The Biot number, one of the factors of the heat transfer coefficient, is computed through computational particle fluid dynamic simulation for the development of Oxy-PFBC technology. This technology enables no additional CO2 separation for its capture by injecting pure oxygen, rather than air into pressurized bubbling fluidized bed boilers. This number is a dimensionless coefficient that is affected by the structure of the combustor and its heat exchangers, determining the degree of heat diffusion in the fluidized bed. In this manner, finding the proper Biot number is important for the development of Oxy-PFBC design program since it directly affects operability and performance. First, to compute the Biot number, the model of the Grimethrope PFBC combustor was demonstrated through the KEPCO-GTI Oxy-PFBC design program. The program showed good prediction of the Grimethorpe bed temperature profile after the calibration of the Biot number. The bed temperature profile for a specific combustor structural design and operation condition was computed; it was used to calibrate the Biot number suitable for the Oxy-PFBC combustor, through 3D computational particle fluid dynamics simulation (Barracuda program). The calibrated Biot number turns out to be ten times smaller, which is from 0.002 to 0.0002. Prior to computing the Biot number, to validate the simulation program, a comparison analysis was conducted with cold-flow fluidization test data. The results showed that the simulation matched well with the actual test data.