Abstract
The coffee industry constitutes an important part of the global economy. Developing countries produce over 90% of world coffee production, generating incomes for around 25 million smallholder farmers. The scale of this industry poses a challenge with the generation of residues along with the coffee cultivation and processing chain. Coffee stems, obtained after pruning of coffee trees, are one of those abundant and untapped resources in the coffee supply chain. Their high lignocellulosic content, the low calorific value ranging between 17.5 and 18 MJ kg−1 and the low ash content make them a suitable solid fuel for thermochemical conversion, such as gasification. This research evaluates the feasibility of using these residues in small-scale downdraft gasifiers coupled to internal combustion engines for power and low-grade heat generation, using process modelling and the Colombian coffee sector as a case study. The producer gas properties (5.6 MJ Nm−3) and the gasifier’s performance characteristics suggest that this gas could be utilized for power generation. A cogeneration system efficiency of 45.6% could be attainable when the system’s low-grade heat is recovered for external applications, like in the coffee drying stage. An analysis of the energy demand and coffee stems availability within the Colombian coffee sector shows that the biomass production level in medium- to large-scale coffee farms is well matched to their energy demands, offering particularly attractive opportunities to deploy this bioenergy system. This work assesses the feasibility of providing coffee stem–sourced low-carbon energy for global coffee production at relevant operating scales in rural areas.
Highlights
1.1 International context of coffee productionCoffee is an important global commodity, with a market that has shown significant resilience in a world with a changing agricultural economy, where coffee production has grown 3.5% per year since 2008, faster than 2.5% overall growth in agriculture [1]
For power generation and combined heat and power generation (CHP), there is a deficiency of effective regulatory frameworks and pricing schemes, where the barrier is even larger for distributed generation and small-scale applications [25]
This paper contributes to the resource awareness by linking the locally available resource potential of coffee stems to the existing local energy demand of the coffee sector
Summary
Coffee is an important global commodity, with a market that has shown significant resilience in a world with a changing agricultural economy, where coffee production has grown 3.5% per year since 2008, faster than 2.5% overall growth in agriculture [1]. This paper explores the resource potential and bioenergy conversion feasibility of coffee stems into energy vectors that could potentially tackle energy access problems in many rural areas of these countries and/or supply low-carbon energy to the coffee agro-industry. It could reduce the impact of the carbon footprint of the production of this internationally traded commodity. The work explores case studies in Colombia, the third-largest coffee producer country, and considers the technical viability of implementation and associated impacts
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