A landfill gas flare bid often has to be reconciled with a detailed client specification written for different equipment. This post draws on a supplier’s written replies to a contractor’s list of queries on a 500 scfm enclosed flare and blower package for a US municipal landfill. It shows which points tend to cause friction: blower surge, auxiliary fuel, turndown, valves and field service time.
The challenge: a specification built around other equipment
The contractor reviewed the proposal against the specification and listed items needing clarification. Many reflected assumptions about belt-driven blowers and propane-fired flares. The supplier’s replies are a good model of how to close those gaps.
The proposed package
- Two direct-drive stainless steel blowers, each 250 scfm, giving 500 scfm together, at about 85 dB(A).
- An enclosed flare with automatic temperature control, a 1,800°F minimum chamber temperature above 25% methane, and 0.7 seconds retention time.
- A landfill-gas pilot line, rather than LPG, so there is no dependence on bottled fuel. If the gas is too weak, the pilot will not light and the flare will not start.
- Thirty feet to the shroud top in the proposal, rising to 40 feet in the reply, with 4 inch ceramic lining.
The queries that mattered
Turndown: 5:1 or 10:1?
The specification required 10:1 and the proposal stated 5:1. The reply confirmed the unit would be supplied with 10:1 turndown.
Auxiliary fuel
The regulator’s approval required an auxiliary fuel for the pilot and to keep the flare burning continuously, with no exception. The client explained that pulling and flaring when gas is insufficient can harm the anaerobic process and gas migration control, but could not get an exemption. The reply confirmed a natural gas pilot and the ability to add natural gas to hold 50% methane, noting that the flare would remain compliant down to 30% methane across a 10:1 turndown, so additions are only needed below that. The supplier also asked for a written caution that it would not be liable for harm caused by misuse of the gas collection system.
Direct drive versus belt drive
Direct drive needs no belt maintenance, only greasing of motor bearings every three months. The proposed blower has a turndown from full flow to zero without surging, which the supplier contrasted with conventional blowers that surge at about 25 to 30% of maximum flow. That also allows the pilot to be established before the main valve opens, because the blower can run at pilot gas flow.
Equivalent components
- Check valves: polypropylene wafer type, proposed as equal or better.
- Expansion joints: stainless steel bellows rather than rubber.
- Moisture separator: polypropylene mesh instead of stainless steel mesh, because it never corrodes.
- Block valve: an electro-hydraulic slam-shut valve that needs no nitrogen bottles.
- Flame arrester: stainless steel mesh, wafer-mounted.
Other points
The burner arrangement was eight stainless-tipped burners with a 60,000 BTU/hr pilot. The flare operating range is 1,400 to 1,800°F with shutdown at 2,000°F. Four thermocouples, two sample ports, an expected weight of about 7.5 tons and a waste heat release of 4.1 MW were all stated. The client felt that field service time was excessive and suggested one or two days. A pressure limit of 10 inches water gauge applied at the flare inlet.
What to consider for your own project
- Read specifications for hidden assumptions (belts, LPG, nitrogen).
- Raise equivalence early, and ask for the basis of “equal or better”.
- Understand regulator requirements on auxiliary fuel.
- Clarify turndown, because mismatches are common.
- Agree liability wording on operation of the collection system.
FAQ
Why is surge important?
A blower that surges cannot run steadily at low flows, which complicates pilot lighting and turndown.
Do all flares need auxiliary fuel?
Not always, but some approvals require it.
Responding to a detailed specification?
Send us the specification and we will review it with you. See also what to put in a flare tender specification.