energetics of coal substitution by briquettes of agricultural residues
TRANSCRIPT
Energetics of coal substitution by briquettes of agricultural residues
Pallav Purohit, Arun Kumar Tripathi, Tara Chandra Kandpal*
Centre for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
Received 20 March 2005; accepted 28 June 2005
Abstract
The suitability of using biomass briquettes to substitute coal is debatable, as a substantial amount of energy is
required for briquetting of biomass. In the present work, an attempt to evaluate the energetic viability of
briquetting of agricultural residues compared with the energy embodied in coal in India has been made.
Briquetting of agricultural residues is not found to be an energetically viable option even for locations at a distance
of about 1500 km from the coal pithead (even if the briquetting unit is located very close to the place of availability
of the agricultural residues). A need for transportation of agricultural residues further pushes this critical distance
upwards.
q 2005 Published by Elsevier Ltd.
1. Introduction
Biomass is the third largest primary energy resource in the world, after coal and oil [1]. In all its
forms, biomass currently provides about 1250 million tonnes oil equivalent (mtoe) of primary energy
which is about 14% of the world’s annual energy consumption [2–3]. The use of biomass feedstock(s)
for the substitution of fossil fuel(s) has an additional importance from climate change considerations
since biomass has the potential to be CO2 neutral. Research and development efforts towards the
conversion of raw biomass feedstocks into improved quality fuels (solid, liquid or gas) through
biological and thermo-chemical conversion processes have been made globally in the last three decades.
Agricultural residues constitute one of the important biomass feedstocks in India, due to its vast
agricultural base. The decreasing availability of fuelwood in most of the developing countries has
necessitated that efforts be made towards efficient utilization of agricultural residues [4–5]. Raw
agricultural residues have many disadvantages as an energy feedstock [6]. These include (i) relatively
Energy 31 (2006) 1321–1331
www.elsevier.com/locate/energy0360-5442/$ - see front matter q 2005 Published by Elsevier Ltd.
doi:10.1016/j.energy.2005.06.004
* Corresponding author. Tel.: C91 11 26591262; fax: C91 11 26582037.
E-mail address: [email protected] (T.C. Kandpal).
P. Purohit et al. / Energy 31 (2006) 1321–13311322
low calorific value, (ii) variability of quality and calorific value, (iii) difficulty in controlling the rate of
burning, (iv) rapid burning, necessitating frequent refueling, (v) difficulty in mechanizing continuous
feeding, (vi) large volume or area required for storage, and (vii) problems in its transportation and
distribution. Several of these disadvantages may be attributed to the low bulk density of agricultural
residues. To improve the characteristics of agricultural residues for transportation, storage, feeding into
furnaces and combustion, it may be necessary to upgrade the raw agricultural residu by increasing its
bulk density. The advantages of briquetting of agricultural residues for boiler applications are that (i) the
rate of combustion can be comparable to that of coal, (ii) burning in grate-fired boilers is possible, (iii)
uniform combustion can be achieved, (iv) particulate emissions can be reduced, (v) the possibility of
spontaneous combustion in storage is reduced, and (vi) transportation, storage and feeding is made more
efficient. Other possible areas of applications of briquetted agricultural residues include firing in
residential, commercial and industrial heating systems. They can also be used as fuel in wood stoves,
external combustion engines and as raw material for pyrolysis and gasification [6].
Some of the commonly used agricultural residues for briquetting in India include arhar stalk, cotton
stalk, mustard stalk, maize stalk, groundnut shells, rice husk, tamarind shells, coir pith, sun flower stalk,
etc. [5]. Raw agricultural residues for briquetting can be broadly divided into three categories (i) fine
granulated, (ii) coarse granulated, and (iii) stalky. In each of these categories, it is possible to make use
of both dry and wet raw materials. Another classification stems from the fact that beside raw agricultural
residues, briquettes of pyrolysed agricultural residues can also be made. Finally, briquettes can also be
categorized on the basis of whether or not a binding material is used in briquetting. Briquetting of raw
agricultural residues without binder is more commonly practiced in India [5]. The factors that mainly
influence the selection of raw materials are moisture and ash contents, flow characteristics and particle
size. Moisture content in the range 10–15% is preferred because grinding of high moisture content
materials is problematic, and more energy is required for drying [4]. The ash content of agricultural
residues affects its slagging behavior together with the operating temperature and mineral composition
of ash. The granular (preferably 6–8 mm in size) homogeneous materials, which can flow easily in
conveyors, bunkers and storage silos, are suitable for briquetting [4–5].
