A Study Report

on

Efficiency Measurement

of

Biogas, Kerosene and LPG Stoves

Submitted to: Biogas Support Program

Lalitpur, Nepal

Submitted by: Center for Energy Studies

Institute of Engineering Tribhuvan University Pulchowk, Lalitpur

July 2001

ACKNOWLEDGEMENT

The Center for Energy Studies, Institute of Engineering (CES/IOE) expresses its

sincere gratitude to Biogas Support Programme (BSP) for entrusting CES to carry out

Efficiency Measurement of Biogas. Kerosene and LPG stoves.

Study and preparation of this report would not have been possible without the

intensive work carried out by the core group members and associates of CES. CES is very

thankful to the all members involved in this study and other people who helped us by words

and deeds.

I would like to thank members of Kabir Ashram. Bishal Sadan at Jhamsikhel for their

co-operation in this study.

Last but not the least: CES expresses its sincere gratitude to Mr. Felix ter Heegde

(SNV/Nepal) and Mr. Sundar Bajgain. Project Manager of BSP. and staff of IOE and CES

for their help in completing this study.

Prof. J. N. Shrestha

Director

Center for Energy Studies

July 2001

Contents

Acknowledgements

1. Introduction 1

2. Literature Review 1

3. Methodology 5

4. Result 8

5. Example 10

6. Conclusion 11

7. Recommendation 11

8. References 12

Annexes

Calculation Software

Software Execution

1. Introduction

An agreement was signed between Biogas Support Programme (BSP) and Center for

Energy Studies. Institute of Engineering (CES/IOE) on 6th July 2001 to find out the

efficiency of biogas stove. For comparison, efficiency of LPG (Liquefied Petroleum

Gas) and kerosene stove (pressure type and wick type) was also studied. The

biogas stove under test was manufactured by Nepal Metal Cast of Butwal. Nepal.

2. Literature Review Cooking stoves operate with a variety of fuels, such as solid, liquid, gaseous and

other fuels. Animal dung, agricultural waste, wood, charcoal, sawdust, biomass

briquette could be considered as solid fuels. Kerosene, alcohol, and other

hydrocarbons are termed as liquid fuels. LPG (Liquefied Petroleum Gas), natural gas.

biogas etc could be considered as gaseous fuel. Efficiency of a stove could be categorized as burning efficiency and overall efficiency.

Burning efficiency of a stove accounts for the capacity of that stove in terms of

combustion of fuel. In other words ability of the stove to change the energy from fuel to

heat energy is related with burning efficiency. The ability of the stove to change the

energy from fuel into the energy gained by the specimen such as water, rice. cum',

milk etc is termed as overall efficiency of the stove. Generally efficiency of stove is

indicated by overall efficiency.

Overall efficiency of stove depends upon different conditions such as temperature,

pressure, wind speed, specific heat capacity of the vessel, bottom and overall shape of

vessel, weight of vessel, size of vessel and amount of specimen. Thus different tests for

efficiency could yield different results of the same stove. Calorific value (MJ/kg or kJ/

Lit) of the fuel is the input energy for stove and should be accounted in course of

efficiency measurement. Calorific values of fuels may vary from sample to sample

procured at different locations.

2.1 Other evidences on calculation of efficiency of different types of stoves: 2.1.1 Efficiencies for major fuels used in Indian Household Stoves are

depicted below in table #1. Kirk R. Smith. R. Uma. V.V.N. Kishore. K. Lata. V.

Joshi. Jufeng Zhang. R.A. Ramussen and M. A. K. Khalil carried out the research on

the topics of Greenhouse Gases from Small-Scale Combustion Devices in

Developing Countries for USEPA in November 1998.

Table #1

Fuel / stove Nominal Combustion Efficiency % Overall Efficiency %

Biogas 99.4 : 57.4

LPG i 97.7 | 53.6

Kerosene i 96.5 49.5

Wood ; 90.1 ; 22.8

Methodology applied by them were as follows:

Overall efficiency = hc * hr

Where.

hc = combustion efficiency

hr = Heat transfer efficiency

Overall efficiency = Percentage of chemical heat that enters the pot.

Nominal combustion efficiency = A rough estimate of combustion efficiency

= The fraction of airborne carbon emissions that

are released as carbon dioxide.

This report could assessed in web: www.energv.demon.nl/GHG/stoves.htm.

2.1.2 The findings of Tata Energy Research Institute (TERI), on efficiency of different

types of stoves are shown in table #2.

Table #2

Types of Stove Efficiency (%)

Biogas Stove 45

LPG Stove 60

Kerosene Stove 43

Wood Stove 10

Improves wood stoves 20

Electric Stove 70

These data could be assessed from the web site of TERI:

www.teriin.org/renew/tech/biogas

2.1.3 Other evidences could be found in the research paper of Tom Red. a

research student, who found out different types of stove efficiencies, which were as

follows:

Table # 3

Types of Stove Efficiency Range (%)

Kerosene Stoves 35-50

Charcoal Stoves 20-35

Firewood Stoves 10-25

Electric Stoves 75-85

These records could be viewed in web in following addresses:

www.ikwb.com/enuff/public_html/stoves_html

www.crest.org/renewables/biomass_info/carbon.shtml

2.2 Calorific value of different types of fuels used in cooking stoves

Calorific value of supplied fuel is a prime data for calculation of efficiency of a stove.

Calorific value of fuel is taken as the input energy while determining the efficiency of

stoves. In practical aspects, due to contamination of different substances and ways of

fuel extraction, calorific values of any fuel varies from specimen to specimen.

2.2.1 Regional Wood Energy Development Programme (RWEDP) in Asia

(GCP/RAS/154/NET) has mentioned calorific values of different fuels in their

publication "Energy and Environment Basics" July 1997. (table # 4)

Table # 4

Fuel Density (kg/nr) Calorific Values (MJ/kg)

LPG 560 45.5

Kerosene 806 43.1

Gasoline (Petrol) 720 44.0

Coal N. A. 29.3

2.2.2 Prof. H S Mukunda (Indian Institute of Science) mentions the calorific values

of cook stove fuels in his publication entitled "Understanding Combustion" as

below in table ~ 5. These values are quite different from values shown in table # 4.

Table # 5

Fuel Calorific Values (MJ/kg)

Bio Gas 32 - 36

Kerosene 42

LPG 44

Producer Gas

2.2.3 According to "Energy Sector Synopsis Report" of 1992/93. published by His

Majesty's Government of Nepal Ministry of Water Resources. Water and Energy

Commission Secretariat. Perspective Energy Plan Supporting Document No. 1. the

calorific values of fuels are shown in table # 6.

Table # 6

Fuel Kilo calories/kg or liter Calorific Values (MJ/kg)

Biogas 5.8 24.28

LPG 11.76 49.24

Kerosene 8.66 36.26

Petrol 8 33.49

As the calorific values of fuel varies that directly affect the value of efficiency

regardless of same experimental and calculation procedure. For each specimen of fuel

the calorific value has to be determined by using a bomb calorimeter. This would

give accurate result in determining the efficiency of stoves under experiment.

2.3 Stove Construction

. The other major factor, which affects the efficiency of the stove, is the constructional

feature of the stove. Biogas stoves are found in market in different shapes and

constructional features. Constructional features of biogas stove which, affect the

efficiency are:

a. Burner type (holes in the burner and their orientation and burner size).

b. Space between burner and tripod or other vessel supporting mechanism.

c. Air control ring and vent, which ensures perfect combustion of fuel.

3. Methodology:

Efficiency of cook stoves could be calculated by several methods. In this study

efficiency of cook stoves was determined by calculating the heat gained by the water

subjected for heating and amount of fuel consumed during this process. In this study,

heating process is classified as Low Power Phase and High Power Phase. Heating

of water from initial water (subjected to boiling) temperature T|°C to boiling point

is termed as High Power Phase(HPP). During this phase water in vessel gains energy

from fuel with the help of burning stove and that value of energy is equivalent to

energy required to raise the temperature of that mass of water from T|°C to boiling

point. In Low Power Phase predetermined weight of water at boiling point was subjected

to boil for five minutes and energy gained by this water is calculated by multiplying

latent heat of vaporization (Lwboii) of water and mass of vaporized water. Fuel consumed

during each process is the input energy for these phases. Overall efficiency is calculated

by dividing output energy by input energy. In this process we have to include the

heat gained by vessel in which water was boiled. Hence.

