Saturated / superheated steam metering system
Xiamen Jing Chuan steam metering system introduced:
Xiamen Jing Chuan Saturated / superheated steam metering system has the following characteristics
① Saturation / one correspondence between the temperature and the pressure of the superheated steam, there is only one independent variable therebetween.
② saturated / superheated steam condenses easily, if heat loss during transmission, and lead to lower temperature and pressure. Strictly speaking, more or less of saturated steam or liquid droplets containing biphasic fluid mist, so different the state can not be described by the same equation of state of gas.
③ accurate measurement of saturated / superheated steam flow more difficult, because the saturated steam dryness is difficult to guarantee, generally can not accurately detect the flow meter biphasic fluid vapor pressure fluctuation will cause the vapor density changes, the meter indication generate additional error So the steam metering must try to keep the measuring point dryness steam to meet the requirements, if necessary compensatory measures should be taken to achieve accurate measurements.
Xiamen Jing Chuan saturated / superheated steam metering system installation diagram
Xiamen Jing Chuan saturated steam metering system installation diagram a (pressure and temperature dual compensation)
Xiamen Jing Chuan superheated steam metering system installation diagram bis (pressure single compensation)
Xiamen Jing Chuan saturated steam metering system installation diagram of three (single temperature compensation)
Currently used steam flow meter measuring the flow rate measurement of single-phase medium are superheated steam or saturated steam for steam-phase flow constantly changing, certainly there will be the problem of inaccurate measurements. The solution to this problem is to keep the steam superheat minimize moisture vapor, such as strengthening the steam pipe insulation measures, to reduce the pressure loss of steam, so as to improve the accuracy of the measurement of steam. However, these methods do not solve the steam flow measurement inaccuracy problem, to solve this problem The fundamental approach is to develop a two-phase flow can be measured media flow meter.
When the steam working condition deviated from the design state, flow indication will generate an error. Also have an impact on the flow measurement, the measurement of steam flow compensation measures need to be taken, and because of changes in the state of vapor compensation factor is relatively complex density of superheated steam by temperature steam, pressure two parameters, and the range of parameters in different forms of expression is not the same density, the same can not be represented by the formula, we can not get a uniform density formula, only individual derivation obtain temperature, pressure compensation formula in temperature, pressure fluctuation range larger occasions, in addition to temperature, external pressure compensation, also need to consider compensation for gas expansion coefficient.
Regardless of saturated steam flow meter detects adopted under steam pressure fluctuations in work pressure compensatory measures must be taken, because the flow equation, contain factors vapor density, working conditions inconsistent with the design conditions, readings will have the size and the size of the working pressure and design pressure deviation error, error related, P solid) P set to appear negative error, otherwise error will appear positive. dryness steam condition is related to the ability to accurately measure steam flow an important condition, is currently being developed online steam dryness instrumentation, to be used in steam dryness meter flow measurement and compensation system, will further improve the accuracy of the measurement of the current should take the following three measures: (1) transport steam pipe the road must have good thermal insulation measures to prevent heat loss. (2) in the steam pipeline to piecewise hydrophobic, at the lowest point on the pipeline and the pipeline should be set before the instrument hydrophobic, timely discharge of condensate. (3) The boiler operation should avoid the phenomenon of drum level is too high, try to reduce the load on big fluctuations.
Compare selection saturated steam flow meter
Currently, the industry as much as the type of flow meter with more than 60 species, mainly vortex flowmeter, differential pressure (orifice, the average rate, elbow) meter, shunt rotor flow meter Annubar float flowmeter and so on. And there is not a history of any fluid, any range, any flow state, and any conditions applicable flow meter, any flow meter has its specific applicability, but also has its limitations. If the flow inappropriate choice of instruments, flow measurement is certainly allowed, but the flow measurement is a complex technology, and a wide range of flow meter, even for a defined application, choose a suitable flow meter will become a highly technical The work requires careful and thorough consideration before making a final choice and weigh many factors associated with measurement problems. Therefore, the right selection is the key instrument used by the instrument, practical applications, too many failures are due to the instrument Selection caused by the irrational, to learn more about working conditions and medium parameters field application, select the appropriate pressure, temperature, protection, explosion-proof rating and materials, structural way to ensure that the instrument can be run in the best condition. steam metered Flow Meter consider when selecting five main factors: measurement methods, performance requirements and instrumentation specifications, the measured fluid characteristics, environmental conditions, economic conditions (acquisition cost, installation costs, operating costs, validation costs, maintenance costs) in our The actual work, whether on the mining industry for the production of district heating operation, maximum use is orifice plate (nozzle type) flowmeter and vortex flowmeter, in this order as an example to compare the two flowmeters Explanation:
Differential pressure flowmeter
Differential pressure flowmeter is installed in pipeline flow detection element (which produce a differential pressure device, referred to as an instrument) generated by differential pressure, flow conditions and a known instrument and piping geometry to calculate the flow meter, by the differential pressure means the impulse tube and differential pressure gauge of three parts. This kind of orifice meter as the representative of differential pressure flowmeter application has a long history, high degree of standardization, the application is very common, may not have actual flow calibration, the difference High standardization and serialization and universal indicator of the degree of pressure, high theoretical precision, wide application range and adaptability, low initial investment costs but through the practical application and found that there are insufficient orifice flowmeter:
① applications on many factors (design parameters and working parameters do not match, the upstream straight pipe length insufficient, plate and pipe misalignment, the orifice A surface contaminated, wear an acute angle, etc.) have a very big impact on the measurement accuracy, it measurement error increases, resulting in reduced accuracy. In particular, to loosen the differential pressure devices often be verified to ensure the accuracy of zero, and often three-way check valve to prevent clogging caused by measurement inaccurate.
