Steam flow meter problems

Integrated Altaba flowmeter with temperature and pressure compensation, choose Honeywell as the transmitter, and choose the mA signal transmitter for temperature

In response to this situation, you can try an elbow flowmeter. Although the accuracy is slightly worse, this phenomenon of large changes in steam pressure can be overcome. Of course, temperature and pressure compensation must be added.

It is recommended to use orifice plate measurement, which can introduce pressure and temperature compensation calculations.

The total error of the orifice flowmeter system is generally less than 2%, which is within the normal range.

You can choose Yokogawa's vortex flowmeter, and then use a platinum resistor and a pressure transmitter for temperature and pressure compensation to obtain accurate measurement values. This program has been applied across the country and is quite mature.

Confirm whether the steam is superheated steam or saturated steam, and try to get the parameters as accurate as possible

You can refer to the following posts: To measure steam flow, should I choose a vortex or orifice plate differential pressure flowmeter? http://bbs.hcbbs.com/viewthread.php?tid=293219&highlight=%D5%F4%C6%FB%C1%F7%C1%BF Which flow form is best for measuring main steam flow? http://bbs.hcbbs.com/viewthread.php?tid=320387&highlight=%D5%F4%C6%FB%C1%F7%C1%BF Discussion in. And information: Discussion on Steam Flow Measurement http://bbs.hcbbs.com/thread-358631-1-1.html

We all use this set of flowmeters for external measurement, and the effect is good.

The vortex street should be relatively better for saturated steam, and the orifice plate should also be good for overheating:)

