Landfill Gas Recovery & Calculations.

 Landfill Gas Site
"Landfill Gas" ---- "Deponiegas" ---- "Stortgas"

My name is Dick van Faassen. I was employed in a Dutch Regional Energy Distribution Company COGAS at Almelo, the Netherlands as Head of the Engineering department.
Although I am retired now, I'm still interested in some of the projects I worked on, e.g. Landfill Gas Projects.

Cogas company is involved in the recovery of Landfill Gas at three places in the Netherlands: DELDEN, VASSE and COLLENDOORN.
Recently COGAS is involved in international projects such as a Landfill Gas Project in South America. This is a landfill near a Brickstone factory in the neighborhood of Lima, the capital of Peru. If feasibility studies are positive, the gas will be used as fuel gas for the brickstone production.

During my work on the above mentioned projects I developed a method for the calculation of the amounts of biogas that possibly can be extracted from a regular landfill.
As landfill gas is generated from organic compounds in the waste, I tried to investigate the composition of the refuge and specially the contents of organic materials.

Quantities Landfill Gas that can be extracted from a Landfill.

An easy way to calculate landfill gas quantities is by analyzing the amount of organic materials in disposed waste.

A simplified example of bio-degradation is as follows (forms for biodegradation). :

Cellulose:

C6H10O5 + H2O ----> 3 CH4 + 3 CO2

Glucose:

C6H12O6 + 2 H2O ----> [ 2 CH3COOH] + [ 2 CO2 + 4 H2 ]

                                             [ 2 CH3COOH ]      ----> 2 CH4    +    2 CO2
                                             [ 2 CO2 + 4 H2 ]      ---->    CH4   +       CO2  +  2 H2O
                                          -------------------------------------------------------------+
so:

C6H12O6 + 2 H2O -----> 3 CH4 + 3 CO2 + 2 H2O

In fact equal amounts of methane and carbon dioxide are generated. A mixture of both gases of  0.740 m3 is developed from 1 kg of organic material:
                  0.5  m3  CH4  @  0.72 kg/m3    =  0.360 kg
                  0.5  m3  CO2  @  1.97 kg/m3   =  0.985 kg
                  ----                                                ------
                  1.0  m3  Bio-gas                        =   1.345 kg
So theoretically from 1 kg of bio-mass will be generated: 1/1.345 = 0.740 m3 Gas.
 

Sorting tests and other investigations in the Netherlands on Municipal Solid Wastes resulted in a table of Refuse compounds with average percentages from 10 years of investigation. Half life times (t) and so the digestion velocity of these organic materials are essential for the calculation of the Specific Gas Production curve.
An example is given for a landfill in the eastern part of the Netherlands ('Het Rikkerink').
In this case reliable records were available.
 

                                                   Table 1,  Composition of Waste.
      Class:                                                                                                                         Half Life Times (in years) 

Total (kg)
Moist,ash,inert
 Dry organic (kg)
         5
         15
          30
Household
357
233.48
123.52
56.94
28.86
37.70
Bulky household
32
11.61
20.39
0.11
1.11
19.17
Light industr.etc.
119
64.56
54.44
2.02
17.83
34.61
Construction,rubble
288
234.37
53.63
0.00
0.00
53.63
Munic.streets,parks
55
23.87
31.13
2.09
3.41
25.63
Agricultural
63
21.34
41.66
14.14
13.32
14.20
Purif. sludge
37
24.42
12.58
0.00
0.00
12.58
Special
49
49
0.00
0.00
0.00
0.00
Total
337.35
75.30
64.53
197.52
Water consumption cellulose
10.00
2.20
1.90
5.90
Total Organic com- pound
347.35
78.50
66.43
203.42
Percent
100
22
19
59
 
 


From these records has been calculated that one ton (1,000 kg) of Refuse consists of 337 kg  dry  organic compound and 669 kg of non-degradable or inert materials. (Figures only valuable for this  landfill,....may be different for others!)
As the conversion of cellulose takes a little consumption of water, for calculations of Gas Production the total amount of bio-degradable organic material is supposed to be 347 kg.
The percentages with their average half life times (t)  are as shown below:

         (a)     Fast convertible       22  %      (t) =  5 years
         (b)     Medium convertible 19  %      (t) = 15 years
         (c)     Slow convertible       59 %      (t) = 30 years.

Basis for the Gas production calculations is a formula for decomposition of the organic materials:

         Qy  =  Q0  ( 1 - (a x 2 -y/ta + b x 2 -y/tb + c x 2 -y/tc))
Half-life time means:  (for y=n; t=n  .....   2 -n/n =  2 -1 = 0.5)
 

          SGP = (Q0 - Qy) x 0.74 x 0.85 in m3/ton.y where the efficiency output is about 85%.

 Construction of the Specific Gas Production curve  for y = 1 to 30:

 Curve of the calculated Gas Production:

The landfill "Het Rikkerink" at Ambt-Delden, the Netherlands was closed in 1984. In that year started the exploitation of Landfill Gas. After extraction by means of Roots Blowers, the gas is dried and via a pipeline of 2 kilometres sold to a Chemical Plant "Servo" in the town of Delden.
Mr. Ton Schoemaker, chief engineering dept. can give all relevant information.

Owner of the Gas Plant is COGAS n.v. (Centraal Overijsselse Nutsbedrijven)
P.O.Box 71,    Tel. ** 31 546 836666  Fax ** 31 546 811267.
7600 AB Almelo, The Netherlands.

 
If you are interested or have comments, please e-mail me at: postbus@dvfaassen.demon.nl