Method for measuring content of calcium carbonate in desulfurization gypsum of power plant

Abstract

The invention discloses a method for measuring the content of calcium carbonate in desulfurized gypsum of a power plant, which comprises the following steps: mixing a desulfurized gypsum sample and a combustion improver, heating and igniting the combustion improver by electromagnetic induction, and releasing a large amount of heat in the combustion process; under the high-temperature condition, CaCO3 in the desulfurized gypsum is decomposed, CO2 is fully released at the same time, carrier gas containing CO2 flows through an infrared analysis pool, the light intensity of mixed gas at the wavelength of 4.26 microns is measured through a high-frequency infrared carbon and sulfur instrument, and the volume fraction of CO2 in the mixed gas is calculated; the content of C in the desulfurized gypsum sample is obtained through integral treatment; based on a wet flue gas desulfurization process treatment mode, almost all C elements in the desulfurization gypsum come from calcium carbonate residues, and the content of CaCO3 in the desulfurization gypsum is calculated through the content of C in a desulfurization gypsum sample. According to the method, interference of other elements can be effectively avoided, the accuracy is high, the operation is simple, the sample dosage is small, complex chemical reagents are not needed, and a reference basis is provided for optimization of a flue gas desulfurization process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical component detection, and particularly relates to a method for determining the content of calcium carbonate in power plant desulfurization gypsum. BACKGROUND

[0002] Thermal power plants are the main body of coal consumption, and the sulfur dioxide discharged by the thermal power plants accounts for more than 50% of the total amount of sulfur dioxide discharged by the whole society. In view of the environmental protection measures for flue gas desulfurization of coal-fired power plants, it is required to install a flue gas desulfurization device. In the desulfurization process, the most commonly used is the limestone / gypsum wet flue gas desulfurization process. Desulfurization gypsum is an industrial by-product generated during the desulfurization process of the flue gas desulfurization process, and the main component is dihydrate gypsum (CaSO4·2H2O), and it also contains some impurities, such as unreacted calcium carbonate, other impurities contained in limestone and a small amount of potassium and sodium salt. The residual amount of calcium carbonate (CaCO3) can directly reflect the desulfurization efficiency, so the detection of the content of calcium carbonate in the desulfurization gypsum of the power plant is crucial, and directly affects the quality of the gypsum, the operation efficiency of the desulfurization system and the resource utilization value.

[0003] At present, the detection method of calcium carbonate in desulfurization gypsum mainly refers to the core method recommended in GB / T 5484-2012 "Gypsum Chemical Analysis Method" and the power industry standard, and most of them adopt the acid-base neutralization titration method to determine the content of calcium carbonate in gypsum. The principle of the method is that calcium carbonate can react with hydrochloric acid and release carbon dioxide, and calcium sulfate does not react with hydrochloric acid. By adding an excess amount of hydrochloric acid standard solution, the calcium carbonate in the sample is fully reacted, and the remaining hydrochloric acid is titrated back with a sodium hydroxide standard solution. The content of calcium carbonate is calculated according to the consumption amount of hydrochloric acid. The disadvantage of the method is poor selectivity, more interference, if the sample contains calcium carbonate and other acid-consuming substances (such as other carbonates, alkaline oxides, etc.) at the same time, they will be titrated together, resulting in a high result; there is a subjective error in the end point judgment; the sensitivity is relatively low; a large amount of reagents are consumed, and waste liquid is generated; the degree of automation is low, and the traditional manual titration process needs manual operation and reading. In addition, the thermogravimetric analyzer (TGA) analysis method is a modern instrument analysis method, which uses the different temperature intervals of calcium carbonate and gypsum in the heating process to distinguish and quantify, but other substances in the sample that decompose at this temperature interval will interfere. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for determining the content of calcium carbonate in power plant desulfurization gypsum. The method overcomes the defects of the traditional calcium carbonate content determination method, can effectively avoid the interference of other elements, has high accuracy, simple operation, small sample amount and does not need complex chemical reagents, and provides a reference basis for the optimization of the flue gas desulfurization process.

[0005] To solve the above technical problems, the method for determining the content of calcium carbonate in power plant desulfurization gypsum of the present application mixes the desulfurization gypsum sample and the combustion improver, then ignites the combustion improver by electromagnetic induction heating under sufficient oxygen supply, and releases a large amount of heat during the combustion process; under high temperature conditions, the CaCO3 in the desulfurization gypsum decomposes and fully releases CO2; the carrier gas containing CO2 flows through the infrared analysis cell, and the light intensity of the mixed gas at a wavelength of 4.26 μm is determined by a high-frequency infrared carbon and sulfur instrument to convert the volume fraction of CO2 in the mixed gas; the C content in the desulfurization gypsum sample is obtained by integral processing; based on the wet flue gas desulfurization process, the C element in the desulfurization gypsum almost comes from the residual calcium carbonate, and the CaCO3 content in the desulfurization gypsum is converted from the C content in the desulfurization gypsum sample.

