Economic performances of anaerobic digestion plants: Effect of maize silage energy density at increasing transport distancesby Jacopo Bacenetti, Marco Negri, Daniela Lovarelli, Luis Ruiz Garcia, Marco Fiala

Biomass and Bioenergy

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Text

erobic digestion plants: Effect of maiz increasing transport

Jacopo Bacenetti a,*, Marco Ne

Marco Fiala a a ronmen . Celor stal, ET work and to the maize ic performances are from the plant cut at nt fed with ear silage. plant; up to 32 km the as, beyond this translts are interesting for stakeholders and policymakers involved in the biogas agro-energy processes, because they td. All rights reserved. 1. Introduction

The EU objectives can be met by the development of all the different renewable energy sources [1,2]. Among these, the biogas deriving from Anaerobic Digestion (AD) of different feedstock has proved to be interesting for energy generation in rural areas in particular, especially when the AD plants are fed with feedstock locally available and the generated energy * Corresponding author. Tel.: þ39 02 50316869; fax: þ39 02 50316845.

Available online at www.sciencedirect.com

ScienceDirect .co b i om a s s a n d b i o e n e r g y 8 0 ( 2 0 1 5 ) 7 3e8 4E-mail address: jacopo.bacenetti@unimi.it (J. Bacenetti).can be useful to reduce the cost of feedstock supply. © 2015 Elsevier LFeedstock supply

Zea maize silage

Ear silage

Renewable energy different scenarios were considered with regard to the subsidy frame biomass yield.

The results show that, for short distances (<3 km), the econom similar for AD plants fed with the whole plant silage and with that 0.75 m; however, they are substantially better than those of the pla

Beyond 14 km ear silage becomes more interesting than the whole plant fed with silage from the high cut is the most profitable where port distance, the ear silage is the best solution. The achieved resuKeywords:

Biogas

The aim of this paper is to evaluate the economic performances of biogas plants fed with different maize silages by considering increasing extra-farm transport distances. TwoDepartment of Agricultural and Envi

Universita degli Studi di Milano, Via G b Departamento de Ingenierı´a Agrofore

Avenida Complutense, 3, 28040, Spain a r t i c l e i n f o

Article history:

Received 25 February 2015

Received in revised form 22 April 2015

Accepted 25 April 2015

Available online xxxhttp://dx.doi.org/10.1016/j.biombioe.2015.04. 0961-9534/© 2015 Elsevier Ltd. All rights resee silage energy density at distances gri a, Daniela Lovarelli a, Luis Ruiz Garcia b, tal Sciences e Production, Landscape, Agroenergy, ia 2, 20133 Milano, Italy

SI Agronomos, Universidad Politecnica de Madrid, a b s t r a c t

In Italy, more than 1150 agricultural anaerobic digestion (AD) plants are currently running.

Their concentration in specific areas resulted in an increase in the biomass price and transport distances. For the AD plants located on farms with small area, often the feedstock are purchased on the market. However, when transport distances increase, it can be less expensive to buy biomasses with high energy density.

With this regard, maize experimental tests were carried out to evaluate the methane production by harvesting the whole plant, the plant cut at 0.75 m and only the ear.Economic performances of anahttp: / /www.elsevier034 rved.m/locate/biombioe

Subsystem 1 is performed by farmers that sell the biomass; b i om a s s a n d b i o e n e r g y 8 0 ( 2 0 1 5 ) 7 3e8 474(above all the heat) [3e5] is used close to the plant [6e12]. In

Europe, Germany is the leading country with more than 9000 agricultural AD plants [12]. However, a considerable development of this agro-energy took place also in Italy, Sweden,

Switzerland and Austria [5,12,13]. Each of these countries is supporting with a different subsidy framework this typology of renewable energy production.

In Italy, nowadays, more than 1150 agricultural biogas plants are running, mainly in the northern regions [6,9,12,14,15]. Most of them operate in co-digestion and, consequently, are fed with energy crops (mainly cereal silage), agricultural residues (animal sewage) and residues from the agro-industry [4e6,13,15e18]. Strong public incentives were granted for electricity produced from biogas, especially for the

AD plants put into operation before the 31st December 2012 and with electrical power lower than 1 MW. An “all-inclusive tariff” (electricity selling price þ subsidy) equal to 280 V MWh1 of electricity was the fixed incentive for the electricity fed into the grid, with no consideration about byproducts utilization for feeding and about heat valorisation.

With the D.M. of 6th July 2012 [19] this incentive has been updated and, generally, strongly reduced (15e35%); in addition, more importance has been paid, by means of the introduction of bonus, to the heat valorisation and by-products utilization.

Nevertheless, for AD plants put into operation before the year 2013, cereal silages are the key feedstock. Compared to animal slurry (themost widespread agricultural by-product in

Northern Italy), these biomasses are characterized by high specific biogas productions (600e650 m3 t1 of volatile solids formaize silage and 450e560m3 t1 of volatile solids for wheat and triticale silages) [9,12], approximately 6e25 times higher than pig and cow slurries [9]. Among cereal silages, the maize one is the most used [12,20e28].

Over the years, the concentration of AD plants in specific areas resulted in the increase of biomass prices and transport distances. For the AD plants located on farms with little agricultural area, which is not sufficient to produce the needed amount of biomass for the supply of digesters, the only achievable solution is to purchase the feedstock from the market. It must be considered that, when transport distances increase, it can be less expensive to buy biomass with high energy density.

In this context, with regard to biogas production from maize silage, themost important portion of the plant is the ear [25]. The ear represents a very good feedstock for biogas production because, given the high starch content, it is characterized by a higher biogas production if compared to thewhole plant silage. Negri et al. [25] evaluated the biogas production from different maize plant portions (the whole plant - WP; the plant cut at 75 cm of height - HC; the ear only - OE). Although the silage production by harvest of the whole maize plant allows maximizing the methane production per hectare, the other two solutions produce silages with a higher specific methane production and, consequently, higher energy density. In more details, the methane production by harvesting and ensiling the whole plant (about 10,400 m3 ha1) is higher than the ones achievable by: only the ear (about 7850 m3 ha1, 24.4%) and the plant cut at 75 cm (9420 m3 ha1, 9.4%).