Optimal integrering av energianvändningen vid ... - Gasefuels AB

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VÄRMEFORSK
Figure 5. Todays combined energy plant where the upgrading technique is changed to
chemical absorption (see figure 1 for English translation of parts in combined energy
plant).
An overview of investment and operating costs for case study 1 is provided in Table 4.
The digestion cost is about twice as large as the biogas upgrading cost. The water
scrubbing technology has a lower cost compared to chemical absorption for case study
1. Chemical absorption is therefore not an economic option in case study 1. The steam
has to have a price less than 0,15 kr/kWh if chemical absorption shall be a better
alternative than water scrubbing technique in case study 1.
Tabell 4. Investerings- och driftskostnader till fallstudie 1.
Table 4. Investment and operational costs to case study 1.
kr/kW
h
Digestion 0,28
Biogas upgrading, water absorption 0,11
Biogas
absorption
upgrading, chemical 0,16
Case study 2 – a big biogas plant with combined drum dryer and band dryer
An energy balance for case study 2 is provided in Figure 6. The ethanol plant steam
demand is reduced by 25% compared to case study 1, because half of the distillery
residues flow goes to the biogas plant. The figure shows the energy flow for biogas
upgrading with chemical absorption. Drying is done with a combination of two types of
dryers, where the evaporated vapors from a drum dryer and condensate from the ethanol
plant is used in a band dryer. Net energy required to the drum dryer is 19 GWh/year and
the band dryer has a net energy demand of 29 GWh/year.