Dry residual biomass as a potential alternative energy source Justo J. Roberts1*, Andrés Z. Mendiburu2, Pedro. O. Prado3, João A. de Carvalho Jr4, Agnelo M. Cassula5 1,2,4,5
Universidad Estadual Paulista – UNESP, Campus of Guaratinguetá – FEG, Brazil 3 Universidad Nacional de Mar del Plata – UNMdP, Argentina * [email protected]
Resumen. El presente artículo evalúa la disponibilidad de biomasa residual y su potencial energético en la localidad de General Pueyrredón, una región al sudeste de la provincia de Buenos Aires, Argentina. Fueron considerados residuos herbáceos y vegetales, derivados de la actividad agrícola que se desarrolla en la región, como también residuos forestales resultantes de la poda de árboles urbanos y del mantenimiento de jardines. Las estimativas se basan en información estadística de la cosecha de 2011-2012 y en una serie de parámetros obtenidos a partir de una extensa revisión bibliográfica. Los cálculos resultaron en una disponibilidad de biomasa residual de 205.630 t/año, lo cual implica un potencial energético de 2.622 TJ/año. Si esta biomasa fuese utilizada para generar electricidad, podría atender la demanda de 180.000 usuarios. Un modelo de gasificación también fue implementado para algunas de las especies de biomasa, resultando en un potencial de energía de gas de síntesis de 349,8 TJ/año. Los autores concluyeron que el potencial energético de la biomasa residual es significativo en la zona de estudio, sin embargo estudios más detallados deben ser realizados para evaluar la factibilidad técnico-económica del uso de la biomasa residual como una fuente alternativa de energía. Palabras Clave: biomasa, disponibilidad, potencial energético. Abstract. The present article assesses the residual biomass availability and its energy potential in the Party of General Pueyrredón, a region located southeast of the province of Buenos Aires, Argentina. There were considered herbaceous and vegetable residues derived from the agricultural activity developed in the region, and forest residues resulting from the pruning of urban trees and garden maintenance. The estimates were based on statistical information of the 2011-2012 harvest and a series of parameters obtained from an extensive literature review. The results showed an availability of residual biomass of 205.630 t/year, implying an energy potential of 2.622 TJ/year. If this biomass is used to generate electricity, it could supply 180.000 users. A gasification model is also implemented for some species of biomass, resulting in a syngas energy potential of 349,8 TJ/year. Finally, the authors concluded that the residual biomass energy potential is significant in the studied region; however a more detailed research is required, in order, to conduct a techno-economic feasibility of residual biomass as alternative energy source. Keywords: availability, biomass, energy potential.
1. Introduction Argentina's energy mix depends greatly on fossil fuels, which provide 90,6% of the primary energy supply. Natural gas presents the largest share with 51,4% of contribution, followed by oil with 34,9% (1), as depicted in see 0. Argentina stands out for the production of biodiesel, being among the leading worldwide exporters of this product. In 2011, biodiesel production reached 4.200 t/year, representing 6.4% of the world biodiesel production. Bioethanol is largely produced in the North and Northeast regions, where the major sugarcane plantations are situated. Until 2012, the entire bioethanol produced in Argentina (310.000 m3) came from sugarcane (2). The use of biomass for bioethanol and biodiesel production in Argentina is a reality; there are currently large production plants with the appropriate technology and know-how to transform the biomass in large scale. However, the utilization of vegetable biomass, charcoal, agricultural and agro-industrial residues for energy production is not a common practice in the country. These types of biomass feature a great unexploited potential for
Crude oil 34.9%
Wood 0.8% Bagace 1.1%
Natural Gas 51.4%
Other primaries 0.5%
Figure 1. Argentina’s energy matrix. Biomass supplies 4.9% of the primary energy through wood, baggage, and oil.
