Techno-economic assessment of the conversion of Cuban sugar cane lignocellulosic residues into liquid biofuels

Samenvatting

Annual sugarcane production in Cuba is currently about 25 million metric tons a year. The main residues from sugarcane processing include bagasse and sugarcane agricultural residues. Sugarcane bagasse is the fibrous material that remains after recovering the sugar containing juice after crushing and extraction. On the other hand, the use of mechanical harvesting also generates significant amount of plant residues (i.e. leafs), hence denoted as sugarcane agricultural residues or trash.

 

A subject of research today is to find a solution to sugarcane residues as energy sources. Current day practices in Cuba include burning the majority of the sugarcane bagasse in low efficiency (< 20 %) boilers for steam generation in order to meet the demands of the local sugar production and at the same time burning provides a means for waste disposal of any excess bagasse. As such, no excess energy (electricity, heat) is being produced and the energy potential of bagasse is largely unused. Although the potential exists for the agricultural residues resulting from harvesting to be used in cattle feed or as a solid fuel, in current day practices in Cuba, these are most often burnt, resulting in environmental burden.

 

Recent advances in boiler technology, with the possibility of cogeneration and the use of high temperature/high pressure steam boilers, has led to higher efficiencies. As a consequence, lower amounts of bagasse and residues are required to be burnt in order to cover the sugarcane processing plant’s energy needs. In the absence of a proper infrastructure to export electrical as well as thermal energy, the surplus bagasse and other agricultural residues become available for alternative processing which can amount up to 50 wt% of the originally generated sugarcane processing byproducts.

 

One of the more attractive alternative technologies to process the bagasse and other agricultural sugarcane residues is fast pyrolysis, whereby solid biomass is mainly converted into bio-oil (a liquid fuel intermediate) and char. The major benefit of fast pyrolysis technology over combustion or gasification technologies is that it effectively decouples fuel production from its application, both in time and in space. The bio-oil is a dense energy and as such, can be stored for later use or exported to remote application sites, using existing fuel transportation infrastructure. The char, being a byproduct from biomass fast pyrolysis can be used as a solid fuel with HHV up to 35 MJ/kg or as a soil amendment to improve fertility and plant productivity. Consequently, the flexibility offered by fast pyrolysis to transform biomass into energy-dense liquid (and solid) biofuels could significantly improve the profitability of sugarcane plantations.

 

Biomass fast pyrolysis platform for bagasse and sugarcane agricultural residues

Figure 1. Biomass fast pyrolysis platform for bagasse and sugarcane agricultural residues.

 

The overall aim of this PhD research is to perform a techno-economic assessment of the conversion of Cuban sugarcane lignocellulosic residues by pyrolysis processes to obtain maximum yields of liquid fuels at low cost. To this end, the PhD project will include experimental as well as modelling specific objectives. For the experimental part, these specific objectives include assessing the suitability of bagasse and other agricultural residues originating from Cuban sugarcane processing as feedstock material for fast pyrolysis; testing the effectiveness of demineralizing the feedstock in terms of reduction of the bio-oil’s ash content and the stability of the bio-oil; and studying the applicability of bio-oil in boilers and internal combustion engines. The specific goals relating to modelling include the development of a full-scale plant model to predict the energetic performance of an integrated sugarcane-fast pyrolysis plant as well as the economic costs and profitability thereof. Apart from the techno-economic feasibility, the environmental impact of the integrated sugarcane processing/fast pyrolysis plant will be assessed as well using life cycle analysis.

 

Feedstocks used in this study

Figure 2. Feedstocks used in this study.

 

Projectadministratie

Onderzoeker: Lizet Rodríguez Machín

Financiering: Bijzonder Onderzoeksfonds (BOF)

Projectduur: 30.09.2017