Heat gained by vessel = Mv * Sv * (Tb - Ti) Joule

Heat gained by water in HPP= Mw * Sw * (Tb - T,) Joule

Heat gained by water in LPP = (Mstesm *Lwboil) Joule

Energy of fuel = (Mfule * Kfuel) Joules

Where.

Mv = Mass of vessel

Sv = Specific heat capacity of vessel

(Tb – T1) = Change in temperature (from Tl to boiling Point)

Mw = Mass of water

Sw = Specific heat capacity of water

Msteam = Mass of evaporated water during LPP

LWboil = Latent heat of boiling of water

Mfuel = Mass of consumed fuel

Kfule = Calorific Values of Fuel

Efficiency (overall) ={MW*SW* (Tb - T,) + (Msteam *Lwboil) + Mv * Sv * (Tb - T,) } /

( Mfule * Kfulel)

Efficiency (overall) = {Heat gained by water in HPP + Heat gained by water in LPP

+Heat gained by vessel} / {Quantity of fuel consumed * unit calorific

values of fuel}

Hence, heat gained by vessel (made from aluminium) is equal to heat gained from T1°C to

Tboil °C and heat gained by water is equal to the summation of heat gained during High

Power Phase and Low Power Phase.

Fuels like Liquefied Petroleum Gas and Kerosene could be weighted by weighing

machines. Mass of cylinder or stove before and after experiment gives the mass of fuel

consumed. But for Biogas, measurement of flow of gas is essential, which gives the

amount of biogas consumed during experiments.

Constants taken for calculation∗ :

■ Specific Heat Capacity of Water = 4190 J/kg °C

■ Specific Heat Capacity of Aluminium = 125 J/ kg °C

■ Calorific value of Kerosene = 42 MJ/kg

■ Calorific value of LPG = 44 MJ/kg

■ Calorific value of biogas = 22 kJ/Lit

Experimental Setup:

Setup for Efficiency Measurement of Biogas Stove:

∗ Source: H S Mukunda, 1998, Understanding Combustion , Macmillan India Limited

Experimental Setup for Kerosene Stove

4. Results 4.1 Efficiency test of biogas stove: Different testing conditions were maintained during experiment. Efficiency biogas stoves for each condition is depicted below. a. Perfectly controlled condition

Water (kg)

Water Evaporated

(kg)

Gas Consumed

in HPP (Liter)

Gas Consumed

in LPP (Liter)

Mass of Vessel

(kg)

T1 Deg °C

T2 Deg

°C

E1out (kJ)

E2out (kJ)

Energy gained by vessel (kJ)

Ein1 (kJ)

Ein2 (kJ)

Efficiency %

1 0.118 36 22 0.49 32 95.5 266.1 3139 357 792 484 49445

b. Semi-controlled condition

Water Water Gas Gas Mass of T1 T2 E1out E2out Energy gained Ein1 Ein2 Efficiency(kg) Evaporated Consumed Consumed Vessel Deg Deg (kJ) (kJ) by vessel (kJ) (kJ) %

(kg) in HPP in LPP (kg) °C UC (kJ) (Liter) (Liter)

0.5 .072 21 16 0.48 24.5 95.5 148.7 191.5 4.26 462 352 438

c. Uncontrolled condition

Water (kg)

Water Evaporated

(kg)

Gas Consumed

in HPP (Liter)

Gas Consumed

in LPP (Liter)

Mass of Vessel

(kg)

T1 Deg °C

T2 Deg °C

E1out (kJ))

E2out (kJ)

Energy gained by vessel (kJ)

Ein1 (kJ)

Ein2 (kJ)

Efficiency %

0.5 0.096 33 25 0.48 24 965 151.9 2554 4 35 726 550 32.26 Where,

Water (kg):- Mass of water at T|"C subjected to test. Water Evaporated: - Mass of water evaporated on low Power Phase (boiling water for five minutes),

Gas HPP: - Volume of gas consumed during I high Power Phase, Gas LPP: - Volume of gas consumed during Lowe Power Phase, Tl: - Initial temperature of water subject to test, T2: - Boiling temperature of water, Elout: - Energy gained by water during High Power Phase, E2out: - Energy gained by water during Low Power Phase, Einl: - Energy content of fuel consumed during I high Power Phase and Einl: - Energy content of fuel consumed during Low Power Phase

