Thomas 2003 - Biogas as Energy Source for South Asia

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Biogas as a Residential Energy Source

For South Asia

Daniel Thomas

ME 5080 Term research paperDecember 11, 2003



Biogas as a Residential Energy Source for South Asia Daniel Thomas, 1

Abst rac t

Because of high population growth and high growth trends in energy consumption, South

Asia will become increasingly important in global energy consumption. The high proportion of

residential energy use for cooking and current high reliance on biomass give sustainable biogas

energy great potential in this region. A first and second law analysis of biogas use, as applied to

domestic cooking, was conducted. 11, 380 kJ of captured cooking heat can be obtained from one

livestock unit per day by digesting the manure and burning the biogas, since the second law

effectiveness of this process is about 47%. Only 9580 kJ/LU-day is obtained from burning the

same quantity of dried manure. In addition, biogas can be generated from other organic feed

stocks and produces an effluent with high fertilizer value in addition to the methane-rich gas.

When other benefits such as financial savings, public health, nutrient retention, time savings, and

convenience are considered, biogas becomes an even more viable energy source for South Asia.




I n t roduc t ion t o reg iona l energy use

South Asia is usually defined as the five nations that comprise the Indian subcontinent:

India, Pakistan, Bangladesh, Nepal and Sri Lanka (Figure 1). This is an area with a rapidly

growing population and energy consumption. Figure 2 shows that the population of the region,

already at 22%, is increasing as a fraction of the world’s population.

Figure 1: Nations of South Asia, with current

population in millions.1

2000 World Population

Africa, 784.3

South Asia, 1342Rest of Asia,

2349.5

USA, 278.4

Rest of

Americas, 550.3 Europe, 729.8

Pacific, 31.2

2025 World Population

Pacific, 40.8

Europe, 703.4

Rest of

Americas, 734.6USA, 325.6

Rest of Asia,

2897.6South Asia,

1833.8

Africa, 1298.2

Figure 2: 2000 and 2025 population of South Asia as

a fraction of world population.2

The energy consumption of South Asia is also increasing rapidly, as demonstrated by

Figure 3. This trend is even more evident in Figure 4, where the normalized growth trends show

that the Middle East, Asia and Oceana are the regions with the largest growth rates in energy

consumption. Looking into this region in more detail, Figure 5 shows that the large countries of

South Asia have energy consumption growth trends significantly steeper than those of the larger

Asia and Oceana region.

The large increases in population stimulate large increases in energy consumption, since

a large proportion of the energy is consumed by the residential sector (Figure 6). With less

developed industry and commercial sectors, much of the consumption is of energy suitable for

household cooking and agriculture. This is reflected in Figure 7, which shows that the heavy




reliance on biomass. Almost 90% of Nepal’s energy comes from biomass, which is a stark

contrast to the 4% shown on the USA series, included for comparison. India has large coal

resources and more industry than the other countries shown, but still relies on biomass for 18%

of its total energy consumption. These patterns are typical of much of the rest of Asia and Africa,

so conclusions reached for South Asia may well be equally applicable in these other regions.

0

20

40

60

80

100

120

140

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Year

C o n s u m

p t i o n ( Q u a d s )

North America

South and Central Am.

Western Europe

Eastern Europe

Middle EastAfrica

Asia & Oceana

Figure 3: Primary energy consumption by region, 1992 – 2001.3

0.5

0.6

0.7

0.8

0.9

1

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Year

F r a

c t i o n o f M a x . C o n s u m p t i o n

North America

South and Central Am.

Western Europe

Eastern Europe

Middle East

Africa

Asia & Oceana

Figure 4: Normalized energy consumption by region, 1992 – 2001.4




0.5

0.6

0.7

0.8

0.9

1

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Year

F r a c t i o n o f M a x . C o

n s u m p t i o n

India

Pakistan

Bangladesh

United States

Figure 5: Normalized energy consumption by country, 1992 – 20015

0%

20%

40%

60%

80%

100%

P e r c e n t

a g e o f t o t a l e n e r g y r e q u i r e m e n t

India Pakistan Bangladesh Nepal Sri Lanka USA

Country

Industry/ Construction Transportation Household/ Agriculture

Energy Convers ion Losses

Figure 6: Energy end-use by sector.6

0%

20%

40%

60%

80%

100%

P e r c e n t a g e

o f t o t a l e n e r g y r e q u i r e m e n t

India Pakistan Bangladesh Nepal Sri Lanka USA

Country

Coal Oil Gas Biomass Other

Figure 7: Energy sources for South Asia countries.7

The countries of South Asia and other developing nations have rapidly increasing energy

demands but are also those that will be most negatively affected by global warming. There hastherefore been considerable interest in moving to sustainable energy sources in their early growth

phase. Because of the high cost involved in renewable energy technologies such as wind and

photovoltaic solar, biomass is a very viable solution, if it can be used in a sustainable way.