In metering work, inaccurate steam flow measurement is a common problem. The main reasons are analyzed as follows. 1.1 Superheated steam Steam is a relatively special medium. Generally speaking, steam refers to superheated steam. Superheated steam is obtained by heating saturated steam. It contains absolutely no droplets or mist and is an actual gas. The temperature and pressure parameters of superheated steam are two independent parameters, and its density should be determined by these two parameters. After superheated steam is transported over a long distance, as the working conditions (such as temperature and pressure) change, especially when the degree of superheat is not high, the temperature will decrease due to heat loss, causing it to enter a saturated or supersaturated state from a superheated state, and transform into saturated steam or supersaturated steam with water droplets. The saturated steam is suddenly greatly decompressed, and the liquid will also transform into superheated steam when it undergoes adiabatic expansion, thus forming a vapor-liquid two-phase flow medium. 1.2 Saturated steam Steam without heat treatment is called saturated steam. It is a colorless, odorless, non-flammable and non-corrosive gas. The content of liquid droplets or liquid mist in saturated steam reflects the quality of steam, which is generally expressed by the parameter dryness. The dryness of steam refers to the percentage of dry steam in unit volume of saturated steam, represented by "x". (3) It is difficult to accurately measure the flow rate of saturated steam because the dryness of saturated steam is difficult to guarantee. General flow meters cannot accurately detect the flow rate of two-phase fluids. Steam pressure fluctuations will cause changes in steam density, causing additional errors in the flow meter indication. Therefore, in steam measurement, we must try to maintain the dryness of the steam at the measurement point to meet the requirements. If necessary, we should also take compensation measures to achieve accurate measurement. 2. Measurement analysis Currently, flow meters are used to measure steam flow, and the measurement medium refers to single-phase superheated steam or saturated steam. For steam whose phase flow changes frequently, there will certainly be problems with measurement inaccuracies. The solution to this problem is to maintain the superheat of the steam and reduce the water content of the steam as much as possible, such as strengthening the insulation measures of the steam pipeline and reducing the pressure loss of the steam, etc., to improve the accuracy of the measurement. However, these methods cannot completely solve the problem of inaccurate steam flow measurement. The fundamental way to solve this problem is to develop a flow meter that can measure two-phase flow media. There are many types of flowmeters used to detect gas flow. Velocity type and volumetric flowmeters are the most commonly used. Their common feature is that they can only continuously measure the volume flow rate under working conditions, and the volume flow rate is a function of the state. The volume flow rate under working conditions cannot accurately represent the actual flow rate. In engineering, it is generally expressed as standard state volume flow rate or mass flow rate. The so-called standard state volume is the gas volume at 0°C and 1 standard atmosphere or the volume at 20°C and 1 standard atmosphere. Using mass flow as the unit of measurement is currently not widely used. Use a calibrated gas flow meter, select the normal temperature and pressure of the gas as the design conditions, and convert the volume flow rate under the design state into a standard volume flow rate or mass flow rate. The conversion coefficient contains the factor of gas density. When the working state of the gas medium deviates from the design state, errors will occur in the flow indication value. In addition, changes in the composition, content or temperature of the gas medium also have an impact on the flow measurement, so the measurement of steam flow requires compensation measures, and the compensation factors are also more complicated due to changes in the state of the steam. The density of superheated steam is determined by the two parameters of steam temperature and pressure. Moreover, within different ranges of parameters, the expression forms of density are also different and cannot be expressed by the same general formula. Therefore, a unified density calculation formula cannot be obtained, and the temperature and pressure compensation formulas can only be derived individually. In situations where temperature and pressure fluctuation ranges are large, in addition to temperature and pressure compensation, compensation for the gas expansion coefficient ε also needs to be considered. No matter what kind of flow meter is used to detect the flow rate of saturated steam, pressure compensation measures must be taken when working under the condition of steam pressure fluctuation. This is because the flow equation contains the factor of steam density. When the working conditions are inconsistent with the design conditions, the reading will produce errors. The size of the error is related to the size of the deviation between the working pressure and the design pressure. If Pactual > P, there will be a negative error, otherwise there will be a positive error. The dryness condition of steam is an important condition related to the ability to accurately measure steam flow. Currently, an online steam dryness detection instrument is being developed. When the dryness meter is applied to the steam flow measurement and compensation system, the accuracy of measurement will be further improved. The following three measures should be taken at present: (1) Pipelines transporting steam must have good insulation measures to prevent heat loss. (2) The steam pipeline should be drained section by section. Drain traps should be installed at the lowest part of the pipe and the pipe in front of the instrument to drain the condensed water in time. (3) During boiler operation, excessively high liquid level in the drum should be avoided and large fluctuations in load should be minimized. 3. Selection of flow meter For steam measurement, five main factors should be considered when selecting a flow meter.: Characteristics of the fluid being measured, production process conditions, installation conditions, maintenance requirements and characteristics of the flow meter. Here, we focus on discussing the characteristics, installation conditions, maintenance requirements and several issues that should be paid attention to when selecting flow meters. At present, the instruments that measure steam flow mainly include vortex flowmeters, differential pressure (orifice plate, velocity equalizing tube, elbow) flowmeters, splitter rotor flowmeters, Annubar flowmeters, float flowmeters, etc. The following uses vortex flowmeters, orifice flowmeters and elbow flowmeters as examples. 