Data & Analytics

Characterisation of biomass resources in Nepal and assessment of potential for increased charcoal production

Description
Characterisation of 27 types of biomass was performed together with an assessment of regional resource availability. Charcoal was produced under two conditions from all samples and their yields were compared. Sugarcane bagasse, sal and pine produced
Published
of 13
0
Published
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Share
Transcript
  Contents lists available at ScienceDirect Journal of Environmental Management  journal homepage: www.elsevier.com/locate/jenvman Research article Characterisation of biomass resources in Nepal and assessment of potentialfor increased charcoal production J. Hammerton a, ∗ , L.R. Joshi b , A.B. Ross a , B. Pariyar c , J.C. Lovett c,d , K.K. Shrestha b , B. Rijal b ,H. Li a , P.E. Gasson d a  School of Chemical and Process Engineering, University of Leeds, LS2 9JT, UK  b Central Department of Botany, Tribhuvan University, Kathmandu, Nepal c  School of Geography, University of Leeds, LS2 9JT, UK  d  Royal Botanic Gardens, Kew, Richmond, TW9 3AE, UK  A B S T R A C T Characterisation of 27 types of biomass was performed together with an assessment of regional resourceavailability. Charcoal was produced under two conditions from all samples and their yields were compared.Sugarcane bagasse, sal and pine produced the best charcoal with a low volatile matter and high calori 󿬁 c value.The amount of high-quality charcoal which can be made within Nepal from the biomass types tested isequivalent to 8,073,000 tonnes of   󿬁 rewood a year or 51% of the yearly demand. The areas which would bene 󿬁 tthe most from charcoal making facilities are the Mid-hills of the Western, Central and Eastern DevelopmentRegions, as well as the Terai in the Central and Eastern Development Regions. The main potential bene 󿬁 t is toconvert agricultural residues which are underutilised because, in their srcinal form, produce large quantities of smoke, to cleaner burning charcoal. The conversion of agricultural residues to charcoal is also a viable alter-native to anaerobic digestion in the Mid-hills. 1. Introduction Nepal is a country which is highly dependent on traditional biomassenergy resources, contributing 85% of the total energy consumption(Pokharel, 2007). Fossil fuels account for 14%, and modern biomass(e.g. briquettes and biogas) and other renewables contribute a mere 1%of the total energy consumption (Water and Energy CommissionSecretariat (W.E.C.S.), 2013). Between the years 2000 – 09, the energyconsumption increased by 20%, 13% and 125% from traditional, fossilfuel and renewable types respectively (W.E.C.S., 2010). The traditionalsolid fuel types which contribute the most to the total energy con-sumption are: fuelwood (71.1%), animal dung (5.1%) and agriculturalresidue (3.5%) (W.E.C.S., 2014). Biomass is expected to remain themost important energy source in Nepal for at least the next 30 years(W.E.C.S., 2013).The residential sector accounts for 88% of the energy used, over half of which is for cooking (W.E.C.S., 2010). Approximately 64% of households primarily use  󿬁 rewood for heat and cooking and 10% usecow dung (National Planning Commission Secretariat (N.P.C.), 2012).The remaining households use clean-burning fuels, most frequentlyL.P.G., but also biogas and kerosene (N.P.C., 2012).The use of traditional biomass combustion technologies, especiallyfor cooking, is of serious concern in Nepal and other developingcountries because the pollutants emitted by the burning of biomass in acon 󿬁 ned space cause serious health problems, leading to the prematuredeaths of approximately 3.3 million people per year worldwide (WorldHealth Organisation, 2014). Smoke from indoor biomass burning isassociated with illnesses such as chronic obstructive pulmonary disease(Perez-Padilla et al., 2010). Switching to charcoal for heating andcooking is one option to reduce the amount of indoor smoke pollution(Obeng et al., 2017).Conversion of biomass resources into charcoal is performed by aprocess called pyrolysis. Volatile matter, which is associated withsmoke emissions, is converted to  󿬁 xed carbon, which burns hotter andslower, therefore improving the safety and value of the material as acooking fuel (Bautista et al., 2009; Protásio et al., 2017). The energy density is also improved making it easier to transport than the un-treated biomass it is made from (Konwer et al., 2007; Somerville and Jahanshahi, 2015).Agricultural residues are an underutilised source of energy with just6% of the total used in Nepal (Webb and Dhakal, 2011). Residues haveother uses which need to remain, as fodder for example, but it is still https://doi.org/10.1016/j.jenvman.2018.06.028Received 13 October 2017; Received in revised form 5 June 2018; Accepted 10 June 2018 ∗ Corresponding author.  