(Deforestation, nutrient loss and smoke are major concerns.)




I n t roduc t ion t o b iogas

Biogas consists mostly of methane, and is the product of anaerobic digestion of organic

material. The production of biogas is a natural process, but it has only been harnessed for energy

production since about 1950. The basic process is shown in Figure 8, and can use crop wastes,

livestock manure, human excrement and urine, by-products of agricultural industries, forest litter

or aquatic wastes and weeds as feedstock. This can be a continuous process, with wastes fed

through one port to the digester and slurry exiting at another. The main requirement of the

digester is that it be airtight so that oxygen does not enter and the biogas is trapped for use. Many

designs have been developed, the most common of which are the fixed dome (Figure 9), floating

dome (Figure 10) and polyethylene bag (Figure 11) digesters.

Figure 8: Basic biogas production process with main product uses.8

Figure 9: Fixed dome bio-digester design developed

and used extensively in China.

Figure 10: Floating dome bio-digester design

developed and used extensively in India

Methane

Generator

Animal WastesNight Soil

Crop ResidueDomestic Waste

Fuel

Sludge

Mechanical Energy

Heat and Light

Electrical Energy

Nutrients returned to soil

Improved soil structure

Increase in organic matter




Figure 11: Short version of the polyethylene bag biogas digester design, shown installed in an earthen ditch.

Eff ic ienc y Analys is o f b iogas energy

In calculating a first-law efficiency for biogas use, it is interesting to compare the

efficiency of using biogas generated from a given quantity of feedstock to the efficiency of direct

combustion of the same material. For an example, cooking was chosen since it is the largest end-

use in most of South Asia. Cattle manure was chosen as the fuel since it is a very widely used

fuel and often the main alternative to fuel wood (the use of which leads to deforestation).

A 500 kg head of cattle (= 1 Livestock Unit, LU) produces about 40 kg manure per day,

as shown in Figure 12. Although cattle produce more manure per livestock unit than other

animals, cattle manure has a higher moisture content, so the amount of volatile solids is about

equal to that for other livestock. Figure 13 shows the composition of manure for several types of

livestock, the majority being carbohydrates of easy (E) or slow (S) digestibility. The typical

composition of cattle manure is given in more detail in Table 1.

3.1

35.4

3.9

37.8

2.0

26.4

4.3

15.7

5.3

26.0

4.0

24.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

P r o d u c t i o

n p e r L i v e s t o c k U n i t ( k g / L U )

Dairy

cattle

Beef

cattle

Swine Sheep Poultry Horses

VS Water

Figure 12: Daily manure production for various

livestock, showing proportion of solids to liquids.9

Figure 13: Composition of manure for various

livestock.10




Table 1: Composition of cattle manure on a mass

basis.11

Component Characteristic Mass

composition fraction

Lignin C6H10O5 12%

Carbohydrates (S) C6H10O5 19%

Carbohydrates (E) C6H10O5 43%

Lipid C57H104O6 7%

Protein C5H7O2N 16%

Volatile Fatty Acids C2H4O2 3%

60.0

36.0

2.0

2.0

72.6

11.9

14.5

1.0

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Mass basis Molar basis

CH4 CO2 H2 N2

Figure 14: Typical Composition of Biogas on mass andmolar basis.

The anaerobic digestion of all of these components can be considered with the basic

reaction:

The yield of methane from this reaction can thus be calculated with Bushwell’s formula:12

If all the volatile solids (using composition given in Table 1) were consumed to produce methane

in this reaction, the theoretical yield of methane and biogas (using the composition given in

Figure 14) would be:

But the lignin, slowly digestible carbohydrates, and volatile fatty acids are not digested in a

typical biogas digester retention period (< 3 months), so the ultimate methane yield from the

same manure would be as follows. The volume of biogas is again found using the typical biogas

composition in Figure 14.

42248248224

CH ban

COban

O H ba

nO H C ban

−++

+−→

−−+

VSCH Th kgm

ban

banY /

1612

4.22)4 / 8 / 2 / ( 3

4

++

⋅−+=

VS BG

VSCH

manure

Th

VFA

ThVFA

protein

Th protein

lipid

Thlipid

carb

Thcarb

carb

Thcarb

lignin

Thlignin

total

Th

kgm

kgm

Y

Y yY yY yY yY yY yY E S

/ 783.0

/ 470.0

)370.0(03.)496.0(16.)014.1(07.)415.0(43.)415.0(19.)415.0(12.

3

3

.

4

=

=

+++++=

+++++=




0.210.24 0.26 0.24

0.22

0.0630.087 0.087 0.091 0.081

0

0.05

0.1

0.15

0.2

0.25

0.3

A c t u a l B i o g a s Y e

i l d ( m 3 / k g )

M a n u r e

w i t h c a t t l e u r i n e

w i t h s u g a r , u r e a

w i t h s u g a r , l i m e

w i t h l e a v e s

24 days digestion 80 days digestion

Figure 15: Actual production of biogas for various

manure mixtures after 24 and 80 days digestion.13

Figure 16: Typical efficiencies and capital cost of

stoves commonly used in South Asia.14

However, lower retention times result in actual biogas yields being less than half of this ultimate

yield (Figure 15). Variations in feedstock composition can also play an important role in

determining this final yield. Once the biogas yield of manure has been calculated, the energy

produced by the combustion of biogas is found using the following balanced combustion

equation, based on values shown in Figure 14.

VS BG

VS BG

VSCH

manure

U

protein

Th protein

lipid

Thlipid

carb

Thcarb

total

U

kgkmol

kgm

kgm

Y

Y yY yY yY E

/ 0100.0

/ 547.0

/ 329.0

)496.0(16.)014.1(07.)415.0(43.

3

3

.

4

=

=

=

++=

++=

222222224 012.3597.1845.)76.3(7985.145.010.119.726. N O H CO N O H N COCH ++→+++++

VS

VS BG BG

BG BGmanure

P e f e R i f i

kgkJ

kgkmolkmolkJ

kmolkJ kmolkJ E

hnhn E

/ 177,6

) / 010.0( / 541,617

) / 711,718() / 170,101(

,,

==

−−−=

∆−∆=

∑∑°°




In cooking the efficiency of the stove in using this energy of combustion varies considerably.

Gas stoves are much more efficient than typical biomass stoves, with efficiencies between 55%

and 60% (Figure 16). This gives a useful heat value of:

With a typical output of 3.1 kgvs /LU·day for cattle (Figure 12), this becomes:

Table 2 shows other typical uses for this same energy output. All across South Asia, manure is

collected and dried for burning, so it is also interesting to compare this output to that given by

simply burning the same quantity of manure. Because of the complex structure of the

hydrocarbons involved, the energy from combustion of the manure is best found from the higher

heating value, calculated using the Dulong formula:15

Tillman gives the following equation for finding the lower heating value from the HHV:16

Table 2: Other uses of calculated energy available

from biogas produced daily by 1 LU.17

Use Quantity

Daily cooking 2.3 persons

Single mantle lamp 10.7 hours

2 hp engine 1.7 hours

24 h refrigeration 1.1 ft3

24 h incubation 2.1 ft3

0

20000

40000

60000

80000

k J / k g o r k J / L U - d a y

Direct combustion Biogas combustion

Qreaction Quseful

Figure 17: Total and useful energy produced by

burning manure directly or the biogas derived from it.

VS

VS

stoveuseful

kgkJ

kgkJ

E Q

/ 3670

/ 611760.0

=⋅=

=η

day LU kJ Quseful ⋅= / 377,11

VS

S H C lb Btu

lb Btu

mmm HHV

/ 517,25

066.06100048.014490

55506100014490 /

=⋅+⋅=++=

[ ]

day LU kJ

kgkJ

lb Btu

kgkJ LHV

m MC HHV LHV

VS

kgKJ

H f lb Btulb Btu

⋅==

⋅⋅⋅+⋅−=

+−=

/ 690,73

/ 770,23

/

/ 326.2)1050065.0910.01050(10970

)105091050(

/

/ /




A typical traditional stove in which the manure would be burnt only has an efficiency of 13%,

giving a final useful energy of:

These results are shown graphically in Figure 17. Although much more heat is produced by just

burning the manure, the lower stove efficiencies cause the final useful heat to be lower than if the

same amount of manure had been used to produce biogas which was used for the cooking.