3.1 Vortex flowmeter The vortex flowmeter is a new type of flowmeter successfully developed based on the Karman vortex principle. Because it has advantages that other flowmeters cannot have, it has developed rapidly since the 1970s. According to reports, now Japan, Europe and the United States and other developed countries * * The proportion of using vortex flow meters has increased significantly. They have been widely used in various fields and will dominate future flow meters. They are an ideal substitute for orifice flow meters. It has the following characteristics: ① Simple and solid structure, no moving parts, very reliable in long-term operation ； ② Maintenance is very convenient and installation cost is low ； ③ The sensor does not directly contact the medium, has stable performance and long life. ； ④ Outputs a pulse signal proportional to the flow rate, has no zero point drift, has high precision, and is easy to connect to the computer for networking. ； ⑤ Wide measuring range, range ratio up to 1:10 ； ⑥ Small pressure loss, low operating costs, and more energy-saving significance ； ⑦ Within a certain Reynolds number range, the output signal frequency is not affected by changes in the physical properties and composition of the fluid. The instrument coefficient is only related to the shape and size of the vortex generator. There is no need to compensate for the volume flow of the measured fluid. There is no need to recalibrate the instrument coefficient after replacing accessories. ； ⑧ Wide range of applications, both gas and liquid flow rates can be measured ； ⑨ The verification cycle is 2 to 4 years. However, this flow meter also has certain limitations.: ① The vortex flowmeter is a velocity type flowmeter. The stability of vortex separation is affected by the flow rate, so it has certain requirements for the straight pipe section, usually 10D in the front and 5D in the back. ； ② When measuring liquids, the upper limit of flow rate is limited by pressure loss and cavitation, generally 0.5 to 8m/s. ； ③ When measuring gas, the upper limit flow rate is limited by the change in compressibility of the medium, and the lower limit flow rate is limited by the Reynolds number and sensor sensitivity. Steam is 8 to 25 m/s. ； ④ Stress-type vortex flowmeters are more sensitive to vibrations, so when installing flowmeters in pipelines with large vibrations, the pipelines must have certain shock-absorbing measures. ； ⑤ Stress type vortex flowmeter uses piezoelectric crystal as the detection sensor, so it is limited by temperature, generally -40~+300℃. 3.2 Differential pressure flowmeters. Differential pressure flowmeters, represented by orifice flowmeters, have a long history of application. They have international standards, high theoretical accuracy, and are widely used. However, after decades of application, it has been discovered that orifice flowmeters also have shortcomings.: ① Many factors in the application (design parameters do not match the working condition parameters, insufficient upstream straight pipe section, inconsistency between the orifice plate and the pipe, contamination of the A surface of the orifice plate, sharp angle wear, etc.) have a great impact on its measurement accuracy, causing the measurement error to increase. ； ② The installation is more troublesome, and the workload of maintenance, disassembly and cleaning is relatively large. ； ③ It needs to be used with a differential pressure transmitter, which increases the maintenance workload. It also needs to lay pressure-guiding pipes, and the pressure-piping pipes need to be insulated in winter and cannot be installed outdoors. ； ④ The flow range ratio is 1:3, which has great limitations. ； ⑤ If installed incorrectly, steam leakage may easily occur. ； ⑥ The pressure loss is large and the operating cost is high. 3.3 Elbow flowmeter Elbow flowmeter is actually a 90-degree standard elbow. There is no flow sensor with a simpler structure than it. With the development of the mechanical processing industry and the continuous improvement of industry standardization and standardized management, standard mechanism elbows used as elbow sensors are becoming more and more cost-effective. Its characteristics are: ① The structure is simple and the price is low. ② Elbow flowmeter sensors are wear-resistant and insensitive to trace amounts of wear. ③ The installation is simple and can be installed by direct welding, which completely solves the trouble of leakage and leakage on site. ④ It has strong adaptability, wide measuring range and loose straight pipe section requirements. As long as the fluid flow in the pipeline can be measured with an orifice plate, vortex street, or uniform velocity tube flowmeter, it can be measured with an elbow flowmeter. Moreover, the elbow flowmeter is far superior to other flowmeters in terms of high temperature resistance, high pressure resistance, impact resistance, vibration resistance, moisture resistance, and dust resistance. ⑤ The range ratio of the elbow flow meter can reach 1:10. For steam, its applicable range is 0~70m/s, which can better meet the requirements of steam flow measurement. ⑥ Due to its special measurement principle, the elbow flowmeter does not have strict requirements for the straight pipe section in practical applications. Generally, it only requires the front 5D and the back 2D, which is far lower than the requirements of other flow measurement devices. ⑦ The elbow flowmeter has high accuracy and good reproducibility. The measurement accuracy can reach 1.14% and the reproducibility accuracy can reach 0.2%. After one installation, it no longer needs to be disassembled and assembled repeatedly. Therefore, its installation accuracy can also be optimally guaranteed. ⑧ The most outstanding feature of the elbow flow meter is that it does not have any additional throttling parts or inserts. * * Reduce the power consumption of fluid transportation in pipelines and save energy, especially for those measurement objects with large systems, large pipe diameters, and low pressure heads. Give an example: In order to maintain the normal operation of an orifice flow meter installed in a heating pipe with a flow rate of thousands of tons per hour, it consumes tens of thousands of additional kWh of electricity in one heating season, equivalent to tens of thousands of RMB. Here we only consider that the pressure loss of the orifice flowmeter is several thousand pascals, which far exceeds this value during actual operation. Even if the pressure loss is several thousand pascals, the additional operating costs it causes cannot be ignored. The additional resistance loss will be much smaller when measured with an elbow flowmeter. If an elbow flowmeter is used instead of an orifice flowmeter for measurement, it can * * Reduce operating costs and obtain considerable economic benefits. To sum up, the selection of steam flow meter is very important, and accurate measurement of steam flow is a prerequisite.

To measure saturated steam, temperature or pressure compensation must be performed, and either a vortex flowmeter or an orifice flowmeter can be used. To measure superheated steam, it is necessary to compensate for temperature and pressure. It is best to use a long-neck nozzle flowmeter. When using a vortex flowmeter, choose a split type.

This post was last edited by Wang Tianze on 2016-1-6 22:32 Vortex flowmeter steam flowmeter with temperature and pressure compensation can be used

Orifice plate, fully compensated for temperature and pressure

Use Rosemount integrated multi-variable orifice flowmeter 3051SFC