Gasification of tea (Camellia sinensis (L.) O. Kuntze) shrubs for black tea manufacturing process heat generation in Assam, India Partha Pratim Dutta a, *, Debendra Chandra Baruah b a Department of Mechanical Engineering, Tezpur (Central) University, Assam, 784028, India b Department of Energy, Tezpur (Central) University, Assam, 784028, India article info Article history: Received 1 May 2012 Received in revised form 29 March 2014 Accepted 31 March 2014 Available online 26 April 2014 Keywords: Biomass Gasification Shrubs Tea drying Process heat Payback period abstract Gasification of uprooted tea shrub (Camellia sinensis (L.) O. Kuntze) is an attractive option for partial substitution of thermal energy in tea manufacturing industries. Chopped and dried uprooted tea branches with moisture content (X < 20%) have high energy contents suitable to generate process heat. Good number of tea processing units in Assam use old design and inefficient coal fired furnace and air heater with a low overall efficiency. Gasification of uprooted tea shrubs may be beneficial partially to substitute these old design coal fired furnaces. The calorific values of uprooted tea branches and generated producer gas were found 18.50 MJ kg 1 and 4.2 MJ m 3 , yielded products at 65% cold gasification efficiency. Fermented tea samples with an average moisture content of 60% could be dried to 3% moisture using biomass gasifier and tea dryer setup. Simple economic analysis shows gasifier cum tea dryer technology may be economically favorable option with an annual saving of 21,067 $ in a medium scale tea factory (990 t per year made tea) if 28% of total thermal energy requirement is substituted by biomass gasification. ª 2014 Elsevier Ltd. All rights reserved. 1. Introduction Tea cultivation and processing units are second most impor- tant after oil and gas industries in Assam. Assam black tea production in the year 2010e11 was estimated as 0.488 Mt which alone accounted for about 50% of all India production [1]. Tea drying is a highly energy intensive chemical engi- neering unit operation amongst all the tea manufacturing operations. The sources of thermal energy for tea drying process in factories located in Assam has been fossil fuel consisting natural gas, furnace oil (known as tea drying oil) and coal. One or more than one sources are used based on local availability and economy. The specific energy consumption (coal) in commercial tea drying has been reported within the range of (0.8 to 1.13) kg kg 1 of made tea. The reported variation could be due to varying level of per- formances and overall efficiency of energy conversion de- vices. Variations of specific energy requirements for tea processing were also observed amongst the fuel types. Specific energy consumptions while using tea drying oil, coal and natural gas had been reported as (23.88, 43.72 and 27.49) MJ kg 1 of made tea respectively [2]. Overall, based on production and average specific energy consumption rate, an estimated 9.42 PJ equivalent thermal energy was found to consume annually for drying operation in tea factories of Assam. The volatile prices and other environmental factors of fossil fuels have caused uncertainties to continue relying on these fossil * Corresponding author. E-mail address: [email protected](P.P. Dutta). Available online at www.sciencedirect.com ScienceDirect http://www.elsevier.com/locate/biombioe biomass and bioenergy 66 (2014) 27 e38 http://dx.doi.org/10.1016/j.biombioe.2014.03.062 0961-9534/ª 2014 Elsevier Ltd. All rights reserved.
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b i om a s s a n d b i o e n e r g y 6 6 ( 2 0 1 4 ) 2 7e3 8
Available online at w
ScienceDirect
http: / /www.elsevier .com/locate/biombioe
Gasification of tea (Camellia sinensis (L.) O. Kuntze)shrubs for black tea manufacturing process heatgeneration in Assam, India
Partha Pratim Dutta a,*, Debendra Chandra Baruah b
aDepartment of Mechanical Engineering, Tezpur (Central) University, Assam, 784028, IndiabDepartment of Energy, Tezpur (Central) University, Assam, 784028, India
b i om a s s a n d b i o e n e r g y 6 6 ( 2 0 1 4 ) 2 7e3 8 37
manufactured was assumed as 2 t ha�1 to compute annual
black tea production for a representative average size tea es-
tate. The total back tea production was calculated by multi-
plying yield of black tea by total mapped area of the tea estate
[32].
