Obtaining hybrid fuel briquettes using local biomass and fossil fuel resources

Ulusoy Tasar, Aslı
This study aims at obtaining a hybrid fossil fuel-biomass fuel by blending olive pomace and lignite in varying amounts (10-50% by weight). The main objective is to combine the positive characteristics of both fuel types to rehabilitate their unfavorable sides that are potential drawbacks against their broader utilization. The suggested hybrid fuel is anticipated to be an effective, environmentally sound, and sustainable fuel alternative. To obtain the hybrid fuel, olive pomace from the Aegean region in Turkey and ROM Tuncbilek lignite characterized with high ash and sulfur content, are used. The project has two major phases: 1. Identification of the fuel characteristics and combustion behavior of hybrid blends; 2. Briquetting of fuel blends to obtain a hybrid fuel form. In the first phase, the fuel and emission characteristics of the olive pomace and lignite on an individual basis as well as in the form of fuel blends, were determined. The liability of both fuel types and their blends to combustion were also identified. The proximate and ultimate analysis, TG/DTG, DSC, and TG-FTIR work revealed that using olive pomace and lignite in blended form results in significant differences in terms of fuel characteristics, combustion behavior, and combustion liability as compared to the fuels on individual basis. Blending olive pomace and lignite resulted in reductions in sulfur contents and SO2 emissions as compared to the lignite alone and the extent of improvement increased as the amount of olive pomace in the blends was increased. This demonstrated that blending high-sulfur lignite with olive pomace could be an effective solution to rehabilitate SO2 emissions. When the liability to combustion was assessed, it was seen that the activation energy of lignite is approximately 2.5 times less than that of olive pomace. This shows that the liability of lignite to combustion is much higher than that of pomace. Activation energies of fuel blends were also less than olive pomace. This implies that the use of olive pomace with lignite in a hybrid fuel form is more favorable than using olive pomace alone as a fuel, since lignite in the fuel blend can rehabilitate the relatively lower combustion liability of olive pomace. Overall, the results of the investigations on fuel characteristics and combustion behavior revealed that using lignite and olive pomace in a hybrid fuel form can bring notable advantages to both fuel types. The negative aspects related to the use of these two fuels on an individual basis, could be significantly rehabilitated, if they are utilized together in the form of a hybrid fuel. The suggested approach is a novel and a favorable solution that fosters the positive sides of lignite and olive pomace in the body of a new fuel alternative. In the second phase, which focuses on briquetting, firstly the briquettability of the lignite alone was identified. Lignite briquettes were obtained using 10% (by wt) molasses as a binder. The effects of particle size, water addition, and briquetting pressure on the strength of the briquettes were investigated. In ideal briquetting conditions, the lignite briquettes can show required levels of drop, abrasion, and breakage resistance designated for Type I briquettes in the TS12055 standard. In obtaining hybrid briquettes from olive pomace-lignite blends, firstly the strength characteristics of binderless briquettes were evaluated for several olive pomace related briquetting conditions (such as the amount of olive pomace in blends, particle size of olive pomace, and moisture content). The binderless hybrid briquettes failed to meet the strength conditions for Type I briquettes. Yet, in ideal briquetting conditions they could meet the required abrasion and breakage resistance levels designated for Type II briquettes, thanks to the limited binding effect of olive pomace. As a last step, olive pomace-lignite blends were briquetted using binding agents to satisfy strength designations for Type I briquettes. The blends were briquetted, firstly, by using only molasses and then by using molasses+lime. The strength properties of the binder-added hybrid briquettes were determined with respect to varying quantities of molasses addition (5-15% by wt.) and lime addition (4-6% by wt.). It was seen that, even with 5% molasses addition, strength requirements for Type I briquettes could be achieved. Obtaining favorable strength features with limited molasses addition was attributed to the binding effect of olive pomace: Pomace in the blends successfully reduced the required binder amount or obtaining fuel briquettes with sufficient strength characteristics. Use of lime as a binder along with molasses could not provide an apparent improvement in the strength of the briquettes. On the other hand, none of the briquetting conditions studied in this project could provide water-resistant briquettes. This is a well-known problem common for most Turkish lignite. To overcome this problem, the hybrid briquettes could be supplied in sealed bags to the market, as suggested in the TS12055 standard. To conclude, this study showed that utilization of olive pomace and lignite in a hybrid fuel form can lead to several benefits in terms of fuel quality, combustion behavior, and SO2 emissions. It is very advantageous to stimulate the positive sides of both fuel types while controlling and reducing the negative features of lignite and olive pomace by utilizing these fuels in a hybrid form. This approach is therefore an effective solution towards an extensive, sustainable, and environmentally sound utilization of these fuel types. Proven briquettability of the olive pomace-lignite blends is another important aspect that would contribute to the broader use of the suggested hybrid fuel.
Citation Formats
A. Ulusoy Tasar, “Obtaining hybrid fuel briquettes using local biomass and fossil fuel resources,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Mining Engineering., Middle East Technical University, 2019.