Before a flare tender is awarded, a careful client will ask detailed questions about booster ratings, valves, thermocouples, venting and access. A supplier’s written answers become part of the contract. This post draws on one such round of clarifications on a 2,050 m³/h landfill gas flare package for a biomass-related scheme, and turns the questions into a checklist you can use on your own tender.
The challenge: a specification that left gaps
After a meeting with the client, the supplier confirmed its answers in writing. Several corrected the original submission, which shows why this step matters.
The questions and the answers
Is the flow actual or normal?
The booster is rated at 2,050 actual m³/h at 86°C, as in the tender data sheet, not normal m³/h as the original submission had stated. Always check the basis of a flow figure: actual and normal volumes differ materially at temperature.
How is flow controlled?
- An actuator with a 4 to 20 mA signal can be added to the trim valve for accurate positioning.
- Each burner bar has its own manual butterfly valve with a notch plate. Two outer bars are rated at 325 m³/h and one central bar at 100 m³/h, to give a wider turndown.
- An inverter for booster speed control can be fitted in its own cabinet with a manual/auto switch, with a remote readout designed in but not supplied.
What if a thermocouple fails?
- Two thermocouples are fitted on a duty/duty basis, one to the external PID with alarm settings and one to an internal alarm unit.
- If either alarms, the plant shuts down and stays down until cleared. A red lamp and a volt-free contact signal the alarm.
- The slam-shut valve can be programmed to close after up to 5 minutes at over-temperature.
- An internal switch allows single-thermocouple running until a replacement arrives.
- Both thermocouples can be reached from the skid without a ladder.
What if the flame goes out?
The unit does not shut down: it continues in vent mode through the combustion chamber, with an alarm, and makes no re-ignition attempt. Operators are expected to shut down in a controlled way.
Can it vent separately or feed an engine later?
A separate 100 mm vent line rising 6 m, upstream of the slam-shut valve, was offered as an extra. A blanked 150 mm flanged port for future engine take-off was another.
How easy is maintenance?
A spare flame arrester element allows the arrester to be cleaned while a clean one is fitted. The knockout pot is designed for rapid changing of the demisting element, with drop-down bolts and thicker flanges.
Size, weight, power and commissioning
The plant footprint is about 3 m by 2 m by 7.25 m high with a weight of about 4.5 tonnes, subject to detailed design. It needs an 11 kW motor and 10 A of auxiliaries. Two days of commissioning were included. The PLC is an Allen Bradley with a ladder diagram written so that operating features can be adjusted without affecting safety functions.
Hazardous areas
A hazardous area zoning exercise is part of the design, with a minimum 500 mm between any potential point of release and non-hazardous equipment. The HSE explains hazardous area zoning.
Using this as a checklist
- State flow on an actual or normal basis.
- Define what happens on thermocouple, flame and power failure.
- Agree who zones the hazardous areas.
- Agree spares, access and ease of servicing.
- Get weight, footprint and power in writing.
FAQ
Why does actual versus normal flow matter?
The same mass of gas occupies a larger volume at 86°C, so a booster sized on the wrong basis would be wrong.
What does vent mode mean?
The gas continues to pass through the chamber unburnt while operators shut down safely.
Preparing a flare tender?
Send us your draft specification and we will point out the gaps. See also what to put in a flare tender specification.