THERMAL ENERGY DEMANDS OF THE TEA INDUSTRY AND THE ROLE OF FUELWOOD TREES IN A SELF SUSTAINING ENVIRONMENT

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1 S. L. J. Tea Sci. 64 (1), 43-50, Prined in Sri Lanka. THERMAL ENERGY DEMANDS OF THE TEA INDUSTRY AND THE ROLE OF FUELWOOD TREES IN A SELF SUSTAINING ENVIRONMENT W. C. A. de Silva 1 (Tea Research Insiue of Sri Lanka, Talawakele, Sri Lanka) The ea indusry is he larges indusrial consumer of fuelwood. To buffer escalaing coss of fuclwood as well as o minimize soil degradaion, esablishmen of environmen friendly self susaining wood energy sysems is suggesed. Taking ino consideraion hermal energy demands in ea processing as well as demands for fuclwood by he esae domesic secor, empirical formulae are presened for purposes of planning ou wood energy planaion a esae/facory level. Means already available or likely o be available in he fuure for improved/reduced wood energy uilizaion by he ea indusry are described. INTRODUCTION The wo main indigenous sources of energy in Sri Lanka are hydro power and biomass (fuelwood). The balance of he energy demand is me by impored oil. As a now, he ea indusry which is he larges indusrial consumer of fuclwood is heavily dependen on fuelwood supplies from rubber planaions, and o a lesser exen on foress and oher non-fores wood los a individual esae level. Rubberwood is now gaining in populariy as imber and lesser and lesser will be available in he fuure for use as fuclwood and ha oo a escalaing coss as shown below in Table 1. In his scenario, in he foreseeable fuure he ea indusry may be forced o mee is energy demand by eiher impored oil or by urning owards foress (naural or man-made) for fuclwood requiremens. Boh hese opions migh creae environmenal degradaion. To mee his siuaion, in he shor erm i is essenial o develop self susaining environmen friendly wood energy sysems a subregional/individual esae level and o adop improved wood energy uilizaion hrough beer echnologies of conversion. In he long erm, replacemen of wood energy, a leas parially, wih non radiional forms of energy needs o be considered. 'Paper presened a 88h Annual Sessions of The Insiuion of Engineers, Sri Lanka held a he BMICH, Colombo in Ocober

2 TABLE 1 - Prices paid for fuelwood delivered o S. Joachim facory during he period 1975 o 1994 Year Price (Rs/cub. yd) / / / / / / /- Energy demand by he ea indusry From an energy poin of view he ea indusry in Sri Lanka is he larges fuelwood consumer uilizing approximaely 33% of he indusrial consumpion. A he same ime i is he larges consumer of elecriciy and one of he major consumers of fuel (Hasening, 1989). Wood fuel/hermal energy demand In he ea indusry fuelwood is required a) for generaion of ho air for wihering b) for generaion of ho air for drying. c) o mee he demand from Esae household secor. The moisure conen of harvesed ea leaf is in he range of 70-80% (we basis) and in wihering operaions moisure conen is reduced o a level ha lends iself o he uni operaions of rolling and roll breaking. A his sage he acceped level of moisure depends on he mehod of manufacure adoped being 54±1.5% (we basis) for high/mid-grown eas having liquoring characerisics; 59±2% (we basis) for low growns manufacured for leaf syle o sui markes in he Middle Eas; and 70 ±2% (we basis) for CTC eas o sui markes requiring small leaf grades having hick coloury liquors. Rolled leaf afer he process of fermenaion (essenially enzymic oxidaion/ polymerizaion of ea polyphenols) is subjeced o he uni operaion of drying. In his operaion he moisure conen is reduced o 3% in eiher Endless Chain Tray Driers or Fluidizcd Bed Driers supplied wih ho air from eiher Air Heaers or Seam Boiler/ Radiaor Sysems. Prior o he oil crisis in 1974, mos up-counry facories and o a lesser exen facories in oher areas resored o he use of oil for hermal energy needed for generaion of ho air in wihering and drying. The reason was obvious oil lends 44

3 iself o beer conrol of operaing parameers and he addiional cos was no of much significance. Wih he oil crisis his siuaion changed and he Indusry by and large sacrificed conrol over process parameers o achieve cos savings. Today, oher han a few facories producing high qualiy eas (corresponding o abou 15% of oal producion), use of fuclwood for he generaion of hermal energy is he common pracice. Considering he recommended operaing parameers during wihering and drying operaions, hermal energy requiremens calculaed heoreically ogeher wih acual hermal energy usage observed in high/mid and low-counry facories by analysis of hisorical daa suppored by daa from energy audis (de Silva, 1993) are presened in Table 2. TABLE 2 - Thermal energy consumpion in ea processing uni operaion wise (MJ/kgMT) MidlUp-counlry Low-counry Acual Lowes Acual Lowes calculaed calculaed limi limi Wihering Drying (Convenional) Toal Thermal energy and mass flow during wihering and drying per uni of made ea for up-counry and low-counry facories using heoreically possible and observed values are depiced in Fig. 1. UP/MID-COUNTRY 2.28 kg MOISTURE 1.22 kg MOISTURE 4.50 kg G. L. ^ WITHERING -» 2.22 kg W. L.-» DRYING 1 kg M. T. 9.0 MJ (ACTUAL) 13.0 MJ (ACTUAL) 5.6 MJ (THEOR) 10.0 MJ (THEOR) LOW-COUNTRY 2.12 kg MOISTURE 1.38 kg MOISTURE 4.50 kg G. L. WITHERING -> 2.38 kg W. L.-> DRYING 1 kg M. T. 9.0 MJ (ACTUAL) 13.7 MJ (ACTUAL) 5.6 MJ (THEOR) 11.2 MJ (THEOR) Fig. 1 - Thermal energy and mass flow for ypical up-counry and low-counry facories (heoreical and acual basis) 45

