Commercial Ebullated Bed Vacuum Residue Hydrocracking Performance Improvement during Processing Difficult Feeds oleh Borislav Enchev Georgiev, Dicho Stoyanov Stratiev, Georgy Stoilov Argirov, Angel Nedelchev, Rosen Dinkov, Ivelina Kostova Shishkova, Mihail Ivanov, Krassimir Atanassov, Simeon Ribagin, Georgi Nikolov Palichev, Svetoslav Nenov, Sotir Sotirov, Evdokia Sotirova, Dimitar Pilev, Danail Dichev Stratiev