Efficiency of cook stove were measured in different conditions for different

types of stoves. For a biogas stove (single burner type manufactured by NMC

Butwal, Nepal) efficiency measurement was carried out for different state of flame,

namely: Perfectly controlled, semi- controlled and uncontrolled. Besides that

experiment was carried out for different adjustments to air control ring. Perfectly

controlled flame indicates the condition of cooking instant when flame from burner is

equal or smaller than the bottom face of the cooking vessel. At that condition no

flame could be seen on top view of vessel. For Perfectly controlled flame the efficiency

of cook stove goes maximum. When the flame from the burner could be seen partially

on top view of vessel then this condition is assumed as semi-controlled flame condition

for cooking. For this condition the overall efficiency of stove is less than the perfectly

controlled condition but cooking process gets faster. When size of flame from

burner is large enough than the bottom size of vessel, most of the flame goes

outwards and this condition is termed as uncontrolled flame condition.

4.2 Efficiency test of Kerosene stoves:

a. Pressure Stove: Down Tank. 01mm burner. Brass Tripod, one-liter capacity

Observation Water (kg)

Water Evaporated

(kg)

Consumed Kerosene

(kg)

Mass of Vessel

Energy gained by Vessel(kj)

Tl "C

T2 °C

El out (kJ)

E2out (kJ)

Ein (kJ)

Efficiency %

1 2.02 0.1414 0.06 0.56 4.9 26.5 96.5 592.5 376.1 2520 38.62 2 1.01 0.075 0.03 0.49 3.89 33 96.5 273 199.5 1260 37.8

Average = 38.21%

b. Wick fed Stove: Down Tank, one-liter capacity

Observation Water (kg)

Water Evaporated

(kg)

Consumed Kerosene

(kg)

Mass of Vessel (kg)

Energy gained by Vessel (kj)

Tl °C

T2 °C

El out (kJ)

E2out (kJ)

Ein (kJ)

Efficiency %

1 1.515 0.1 0.045 0.49 4.22 27.5 96.5 438 266 1890 37.24 2 1.01 0.1 0.035 0.48 4.14 27.5 96.5 292 266 1470 38.2 3 2.02 0.15 0.065 0.56 4.83 27.5 96.5 584 412 2730 36.6

Average = 37.37%

4.3 Efficiency test of LPG stoves:

Observation Water (kg)

Water Evaporated

(kg)

onsumed LPG (kg)

Mass of Vessel (kg)

Energy gained by Vessel (Id)

Tl "C

T2 "C

Elout (kJ)

E2out (kJ)

Ein (kJ)

Efficiency %

1* 2.02 0.16 0.045 0.56 5.005 25 96. 605.2 425.6 1980 52.31 2 1.515 0.12 0.032 0.49 4.25 27 96.5 441.2 319.2 1408 54.30 3 1.58 0.13 0.035 0.49 4.28 26.5 96.

5463.4 345.8 1540 52.82

Average = 53.15%

5.0 Example*

In case of LPG stove with aluminium vessel containing two liter of water.

Energy Gained by water in High Power Phase = Mass of water x Specific Heat

Capacity of

Water x Rise in Temperature

= 2.02 x 4.19 x (96.5-25) kJ = 605.2 kJ

Energy Gained by Vessel = Mass of Vessel x Heat Capacity of Vessel x

Rise in temperature

= 0.56 x 0.125 x (96.5-25) kJ

= 5.005 kJ

Energy Gained by water in Low Power Phase = Mass of Water vaporized x Latent Heat of

Boiling of Water

= 0.16* 2660 kJ

= 425.6 kJ

Energy content of consumed fuel = Quantity of Fuel x energy content of unit

amount of fuel

= 0.045 x 44 xl03kJ

=1980 kJ

Hence, Overall Efficiency = [(Energy gained by water in HPP + Energy gained by water in LPP + Energy Gained By vessel) / Energy content of consumed fuel] x 100%

= [(605.2 + 425.6 + 5.005) / 1980] x 100% = 52.31%

6. Conclusions The efficiency of biogas stove calculated as per adopted methodology mentioned above is

found to be 49.44%. 43.8% and 32.26% for perfectly controlled, semi-controlled and

uncontrolled conditions. The efficiency of a given stove is not constant. It could vary on

the basis of surrounding conditions and quality of fuel used. A high value of efficiency

could be obtained under controlled conditions. But in practice this value is normally lower than

the value found in the controlled laboratory condition. The efficiency of stove depends upon

following conditions:

a. Environmental conditions, such as wind, temperature, pressure

b. Shape, specific heat capacity and weight of vessel.

