Landfill gas is usually saturated at a temperature above the one at which it enters the engine, so it forms a lot of highly contaminated condensate on the way. Chilling and then reheating the gas removes that moisture before it reaches the engine. This article describes a 500 m³/h landfill gas delivery unit quoted for a landfill in Malaysia, and how each stage protects the engine.

The challenge: condensate that damages engines

The condensate from landfill gas often contains high levels of ammonia. If it reaches the engine it can cause damage very quickly. The design conditions were a maximum ambient of 40°C, gas at up to 35°C and 100% humidity, and an exit gas at no more than 35°C and 70% relative humidity.

The approach: cool, drop out the water, reheat

1. Knockout pot. A stainless steel pot with a demister removes free moisture, with a drain, a sight gauge and a high-level alarm switch.
2. Booster. Two stainless steel twin-stage blowers, each 500 Nm³/h at about 300 mbar, run duty and standby. Variable speed drives hold the outlet pressure for the engines.
3. Pre-cooling. A gas-to-gas heat exchanger and an air blast cooler take heat out first, which reduces the load on the chiller.
4. Chilling. Two chillers in duty-standby cool the gas from 35°C to 15°C. The chosen units are electrically driven absorption chillers. The estimated electrical load is about 20 kW.
5. Separation. A cyclone and float trap collect the condensate.
6. Reheat. The gas is reheated by at least 5°C against incoming gas, which lowers relative humidity and keeps it well clear of its dew point.
7. Filtration. A rigid 5-micron filter with a bypass valve allows filter changes without stopping the engine.

Protection and control

• A pneumatic inlet valve closes on loss of power or in an emergency.
• Low- and high-pressure switches indicate a blocked line, a blower failure or a downstream obstruction.
• A chilled-water flow switch and a high-temperature switch warn of cooling failure.
• An orifice plate flowmeter with totaliser reports flow to the control panel.
• An elevated flare rated at 500 m³/h with a 310 stainless steel tip, a 7 m stack and manual temperature adjustment to about 850°C handles surplus gas. An enclosed flare was offered as an option, with automatic temperature control, a 5:1 turndown and CDM-compatible monitoring.

The condensate drain lance and its installation were excluded. Normally condensate drains back into the waste or goes to leachate treatment.

Testing and delivery

The scope included a six-hour continuous test and a seven-day reliability test, with operator training and certificates. Delivery was four months from order, with the booster set air freighted to meet that date.

What to consider for your own project

1. Dry the gas, don’t just filter it. Chilling and reheating protects the engine from condensate.
2. Specify duty-standby for blowers and chillers if engine uptime matters.
3. Plan condensate disposal. It is contaminated and needs a route.
4. Agree acceptance tests up front.

For UK practice see the Environment Agency’s LFTGN03 and LFTGN05.

FAQ

Why reheat gas after chilling?

To lower its relative humidity so no condensate forms in the engine inlet.

Why is ammonia in the condensate a problem?

It can damage engine components quickly.

Is the flare optional?

An elevated flare was included, and an enclosed flare was an option.

Conditioning gas for an engine?

Send us your gas conditions.