Briquetting of Turkish lignite coal with using organic additives

In this study, lignite coal (1-5 mm particle size and provided from Soma, western region of Turkey) was briquetted with different kinds of additives (tea waste, nutshell, verbascum and astragalus). Additives were used in different ratios (0-100 % w/w) and compression pressures varied from 5 to 25 MPa. For characterisation, chemical analysis (ash, calorific value and moisture amounts) and physical tests (shatter index and resistance to water) were applied to hybrid briquettes. In addition, torrefaction process was applied to additives and torrefied samples were compared to coal. It is concluded that; particle size of additives, compression pressure, additive types and ratios of additive amounts affected the chemical and physical properties of briquettes. However, compression pressure and particle size had not a remarkable effect on ash contents and calorific values. Most effective parameter on ash content was additive amounts. Compared to coal, hybrid briquettes had lower ash contents. Acetic acid was used for hydrolyse resin binders and usage of acetic acid have an effect on this decrease of ash contents. When the effect of each parameter on calorific value is compared, it can be said that; although particle size and compression pressure are not effective on calorific value, there is an inversely proportional to relationship between additive amount and calorific value. This result showed that, optimum additive amount is 25 % for each type of additive. Maximum calorific value is obtained by using tea waste as additive and this result is found to be 6% lower than lignite coal. Physical tests showed that, increasing additive amount made positive effect on Shatter index results. The best Shatter index values obtained by using verbascum and astragalus as additive. Water resistance tests gave the best results for the briquettes that have hazelnut shell (>72 hours) and sequenced as tea waste (24 hours), astragalus (24 hours) and verbascum (1 hour). During the torrefaction process of additives, temperature has found to be the most effective parameter. Calorific values of these samples are found to be comparable with lignite coal, depending on the residence time and process temperature.