11 – Methane capturing
11 – Methane capturing
11 – Methane capturing
Overview
11.1 Types of extraction systems
11.2 Operational aspects
11 – Methane capturing
11.1 Types of extraction systems11 – Methane capturing
Landfill gas dynamics
Three main factors influence the migration of landfill gases:
Pressure
Permeability and
Diffusion
11 – Methane capturing
Landfill gas extraction
Landfill gas is:
explosive in air
a Greenhouse Gas (GHG) and
toxic to humans
….and therefore should be controlled on landfills
11 – Methane capturing
Landfill gas extraction
There are two types of landfill gas extraction:
1.
passive
2.
active
11 – Methane capturing
Passive landfill gas extraction
11 – Methane capturing
Active landfill gas extraction
Active landfill gas extraction demands the following:
1.
Extraction system
2.
Compressor
3.
Flare installation or
4.
Landfill gas utilization
11 – Methane capturing
Extraction system
There are several types of active landfill gas extraction
systems:
1.
Vertical
2.
Horizontal
3.
Slope
4.
Point
11 – Methane capturing
Vertical
Conventional Cell wise
Build up GRAVEL Build up + early extraction
HDPE piping (perforated)
HDPE piping (non -perforated)
11 – Methane capturing
Horizontal
11 – Methane capturing
Slope
11 – Methane capturing
Point
11 – Methane capturing
Gas well connection
RULE OF THUMB: 4 GAS WELLS PER HA
11 – Methane capturing
Gas well connection
11 – Methane capturing
Compressor
11 – Methane capturing
11.2 Operational aspects11 – Methane capturing
Explosive conditions during start up
Due to safety procedures, explosive conditions must be avoided at all times. The start up procedure to avoid explosive conditions is as follows:
1. Every valve in the extraction system must be opened;
2. At the flare installation or the booster station venting piping needs to be constructed at safe place within landfill boundaries (NOT nearby housing, scavengers or registration offices) and
3. Under current conditions, landfill gas will force out the air naturally. 4. Flare and extraction system full with landfill gas
5. Start up flare at lowest extraction rate
6. Monitor landfill gas quality and explosion limits frequently
11 – Methane capturing
Explosive conditions
Landfill gas contains methane
Explosive conditions of methane in air achieved between 5 - 15%
Over extraction of the extraction system could result into high infiltration of ambient air and explosive conditions could be reached
Monitoring again is essential!
11 – Methane capturing
Landfill gas monitoring
Monitoring equipment
11 – Methane capturing
Landfill gas monitoring
Gas analyser can measure:
1.
CH
42.
CO
23.
O
24.
N
2(= 100% - CH
4% - CO
2% - O
2%)
11 – Methane capturing
Landfill gas monitoring
If CH
4and O
2concentration respectively in a gas
well is:
> 50% and < 1% then
more extraction
< 50% and > 1% then
less extraction
11 – Methane capturing
Landfill gas monitoring
If N
2:O
2ratio is:
> 5
indicator suction of ambient air
< 4
indicator leakage piping extraction
system
11 – Methane capturing
11.3 Management and
Maintenance
11 – Methane capturing
Check at the flare installation:
Flowmeter and indicator function (CDM requirements)
State O
2analyser
Automatic shut down in case of explosive mixtures
..on a regular basis
11 – Methane capturing
Maintenance should be performed by:
Maintenance scheme
Arrange spare part list critical items (compressor, flare,
extraction system)
The later enables planning and minimises down-time of
extraction system and, therefore, minimises greenhouse gas
