A techo-economic assessment of the generatión and usage of biógenic gases in Chile as a substitute of natural gas

Abstract

In Chile, the energy that can potentially be obtained from the anaerobic digestion of residual biomass was calculated using a holistic approach. The pathways of electricity generation vía direct combustionof biogas and upgraded biogas produced as bio-substitute natural gas (Bio-SNG) for injection into the gas grid were assessed and compared. In each case, these conversion routes, biogas-to-energy and biogas-to-BioSNG, were evaluated using proveo technology.The primary data necessary for the potential analysis was gathered from a variety of primary sources, and afterwards organised in such a way that the geographical distribution could be distinguished across the country at a county level; additionally, the sources of biomass were classified in the following sectors: i) municipal solid waste; ii) wastewater treatment; iii) livestock farm; and iv) agricultural. Finally, technical and economic information was drawn principally from the literature, in order to conduct the economic modelling linked with the potential analysis.Through a mathematical modeling relying on limits of potential (i.e. physical limit, geographical limit, technicallimit and economic limit), supply-cost curves were constructed to estímate the representativegeneration cost of both secondary energy end-products as well as their technical and economic potentials for each of the aforementioned sectors. The results of the technical potential were then integrated into a geographical information system (GIS) to show the distribution of energy potentialnationwide. Finally, a cross-assessment comparison was conducted, and the cost distribution was compared to the market price of electricity and natural gas, respectively, in order to elucidate the economic attractiveness ofthe two assessed options.Based on the results, it was concluded that the municipal solid waste offers the largest economic potential for electricity when recovering landfill gas (1.1 TWhey-1) or when processing unsorted municipal residue through a waste-to-energy route (2.1 TWhey-1). Wastewater treatment plants and livestock sectors bring a similar economic potential for electricity (approximately 0.8 TWhey-1 for each one), while the potential from agricultura! sector is slightly higher (1.1 TWhey-1). The option of co-digesting feedstock from the livestock sector (manure) and agricultural sector (annual crop residue)is feasible to sorne extent, and it can appreciably improve the economics of biogas processing as compared to mono-digestion. Moreover, the wide range of biomass technical potential gives rise to a representative generation cost ranging form 11.0 ct€ kWhe- 1 to 25.0 ct€ kWhe-1. For the option ofproduction of Bio-SNG, the largest economic potential was found in the agricultural sector (280 MM Nm3y-1), and the smallest one in waste water treatment one (19 MM Nm3y-1). The economic potential from municipal solid waste (224 MM NmV1) and the livestock sector (134 MM Nm3y-1) are still significant. As far as the representative generation cost for this conversion route is concemed, it rangesfrom 9.5 € MMBTU-1 to 98 € MMBTU-1 thus severely restricting the commercial implementation of this option, based on the present price of natural gas.The energy potential was observed to be highly concentrated in only some administrative regions of Chile. For municipal solid waste, wastewater treatment plants and feedstock sectors, the most relevant fraction of the economic limit is located in the XIII region (Metropolitan), whereas the agricultural sector is predominantly distributed between the VI, VII and IX regions.The dichotomy of biogas for electricity and biogas for upgrading generation in the framework under analysis was addressed in this thesis. The study revealed a pattem of results which could be interpreted in two ways. Firstly, the electricity option appears to be more versatile and advantageous in terms of possible producís of interest (electricity and heat) and flexibility in the scale in which the biomass feedstock is available. Secondly, the skeleton of a macro-policy for the generation and enhancement ofbiogas should target increased energy generation from an existing fraction ofthe economic limit that is profitable without subsidisation from the state.