For the production of compliant H gas with technical combustion characteristics matching North Sea I specifications, conditioning by admixing LPG is examined below.

The figures 2 to 5 show the potential composition of biogas mixtures, based upon methane levels in the processed bio-gas of 94, 96, 98 and 99,5 vol..-%, to which propane/butane (in a ratio of 95 / 5) is added. The necessary LPG admixtures for the desired calorific range for a methane content of 94, 96 and 98 vol -% in the treated biogas, lie above the limits as defined in G 486-B2 and DIN 51624, at 9.4 to 12.6 Vol -%, from 8.1 to 11.3 Vol -% and 6.8 to 9.9 vol -%. For processing to a methane content of 99.5 Vol -%, the limit according to G 486-B2 for pressures <100 bar is numerically satisfied up to a propane / butane admixture of 6.5 vol -%. The applicability criteria as described in section 2 apply. On the basis of this restriction, only an admixture of 5.8 to 6.5Vol.-% of LPG for an initial methane content of 99.5Vol.-% is possible. This would then cover a calorific range of 11.971 to 12.080 kWh/m3.

— Wobbe-Index	— relative Dichte
—■— LPG-Zugabe
Methan
16,5
0,74
16,0 H-Gas-Grenze
0,72
0,70
15,5
0,68
15,0
0,66
0,64
14,5
0,62
14,0
0,60
0,58
13,5
0,56
13,0
H in kWh/m8
Fig. 2. Possible H gas mixtures by admixing LPG to an initial concentration of 94 Vol. -% methane
0,74
0,72
0,70
0,68 ф 0,66 I Q Ф > 0,64 Ф
0,62
0,60
0,58
0,56

■— relative Dichte
LPG Zugabe	— Wobbe-Index
Methan
16,5
0,74
16,0
0,72
0,70
15,5
0,68
15,0 s” ф 14,5
0,62
14,0
0,60
0,58
13,5
0,56
13,0
Fig. 4. Possible H gas mixtures by admixing LPG to an initial concentration of 98 Vol. -% methane
—Methan —LPG Zugabe —Wobbe — Index —relative Dichte

Table 8 shows a summary of LPG additions necessary to achieve an average target calorific value of approx.12.2 kWh/m3.

4.1 Target properties: Weser ems L gas

For the production of compliant, low calorific L gas, conditioning by the addition of air is described in the following sections.

Figures 6 to 9 inclusive show possible fuel gas mixtures with a calorific value range of 9.653 to 10.047 kWh / m3, which can be achieved by the addition of air.

Figure 6 shows the possible mixture compositions, when air is added to an initial methane content of 94 vol -% . When interpreting this, please note that the data points for the Wobbe index, the methane content and the air belong together along the line of constant calorific value. A +/- 2% range has been set for the calorific value limits, based on the calorific value defined in DVGW worksheet G 260. All values with a Wobbe index of less than 13 kWh / m3 and an O2 content of less than 3 vol -% meet requirements. All other boundary conditions are shown in the table above.

Figure 7 show the possible mixture compositions, when air is added to initial methane content of 99,5 Vol.-%.

The two cases presented with initial methane contents of 94 and 99.5 Vol -% in the biogas, clearly show that increases in methane content also make necessary increased amounts of air, in order to achieve the desired calorific value and Wobbe index.

12,0

s*

11,5

Table 9. Air admixture to Weser Ems L-Gas and corresponding Wobbe-Index

The higher the initial content of methane in the biogas is, the greater is the approximation to the maximum compliant O2 content of 3 vol -% from conditioning.

Thus the O2 levels upon reaching the lower calorific value band are:

1,776% vol. O2 2,177% vol. O2 2,562% vol. O2 2,836% vol. O2

Reaching of the required calorific value band (9.653 to 10.047 kWh / m3) is possible from all four initial methane contents.

Figure 8 shows a summary of the air admixture ranges of the four initial methane levels. The red line indicates the maximum permissible volume fraction of 3% of O2 in the mixture.