② large workload installation works, more cumbersome and demanding, require regular maintenance and washable larger.
③ be equipped with differential pressure transmitter used to increase the maintenance workload, it takes another impulse pipe laying, and in winter the need to guide pressure pipe insulation, can not be installed outdoors.
④ flow turndown ratio of 1:3 to 1/4 range is low, the measurement of small flow difficulties, narrow flow range.
⑤ pressure loss larger scale nonlinear, high operating costs.
Jing Chuan Chuan series orifice flowmeter series differential pressure transmitter + finishing + fine Chuan series of high temperature pressure transmitter + fine Sichuan Chinese Flow Totalizer + Armored thermal resistance (not for totalizer for reference)
Jing Chuan Series V cone flowmeter + finishing + fine Chuan Chuan series differential pressure transmitter series of high temperature pressure transmitter + fine Sichuan Chinese Flow Totalizer + Armored thermal resistance (not for totalizer for reference)
Vortex flowmeter is based on the principle of Karman vortex street and the successful development of a new type of meter. 70-80 years is the vortex flowmeter rapid development period, the development of many types of barrier fluid and detection of vortex flowmeters, and a large number of put on the market in our country in the development of the vortex peak, has reached dozens, it should be said, the vortex flowmeter is still developing the product, but because it has advantages over other flowmeters can not have both, using vortex flowmeter a substantial increase in the proportion has been widely used in various fields, will dominate the future flow meter is an ideal alternative orifice flowmeter which has the following characteristics:
① simple solid structure, measurement part no moving parts, very reliable long-term operation.
② less maintenance and maintenance is very convenient, low installation costs.
③ output pulse signal proportional to the flow, no zero drift, high accuracy, and convenience and computer networking.
④ wide range of applications, suitable for flow measurement of gases, vapors and liquids.
⑤ wide flow measurement range, turndown ratio of up to 1:10.
⑥ pressure loss, low operation cost, more energy-saving significance.
⑦ Reynolds number in a certain range, the output signal frequency is independent of fluid properties and composition affect the physical changes, the meter factor only about body shape and size occur with whirlpool, measure the volume of fluid flow without compensation, without re-calibration after replacement parts Meter factor.
However, the meter also has some limitations
① vortex flowmeter is a velocity flowmeter, the stability of vortex separation by velocity impact, so its straight pipe have certain requirements, usually before 10D, after the 5D.
② When measuring liquid, the upper limit of the flow rate of compression damage and cavitation limits, generally (0.5 ~ 8) m / s.
③ When measuring gas, the upper limit of the flow rate limited by the compressibility of the medium changes, the lower flow velocity and Reynolds number is limited by the sensitivity of the sensor, the steam is (8 ~ 25) m / s.
④ stress vortex flowmeter is more sensitive to vibrations, so when a large vibration meter pipe installation, pipe have a certain damping measures.
⑤ stress vortex flowmeter uses a piezoelectric crystal as a detection sensor, so the limiting temperature of its subject, usually (-40 ~ + 300) ℃, the measured temperature is not higher than 400 ℃, otherwise probe vulnerable to aging and misalignment .
⑥ anti-electromagnetic interference and radio frequency interference difference.
⑦ When the fluid medium is a two-phase flow or pulsating flow measurement when influential.
Jing Chuan series vortex flow meter (250 degrees) + finishing Chuan series of high temperature pressure transmitter + fine Sichuan Chinese Flow Totalizer + Armored thermal resistance (for reference, not for totalizer)