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Early smouldering detection in spray dryers
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Drying of powders entails a serious fire risk. By far the greater part of fires in drying installations start by self-ignition of the product (smouldering). In many situations, experience and alertness of operators proved to be inadequate for early detection. NIZO food research therefore developed an on-line system (NICOSYS) that detects smouldering powder before it starts burning. NICOSYS has proven its value and is now installed worldwide for drying applications. Smouldering starts as a result of exothermic reactions occurring in the product due to exposure to hot or warm air. One of the reaction products in these reactions is carbon monoxide (CO) gas. NICOSYS is based on the measurement of the carbon monoxide concentration. It is being marketed by Hobré Instruments and has found its way to many applications, e.g. milk, coffee and cocoa based powders. Every product is unique. In order to decide whether a smouldering detection system is suitable for a specific product in a specific drying process, the smouldering properties of the powders need to be known. These are: the minimum self-ignition temperature, the minimum size of a lump of powder to self-ignite and the CO production of smouldering product. NIZO food research can determine all these smouldering properties. Based on these data advice can be given for the application of a smouldering detection system. |
