Landfill gas must be chilled, dewatered and boosted before it reaches a gas engine, because saturated gas carries condensate that contains ammonia and other contaminants which damage engines quickly. A conditioning and flaring package designed for a landfill in southern Africa did this with a gas chiller, two blowers and a standby flare, all sized for 3,500 Nm³/h of raw gas.

The challenge: gas that is wet, dirty and low in pressure

Landfill gas leaves the waste warm and saturated with water vapour. As it cools in pipework it condenses, and the condensate often carries ammonia and other contaminants. In a gas engine this causes corrosion and wear. Fine particles in the gas wear engine components as well.

The client was developing a landfill gas utilisation project and asked for a package covering:

• A gas chiller to remove moisture.
• Boosters to deliver gas to the engines at a regulated pressure.
• A flare for gas that the engines cannot use, which is mainly a standby flare.

The approach: three stages in one package

1. Chilling and condensate removal

The design gas was saturated at about 32°C, with 25 to 60% methane and up to 5% oxygen. The chiller cools it to about 12°C. Cooling capacity is around 92 to 100 kW and electrical consumption about 34 kW at full load. The design condensate rate is about 85 litres per hour.

The chain of equipment is:

1. A coarse stainless steel filter to keep large particles out of the condenser.
2. A stainless steel condenser, with a maximum pressure loss of 30 mbar at full flow.
3. A cyclonic pot with a polypropylene demister, to separate the condensate.
4. Spare blanked ports for adding further gas cleaning later.

The electric chiller was sourced locally, to make support and servicing easier. The rest of the plant was manufactured elsewhere and shipped.

2. Boosting

Two centrifugal gas blowers, each handling 2,000 Nm³/h at about 250 mbar, run in duty and duty mode. They are gas-tight, built for hazardous-area zone 2 and driven by variable speed drives. The drives let the blowers match their output to the engines’ demand, or control the suction on the gas field, and this keeps power use down.

A useful side effect: compressing gas warms it. After the blowers, the relative humidity of the gas falls below 70%, which suits engines.

3. The flare

The standby flare is an enclosed ground flare designed for:

• A maximum of 1,500 Nm³/h and a minimum of 300 Nm³/h, a 5:1 turndown.
• A combustion chamber temperature above 1,000°C and a residence time of at least 0.3 seconds.
• Compliance with TA Luft emission standards and the UK Environment Agency’s best practice guidance for flaring landfill gas.

A PID controller adjusts a combustion air louvre to hold the temperature. Ignition is automatic, controlled by a PLC. A UV sensor confirms the flame, and a pneumatic slam-shut valve closes on a fault or loss of power.

Why continuous gas analysis matters

The package includes online analysers for oxygen, methane and carbon dioxide. Each tells you something different:

• Oxygen shows air being drawn into the gas field. An alarm can shut the plant down at a set level, typically 8% in the UK and 6% in Germany.
• Methane shows the fuel value for the engines and flare.
• Carbon dioxide allows the nitrogen content to be worked out, because nitrogen is the balance. Rising nitrogen suggests the gas collection system is unbalanced.

A data recorder logs the flare temperature, suction pressure, flare delivery pressure, flow, atmospheric pressure and gas composition.

Why the blowers are in a container

The blower package is housed in a 40-foot container. That protects it from weather, allows factory testing before shipment, and makes installation simpler. The flare and chiller remain outdoors on skids. Expected delivery was about 22 weeks from order, with five days of on-site commissioning and training.

What to consider for your own project

1. Dewater before the engines. Condensate chemistry makes it a reliability matter as well as a nuisance.
2. Size the blowers for the field. Allow for both engine demand and the gas-field suction you need.
3. Treat the flare as part of the system. It will handle every shutdown and surge, so it must be reliable.
4. Plan for local service. A locally sourced chiller can reduce downtime.
5. Check regulatory requirements. In the UK, see the Environment Agency’s guidance on managing landfill gas.

FAQ

Why chill landfill gas?

Cooling the gas below its dew point drops out moisture and the contaminants dissolved in it, protecting engines and pipework.

Why is the flare a standby?

The engines are the primary use for the gas. The flare burns whatever the engines cannot, such as during engine maintenance or surplus production.

What does a pressure of 250 mbar do?

It pushes the gas through the dewatering equipment and delivers it to the engines at the pressure they require.

Can the chiller remove siloxanes?

This design chills for moisture only. Where siloxanes are a concern, a deeper chill to about -30°C followed by an activated carbon bed can bring them below 1 mg/Nm³, but that is a different specification.

Planning a landfill gas utilisation scheme?

Send us your gas flow and quality and we will outline the conditioning and flaring equipment you need.