Agricultural residues have several other competing applications which include their use as fuels for
domestic cooking, water and process heating, fodder for livestock, feedstocks for fertilizer, materials for
roof construction, direct burning in boilers, etc. However, due to the availability of substantially large
amounts of a wide variety of agricultural residues in the country it is possible to use non-fodder, non-
fertilizer agricultural residues as fuels to meet industrial process heating requirements. Some of these
agricultural residues are presently used directly as boiler feedstock.
Coal accounts for about 67% of the total primary energy consumption in India. Transportation of
coal between production and consumption points requires considerable energy inputs. In India, about
53.5% of coal is transported by the railways [7]. In view of high ash content (and low calorific value)
of Indian coal and consequently higher cost of transportation and associated adverse environmental
implications the possibility of using briquettes of agricultural residues as a substitute for coal in
boiler applications in India is being explored. However, a substantial amount of energy is required
for briquetting of agricultural residues. It may therefore be necessary to critically analyze the
energetic viability of using briquettes of agricultural residues for substituting coal in boiler
applications. In this study, an attempt has been made to evaluate the energetic viability of briquetting
of agricultural residues compared with the energy embodied in transportation of coal. The primary
energy embodied in coal mining and transportation of unit amount of coal (from the coal pithead to
P. Purohit et al. / Energy 31 (2006) 1321–1331 1323
the end use point) per unit of useful energy delivered by coal has been estimated and compared with
the primary energy embodied in the briquettes of agricultural residues (at the end use location) per
unit of useful energy delivered by briquettes. The results of the study can be used to identify niche
areas for briquetting of agricultural residues.
2. Analysis
2.1. Availability of agricultural residues
Availability of agricultural residues as energy feedstocks depends upon the total amount of crop
produced, residue to crop ratio for the crop, collection efficiency (which also includes storage-related
considerations), and amount used in other competing applications. The effective crop residue availability
for ith crop (Reff,i) per unit amount of crop produced can therefore be expressed as
Reff;i Z RCið1KAiÞð1KBiÞ (1)
where RCi represents the residue to crop ratio for ith crop, Ai the fraction of the total amount of crop-
residue lost in collection, transportation, storage, etc. and Bi the fraction of remaining crop residues used
in other competing applications.
2.2. Critical distance of coal transportation
At the end-use location, the total primary energy embodied in coal depends upon the energy used in
coal mining, and its transportation from coal pit-head to the end-use location [8–11]. Mining of coal
includes various operations such as hoisting, drilling, ventilation, dewatering, break and convey and
ancillary [10–12]. The primary energy embodied in coal (EIc) at the end use location can be estimated as
EIc Z EIcm CEIFTctDplc (2)
where EIFTct represents the primary energy intensity of freight transportation (MJ/tonne-km), Dplc the
distance (km) between the coal pithead and end-use point, and EIcm the primary energy embodied in coal
mining (MJ/tonne).
The primary energy embodied in coal per unit of useful energy delivered (PEIc) can be expressed as
PEIc ZEIcm CDplcEIFTct
CVchc
� �(3)
where CVc represents the calorific value of coal (MJ/kg) and hc the efficiency of utilization (fraction) of
coal in the boiler.
Briquetting of agricultural residues primarily involves drying, grinding, sieving, compacting and
cooling operations. Any moisture in the raw material (wet agricultural residues) is first removed in a
dryer [5], and the dried material is ground in a hammer mill grinder. The ground material is then passed
through a screen for sieving and thereafter stored in a bin placed over the briquetting press to ensure a
regular flow of materials into the press. The ram in the press continuously packs the material through a
taper die and the briquettes are produced [5].
P. Purohit et al. / Energy 31 (2006) 1321–13311324
The total primary energy embodied in briquettes of agricultural residues may normally consist of (a)
share of energy used in crop production, harvesting, etc., (b) energy embodied in transportation of agri-
cultural residues to the briquetting plant, (c) energy embodied in briquetting, and (d) energy embodied in
packaging, storage and transportation of briquettes to the end use point. Therefore, at the end use location,
the total primary energy embodied in briquettes of agricultural residues, EIb, (MJ/tonne) can be estimated
as
EIb Z EIcropg CEIbtDfl CEIb (4)
where EIcrop (MJ) represents the energy embodied in crop production, g the energy embodied in the
production of agricultural residues as a fraction of EIcrop, EIbt the primary energy intensity of freight
transportation (MJ/tonne-km) by truck and/or trolley, Dfl the distance (km) between farm/processing unit
to the end use location, and Dfl the distance (km) between briquetting unit to the end use location.