E-mail address:  pmjh@leeds.ac.uk (J. Hammerton). Journal of Environmental Management 223 (2018) 358–3700301-4797/ © 2018 Elsevier Ltd. All rights reserved.    estimated that 75% of the total energy need for cooking could be metwith this fuel type (K.C. et al., 2011). W.E.C.S. (2014) estimated higher,suggesting that the energy potential of agricultural residues is largerthan the total yearly  󿬁 rewood consumption. One reason for the un-derutilisation is the increase in indoor air pollution when used com-pared to  󿬁 rewood (Das et al., 2017). Pyrolysis is one thermochemicalroute to converting residues to a clean fuel. It is, however, limited inthat high moisture content materials are unsuitable as the evaporationof this water creates signi 󿬁 cant energy losses. Residues, such as strawand potato tops are therefore more suited to anaerobic digestion as aconversion method to clean biofuels (Mussoline et al., 2013; O'Toole et al., 2013; Parawira et al., 2008; Wu et al., 2012). The main crops by output in descending order are: rice (27.9%), sugarcane (18.3%), maize(12.6%), potato (11.8%) and wheat (10.4%) (Ministry of AgriculturalDevelopment (M.O.A.D.), 2014).Natural forests are the main source of household fuel but havehistorically been under pressure for conversion to agriculture and fromoverexploitation. In Nepal, a period of deforestation began shortly afterthe nationalisation of the nation's forests in 1957, replacing communityforestry systems that had previously been successful (Pokharel, 2003).Reintroduction of community forestry policies in the 1990s sig-ni 󿬁 cantly reduced the rate of deforestation (Shrestha et al., 2014). Byputting forests under the control of local communities, those using themhave an interest in preserving the resource. Between the years of 2010 – 2015, the area of land covered by forest was unchanged (Foodand Agricultural Organization (F.A.O.), 2015). In 2013, there wereover 17,810 community forest user groups (C.F.U.G. ’ s) controlling1,665,419ha (K C et al., 2015). An estimate from 2008/09 quanti 󿬁 esthe amount of sustainable  󿬁 rewood available in reachable areas as 12.5million tonnes per year- 80% from forests, 9% from cultivated land andthe rest from shrubland, grassland and non-cultivated inclusion (landpredominantly used for grazing) (W.E.C.S. 2010). The majority of the 󿬁 rewood from forests is produced on land controlled by C.F.U.G. ’ s,totaling 7.1 million tonnes per year (W.E.C.S. 2010).Forests in Nepal are diverse owing to the range of climates occurringfrom the large variation in altitude. In the more tropical Terai along thesouth of the country, the dominant species is  Shorea robusta , knownlocally as sal (Paudel and Sah, 2015). In the Mid-hills, which covers58% of the nation, the forests are varied containing pine and broadleaf species such as  Schima wallichii, Alnus nepalensis, Pinus roxburghii  and  Rhododendron  spp. (Pandey et al., 2014). Forests in the Mountains re-gion mostly consist of conifers, oak and  Rhododendron  spp. (Rana et al.,2016).There are many studies relating to the consumption of   󿬁 rewood inNepal, but there are often marked di ff  erences in the results obtained.Frequently, this is a result of the methods employed to estimate use. Fox(1984) found that a survey asking respondents for an average of thequantity of   󿬁 rewood they burn on a hot and a cold day was a factor of two higher than a weight survey of wood collected. Other reasons forthe large discrepancy in consumption estimates have been thought to becaused by the array of climates, forest accessibility, education and casteleading to a range of 200 – 2000kg per person per year (kg/ppyr) of  󿬁 rewood consumed (Webb and Dhakal, 2011). A study by Rijal and Yoshida (2002) weighing the amount of collected  󿬁 rewood found theaverage  󿬁 rewood (including crop residues) consumption in a mountainregion was 1130kg/ppyr but as little as 348kg/ppyr in a Mid-hillsregion. However, the survey was brief with only a small number of households involved over few measurement days. Most studies estimatethe average  󿬁 rewood consumption in the range of 450 – 700 kg/ppyr(Bhattarai, 2013; Fox, 1984; Kandel et al., 2016; Pokharel, 2003; Shrestha, 2005; Webb and Dhakal, 2011). Nepal et al. (2010) used a survey containing a nationally re-presentative sample of 3912 households to investigate how the type of cookstove and main fuel use a ff  ects 󿬁 rewood consumption. It was foundthat the type of biomass cookstove had little impact on the amount of  󿬁 rewood used. Households reporting to predominantly use kerosene/gas cookstoves used less  󿬁 rewood, but a signi 󿬁 cant amount was con-sumed for other activities.The aim of the paper is to identify biomass available in Nepal whichis suitable for charcoal making. The geographical distribution of sui-table resources is also assessed and compared to where demand forbiomass fuels exist to determine which locations could bene 󿬁 t mostfrom charcoal making. 2. Materials and methods  2.1. Estimation of   󿬁 rewood consumption throughout Nepal Data on  󿬁 rewood use by stove used in households from Nepal et al.(2010) and census data on households were used to make an estimate of the regional biomass demand (N.P.C., 2012). From the data, it wasestimated that households on average used 2.62 tonnes of biomass peryear if woodstoves were used and 1.50 tonnes if kerosene/gas stoveswere used. The census data was then used to calculate the regionalconsumption of   󿬁 rewood by multiplying the two cookstove factors bythe number of households reporting each cookstove type.  2.2. Sample collection The 󿬁 eld sites for collection of biomass samples represent the typicalMid-hills physiography in Central Nepal (Fig. 1). The sites lie within thethree adjoining districts  viz.  Kathmandu (the capital city of Nepal, co-ordinates: 27°33 ′ 48.9 ″ - 27°58 ′ 38 ″  N and 84°48 ′ 49.5 ″  - 85°15 ′ 22.5 ″  E),Makawanpur (coordinates: 27°33 ′ 49.8 ″  - 27°36 ′ 22.5 ″  N and 83°12 ′ 18 ″  -85°13 ′ 07.1 ″  E) and Dhading (coordinates: 27°56 ′ 40 ″  - 28°02 ′ 30.4 ″  Nand 84°48 ′ 51.1 ″  - 84°51 ′ 23 ″  E) districts within the elevation rangesfrom 500m to 1870m above sea level (A.S.L.). Agricultural residueswere collected from the market and/or households in Kathmandu andArughat.A total of 27 di ff  erent types of biomass were chosen, 12 tree species,4 shrubs, 4 herbaceous plants and 7 agricultural residues. The selectionwas based on the total quantity throughout Nepal. After analysis of theraw material and charcoal produced from them, the samples werenarrowed further, focusing on the most relevant types for charcoalproduction. Additional information regarding the location of collectionsites is contained in Appendix 1. The tree species selected were:  Alnusnepalensis  (Nepalese alder),  Castanopsis inidica  (chinkapin),  Choer-ospondias axillaris  (Nepali hog plum),  Ficus semicordata  (drooping  󿬁 g),  Lagerstroemia parvi  󿬂 ora  (crepe myrtle),  Melia azedarach  (chinaberry),  Myrica esculenta  (box myrtle),  Pinus roxburghii  (pine),  Quercus seme-carpifolia  (oak),  Rhododendron arboreum  (rhododendron) and  Schimawallichii  (schima) and  Shorea robusta  (sal). All were collected fromNepal and exported for analysis, except for  Shorea robusta  which cannotbe legally exported for analysis. An alternative non-living sample wassourced from the Royal Botanic Gardens, Kew, srcinally collected fromDarjeeling, India. The shrubs collected were:  Gaultheria fragrantissima (fragrant wintergreen), the invasive  Lantana camara  (wild sage),  Lyoniaovalifolia  (angeri),  Woodfordia fructicosa  ( 󿬁 re  󿬂 ame bush) and  Zan-thoxylum armatum  (winged prickly ash). The herbaceous plants were:  Artemisia indica  (oriental mugwort), the invasive  Eupatorium adeno- phorum  (crofton weed), and  Thysanolaena maxima  (Nepalese broomgrass). The agricultural residues were:  Brassica campestris  (rapeseedmustard),  Eleusine coracana  ( 󿬁 nger millet straw),  Oryza sativa  (ricehusk),  Saccharum o  ffi cinarum  (sugarcane bagasse) and  Zea mays  (maizecob, stover and shell).Samples from each of the forestry plants were obtained from theprimary branch of mature specimens. The circumference of the primarybranch of specimens sampled was less than 25cm. The reason isbranches with larger circumferences are often used instead for timber.  