Techno-economic feasibility of extrusion as a pretreatment step for biogas production from grass

Grass clippings have a good biomethane potential and, if acquired from roadside verges, nature management or natural grasslands do not compete for arable land, avoiding the food versus fuel debate. However, before the grass is processed in a wet anaerobic digester, a pretreatment step is advisable to minimize the problems associated with its fibrous nature. In this study, the effects of a semi-industrial extrusion pretreatment on fresh and ensiled grass were investigated through an energetic and economic assessment. Extrusion improved the mixing properties of the grass feedstock and reduced the formation of a floating layer even at a solid concentration of 10% (w/v). This pretreatment also enhanced the biomethane potential of ensiled grass and fresh grass by, respectively, 18 and 11% on a fresh matter basis, while shredding reduced this value by 14% when compared to fresh grass. This was attributed to changes in the volatile solids (VS) content of the treated samples, as all conditions resulted in similar biomethane yields when calculated per ton of VS, ranging from 325.5 to 337.6 Nm(3) CH4/ton VS. However, ensiling resulted in a longer lag phase during biogas production attributed to the leaching of readily available sugars from the ruptured plant cells; nevertheless, this is not expected to be significant in a buffered industrial system. The revenue resulting from the extrusion treatment, between euro6 and euro17 per tonne of FM, compensated the cost of this additional step, indicating that extrusion would be a techno-economically sound process for the anaerobic digestion of grass

A techno-economic evaluation of a biomass energy conversion park

Biomass as a renewable energy source has many advantages and is therefore recognized as one of the main renewable energy sources to be deployed in order to attain the target of 20% renewable energy use of final energy consumption by 2020 in Europe. In this paper the concept of a biomass Energy Conversion Park (ECP) is introduced. A biomass ECP can be defined as a synergetic, multi-dimensional biomass conversion site with a highly integrated set of conversion technologies in which a multitude of regionally available biomass (residue) sources are converted into energy and materials. A techno-economic assessment is performed on a case study in the Netherlands to illustrate the concept and to comparatively assess the highly integrated system with two mono-dimensional models. The three evaluated models consist of (1) digestion of the organic fraction of municipal solid waste, (2) co-digestion of manure and co-substrates, and (3) integration. From a socio-economic point of view it can be concluded that it is economically and energetically more interesting to invest in the integrated model than in two separate models. The integration is economically feasible and environmental benefits can be realized. For example, the integrated model allows the implementation of a co-digester. Unmanaged manure would otherwise represent a constant pollution risk. However, from an investor's standpoint one should firstly invest in the municipal solid waste digester since the net present value (NPV) of this mono-dimensional model is higher than that of the multi-dimensional model. A sensitivity analysis is performed to identify the most influencing parameters. Our results are of interest for companies involved in the conversion of biomass. The conclusions are useful for policy makers when deciding on policy instruments concerning manure processing or biogas production. (C) 2012 Elsevier Ltd. All rights reserved