Pelletization: An alternative for polygeneration in the palm oil industry

Agricultural residues continue to attract interest for energy recovery purposes as a renewable, CO₂ neutral and increasingly cost-competitive alternative to traditional fossil fuels. Furthermore, some of these residues, like palm oil residues, represent a disposal problem for the processing industries, or they are not used efficiently. Several palm oil mills (POM) lack efficient energy systems and thus there is a considerable potential for improvement. These factors represent a strong driving force for the development of innovative polygeneration plants with combined electricity, heat and refined fuel production based on conversion of solid residues. This paper aims at analyzing the use of agro-industrial residues as fuel. For that, we propose different technology configurations based on the case of a small-scale palm oil mill in Colombia processing 30 tons of fresh fruit bunch per hour. The technology configurations include steam cycles using backpressure turbines, condensing-extraction turbines and also gasification-gas engine cycles in hybrid configurations. The possibilities to produce pellets from the residues from palm oil were also analyzed. The steam cycle base operational parameters were 20 bar and 350 °C. However, more advanced steam conditions (40 bar) were also considered and evaluated. All the analyses performed included a maximum of 60 % of the empty fruit bunch (EFB) produced in the POM for energy purposes due to its value as natural fertilizer in the palm oil plantations. The results show that the POM under study and other POMs that use electricity from the national grid have the capacity of being self-sufficient to cover of all their energy needs using the solid residues available. This means that POMs that currently only generate the required heat for the process can generate the electricity required and in some cases even an excess of energy that could be sold to other users with an adequate use of the residues available. Furthermore, based on the modeling done in Aspen Utilities Planner® it is shown that it is possible to cover the demand of the POM, the required energy demand for EFB preparation included possible pelletization of these residues and even generate an excess of electricity. In several of the configurations, excess electricity generation could be achieved in the range of 0.5-8 MW.