J. Hammerton et al.  Journal of Environmental Management 223 (2018) 358–370 359   2.3. Sample preparation During collection, the biomass samples were cut into approximately30cm long pieces unless the size was already less, for example, maizecob. The initial weights of the samples were recorded and then air driedfor 3 – 5 days. The larger sized samples were chipped and passed througha 10mm sieve in a Retsch Cutting Mill SM 100. All the samples werethen further micronized and homogenised using a grinder.  2.4. Proximate and ultimate analysis The proximate values (moisture, volatile matter,  󿬁 xed carbon andash) of each of the untreated and charcoal samples were determinedusing a Mettler Toledo TGA/DSC 1 Thermo-Gravimetric Analyser(T.G.A.). Approximately 10mg of sample was  󿬁 rst heated to 105°C inan inert atmosphere. The associated weight loss during this step re-presented the percent moisture content. The sample was then heated to900°C- the mass loss during this section determined the volatile content.The gas  󿬂 owing through the analyser was switched from nitrogen to airto burn the remaining  󿬁 xed carbon. The ash content was measured asthe remaining material after the test. Ultimate analysis was determinedusing a Thermo EA112 Flash Analyser. Oxygen was calculated by dif-ference from the sum of carbon, hydrogen, nitrogen and ash on a drybasis. Calori 󿬁 c value is approximated using Dulong's formula(Wanignon Ferdinand et al., 2012). The energy recovery (E.R.) is de-termined by: =  E R mass yield x charcoal gross calorific valueraw sample gross calorific value . . (%) (1)Energy recovery quanti 󿬁 es how much of the srcinal energy fromthe sample is retained in the charcoal made. Proximate and ultimateanalysis for all species sampled can be found in Appendix 2.  2.5. Inorganic analysis To a quartz tube, 10ml of 69% nitric acid and 0.2g of biomasssample was added before sealing. The sample was digested using anAnton Parr Multiwave 3000 microwave. The digested sample was thendiluted to 50ml with deionised water and  󿬁 ltered to remove any re-maining solid material. This was performed on all the collected sam-ples.The digested samples were analysed using ICP-OES to determinetrace element composition of Ca, K, Na, Mg, Cr, Cu, Fe, Li, Mn, Ni, Sr,Zn, Mo, V, Ba, Sn and S. Phosphorus was determined by colorimetryusing ammonium molybdovanadate as the chromogen. Absorbance wasmeasured at a wavelength of 430nm.X-ray Fluorescence (XRF) was also used to determine elements lesssoluble after nitric acid digestion such as aluminium and silicon. Thesamples were prepared by calcining the samples at 550°C for two hoursand then a further two hours at 900°C. The ash was collected, mixedwith lithium borate 󿬂 ux and fused at 1050°C using a Katanax K1 Prime.  2.6. Preparation of charcoal from collected samples A pyrolysis reactor (Fig. 2) was used to produce charcoal from eachof the biomass samples. It consisted of a sealed tube furnace above acondenser set to 4°C which cooled the hot gases from the furnace. Thepyrolysis tars were collected in a catchpot below the condenser. Ni-trogen was fed through the top of the furnace at a rate of 100mlmin − 1 to remove volatile compounds and create an inert atmosphere. Theexhaust gases passed through two impingers-the  󿬁 rst contained waterand the second, quartz wool to remove any further liquid or solid re-sidue in the exhaust stream. Approximately 3g of sample was added to25ml nickel crucibles, 18 of which were inserted into the tube furnacesection of the pyrolysis reactor each time. The heating rate of the Fig. 1.  Sampling locations in Nepal.  J. Hammerton et al.  