In combination with the problems encountered during the installation, selection and use of the steam flow meter, the following recommendations are made to ensure accurate measurement of the steam flow:
First, the density compensation of steam should be scientific and accurate
In order to properly measure the mass flow of steam, the change in vapor pressure and temperature must be considered, and the vapor density is compensated by a flow totalizer. The platinum resistance for measuring the steam temperature must be installed in a standard way: the temperature of the platinum thermal resistance is inserted into the center of the pipe, the platinum thermal resistance is installed at the pipe diameter of 5 times downstream of the flowmeter, and the pipe position of the Huai'an Sanchang platinum thermal resistance is installed. To ensure that the measured temperature values ​​are accurate. In the measurement of steam pressure, it must be noted that if the pressure of the pressure tube is used, zero point migration must be carried out (because the gravity of the condensate in the pressure tube will cause a certain pressure between the pressure measured by the pressure transmitter and the actual pressure. The difference, which causes the error in the density compensation, can also be corrected in the flow totalizer. The pressure transmitter () is installed at the pipe diameter of 4 times downstream of the steam flow meter. The valve and gasket in front of the pressure transmitter should be well-connected to ensure accurate measurement of steam pressure. If the set pressure and temperature are used for compensation, the set value should be close to the actual value, otherwise the error is very large, and it is generally not recommended.
Correctly setting the operating state of the steam flow meter in the flow totalizer is critical to the correct calculation of steam costs. For the occasions where the steam state is not well defined, 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 sections of the steam flow meter
For the traditional vortex flowmeter, the requirements for the straight pipe sections before and after installation are 20 times pipe diameter and 5 pipe diameters respectively (this is the technical requirement of no obstacles such as valves in front of the flowmeter; there are also obstacles to increase the straight pipe section. See the manufacturer's instructions for details). If the upstream and downstream straight pipe sections are not enough, the steam flow in the pipeline will not fully develop and the flow velocity distribution profile will be distorted. The user can adjust the flow velocity distribution of the pipeline by installing a flow regulator before the steam flow meter or adding a straight pipe section, so that the fluid at the Huai'an Sanchang steam flowmeter () is fully developed. . For some large diameter steam flow meters, it is more important to meet the installation requirements of the upstream and downstream straight pipe sections.
Third, the flowmeter ratio of the steam flowmeter should be reasonable
The turndown ratio is the ratio of the maximum flow to the minimum flow that a flowmeter can measure within a given accuracy range. The user should select the flow meter according to his actual usage. In theory, the range of the steam flow meter to be selected should completely cover the user's use range. Exceeding the upper and lower flow limits will cause serious misalignment of the steam flow meter. For example, a vortex flowmeter with an actual average flow rate of 5t/h should generally select a vortex flowmeter with a diameter of 150mm, but when the flow rate is reduced to 0.3t/h or exceeds 15t/h, the flowmeter will be severe. Inaccurate measurement.
Fourth, the existing vibration and electromagnetic interference should be avoided
The most widely used vortex flowmeter in steam metering is influenced by the design principle, sensitive to mechanical vibration, and the measurement result is susceptible to vibration interference. The front and rear sections of the steam flowmeter should be reliably supported, and vibration buffer components such as pipeline vibration should be installed. Inevitably, a steam flow meter with relatively strong anti-interference ability (such as gas ultrasonic flow meter, intelligent vortex flow meter, differential pressure flow meter, etc.) should be selected. If there is vibration interference at the steam flowmeter, it will affect the low-frequency pulse signal generated by the Huai'an Sanchang Vortex steam flowmeter. The steam flowmeter will transmit these pulses as flow signals to the flow totalizer. The cumulative flow rate causes some vortex steam flow meters to still have a certain amount of value accumulation without using steam for a period of time. This is the reason why “the flow meter is not used without steamâ€. Therefore, if the steam user does not use steam, it should also keep a record of the bottom of the watch with the steam supply unit to prevent the steam flow meter from “running emptyâ€.
5. Regular verification according to law is very important
The "Measuring Law" and GB17167-2006 "General Rules for the Provision and Management of Energy Metering Apparatus for Energy-using Units" clearly state that the mandatory measuring instruments and energy measuring instruments should be periodically checked, and all measuring instruments that fail to meet the requirements are not allowed to be used. . The steam flow meter must be periodically verified, which is a prerequisite for ensuring proper metering of the steam flow. Therefore, the majority of users will send the Huai'an Sanchang steam flowmeter used to the local legal metrology technical organization for metrological verification every year. If the steam flow meter is qualified, but the actual use feels “not accurateâ€, then the user should look for whether the meter is correctly installed, selected, the instrument operating state setting, external interference, or the actual state of the steam changes. way of solving the problem.
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