Among the various carbon capture technologies, oxyfuel combustion provides an effective way to reduce CO2 emissions, because of similar flame characteristics, relative to those of air combustion, and its ability to be retrofitted in the existing plants. In this work, combustion of liquid fuel in O-2/CO2 environment inside a water-tube boiler has been modeled numerically, and the results were compared with that of the air combustion case. Two cases of oxycombustion were studied: (i) OF21 (21% oxygen (by volume) aand 79% CO2 (by volume)) and (ii) OF29 (29% oxygen (by volume) and 71% CO2 (by volume)). The model was extended to study the effects of droplet size and swirl number on the combustion Characteristics of the liquid fuel. Probability density function (PDF) was applied to solve the turbulence-chemistry interaction. It Was found that the replacement of N-2 from air with carbon dioxide significantly reduces the temperature level.. It was also found that reducing the CO2 concentration results in an increase in the flame temperature. For the air combustion case, heat transfer the water jackets was Much higher than that of oxycombustion cases.