Four aspects should be paid attention to in order to accurately measure the steam flowmeter

by:Kaidi Sensors     2022-04-28
There are often feedbacks from customers that the steam flowmeter always has small problems of this kind during operation, and I don’t know how to solve it. In fact, there are many reasons for this, such as man-made, on-site, and quality itself. For example The total pipeline flow is 100 cubic meters a day, and the pipeline is 50 cubic meters when it arrives. Therefore, when a problem occurs, we need to find the problem and check the problem from the source. Below we will explain the four aspects of the accurate measurement of the steam flowmeter. aspects should be noted. It is not terrible to have inaccurate measurement. The most terrible thing is that many of our customers do not know where the problem is. Sometimes it is very laborious to investigate. Analysis of the reasons for the inaccuracy of steam flow meters The steam mentioned in the case refers to superheated steam. Superheated steam is a common power source, which is often used to drive steam turbines to rotate, and then drive generators or centrifugal compressors to work. Superheated steam is obtained by heating saturated steam. There is absolutely no droplet or liquid mist in it, and it is an actual gas. The temperature and pressure parameters of superheated steam are two independent parameters, and its density should be determined by these two parameters. After the superheated steam is transported over a long distance, with the change of working conditions (such as temperature and pressure), especially when the superheat degree is not high, it will enter saturation or supersaturation from the superheated state due to the reduction of the heat loss temperature. state, transformed into saturated steam or supersaturated steam with water droplets. The saturated steam is suddenly greatly decompressed, and the liquid will also be transformed into superheated steam when adiabatic expansion occurs, thus forming a vapor-liquid two-phase flow medium. Difficulty in measurement, resulting in inaccurate measurement. 2. Analysis of measuring instruments At present, flow instruments are used to measure steam flow, and the measuring medium refers to single-phase superheated steam or saturated steam. For steam with frequently changing phase flow, there will definitely be inaccurate measurements. The solution to this problem is to maintain the superheat of the steam and reduce the water content of the steam as much as possible, such as strengthening the insulation measures of the steam pipeline and reducing the pressure loss of the steam, so as to improve the accuracy of the measurement. However, these methods cannot completely solve the problem of inaccurate steam flow measurement. The fundamental solution to this problem is to develop a flow meter that can measure two-phase flow media. 3. Insufficient turndown ratio The turndown ratio refers to the ratio of the maximum flow rate and the minimum flow rate that can be measured within the range that a flowmeter can ensure a given accuracy and reproducibility. But we must be careful when it comes to the turndown ratio, because the turndown ratio is based on the actual flow rate, the general maximum allowable speed of the steam system is 35m/s, and higher flow rates will cause system erosion and noise. The minimum flow rate allowed by different flow meters is different. Generally, the minimum steam flow rate that can be measured by a vortex flowmeter is 2.8m/s. If the range ratio is insufficient, the Gilflo ILVA flowmeter with a large range ratio should be used. The minimum allowable flow rate is 0.6m/s, and the maximum turndown ratio can reach 100:1 or select multiple flowmeters in parallel. Fourth, the density compensation of steam is incorrect In order to measure the mass flow of steam correctly, changes in steam pressure and temperature must be considered, that is, steam density compensation is shown in Figure 1. Different types of flowmeters are affected in different ways by density changes. The signal output of the steam flowmeter is only related to the flow rate, and has nothing to do with the density, pressure and temperature of the medium. The mass flow of the differential pressure flowmeter is related to the geometric shape of the flowmeter, the square root of the differential pressure and the square root of the density. Therefore, steam flowmeters are more affected by density changes than differential pressure flowmeters. Figure 1 A good steam flowmeter is inseparable from the common cooperation of on-site instrument workers. If the measurement is inaccurate, you should first find the problem on the spot, so that you can find the reason for the measurement!
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