Superheated steam metering

Superheated steam is a special medium. In general, superheated steam refers to superheated steam.

1、Superheated steam is a common power source. It is often used to drive the steam turbine to rotate, and then drive the generator or centrifugal compressor to work.

2、Superheated steam is obtained by heating saturated steam, which contains no droplet or liquid mist and is a real gas.

3、The temperature and pressure parameters of superheated steam are two independent parameters and their density should be determined by these two parameters.It can be found by superheated steam density meter.The superheated steam, after being transported for a long distance, changes along with the operating condition (such as temperature, pressure, etc.), especially under the condition of low over-heat, will change from the superheated state into the saturated or oversaturated state due to the reduction of heat loss temperature and change into the saturated steam or the supersaturated steam with water drop.When saturated steam suddenly depressurizes dramatically, the liquid will also turn into superheated steam when adiabatic expansion occurs, thus forming a vapor liquid two-phase flow medium.

●Measurement analysis

Three measures should be taken at present:

(1)Piping for conveying steam must be well insulated to prevent heat loss.

(2)In the steam pipe road to be section by section of steam, in the lowest point of the pipe and the instrument before the pipe should be set steam traps, timely discharge condensed water.

(3)The boiler operation should avoid the phenomenon of excessive liquid level in the drum and reduce the large fluctuation of the load as far as possible.

●Selection comparison of superheated steam flow meter

At present, there are more than 60 kinds of industrial flow meters, mainly including vortex flowmeter, differential pressure type (orifice flowmeter, equal speed tube, curved tube, V cone flowmeter), split rotor flowmeter, ox pa flowmeter, float flowmeter and so on.In history, there has not been a flow meter applicable to any fluid, any range, any flow state and any use conditions. Any flow meter has its specific applicability and limitations.If the flow meter is not properly selected, the flow measurement must be inaccurate.However, flow measurement is a complex technology, and there are many kinds of flow meters. Even for a certain application, choosing a proper flow meter becomes a very technical work, which requires carefully and deeply considering and weighing many factors related to the measurement problem before making the final choice.

Therefore, the correct selection of the instrument is the key to the normal use of the instrument. In practical application, too many faults are caused by the unreasonable selection of the instrument. Understand the working conditions and medium parameters of the field application in detail, select the appropriate pressure and temperature, Protection, explosion-proof grade and material, structure to ensure that the instrument can run in the best condition.

Steam metering should take into account five main factors when selecting flow meter: measuring method, performance requirement and instrument specification, fluid characteristic, environmental condition, economic condition (purchase cost, installation cost, operation cost, check cost, etc.) Maintenance costs) In our practical work, the orifice plate (nozzle) Flowmeter and vortex Flowmeter are mostly used in the central heating work of production in industrial and mining enterprises. The comparison between these two Flowmeters is given here as an example.

●Differential pressure flowmeter

A differential pressure Flowmeter is a flow meter that is calculated by a flow detector installed in a pipeline (I. e., a differential pressure device for short), a known fluid condition and the geometry of a primary instrument and a pipe, and a differential  pressure device is used to calculate the flow meter. The lead pressure tube and differential pressure gauge are composed of three parts. This kind of differential pressure Flowmeter, represented by orifice plate Flowmeter, has a long history of application, high degree of standardization, very common application, and can be used without real flow calibration. The standardization, serialization and generalizability of differential pressure display instruments are high, and the theoretical accuracy is high. Wide range of application and strong adaptability, low initial investment cost. However, through practical application, it is found that the orifice plate Flowmeter is also Shortcomings:

①In the application, many factors (design 

parameters are inconsistent with operating conditions, length of upstream straight pipe is

insufficient, hole plate and pipe are different centers, hole plate A is polluted, sharp Angle wear, etc.) have A great influence on the measurement accuracy, which increases the measurement error and reduces the accuracy.In particular, the differential pressure transmitter shall be calibrated frequently to ensure the accuracy of zero and the three-way valve shall be checked frequently to prevent the measurement misalignment caused by blockage.

②The installation works are large, troublesome and demanding, and the workload of frequent maintenance and cleaning is large.

③The operation of differential pressure transmitter is required, which increases the maintenance workload. In addition, the pressure pipe should be laid, and the heat insulation of the pressure pipe should be carried out in winter. The pipe should not be installed outdoors.

④The flow range ratio is 1: 3～ 1: 4, the range is low, the measurement of small flow is difficult, and the flow range is narrow.

⑤High pressure loss, non - linear scale, high running cost.

LGK series orifice plates +P23 differential pressure transmitter +P21 pressure transmitter +XSR intelligent double compensation flow integrator + temperature sensor (for integrating calculation)

LGV series V-cone +P23 differential pressure transmitter +P21 pressure transmitter +XSR intelligent double compensation flow integrator + temperature sensor (for integrating calculations)

●Vortex Flowmeter

Vortex Flowmeter is a new type of Flowmeter developed successfully on the basis of Carmen Vortex principle. During the period of rapid development of Vortex Flowmeter from 1970 to 80's, many types of Vortex Flowmeter have been developed and put on the market in large quantities. During the peak period of development in China, there were dozens of vortex Flowmeters. It should be said that Vortex Flowmeters are still a developing product, but because they have the advantage that other Flowmeters cannot be obtained, the proportion of using Vortex Flowmeters has increased substantially. It has been widely used in various fields and will dominate the flow meter in the future. It is an ideal substitute for orifice Flowmeter. It has the following characteristics:

①The structure is simple and solid, the measuring part is not movable, the long-term operation is very reliable.

②Low maintenance and easy to maintain, low installation cost.

③Output and flow proportional to the pulse signal, zero drift, high accuracy, and easy to network with the computer.

④Wide range of applications, applicable to various gas, steam and liquid flow measurement.

⑤Flow measurement range is wide, range ratio up to 1:10.

⑥Low pressure loss, low operation cost, more energy-saving significance.

⑦In a certain range of Reynolds numbers, the frequency of the output signal is not affected by the physical properties of the fluid and the variation of the composition. The instrument coefficient is only related to the shape and size of the vortex generator, and there is no need to compensate for the measurement of the volume flow of the fluid. There is no need to calibrate the coefficient of the instrument after changing the fittings. 

But the Flowmeter also has some limitations

①Vortex flowmeter is a kind  of  velocityflowmeter. The stability of vortex separation is affected by the flow rate. Therefore, it has certain requirements on the straight pipe section, generally 10D before and 5D after.

②When measuring liquid, the upper flow velocity is limited by pressure loss and cavitation phenomenon, usually (0.5 ~ 8) m / s.

③When measuring gas, the upper limit velocity is limited by compressibility change of medium, the lower limit velocity is limited by Reynolds number and sensor sensitivity, and the steam is (8 ~ 25) m/s.

④The stress vortex flowmeter is sensitive to vibration, so it is necessary to install flow timing in the pipeline with large vibration, and

The pipeline should have certain shock absorption measures.

⑤The stress-type vortex Flowmeter uses piezoelectric crystal as the detection sensor, so it is limited by temperature, which is (-40 ~ 300) ℃, and the measuring temperature is not more than 400 ℃. Otherwise, the probe will easily lose its accuracy due to aging.

⑥Anti-electromagnetic interference and radio-frequency interference are poor.

⑦The measurement is affected when the fluid medium is two-phase flow or pulsating flow.

LUGB series vortex flow meter (over 250 degrees) +P21 high temperature pressure transmitter +XSR intelligent double compensation flow integrator + temperature sensor (for integrating calculation)