There are several literature where you can found some explanation about that:
-Jakob, Russ R., “Coke Quality and How to make it” Hydrocarbon Processing, Sep-71
-Marsh, H, Clavert, Bacha,J., “Structure and Formation of Shot Coke”- A microscopy study”, Journal of materials Science, March 13, !894, Chapman and Hall Ltd, PP 289-302
-Ellis, PaulJ, Bacha, John D. “Shot Coke” Ligth Metal 1996, PP 477-484
-Ellis, PaulJ., Hardin, Edward E.,”How Petroleum Delayed Coke form In a Drum” Light Metal 1993 pp 509-515
-Ellis, Paul J. Hardin “Pilot delayed Coker” Light Metal 1992 pp 609-615
Best Regards