ST51 Mass Flowmeter Comes With Safety Approvals

The ST51 mass flowmeter from Fluid Components International (FCI) comes with various stringent safety approvals. These include FM, CSA/CRN, Class 1, Div 1, Groups B, C and D; Class 1, Div II, Groups A-D, Atex Zone 1, II 2 G Ex d IIC T6 to T3, II 2 D Ex tD A21 IP67 T90C to T300C. The ST51 flowmeter is suitable for measuring methane (CH4) and other combustible greenhouse gases. The entire Model ST51 system, including the instrument and the transmitter, is submitted for agency testing.

This is done to ensure reliability and safety, taking into account the sensor and seal requirements as well as the temperature ratings. The ST51 flowmeter is an explosion-proof instrument that is simple to install and that requires virtually no maintenance, according to the company. It features a no-moving-parts, non-clogging design and operates over a wide flow range with low-flow sensitivity. The flowmeter is packaged in an explosion-proof transmitter and the calibration is matched to the user's actual gas composition and installation conditions.

Greenhouse-gas flow measurement in anaerobic digester-produced biogas is a challenge because of the wet, dirty nature of biogas. This type of biogas is a potentially dangerous mixed composition of primarily CH4 and CO2, with smaller percentages of hydrogen sulphide (H2S) and other gases. The wetness, H2S and other particulates in the gas create a corrosive condensate that deposits itself on the pipe wall and instruments in the pipe. The gas flow also varies, based on fluctuating plant process demands and seasonal variations in temperature and humidity.

FCI has designed the ST51 flowmeter specifically to measure biogas and all CH4 composition gases including natural gas. It features a thermal-mass, insertion-style flow element with flow accuracy to +/-1 per cent of the reading over a flow range from 0.3 SFPS to 400 SFPS (0.08 MPS to 122 MPS) and a repeatability of +/-0.5 per cent of the reading. The flow element is available for use in line sizes from 2in to 24in (51mm to 610mm) in diameter. It operates over a turndown range of 100:1, which is essential owing to the variable gas flows in landfill gas recovery and wastewater treatment.

It operates at temperatures from 0F to 250F (-18C to +121C) and withstands pressures up to 500psig [34bar(g)]. The ST51 flowmeter's thermal mass flow sensing element has no moving parts and no orifices to clog or foul to attain virtually maintenance-free service in wet, dirty biogas applications. The flow element is constructed with a 316L stainless-steel body and Hastelloy C-22 thermowell sensors to resist corrosion. It also includes built-in temperature compensation circuitry for accurate, repeatable measurement all year round as temperatures rise and fall seasonally.

The flowmeter features a variety of outputs for user interfaces and information. Dual 4-20mA analogue outputs are user assignable to flow rate and/or temperature and there is a 0-1kHz pulse output for totalised flow. The transmitter's digital communications include an RS-232C port and, with units that have the digital display option, there is a wireless infrared link for use with personal digital assistants. The ST51's optional integral digital display features a two-line, 16-character LCD screen that is said to be simple to read and can be rotated in 90deg increments.

The LCD screen's top line is assigned to flow rate and the bottom line is user assignable for temperature readings or totalised flow. For applications with difficult access or display readability, the ST51's flow transmitter is also available in a remote-mount configuration that can be mounted up to 50ft (15m) away from the flow element inserted the pipe. Both the remote-mount and integral transmitters are housed in aluminium enclosures that are Nema 4X approved and meet IP67 requirements for water and dust ingress protection. Input power for the ST51 can be selected as either 18-36VDC or 85-265VAC.


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