1) production of landfill gas

Production of LFG,

Conditions for gas production,

Quality, Quantity,

Gas Yield

and Energy Value

1

Source of Landfill Gas

Municipal Solid Waste (MSW) is

deposited in the Landfill, preferably

in a Sanitary Landfill, with bottom

lining, capping, leachate and LFG,

well-field management and highly

trained staff.

2

Anaerobic decomposition of MSW

• MSW contains different carbon-compounds

• A part of it is degradable organic carbon DOC

• Every ton of MSW (household waste) may

contain 150 to 200kg of DOC

• Also it contains water as waste moisture and

rain water

• Bacteria degrades in a natural way the organic

carbon (nutrients) in combination with moisture

• Under anaerobic conditions Methane bacteria

produce LFG, mainly containing CH4 and CO2

LFG is produced by bacterial decomposition

3

Anaerobic decomposition in Landfill

Transformation of organic

matter into LFG in steps:

1) Hydrolysis and

Fermentation

2) Acetogenesis

3) Methanogenesis

Strictly under anaerobic

conditions to LFG with

~60%CH4+ ~ 40%CO2

and H2O

Hydrolysis and Fermentation

Acetogenesis

Methanogenesis, pH 6.5 to 8.0

H2, CO2Acetate

Fatty Acids (VFAs),

Amino acids, Sugars

CH4 , CO2 , H2O

Organic materialProteine, Carbohydrates, Fats

4

Anaerobic decomposition of MSW

• Anaerobic conditions, means strictly under exclusion of

Air / Oxygen

• Methanisation is sensitive to pH-value of the leachate,

condition between pH6.5 and pH8 are necessary

• Temperature is a critical element, optimally 35 to 55°C

• Limitation of toxic substances such as heavy metals,

Chlorinated and Fluorinated compounds, detergents, etc.

• When conditions are not fulfilled, then the methane

production will slow down and may even stop

Conditions for successful methanisation are:

5

The 5 phases of Landfills life

Generation of LFG

6

Native Landfill Gas

When Gas produced in the Landfill is not extracted

by a pumping system, then we say it is Native

Landfill Gas.

Methane CH4 up to 60 %

Carbon dioxide CO2 up to 40 %

Nitrogen N2 <2 %

Oxygen O2 0 %

In “young” Landfills, temperature in the waste body

can be as high as 50..60°C

Typically composed of:

7

Methane CH4 40 - 50 %

Carbon dioxide CO2 35 - 45 %

Nitrogen N2 5 - 15 %

Oxygen O2 0 - 3 %

The gas is saturated with water vapour (moisture)

- at 40°C as much as 50gH2O/m3LFG

- cooling to 10°C containing 10gH2O/m3LFG

- condensation occurs of 40gH2O/m3LFG

On the other hand when Landfill Gas is extracted

steadily by a degassing plant, then the

composition changes:

Characteristic of LFG

8

Hydrogen sulphide H2S 100 - 500 mg/m3

Mercaptane (e.g CHnSH) << (very little)

Chlorinated compounds HCI 20 - 100 mg/m3

Fluorinated (e.g. Freons) FI 10 - 50 mg/m3

Polyaromatic Hydrocarbons PAHs 0 - 50 mg/m3

(or BTEX: Benzene, Toluene, Xylene)

Siloxane (Silicone compounds) 0 - 50 mg/m3

Trace substances in LFG

Landfill Gas usually trace substances which are

harmful to equipment and environment, like:

9

Facts of O2 in LFG

When extracting gas from the Landfill O2 is

usually available in more or less quantities !

• When the gas extraction is done correctly, low

concentrations of O2 less then 2 % can be

considered as normal, safety is granted

• O2 concentrations of near 3% are indicator for a

malfunction of the gas extraction, the system is

still safe but corrective measures are to be done

• When O2 is reaching 6%, then a potential

danger of explosion is given. In such a case

safety of the system is not any more fulfilled!

This is a potentially dangerous situation!10

• Gas piping is damaged (mechanically)

• Gas wellhead is damaged or bent

• Bad sealing of wellhead, clay filling dried out

• Bad landfill cover, fissures washed out by rain

• Hydraulic seals of gas system are faulty

• Aspiration of air through leachate system

• Suction at the gas wells too strong, “overpull”

• Incorrect operation of the gas plant, wrong

regulation of flow/pressure at the gas wells

O2 is present in LFG because:

Reasons for having O2 in LFG

11

Issues from Siloxane

In gas engines, siloxanes

are oxidised to silicon

dioxide forming solid, hard

and abrasive crystals.

