Natural Gas Flow Measurement
Posted on | October 2, 2009 | 1 Comment
In the measurement of gas flow rate, there are several types of systems-meter (gauge) commonly used, among others:
1. Diaphragm Meter
2. Turbine Meter
3. Orifice Meter
4. Ultra Sonic Meter (USM)
Diaphragm Meter
Diaphragm Meter
Diaphragm meter is usually used to measure the gas consumed by households, small commercial firms and other consumers. With these tools necessary gas pressure and low flow rate. This tool is able to measure accurately the volumetric flow in the overall value and does not require any additional energy source (electricity). The problem faced only if the pressure is too low and is unable to rotate or move the recorder, which should have a minimum pressure for operation. Maximum working pressure of about 1000 mmH2O.
This tool consists of the machine:
- Diaphragm that divides the two parts with 4 drive gas flow will move the field diaphragm, forwarded to the shaft (lever) and play the recorder (counter). Style that encourages the flow of gas turns diaphragm field, resulting in movements that rotate around the needle recorder. Materials used for the diaphragm of oil resistant rubber imitation.
- Sliding valve (sliding valve) the valve is made of Bakelite or teflon Graphite phenol resin. Its function is to open and alternately close two valves for gas entry and gas exit. Valve sliding movement comes from two diaphragms are driven by the gas flow.
The capacity of measurement gas flow rate by diaphragm meters is minimum at 0.016 m3/hr and maximum at 7 m3/hr in 50 kpa pressure. The tool is typically used to measure natural gas, LPG, and gas anti-corrosion. To obtain a certificate of operation of gas meters must be tested first. Testing used for testing the air; Qmin, 2Qmin, 0.2 Qmax, Qmax with the standard tester and have tested again after 5 years of operation (re-calibration).
Turbine Meter
In broad outline meters turbine components consist of:
1. The body,
2. The measuring mechanism,
3. The output and readout devices.
Turbine meters consist of a straight flow pipe (tube), in which rotates a turbine or fan (fan), a free mempuyai axle bearings held by the pipe (tube) and installed a panel to record the measurement results.
Turbine Meter
Flow velocity is proportional to the force on the turbine blades (fan) is distorted by the flow of fluid and is proportional to flow rate (flow rate). Fan / turbine blade affixed to a rotating magnet on its axis. Turbine installed around the coil (coil) so that when the magnet moves the magnetic field changes this by an induction coil because there will generate electromotive force AC (Alternating current) with a voltage (voltage) and generate a specific pulse and can be recorded. The number of pulses or the frequency of the coil will be proportional to the speed of the turbine flow meters. Location of the coil can be installed in the tube is also mounted on the outside of the tube.
Precision turbine flow measurement will depend on the accuracy of making fan (blade) turbine made, the more sensitive to the motion flow is more accurate measurement results. Turbine meters are used for discharging the medium, such as industry.
Orifice Meter
Orifice meters are a set of tools is placed in a pipe to block flow of fluid and cause pressure drop. Measurement of flow rate (flow rate) obtained from the difference in pressure drop due to the pressure. This measurement method is called Inferential or rate meter. So do not directly measure the quantity of fluid.
Orifice Meter
Type of orifice meters are widely used and already there it’s standard, is concentric, square edge, Flange tap orifice meter. In addition to orifice plate, flow nozzle and venturi tubes also entered into this type of flow meter. To be used for measurement, instrument calibration is necessary at empirically. Ie by passing a certain volume of fluid and record the reading to get the standard quantity to measure other fluids. By following the standard mechanical construction, re-calibration is not required. An orifice plate mounted on the line, the image shown below. A smaller area while the jet fluid through the orifice hole (orifice bore) is called the “vena contracta”.
Systematic work is orifice meters measure gas flow in the pipe which reduced the flow to the orifice hole (small hole), there will be friction and there is the pressure difference between before the orifice (upstream) and after the orifice (downstream). To determine the differential pressure gauge is used with a differential pressure merqury bellows or float.
Orifice Principple
When the fluid flow orifice approach, the pressure rises slightly and then falls suddenly so through a hole in the orifice plate. This pressure continued to fall until the “vena contracta” is reached, then the land gradually rises back to near 5 to 8 in diameter, the highest pressure achieved which is still lower than before the fluid pressure to the orifice msuk. When the fluid pressure drop through the orifice as a result of the increase in fluid velocity through the hole after the orifice plate. After velocity down, the pressure tends to rise back to the original pressure. All the pressure loss (pressure loss) can not return because of the loss of friction and turbulence losses in the pipe. The pressure falls on the orifice will rise in line with the increase in flow rate (flow rate) of fluid. If there is no flow, no pressure difference. Differential pressure velocity proportional to the square, thus, if all factors remain, then the pressure difference proportional to the square flow rate.
Measurement with standardized orifice by API (API Publication Manual of Measurement Standards). Another standard is the American Gas Association, Gas Measurement Committee (AGA Report No. 3) and ANSI / API 2530.
There are two types of orifice meters depending on the location of the measured differential pressure in the pipe between the upstream and downstream of the orifice plate: 1) Flange tap and 2) Pipe tap
In operation, calculation of flow rates measured by using flow meters orifice computer with input from the transmitter (pressure, temperature, differential pressure) is installed on orifice meters. In the flow computer has been there calculation methods are tailored to the contract, including the calculation of calorific value of the input data from the online gas chromatography. Standard calculation of calorific value / heating values used are: GPA 2172 or ISO 6976.
In addition to the flow computer, the meters are also provided orifice chart recorder that serves as a data backup transmitter. From the data in these charts can be calculated an average value of pressure, temperature, and diff. pressure by using a planimeter. Data P, T, and the DP obtained calculated using AGA 3 standards, to obtain the gas flow rate data, usually in units of MMSCF (Million metric standards cubic feet).
Ultrasonic Meters (USM)
Ultrasonic Meter
Types of gas meters is much more complex than a purely mechanical meters, because they require significant signal processing and computing capability. Ultrasonic meters measure the speed of movement of gas by measuring the speed of sound traveling in the medium of gas in the pipe. Standards referred to the AGA Report No. 9 includes the proper use and installation of meters, and set the standard speed of sound calculations that predict the speed of sound in a gas with a known pressure, temperature and gas composition.
The basic principle of USM is working:
- Sound waves propagate with a certain speed in a medium.
- The speed of propagation of sound waves depends on the composition of the propagation media and the influence of pressure and temperature.
- When sound waves / sound formed in a medium which flows the wave propagation speed is equal to the vector sum of the wave itself and the speed of the medium.
- Effect is used for measuring the velocity of the gas so that measurements reflect flow.
The principle of measurement by Doppler Method can be described as follows:
USM Mechanism
USM Mechanism
- Emitter sends ultrasonic waves with a frequency (1 – 5 MHz) with a certain angle to the flow of fluid.
- Ultrasonic wave will be about the particle flow stream moving with a certain speed.
- By using these basic principles, then the obtained equation: f2-f1 = (2.vp.f1.cos α) / c
- From the equation obtained magnitude values of (vp) which is the flow velocity in the pipe which reflects the amount of flow (flow) that passes through the pipe.
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One Response to “Natural Gas Flow Measurement”
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February 27th, 2010 @ 08:54
Saya mohon info ttg perancangan orifice plate dan pengaruhnya terhadap aliran fluida gas