Journal of Environmental Management 223 (2018) 358–370 360  furnace was between 4.5 and 7.2°C/min. The reactor was maintained atthe pyrolysis temperature for 1h under a constant  󿬂 ow of nitrogen.After this period, the heater was switched o ff   and the furnace cooled ata rate of 0.4 – 1.4°C/min. The produced charcoal samples were thenremoved from the furnace and weighed to determine the mass yield of charcoal on a percentage basis. Each sample underwent pyrolysis at twotemperatures, 400 and 600°C. At each temperature, the test was per-formed three times per sample, and the mass yield averaged.The total potential for high-quality charcoal was normalised tomake a comparison against the current consumption of traditionalbiomass in Nepal. The  󿬁 rewood equivalent (tonnes) accounts for thesuperior thermal e ffi ciency of cooking on charcoal and the increasedcalori 󿬁 c value using the equation: = × Firewood equivalent m η CV CV  charcoalcharcoal wood  (2)where m charcoal  is the total mass of charcoal that can be produced,  η  isthe increased thermal e ffi ciency factor taken as 1.5 of   󿬁 rewood(Wiskerke et al., 2010), CV charcoal  (MJ/kg) is the estimated upper ca-lori 󿬁 c value by Dulong's formula and CV wood  is the calori 󿬁 c value of wood which is approximated as 16.8MJ/kg. 3. Results and discussion Fig. 3a) shows the distribution of agricultural residues across Nepalis primarily located in the low lying Terai regions and the least in thecolder and less populated mountain regions. Fig. 3b) shows the dis-tribution of above-ground forestry growing stock across Nepal in gov-ernmental and C.F.U.G. controlled forests. The six key tree species re-present slightly over half the total growing stock of the nation's forests.Forestry stock is the highest in the Mountains and, in particular, theMid-far Western region, which is the largest by area. There is less stockin the Terai because much of the land has been cleared for growing anumber of cash crops. Of the agricultural residues present but notanalysed in this article, rice straw is the largest contributor in the Teraibut is omitted as anaerobic digestion is more suitable because of thehigh moisture content. In this region, sugarcane bagasse, rice husk andmaize residue are found in similar quantities and account for roughly aquarter of the total resource. In the Mid-hills, there is a large amount of rice residue but almost half of the agricultural residues come frommaize cropping. Within the Mountains region, there is little agriculturalresidue as it is so sparsely populated.Ministry of Forest and Soil Conservation (2009) predicted that 2.1tonnes of  󿬁 rewood can be sustainably harvested from a hectare of forestevery year in Nepal, which is 1.1% of the total mass of forestry growingstocks and approximately 10.4 million tonnes a year. The yearly mass of all agricultural residues in Nepal is more than double this  󿬁 gure. To beable to utilise agricultural residues by charcoal making, anaerobic di-gestion or other modern renewable technologies would, therefore, havegreat bene 󿬁 t to the prevention of deforestation for energy.Fig. 4a) shows the ten tree species produce charcoal with similarcharacteristics but some minor di ff  erences. The calori 󿬁 c value is similarand ranges from 25 to 28MJ/kg at 400°C, and 26 to 32.5at 600°C.Pine and sal produce the best charcoal because they contain the lowestvolatile matter, lowest ash and have a high calori 󿬁 c value at bothpyrolysis temperatures. Crepe myrtle charcoal is poor as it is high involatile matter, particularly at the lower pyrolysis temperature, and hasa low calori 󿬁 c value.In Nepal, agroforestry is also an important part of agricultural sys-tems with many species cultivated for shade, fruit, 󿬁 rewood and timber.  Schima wallichii  is common to natural forests and farmland where it iscultivated as a shade tree. Charcoal from drooping  󿬁 g and  Schimawallichii  branches are poorer than other species but are still usable asthe volatile matter is low.Fig. 4b) shows the mass yield, proximate and calori 󿬁 c values of theagricultural residues tested and their associated chars. The sugarcanebagasse charcoal produced at 600°C has the highest calori 󿬁 c value andlowest amount of volatile matter. However, the highly  󿬁 brous structureof the material makes it harder to handle and so likely requires bri-quetting (compaction by mechanical means to improve density). Maizecob is a very suitable candidate for pyrolysis if a lower temperature of 400°C is used because the proportion of volatile matter is already muchreduced. Of the maize residues, the stem is the worst part for charcoalproduction because there is more volatile matter remaining. Rice huskis a poor choice for producing charcoal because the calori 󿬁 c value islow, which results in poor combustion. Fig. 2.  