The effects of thermal spreaders on reducing thermal cracks in heat recovery steam generators

Thermal cracks occur on heat recovery steam generator (HRSG) casing, leading to heat loss. The possibility of reducing the number of thermal cracks appearing in HRSG casing with the use of thermal spreaders was investigated. Before designing thermal spreader, measuring temperature and numerical analysis were performed to find the reason of thermal cracks in HRSG. Temperatures were measured at different heights on the HRSG casing, enabling to determine the temperature gradient in the casing. The largest temperature gradient occurred toward the lower region of the HRSG casing. Then, the highest thermal stress and thermal cracks were showed in this lower region due to the large temperature gradient. To reduce thermal stress in this region, thermal spreader which has large thermal conductivity was designed. Designed thermal spreaders were installed on the HRSG casing to reduce the temperature gradient of the HRSG casing. Where thermal spreaders were used, the average temperature gradient of the HRSG casing decreased from 52 °C to 16 °C. The maximum thermal stress was reduced by 16% and the average thermal stress was reduced by 26%.