Using CFD to Study Combustion and Steam Flow Distribution Effects on Reheater Tubes Operation

The thickness measurements showed that boilers of the Shahid Rajaee power plant have a non-uniform thickness in some regions of the final reheater tubes after 80,000 h of operation. Experimental tests on areas such as thickness, hardness, metallography, and recorded temperature showed that high temperature erosion is the most obvious reason for thinning in these tubes. Therefore, two possible reasons for the non-uniform tube thinning (problems due to combustion and steam mal-distribution in the tubes) were explored. This paper presents simulations of combustion, flow distribution in reheater tubes, and heat exchange process in Pass 1 of the boiler using FLUENT software. Combustion simulation results showed temperature distribution and mass flux of combustion products are not uniform at the chamber outlet. But these non-uniformities are not proportional to the tubes’ thickness non-uniformity; whereas, simulations showed steam is mal-distributed in the tubes so that steam maldistribution is proportional to the tubes’ thickness non-uniformities. Because steam maldistribution was due to mal-feeding and offloading of headers (U-type headers), all possible ways of feeding and offloading of headers were studied, and the results showed that the H-type configuration has the most uniform flow distribution.