Abstract: The steam flowmeter is a measurement system consisting of multiple measuring instruments. It is not easy to disassemble during the actual working conditions, and many steam flowmeters are used for trade settlement, which requires mandatory verification. (After you doing steam flow meter selection)How to improve on-site inspection technology has become especially important. Some parts need to be qualitatively judged on site, and some parts are inspected on site,in order to improve the accuracy of the steam flow meter.
Steam is widely used in industrial production as an important secondary energy source. The measurement of steam is an important part of the process of steam use. The accuracy of the steam flow meter is related to the economic interests of both parties. The steam flow meter is in turn a metering system consisting of a plurality of measuring instruments. Most of the steam flowmeters are installed on high-temperature and high-pressure steam pipes, which is inconvenient to disassemble. How to improve the on-site detection technology of steam flowmeters becomes very important.
There are generally two types of flow meters commonly used for metering steam: vortex flowmeters and differential pressure flowmeters. The vortex flowmeter is mainly composed of a vortex flow sensor, a flow totalizer, a pressure transmitter, and a temperature platinum thermal resistor. The differential pressure flowmeter is mainly composed of a standard orifice plate, a differential pressure transmitter, a flow totalizer, a pressure transmitter, a temperature platinum thermal resistance and the like.
Know more about what is a pressure transmitter.
The vortex flowmeter has simple structure, firm structure and convenient installation and maintenance. At present, the application in the market is more and more extensive. Schematic diagram of the installation of vortex flowmeter is shown in Figure 1:
The verification of the vortex flow sensor complies with the national verification procedure of JJG1029 - 1007 "Vortex Flowmeter". The critical flow venturi nozzle method gas flow standard device is used in the laboratory for verification. The vortex flowmeter is a volumetric flowmeter, that is, the fluid Reynolds number is within a certain range, and its output is only proportional to the volume flow. In the on-site inspection environment, since the vortex flow sensor is installed on the steam pipe, it cannot be disassembled and sent to the laboratory for verification. The oscilloscope generally receives the square wave pulse signal output from the vortex flow sensor in the working state. Through the analysis of the waveform, the working state of the vortex flow sensor is qualitatively judged.
The pressure transmitter is generally installed on the buffer tube. By closing the needle valve on the buffer tube, the pressure transmitter is removed, and the pressure transmitter is brought to the environment that meets the requirements of the verification procedure. Verification. The entire verification process follows the national verification procedures of JJG 882 - 2004 Pressure Transmitter. Differential pressure transmitter on-site inspection reference pressure transmitter on-site detection method.
The on-site verification of the flow totalizer complies with the national verification procedure of JJG1003 - 2005 "Flow Totalizer".
The frequency output vortex flowmeter measures the mass flow expression:
Where: qm—mass flow, kg /h;
F—Vortex flowmeter output frequency, P / s;
Kt—flow coefficient under working condition, P / L;
Ρf—fluid density, kg / m3.
The vortex sensor is DN80 with a meter factor of 1. 2P /L, the pressure transmitter has a range of (0 to 1. 6) MPa, and the temperature platinum resistance is pt100 for the totalizer.
The instantaneous mass flow can be obtained by equation (1):
With the development of computer technology, the application of microprocessors. Now the intelligent calculator integrates the steam density meter into its memory. Under the control of the CPU, it simulates the method of manual table lookup. Using the combination of computer look-up table and linear interpolation, the steam density can be obtained and manually checked. The table has the same accuracy.
Some studies have shown that a phase change occurs when the steam is decompressed in a critical saturated state, that is, from a saturated state to a superheated state. At this time, taking ρf as a saturated steam will inevitably introduce a large error, if this happens. Temperature pressure compensation should be performed. The relationship between the density of superheated steam and the change in steam temperature and pressure is a curved surface in three-dimensional space with two independent variables. Therefore, the accuracy of the temperature measurement is directly related to the accuracy of the overall measurement of the vortex flowmeter. The specific practices at the site of use are as follows: Pull the PT100 out of the casing and bring it to the laboratory for verification. Insert a qualified PT100 into the casing to ensure proper operation of the steam flow meter. The calibration of the temperature platinum resistance is in accordance with JJG229-98 "Industrial Platinum and Copper Thermal Resistance Verification Regulations".
A system consisting of multiple measuring instruments that measure steam. The accuracy of each measuring instrument has an influence on the measurement of steam, and the trade settlement of steam, these measuring instruments that affect steam metering should be compulsory. In the field of steam flowmeter use, there are many factors affecting the accurate measurement of the flowmeter. We also need to pay attention to the selection, installation and use environment of the flowmeter. Ensure accurate metering of the steam flow meter.