1. Selection principle
When selecting flow meters in the chemical industry, relevant enterprises and technicians should pay enough attention to the following principles:
(1) The flowmeter shall be selected based on various process parameters, such as fluid velocity, state, temperature, density, viscosity, pressure, etc. under maximum and design working conditions, and comprehensive consideration shall be given to specific changes in its operating mode and operating conditions under abnormal conditions, such as commissioning, commencement and emergency conditions.
(2) In the specific selection of flow meters, chemical enterprises also need to consider whether there are corresponding requirements for special processes, such as whether there are solid particles in the medium, whether there is erosion and corrosion, etc.
(3) If the flowmeter needs to be installed inside the chemical pipeline, its material and grade requirements should be fully considered, and its pressure loss should be smaller than the allowable maximum pressure loss in the process pipeline.
(4) In specific selection, it is necessary to ensure that the measurement accuracy, stability and price of the flowmeter are in direct proportion to each other, so as to achieve good control of cost performance ratio.
(5) In order to ensure the application effect and safety of the flowmeter, enough attention must be paid to its installation requirements in the specific selection, and the flowmeter shall be reasonably selected according to the actual vibration of the installation location and the flow direction of the fluid.
2. Specific model selection
(1) In the selection of differential pressure flowmeter, the maximum allowable pressure drop requirements of throttling element and the physical characteristics of measuring medium shall be mainly considered. For example, when measuring high-pressure steam, nozzle can be selected; When measuring the flow of short straight pipe section, balance flow instrument can be selected; When measuring the gas flow with small maximum allowable pressure drop, the venturi can be selected; Wedge type throttling element can be selected when measuring the liquid flow with large viscosity.
(2) In the selection of vortex flowmeter, chemical enterprises and technicians should pay attention to the following points: First, it is better that the Reynolds number should exceed 2000040000, and the measurable flow value must be lower than the minimum flow value in specific applications; Second, such flowmeter shall not be selected for two-phase flow measurement of wet steam or wet gas; Third, in corrosive, waxy or viscous media, such flow meters should not be selected; Fourth, in order to ensure its good operability under the condition of minimum flow, its diameter needs to be 1-2 grades smaller than the pipe diameter in specific selection.
(3) In the selection of electromagnetic flowmeter, chemical enterprises and technicians should pay attention to the following points: First, the minimum conductivity should be selected according to the recommendations of the manufacturer, which usually needs to be controlled within 0.05-20 μ S/cm； Second, it is necessary to reasonably select the lining materials. Table 1 shows several common lining materials in electromagnetic flow meters and the problems to be noted in their selection. Third, in the process of selecting electrode materials, it is not only necessary to fully consider the corrosion resistance of the measured medium, but also pay attention to prevent electrode surface effects.
(4) For the selection of mass flowmeter, chemical enterprises and technicians should pay attention to the following points: First, there are restrictions on the grade and caliber of such instruments. If one cannot meet the actual application requirements, two or more can be selected; Second, this type of flowmeter can be used for chemical injection, but this application must be verified by the authority; Third, the flow tube of this type of flowmeter has many materials, but if there is halogen in the medium, stainless steel materials cannot be selected; Fourth, if there are normal and abnormal working conditions, the pressure drop must be paid attention to in the model selection, and it cannot be used under the condition of corrosive gas to avoid serious damage to the flowmeter; Fifth, this type of flowmeter can also be used to measure gas flow, but its manufacturer should be consulted in specific applications to ensure its stability, especially for fluids with low density, whose measurement accuracy may be affected; Sixth, such flowmeter should not be selected for two-phase flow measurement; Seventh, in order to prevent the instrument from being corroded, the airtight sensor should be reasonably applied under salt fog or wet conditions.
Post time: 23-11-22