Company Profile

Flare Gas Ultrasonic Flow Meter: Transit-Time Transducers for Refinery Stack Lines

Quick Answer: Silver Instruments ultrasonic flow meter with transit-time transducers handles wet, dirty flare gas in refinery stack lines from 0.5 bar up to 10 bar and temperatures up to 200°C. No moving parts, ATEX Zone 1 certified. Send your pipe size (DN), pressure (bar), temperature (°C), and typical gas composition to [email protected] for a specific quote and model recommendation.

Why Refinery Flare Lines Need a Different Flow Meter

Flare gas is not a clean, dry process stream. It contains moisture, hydrogen sulfide, soot particles, and droplets of heavy hydrocarbons. The flow can swing from near zero during purging to a sudden surge during an emergency release. Differential pressure devices like orifice plates foul quickly in this service. Thermal mass meters drift when gas composition changes. Mechanical meters clog. So plant engineers keep looking for a meter that stays accurate without weekly maintenance.

Here is the thing. A transit-time ultrasonic flow meter designed for flare gas solves most of these headaches. Silver Instruments builds these meters specifically for dirty, low pressure gas in stack lines. We have seen this on customer sites many times. A simple wetted transducer without cleaning ports fails in three weeks. Our solution uses insert transducers with optional automatic purge, suitable for continuous operation on a flare header feeding a 24 inch stack at a refinery in Malaysia.

How Transit-Time Ultrasonic Technology Works on Flare Gas

Transit-time meters send an ultrasonic pulse upstream and downstream through the gas. The difference in travel time gives the average flow velocity. No bypass lines, no impulse tubing, no condensation traps. The key is the transducer design and signal processing. Silver Instruments uses high power titanium face transducers that punch through dampening effects of wet gas and low density at 0.5 bar(a). The electronics measure transit time with sub nanosecond resolution and reject false echoes from pipe wall ringing.

In practice, most engineers skip the signal quality indicator. Do not do that. A clean signal path with automatic gain control gives you reliable readings even when gas goes from 0.2 m/s to 30 m/s within one minute. The meter also outputs 4-20 mA HART and Modbus RTU, so your DCS gets real time mass flow or corrected volumetric flow. Silver Instruments supplies dynamic compensation with live temperature and pressure inputs, converting actual flow to standard cubic meters per hour.

Installation, Pipe Sizes and Wet Gas Handling

Transit-time transducers mount on a flanged spool piece or insert through a ball valve under pressure. Pipe sizes from DN50 up to DN600 are common in Southeast Asian refineries. For a stack line with DN300, we recommend a two path configuration to handle swirl and asymmetric flow profiles downstream of a bend. Straight run requirements are 10D upstream, 5D downstream, but we can model installation effects from your isometric drawing.

Wet gas with entrained liquid droplets causes signal attenuation. So we add a hydrophobic coating on the transducer face and a small nitrogen purge port. A refinery in Vietnam reported stable readings for 8 months without manual cleaning after switching to this setup. Their previous differential pressure transmitter needed rodding every two weeks. The cost saving on maintenance alone justified the meter price in under 12 months.

Typical Flare Gas Application Parameters

Customers send us these numbers when requesting a proposal.

Gas pressure 0.8 bar(g) to 3 bar(g), temperature 100°C to 180°C, pipe DN200, flow range 200–8000 Nm³/h, gas contains 3% H2S and traces of benzene. We select the model with ATEX Zone 1 Ex d IIC T4 certification, insert transducers rated for 200°C, an