Optimization of coagulation process of coke microparticles for filtration and gravity separation systems

Remarkable amounts of coke microparticles are discarded along with the effluent of decoking and olefin units and their separation methods have not been studied as the environmental pollutants. In this work for the first time the appropriate flocculant was determined for the separation of coke microparticles and then, the optimized conditions of simultaneous-experimental coagulation/flocculation process were determined based on the maximum amounts of sedimentary particles. After that, using the hypothesis of extreme agglomeration, the optimal conditions were calculated based on the maximum efficiency of filtration of gravity separation of coagulated particles. A set of purposeful experiments were performed based on the response surface method and using FeSO4, Al2(SO4)3 and FeCl3 coagulants at concentrations of 10, 15 and 20 ppm and with cationic (Zetafloc 7563), natural (Besfloc K300N) and anionic (Megafloc 3045PWG) poly acrylamide flocculants at concentrations of 3, 5 and 7 ppm in solutions with pH levels of 5, 7 and 9. According to the diameter criteria of sedimentary particles (d>21μm) the uniformity/curvature coefficients were obtained for the optimal conditions of particle coagulation. The results revealed that according to the negative surface charge of coke particles the maximum number of precipitable particles is formed with a yield of 96% using iron chloride(III) coagulant (8ppm), anionic polyacrylamide flocculant (2ppm) at pH=6. Moreover, based on the uniformity/curvature coefficients the results showed the priority of iron sulfate(II) as coagulant for enhancement of filtration efficiency since the diameter distribution of coagulated coke particles maximizes the porosity of filter-cake, the operation time of filter and the volume of accumulated cake. While the type of coagulant has no effect on the gravity-based separation efficiency of coagulated coke particles. Based on the results, the optimum ratio of coagulant to flocculant concentrations were determined to be 3 and less than 3 (1.5–3) for filtration and gravity separation systems.