Gaseous products and particulate matter emissions of biomass residential boiler fired with spent coffee grounds pellets

In this present work, energetic characteristics and combustion behavior of agro-pellets, produced from pure spent coffee grounds (SCGs) or blended with pine sawdust in a commercial residential pellet boiler, were examined. Hence, thermal and chemical properties such as calorific value, ash content, bulk density, fixed carbon and elemental analysis obtained from blend and pure biomasses were firstly examined. Moreover, combustion tests were performed in 8-12 kW Okofen Boiler, carbon monoxide (CO) and volatile organic compounds (VOCs) were analyzed according to French standards. The emissions of some gases were also monitored during combustion tests: O-2, CO2, NO and NO2. An Electrical Low Pressure Impactor (ELPI) was used to collect particles from 29 nm to 10 mu m into 12 size fractions to determine mass and number concentrations. The exhaust gaseous and particles emissions of SCG and blend pellets were compared with emissions of wood pellets (DIN + standard). It was found that, despite its high LHV, the use of pure SCG as fuel lead to a lower boiler efficiency, which was followed by an increase of particle and gas emissions. However, when SCG was mixed with pine sawdust (50/50 wt.%), combustion parameters (emissions and boiler efficiency) were very close to those obtained for wood pellets. According to the presented results, although it seems reasonable to consider SCG pellets as a promising alternative fuel, the use of SCG blending up to 50% with pine sawdust is essential to meet French Standards (NF agro-pellets). Hence, this pellets production may be a promising issue for SCG valorisation. (c) 2012 Elsevier Ltd. All rights reserved.