Gasiﬁcation of agricultural residues in a demonstrative plant: Corn cobs Enrico Biagini a,⇑ , Federica Barontini a,b , Leonardo Tognotti a,b a Dipartimento di Ingegneria Civile e Industriale (DICI), Università di Pisa, L. Lazzarino, 56126 Pisa, Italy b Centro di Ricerca Interuniversitario Biomasse da Energia (CRIBE), Via vecchia di Marina, 6, 56122 Pisa, Italy highlights  Experimental gasiﬁcation tests are carried out with a biomass waste (corn cobs).  The gasiﬁer is a downdraft reactor at a demonstrative scale (350 kWth).  Material and energy balances revealed interesting gas production and power efﬁciency.  Fluctuations in gas composition and pressure drop are imputed to the reactor dynamic. article info Article history: Received 25 July 2014 Received in revised form 16 September 2014 Accepted 17 September 2014 Available online 28 September 2014 Keywords: Biomass fuels Biomass to energy Power production Cogeneration abstract Biomass gasiﬁcation couples the high power efﬁciency with the possibility of valuably using the byprod- ucts heat and biochar. The use of agricultural wastes instead of woody feedstock extends the seasonal availability of biomasses. The downdraft type is the most used reactor but has narrow ranges of feedstock speciﬁcations (above all on moisture and particle size distribution), so tests on a demonstrative scale are conducted to prove the versatility of the gasiﬁer. Measurements on pressure drops, syngas ﬂow rate and composition are studied to assess the feasibility of such operations with corn cobs. Material and energy balances, and performance indexes are compared for the four tests carried out under different biomass loads (66–85 kg/h). A good operability of the plant and interesting results are obtained (gas speciﬁc pro- duction of 2 m 3 /kg, gas heating value 5.6–5.8 MJ/m 3 , cold gas efﬁciency in the range 66–68%, potential net power efﬁciency 21.1–21.6%). Ó 2014 Published by Elsevier Ltd. 1. Introduction Gasiﬁcation with air in a downdraft reactor coupled to an inter- nal combustion engine is one of the most promising biomass- to-energy applications on a small scale, because of the higher power efﬁciency with respect to any direct combustion based system. Further advantages of this solution are the relatively higher quality of syngas produced compared to other gasiﬁers (Hasler and Nussbaumer, 1999), with potential conversion to valuable chemicals, like methanol and hydrogen, the possibility of utilizing the by-products (biochar as a soil amendment, recovery heat for cogeneration), the low emissions due to the combustion of a gas instead of a solid. The open issues concern the limitations on feedstock speciﬁcations (low moisture, narrow dimensional range, as discussed in Simone et al., 2009; Martinez et al., 2012), the high level required in the syngas cleaning (especially for tar and dust), and the disposal of waste water and/or ﬁlter media used for the clean-up. Most studies on downdraft gasiﬁers used woody materials (chips, briquettes, pellets) as feedstock (see for instance Zainal et al., 2002; Sharma, 2011; Simone et al., 2012). It is important to prove the operability of the gasiﬁer with feedstocks other than the reference ones in order to extend the diffusion of this technol- ogy and make it more attractive to farmers. This would overcome the supply limitations related to the seasonal availability of bio- masses. Agricultural by-products and food residues are among the most interesting, and sometimes cheapest, candidates for (entirely or partially) substituting the woody feedstock in a down- draft gasiﬁer. Due the wide variety in origin, composition, particle size distribution, many of them represent out-of-speciﬁcation fuels and are not suitable for the direct gasiﬁcation. Low temperatures (due to high moisture content, for instance), scarce ﬂowability or obstructions (due to the presence of ﬁnes or long particles) inside the reactor, can compromise the operations of ﬁxed bed reactors (see for instance Wander et al., 2004). Pretreatments (drying, chip- ping, sieving, densiﬁcation, see Erlich and Fransson, 2011), mixing http://dx.doi.org/10.1016/j.biortech.2014.09.086 0960-8524/Ó 2014 Published by Elsevier Ltd. ⇑ Corresponding author. Tel.: +39 050 2217840. E-mail address: e.biagini@ing.unipi.it (E. Biagini). Bioresource Technology 173 (2014) 110–116 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech