Figure 2: Typical Flowing Flare Gas Low Vs High Flow Ranges
Thermal flow sensing provides direct mass flow measurement, which is ideal for measuring gas flow. Two platinum RTD temperature thermowells are used as the sensor. One RTD is heated while the other measures the process temperature. The difference in temperature between these RTD’s results in an analog output that is proportional to the media cooling effect and compensates for changes in pressure and temperature to give a direct mass flow output without additional instrumentation.
Thermal Flow Meters
Whether the flare system is a single flare line or a large header with a complex array of feeder lines, thermal flow meters provide the lowest installed cost and the lowest lifecycle cost solution. From detecting the smallest gas flows of 0.08 NMPS [0.25 SFPS] to 305 NMPS [1000 SFPS] to measure major upset conditions at high flows, thermal flow meters offer an accurate, dependable, low maintenance and long-life flaring solution.
For example, the ST100 Series Thermal Flow Meter (Fig 1) from Fluid Components International (FCI) consists of an easy to install insertion flow element with a rugged and powerful electronics/ transmitter. With specific calibrations for mixed gas compositions, if needed, the split-range/dual calibration feature with three 4-20 mA analog outputs or digital bus communications (HART, Foundation™ Fieldbus, Profibus or Modbus) make it ideal for flare applications.
Split-Range Calibrations
Many oil/ gas operators, refineries and chemical plants have flare applications uniquely challenged with two diverse operating flow conditions: (1) very low flow under normal conditions and (2) very high flow during an upset/blowdown condition (Fig 2). Site
or plant operators are then further challenged to comply with environmental and emissions regulations that stipulate meter accuracy of ± 5% of reading over the entire measuring range. This meter’s split-range/dual calibration feature supports both requirements.
Dual-Element Systems
In pipe sizes larger than 406 mm [16 inches] a dual-probe averaging flow sensor system can provide improved accuracy compared to a single probe system (Fig 3). Dual probe sensors are connected via a single flow transmitter to provide an averaged output.
Calibration Verification
With the newest environmental regulations requiring routine flow meter calibration verification, a simple-to-use tool to validate the meter’s calibration is an option. VeriCal is a ‘wet’ verification where gas is pressure controlled through a sonic nozzle on to the sensor. Flow versus pressure is used to verify the performance of the flow meter. This can be done without removing the flow meter from the process.
Conclusions
As the importance of reducing carbon emissions grows, the installation of accurate and dependable flare gas flow meters also becomes an essential must-do plant or site requirement. There are multiple flare gas flow meter technologies available on the market, but thermal flow meters provide direct gas mass flow measurement without the addition of pressure or temperature sensors. They feature a no-moving parts design with low pressure drop, which is virtually maintenance free for a low installed cost and a long life-cycle solution.
Figure 3: Dual Element ST102 Flow Meter
Author Details
Jim DeLee, Sr Member Technical Staff Fluid Components International (FCI) 1755 La Costa Meadows Dr, San Marcos, CA, 92078 USA
• Tel: 760-744-6950 • Email:
fcimarcom@fluidcomponents.com • Web:
www.fluidcomponents.com
OCTOBER / NOVEMBER •
WWW.PETRO-ONLINE.COM
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