SiO2 will deposit on cylinders,

pistons and valves. Engine

maintenance will rise abruptly and

often cause breakdown of the

engine. Many cases of destroyed

engines are known!12

Other harmful matter in LFG

Condensate water

Dust

Solid particles like

sand, stones, plastic

chips, etc.

Furthermore Landfill Gas will carry along other

matter hindering and damaging components, like:

A degassing plant need to be outfitted with

Pre-Dewatering unit

Gas Filter Unit

at the entry of the gas station! 13

Gas pre-dewatering and filtering

14

Favourable to gas production

Household waste (MSW), with much moisture15


Plastic bags must be tear open!16


Spreading and compacting the waste 17


After smashing with compactor 18


Garden and park waste, decomposable19


Food waste20


Overripe fruits, a full load of melons (unusual)21

Inhibitors to LFG production

Wood is organic matter but will not produce gas!22


Industrial waste, plastics, metals, no gas at all!23


Building rubble, concrete blocks24

Harmful and toxic waste

All this kind of waste is toxic and harmful to

humans and environment and should never be

deposited in a Landfill!

Pressurised cans containing residual propellant

Freon, i.e. from disposed fridges

Batteries of any kind

Chemical stuff or components containing them

Hospital and medical waste

Waste containing radioactive traces (?)

Can be for example:

25

Duties of Landfill Owners

• LFG is continuously generated in a Landfill

• Gas escapes into the atmosphere when landfill

is under pressure, polluting the environment

• CH4 contributes 21 times more to the

greenhouse effect than CO2, is therefore harmful

to the environment

• LFG contains traces of hazardous components

• Can create potentially explosive mix with air

• LFG must therefore be collected and disposed

safely with thermal treatment26

Benefits for Landfill Owners

LFG also provide advantages and benefits:

• LFG has a energetical value of 4..5kWh/m3

• Electricity can be generated and supplied into grid

• Can be fired into boilers for production of hot

water, steam, hot air, etc.

• Make CNG / LNG as vehicle fuel

• Excess gas will be safely disposed HT Flares, for

the safeguard of our environment

• Every Landfill should therefore be outfitted with

a good functioning gas extraction plant

and with gas utilisation facilities!27

Depending largely from conditions on site:

How much LFG from MSW?

Type of waste disposal: waste dump or sanitary

landfill (engineered landfill)?

Composition of waste: mainly household waste

with 150..220 kg/to DOC, or inert matter?

Age of waste and disposing time?

Wet waste or dry waste?

Water table / water pockets in the landfill?

Well field management, maintenance, measuring,

and regulation of the gas wells done?

28

Landfill with: 1’000’000 tons MSW

Filling period: 10 years

Peak gas extraction: 1’000 m3/h

Long term gas yield: 400 m3/h (over 10 years)

Energy content of 400m3/h: ~2’000 kWh

Electricity production: ~750 kWel

(during a period of 10 years)

“Rule of thumb”

1 Mio tons of waste to produce 0,75 MW or

1.3 Mio tons waste to produce 1 MW29

LFG forecasting (calculation)

LFG production can be calculated with the help of

a tool basing on a mathematical FOD model:

Is the first step to get knowledge of the gas yield

Input data need to be collected accurately and

reality-close in order to make a gas calculation

Wrong input data will end in wrong results!

An on-site survey by an experienced person

capable to gather all relevant data and

information is necessary

30

Example of LFG forecasting

31

We recommend to consolidate the forecasting by

doing a Gas Pumping Trial in an advanced stage

• The GPT is used to validate the gas forecasting for the

particular year of the Gas Pumping Trial (GPT)

• By mean of a mobile degassing plant with flare, LFG will be

extracted according to a site tailored methodology

• Dynamic gas quality and quantity are regularly measured

for a period in order to determine the steady state gas yield

• The results of the GPT will be compared to the gas

calculation for the particular year of the pumping trial, to

constrain the future forecast

• The gas yield can be better predicted for the future, relying

on calculations and on field exploration

Consolidation of gas forecasting

32

Thanks for your attention!

Feel free to ask questions and add

comments.

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Annoyances of LFG

35

1) production of landfill gas

Environment