Biogas as an alternative to natural gas?

science • technique
Biogas as an alternative to natural gas?
Jadwiga, HOLEWA, Anna KRÓL, Ewa KUKULSKA-ZAJĄC – Oil and Gas Institute (INiG), Cracow,
Poland
Please cite as: CHEMIK 2013, 67, 11, 1073–1078
Introduction
Natural gas is one of the most popular fossil fuels. Wide
recognition, as fuel, gained thanks to its properties, and methane
contained in the fuel is a very valuable substrate. Natural gas is used
to generate electric energy or, in combination, to generate heat and
electric energy (so-called cogeneration), and heat, electric energy
and cool (so-called trigeneration). Moreover, compressed natural gas
can be used as automotive fuel. Wide use of the fuel in the power
industry, heat engineering, transport as well as in the chemical industry,
with limited access to its deposits, involves searching for alternative
fuels which would be a natural gas substitute. It seems an alternative
might be biogas which is a gas mostly composed of methane and
carbon dioxide, obtained during anaerobic fermentation of biomass.
Substituting natural fossil fuel for renewable fuel might benefit the
environment; might be also a significant element of diversification of
the energy sources.
Characteristic of biogas
An anthropogenic source of biogas are landfills, sewagetreatment plant and special biogas plants which process agricultural
waste and waste from the food industry. A place and a method of
biogas production has important influence on its quality and amount.
Biogas which comes from different sources can be characterized
by different content of methane, therefore different content of
energetic parameters of the gas and different content of each
contamination. Considering three basic sources of biogas, it can be
shown that [1]:
• biogas which comes from landfills is characterized by high variability
of gas content
• both biogas produced in digesters located in sewage-treatment
plant and agricultural biogas are characterized by higher stability
of gas content
• typical landfill gas is characterized by content of methane between
25–65% and calorific value averages from 16.0 to 23.5 MJ/m³ [2]
• methane content in biogas from a sewage-treatment plant
averages from 57 to 65%, and its calorific value averages from 20.5
to 23.4 MJ/m³ [3]
• fuel with the highest calorific value can be obtained in agricultural
biogas plants, calorific value of biogas produced in the biogas plants
averages from 18.7 to 30.6 MJ/m³ [2]
It is important that in spite of the source, biogas is characterized
by lower calorific value than E natural gas. Assuming that E natural
gas is characterized by calorific value around 34.5MJ/m³, in order
to obtain the same amount of energy that can be obtained from 1 m³
of natural gas, it has to be burned: from 1,5 to 2.2m³ of landfill gas;
from 1.5 to 1.7 m³ of biogas from the sewage-treatment plant and
from 1.1 to 1.8 m³ of agricultural biogas.
Lower calorific value of biogas in comparison with natural gas might
be a problem for its use, however, not the only one. Unlike natural
gas, biogas can contain many different contaminations. Their type and
concentration depends on the source of biogas and the biomass from
which the gas was produced. As contaminants contained in biogas, in
terms of biogas usability, should be considered all substances which
occur in the gas except methane. It can be chemical contaminants
(ammonia, compounds of chlorine and fluorine), mechanical (e.g.
silicon, dust) and biological (bacteria and fungi) mechanical (bacteria,
1076 •
fungi). Contaminants contained in biogas might adversely have an effect
on biogas burners, some of them might have adverse health effect.
Contaminants contained in biogas next to its low calorific value, are
also important factor which can make use of the gas as an alternative
for natural gas difficult.
Possibility of replacing natural gas with biogas in many different
industries
Knowing that accessible resources of natural gas are decreasing; an
interesting questions arise, whether natural gas used on a large scale
in many industries, can be replaced by biogas – renewable fuel? If such
change is possible in each industry?
The power industry and heat engineering in Poland use about
10% of demand for natural gas [4]. Exactly for these economic
sectors biogas might be a valuable source of energy. Most of biogas
produced in Europe is burned in CHP units during generation of
electric energy and heat. This is the way of use of biogas which is
produced in landfills or sewage-treatment plant. However, in this type
of facilities, energy generated from biogas and useful heat, are used
for their own needs. It looks differently in case of agricultural biogas
plants which aim is to generate electric and thermal energy from gas
obtained in the biogas plants. The number of this type of facilities in
Poland is small; currently operating 34 agricultural biogas plants with
total electric power 38.78 MWe, and thermal power 40.034 MWt
[5]. Use of biogas during generation of electric and thermal energy
has also minimal limitation. According to many different gas engine
producers, it is [5]: calorific value below 14.4 MJ/m³; content of total
sulfur above 715 mg/m³ or content of sulfane above 0.15%; content
of ammonia above 55 mg/m³ of methane; total content of chlorine
and fluorine above 100 mg/m³ of methane and content of silicon
above 10 mg/m³ of methane.
According to such data, use of biogas to generate electric and
thermal energy seems to be the simplest way of management of this
valuable fuel. Additionally, biogas for energy enterprises, according
to the guidelines on annual inventories of carbon (IV) oxide emission,
is low-emission fuel. However, use of biogas for energy and thermal
purpose has some disadvantages; biogas plants are built mostly in
agricultural area, distant from urban area, therefore the level of use of
generated heat is unsatisfactory.
Another method of use of biogas which comes from different
sources is gas injection into the gas network. This method enables
to deliver biogas from rural area, where biogas is produced, to urban
area where can be fully used. It takes place in many countries of the EU
(Germany, Denmark, Sweden, France, Holland, Austria, Switzerland).
Because in Europe there are no harmonized requirements for quality
of biogas which is injected into the gas network, all mentioned courtiers
developed their own legal and technical procedures. Requirements for
each country are shown in Table 1.
The analysis of Table 1 confirms that each country has different
technical solutions for injection of biogas into the gas network.
Germany leads the filed in this kind of investments. Production and use
of biogas in this country is strongly supported by the government which
guarantees priority access to the gas network and the power network
to all renewable sources of energy [9]. In Germany the gas is injected in
two ways. The first of them enables injection, into the H gas network,
unlimited amount of biogas, only if the gas meets requirements from
nr 11/2013 • tom 67
Biogas can be also used in transport and as a reactant, however, this
kind of use requires earlier purification. There are many technologies
of biogas purification which remove from the gas all contaminants
or useless components. By means of suitable methods biogas can
be purified, deprived of carbon(IV) oxide and trace compounds, and
biomethane containing above 95% of methane can be obtained.
However, obtaining such effect requires use of many different and
expensive purification methods. Use of biogas as a reactant requires
exsiccation and removal of all sulphur compounds which even in a small
amount can be dangerous to catalysts used in synthesis, resulting in its
intoxication. The most efficient methods of desulfurization of biogas
consists in physical absorption of sulfane on active carbon or ceramic
filters. Both methods guarantee that in biogas after desulfurization,
content of sulfane and other sulphur compounds is trace. However,
both methods are expensive and their cost depends on the amount
of sulfane contained in crude gas, because along with increase of
concentration of sulfane, increases the amount of sorbent. In case of
active carbon, 1 kg enables to remove from 0.2 to 0.5 kg of sulphur
in biogas [12]. Use of biogas in transport also requires prepurification
to biomethane, however transport has not such restrictive requirements
for purity of methane. Use of compressed biomethane in transport
has many advantages, first of all biomethane is ecological and lowemission fuel. Moreover, vehicles can be provided with biomethane
by existing CNG filling stations. High cost of biogas purification might
make development of this sector difficult. Some European countries
(Germany, Switzerland) trying to help the sector by enforcing tax
exemption for the fuel – biomethane, what has increased use of
biomethane as fuel used in transport [13].
carbon(IV)
oxide, %
<6
<3
<2
<3
total sulphur,
mg/m3
<30
<23
<75
<10
<45
<30
Summary
An increase in energy consumption in the world parallel
to decreasing access to deposits of fossil fuels, is a reason of the
search for alternative sources of energy. It is also advantageous if
such sources are not only renewable, environment-friendly but
also similar to the known conventional fuels. It enables to adapt
conventional fuel systems to supply with renewable fuel. Such
properties has biogas which after proper purification can successfully
replace natural gas. Biogas generates much interest because it can
be used to generate electric and thermal energy, since this solution
does not require expensive process of biogas purification. However,
with proper support from the government, biogas would be used
on a large scale also in different industries. The fuel which is a great
alternative to natural gas, still requires separate legal regulations and
quality standards; by reason of its origin biogas, in terms of content
and properties, is much different than natural gas.
sulfane, mg/m3
<5
10 ppm
<5
<5
<5
<5
References
Oxygen, %
<0.5
<1
100 ppm
<0.5
<0.5
<0.5
Hydrogen, %
<5
<0.5
<6
<4
<-5°C
-8°C at
40 bars
Table 1
Detailed requirements for quality parameters for injection of biogas
into the gas network in chosen countries [7, 8]
Feature
Methane, %
Water/ dew
point
Germany
no limit
Sweden
>97
Equal to
<32 mg/m3
temperature
France
no limit
Austria
Holland
>96
>85
no limit
no limit
Switzerland
>96
<4
<5
<60%
<32 mg/m3 relative air
humidity
48.2–56.5
** (H gas)
Wobbe index
* kWh/m
3
13.3
10.5–15.7* 45.5–48.5**
** MJ/m3
15.7 *
43.6–44.1** 13.3–15.7*
42.5–46.8
** (gas L)
Chlorine
compounds,
mg/m3
no limit
no limit
Siloxanes,
mg/m3
no limit
no limit
Cl<1
F<10
no limit
0
<10
< 25
no limit
no limit
no limit
nr 11/2013 • tom 67
1. Holewa J., Kukulska-Zając E., Pęgielska M.: Analiza możliwości wprowadzania biogazu do sieci przesyłowej. Nafta – Gaz, sierpień 2012 r.
2. Grzybek A.: Ekspertyza – Ocena strategii rozwoju energetyki odnawialnej oraz
kierunki rozwoju energetycznego wykorzystania biogazu wraz z propozycją
działań. Warszawa, 2005.
3. Kalina J., Skorek J.: Paliwa gazowe dla układów kogeneracyjnych. Materiały
konferencyjne: Elektroenergetyka w procesie przemian.
4. www.pgnig.pl
5. Szwarc M.: Biogazownie rolnicze w Polsce raczkują. AgroNews.com.pl.
6. Dudek J., Klimek P., Kołodziejak G., Niemczewska J., Zaleska-Bartosz J.:
Technologie energetycznego wykorzystania gazu składowiskowego. Prace Naukowe Instytutu Nafty i Gazu nr 174, Kraków, 2010.
7. Marcogaz. Final Recommendation, Injection of Gases from Non-Conventional Sources onto Gas Networks. WG-biogas-06–18, 2006.
8. Huguen P.: Perspectives for a European standard on biomethane: a Biogasmax
proposal, 2010.
9. Verordnung über den Zugang zu Gasversorgungsnetzen (Gasnetzzugangsverordnung – GasNZV) vom 3. September 2010 (BGBl. I S. 1261).
• 1077
science • technique
the regulations DVGW G 260 and 262. If the gas does not meet the
requirements, can be injected into the gas network in limited way,
however the amount of injected biogas has to be suitable to create
a mixture of natural gas and biogas which meets the quality requirements.
Very similar solution for injection of biogas into the gas network use the
Swiss. Completely different solutions use the Swedes and the Danes. In
these countries biogas is injected only into the local, specially designed
gas network. In Sweden biogas is transported with old gas pipings
which are used to distribute town gas or mixture of natural gas and air
[10]. Analysing European experience in injection of biogas into the gas
network, shows that Poland has still a lot to do in this filed. Until middle
of 2011, there were no legal regulations in Poland which were defining
injection of biogas into the gas network. Regulation of the Minister
of Economy of 24 August 2011 on detailed scope of the obligation
towards confirmation of data concerning produced agricultural biogas
injected into the gas distribution network[11], allows to inject biogas
into the gas network. However, the quality requirements included in the
regulation for biogas were directly from the requirements for natural
gas transported in the gas network, included in Regulation of Minister
of Economy of 2 July 2010 on detailed conditions on the functioning
of gas system. This kind of legal situation restricts injection of biogas
into the gas network by excluding the limited way of injection of the
fuel. It also does not guarantee quality of the gas to the gas consumers,
because there are no limits for hazardous substances which do not
occur in natural gas but occur in biogas. Injection of biogas into the
gas network might considerably contributes to increase of use of the
gas in Poland and other European countries. A major barrier which
restricts injection of biogas into the gas network is lack of suitable,
uniform regulations in Europe for the fuel. The regulations should
consider both broad possibilities in purification of biogas as well as
that gas which is product in many different conditions might contain
contaminants. Therefor limits for content of each component of biogas
should concern not only energetic parameters of gas but first of all
gas transport safety and safe consumption of the fuel. Enforcement
of suitable legal regulations should contribute to development of
the biogas sector.
science • technique
10. Jönsson O., Hammar A., Ivarsson S.: Biogas feeding to the natural gas grid
and digestate use in the Swedish biogas plant of Laholm.
11. Rozporządzenie Ministra Gospodarki z dnia 24 sierpnia 2011 r. w sprawie
szczegółowego zakresu obowiązku potwierdzania danych dotyczących
wytwarzanego biogazu rolniczego wprowadzonego do sieci dystrybucyjnej
gazowej (Dz. U. 2011 nr 187. poz. 1117).
12. Kujawski O.: Przegląd technologii produkcji biogazu (część trzecia). Czysta
Energia 2010/2, nr 102.
13. Rogulska M.: Jazda na (bio)gazie. Instytut Paliw i Energii Odnawialnej, Warszawa,
Anna KRÓL – M.Sc., graduated in Chemistry from Jagiellonian University.
She works in the Department of Environmental Protection of the Oil and Gas
Institute in Cracow. She is working in the area of environmental protection
in oil and gas mining, including waste management and monitoring of the
environment in the oil and gas industry.
e-mail: [email protected]
Translation into English by the Author
Jadwiga HOLEWA – M.Sc., graduated in Chemistry from Jagiellonian
University, field of study – environmental protection. She works in the
Department of Environmental Protection of the Oil and Gas Institute in
Cracow. She is working in the area of environmental protection in oil
and gas mining, including reduction of greenhouse gases emission and
monitoring of natural gas and biogas quality.
e-mail: [email protected]
Ewa KUKULSKA–ZAJĄC, PhD – obtained her PhD in Chemistry
from Jagiellonian University. She is a manager of the Department of
Environmental Protection of the Oil and Gas Institute in Cracow. Her main
area of interest is environmental protection in oil and gas mining, including
reduction of the emission of greenhouse gases and waste management.
e-mail: [email protected]
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