In this case the first law analysis allows the most useful comparison between different

uses for the original biomass fuel. A second law analysis using the availability of the manure

would be difficult, due to the complicated organic components; the standard chemical

availability of proteins, carbohydrates or lipids is not available. However, a useful second law

analysis of the biogas combustion can be done beginning with the balanced combustion

equation:

The adiabatic flame temperature for the reaction is found by satisfying the following equation:

However, the actual flame temperature is usually significantly lower, as confirmed by Gatade

and Rao18

, and can be found using Gaydon and Wolfhard’s correction factor:19

The chemical availability is as follows, using the standard chemical availability of the methane

and hydrogen components of the biogas:

This gives a second law efficiency of:

day LU kJ

day LU kJ

LHV Q stoveuseful

⋅=⋅⋅=

=

/ 580,9

/ 690,7313.0

η

222222224 012.3597.1845.)76.3(7985.145.010.119.726. N O H CO N O H N COCH ++→+++++

K T

hnhnhn

ad

P

e f e

R

i f i

P

ee

1981

,,

=⇒

∆−∆=∆ ∑∑∑ °°

C K

T T ad actual

°===

11121585

)8.0(

ch

f

useful R

a

QT T ) / 1( 0−=ε

BG

BG

chi

i

ich

f

kmolkJ

kmolkJ

ana

/ 251,637

/ 382,235145.0745,830726.0

=⋅+⋅=

=∑




This second law efficiency would be useful in improving the efficiency of the biogas stoves, or

other uses of the gas (Table 2).

Advantages and d isadvantages of b iogas energy

Economics: Since biogas digesters currently being developed and used in South Asia are largely

for rural, low-income family cooking the economic benefits of the energy source are very

important. The initial capital cost is high, but this has been lowered by government subsidy and

micro-loan programs.

In a field study of four 3 m3 /day biogas digesters operating in rural India, Pande found all

produced net annual savings of Rs. 1000 – 3000.20 The plant shown in Table 3 was financed

partially by government subsidy but mostly by the owner through initial payment and loan. This

analysis accounts for regular maintenance as well as eventual replacement of parts and

construction repair. Table 4 shows another analysis which shows similar net savings in situations

in which the manure was previously used for either fuel or fertilizer. If this plant were financed

with 25% government subsidy and a loan paid in five installments, net savings would be about

Rs. 500 for the first five years and about Rs. 1500 after repaying the loan.

Table 3: Typical costs and savings of a 4 m3 /day biogas digester in rural India.21

CONSTRUCTION: OPERATION:

Construction cost: 4,980.00 Annual Expenses 2,867.00

Bricks (4000) 1,920.00 Manure (36 tons) 2,000.00

Cement (30 bags) 1,440.00 Interest on loan (12%) 357.00

Brick ballast 250.00 Depreciation on equipment (10%) 64.00

Sand (100 ft3) 150.00 Depreciation on construction (7%) 334.00

Morang (80 ft3) 320.00 Maintenance 112.00

Labour 900.00 Gross Annual Savings 3,640.00

Other costs: 641.00 Annual fuel and lighting expenses 2,040.00

Pipe (20 ft) 160.00 Value of improved manure (20 tons) 1,600.00

Sockets and valves 62.00 Net Annual Savings 1,171.00Paint (2 l) 44.00 Gross savings - expenses 773.00

Stove 250.00 Add back depreciation 398.00

Lamp 125.00

Total 5,621.00 Average Net savings while repaying loan 871.00

Initial payment by owner 621.00 (first 7 years)

Government subsidy 2,140.00 Net savings after repaying loan 1,528.00

Loan 2,860.00 (after 7 years)

%1.47

/ 251,637

/ 541,617)6.0()1585 / 3001(

=

−=

BG

BG

kmolkJ

kmolkJ K K ε




Table 4: Cost and Income analysis of a 6 m3 /day biogas plant.

22

Operation: In a study of 97,000 biogas plants installed in India by the non-government

organizations Action for Food Production and Canadian Hunger Foundation, 87% of the plants

were still operating after about 10 years, although many were running inefficiently.23

Much of

the inefficient operation was due to not feeding the digester sufficiently, as were about 30% of

the non-functioning plants. However, as shown in Figure 18 defects in plant and stove

components were also major problems. Problems with defective components also accounts for

the low rate of operation for plants installed over 10 years before the study (Figure 19).




Social Problems: loss of cat tle, moving of cattle, f amily dispute, etc.

Technical Problems: pipelin leak, broken dome valve, etc.

Construction Defects: dome cracking

Others: flooding, not feeding, fire, lack of space, sickness, etc.

Figure 18: Reason for digester non-functionality.24

0

10

20

30

40

50

60

70

80

90

100

P e r c e n

t

Till 1990 1990-94 1994-96 1996-98

Year of Installation

Functional Non-Functional

Figure 19: Functionality rate and age of digesters.25

Public Health: The lack of oxygen in a biogas digester that results anaerobic digestion also

means many other micro-organisms are not able to survive. There are a few pathogens that

survive (e.g. Ascaris lumbricoides, ringworm), but most have a high die-off rate (Figure 20). The

National Academy of Sciences report on biogas generation from human and animal wastes

concluded that anaerobic digestion is most effective practical treatment of human excreta.26

Because of the harsh conditions in the slurry product, die-off continues outside of digester.