The primary energy embodied in briquettes per unit of useful energy delivered by briquettes (PEIb) in
boiler applications, may therefore, be expressed as
PEIb ZEIcropg CEIbtDfl CEIb
CVbhb
� �(5)
where CVb represents the calorific value of the briquettes of agricultural residues (MJ/kg) and hb the
efficiency of utilization (fraction) of briquettes in boiler applications.
Local production of briquettes from raw agricultural residues can be energetically justified only if the
primary energy input embodied per unit of useful energy delivered by briquettes is less than the primary
energy input required in coal mining, preparation and transportation per unit of useful energy delivered
by coal. Therefore,
EIcm CDplcEIFTct
CVchc
� �R
EIcropg CEIbtDfl CEIb
CVbhb
� �(6)
From Eq. (6) the critical distance of coal transportation beyond which briquetting of agricultural
residues could be preferred over coal transportation, Dplc, can be determined as
Dplc Z1
EIFTct
� �CVchc
CVbhb
� �ðEIcropg CEIbtDfl CEIbÞKEIcm
� �(7)
By comparing the energy embodied in coal mining and transportation with the energy embodied in
transportation and briquetting of agricultural residues (i.e. the energy embodied in crop production has
not been taken into account) The critical distance of coal transportation, DðIÞplc, can be estimated as
DðIÞplc Z
1
EIFTct
� �CVchc
CVbhb
� �ðEIbtDfl CEIbÞKEIcm
� �(8)
In the case of on farm briquetting (i.e. there is no need of agricultural residues transportation), the
critical distance of coal transportation, DðIIÞplc , can be estimated as
DðIIÞplc Z
1
EIFTct
� �CVchc
CVbhb
� �EIbKEIcm
� �: (9)
P. Purohit et al. / Energy 31 (2006) 1321–1331 1325
3. Key assumptions and input parameters
Agricultural residues are the most commonly used biomass feedstocks for briquetting in India [5,13].
Table 1 presents some of the alternative uses of agricultural residues along with the agricultural residue
availability (kg) per tonne of grain produced based on the available data on residue to crop ratio [14]. It
may be noted that wheat straw is used as cattle feed in rural India. Paddy straw is used as domestic fuel,
as cattle feed, in manufacturing straw board, as a raw material for paper and hardboard units, as packing
material for glasswares, etc. Similarly, bagasse is mostly used for meeting the thermal energy
requirement of sugar mills. Therefore, in this study these agricultural residues have not been considered
for biomass briquetting.
Using the simple framework briefly presented in Section 2 estimated potential availability of
agricultural residues for energy applications of some crops in different states is presented in Table 2 [14,
15]. For the estimates presented in Table 2, the fraction of the total amount of agricultural residues lost in
collection, transportation and storage, etc. has been assumed as 0.10 and the fraction of remaining
amount of agricultural residues used in other competing applications has been taken as 0.15 [14].
Coal is one of the primary fuels used in boiler applications in India [16]. Therefore, in this study it is
assumed that (i) the user has only two options to meet the thermal energy demand-use of either coal or
agricultural residues, (ii) it is advantageous to use the agricultural residues in the form of briquettes and
not in loose or raw form (either the agricultural residues cannot be used directly or it is technologically
more efficient/convenient/economic to use it as briquettes instead of direct firing) and (iii) either of the
fuels (coal or briquettes of agricultural residues) is used independently (i.e. co-firing is not considered).
The values of the input parameters used in Eqs. (2–9) for studying the energetics of coal substitution
by briquetting of agricultural residues of some commonly used agricultural residues are given in Table 3
Table 1
Agricultural residue availability (kg) per tonne of grain produced and its alternative uses [14]
Crop Crop-residue Residue to
crop ratio
Agricultural residue
availability (kg) per tonne
of grain produced
Potential alternative uses
Groundnut Groundnut
shell
0.33 330 Domestic fuela, cattle feed
Wheat Wheat straw 1.47 1470 Cattle feed
Paddy Rice husk 0.33 330 Domestic fuel, cattle feed, construction
materials etc.