[0006] Further, the desulfurization gypsum sample is pretreated by drying in an oven at 105°C until constant weight, grinding to a particle size of less than 0.125 mm, and storing in a desiccator at room temperature for carbon content determination.

[0007] Further, the combustion improver is pure iron combustion improver and tungsten-tin mixed combustion improver, the desulfurization gypsum sample is placed in a porcelain crucible pre-fired (1000°C, 2h) and coated with pure iron combustion improver, and covered with tungsten-tin mixed combustion improver, and burned by electromagnetic induction heating.

[0008] Further, the porcelain crucible is pre-fired to 1000°C and kept for 2h. Since the method for determining the content of calcium carbonate in power plant desulfurization gypsum of the present application adopts the above technical solution, i.e., the method mixes the desulfurization gypsum sample and the combustion improver, then ignites the combustion improver by electromagnetic induction heating under sufficient oxygen supply, and releases a large amount of heat during the combustion process; under high temperature conditions, the CaCO3 in the desulfurization gypsum decomposes and fully releases CO2; the carrier gas containing CO2 flows through the infrared analysis cell, and the light intensity of the mixed gas at a wavelength of 4.26 μm is determined by a high-frequency infrared carbon and sulfur instrument to convert the volume fraction of CO2 in the mixed gas; the C content in the desulfurization gypsum sample is obtained by integral processing; based on the wet flue gas desulfurization process, the C element in the desulfurization gypsum almost comes from the residual calcium carbonate, and the CaCO3 content in the desulfurization gypsum is converted from the C content in the desulfurization gypsum sample. The method overcomes the defects of traditional calcium carbonate content determination, can effectively avoid the interference of other elements, has high accuracy, is simple to operate, requires less sample, does not need complex chemical reagents, and provides a reference for the optimization of flue gas desulfurization process. BRIEF DESCRIPTION OF DRAWINGS

[0009] The present application will be further described in detail below in combination with the drawings and embodiments: Figure 1 The carbon content curve of the power plant desulfurization gypsum sample 5A of the present method is shown in the figure; Figure 2 The schematic diagram of the sample 5A of the power plant desulfurization gypsum of the method is added to the sample carbon content curve; Figure 3 The schematic diagram of the blank carbon content value measured by the high-frequency infrared carbon-sulfur instrument. DETAILED DESCRIPTION

[0010] The method for measuring the calcium carbonate content in the power plant desulfurization gypsum of the application mixes the desulfurization gypsum sample and the combustion improver, ignites the combustion improver by electromagnetic induction heating under the condition of sufficient oxygen, releases a large amount of heat in the combustion process, decomposes CaCO3 in the desulfurization gypsum under high-temperature conditions, and fully releases CO2. The carrier gas containing CO2 flows through the infrared analysis cell, the light intensity of the mixed gas at 4.26 μm wavelength is measured by the high-frequency infrared carbon-sulfur instrument, the volume fraction of CO2 in the mixed gas is converted, the C content in the desulfurization gypsum sample is obtained by integral processing, the C element in the desulfurization gypsum almost all comes from the residual calcium carbonate based on the wet flue gas desulfurization process, and the CaCO3 content in the desulfurization gypsum is converted by the C content in the desulfurization gypsum sample.

[0011] Preferably, the desulfurization gypsum sample is pretreated, the desulfurization gypsum sample is placed in an oven and dried at 105°C to constant weight, is ground and processed to a particle size of less than 0.125 mm, and is stored in a desiccator at room temperature for carbon content measurement.

[0012] Preferably, the combustion improver is pure iron combustion improver and tungsten-tin mixed combustion improver, the desulfurization gypsum sample is placed in a porcelain crucible pre-fired (1000°C, 2h) and paved with pure iron combustion improver, is covered with tungsten-tin mixed combustion improver, and is combusted by electromagnetic induction heating.

[0013] Preferably, the porcelain crucible is pre-fired to 1000°C and is kept for 2h.

[0014] Precision test of the method The calcium carbonate content of the actual power plant desulfurization gypsum sample 5A and the sample added with a standard (the standard addition amount is 0.05g of high-purity calcium carbonate) is measured for 6 times, and the test results are shown in Figure 1 and Figure 2 As can be seen from the figure, the precision of the carbon content measurement results of the sample and the standard-added sample is good. The average value, standard deviation, relative standard deviation, and relative deviation of parallel results of the sample and the sample added with a standard are further calculated, and the test results are shown in Table 1. As can be seen from Table 1, the relative standard deviations of the gypsum sample and the sample added with calcium carbonate are 0.20% and 2.52% respectively, and the relative standard deviation values are both low. The precision of the method for measuring calcium carbonate is good.