energy generation (heat and electricity) for supplying the residential, commercial and industrial sectors. According to the a study conducted by the Argentinian Energy Department and the SAGPyA1 in partnership with the FOA, in 2009, the available biomass energy potential reaches 1.42 EJ, which represents approximately 40% of the country's primary energy supply, in 2012 (see 0) (3). The Argentinian Government has developed various legal instruments for the promotion, incentive, and economical support of projects based on renewable energy (4). At a national level, the first legal instrument to incentivize the renewable energy sources was the law 25.019 (Ley Nacional nro. 25.019 - Régimen Nacional de Energía Eólica y Solar) for wind and solar energy, which stated wind and solar electricity generation as one of the main national interests. Subsequently, by the end of 2006 it was modified by the law 26.190 (Ley Nacional nro. 26.190 - Regimen de Fomento Nacional para el uso de fuentes renovables de energía destinada a la producción de energía eléctrica), establishing a target of 8% of renewable energy participation by 2015 (excluding hydropower) (5). The promoting instruments are mainly economic; subsides for MWh effectively generated by renewable sources during 15 years, as well as taxes devolution (4). Currently there are two main programs for the promotion of renewable energies in Argentina: the PERMER (Renewable Energy Project in Rural Markets) program, which started in 1998 with the main objective of providing basic electricity service in a sustainable manner to communities that are still beyond the reach of the grid; and the GENREN (Auction of Electricity Generation from Renewable Sources) program which began in 2009 to contract at least 1GW of renewable energy, to be sold into the grid at fixed rates for 15 years (6). In the case of biomass, in 2013 it was created the PROBIOMASA (Project for the Promotion of Energy from Biomass) aiming to boost production, management and sustainable use of biomass for energy purposes. In its initial stage the program targets to generate from biomass a total of 200 electric MW and 200 thermal MW by 2016. This would entail an increase in the share of biomass in the energy mix from current 4,9% to 10% (7). The Party of General Pueyrredón is one of the 135 administrative districts of the Buenos Aires Province, located in its southeast region, on the Atlantic coastline. Initially, the area was mainly utilized for livestock raising. Subsequently, it was introduced the extensive farming of crop and oilseeds, with annual double-crop. Later on, intensive productive 1 SAGPyA - Secretariat of Agriculture, Livestock, Rural Development, Fisheries and Food.
activities, such as horticulture, and the production of fruits and flowers were adopted also (8). Hypothetically, this region counts with a good availability of herbaceous biomassderived residuals, especially from cereals, vegetable biomass residuals derived from the extensive horticultural activity developed in the region, and forest biomass residuals originated in urban tree pruning and garden maintenance. However, there are no works dedicated to estimate the real availability of residual biomass for use as an alternative energy source in this region. Therefore, the present paper has as main objective to assess the actual availability of residual biomass in the Party of General Pueyrredón, and estimate the available energy potential. In order to accomplish this goal, an extensive literature review was carried out to gather information about the physical properties of the crops found in the region, as well as indices related to the rate of residue generation and its availability for alternative uses. The results show the energy potentials of the residual biomass available in the region for direct combustion processes utilization. Additionally, a gasification model is implemented to estimate the syngas energy potential of some species of biomass present in the region of study. 2.
Statistical information was obtained from official agencies, such as: National Institute of Agricultural Technology (INTA), Mar del Plata unit, from which it was obtained statistical information of the 2011-2012 harvest concerning the cultivated area, crop type, and yield of crops, for agricultural herbaceous biomass, cereal crops and horticultural crops. Division of Urban Forestry, Planning and Services Department (ENOSUR), from which it was obtained the availability of forest biomass residues derived from the pruning of urban trees in the years 2009 and 2010. Additionally, a literature review was conducted in order to gather information related to: Coefficients to estimate the residual biomass according to crop productivity and cultivated area; and Physical properties of biomass residues; calorific value and moisture content of agricultural herbaceous biomass residues and forest biomass residues. 3. Methodology In order to estimate the available energy potential from residual biomass, the next methodology was implemented: Step 1: Identification and characterization of available biomass in the region of study in terms of types and species of biomass, harvest periods, and geographical location. Creation of a statistical database with the cultivated area and the productivity of all the identified species in the region. Step 2: Creation of a new database containing the physical properties of biomass and the rate of residue generation for each biomass species. Step 3: Computation of the energetic potential according to the estimated amount of available biomass residues and its heating value, with characterization of seasonal resource availability.
