Guarantee accurate measurement of steam flow meter

The technical personnel of Heshunda flowmeter summarized the experience of overhauling steam flowmeters for many years, combined with the problems encountered in the installation, selection and use of steam flowmeters, and made the following recommendations to ensure the accurate measurement of steam flowmeters:

First, the density of steam compensation must be scientifically accurate

In order to correctly measure the mass flow of steam, changes in steam pressure and temperature must be considered, and the steam density is compensated by the flow totalizer. The platinum resistance for measuring the steam temperature must be specified and installed: the platinum thermal resistance is inserted into the center of the pipe, the platinum thermal resistance is installed at the pipe diameter 5 times downstream of the flowmeter, and the piping is installed with the platinum thermal resistance to ensure insulation. The temperature value obtained is accurate. In the measurement of steam pressure, it must be noted that if the pressure is introduced by the pressure pipe, zero point migration must be carried out (because the gravity of the condensed water in the pressure pipe causes a certain amount of pressure between the pressure measured by the pressure transmitter and the actual pressure. The difference, which causes the density compensation error, can also be corrected in the flow totalizer. The pressure transmitter is installed at the pipe diameter 4 times downstream of the steam flowmeter. The valve and gasket in front of the pressure transmitter should be unblocked to ensure accurate measurement of the steam pressure. If the set pressure and temperature are used for compensation, the set numerical stress should be close to the actual value, otherwise the error is very large and generally not recommended.

The correct setting of the steam meter's operating conditions in the flow totalizer is critical to the correct calculation of steam costs. For the occasion where the steam state is not clearly determinable, it is recommended to use an intelligent flow totalizer with platinum resistance and pressure transmitter for temperature and pressure compensation so that the measured mass flow of steam is the most accurate.

Second, the correct installation of the upstream and downstream straight pipe section of the steam flow meter

For conventional vortex flowmeters, the installation of straight pipe sections before and after it is required to be 20 times the pipe diameter and 5 times the pipe diameter (this is the technical requirements for the flowmeter without obstacles in front of the flowmeter; there are obstacles but also increase the straight pipe section, See the manufacturer's instructions specifically). If the upstream and downstream straight sections are not enough, the steam flow in the pipeline will not fully develop and the flow velocity profile will be distorted. The user can adjust the flow rate distribution of the pipeline by installing a flow regulator or adding a straight pipe section before the steam flow meter, so that the fluid at the steam flow meter is fully developed. For some large-caliber steam flow meters, it is more important to meet the installation requirements of the upstream and downstream straight pipe sections.

Third, the steam flow meter has a reasonable range ratio

The turndown ratio refers to the ratio of the maximum flow and minimum flow that a flowmeter can measure within a given accuracy range. The user should select the flow meter according to his own actual usage, theoretically the range of the steam flow meter to be selected should completely cover the user's use range. Exceeding the upper limit of the flow and lower than the lower limit of flow may cause serious inaccuracies in the measurement of the steam flow meter. For example, a vortex street steam flowmeter with an actual average flow rate of 5 t/h should generally use a vortex flowmeter with a bore diameter of 150 mm. However, when the flow rate is reduced to 0.3 t/h or more than 15 t/h, the flow meter will become serious. Measurement inaccurate.

Fourth, the presence of vibration and electromagnetic interference should be avoided

The most widely used vortex flowmeters in steam metering are affected by the design principle, are sensitive to mechanical vibration, and the measurement results are vulnerable to vibration. The reliable support design for the front and rear pipe sections of the steam flowmeter is implemented, and vibration buffering components such as pipeline vibration are added. Inevitably, steam flow meters with relatively strong anti-interference ability (such as gas ultrasonic flow meters, smart vortex flow meters, differential pressure flow meters, etc.) should be used. If the steam flowmeter has vibration interference on the spot, it will have a low-frequency pulse signal effect on the vortex steam flow meter in use, and the steam flowmeter will send these pulses as a flow signal to the flow integrator to form a cumulative flow. As a result, some vortex street steam meters will still have a certain amount of accumulated value when steam is not used for a period of time. This is the reason why “there is no steam and flow meter”, so steam users should remember the bottom of the table together with the steam supply unit without using steam to prevent the steam flow meter “run empty”.

V. It is very important to verify regularly according to law

"Measurement Law" and GB 17167-2006 "Energy-consuming Unit Energy Measurement Instruments General Provisions and Management" clearly states that: compulsory measurement of measuring instruments and energy measurement instruments should be regularly tested, and any measurement of non-compliant instruments are not allowed to use . Steam flow meters must be regularly calibrated. This is a prerequisite for ensuring correct steam flow measurement. Therefore, the vast number of users will be used every year to send to the local statutory metrology agencies for measurement verification. If the steam flow meter is qualified and the actual use feels "inaccurate metering," then the user will have to look for whether the meter is correctly installed, the model selected, the instrument operating status setting, external interference, and whether the actual status of the steam changes. way of solving the problem.

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