Experiments on novel heat recovery systems on rotary kilns

Highlights: • A novel heat recovery system with better heat recovery performance was proposed. • The heat recovery performance was investigated based on large-scale experiments. • The heat transfer correlations of heat recovery exchangers were deduced. In this paper, we have proposed a novel heat recovery system installed on the rotary kiln. The experimental measurements are carried out to investigate the heat transfer characteristic and fluid flow performance of the nine heat recovery exchangers in the heat recovery system. The experimental platform is set up to study the operational characteristic of the system. The measurement results show that the outlet temperatures of the heat recovery exchangers mostly varies as the inlet temperatures increases while the experiments have certain hysteresis. Besides, the outlet pressure of the heat recovery exchanger varies as the inlet pressure changes. The measurement parameters of the inlet and outlet pressure have the same variation trend and quick responses with no hysteresis. When the inlet mass flow rate varies from 0 to 6 kg/s, the heat recovery exchangers with coiled pipes could effectively improve the heat recovery performance compared with the radiant type. Then the heat recovery performance of three different types of heat recovery exchangers in the system are investigated to obtain the heat transfer surfaces with better thermal efficiency on rotary kilns. The experimental measurements indicate that the heat recovery performance of the heat recovery exchanger with two layer of coiled pipes is better than the others. Furthermore, the heat transfer rate of the heat recovery exchanger with two layer of coiled pipes is increased by 15.3% compared with the existing heat recovery exchanger in literatures.