Rugged ST100 digester gas flow meters for safety and compliance

AMS Instrumentation and Calibration presents the new rugged range of
thermal flow meters from Fluid Components International (FCI) to provide
precision mass flow measurement in municipal or industrial wastewater
treatment, biogas, landfill gas and similar applications.

Engineers and operators responsible for accurately measuring gas
production from digester tanks at municipal or industrial wastewater treatment
operations can depend on FCI’s rugged ST100 Series thermal flow meters.

Digester waste gas is a combination of methane (CH4) and carbon dioxide
(CO2) with a small percentage of other trace gases; however, the gas
composition can vary with the process and temperature but a typical average is
in the range of 65% (±5%) CH4 and 35% (±5%) CO2. Digester gas is also a
wet/moist and dirty gas, typically containing entrained hydrogen sulphides,
which condense and deposit on pipe walls and anything else in the pipe.

The accurate measurement of digester gas flow resulting from the
wastewater treatment processes is important for process productivity and
environmental regulations reporting. The measurement of gas production is
proportional to the effectiveness and efficiency of the digester process
itself. If the gas is harvested for use as fuel in a CHP or Cogen system, the
amount of gas being sent to the engine(s) is a key control variable. Further,
if any gas is released or flared, because both methane and carbon dioxide are
known polluting greenhouse gases (GHG), local environmental regulations
typically mandate reporting of the quantity of gases emitted or flared.

Two other factors that influence the selection of a digester gas flow
meter are installation safety and service access. Since CH4 is a combustible,
potentially explosive gas, any instrumentation should carry agency approval
certification for Div.1/Zone 1 HazEx installations. If the flow meter’s
installed location is prior to gas drying/cleaning or without that altogether,
then engineers must also consider measuring success in moist gases, plugging or
fouling of orifices or moving parts due to H2S deposits, and cost and ease of
access for periodic cleaning to remove H2S residue.

With no moving parts, simple insertion-style design, and comprehensive
global HazEx approvals, the ST100 flow meter is an ideal solution for digester
gas flow measurement.

The ST100 flow meter can be calibrated for the specific digester gas mix
composition and processes temperature conditions in flow ranges from 0.07 NMPS
to 305 NMPS and with accuracy to ±0.75 percent of reading, ±0.5 percent of full
scale. ST100’s constant power thermal dispersion mass flow technology has
proven superior in applications with moist, dirty gases. It can be installed in
the pipe with a simple, retractable compression fitting or through a ball valve
for easy access, saving significant costs over spool-piece technologies that
require installation of extra, extensive bypass pipe networks for service

The ST100 meter offers users multiple options to communicate with DCS,
PLC or SCADA, including 4-20 mA analogue, frequency/pulse, or certified digital
bus communications of HART, Foundation Fieldbus, Profibus PA or Modbus RS485. Key
features also include a graphical, multivariable backlit LCD display, providing
a sophisticated, continuous readout of all process measurements and alarm
status for easy on-site viewing by technicians; ability to query for service
diagnostics; USB port, set-up and configuration software; an on-board data
logger capable of storing 80M readings; and a 3-point in-situ calibration check
capability. The transmitter/electronics can be integrally mounted with the flow
element or may be remote mounted to 1000 feet (305m) away.

The transmitter enclosure is NEMA4X/IP67 rated and available in painted
aluminium or stainless steel. FCI’s ST100 digester gas flow meter’s HazEx
agency approvals are on the entire instrument, not just the enclosure and
include FM, FMc, ATEX, IECEx, EAC/TRCU, CPA, NEPSI, and Inmetro, and all are CE

For further information, please visit the AMS Instrumentation and
Calibration website,
or call 03-9017 8225, or Freecall (NZ) 0800 442 743.

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