In chemical production process, will encounter a lot of process instruments, in the face of all kinds of flow meter
s, such as chemical plant in the electromagnetic flowmeter
, turbine flowmeter, differential pressure flowmeter, rotameter, thermal mass flowmeter is a very typical instrument, according to flow, flow pattern, installation requirements and environmental conditions, economic factors, such as reasonable selection, is the basis and prerequisite for application of well flow meter in a chemical plant to correctly and effectively select and use the flow measurement methods and instruments, must be familiar with production process flow meter and fluid characteristics of these two aspects of technology, at the same time should also consider economic factors.
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Flow meter is one of the categories of instruments for process automation instrument and apparatus, it is widely used in metallurgy, electric power, chemical, oil, transportation, environmental protection, and the People's Daily life and so on various fields of national economy.
In process automation instrument and apparatus, flow instrument has two functions: as a process automation control system of the testing instrument and measuring the amount of material quantity table.
The correct flow measurement is essential means of production, and the assessment of energy in improving production efficiency and ensure production safety, and put an end to energy waste and other aspects play an irreplaceable role.
But the amount of traffic is a dynamic, it is a only real movement occurs when the fluid quantity, so it is not only a basic amount of static combination and due to its dynamic properties, flow value influenced by many complex factors, such as microscopic molecular interactions between fluid, macroscopic turbulence and vortex movement, also by boundary conditions in the concrete pipe (
In the face of all kinds of flow meters, according to flow, flow pattern, installation requirements and environmental conditions, economic factors, such as reasonable selection, is the basis and prerequisite for application of well flow meter.
Britain's famous traffic experts F.
Kinghom said: flowmeter is to use one of the few instrument is much more difficult than manufacturing, in this article, according to the experience, the author actually use simple flowmeter selection guidelines commonly used chemical plant is introduced.
Flowmeter selection guideline flowmeter selection guideline is to point to in accordance with the requirements for production, starting from the actual situation of instrument product supply, synthetically considering measuring safe, accurate and economical efficiency, and according to the nature of the current body condition determine the flow sampling device and flow and measuring instrument type and specification.
The flow measurement of safe and reliable, * first measurement method is reliable, is not going to happen in the operation of the sampling device in the electric circuits of the mechanical strength or failure caused by the accident;
2 it is measuring instrument both under the condition of normal production or malfunction does not affect the safety of production system.
For power plants, for example, high temperature and high pressure main steam flow measurement, a measuring element in its installation in the piping must be strong, to ensure that the damage will not occur mechanism under high speed steam flow washed away.
Generally preferred to choose the standard throttling device, therefore, not choose double cantilever beam type horn tube or insert flowmeter and other non-standard devices, as well as the structural strength low target type, turbine flowmeter, etc.
Fuel power plants and combustible gas in the situation, should choose explosion-proof type instrument.
On the basis of guarantee the safe operation of the instrument, and strive to improve the accuracy of the instrument and energy saving.
Therefore, not only to choose display instrument that could satisfy the requirement of accuracy, but also to choose according to the characteristics of the measured medium reasonable way of measurement.
Main generator steam flow measurement, because of its safety and economical efficiency of the coal-fired power plant is crucial, generally USES the mature standard throttling the load with differential pressure flowmeter, chemical water treatment of sewage and fuel respectively belong to the dirt flow and low viscous flow Reynolds number, don't apply standard throttling.
Of dirt flow generally selected segmental orifice and other non-standard throttling with differential pressure gauge or ultrasonic doppler flowmeter, and viscous flow can target type or cuneate, displacement and flow meter, etc.
Population of water turbine, condenser circulating water and heat recovery unit of heat recovery steam etc are all big diameter (
More than 400 mm)
Flow measurement parameters and to create difficulties and pressure loss is big, do not choose standard throttling device.
According to the measured medium, and the measurement accuracy requirements, inserting type flowmeter, velocity components are respectively with differential pressure meter, ultrasonic flow meter, or tag method and simulation method can damage way flow measurement.
In order to guarantee the service life of the meter and the accuracy, also note the instrument model selection of the vibration control requirements.
In hot and humid region should choose wet and heat meter.
To correctly choose the specifications of the instrument, but also to ensure the service life of the instrument and the accuracy is important one annulus.
Should pay special attention to static pressure and temperature resistant selection.
The static pressure of the compression degree, it should be slightly more than the working pressure of measured medium, typically take 1.
25 times, in order to make sure no leak or an accident.
Span the range of choice, mainly instrument calibration limit choice.
Choose the small, easy to overload, damage the instrument;
Choose the big, impedes the accuracy of the measurement.
Generally selected as the actual operation flow value of 1.
Installed on the production line long running contact instrument, should also consider the energy loss caused by the flow measurement device.
In general, not in the same production line should choose pressure loss of the multiple large measuring element, such as throttling element.
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