Optimized kiln operation by keeping kiln shell temperatures at set point with controlled water cooling

The increasingly powerful and sophisticated kiln firing process conditions make it necessary to cool the kiln shell in order to protect the refractory material and the steel body from overheating and wear. Traditionally the cooling is done with high performance blowers and only a few plants in the world are actually working more or less successfully with cooling by water evaporation. In 2014 a team consisting of the VDZ and a Cement Manufacturer, decided to conduct as an expert in measurement and control technologies. The aim was to develop an efficient cooling system with the medium of water. The goal was to determine at first how much water is needed to produce not an equivalent cooling effect as achieved with a conventional cooling fan. Advantages of the water cooling are obvious: Higher cooling effect Electrical energy consumption is very low Opportunity to cool a more precise point or region Low noise emissions. To accomplish a precise and robust control for the amount of water, a control unit was constructed by the supplying company, which has extensive monitoring mechanisms. Besides monitoring the kiln shell temperature using an infrared pyrometer, the amount of water per nozzle and the water pressure of the four separate cooling units are constantly checked. According to a freely selectable desired value (target temperature) for each cooling unit, the respective water nozzle is only supplied with water via a solenoid valve while the reference value is exceeded. Each of the 4 cooling units is thus adapted to the ideal kiln shell temperature and is therefore only spraying water on the local area, as long as it is above the target temperature. The selective cooling of a very hot local area even offers the opportunity to reduce the extreme stress to the surrounding area, thereby preventing excessive stretching, which is particularly advantageous for the refractory material. Within more than 20 installations world-wide operators confirm that it was possible to extend the kiln operation using the patented system for several weeks-sometimes months, so that they could avoid an unplanned kiln stop due to furnace hot spots. The following article describes the system developed by a German measurement and control company together with a Cement Producer and the German Cement Producers Association and shows case studies from all over the world.