Is it time for agricultural crop residues?
Cenicaña carries out experiments and adapts methodologies for the partial use of agricultural residues from the sugarcane harvest in order to advance in the diversification of the agro-industry.
On the road to diversification, for some years the Colombian sugarcane agribusiness has set its sights on agricultural crop residues (RAC). And it is not for less: from these it is possible to obtain second generation ethanol, bioplastics and solvents, and generate electrical energy with the use of briquettes or bales, to mention some of the products.
If to this is added the growing worldwide concern for the environmental performance of the productive sectors, everything seems to indicate that in the future the sugarcane agroindustry will not take its eyes off the RAC. Even more so if it is estimated that Colombia generates nine million tons of agricultural waste (in fresh weight) per year, of which 25% would be usable.
To convert this waste into sustainable and profitable alternatives for mills and growers, Cenicaña is working on two research projects.
One of these projects is the production of briquettes for use as fuel.
Briquetting allows the behavior of the combustion processes to be similar to that of coal, facilitating its use in the boilers of the mill factories.
Since 2010, the Research Center began to develop equipment for densification and in 2016 technologies such as briquetting were implemented, seeking that RAC, with a density of 21 kg / m3, had a density similar to briquettes for commercial use: between 700 to 800 kg / m3.
After several experimental evaluations, RAC briquettes with a density of 1100 kg / m were achieved.3.
It should be noted that the higher the density, the lower the cost of transporting the waste and, therefore, its use in industrial processes is viable.
But not only the physical characteristics are important. In order to take advantage of waste as fuel, it is essential to understand the effects of manufacturing variables such as pressure, temperature and particle size on the mechanical and thermal characteristics of the briquette.
In the evaluations, the RAC briquettes had values comparable to those of commercial wood or wheat straw in their diametral strength, impact resistance, calorific value, and ignition and combustion times. Although these characteristics are associated with the handling, storage and performance of briquettes as fuel, achieving them is an important advance in the search for added value to the by-products of agribusiness.
In addition, from these investigations today it is known how each manufacturing parameter affects these characteristics.
According to Julián Lucuara, mechanical engineer from the Cenicaña Factory Process Program, understanding the RAC briquetting process will allow us to continue with the selection of pilot and commercial-scale technologies to evaluate the production of briquettes and their performance as fuel in the boilers of the sector.
The implementation of briquetting technologies would also open the doors to the European market, one of the main importers of densified products (briquettes or pellets) from biomass.
Biochemical use of the RAC
RAC is mainly composed of three types of polymers: cellulose, hemicellulose and lignin, which through biochemical processes can be transformed into a material with a high content of fermentable sugars to produce ethanol or other compounds (See diagram).
In order for the Colombian sugarcane agribusiness to advance towards the production of second generation ethanol from RAC, Cenicaña is working on adapting methodologies to quantify the structural carbohydrates, ash and moisture present in the residues of the cane harvest.
The evaluations on an experimental scale with residues of the variety CC 85-92 showed high contents of cellulose and hemicellulose (33% and 22% on a dry basis respectively), which support their potential use for the production of fermentable sugars.
In an experimental way, the conversion of cellulose to glucose up to 65% was achieved, which shows the good response of commercial yeasts for the production of ethanol using enzymatic hydrolyzates of harvest residues as substrate. The research will continue with the evaluation of different conditions to maximize the hydrolysis of cellulose and obtain hydrolyzates with a high content of fermentable sugars that can be transformed into ethanol.
Although the results of these investigations are still preliminary and many stages have to be overcome so that the use of the RAC on a commercial scale is a reality, the truth is that the Colombian cane industry has the potential to participate in new markets and continue to provide sustainable solutions to society