Double orifice meter application in gas measurement
Abstract: the orifice meter is more traditional in the field of two kinds of detection method, henan SIKE measurement and control technology co., LTD., mature technology, instrument industry widely used products, have higher credibility, because of the increase in current manufacturing precision so whatever in measuring accuracy, reliability, maintenance and other aspects are better than other meter has its advantages. For gas production process, the characteristics of measurement, introduces the application of double orifice flow meter in the measurement system, this paper expounds the measurement system of related instrument selection principle, through the installation and maintenance of orifice plate, using chart calculation and analysis of double orifice flow meter in the measurement of economy advantage and double orifice in running and disadvantage in the early stage of the project investment; Also analyses the measuring related patterns, different measuring combination on measurement accuracy, stability and the cost will be big impact.
Keywords: orifice flow meter, measuring, meter accuracy
Preface: production from natural gas with natural gas as raw material to produce production technology, reforming reaction with water vapor, product, and then through the tubes to the customer. Compared with other gas, the price is too expensive, so the measurement accuracy of above not only the relationship between the supply and demand for fair trade settlement, also related to cost control, so the whole measurement system attaches great importance to by the parties.
As shown in figure 1, the whole measuring system by double orifice, differential pressure transmitter, pressure transmitter, thermal resistance, flow integrating instrument. Orifice plate combined with differential pressure transmitter to collect the differential signal, pressure transmitter signal sampling pressure signals and heat resistance temperature combination is used for temperature compensation, after integrating the display in the flow integrating instrument.
Two pieces of orifice plate can be series and parallel measurement according to the actual production, single at the same time a orifice plate only value for trade settlement. When in the process of running found two pieces of orifice plate has a large deviation, the operator will view the historical trend, timely find out by its process flow a mutation, the third-party units for verification in a timely manner.
This adopts double orifice flow method, although in some beauty construction of the high cost of initial investment, but if there is deviation appears, failed to timely intervention, can cause great economic loss.
❶ flowmeter selection
Flowmeter with henan cisco tt&c SKLG series orifice. According to Bernoulli equation, fluid flow in the pipeline, when close to block, a part of the fluid potential energy into kinetic energy, in front of the orifice of the entrance end face pressure to increase; When after throttling, flow gradually shrink, velocity increases, the least stressed, so in the orifice of both upstream and downstream side production pressure difference, the greater the flow rate, the greater the pressure difference, orifice is embodied by measuring the differential pressure flow.
❷ temperature pressure compensation
Due to the other can be compressed, as the change of pressure, temperature, volume change accordingly, so the condition of gas flow must be converted to the condition of the volume flow measurement, the state of a standard physical atmospheric pressure when the flow rate, pressure compensation of temperature,
❸ flow integrating instrument
Flow integrating instrument used to deal with a variety of data types, 4 ~ 20 ma, 1 ~ 5 v, ohm, switch as well as the pulse input, switch output, etc., can also realize flow section of temperature, pressure compensation and flow measurement. According to the provisions of the contract, set the flow section values within the program, can automatically generate and monthly. Operators only need to select to print the date, and daily or monthly, can't modify any data.
1, installation and use of double orifice
Instrument installation is an important part of instrument operation, hole surface installation requirements is particularly high, and it directly affect the error of measurement. The installation of double orifice compared with single orifice, more strict.
1) orifice plate installation direction
Orifice plate face upside, traffic will be lower than the actual flow, at the beginning of the installation should check the pipeline flow, also have the arrow mark on orifice, the direction of the arrow to the flow direction of medium and consistent. In selecting pressure near the mouth should be marked with "+" end connected to the fluid upstream section, marked with "-" should be connected to the flow downstream section at the end of the.
(2) the center line
The center of the orifice, flange, pipeline center should be on the same axis.
(3) straight pipe length
(no cases orifice flow regulator with diameter between the straight pipe section) for different situations in the straight pipe orifice detailed classification, in benzene project, using two pieces of orifice plate A and B, due to the upstream side of two pieces of orifice choke thing is different, so the straight pipe section of the request is not the same.
According to the orifice calculation values obtained, the upstream side of the orifice plate A as A full bore ball valve and A tee, straight pipe, need 12 d; B the poor quality of orifice flow, on its upper side has a ring valve and a 90 ° elbow, a tee, need to 28 d straight pipe.
Due to the limited site installation orifice, cannot satisfy the requirement of the 28 d straight pipe, in order to be able to achieve a better quality of fluid, the measurement meet the precision requirement, therefore USES the rectifier in front of the orifice plate. Solve the problem of insufficient installation space.
2, metering system pattern choice
Double orifice measurement and measurement of single span plate is not colleagues choose to double the number of detecting, so in addition to the need to satisfy the requirement of accuracy, cost, and the third party identification is also need to think a lot about the problem.
Smart transducer detecting can be divided into many parameters with single transmitter refs. Multiple parameter transducer by a detector temperature, pressure, differential pressure detection at the same time, and display in the header. Generally applied in no piecewise measuring model, the accumulation of settlement on the basis of just flow value, monthly agreement read values between two parties in a certain time. Simple and convenient advantage is third party identification, transmitter can come alone, can also be verified with flow meter; Defect is the function of the transducer itself is not stored data, the data may need to be done to the HMI in storage, and cumulative flow need to convert communication protocol by Modbus485 to Modbus TCP/IP will be lost to HMI, hardware cost will be increased correspondingly, and easy to lose data. Therefore, no multi parameter transducer in this project.
3, double orifice deviation calculation
If two pieces of orifice plate deviation, higher than the actual production demand value will result in great economic loss, need timely find the reason, solve the problem.
4, the advantages and disadvantages and application of double orifice meter
The advantages and disadvantages and application of double orifice flowmeter
I) orifice plate structure is simple;
II) orifice plate belongs to the standard throttle device, recognised by international organizations, geometric measurement method can be used, need not real flow calibration;
III) the pressure loss of the orifice of the relatively small;
Iv) can be used with different manufacturer transducer;
V) two pieces of orifice plate has an advantage when found flow deviation is very big, can find problems in time, avoid the economic loss.
The problems existing in the double orifice meter
Ⅰ) in the accuracy of orifice flowmeter belongs to medium level, many factors can affect the accuracy, the flow the range 30% smaller, especially;
Ⅱ) pressure loss;
Ⅲ) narrow measuring range, range than small;
Ⅳ) have long straight pipe length, asks to install enough space;
Ⅴ) orifice hole within acute Angle line to ensure accuracy, for corrosion and wear, scale, dirt, sensitive, hard to ensure the long-term use of precision, need to remove the strong checked once a year;
Ⅵ) with flange connection, easy to run, run, drip, leak problems, greatly increases the maintenance workload;
Ⅶ) in double orifice flowmeter metering should be negotiated with the customer and settlement method, lest cause dissent;
Ⅷ) costs, increased maintenance.
5, summary
Because the metering station for unattended station, usually bring certain difficulty to maintain daily, so measurement scheme should fully consider the design brief sex, operation, maintenance, simple operation, easy maintenance, and to be very reliable, so double orifice can achieve such purpose.
In actual application of double orifice meter does not see more, mainly the cost increase and not widely used. But in trade settlement, one of the most important principle is to ensure that measuring accuracy, the deviation is positive or negative, is not fair to both buyers and sellers, so the two pieces of orifice plate, the deflection should be timely analysis of the reason, solve problems, avoid to cause the economic losses of both sides. Although one-time investment cost is higher, but from the perspective of long-term, stable running, is more efficient than single board.