Proceedings World Bioenergy 2010

BIOGAS UPGRADING BY TEMPERATURE SWING ADSORPTION
Tamara Mayer, Michael Url, Hermann Hofbauer
Institute of Chemical Engineering, Vienna University of Technology
Getreidemarkt 9/166, 1060 Vienna, Austria
Phone: +43 1 58801 15901, Fax: +43 1 58801 15999, Mail: tamara.mayer@tuwien.ac.at
ABSTRACT: This paper presents a novel process for biogas upgrading by means of temperature swing adsorption.
Temperature swing adsorption process experiments were carried out in a laboratory test rig focusing on the process
step of desorption. Desorption experiments were performed using three different variations of regeneration. Further
on, performance and efficiency of the applied desorption variations were investigated. As a result, desorption by any
combination of direct and indirect heating is considered as the best and most efficient way. Referring to the
adsorption step, separation performance is excellent, carbon dioxide is fully adsorbed and pure methane can be
obtained.
Keywords: biogas, upgrading, adsorbents
1 INTRODUCTION
Natural gas had a share of 24% in the gross energy
consumption of the EU-27 in the year 2007. Therefore
Europe’s dependence on natural gas can be considered as
quite high. Due to the fossil origin of natural gas, it has
two drawbacks. First, it will for sure run out at some
point in the future and second, emissions deriving from
natural gas are not carbon neutral but they affect the
climate involving the whole issue of green house gas
emissions and global warming. For these two reasons
alternatives for natural gas have to be found and biogas
represents one option thereby.
Biogas is a renewable energy source deriving from
anaerobic digestion of organic matter. If biogas should
replace natural gas, it has to possess a certain quality
similar to natural gas. In order to achieve this quality and
to obtain gas which is suitable for replacing natural gas,
biogas must be upgraded.
This paper investigates a novel process for biogas
upgrading based on the principle of temperature swing
adsorption (TSA).
2 OVERVIEW OF BIOGAS UPGRADING
TECHNOLOGIES
Biogas typically consists of about two thirds methane
balanced by about one third carbon dioxide and
impurities such as hydrogen sulphide [1]. Moreover,
biogas is usually saturated with water when leaving the
anaerobic digestion plant. If biogas should be injected
into the natural gas grid, it needs to exhibit a certain
quality similar to natural gas which consists mainly of
methane. Hence, gas components such as carbon dioxide
and hydrogen sulphide have to be removed from biogas
in order to obtain a high amount of methane.
The entire process of biogas upgrading roughly
comprises separation of water and hydrogen sulphide as
well as methane enrichment.
2.1 Overview
Among currently available biogas upgrading
technologies, water scrubbing and pressure swing
adsorption are clearly the two most applied ones [2] and
they can therefore be classified as state of the art for
biogas upgrading. Other technologies like chemical or
organic physical absorption processes along with
membrane based techniques are in an advanced state of
development or even under demonstration. Although
there are established technologies, which are already well
developed and going to be continuously improved and
optimized, innovative technologies find their way. These
emerging biogas upgrading technologies include for
instance cryogenic upgrading or in situ methane
enrichment.
Comprehensive reviews of biogas upgrading
technologies and further related information are given
elsewhere (e.g. in [3] or [4]).
2.2 Comparison of biogas upgrading technologies
Biogas upgrading processes can be categorized into
wet and dry processes depending on whether a liquid
phase is required or not. Accordingly, all kinds of
absorption processes are related to wet processes whereas
dry processes involve adsorption processes and
membrane processes like gas permeation. Wet biogas
upgrading processes are characterized by the need of a
liquid such as water or organic solvents in order to
perform removal of carbon dioxide along with further
undesired components. Disadvantages deriving from
utilization of any kind of liquid are on the one hand the
need of disposal and on the other hand possible treatment
of the liquid before disposal. Moreover, wet processes
require drying of the upgraded gas before it leaves the
plant, what represents an additional process step
compared to dry processes. However, pressure swing
adsorption processes use activated carbon beds as guard
filter for protection of the actual adsorbent which is a
carbon molecular sieve. This process configuration
causes the need of disposal of saturated activated carbon.
Furthermore, biogas upgrading processes can be
categorized according to the need of pressurization of
raw gas. Correspondingly, the processes of pressure
swing adsorption, water scrubbing, organic physical
scrubbing as well as gas permeation require the raw gas
to be compressed in order to perform the upgrading.
On the contrary, chemical scrubbing with amines and
the temperature swing adsorption process presented in
this paper are so called pressure less processes. Further
similarities of these two processes are utilization of
amines as sorbent, low methane losses during the process
and high methane content in the upgraded gas (98% or
even above) because of excellent selectivity of the amine
for carbon dioxide. However, there are differences
concerning regeneration of saturated amines. Regarding
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