98.589

99 10090

100

0

20

40

60

80

100

D i e - o f f , %

P o l i o v

i r u s

S a l m o n

e l l a

s s p

.

S a l m o n

e l l a

t y p h o

s a

M y c o b a c t e r i u m

t u b e r c u l o s i s

A s c

a r i s

P a r a s i t e c y s t s

Figure 20: Pathogen die-off during anaerobic

digestion.27

1.8695

0.401

1.8515

0.014

0

1

2

3

g N / k g d u n g

Fresh slurry Evaporated slurry

Organic N Ammonia N

Figure 21: Nitrogen retention in biogas digester

slurry.28






0

1

2

3

4

5

6

7

7 14 23 30 43 60

Digestion period (days)

B i o g a s p r o d

u c e d ( l i t e r s )

0% W.H.

30% W.H.

50% W.H.70% W.H.

100% W.H.

Figure 24: Effect of substitution of water hyacinth for cattle manure on biogas production.33

(Total feedstock mass =500 g)

Other benefits: Other important benefits of biogas energy include the following:

• It is a clean burning fuel (manure combustion is especially sooty).

• It allows time savings in fuel collection and cooking. One study showed savings of at

least 1 hour in households using biogas.

• The fuel is easy to store and use.

• It results in reduced transfer of fungus and other pathogens to next year’s crop.




References

1AskAsia Resources. Maps. www.askasia.org/image/maps/asias1.htm 12-13-2003.

2Johnstone, Patrick, and Mandryk, Jason, “Operation World,” WEC International: Bulstrode, 2001.

3Energy Information Agency, “International Total Primary Energy and Related Information,” Table E1: World

Total Primary Energy Consumption, www.eia.doe.gov/emeu/iea/tablee1.html 12-13-2001.4Ibid.

5Ibid.

6United Nations Statistics Division, 1998 Energy Balances and Electricity Profiles,

http://unstats.un.org/unsd/energy/balance/tables.htm7 Ibid.8

National Academy of Sciences. “Methane Generation from Human, Animal, and Agricultural Wastes.” NAS:

Washington, D.C., 1977. p 6.9

National Academy of Sciences, p 41.10

Moller, H. B., Sommer, S. G., Ahring, B. K. “Methane productivity of manure, straw and solid fractions of

manure.” Biomass and Bioenergy. July 2003. p 7.11

Ibid.12

Moller, H. B., et al. p 6.13

National Academy of Sciences, p 69.14U.S. Congress, Office of Technology Assessment, “Fueling Development: Energy Technologies for Developing

Countries,” OTA-E-516 Washington, DC: U.S. Government Printing Office, April 1992.15

Hougen, O. A., Watson, K. M., Ragatz, R. A., “Chemical Process Principles: Part I, Material and Energy

Balances.” 2nd

Ed. New York: Wiley, 1954. p 401.16

Tillman, D. A. “The Combustion of Solid Fuels and Wastes.” San Diego: Academic P., 1991. p 87.17


Gatade, S. P., Rao, B. H. “All India Seminar on Renewable Sources of Energy.” Burning Characteristics of

Gobar Gas. Allahabad, India: Eastern P, 1982. p B-5.119

Tillman. p 37.20

Pande, B. M. “Performance of Bio-Gas Plants: A Field Study.” Lucknow, India: Appropriate Technology

Development Association, 1985. p 49.21

Ibid.22

National Academy of Sciences, p 121.23 Dutta, S., Rehman, I. H., Malhotra, P, Venkata, R. P. “Biogas: the Indian NGO Experience.” New Delhi: Tata

Energy Research Institute, 1997. p 16.24

Ibid.25

Ibid. p 1726


Ibid. p 55.28

Ibid. p 50.29

Chau, Le Ha. “Biodigester effluent versus manure from pigs or cattle as fertilizer for production of cassava

foliage.” Livestock Research of Rural Development. Vol 10. No. 3, 1998.

<www.cipav.org.co/lrrd/lrrd10/3/chau1.htm>30

Singh, S., Kumar, M. “All India Seminar on Renewable Sources of Energy.” Utility of Eichornia Crassipes as a

Source of Bio Gas. Allahabad, India: Eastern P, 1982. p B-3.331

Chau, Le Ha.

32 Ibid.33

Singh, S., Kumar, M. p B-3.1

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Thomas 2003 - Biogas as Energy Source for South Asia