4 From he above he oal average hermal energy usage in ea processing (wihering and drying) could be aken as 22.4 MJ per kg of made ea. As already saed mos ea facories depend on fuelwood for hermal energy requiremens. The moisure conen of fuelwood used varies from 25 o 45% and depending on his, fuelwood demand for ea processing varies from 1.8 o 2.2 kg fuclwood/kg made ea a fuelwood moisure conens of 25 o 35% respecively. A saisically designed sudy of household fuel consumpion conduced in 1983 has shown ha he per capia consumpion of biomass fuel for household cooking was 496 kg yr 1 for he island as a whole and 526 kg yr 1 for he rural secor, which used biomass fuel exclusively (Wijcsinghe, 1984). The recenly conduced Foresry Maser Plan revision sudies (unpublished daa) have shown ha in he esae secor he per capia fuelwood consumpion varies from 606 kg yr 1 in he Badulla disric o 770 kg yr 1 in he Nuwara Eliya disric. Up o he presen ime he esae domesic requiremen of fuelwood has been largely me by he removal of prunings and o a lesser exen from shade rees and oher ouside sources. I is ineresing o noe ha on a 4 - year pruning cycle he average fuelwood yield from prunings is 13.1 m-'ha' 1 (Nanayakkara, 1986) which is consisen wih TRI findings for seedling ea. Prunings, if used as fuelwood, are sufficien o susain he household fuelwood requiremens of a labour force (including children and dependens) of 2.7 o 3.4 per hecare based on a per capia consumpion of 606 o 770 kg yr' 1 a a fuelwood moisure conen of 20%. However, removal of prunings causes environmenal soil degradaion and o mainain a susainable ea growing environmen, ea prunings should be kep in he fields for mulch while domesic requiremen of fuelwood by labour should be me from oher sources. Self susaining wood energy sysems should be planned, based on he aforemenioned esimaes for fuelwood consumpion by he indusrial and household arms of he ea indusry. The proporion of land ha should be se apar for his purpose mus ake ino accoun he produciviy of he esae (yield/hecare), specific fuelwood consumpion in processing (kg kg" 1 MT), mean annual incremen of fuelwood species (m 3 ha" 1 an 1 ) seleced for planing and is years of roaion, as well as he esae household populaion densiy (persons/hecare). Addiional areas under fuelwood would be necessary for facories dealing wih ouside leaf. A he same ime he energy policy of an Esae/Facory mus be inegraed wih he overall developmen objecives. Self susaining wood energy sysems If he demand is o be me a esae level he land area ha should be se apar for fuelwood in ea processing and for he esae household secor, could be esimaed 46

5 by he following formula: 8(PF + 770p) Af =.A ; A f 0 (Ms) [Nomenclaure used is given in Appendix] This formula was derived aking ino consideraion all he influencing facors already enumeraed. Applicaion of formula o develop self susaining wood energy sysems ]) Case of planaions For an esae of 400 ha yielding 1,500 kg yr 1 he land area required (subdivided ino equal los depending on roaion years) under say Eucalypus grandis wih a Mean Annual Incremen of 42.5 m 3 ha"' an" 1 on a 10 year roaion, depending on varying condiions, are as follows : a) Caering o he needs of processing esae leaf only. A specific fuelwood consumpion of i) 2 kg kg"' MT Af = A (i.e. 11.3% of ea area) ii) 1.5 kg kg"' MT Af = A (i.e. 8.5% of ea area) b) Caering o he needs of processing esae leaf (requiring 2 kg kg" 1 MT) and esae household secor (assuming a populaion densiy of 4 persons per hecare of ea in bearing). Af = A (i.e. 22.9% of ea area) c) Caering o he needs of i) processing esae leaf (600,000 kg MT)' ' fuelwood usage a 2 kg kg" 1 MT ii) processing ouside leaf (120,000 kg MT) iii) Esae household secor (populaion densiy of 4 persons/hecare of ea) Af = A (i.e. 25.1% of ea area) 47