Pyrolysis reactor and basket assembly for producing charcoal.  J. Hammerton et al.  Journal of Environmental Management 223 (2018) 358–370 361  There are some di ff  erences in energy recovery. Pine and  Schimawallichii  both retain less energy than other forestry species. Sugarcanebagasse, sal, crepe myrtle, chinkapin and oak have very high energyrecoveries meaning that they are more e ffi ciently converted to char-coal.The composition of the ash in the charcoal also in 󿬂 uences theburning characteristics. The build-up of deposits, fouling, on cookstovescan occur in the presence of large amounts of alkali elements becausethey melt at lower temperatures (Saddawi et al., 2012). Table 1 shows this is a potential issue for agricultural residues from maize cob andsugarcane bagasse. Liu et al. (2013) and Gómez et al. (2016) found that removing alkali metals from biomass by leaching increases the tem-perature at which devolatilisation occurs and therefore reduces smoke.As the temperature at which fuels with less alkali metal burns is higher,the heat transfer coe ffi cient will also be higher. Woody species sampledthat were found to contain low levels of alkali metals include rhodo-dendron, pine, sal, Nepali hog plum and chinaberry. The presence of high alkali metal content in agricultural residues raises questions aboutthe potential to create smoke which needs further investigation.Fig. 5 shows the regional supply for high-quality charcoal producedat 600°C and energy demand. It was predicted that the total biomassdemand in Nepal is 15,964,000 tonnes per year. The biomass demand isconcentrated within the Mid-hills and Terai of the Western, Central andEastern Development Regions. All the forestry species and agriculturalresidues, excluding rice husk, can be converted to high-quality charcoalat at 600°C. The theoretical maximum high-quality charcoal that can beproduced is 9,945,000 tonnes of   󿬁 rewood equivalent each year. Whilstthe Mountains regions contain some of the largest resources they con-tain the lowest demand. The areas with the most potential are the Mid-hills in the Eastern, Central and Western Development Regions and thecentral Terai which has a very large output of sugarcane. In the sparselypopulated Mountains regions, the demand is much less than the theo-retical source, hence the estimate is reduced by this di ff  erence(1,872,000 tonnes of   󿬁 rewood equivalent) to account for the in-feasibility of collection, production of charcoal and transport to lowerlying regions where demand is higher. After considering accessibilityand proximity of demand, the potential amount of high-quality char-coal which can be produced is estimated to be approximately 8,073,000tonnes of   󿬁 rewood equivalent a year. Compared to the current total useof biomass of 15,964,000, charcoal could provide 51% of the totalenergy need.Of the total  󿬁 rewood collected in Nepal, between 60 and 70% isthought to be collected from state and community managed forests, therest from private land (Bhattarai, 2013; Shrestha, 2005). The private land source hence equates to roughly 4,300,000 tonnes of   󿬁 rewood ayear. Agroforestry, a traditional yet growing practice is one of the keysources of   󿬁 rewood from private land (Dhakal et al., 2015). The maindrivers for the uptake include lack of access to public forest stocks,higher levels of education, larger farm size and a large labour force(Regmi and Garforth, 2010). Drooping  󿬁 g trees planted in a  󿬁 eld of  Fig. 3.  a) Regional yearly production of agricultural residues from cereal and cash crops, and 3b) Regional distribution of forestry resource outside protected regions.The line represents the proportion of the total resource the key species which were analysed account for (Department for Forest Research and Survey (D.F.R.S.), 2015;Koopmans and Koppejan, 1997; M.O.A.D. 2014).  J. Hammerton et al.  Journal of Environmental Management 223 (2018) 358–370 362
Search
Similar documents
View more...
Tags
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks
SAVE OUR EARTH

We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

More details...

Sign Now!

We are very appreciated for your Prompt Action!

x