e. Burner size of stove and size of bottom face of cooking vessel.

d. Energy content of fuel and quality of fuel

7. Recommendations

a. Further study is essential for improvements of biogas stove and other types of stoves

for different purpose of cooking and conditions.

b. Actual efficiency measurement could be determined only when actual calorific value

of fuel is known. For this, calorific values at laboratory should be measured where

efficiency measurement of stoves is to be conducted.

c. Efficiency of biogas stoves under operation in different locations, of Nepal should

carried out as soon as possible and after analyzing the result necessary actions

should be taken so that energy from biogas plant is used as effectively as possible.

d. The users of biogas plants have to be informed on optimum application of

flame flaring.

8. References

■ RWEDP Bangkok. (July 1997). "Energy and Environment Basics". RWEDP Report No.

29

■ Mathias Gustavsson ( 2000). "Biogas Technology-Solution in Search of Problem", A

Study of Small-Scale Rural Technology Introduction and Integration. Human Ecology

Reports Series 2000:1

■ H S Mukunda. (1998). "Understanding Combustion" , Indian Institute of Science,

Published by Macmillan India Limited

■ B Lai & S. Sub. (1998). "Heat and Thermodynamics". Published by S.Chand and

Company. India

■ http: //www .he.au.se

■ vvww.seen.org/energy

■ www.rterrin.0rg/renew/biogas

■ www. gate.gtz.de/vaxtnaring/anna/mrsminh.htm

■ www.panasia.ore.se/nepalnet/technology

■ www'.fao.ore/sd/EGdirect

■ www, newenerev.ore.cn

■ www.msek.lth.se

■ www.climatechaneeindia.com

■ www.citvfarmer.ore

■ www.bspnepal.com/biogas

Annexes Annex-1

//Computer program in C++ to calculate the efficiency of stoves #include<stdio.h> #include<stdlib.h> #include<conio.h> void main (void)

{ float Mv.Mvv.Mf.Sv.Svv.Tl.Tb.Lwb.Mew.Kf:

clrscr( );

// Data input

printf("\nEnter Mass of vessel in kg = ");

scanf("%f. &Mv);

printf("\nEnter Specific Heat CApaciry of Vessel in kJ/kg'degree centigrade = ");

scanf("%f". &Sv);

printf("\nEnter Initial Temperature of Water in degree centigrade = ");

scanf("o/of'. &T1):

printf( "'nEnter Boiling Point Temperature of Water degree centigrade = ");

scanf("%f. &Tb):

printf("\nEnter Mass of Water in kg= ");

scanf("%f'. &Mw);

printf("\nEnter Specific Heat Capacity of Water in kJ/kg'Degfree

centigrade = ");

scanf("%f. &Sw);

printf("\nEnter Latent Heat of Boiling for Water in kJ = "):

scanf("%f", &Lwb);

printf("\nEnter Mass of fuel in Kg or Litre = "):

scanf("%f". &Mf);

printf("\n Enter Calorific value of fuel in kJ/kg or in kJ/litre = ");

scanf("%f'. &Kf);

printf("\nEnter Mass of evaporated water in kg = ");

scanf("%f'. &Mew);

//Calculation and output

printf(" The Overall Efficiency of stove is %f %", 100.*((Mw*Sw*(Tb-

T1 ))+(Mew* Lwb)+(Mv*Sv*(Tb-T 1 )))/(Mf* Kf));

}

//End of program

Annex-2

Software Execution

Biogas Efficiency on uncontrolled flame condition

Enter Mass of vessel in kg = .48

Enter Specific Heat Capacity of Vessel in kJ/kg/degree centigrade = .125

Enter Initial Temperature of Water in Degree centigrade = 24

Enter Boiling Point Temperature of Water degree centigrade = 96.5

Enter Mass of Water in kg= .5

Enter Specific Heat Capacity of Water in kJ/kg/Degfree centigrade = 4.19

Enter Latent Heat of Boiling for Water in kJ = 2660

Enter Mass of fuel in Kg or Litre = 58

Enter Calorific value of fuel in kJ/kg or in kJ/litre = 22

Enter Mass of evaporated water in kg = .096

The Overall Efficiency of stove is 32.256858 %