6 2) Case of bough leaf facories Consider he case of a bough leaf facory depending on village labour for producion. In his siuaion he formula giving he land area required o mainain a susainable supply of fuelwood reduces o 8 KF Af = ; A = 0 (Ms). 10' Thus for a bough leaf facory, for example, producing 750,000 kg MT annum" 1 a a fuelwood consumpion rae of 2 kg kg"' MT, he area required under Eucalypus grandis (wih MAI OF 42.5 m 3 ha' 1 an"' ) o mainain a susainable supply of fuelwood is abou 56 ha. Improved wood energy uilizaion The presen wood combusion sysems used in he ea indusry hough simple are quie waseful and his is furher aggravaed by he use of fuelwood wih high moisure conens. Saving energy is as good as creaing/growing i. Thus, here is a need for improvemen of wood energy uilizaion hrough beer echnologies of conversion. Even hough air drying of fuelwood from abou 50% (we basis for fresh wood) o abou 20% moisure (we basis) has been advocaed, his is hardly adhered o by he Indusry for various reasons. The moisure conen of fuclwood as used by he ea indusry varies from 25% o 45%. A saving of 8.4% in fuelwood could be achieved by he use of fuelwood dried o 20% moisure when compared wih he use of fuelwood a 45% moisure. Savings could be furher enhanced o abou 10% if furnace flue gases are used o reduce he moisure level o 10%. A he same ime, even hough he use of spli firewood (45cm or 18" by 20 cm or 8" girh) has been advocaed, very many facories coninue o feed logs o furnaces. The use of cu fuelwood in opimum size pieces will help o reduce fuelwood consumpion by a leas a furher 10-15%. Thus i is seen ha spliing and drying is a criical fuclwood conservaion measure. If his pracice is adoped immediae oal saving of abou 22% is wihin he reach of he ea indusry. I mus also be conceded ha he presen wood combusion sysems used in he ea indusry hough simple are quie waseful. Improvemens in air heaer efficiencies could be achieved by using economizer or addiional hea exchanger o uilize residual hea in flue gases from exising air heaers. However ulimaely he presen low efficien wood fired air heaers need o be replaced wih beer designed heaers having efficiencies of he order of 75%. Such air heaers obained under a programme funded by he Neherlands Governmen were field esed in wo facories (Haskoning, 1990). Even hough hese furnaces were concepually sound hey were mechanically defecive, 48

7 resuling in consan furnace failures under operaing condiions in our facories. From he experience gained, a local engineering firm has now designed and commissioned an air heaer giving a minimum efficiency of 75%. Counry-wide applicaion of such air heaers will lead o fuelwood saving of a leas 50%. Improved wood energy uilizaion could also be brough abou by wood gasificaion. Field esing of wo gasifier sysems are in progress a he low-counry saion of he Tea Research Insiue. Performance daa indicae ha fuel savings of he order of 30-50% could be achieved once echnical problems associaed wih wood gasificaion are overcome. Non-radiional energy resources Peering ino he fuure, he use of solar energy in Sri Lanka is paricularly aracive as number of day ligh hours per year exceeds 4,000 wih inense direc sunligh exceeding 1,800 h year 1 in mos ea growing disrics. Use of solar collecors o obain he full energy requiremens of drying/wihering will be cos prohibiive. However, use of low cos fla plae collecors using as far as possible locally available maerials for pre-heaing air (wihou sorage) needed in drying operaions during day hours needs invesigaing. This will be carried ou in a projec sponsored by SAREC wih he Universiy of Peradeniya and Royal Insiue of Technology, Sockholm collaboraing wih he TRI. A solar fracion of 30% of energy requiremens in drying is aimed a. REFERENCES DE SILVA, W. C. A. (1993). Saus review of energy uilizaion of he ea indusry in Sri Lanka pp In Energy Prespecive in Planaion Indusry, eds, Planaiappan, G, Kumar, S. and Haridasan, T.M.) Kean Anad, India. I1ASKON1NG, Royal Duch Consuling Engineers and Archiecs (1989). Energy Conservaion in he ea indusry of Sri Lanka, 206pp. HASKONING, Royal Duch Consuling Engineers and Archiecs (1990). Repor on he monioring of wo fuelwood fired efficien, air heaers for he ea indusry in Sri Lanka, 25pp & Annexures. NANAYAKKARA, V. R. (1986). Wood Energy Sysems for rural and oher indusfrics (Sri Lanka). FAO publicaion. 88pp. WIJESINGHE, L. C. A. de S. (1984). A sample sudy of biomass fuel consumpion in Sri Lanka households. Biomass 5,

8 i Appendix NOMENCLATURE Af = Area under fuelwood (hecares) A = Area under ea (hecares) F = Specific fuelwood consumpion in ea processing, reckoned a 20% M.C. for fuelwood (kg -1 MT) K = Producion of ouside (bough) leaf (kg MT an 1 ) M = Mean Annual growh incremen (MAI) of species seleced for fuelwood (m 3 ha" 1 an 1 ) P = Facory Producion/hecare of ea in bearing (kg MT ha 1 ) defined by (Y+K/A) P = Populaion densiy of household secor (persons/ha) r = Roaion years of fuelwood species s = Specific graviy of fuelwood species (dimcnsionlcss) Y = Yield Produciviy of Esae (kg MT ha"' an" 1 ) NON STANDARD ABBREVIATIONS USED GL - Green Leaf MT - Made Tea WL - Wihered Leaf MC - Moisure Conen 50