Experimental investigation of a radiative heat pipe for waste heat recovery in a ceramics kiln

Following the energy crisis in the 1980s, energy-saving technologies have been investigated and implemented in order to decrease the energy consumption and greenhouse gas emissions of major industrial sectors such as metals, ceramics and concrete. The ceramics industry is still, in Europe, one of the major energy consuming manufacturing processes. Hence energy saving solutions have been investigated in order to decrease the energy consumption of the manufacturing process. The main energy-consuming process is the firing stage with more than 50% of all of the energy required for the process. The energy used during the firing stage is then released during the cooling stage. To improve the heat recovered during the cooling stage, a radiative heat pipe ceiling has been investigated. The heat recovered during the cooling stage is then sent to the drying stage. The proposed system is composed of a radiative heat pipe, a kiln and a ceramics heater. The radiative heat pipe is made of ten parallel pipes of 28 mm diameter and a wall thickness of 2 mm the tubes are connected at the bottom by a 28 mm pipe and a condenser section of 50 mm the condenser is a shell and tube system with 9 pipes of 10 mm. The system was cooled by water. The radiative heat pipe has been tested at different flow rate and ceramics heater temperature. The experimental results shown that the radiative heat pipe was able to recover heat using radiation and natural convection in an enclosed kiln. The system was able to recover up to 4 kW. This paper describes this innovative solution for recovering heat from the cooling stage of an earth roller kiln for tile ceramics manufacturing, transformed into hot clean air for the drying stage of the ceramics manufacturing process.