continuously dispersing an oleic acid water emulsion with the concentration of 13% and the addition amount of 3.0% for 40min under the high shearing action, so that the light calcium finished slurry is obtained. (note: no surface treatment is required if it is ordinary light calcium);
(6) The light calcium finished product slurry is subjected to solid-liquid separation by a plate-frame filter press to obtain a filter cake with solid content of more than 63%, and filtrate is returned to a digestion system for recycling after being treated by a water treatment system;
(7) Adopts a multi-heat source cooperative distributed multi-stage drying mode to obtain the Q 1 、Q 2 And Q 3 And (3) drying the filter cake in the step (6) as a heat source, and then crushing, classifying and packaging to obtain a light calcium carbonate product, wherein the sampling number is GF-PCC-2. The production process flow chart of the embodiment is shown in fig. 2, and the comprehensive utilization route diagram of the production system heat energy is shown in fig. 3.
Index comparison conditions of the light calcium carbonate products obtained in the comparative examples and the examples and economical and environmental protection comparison conditions of two process operations are shown in tables 2 and 3 respectively:
table 2: index comparison table of light calcium products obtained by the embodiment of the invention and traditional process products
As can be seen from Table 2, the light calcium carbonate GF-PCC-2 prepared by the process of the invention is significantly better than SF-PCC-1 in four indexes of whiteness, pH, oil absorption value and thixotropic index than SF-PCC-1 under the condition that the overall technical indexes are equivalent to those of the light calcium carbonate SF-PCC-1 obtained by the traditional process. The method mainly benefits from the multi-heat source cooperative distributed drying mode adopted by the invention, the drying medium is in direct contact with the materials, and the heat exchange is direct and full; the drying temperature is low, the three-stage drying temperature gradient is reasonable, and the thermal ageing of organic active substances on the surface of the product is inhibited.
Table 3: economic and environmental protection index comparison table of the embodiment and the comparative example
The comparison of the economic and environmental protection indexes in table 3 shows that compared with the traditional process, the process has technical advantages, namely, on the premise of equal output, the new process can realize less energy consumption, lower pollutant emission and lower production cost, and the process has definitely important practical significance for removing the hat in the traditional high-energy-consumption and high-emission industry of light calcium carbonate and realizing transformation upgrading and quality improvement and efficiency improvement.
Claims (7)
1. A low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat is characterized by comprising the following steps:
A. calcining limestone, and separating solid and gas of the calcined product to obtain calcium oxide and heat Q 1 Is a kiln gas;
B. performing dry digestion by taking the calcium oxide obtained in the step A as a raw material to obtain digestion reaction heat Q 2 And calcium hydroxide powder;
C. b, adding the calcium hydroxide powder obtained in the step B into warm water to prepare calcium hydroxide slurry, and performing tempering and impurity removal to obtain calcium hydroxide slurry with concentration and temperature meeting carbonization requirements;
D. reacting the calcium hydroxide slurry obtained in the step C with kiln gas obtained in the step A to obtain carbonization reaction heat Q 3 Light calcium carbonate slurry and carbonized tail gas;
E. dehydrating the light calcium carbonate slurry generated in the step D to form light calcium carbonate wet powder, and using Q 1 、Q 2 、Q 3 Drying the wet light calcium carbonate powder, and crushing and grading to obtain a light calcium carbonate product;
the kiln gas obtained in the step A is high-temperature kiln gas, the light calcium carbonate wet powder obtained in the step E is firstly used as a heat source to carry out primary drying heat exchange to obtain medium-temperature kiln gas, the medium-temperature kiln gas is sequentially subjected to primary heat exchange and secondary heat exchange, the digestion steam and the process backwater are sequentially heated, the heat exchange and the temperature reduction are carried out to obtain low-temperature kiln gas, and the low-temperature kiln gas is further used for carbonization reaction of calcium hydroxide slurry in the step D;
in step B, the heat of digestion Q generated by dry digestion of calcium oxide 2 C, taking steam as a carrier, heating the carrier into superheated steam through medium-temperature kiln gas, and performing secondary drying on the light calcium carbonate wet powder obtained in the step E by taking the superheated steam as a heat source;
in the step D, the carbonization reaction heat Q generated by carbonization reaction of the calcium hydroxide raw slurry and the low-temperature kiln gas 3 And E, performing tertiary drying on the light calcium carbonate wet powder obtained in the step E as a heat source.
2. The low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat according to claim 1, wherein in the step E, a multi-heat source synergistic distributed multi-stage drying mode is adopted for the wet powder of the light calcium carbonate: using high temperature kiln gas as heat source Q 1 And working medium, carrying out primary drying in an air flow dryer, and reducing the water content of the light calcium carbonate wet powder to 35%; by using the heat of digestion Q 2 And the primary drying waste heat generates high-temperature steam, and the high-temperature steam is used as a heat source and working medium to carry out secondary drying in a steam drum dryer, so that the water content of the light calcium carbonate wet powder is further reduced to 25%; by using the heat of carbonization Q 3 And the secondary drying waste heat is used for heating the circulating air through a high-efficiency heat converter to generate high-temperature air, and the high-temperature air is used as a heat source and working medium to be subjected to tertiary drying in a belt type through-flow dryer, so that the water content of the wet light calcium carbonate powder is reduced to below 0.5%, and the wet light calcium carbonate powder is crushed and graded to finally obtain a light calcium carbonate product.
3. The low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat according to claim 1, wherein in the step A, the kiln temperature is 240-300 ℃; in the step D, the light calcium carbonate wet powder is dried by adopting an air flow dryer, wherein the average temperature of the air inlet end of the air flow dryer is 260+/-5 ℃, and the average temperature of the air outlet end of the air flow dryer is 160+/-5 ℃.
4. The low-carbon process method for producing light calcium carbonate by comprehensively utilizing chemical reaction heat according to claim 1, wherein in the step B, dry digestion is carried out in a closed heat insulation reactor, the solid-liquid mass ratio of calcium oxide to water is 1:1.0-1.2, the digestion is carried out immediately when the temperature of the calcium oxide after the calcium oxide is discharged from a kiln is not lower than 80 ℃, the digestion water is preheated by medium-temperature kiln gas, the temperature is not lower than 60 ℃, dynamic digestion is adopted in the digestion process, and the digestion is converted into static digestion after the liquid phase disappears.
5. The low-carbon process for producing light calcium carbonate by comprehensively utilizing chemical reaction heat according to claim 1, wherein the temperature of the calcium hydroxide slurry obtained in the step C is not higher than 35 ℃ and the concentration is not higher than 15%.
6. The low-carbon process for producing light calcium carbonate by comprehensively utilizing chemical reaction heat according to claim 1, wherein in the step D, a two-stage serial bubbling carbonization process is adopted in the carbonization reaction, and a water circulation jacket is arranged in the carbonization reactor to extract carbonization reaction heat Q 3 The initial carbonization temperature is not higher than 35 ℃ and the final carbonization temperature is not higher than 75 ℃.
7. The low-carbon process for producing light calcium carbonate by comprehensively utilizing chemical reaction heat according to claim 6, wherein the kiln gas generated in the step A contains CO 2 The concentration is 32-37%, CO 2 Performing two-stage serial bubbling carbonization reaction in the step D as a carbon source, absorbing the carbon source by calcium hydroxide, and carbonizing residual CO in tail gas 2 The concentration is 5% -7%; after the heat energy carried in kiln gas is recovered, the heat energy is led into the light calcium carbonate cooked pulp at a low flow rate to further absorb CO 2 Final evacuation of CO from exhaust 2 The concentration is lower than 3%.
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