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Automation Technologies 3/2015

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Automation Technologies 3/2015

Robust solution in a

Robust solution in a Chinese steelworks Lin Qiang At a Chinese steelworks with coking plant, the Turck HF-RFID system BL ident monitors the position of the coke ladle lift in the CDQ unit. The system has been working with 100% reliability for several years despite extremely harsh operating conditions. Author: Lin Qiang is Market & Product Manager for Turck in China

SENSORS AND MEASUREMENT next page The Chinese environmental and economic authorities recently identified a procedure for the quenching of coke as a key energy saving technology, and promote the process as a major environmental protection measure: The procedure is called coke dry quenching (CDQ). During coke production, coking coal is usually heated under vacuum to over 1,000 to 1,400 °C, and baked into coke for 17 to 25 h. Coke is primarily used as fuel in steel production. Towards the end of the process, the coke still holds a temperature of around 1,000 °C. Any contact with oxygen would result in immediate combustion. The coke therefore has to be cooled or “quenched” to prevent it bursting into flame. The traditional and technically unsophisticated procedure was a wet quenching, in which the coke was cooled with water. The energy in the coke in the form of heat simply dissipated without being harnessed. Energy-saving CDQ A modern and technically more sophisticated and also energy-saving and more eco-friendly procedure is coke dry quenching. In a cooling chamber of a CDQ plant, coke at around 1,000 °C is cooled using an inert gas – mostly nitrogen. The nitrogen heats to 850 to 950 °C, cooling the coke to below 200 °C. The heated inert gas generates process steam via a heat exchanger, which is then conducted to a power generation unit, where it generates electricity via a gas turbine. After quenching, the cooled coke is transported via a conveyor belt to the coke repository and the screening plant. The CDQ plant consists of a motor, a ladle, a lift, the coke feeder, the CDQ cooling system, the coke storage unit, and the heat exchanger and nitrogen circulation system. A crane lifts and lowers the coke ladle with the hot coke to feed the CDQ cooling system. The crane must speed up and slow down to prevent accidents with falling coke or the coke ladle. The exact position of the lift must be monitored to allow the dynamic control of the lift system. 01 The RFID read/write heads mounted on the steel beam monitor the passing coke ladle and decelerate the travel speed of the lift 02 All data from the read/write heads converges at the BL67 gateway and the RFID-S modules Error-prone sensor information The operator had for a long time used inductive proximity switches located in the groove to capture the vertical position of the coke ladle in the lift. However, the switches often fell out of the groove due to the extreme environmental conditions. Since the plant is an open air facility, severe snowfall or rain, as well as disruptions in the magnetic field were enough to cause process errors. All these problems were solved with the introduction of the HF-RFID system BL ident as a replacement for the sensors. A data medium was mounted at the upper hook of the coke ladle. The read/write head is located on the steel beam of the lifting crane. The solution not only resolved wiring issues, but also the installation problem. Eight read/write heads monitor the data medium in motion – four at the upper edge and four at the lower end of the travel distance. The first read/write head initiates the delay when the crane lifts, decelerating its speed from 20 to 10 m/min. The second read/write head initiates the braking process from 10 down to 4 m/min. The third signals the crane driver AUTOMATION TECHNOLOGIES 3/2015