Measurement method of slurry density of limestone wet flue gas desulfurization system

Abstract: The information of slurry density measurement method of limestone wet flue gas desulfurization system is provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. 1. Overview There are at least two working fluid densities in the limestone wet flue gas desulfurization system that must be accurately measured in real time, namely the density of the limestone slurry entering the absorption tower and the density of the gypsum slurry on the outlet pipeline of the absorption tower slurry discharge pump. The former is related to desulfurization efficiency. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the article details of the slurry density measurement method of the limestone wet flue gas desulfurization system. 1. Overview There are at least two working fluid densities in the limestone wet flue gas desulfurization system that must be accurately measured in real time, namely the density of the limestone slurry entering the absorption tower and the density of the gypsum slurry on the outlet pipeline of the absorption tower slurry discharge pump. The former is related to desulfurization efficiency, which controls the quality of the gypsum produced by the absorption tower. However, because of the complicated process of wet desulfurization system, the density of working fluid at these two locations is not easy to measure. The limestone slurry in the desulfurization process has the following characteristics after contact with the flue gas: (1) The slurry contains sulfate and sulfite, which is weakly acidic, and the pH value is generally 5.2-6.2; (2) The slurry contains 2% chloride ions and fluoride ion, which will accelerate acid corrosion; (3) the content of solid matter in limestone slurry is high, reaching 20% ​​to 30%; the slurry after desulfurization contains a large amount of gypsum crystals, which is highly abrasive. Therefore, the selection of slurry density measuring instrument for desulfurization system should fully consider various factors such as corrosion, abrasion, deposition of suspended solid particles, scaling, etc. of desulfurization slurry, and take into account its availability, reliability and controllability as much as possible. 2. Several slurry density measurement methods 2.1 Radioactive densitometer The measurement principle of radioactive densitometer is that when the ray passes through the substance, attenuation occurs, and the degree of attenuation depends on the density of the measurement channel and the substance. When the measurement channel is constant, the attenuation is the substance function of density. The radiodensity meter can measure parameters such as material density in the container without touching the object to be detected, especially in the case of high temperature, high pressure, high corrosiveness and toxicity, and the price is relatively cheap. When used in desulfurization system, since the radioactive density meter is installed outside the slurry pipe and does not directly contact with the slurry, the installation is convenient, the maintenance amount is small, and the pressure loss of the slurry will not be caused. However, the radiodensity meter also has some shortcomings, such as the measurement signal is not linear with the concentration, and the scaling and wear of the inner wall of the pipeline will cause measurement errors. In addition, in practical applications, due to the cumbersome approval procedures for radioactive instruments and strict management and inspection of radioactive sources, this type of densitometer is only used in early desulfurization projects. 2.2 Mass flow meter At present, the most widely used slurry density measuring instrument in flue gas desulfurization projects is mass flow meter. The measuring tube vibrates continuously at a certain resonance frequency. The vibration frequency changes with the density of the fluid, so resonance Frequency is a function of fluid density, which can be obtained by measuring the resonant frequency of the tube. The biggest feature of mass flowmeter is that it can measure mass flow and density at the same time, and has high measurement accuracy and stable operation, but its biggest disadvantage is that it is easy to wear and tear, and the measuring tube must be replaced after 1-2 years of operation. Moreover, since the price of the mass flow meter increases rapidly with the increase of the nominal diameter of the pipeline, in order to save costs, in practical applications, a separate measuring branch is drawn from the pipeline to be measured to measure the slurry density. Therefore, in the design, it is necessary to accurately calculate the medium flow rate in the measuring tube, and strictly control it within 3m/s. In a power plant, all the desulfurization medium passed through the density measuring tube, which caused the flow rate of the medium in the tube to rise sharply, causing the mass flowmeter to be worn out in a short time. 2.3 Differential pressure method density measurement Differential pressure method density measurement is to indirectly calculate the density of the slurry through the liquid pressure calculation formula △p=Pgh (the position of the measurement point for measuring the slurry density of the absorption tower is shown in Figure 1). In the formula, △p is the differential pressure between two points from 2; g is the acceleration of gravity; P is the density of the slurry; h is the distance between the pressure sampling position 1 on the low pressure side and the pressure sampling position 2 on the high pressure side. In the formula, h is a fixed value (because the position between points 1 and 2 can be pre-designed), so only the pressure difference between these two points is required to calculate the corresponding slurry density. Considering the easy crystallization and solidification characteristics of limestone slurry, the differential pressure transmitter is selected as a double flange diaphragm type (with capillary). The advantage of measuring slurry density by differential pressure method is that it is simple and easy to operate, and is suitable for various types of absorption towers. However, it also has some obvious shortcomings: (1) The representativeness is poor, the measured density is only the density of the slurry in a limited range (between pressure measurement points 1 and 2) in the absorption tower, and cannot represent the density of the slurry at the outlet of the gypsum discharge pump, Therefore, the measured density needs to be corrected. (2) The measurement location conditions are poor. If the pressure measurement point is close to the agitator of the absorption tower, it will be disturbed by the agitator, resulting in a large fluctuation of the pressure measurement value.The meaning of measurement is lost; if it is far away from the stirrer, the measuring hole of the instrument is easily blocked by crystals, and even if the projecting flange is used, it is difficult to ensure long-term operation. (3) The measurement error is large. If the distance between the two pressure measurement points is too close, the pressure difference will be very small, which is difficult to measure accurately and easily disturbed; if the distance is too far, the density difference between the two points will be large, which is not representative.
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