Paddy straw 1.53 1530 Domestic fuel, cattle feed, straw board, raw
material for paper and hardboard units,
packing material for glasswares, etc.
Sugarcane Bagasse 0.25 250 Energy feedstock in sugar mills, Paper and
pulp industry
Cotton Cotton stalk 3.00 3000 Domestic fuel
Arhar Arhar stalk 1.32 1320 Domestic fuel
Corn Corn cobs 0.30 300 Domestic fuel
Corn stalks 1.56 1560 Cattle feed, domestic fuel
Jute Jute sticks 2.30 2300 Domestic fuel
Mustard Mustard stalks 1.85 1850 Domestic fuel
a Domestic fuel for cooking, water heating and space heating.
Table 2
Estimated annual potential availability of agricultural residues for energy applications in different states of India
State Agricultural residues (million tonnes)
Rice husk Corn
stalks
Corn cobs Groundnut
shells
Cotton
stalks
Arhar
sticks
Mustard
stalk
Coconut
coir
Punjab 2.33 0.55 0.11 NA* 0.47 NA 0.10 NA
Haryana 0.68 NA NA NA 0.54 NA 0.78 NA
Rajasthan NA 1.21 0.23 0.05 0.32 NA 1.85 NA
Gujarat 0.26 0.74 0.14 0.17 0.45 0.11 0.33 NA
Uttar Pradesh 2.94 1.78 0.34 0.03 NA 0.50 1.27 NA
Kerala 0.19 NA NA NA NA NA NA 840.89
Maharashtra 0.50 0.26 0.05 0.12 0.70 0.67 NA 37.33
Tamilnadu 1.84 0.23 0.04 0.37 0.13 0.06 NA 483.17
Karnataka 0.95 2.52 0.48 0.23 0.38 0.26 NA 268.36
West Bengal 3.17 0.11 0.02 NA NA NA 0.59 50.64
Andhra Pradesh 2.92 1.71 0.33 0.51 0.65 0.22 NA 167.23
Madhya Pradesh 0.24 1.43 0.28 0.06 0.09 0.23 0.51 NA
Bihar 1.38 1.74 0.34 NA NA 0.06 0.14 NA
Orissa 1.18 NA NA 0.02 NA 0.08 NA 16.83
Assam 1.02 NA NA NA NA NA 0.20 20.81
Chattisgarh 0.83 NA NA NA NA NA NA NA
Jharkhand 0.42 0.13 0.03 NA NA 0.03 NA NA
Goa NA NA NA NA NA NA NA 19.13
Himachal Pradesh NA 0.81 0.16 NA NA NA NA NA
Jammu and Kashmir NA 0.63 0.12 NA NA NA NA NA
Others 0.79 0.56 0.11 0.02 0.04 0.05 0.18 22.95
All India 21.64 14.40 2.77 1.57 3.76 2.28 5.96 1927.34
NA, not available.
P. Purohit et al. / Energy 31 (2006) 1321–13311326
[5,7,11,13,16,17]. In India, F-grade coal is predominantly being used for boiler applications [17,18].
Therefore, in this study, it is assumed that the briquettes of agricultural residues substitute F-grade coal
with a calorific value of 14 MJ/kg [16]. The value of energy intensity of freight transportation of coal
through railways has been taken as 0.23 MJ/tonne-km [17]. Due to unavailability of data the values for
primary energy consumption in coal mining has been taken from Doctor et al. [11]. A 1000 kg/h capacity
briquetting unit based on piston press technology has been considered in this study. The energy intensity
of freight transportation by trucks has been taken as 1.15 MJ/tonne-km [17].
