What flow meter, commonly used flowmeter selection and comparison
What are the flow meters? Due to the variety of commercial users, the amount of gas consumed by different enterprises varies. Therefore, it is necessary to select the gas meter reasonably according to the different conditions of enterprises, so as to achieve the purpose of accurate measurement and cost saving.At present, gas metering meters for gas users mainly include turbine flowmeter, ultrasonic flowmeter, waist wheel (roots) flowmeter and membrane flowmeter. The following is an analysis of the selection of gas metering meters for commercial users based on their respective characteristics.
Ultrasonic flowmeter is a speed-type measuring instrument that measures volume flow through detecting the effect of fluid flow on ultrasonic beam (or ultrasonic pulse). The measuring principle of ultrasonic flowmeter for natural gas is propagation time difference method.A set of ultrasonic sensors is installed in the measuring tube;Simultaneously measure the arrival time of sound waves between each other.
Because it is all electronic, no mechanical part, not affected by mechanical wear and failure, the reliability and accuracy of the product has improved a lot.Small volume, light weight, good repeatability, small pressure loss, not easy aging, long service life;Intelligent, all-electronic structure, can be extended to advance fee meter or wireless meter reading function.The special function is the small flow can be measured, has the pipe leakage sensing function, the pressure loss is zero.
Main features: 1. It can measure two-way flow beam; 2.
2. Process parameters (pressure, temperature, etc.) do not affect the measurement results;3. No contact measurement system, no pressure loss in flow measurement process;4. Accurate measurement of pulsating flow;
5. Good repeatability, speed error ≤5mm/s;6. The range is very wide, qmin/qmax=1/40~1/60;
7. Without considering rectification, only 100mm in the upstream and 50mm in the downstream can remain the installation gap;
8. The sensor can be replaced without gas, which is convenient for operation and maintenance.Factors affecting ultrasonic measurement:
The sources of uncertainty in ultrasonic measurement are as follows:
1. Mechanical, related to the geometric size of the pipe segment;2. In physics, it is related to the velocity distribution of the fluid;3. Electronic, related to propagation time measurement.Main reasons affecting ultrasonic signal:
1. Serious electronic noise;2. Ultrasonic acoustic noise;3. Serious signal attenuation;4. Multi-directional flow in the measurement section;5. The transducer is contaminated;
6. Serious measurement gradient occurs in the measurement section;Severe turbulence.In general:
Compared with traditional orifice and turbine flowmeters, ultrasonic flowmeters have great advantages in structure, measurement accuracy, pressure loss, range ratio and other indicators.The main problems in the application of ultrasonic flowmeter lie in the fact that there are many unfavorable factors to improve the signal-to-noise ratio in the process of gas transmission, especially because of the influence of the noise caused by the pressure regulating device, the rapid attenuation and installation effect of ultrasonic in the gas.
The scope of application of ultrasonic flowmeter is very wide, but due to the impact of economic cost performance and operating environment, it is more suitable for the main pipe network with large diameter, high pressure and long conveying distance.
Diaphragm gas meter belongs to the volumetric flowmeter, simpler structure, measuring principle is: by measuring the component diaphragm in the import and export gas alternating movement under the action of pressure difference, the gas will be full of measuring indoor is divided into a single measurement volume toward the exit side by side, through mechanical transmission mechanism connected to counter, implement transfer operations on a single measurement volume of statistics and final amount of gas measured flow measurement.
Comparison of main performance of flowmeter:
Project range than initiating the flow measurement precision pressure loss intelligent temperature pressure compensation turbine flowmeter ultrasonic flowmeter membrane roots flowmeter flowmeter 1/10 ~ 1/20 high big small 1/40 ~ 1/60 smaller without no 1/10 ~ 1/20 high big 1/30 ~ 1/60 smaller generally small small no impact on the velocity distribution sensitive sensitive temperament and high installation requirements is not sensitive to the high sensitive sensitive low straight pipe before and after the general requirements, pipeline purging,Installation filter pipe purging, general installation filter maintenance and maintenance cleaning filter can be on-site maintenance device, on-site disassembly and maintenance cleaning filter site can not maintain the device, the service life of the site disassembly and maintenance and maintenance price is high expensive high cheap low six.Selection of flowmeter
1. The relative error of roots gas flowmeter, membrane gas meter and turbine gas flowmeter are all ±2%. The measured gas flow value can only be accurately measured within the measuring range of the flowmeter.Under the condition of ensuring the measurement accuracy, it is necessary to select the appropriate flowmeter specifications and models according to the actual flow rate range of the measured gas, especially for the lower limit of the gas flow rate.
2. Under normal working conditions, gas consumption load of gas equipment is the main reference basis for gas flowmeter selection.In the case of extreme use, the gas load is only used as a reference in the selection of gas flowmeter.So-called extreme use state, it is to point to gas equipment less appear make
With a state.
3. The accuracy of measurement of gas flow meter is an important reference factor, but it is not the only condition of gas flowmeter lectotype, the actual selection process, combined with the operation of gas equipment, all think the price of gas flowmeter, on the installation, use and maintenance cost, to comprehensively consider the cost performance of fuel gas flowmeter, selection of scientific and reasonable.
4. For users in the catering industry (canteens, restaurants, etc.), roots gas flowmeter and membrane gas meter are usually preferred.If the maximum gas flow of gas equipment is within the range of 65 ~ 650 cubic meters per hour, roots gas flowmeter is suitable for selection. If the maximum gas flow of gas equipment is less than or equal to 65 cubic meters per hour, membrane gas meter is suitable for selection.
5. For users of similar boilers and hot water tea boilers, intelligent roots gas flowmeter can usually be selected and temperature and pressure compensation devices are required.
6. For large boilers, industrial furnaces, as well as chemical gas equipment such as large users, but the gas flow rate is more than 650 cubic meters per hour, will usually choose the turbine fuel gas flowmeter, and on various gas equipment installation flowmeter alone, as far as possible to the intelligent degree of the demand is higher, can realize remote and automation, which is convenient for the user's actual user status online monitoring, etc.