• Energy Research

AbstractThe 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.

AbstractThe 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.

The UK is the first major economy to legislate the reduction of all GHG emissions to net-zero. Greenhouse gas removal (GGR) approaches are likely to be required to support the 2050 net-zero target by offsetting residual emissions from ‘hard-to-abate’ sectors. Bioenergy with carbon capture and storage (BECCS) is investigated as one technical solution for GGR. This research used process modelling and lifecycle assessment to identify the GGR potential of three BECCS supply chains. Results show that the BECCS supply chains have significant GGR potential with net-negative emissions as CO2e between −647 and −1137 kg MWh−1. Emissions were compared per unit energy output, biomass and area required for each supply chain to assess the GGR potential and BECCS sustainability implications. The large-scale BECCS supply chain features robust technologies with high capacity factor. It produces the greatest electricity generation and annual GGR, however, demands large amounts of biomass raising potential sustainability issues. The medium-scale (CHP) BECCS provides the greatest GGR potential per energy due to its higher energy efficiency. Limitations are a low capacity factor, energy demand-supply balance and non-existent decentralised CCS infrastructure. The (hydrogen) BECCS supply chain is more versatile, producing hydrogen with the potential to support the decarbonisation of not just power, but heat and transport sectors. The GGR potential sits in the middle and has greater benefits from a biomass sustainability perspective, yet, hydrogen infrastructure is not established, and costs remain uncertain. The relative performance of alternative BECCS supply chains should consider direct links between CO2 removal and sustainable biomass and land use, as well as GGR potential.

The UK is the first major economy to legislate the reduction of all GHG emissions to net-zero. Greenhouse gas removal (GGR) approaches are likely to be required to support the 2050 net-zero target by offsetting residual emissions from ‘hard-to-abate’ sectors. Bioenergy with carbon capture and storage (BECCS) is investigated as one technical solution for GGR. This research used process modelling and lifecycle assessment to identify the GGR potential of three BECCS supply chains. Results show that the BECCS supply chains have significant GGR potential with net-negative emissions as CO2e between −647 and −1137 kg MWh−1. Emissions were compared per unit energy output, biomass and area required for each supply chain to assess the GGR potential and BECCS sustainability implications. The large-scale BECCS supply chain features robust technologies with high capacity factor. It produces the greatest electricity generation and annual GGR, however, demands large amounts of biomass raising potential sustainability issues. The medium-scale (CHP) BECCS provides the greatest GGR potential per energy due to its higher energy efficiency. Limitations are a low capacity factor, energy demand-supply balance and non-existent decentralised CCS infrastructure. The (hydrogen) BECCS supply chain is more versatile, producing hydrogen with the potential to support the decarbonisation of not just power, but heat and transport sectors. The GGR potential sits in the middle and has greater benefits from a biomass sustainability perspective, yet, hydrogen infrastructure is not established, and costs remain uncertain. The relative performance of alternative BECCS supply chains should consider direct links between CO2 removal and sustainable biomass and land use, as well as GGR potential.

Abstract The coffee sector generates vast amounts of residues along its value chain. Crop residues, like coffee stems, are burned in the field, used for domestic cooking or coffee drying in processing plants having significant environmental and health implication to rural communities. This research investigated the environmental impacts of replacing current practices with modern bioenergy applications in the Colombian coffee sector. A biomass gasification system to produce decentralised energy from coffee stems was considered, and the environmental impacts of such bioenergy implementation were evaluated. A lifecycle assessment was conducted to quantify the environmental performance of this bioenergy system and compare it to current residues uses and energy needs that feature small-to large-scale coffee farms. The results show that deploying modern bioenergy could result in reductions in 48–86% greenhouse gas (GHG) emissions and up to 98% less particulate matter formation when current practices and fossil-based energy are replaced. However, negative impacts should be considered as substituting grid electricity, largely generated from hydro-electricity, could increase GHGs by 68% and fossil fuel consumption by 73%. The results also show the relevance of understanding the environmental performance of bioenergy systems compared to reference scenarios; this allowed to evaluate and identify environmental trade-offs from modern bioenergy implementations. To maximise benefits and minimise the limitations of these systems, it is important to conduct whole-system assessments that inform on the wider environmental impacts of using agri-residues for bioenergy generation in a region- and system-specific context.

Abstract The coffee sector generates vast amounts of residues along its value chain. Crop residues, like coffee stems, are burned in the field, used for domestic cooking or coffee drying in processing plants having significant environmental and health implication to rural communities. This research investigated the environmental impacts of replacing current practices with modern bioenergy applications in the Colombian coffee sector. A biomass gasification system to produce decentralised energy from coffee stems was considered, and the environmental impacts of such bioenergy implementation were evaluated. A lifecycle assessment was conducted to quantify the environmental performance of this bioenergy system and compare it to current residues uses and energy needs that feature small-to large-scale coffee farms. The results show that deploying modern bioenergy could result in reductions in 48–86% greenhouse gas (GHG) emissions and up to 98% less particulate matter formation when current practices and fossil-based energy are replaced. However, negative impacts should be considered as substituting grid electricity, largely generated from hydro-electricity, could increase GHGs by 68% and fossil fuel consumption by 73%. The results also show the relevance of understanding the environmental performance of bioenergy systems compared to reference scenarios; this allowed to evaluate and identify environmental trade-offs from modern bioenergy implementations. To maximise benefits and minimise the limitations of these systems, it is important to conduct whole-system assessments that inform on the wider environmental impacts of using agri-residues for bioenergy generation in a region- and system-specific context.