Combustion tests of grape marc in a multi-fuel domestic boiler

Abstract

New sources of renewable energy have to be found in order to cope with possible fossil fuel scarcity. Among the renewable energy mix, biomass burning has an almost neutral CO2 balance, especially when local biomass sourcing is possible. Among the diverse biomass sources, agricultural by-products such as rice husk, corn waste, palm waste, sugarcane, date palm, olive mill wastewater… can be seen as renewable biomass fuels. The present study considers the combustion process of grape marc in a domestic boiler. The optimization of the heat recovery process was mainly carried out using grape marc blended with wood pellets and/or miscanthus. The combustion process was assessed considering the molar carbon ratio ([CO]/[CO]+[CO2]) and the total heat losses. These parameters have been chosen as they represent respectively the quality of the combustion in terms of CO conversion and the total efficiency of this combustion process. Gas and particulate matter emissions were estimated. It has been observed that the addition of grape marc with mass ratios in the range 25–33wt% has no significant effect on the combustion efficiency (molar carbon ratio lower than 1.3%) and on the Total Suspended Particles emissions (TSP ranged from 20 to 40mgNm−3 at 10% O2) for both mixtures. An efficient combustion of the blend miscanthus/grape marc at weight proportion 50/50 could also be achieved. The homogenization of mixtures of wood pellets and grape marc at 50/50wt% was difficult to realize and led to relative high CO emissions. Is has also been observed that Nitrogen Oxides (NOx) emissions depend on the nitrogen content of the blend but remaining acceptable (less than 260mg/Nm3 at 10% of O2). The feasibility of grape marc burning at domestic scale was therefore proved.