Table 4 presents the primary energy embodied in briquette production for piston press type
briquetting machines of different briquette production capacities manufactured by a leading
manufacturer in India [5,13]. However, as per sample studies carried out by independent agencies,
these losses have been estimated to be as high as 50% in some states. As per the report on the Working of
State Electricity Boards and Electricity Departments of the Planning commission, out of the total
electricity generated, nearly 7% is used for auxiliary consumption and 30–31% is lost in the
Transmission and Distribution [19]. To estimate the primary energy embodied in briquette production
the average transmission and distribution losses of electricity have been taken as 22% [17]. The overall
efficiency of coal thermal power plants is assumed to be 35% [17,18]. It may be noted that drying of
agricultural residues requires a substantial amount of energy. For a 1000 kg/h briquetting unit, in case of
Table 3
Input parameters used in studying the energetics of coal substitution by briquettes of agricultural residues
Parameter Symbol Unit Value
Energy intensity of freight transportation by goods train EIFTct MJ/tonne-km 0.23
Calorific value of coal (F-grade) CVc MJ/kg 14.04
Efficiency of utilization of coal in the boiler hc Fraction 0.85
Efficiency of utilization of biomass feedstock in the boiler hb Fraction 0.80
Average losses in electricity transmission and distribution – Fraction 0.22
Overall primary energy to secondary energy conversion efficiency
of the coal thermal power plant
– Fraction 0.35
Energy intensity of freight transportation (road transport by
trucks)
EIbt MJ/tonne-km 1.15
Distance between farm/processing unit to the end-use location Dfl km 100
Primary energy consumption in coal mining EIcm MJ/tonne 187.4
P. Purohit et al. / Energy 31 (2006) 1321–1331 1327
the fine granulated material (such as rice husk, saw dust, coffee husk, etc.) the energy embodied in the
briquetting of wet agricultural residues is 30% higher than the energy embodied in the briquetting of dry
agricultural residues. In India, agricultural residues are also transported by truck/trolley from the farm/
processing unit to the briquetting plant [13,16]. Three values of the distance of agricultural residue
transportation has been taken (50, 100 and 200 km) for comparing the energy embodied in coal mining
and transportation with the energy embodied in agricultural residue transportation and briquetting for the
delivery of the same amount of useful energy.
4. Results and discussion
Agricultural residue availability (kg) per tonne of grain produced and its alternative uses presented in
Table 1 indicate that groundnut shell, rice husk, cotton stalk, arhar stalk, corn cobs, corn stalks, jute
sticks and mustard stalks are some of the potential feedstocks for the energy applications in the country.
Estimated annual availability of agricultural residues for energy applications in different states of India
is presented in Table 2. The annual potential of rice husk for energy applications in Punjab and Uttar
Pradesh has been estimated to be 2.33 and 2.94 million tonnes, respectively. Similarly, the annual
Table 4
Primary energy requirements of biomass briquetting units [6]
Briquette production
capacity (kg/h)
Primary energy requirement (MJ/tonne)
Fine granulated material Coarse granulated material Stalky material
Dry Wet Dry Wet Dry Wet
250 923 1398 1899 2374 2295 2769
500 659 897 1147 1385 1345 1582
750 571 730 1029 1187 1292 1451
1000 666 864 1332 1530 1530 1727
1500 576 708 954 1086 1086 1218
2250 574 662 826 914 914 1002
Table 5
Estimates for critical distance of coal transportation for different agricultural residues
Agricultural
residue
Calorific
value
(MJ/kg)
Primary energy
intensity of biomass
briquetting (MJ/
tonne)
Critical distance of coal transportation (km)
With agricultural residue transportation Without agricul-
tural residue trans-
portation
Dry
material
Wet
material
Dry material Wet material Dry
material
Wet
materialDflZ50
DflZ100
DflZ200
DflZ50
DflZ100
DflZ200
Groundnut
shell
18.81 1332 1530 3963 4160 4556 4643 4841 5237 3765 4446
Rice husk 13.38 666 864 2683 2961 3517 3641 3919 4475 2405 3363
Saw dust 18.48 666 864 1718 1919 2322 2411 2612 3015 1517 2210
Cotton stalk 17.85 1530 1727 4937 5146 5563 5651 5860 6276 4729 5443
Arhar stalk 14.85 1530 1727 6098 6349 6849 6956 7207 7707 5848 6706
Coconut
coir
17.79 666 864 1815 2024 2443 2535 2744 3162 1606 2326
Coffee husk 17.56 666 864 1850 2062 2486 2580 2792 3215 1639 2368
Corn cobs 15.23 1530 1727 5926 6170 6658 6762 7006 7495 5682 6518
Corn stalks 13.79 1530 1727 6628 6898 7437 7552 7822 8361 6359 7282
Jute sticks 19.00 1530 1727 4588 4784 5175 5259 5454 5846 4393 5063
Mustard
stalks
18.81 1530 1727 4643 4841 5237 5321 5519 5914 4446 5123
P. Purohit et al. / Energy 31 (2006) 1321–13311328
potential of mustard stalk for energy applications in Rajasthan and Uttar Pradesh has been estimated to
be 1.85 and 1.27 million tonnes, respectively. The results indicate that the northern states of the country
such as Punjab, Haryana, Rajasthan, Uttar Pradesh and Gujarat have large amounts of agricultural
residues available for energy applications.
Estimated values of the critical distance of coal transportation beyond which briquetting of
agricultural residues is found to be an energetically viable option are presented in Table 5 for the cases
of both dry and wet agricultural residues. It may be noted that the critical distance of coal transportation
to ensure the energetic viability of briquetting agricultural residues strongly depends upon the
characteristics of the agricultural residues. For the case of agricultural residue transportation distance of
100 km, the estimates for the critical distance of coal transportation vary from a value of 1919 km for
saw dust to 6898 km for corn stalks. In the case of wet agricultural residues, the critical distance varies
from 2612 km for saw dust to 7822 km for corn stalks. In the case of on farm briquetting, the estimates of
critical distance of coal transportation have been found to vary from 1517 km for saw dust to 6359 km
for corn stalks for dry feedstocks. The critical distance varies from 2210 km for saw dust to 7282 km for
corn stalks in the case of wet feedstocks.
Fig. 1 presents the results of a sensitivity analysis undertaken to study the effect of uncertainties
associated with some of the important input variables. The critical distance of coal transportation is
found to be quite sensitive to the efficiency of utilization of briquettes of agricultural residues in the end
use device, energy intensity of freight transportation of coal, energy intensity of briquettes of agricultural
residues, efficiency of utilization of coal, and calorific value of coal. The other factors, such as, distance
Fig. 1. Sensitivity analysis for critical distance of coal transportation for a 1000 kg/h briquetting unit in case of saw dust with
respect to (i) calorific value of coal CVc, (ii) efficiency of utilization of agricultural residues in the end use device nb, (iii)
efficiency of utilization of coal in the end use device nc, (iv) energy intensity of agricultural residues transportation EIbt, (v)
energy intensity of briquette of agricultural residues EIb, (vi) energy intensity of freight transportation of coal EIFTct, (vii)
energy intensity of coal mining EIcm, (viii) distance between farm to the end use location Dfl.
P. Purohit et al. / Energy 31 (2006) 1321–1331 1329
between farm to the end use location, energy intensity of agricultural residue transportation, and energy
intensity of coal mining have a rather moderate effect on the critical distance of transportation of coal.
In India, most of the coal production is restricted to the eastern and south-eastern parts of the country
(i.e. the states of Jharkhand, Orissa, Chattisgarh, West Bengal, Andhra Pradesh and Assam). However,
the consumers for boiler applications are also located in north and north-western states (i.e. the states of
Rajasthan, Gujarat, Haryana, Uttar Pradesh and Punjab) of the country. The use of coal in the northern
states of India may necessitate transportation of coal to distances more than 1000 km. Some of these
states are major crop producing states with substantial availability of agricultural residues. Briquetting of
locally available agricultural residues may not be an energetically viable option for boiler applications
even at these locations.
Some of the typical locations and their distance from the Jharia coal field are mentioned in Table 2.
The distance of these energy end use locations is far below from the estimates of the critical distance of
coal transportation presented in Table 5. The critical distance of coal transportation (Table 5) is very
high as compared to the actual distance of some typical locations from coal pit head (Table 2). This
clearly justifies the energetic unavailability of coal substitution by biomass briquettes.
P. Purohit et al. / Energy 31 (2006) 1321–13311330
5. Concluding remarks
The estimates of the critical distance beyond which briquetting of agricultural residues could be an
energetically viable option are presented. It is found that even for places at moderate distances from the
coal pithead, briquetting of agricultural residues could not be an energetically preferred option over coal
for boiler applications. It is worth mentioning that briquetting technology in India has not yet reached
maturity and there is considerable scope for design improvements, leading to increased reliability and
reduced energy consumption for the briquetting of agricultural residues. The scope of this study is
restricted to the comparison of the primary energy embodied in coal mining and transportation of unit
amount of coal (from the coal pithead to the end use point) per unit of useful energy delivered by coal
with the primary energy embodied in the briquetting of agricultural residues (at the end use location) per
unit of useful energy delivered by briquettes due the unavailability of detailed data.
Acknowledgements
The financial assistance provided by the Council of Scientific and Industrial Research (CSIR), New
Delhi to the first author (Pallav Purohit) is gratefully acknowledged.
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