Lime is used extensively in steel industry as fluxing material. Lime is produced by calcination of limestone in a lime kiln. Kilns have several lances for injecting fuel for the calcination process.
Lance tip temperature during firing is about 900-10000C. Lance choking causes disturbance in the temperature profile inside the kiln thus impacting the consistency in quality of lime. If lance choking leads to calcination temperature below 900oC then it can lead to lower production rate and poor quality of lime. Hence, it becomes very important to maintain stringent temperature profile in all the zones of lime kiln.
Kiln operators find it difficult to identify the specific location in the kiln periphery where deposition/choking is happening in lance, since the lance is not accessible during calcination process. Lance tip is always maintained at a positive pressure i.e. fuel is flowing through the lance while firing and air is flowing through the lance while in idle condition. At present, operators come to know about the choking only when improperly calcined lime is detected during daily inspection. By this time, lance choking would have already started impacting lime quality in that zone.
Coke Oven Gas and Blast Furnace Gas are used as fuel in lime kiln. The input fuel gas contains certain amount of moisture. During high moisture conditions (eg rainy season), the raw material i.e. limestone also absorbs moisture from the atmosphere. This moisture results in Ca(OH)2 which sticks easily on the lance and nozzle openings, leading to choking. Lance choking generally starts within 15 days from the last lance cleaning and sometimes a lance gets completely choked within 30 days. A cleaned lance hole vis-à-vis choked lance hole image is shown in Figure 1. It requires 6 hours of downtime to clean the choked lance. Cleaning of lance is currently done using steel ropes and it’s a tedious process.
Solutions are invited for non-invasive techniques that will solve one or several of the below challenges: