comparative casestudy of biogas utilization from livestock manure in vietnam (focussing on co2 balance

At household scale, biogas is utilized mostly for cooking and such tons of greenhouse gas can be reduced from one household per year, mostly from correct livestock manure management and

TRƯƠNG THỊ KIM DUNG

COMPARATIVE CASE STUDY OF BIOGAS UTILIZATION FROM

LIVESTOCK MANURE IN VIETNAM

(FOCUSSING ON CO2 BALANCE) Field: waste management and contaminated site treatment

MASTER THESIS

Supervisor:

Dr.-Ing Christoph Wünsch

ACKNOWLEDGEMENT

Firstly I would like to thank to the Hanoi University of Science, Vietnam National University and Techniche Universtät Dresden, Institute of Waste Management and Contaminated Site Treatment, whose have established a good study program for us to learn a good new field of environment

I would like to thanks to Prof Bernd Bilitewski, Prof Nguyen Thi Diem Trang and Dr Hoang Van Ha, whose always keep an eye on our study and help us so much

My sincerely thanks to my supervisor Dr Christoph Wünsch, Dipl Veit

Grundmann , who guide and help me hold-heartedly during the time I did the thesis And I also want to thanks to Dr Catalin Stephan and Dipl.Hoang Mai I still remember our discussion, small parties as well as your encouragements It helps me more self-confident in my ability

Finally I want to thanks so much to my family You are my motivation to overcome difficulties in my life

ABSTRACT

From 2003 Livestock Production Department under Ministry of Agriculture and Rural Development - MARD cooperates with Netherlands Development Organization – SNV to deploy of domestic biogas program for livestock production in rural area

The program not only solve environment problems in terms of pollution and improve rural life quality, it also contributes to greenhouse gas reduction considerably

At household scale, biogas is utilized mostly for cooking and such tons of greenhouse gas can be reduced from one household per year, mostly from correct livestock manure management and fossil fuel substitution

At farm scale, biogas can be utilized for electricity generation, thousands KWh

of electricity can be produced and such thousand tons of greenhouse gas can be reduced per farm per year

It should be encouraged to apply this treatment method for all kinds of livestock

of the country The greenhouse gas emission reduction will be much more significantly, contribute to meet the aim of the Kyoto Protocol “to achieve stabilization

of atmospheric concentration of greenhouse gases at a level that would prevent dangerous anthropogenic interference with the climate system” that Vietnam signed in

Contents

INTRODUCTION 6

I BACKGROUND 1

1.1 Greenhouse effects and climate change 1

1.1.1 Greenhouse effects 1

1.1.2 Climate change 3

1.2 Greenhouse gas emission situation in Vietnam 7

1.3 Livestock growing situation in Vietnam 12

II OVERVIEW ON BIOGAS 16

2.1 Scientific theory of anaerobic digestion (biogas formation) 16

2.2 Composition of biogas 19

2.3 Substrates for anaerobic digestion 22

III BIOGAS PROJECT IN VIETNAM 22

3.1 Project overview 22

3.2 Technology of anaerobic digester used in the project 23

3.2.1 Structure of the anaerobic digester 23

3.2.2 Operation of the biogas plant 25

3.2.3 Treatment efficiency of biogas plants 26

3.3 Utilization of outputs from biogas plants 27

3.3.1 Utilization of biogas 27

3.3.2 Utilization of bio-slurry 31

IV CASE STUDY 35

4.1 Project scenario 35

4.2 Methodology 36

4.2.1 GHG reduction from manure management 36

3.2.2 GHG reduction from the fossil fuel substitution in thermal application or electricity generation 42

3.2.3 GHG reduction from chemical fertilizer substitution by bio-slurry 46

4.3 Calculation and results 48

4.3.1 GHG reduction at household scale 48

4.3.2 GHG reduction at farm scale 64

4.4 Outlook 67

IV CONCLUSION 71

ABBREVIATION

LIST OF TABLES

Table 1: National greenhouse gas emission inventory by sector of Vietnam in 2000 7

Table 2: greenhouse gas emission from agriculture sector 8

Table 3: total primary energy consumption by type of energy 9

Table 4: GHG emission from fuel combustion by type of fuel in 2000 10

Table 5: GHG emission from fuel combustion by sub-sector 10

Table 6: GHG emission from fuel combustion by type of gas 11

Table 7: Livestock population growth (thousands) 13

Table 8: livestock and milk production, million metric tons 14

Table 9: total livestock waste (solid) generation in 2006 16

Table 10: Environmental requirements 19

Table 11: Biogas composition 19

Table 12: Biogas composition compared with natural gas 20

Table 13: General energy characteristics of biogas 21

Table 14: Treatment efficiency of biogas plants 26

Table 15: Limited parameters for surface water quality according to the National technical regulation 2008 27

Table 16: comparative values of biogas and other fuels 28

Table 17: consumption of biogas and kerosene fuel in lighting according to the experience of the Institute of Energy 30

Table 18: Nutrient concentrations in the bio-slurry 32

Table 19: concentration of some heavy metals in bio-slurry 33 Table 20: nutrient contents in compost fertilizer made from bio-slurry and agricultural

Table 23 input parameters for indirect nitrogen oxide emission calculation from the baseline scenario (unrecoverable anaerobic lagoon) and project scenario (biogas plant)

51

Table 24: result of GHG emission reduction from manure management 52

Table 25: combustion efficiencies of combustion equipments with different fuels 53

Table 26: GHG emission factor of coal 54

Table 27: input parameters for GHG emission reduction calculation from fuel substitution in thermal application for at household scale 54

Table 28: GHG reduction results for a household growing 6 pigs 56

Table 29: Emission factors for stationary combustion in the residential and agricultural/forestry/fishing/farms 58

Table 30: Results of GHG reduction in case different fossil fuel used in absence of the project 59

Table 31: GHG emission reduction according to population of livestock (pig) 61

Table 32: the utilized biogas yield according to population of livestock (pig) 63

Table 33: GHG reduction for a farm growing 100 pigs with utilization of biogas for electricity generation 66

Table 34: input parameters for GHG emission reduction calculation from biogas destruction in the outlook 67

Table 35: The result of GHG emission reduction from biogas destruction in the outlook 68

Table 36: input parameters for GHG emission reduction calculation from nitrogen oxide emission reduction in the outlook 68

Table 37: The result of GHG emission reduction from nitrogen emission reduction in the outlook 69

Table 38: The result of GHG emission reduction from manure management in the outlook 69

Table 39: input parameters for GHG emission reduction calculation fuel substitution in thermal application in the outlook 70 Table 40: GHG emission reduction calculation fuel substitution in thermal application

in the outlook 70 Table 41: Total GHG emission reduction in the outlook 71

LIST OF CHARTS

Chart 1: GHG reduction for a household growing 6 pigs with utilization of biogas for cooking purpose 57 Chart 2: GHG reduction in case different fossil fuel used in the absence of the project 60 Chart 3: GHG emission reduction according to number of livestock 62 Chart 4: GHG reduction for a farm growing 100 pigs with utilization of biogas for electricity generation 66

LIST OF FIGURES

Figure 1: The greenhouse effect principle 3

Figure 2: changes in temperature, sea level and Northern Hemisphere snow cover 5

Figure 3: National greenhouse gas emission inventory by sector of Vietnam in 2000 8

Figure 4: Growth rate of pork production 15

Figure 5: the anaerobic digestion process 18

Figure 6: Types of fixed dome biogas plant used in the project are KT1 and KT2 24

Figure 7: two limit stages of fixed dome plant 25

Figure 8: diagram of biogas burner 27

Figure 9: Structure of biogas lamp 29

Figure 10: A biogas water boiler device 31

Figure 11: Project scenario 35

Figure 12: baseline scenario boundary of GHG reduction source: biogas destruction 38 Figure 13: project scenario boundary of GHG reduction source: biogas destruction 39

Figure 14: Baseline scenario boundary of GHG reduction source: fossil fuel substitution in thermal application 43

Figure 15: project scenario boundary of GHG reduction source: fossil fuel substitution in thermal application 43

Figure 16: Baseline scenario boundary of GHG reduction source: fossil fuel substitution in electricity generation 44

Figure 17: Project scenario boundary of GHG reduction source: fossil fuel substitution in electricity generation 45

INTRODUCTION

Above the environment pollution problems from the rapid growing in livestock production without livestock manure treatment, the situation of lack of energy, and the overuse of chemical fertilizer production for crop production From 2003 Livestock Production Department under Ministry of Agriculture and Rural Development - MARD cooperates with Netherlands Development Organization – SNV to deploy of domestic biogas program to solve the short term of environment problems and also have the long term objective of improving the livelihood and quality of life of rural farmers in Vietnam

Until now there are more than 106000 biogas systems constructed in over 50 provinces nationwide, millions tons of livestock manure are treated There are also some evaluation reports on economical and social effects But there isn’t any detail report evaluating on environmental effects, especially greenhouse gas reduction from that project

The aim of this research is the detail assessment of GHG emission balance from livestock manure treatment method by anaerobic digesters (biogas plants) in the project

to provide the reference data about the benefits of that project in term of GHG emission balance

is higher than it would be if direct heating by solar radiation were the only warming

mechanism” http://en.wikipedia.org/wiki/Greenhouse_effect

From 1827, Joseph Fourier recognized the importance of the greenhouse effect for the Earth’s climate He emphasized that the atmosphere is relatively transparent to solar radiation, but highly absorbent to thermal radiation and that this preferential

trapping is responsible for raising the temperature of the Earth’s surface [Isaac M

Held, Brian J Sodden, 2000] “The natural greenhouse effect means the short-wave

energy from the sun is absorbed at the earth’s surface and reradiated in the form of infrared Chart (long wave) radiation The greenhouse gas (some of low concentrate gases in atmospheric notably CO2, CH4, NOx, CO, etc.) absorb and emit long wave radiation The increase in the atmospheric concentration of GHG leads to an incremental absorption and emission of long-wave radiation All of them would result

in a warming of the lower atmosphere and the surface of earth This effect is referred as

“greenhouse effect” Human beings and most other living creatures can not survive without Natural greenhouse effect The greenhouse effect keeps the temperature of biosphere stable and filters some harmful radiations and hence protects the ecological

system” [Jia Xiaodong, 2009]

Because of influence from human activities, greenhouse gas is increased, leading to enhanced greenhouse effect and climate change Expressions of the climate change include temperature change in global scale, sea level rise, precipitation change

and the increase of extreme weather events [IPCC, 2008]

Figure 1: The greenhouse effect principle

Source: http://en.wikipedia.org/wiki/Greenhouse_effect

1.1.2 Climate change

* Definitions of climate change

The definitions of climate change are different of the Intergovernmental Panel

on Climate Change (IPCC) and the United Nations Framework Convention on Climate Change (UNFCCC)

According to IPCC, “the climate change refers to a change in the state of the climate that can be identified (e.g using statistical tests) by changes in the mean and/or the variability of it property, and that persists for an extended period, typically decades

or longer It refers to any change in climate over time, whether due to natural variability or as a result of human activity”

The climate change according to UNFCCC is a change of climate that is contributed directly or indirectly to human activity that alters the composition of the global atmosphere and that is in addition to natural climate variability observed over

comparable time periods [IPCC, 2008]

* Climate change over the world

Global warming is now evident from increases of global air, ocean temperatures and widespread melting of ice and snow and rising global sea level

According to the instrument record of global surface temperature from 1850, the eleven

years of the rank from 1995 to 2006 is the warmest years [IPCC, 2008]

The linear trend of the global average temperature in the same long period of

100 years from 1906 to 2005 is 0.74 [0.56 to 0.92], higher than the 100-year period from 1901 to 2000 that is 0.6 [0.4 to 0.8] The linear warming trend over the 50 years from 1956 to 2005 (0.13 [0.10 to 0.16]°C per decade) is nearly twice higher than the

period of 100 years from 1906 to 2005 [IPCC, 2008]

Figure 2: changes in temperature, sea level and Northern Hemisphere snow cover

Source: [IPCC, 2008]

The temperature increase has taken place at global scale The increase rate of temperature in Acrtic is almost twice higher than the global average rate in the past 100 years Land regions are warmed faster than the oceans

The increase of sea level is correlative with warming of the earth (figure 2) The sea level rose have been clearer in recent years The global sea level rise rate from

1993 to 2003 is 3.1 [2.4 to 3.8] mm per year that is higher than the rate of 1.8 [1.3 to

2.3] of the period from 1961 to 2003 [IPCC, 2008] That increase is contributed by the

thermal expansion of the oceans (57%), by the decreases in glaciers and ice caps (28%)

and losses from polar ice sheets (15%) [IPCC, 2008]

The decreases of snow and ice are also relative with warming of the earth (figure 2) The annual average sea ice in Arctic has shrunken about 2.7 [2.1 to 3.3]% per decade, and this number is higher in summers of 7.4 [5.0 to 9.8]% per decade Glaciers and snow in mountains in both hemispheres also have declined The frozend ground extent in the Northern Hemisphere has decreased about 7% since 1900 From the 1980s up to now, the temperature at the top of the permafrost layer in Arctic

increased by up 3°C [IPCC, 2008]

The precipitate also changed much in many regions “Globally, the area affected

by drought has likely increased since the 1970s” [IPCC, 2008]

The extreme changes of the weather have happened frequently over the last 50 years: “it is very likely that cold days, cold nights and frosts have become less frequent over most land areas, while hot days and hot nights have become more frequent It is likely that heat waves have become more frequent over most land areas It is likely that frequency of heavy precipitation events has increased over most areas And it is likely that the incidence of extreme high sea level has increased at abroad range of sites

worldwide since 1975”[IPCC, 2008]

The average temperature in the Northern Hemisphere during the second half of the 20th century is higher than any 50-year period in the last 500 years and is the

highest in at least past 1300 years [IPCC, 2008]

* Climate change in Vietnam

Vietnam is one of the countries that are suffered mostly of climate change

November The sea level has risen at average rate about 2.5 – 3 cm per decade Storms, floods and droughts have taken more frequently recent years

Because of the climate change, the sea water level of Vietnam is forecasted to be raised by 33 cm in 2050 and 45 cm in 2070 And if the sea level increases up to 90 cm

in 2100, a huge area in the Red River Delta, north central coastal area and Cuu Long

delta area will be submerged under water [MARD, SNV, 2007]

Vietnam has contributed around 151 million tons of CO2 equivalent in 2000 in which agriculture sector is the largest source (43.1%), then is from the energy sector (35.0 %) and at least from industrial sector (6.6 %) and from waste (5.3 %) as in the table 1 and figure 3

Table 1: National greenhouse gas emission inventory by sector of Vietnam in 2000

Sector

CO2 (thousand tons)

CH4 (thousand tons)

N2O (thousand tons)

CO2e (thousand tons)

Percentage (%)

Land use, land-use

CH4 (thousand tons)

N2O (thousand tons)

CO2e (thousand tons)

Percentage (%)

Table 3: total primary energy consumption by type of energy:

Unit: kilo tons of oil equivalent

Table 4: GHG emission from fuel combustion by type of fuel in 2000

Unit: thousand tons

Table 5: GHG emission from fuel combustion by sub-sector

Unit: thousand tons

Table 6: GHG emission from fuel combustion by type of gas

Gas

GHG emission (thousand tons)

CO2e (thousand tons)

Related to the aim of greenhouse gas reduction in the Kyoto Protocol, Vietnam has had a number of environment protection laws and regulations including:

 Environmental Protection Law No 52/2005/QH11 dated 29th November 2005

 Water Resources Law No 08/1998/QH10 dated 20th May 1998

 Petroleum Law (1993) No 10/2008/QH12 dated 6th July 1993 (amended twice

on 9th June 2000 and 3rd June 2008)

 Law on Minerals No 2/1996/QH9 dated 1st September 1996 (amended on 27th

June 2005)

 Law on Forest Protection and Development No 29/2004/QH11 dated 3rd

December 2004 (replaces the 1991 Law on Forest Protection and Development)

 Law of Electricity No 28/2004/QH11 dated 3rd December 2004

 Law on Safe and Efficient Use of Energy No 50/2010/QH12 dated 28th June

2010

Vietnam also has had the national strategies and programs related to GHG reduction The National Environment Protection strategy 2003 aims to apply of clean technologies, cleaner production processes and use of environment-friendly fuels and materials The National Target Program 2006 enforces on regulations on energy conservation and efficiency And the National Target Program 2008 to respond to climate change, in which the development and implementation of GHG reduction options contributes an important role in this program Replace cooking coal by biogas

is one of options of the Government towards to reduce GHG emission

Vietnam is on the trend of development, which the increasing growth rate in GDP

is stable around 6.5 percent from 1998 to 2003 Although the agriculture just contributes 20% to of GDP in 2007, but Vietnam is still an agricultural country, most

of the population lives based on agriculture production The livestock production

contributes 20% to agricultural GDP [General Statistic Office of Vietnam, 2007, 2008]

The main types of livestock are swine, cattle, buffalo and poultry The table 7 shows the livestock production growth from 2000 to 2010, in which the pig population is most and increase continuously fast from 20,194 to 26,701 thousands of heads

Table 7: Livestock population growth (thousands)

Source: [General Statistic Office of Vietnam, 2007, 2008, 2010]

Vietnam is also one of countries which export mostly pork over the world (2.55 million metric tons in 2008) The table 8 shows product productions from livestock, in which pork is the most significant contributor (71% of total livestock production)

Table 8: livestock and milk production, million metric tons

Source: [General Statistic Office of Vietnam, 2008]

The figure 4 shows the fast increasing growth rate of pork production from 2003

to 2007

Figure 4: Growth rate of pork production

Source: [General Statistic Office of Vietnam, 2008]

Livestock production brings quiet high financial benefits to farmers, but it also generates environmental problems The table 9 shows most of manure from livestock is not treated properly, causes smell, water and soil pollution as well as greenhouse gas emission

Table 9: total livestock waste (solid) generation in 2006

(Thousands)

Manure (Million metric tons)

Untreated (Percent)

Source: [Eastern research Group et al, 2010]

The anaerobic digestion is a complex process that can be divided up into four stages

acids, fatty acids and water under the influence of enzymes of facultative and obligatorily anaerobic microorganisms

The facultative anaerobic microorganisms use oxygen dissolved in water and create the low redox potential that necessary for obligatorily anaerobic microorganisms

 Stage 2 - Acidogenesis: this stage is done by the acid-forming microorganisms, which degrade lower-molecular compounds from the first stage into short-chain organic acids, C1 – C5 molecules (e.g., butyric acid, propionic acid, acetate, and acetic acid), alcohols, hydrogen, and carbon dioxide

 Stage 3 – Acetogenesis: The products from acidogenic phase serve as substrate for other microorganisms In which, homo-acetogenic microorganisms constantly convert exergonic H2 and CO2 to acetic acid for the next step according to the following reaction:

Figure 5: the anaerobic digestion process This process is biological, so any change in temperature, substrates or substrate concentration can lead to shutdown the gas production The following table is the optimal environment parameters for an optimum fermentation process

Table 10: Environmental requirements

Source: [Dieter D, Angelika S, 2008]

Biogas compared to other methane-containing gases: natural gas is the most well-known methane-containing gas that is divided into two groups H-gas and L-gas The table 12 shows a comparison of specifications of natural gases with biogases (agricultural biogas, biogas from sewage plants, landfill gas)

Table 12: Biogas composition compared with natural gas

Group H (US)

Group H (North Sea)

Group L (Holland)

25

s

<0.1 – 5.0 Benzene,

<0.1 – 5.0

Source: [Dieter D, Angelika S, 2008]

When comparing biogas with the natural gas, biogas contains methane less than natural gas but it is still flammable The following table presents the general energy characteristic of biogas

Table 13: General energy characteristics of biogas

Biogas characteristics

Source: [Dieter D, Angelika S, 2008]

2.3 Substrates for anaerobic digestion

Generally, all types of biogas can be substrates for the anaerobic digestion as long

as they contain carbohydrates, proteins, fats, cellulose and hemicelluloses as main components, such as liquid manure, domestic waste, sewage sludge…

The practical methane yield that is attained from the anaerobic digestion depends

on many factors such as composition, grain size, and proportions of the assigned substrates, on microbial degradability of biomass, the content of dry matter and organic dry matter and the relationship of the nutrients to each other And it also depends on characteristics of the technology used, such as the number of stages, the temperature, the residence time of the substrate, and the quantity and frequency of the substrate addition These parameter should be analyzed and measured before constructing anaerobic plants

3.1 Project overview

The support project to biogas program for the animal husbandry sector in Vietnam

is implemented by Livestock Production Department (under MARD), in cooperation with Netherlands Development Organization – SNV, that has been started since 2003 and done until now

The long term objectives: Improve the livelihood and quality of life of rural farmers

in Vietnam

The short term objectives:

- Provide bio slurry for cultivation and livestock production to produce clean products;

- Additionally support to establish socioeconomic organizations and enterprises doing the biogas services; contribute to improve the livelihoods and quality of life of the rural farmers in Vietnam

http://210.245.92.22/english/Home.aspx

3.2 Technology of anaerobic digester used in the project

3.2.1 Structure of the anaerobic digester

The biogas technology used in the project is designed and developed by Vietnamese engineers to make it suitable with the environment conditions in Vietnam, named the “fixed dome biogas plant” That is the digester with simple structure and

continuous feeding mechanism, including six main parts [MARD, SNV, 2007]:

(1) Mixed tank: is a place to discharge feedstock

(2) Inlet pipe: lead input materials to digester

(3) Digester: the main part of biogas plant Slurry is contained and fermented in the digester for biogas production

(4) Outlet pipe: similar in the structure with the inlet pipe However inside diameter of outlet can be smaller than or as big as the inlet pipe

(5) Compensation tank is a dome shape and with a function to regulate gas pressure in digester Additional this tank also contains bio-slurry and act as a valve to protect digester

(6) Gas pipe: is connected to the gasholder of the digester to collect and transport gas out of the digester

[MARD, SNV, 2007]

Figure 6: Types of fixed dome biogas plant used in the project are KT1 and KT2

Source: [MARD, SNV, 2007]

KT 1 type of biogas plant is applied for provinces in the North and KT2 type is applied for provinces in the South to make them suitable with the weather of each area

Advantages of these types:

- Saving construction materials because the surface area is small and bricks are laid slantingly which result in best strength

- Use common materials and minimize using of steel

- Area of sphere gas storage is small, without corners to reduce gas loss and avoid cracks

- Digester’s surface is underground and thus it can save space, limit the influence of low temperature outside and keep temperature stable