Annual black tea manufactured by an average size tea es-
tate in Sonitpur district (Assam) was 990 t (GIS mapping). The
corresponding coal requirement is 792 t (Coal 0.8 kg kg�1 of
black tea manufactured). It was also observed from this study
that thermal efficiency was 20% for a conventional coal fired
furnace and 80% for proposed producer gas fired furnace.
Therefore producer gas fired furnace is a better option over
coal fired system. Coal international prices was 95 $ t�1, Birol
et al. [33] and that of woody biomass was 11 $ t�1 in the year
2011. A 150 kW thermal woody biomass gasifier was consid-
ered that could substitute 28% of this thermal load [34]. The
payback period of the system is 15 months and benefit to cost
ratio 1.22 (Tables 7, 8 and 9). The annual carbon-dioxide
reduction 1299.5 t is achievable [35]. It is a very attractive op-
tion in addition to green fuel application in teamanufacturing,
emission reduction, waste utilization and clean development
mechanism.
4. Conclusions
There are potential advantages in application of gasification
technology for tea manufacturing industries in Assam, India.
The surplus uprooted tea branches, shrubs, shading trees are
in house generation of biomass in a tea manufacturing unit.
Therefore, a downdraft gasifier performance with uprooted
tea shrubs as feed stock and its economics in thermal mode
to substitute conventional inefficient coal fired furnace have
been summarized in the present studies. The uprooted tea
shrub has high energy densities (18 MJ kg�1, HHV) for gasifi-
cation. It was observed that gasifier under study performed
well in respect of gas quality given by gas chromatograph and
calorific value at 0.27 equivalence ratios. The maximum
volumes of CH4, H2 and CO were reported as 1.4%, 18% and
24% respectively at above equivalence ratio. The average
calorific value was observed as (4.2 MJ m�3) from Junker Gas
Calorimeter. This is a satisfactory result with uprooted tea
shrubs as gasifier feed stock. The maximum cold gasification
efficiency was found as 65% near air fuel equivalence ratio of
0.27 and then it declined by increasing the gas flow rate. It
may be concluded that if only 28% thermal energy for tea
drying comes from biomass gasification in a typical medium
scale tea estate, the annual net saving in fuel cost is
computed as 21,067 $ and equivalent reduction of CO2
emission of 1299.5 t. A 150 kW biomass gasification unit can
give rise to a payback period of 15 months and hence the
investment seems attractive and environmentally sustain-
able for tea estate of Assam, India. However, the proposed
28% thermal energy requirement may not be possible by in-
house generation of above biomass in a representative tea
estate. Supplementary plantation of some fast growing vari-
ety trees in addition to biomass generated from tea planta-
tion itself may be required. Wherever there is a scarcity of in
house biomass production, deficit biomass may be procured
from nearby market.
Acknowledgment
DST_SERB Research Project Government of India (2012e2015):
Development of an innovative model of Combined Heat and
Power from Purely Producer Gas Based Engine Alternator
System for Partial Conventional Energy Substitution of Tea
Processing Industries in North-East India.
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Nomenclature
AAFR: actual air fuel ratioASTM: American Society of Testing MaterialCV: calorific valueD: diameter of gas flowing pipeFC: fixed carbonFD: forced draftFn: future amount of money at end of n yearFSD: full scale deflectionGC: gas chromatographHHV: higher heating valueID: induced drafti: rate of interestkW: kilowattMNRE: Ministry of New and Renewable Energyn: numbers of yearsNPV: net present valueP: principal amountDPG: pressure drop across gasifierDPN: pressure drop across nozzleSAFR: stoichiometric air fuel ratioVM: volatile matterWBG: woody biomass gasifierX: moisture percentage (wet basis)
Greek symbols
F: air fuel equivalence ratiohcold_gas: cold gasification efficiency