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Inaccurate factors of steam flow measurement and how to solve them

by:Sincerity Group     2022-08-20
Abstract: The inaccurate factors of steam flow measurement and how to solve the information are provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. Abstract: This paper analyzes various common factors that affect the correct measurement of steam flow, expounds the main performance of the steam flowmeter, introduces the principle and characteristics of the spring-loaded variable area flowmeter, and the points for attention in the installation of the steam flowmeter system. 1 ago. More flowmeter manufacturers choose models and price quotations. Welcome to inquire.Below are the details of the steam flow measurement inaccuracy factors and how to solve them. Abstract: This paper analyzes various common factors that affect the correct measurement of steam flow, expounds the main performance of the steam flowmeter, introduces the principle and characteristics of the spring-loaded variable area flowmeter, and the points for attention in the installation of the steam flowmeter system. 1 Introduction Since the industrial revolution, steam has been widely used as a working fluid or heat transfer medium due to its easy generation, transportation, control, high heat capacity, non-toxicity and odorless characteristics. The measurement of steam flow has always been one of the important contents of steam applications. The main purposes of using a steam flowmeter include: improving the efficiency of the plant, determining the peak time and equipment of steam consumption, rationally using the steam manufacturing method, and avoiding the overload operation of the boiler; monitoring the efficiency of energy use; improving the control of the process; measuring steam The usage is billed internally or externally. However, since the measurement of steam is different from other fluids such as water and air, there are many factors that affect its accurate measurement in actual measurement. At the same time, there are many misunderstandings about steam measurement in China. Aiming at some factors affecting the correct measurement of steam flow, the solution is put forward, and the main performance of the flowmeter and the matters needing attention in the actual installation and use are expounded. 2 Factors affecting the correct measurement of steam flow Whether the steam flow can be measured correctly is not only affected by the measurement performance of the flowmeter itself, but also affected by many factors, some of which will be discussed below: 2.1 Changes in steam flow In order to ensure that the obtained flow information can be To properly represent steam flow over the entire range of process conditions or demands, the flow meter must be able to measure the entire range from extreme low loads to maximum loads. The actual steam load may not be known or vary widely, so the flowmeter has the largest possible turndown ratio under possible flow conditions. But we must be careful when it comes to the turndown ratio, because the turndown ratio is based on the actual flow speed, for example, the maximum allowable speed for a steam system is 35m/s, and a higher flow speed will cause system erosion and noise. Different flowmeters allow different minimum flow rates. For example, the minimum steam flow rate that can be measured by a general vortex tip flowmeter is 2.8m/s, while the minimum allowable flow rate of a GilfloILVA flowmeter is 0.6m/s. Therefore, for systems with large flow changes, it is easy to cause the fact that some flowmeters cannot measure correctly or cannot be measured at low flow (low flow rate). 2.2 Density changes caused by changes in steam pressure and temperature Under ideal conditions, the pressure of steam can be kept absolutely constant. However, in the real world, changes in steam system load, system pressure drop and process parameters can cause pressure changes, sometimes large. In a superheated steam system, changes in the degree of superheat will cause changes in steam density even when the pressure is constant. In order to correctly measure the mass flow of steam, changes in steam pressure and temperature must be considered. The steam flowmeter must have built-in line pressure and temperature compensation, namely steam density compensation. However, most flowmeter systems currently used to measure steam mass flow do not have automatic pressure and temperature compensation and are specified to operate at a certain pressure. It is fine if the line pressure (including temperature for superheated steam) can be truly fixed, but even relatively small pressure changes can affect measurement accuracy. Different types of flowmeters affect in different ways: a. Velocity flowmeters such as vortex tip flowmeters: The signal output of the vortex tip flowmeter is only related to the flow rate, and has nothing to do with the density, pressure, and temperature of the medium. That is, for a given flow velocity of 3barg and 17barg of steam, the output signal of the same vortex tip flowmeter is the same. Therefore, for a vortex tip steam flowmeter specified to work at a certain pressure, but actually operating at a different pressure, the error can be simply calculated by the following methods: b. Differential pressure flowmeter such as orifice flowmeter: orifice and differential pressure The output of the transmitter is a differential pressure signal. Its mass flow is related to the geometry of the flowmeter, the square root of differential pressure and the square root of density. Therefore, for a given flowmeter, under a certain differential pressure, the error caused by the pressure change is as follows: 2.3 The influence of steam dryness on saturated steam At present, most of the flowmeters used to measure steam flow are volumetric flowmeters. First measure the volume flow, then calculate the mass flow from the density of the steam (fixed density or compensated according to temperature and pressure), assuming that the steam is completely dry. However, the steam is not completely dry, which is applicable to almost all situations, especially the quality of the steam produced in China is generally poor, and there is no effective condensate discharge in the steam pipeline. Therefore, the steam quality measured by the above method is not correct. If the effect of steam dryness is not considered, the data obtained will be lower than the actual flow rate.
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