[0015] Table 1: Accuracy test of the method The accuracy of this method was verified by using a certified standard sample of calcium carbonate. The results are shown in Table 2. The relative error range is only 0.00% to 0.34%, which meets the uncertainty requirements of the standard sample.

[0016] Table 2: The samples were spiked for testing. The actual sample 5A of the power plant desulfurization gypsum was spiked for analysis. A certain amount of high-purity calcium carbonate was added to each actual sample and the results were measured in parallel six times. The spike recovery rate was calculated for each sample. The test results are shown in Table 3. The spike recovery rate was between 90.5% and 113%, which met the requirements.

[0017] Table 3: Comparison of data from this method and acid-base neutralization titration method To further verify the applicability of this method for determining the calcium carbonate content in power plant desulfurization gypsum, 10 actual gypsum samples were selected and compared with the original acid-base neutralization titration method to check the differences between the two methods. The test results were then subjected to a t-test to check the consistency of the results of the two methods and to verify whether there was a significant difference between the two methods. The method comparison data are shown in Table 4.

[0018] Table 4: t 比对 = 1.936 <t 0.05（9） = 2.262 As shown in Table 4, in the paired observation comparison test of the 10 selected actual gypsum samples, the t-value was 1.5936, which is less than t0. This indicates that there is no significant difference between the acid-base neutralization titration method and this method in determining the calcium carbonate content in power plant desulfurization gypsum. The results of the two methods are consistent, thus ensuring that the results of this method in determining the calcium carbonate content in power plant desulfurization gypsum are accurate and reliable.

[0019] When this method is used to determine the carbon content in desulfurization gypsum from power plants, the blank determination shows a low content, such as... Figure 3 The blank sample showed virtually no carbon content and no background interference. The precision and accuracy were good. Ten actual gypsum samples were selected and analyzed using both the existing acid-base neutralization titration method and this method to compare the results and check the differences between the two methods. The results from both methods were consistent. Therefore, this method can be used for the analysis of calcium carbonate content in desulfurization gypsum from power plants.

[0020] The acid-base neutralization titration method has many operation steps, many reagent preparations, and many human observation interference factors. The method uses high-frequency infrared carbon and sulfur instrument to determine the calcium carbonate content, only needs to weigh the sample, and directly determines the instrument. The operation is simple, the precision is high, the accuracy is good, and the human factor influence is small. It provides a simple and reliable determination method for accurately determining the calcium carbonate content in the desulfurization gypsum of power plant.

Claims

1. A method for determining the calcium carbonate content of power plant desulfurization gypsum, characterized by: After mixing the desulfurization gypsum sample and the combustion improver, the combustion improver is ignited by electromagnetic induction heating under sufficient oxygen supply, and a large amount of heat is released during the combustion process; under high temperature conditions, CaCO3 in the desulfurization gypsum is decomposed, and CO2 is fully released; the carrier gas containing CO2 flows through the infrared analysis cell, and the light intensity of the mixed gas at 4.26 μm wavelength is measured by the high-frequency infrared carbon and sulfur instrument to convert the volume fraction of CO2 in the mixed gas; the C content in the desulfurization gypsum sample is obtained by integral processing; based on the wet flue gas desulfurization process, the C element in the desulfurization gypsum almost comes from the residual calcium carbonate, and the C content in the desulfurization gypsum sample is converted to the CaCO3 content in the desulfurization gypsum.

2. The method for determining the calcium carbonate content in power plant desulfurization gypsum according to claim 1, characterized in that: The desulfurization gypsum sample is pretreated by drying the desulfurization gypsum sample in an oven at 105°C to a constant weight, grinding and processing to a particle size of less than 0.125 mm, and storing in a desiccator at room temperature for carbon content determination.

3. The method for determining the calcium carbonate content of power plant desulfurization gypsum according to claim 1 or 2, characterized in that: The combustion improver is pure iron combustion improver and tungsten-tin mixed combustion improver, the desulfurization gypsum sample is placed in a porcelain crucible pre-fired (1000°C, 2h) and covered with pure iron combustion improver, and the tungsten-tin mixed combustion improver is covered, and the combustion is carried out by electromagnetic induction heating.

4. The method for determining the calcium carbonate content in power plant desulfurization gypsum according to claim 3, characterized in that: The porcelain crucible is pre-fired to 1000°C and kept for 2h.

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