GASEOUS EMISSION PERFORMANCE OF NOVEL BIOFUELS DURING FIXED-BED CONVERSION Maryori Díaz-Ramírez1,2,3*, Fernando Sebastián Nogués2, Christoffer Boman3, Adeline Rezeau2 Javier Royo1and Dan Boström3 1 Department of Mechanical Engineering, University of Zaragoza, María de Luna 3 E-50018 Zaragoza, Spain 2 Natural Resources Division-BERA Group, Centre of Research for Energy Resources and Consumption (CIRCE), Mariano Esquillor, 15 - Edificio CIRCE. Campus Río Ebro - University of Zaragoza, E-50018 Zaragoza, Spain. 3 Energy Technology and Thermal Process Chemistry, Umeå University, SE-901 87 Umeå, Sweden * corresponding author:
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ABSTRACT Limitations in terms of biomass availability and increasing energy demands have enforced to consider dedicated energy crops for supplying heating needs. Variability expected to their chemical properties because of species used or factors related to the production process as fuels might affect quality requirements of the final users. Therefore, to achieve consumer acceptability and sustainability of the energy sector based on the novel fuels, impacts associated to their conversion should be primarily assessed before a definitive introduction as a fuel to the heating market. To advance on these issues, the environmental behavior of two energy crops cultivated and pelletized Spain have been tested in two different size commercially available grate conversion units, with a nominal heat output of 25 kWth and 250 kWth. The environmental performance of these two systems have been assessed in terms of CO and NO X emissions level and thermal efficiency, and results compared to European limits established to standardized fuels. The experimental data revealed that combustion quality can be achieved under acceptable level of gaseous emission pollutants for the two crops in both systems. Nevertheless, applicability of conversion of these pelletized crops at the residential scale perhaps should be considered still rather limited, mainly because of restrictions of the system to manage the fuel ash properties, which may significantly increase maintenance needs and undesired emission level of pollutants.
KEYWORDS: COMBUSTION.
BIOMASS,
PELLET,
ENERGY
CROPS,
GRATE
INTRODUCTION Generally, stemwood pellets have been preferred among biofuels for heating supply because they are easier to burn rather than other pelletized biofuels. Nevertheless, availability limitations of these forest sources, and growing economic and environmental pressures related to fossil fuels have contributed to address efforts on seeking for novel opportunity biofuels, such as dedicated energy crops [1-4]. These fuels are typically characterized by high variability of the physical and chemical biofuel properties, which might lead to undesired effects during fuel combustion [5-9]. This condition enforces to evaluate capability of existing combustion technologies to manage the novel fuel characteristics in order to determine required improvements before being introduced as fuels for the heating market. In this sector, grate conversion has been the most extended fixed bed technology to direct combustion of solid biofuels. The foremost advantage for its commercial applicability in the heating sector, is its rather low investments and operating costs with respect to other combustion technologies. Although this type of conversion units have been satisfactorily managed heterogeneity of fuel properties, rather few experiences have been perform with dedicated energy crops. This fact is basically attributed to the recent incorporation of these novel fuels as potential bioenergy alternatives, and therefore, their suitability level should be assessed seeking for a sustainable development of the heating sector. To gain knowledge on these issues, two energy crops, one herbaceous energy crop and one short rotation coppice, both cultivated and pelletized in Spain have been tested in two different sizefixed bed grate conversion units, with a nominal heat output of 25 kWth and 250 kWth. Main purpose of the combustion tests done on these two facilities was to evaluate capability of the commercially available combustion systems to manage the fuel properties in order to fulfill standard requirements for CO and NOX emissions and efficiency.
1 MATERIALS AND METHODS 1.1 Fuel chemical characterization Two varieties of energy crops; a herbaceous energy crop, Brassica carinata, (brassica), and a short rotation coppice, Populus sp., (poplar) were assessed in this work. Main fuel properties of these pellets are provided in Table 1. The ash chemical composition of fuels is listed in Figure 1 and given on a mole per mass fuel dry basis (d.b.). As indicated in Table 1, combustion fraction of the two crops is relatively similar and basically, main differences are identified to the ash fraction. According heating value, brassica is characterized by a lower heating value than poplar, and therefore, a higher load will be needed to provide similar heating demands. Concerning the proximate analysis, main differences are related to the ash characteristics. Ash content of the energy crops samples is high, reaching values up to 17 times higher than ash content requirements for DINplus certification, which is set at