- The slurry surface is always up and down, reduce the formation of scum

- Use common struction materials which are available in province and local mason can do the construction work

3.2.2 Operation of the biogas plant

Figure 7: two limit stages of fixed dome plant The operating cycle of a digester consists of two stages:

- Stage 1: gas accumulation

- Stage 2: gas consumption

Stage 1: gas accumulation: At the initial state of the cycle, the surface of the slurry in the digester, the inlet and outlet is equal and is at the “zero level” The biogas have not been formed yet and the biogas pressure in the digester is equal to 0 (P = 0)

Then gas is generated and accumulated in upper part of digester, create the pressure on the surface of slurry and push slurry up to the compensation tank and inlet pipe The inlet pipe is small, so just a little slurry is pushed through the inlet pipe The slurry that is pushed out of the digester is mainly stored in the compensation tank

The more gas is generated, the lower surface of slurry is and the higher surface

of slurry in the compensation tank is

Finally the slurry in the compensation tank rises to the highest level named

“overflow level”, the slurry in the digester is pressed to the lowest level, and the gas

pressure reaches the maximum value (P = Pmax) [MARD, SNV, 2007]

Stage 2: gas consumption: When gas is released through the valve for consumption, the gas pressure in the digester will reduce and the slurry from the compensation tank will flow down the digester The surface of the slurry in the compensation tank lowers meanwhile the surface of the slurry in the digester rises up

“Finally when the difference between these two surfaces of the slurry is equal zero, the biogas plant returns to the initial state of the operation cycle (P = 0) and the gas outflow stops The volume of gas that can be extracted for consumption is equal

with the volume of the slurry contained in the compensation tank.”[MARD, SNV, 2007]

3.2.3 Treatment efficiency of biogas plants

Practical studies about treatment efficiency of biogas plants were taken by the project The results show biogas plants reduce significantly organic substance and meet the environmental hygienic standard for surface water quality as the table 14 and table

15

Table 14: Treatment efficiency of biogas plants

Table 15: Limited parameters for surface water quality according to the National technical regulation 2008

(mg/l)

COD (mg/l)

 Utilization of biogas for cooking

Biogas stove is the most popular equipment for utilizing of biogas in cooking with quiet high efficiency

Figure 8: diagram of biogas burner

1 Gas tube; 2 Gas valve; 3 Flame port; 4 Mixing chamber; 5 Air regulating shutter; 6 Burner head; 7 Nozzle

Source: [MARD, SNV, 2007]

Working principle of biogas stove:

It is similar with the atmosphere burner When the gas valve is opened, biogas is pushed at a high speed through the nozzle to create gas pressure which sucks air needed for the combustion Biogas and air is mixed in the mixing chamber to create a combustible biogas “Mixtured biogas is distributed to flame ports homogeneously in order to fulfill complete combustion.”

“The biogas stove has high efficiency (up to 60%) owing to the appropriate

biogas supplied" [MARD, SNV, 2007]

Table 16: comparative values of biogas and other fuels

Efficiency (%)

Amount of biogas equivalent

Electric

 Utilization of biogas for lighting

Biogas is also can be used for lighting using biogas lamp

Figure 9: Structure of biogas lamp

1 Nozzle and injector; 2 Hanger; 3 Connecting piece; 4 Inlet for the primary air; 5 Injector; 6 Nut; 7 Washer; 8 Upper cover; 9 Clay head; 10 Air vent; 11 Clip pin;

12 Lift reflector; 13 Glass cover

Source: [MARD, SNV, 2007]

Working principle of the biogas lamp:

The operating principle of biogas lamp is similar with the biogas stove because the nozzle and injector is designed is also based on the atmosphere stove Biogas is used to burn the mantle that is made by cotton, ramie or synthetic fibers and covered by

a solution of thorium oxide (90%) and cerium oxide When burning the thorium oxide

and cerium oxide will luminesce to provide light [MARD, SNV, 2007]