(628b) Comparison of the Synthesis Gas Production Via Gasification and Combustion from Coffee Cut-Stems

The use of agro-industrial wastes as an alternative renewable energy to reduce the dependence on fossil fuels, in recent years, has gained great importance. Coffee crop residues have high energy potential and high availability as raw material. According to [1], an annual turnover rate of Coffee crops of about 80.000 Hectares from which about 16 ton/Ha of Coffee Cut-Stems can be obtained. Most of these coffee crops residues are used directly in combustion processes for cooking and heating in agricultural farms, where the energy density is lower and causes environmental issues. New paths for the use of these wastes to obtain high value-added products is of great interest to Coffee producers countries.

Wide range of technologies exists for transforming this energy rich biomass. Thermochemical technologies such as pyrolysis, combustion and gasification are the most interesting concepts, focusing on the use of biomass as source for energy at positive net balances [2]. Agricultural biomass is mainly used for energy purposes in combustion process. It is currently sold as fuel for industrial units and as energy source for the household and services sectors. On the other hand, gasification processes have gained great interest in the last years given a high energy yield compared to the combustion and less emissions. The gas obtained via gasification can be used as platform for other processes such as the production of bioethanol, ethylene glycol and cogeneration processes. Meanwhile the main use of the combustion gases is related to the thermal energy generation.

There are no major differences between the combustion process (during which organic materials react against oxygen) and the gasification process [4]. Gas produced composition is the main difference between these two processes, which is related to the air/fuel ratio applied [3]. Considering that biomass has the composition of cellulose (C₆H₁₀O₅), gasification and combustion can be represented through global chemical equations, as follows:

This paper evaluates the production of synthesis gas and the combustion gas by means of energy and environmental analysis using as raw material Coffee Cut-Stems. Feedstock was obtained from producer coffee farms in Chinchiná, Caldas, Colombia (4° 58′ 50″ N, 75° 36′ 27″ W). The raw material was characterized by measuring extractives content (NREL/TP-510-42619), ash content (NREL/TP-510-42622), holocellulose content (ASTM Standard D1104), cellulose content (TAPPI 203 os-74 method) and acid-insoluble lignin (TAPPI T222). The energy analysis was carried out using the commercial simulator Aspen Plus v8.0 (from Aspen Technology, Inc., USA). Besides, eight environmental categories were evaluated using the waste reduction algorithm developed by the Environmental Protection Agency (EPA).  Verification experiments were developed at small scale using “GEK Gasifier (20 KW/h) Power Pallet” and a furnace. The gas produced by both technologies was analyzed using a portable syngas infrared analyzer (GASBOARD-3100P)

Biomass gasification seems to be the most promising technology for the use of Coffee Cut-Stems with high energy yields and low environmental issues. However, the combustion, for being a process with a low capital investment, has more applicability to industrial level than gasification technology.

References

[1] Farfán. F, El zoqueo del café conserva el bosque nativo, Avances Técnicos de Cenicafé, 2000.
[2] Demirbas. A, Potential applications of renewable energy sources, biomass combustion problems in boiler power systems and combustion related environmental issues, Progress I Energy and Combustion Science, Vol 31, pp. 171-192, 2005.
[3] Thermie – European Community Programme, Combustion and Gasification of Agricultural Biomass – Technologies and Applications, 1995.
[4] Valencia. M, Cardona. C, Carbon dioxide from combustion stream: A conceptual approach, Revista Facultad de Ingeniería, Vol. 22, pp. 45-53, 2013.