Biogas upgrading – Review of commercial technologies - SGC

SGC Rapport 2013:270
2 Description of the available upgrading technologies
This chapter, which constitutes the main part of this report, aims to thoroughly describe
the five commercially available upgrading technologies, amine scrubbing,
water scrubbing, pressure swing adsorption, membrane separation and physical
scrubbing with organic solvents. This chapter has been written in cooperation with
several manufacturers of upgrading plants. Significant parts of the data have been
supplied by the manufacturers, and compared with data from the literature. The
investment costs are presented as intervals of specific investment cost, as it may
vary with several factors, e.g. location, integration with existing equipment and
other site specific information.
2.1 Amine scrubbing
This chapter has been written in cooperation between the authors and the company
Purac Puregas which is active within the area of biogas upgrading.
The use of reactive systems for removing CO2 from biogas is not a brand new
notion, but it is less common compared to other technologies such as PSA and
water scrubbing. The synopsis of features of the technology is to use a reagent
that chemically binds to the CO2 molecule, removing it from the gas. This is most
commonly performed using a water solution of amines (molecules with carbon and
nitrogen), with the reaction product being either in the molecular or ion form. The
most common amines used historically for the purpose of sour gas removal (carbon
dioxide and hydrogen sulphide) are methyldiethanolamine (MDEA), diethnolamine
(DEA) and monoethanolamine (MEA) (Kohl & Nielsen 1997). Some of
these are still used, however, to the authors’ knowledge, the most common amine
system used industrially today is a mixture of MDEA and piperazine (PZ) often
termed activated MDEA (aMDEA). This system was introduced by BASF (Appl et
al. 1982), but is today supplied by several major suppliers of chemical such as
BASF, DOW chemicals and Taminco.
This chapter will deal with the purification of biogas with water solutions of
amines, the general process layout, operation and the effect of contaminants as
well as vendor information on costs and consumables.
2.1.1 Process description
Absorption of CO2 from biogas using amines in today’s biogas industry is mainly
performed using aMDEA. The process may be described generically but actual
vendors each have their variations of the process. In general terms the technology
consists of an absorber, in which the CO2 is removed from the biogas, and a stripper
in which the CO2 is removed from the amine solution. A general process overview
is shown in Figure 3.
16 Svenskt Gastekniskt Center AB, Malmö – www.sgc.se