Identification and characterization of biomass resource
The present study focuses on agricultural herbaceous residual biomass, derived from cereal crops and horticultural crops, as well as on forest residual biomass. The final disposition of this type of residual biomass supposes not only a logistical problem for the community, but also an environmental problem, since the residues of biomass not used for agricultural or livestock purposes are often burned in the open field in an uncontrolled combustion process, thus emitting harmful emissions to the atmosphere. Forest residues are also burned in open dumps, causing similar problems. These facts exalts the necessity of making better use of the biomass residues, for which the generation of energy represents a good alternative (9). The agricultural crops and forest species assessed in this study are presented in 0. In the first and second column of 0, the cultivate area (ha) and the crop yield (t/ha) for each species of herbaceous biomass and open field and greenhouse horticultural biomass are indicated. These data was collected in the period 2011-2012, according to the INTA (10). Table 1. Types of biomass residues for the energy potential assessment performed in this study. Biomass Subgroup Species Type of Residue Types Oat Straw Barley Straw Rapeseed Straw Herbaceous Crops Sunflower Head, hull Corn Spike, straw Soybean Straw Agricultural Wheat Straw Residues Pepper Horticultural Crops in open field Tomato Lettuce Biodegradable waste Pepper Horticultural Crops in greenhouse Tomato Lettuce Eucalyptus Pine Vegetable residues, mainly Forest Urban Trees generated by tree pruning and Platanus Residues garden maintenance Other Species
The total area cultivated with herbaceous biomass corresponds to 34,5% of the total territory of the Party of General Pueyrredón, whereas the horticultural biomass occupies 2,4% of the territory, considering open field and greenhouse plantations. At this point, it is important to state that other species of horticultural crops are grown in the region of study, but these were not included in the calculations due to the lack of information concerning the physical properties of these crops (such as moisture content and LHV), as well as the residue to crop generation rates. According to INTA statistics (10), the total area cultivated with horticultural crops was 6.055 ha in 2012, almost twice the area considered in the present work. This fact reveals that the real energy potential of the region may be even greater the estimations presented in this study. The highest yield among herbaceous crops corresponds to corn, with more than six tons per cultivated hectare. With respect to horticultural crops, it is notice that productivity
can be reasonably increased when the same species are grown in greenhouses rather than in open field, such is the case of tomato and pepper. 4.2. Available residual biomass assessment The energy potential assessment for herbaceous and horticultural biomass was performed from a territorial approach, i.e. taking as base information the surface occupied by each crop. However, for the case of forest biomass, the estimation was founded on information of forest residues availability from the largest urban center in the region, the city of Mar del Plata. 4.2.1. Agricultural residual biomass The availability of residual biomass was estimated using the Residue-to-Product-Rate ( RPR ) since it is considered a more accurate estimator. For some specific types of horticultural biomass, the Residue-to-Area-Rate ( RAR ) was used due to not availability of RPR . The residual biomass generation was calculated according to equation (1), when using the RPR , and (2) when using the RAR (11).
RB S RPR
RB S RAR
in which RB represents the annual rate of residual biomass production (t/year), S is the cultivated area (ha), and is the crop yield (t/ha). Not all of the residual biomass can be used for energy purposes, a part of it must be left over in the ground to prevent moisture losses, soil erosion, and as a source of organic matter to preserve the ecosystem's nutrient balance (2). The portion of residual biomass that cannot be collected varies from one region to another. In the present paper, it is considered the residue availability rate, RA (%), which represents the maximum amount of residue that is actually available for energy use. The RA adopted were taken from the literature. Therefore, it was possible to calculate the actual amount of available biomass, RBavailable (t/year), for each type of crop according to equation (3).
RBavailable RB RA
4.2.2. Forest residual biomass In the case of forest biomass, information of the residue availability in tons per month provided by the Division of Urban Forestry, Planning and Services Department of the city of Mar del Plata was utilized for the calculations. In order to estimate the amount of residues of each species from the total amount of residues reported by the entity, the following percentages were adopted: 5% for eucalyptus, 5% for the pine, 80% for platanus, and 10% for other species (12). Finally, for calculating the actual available forest biomass, equation (3) was utilized along with the residue availability rates corresponding to forest biomass. 4.3.Calculating the energy potential derived from residual biomass Once the available residual biomass was calculated, the energy potential (TJ/year) can be estimated using the Lower Heating Value (LHV) and the moisture content of each type of biomass (11). The LHV was calculated using the Higher Heating Value (HHV) on a 53
dry basis, i.e. 0% moisture content, and the biomass residue moisture content, with equation (4) (13): w w h w LHVw HHV0 1 2,447 9,011 2,447 100 100 100 100
where LHVw is the lower heating value (MJ/kg) at moisture “w”; HHV0 is the higher heating value (MJ/kg) in dry basis; w is the moisture content on mass fraction; and h is the hydrogen content on mass fraction (adopted as 6%, in dry basis). The available energy, AE , derived from the residual biomass (TJ/year) was calculated using: AE RBavailable LHVw
4.4. Biomass gasification Biomass gasification is also a plausible option that would allow the utilization of biomass materials in more applications. The gasification of a solid feedstock yields a combustible gas known as synthesis gas, this gas can be used to produce electricity internal combustion engines or gas turbines. An interesting option would be to produce synthesis gas in downdraft gasifiers and to use this gas for distributed power generation. In this section, the gasification in downdraft gasifiers of some of the considered biomass materials is assessed. The synthesis gas composition and its LHV are presented here for gasification at atmospheric pressure. In order to obtain the synthesis gas composition and LHV a non-stoichiometric constrained equilibrium model was used, the details and validation of the used model can be found in a previous work of Mendiburu et al. (14). Also, the use of the synthesis gas in internal combustion engines and micro gas turbines has been assessed in previous work of Mendiburu et al. (15), and it was found that for a synthesis gas flow of 264,21 Nm3/h, the maximum power outputs obtained in the calculations were 204,74 kW for the spark ignition engine system with a compression ratio of 12, 171,04 kW for the compression ignition engine system with a compression ratio of 20, and 149,73 for the micro gas turbine system with a compression ratio of 18. There is also the possibility to implement a gasification model based in stoichiometric equilibrium, and including some modifications to the equilibrium constant, such a model was also developed by Mendiburu et al. (16) in previous work. As an example the synthesis gas composition obtained from the model for some biomass material is presented in 0. The results presented in 0 were obtained from gasification of biomass in downdraft gasifiers with atmospheric air as the gasification agent and operating at atmospheric pressure. Other important parameters as equivalence ratio (ER), gasification time (t) and the calculated carbon conversion efficiency (CCE) are also presented. It was not possible to calculate the syngas LHV for all the species of residual biomass, due to unavailability of data related to the ultimate analysis for the residues. The syngas LHV values calculated are presented in 0. 5. Results The calculations performed using the information of the Party of General Pueyrredón 54
resulted in an estimated generation of agricultural and forest residual biomass of 205.630 tons per year, which implies an energy potential of 2.622 TJ/year if considering direct combustion of it. The species that were used in the gasification model represent 42% of the total amount of residual biomass available, resulting in a syngas energy potential of 349,8 TJ/year. The overall results of the analysis are depicted in 0. From the total amount of residues, 53% derive from the agricultural herbaceous crops, followed by the vegetable crops (open field and greenhouse cultivations) with a share of 28% and the forest biomass with 19%. Considering a scenario where the residual biomass is used for electricity generation and adopting an efficiency of transformation of the resource into electrical power through direct combustion of 40% (17), the residual biomass has the potential to provide 291 GWh/year, this means supplying approximately 180.000 inhabitants. Table 2. Synthesis gas composition and LHV for some biomass materials.
H2 (%) CO (%) CO2 (%) CH4 (%) H2S (%) N2 (%) LHV (MJ/Nm3) T(ºC) CCE (%) ER (%) MC (%) t (min)
Oat 15,92 18,58 13,83 2,13 0,037 49,50 4,83 901 84,65 0,32 15,00 60,00
Rapeseed 17,66 19,02 15,41 2,14 0,00 45,78 5,08 899 92,11 0,32 15,00 60,00
Sunflower 17,55 21,36 11,45 2,25 0,014 47,38 5,40 913 93,25 0,32 12,00 60,00
Corn 15,79 17,23 14,36 2,63 0,45 49,94 4,83 896 84,74 0,32 7,53 60,00
6. Conclusions In the present work it was assessed the energy potential of residual biomass derived from herbaceous and horticultural crops, and urban forests in the Party of General Pueyrredón, Argentina. Taking into account the calculations performed, it can be concluded that the potential of residual biomass is relevant and should be included in the municipal and national energy action plans. Nonetheless, future researches should be oriented toward technical and economic assessment of the different technological alternatives that could be used for transforming the biomass residues into useful energy in the region studied.
Table 3. Overall results of the residual biomass energy assessment carried out in Party of General Pueyrredón. Source of Residue
Herbaceous Oat Barley
Horticultural Open field Pepper
Total Forest Total
S cultivated land, crop yield, RPR residue-to-product ratio, RAR residue-to-area rate, AR availability rate, LHVsyngas syngas lower heating value, AE available energy, n/a not available.
RBavailable available residual biomass, w
LHV lower heating value,
2. 3. 4. 5.
8. 9. 10. 11. 12.
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