MILLING TRAIN MACERATION CONTROL UTILISING NIR TECHNOLOGY

IN RECENT TIMES, Australian sugar factories have tried to maximise throughput. This trend has continued with factory rationalisation and a need to maximise utilisation of existing capital. The amount of maceration applied to the crushing mills has a great effect on reducing pol loss in final mill bagasse. It is generally recognised that other things being equal, the more maceration the better the extraction. However the down side is that evaporators have to be able to boil off the extra water. The capacity of the evaporators to boil off that water in turn limits crushing capacity. Other issues associated with higher maceration rates are the evaporators scale quicker and the amount of steam required to maintain crushing capacity increases. Traditional maceration rates have been determined by using a fixed percentage of water at a daily average fibre rate which is at least a 24 hours out of date. Near Infra Red (NIR) measurement was introduced to Mackay sugar mills in 2006 and can be used to determine the quantities of fibre, pol and ash contained in the incoming cane. NIR gives a real time measurement of cane parameters and has allowed fibre rates through the mills to be measured accurately. Those measurements have been combined with cane crushing rates to provide a control value for maceration addition. This accurate control of maceration rate gives the following advantages over the traditional method of controlling maceration flow: mills have a consistent maceration % fibre which means there is always sufficient water to get the required pol recovery regardless of the cane characteristics; mills are not using extra maceration – just the right amount to give the right balance between bagasse loss, evaporator capacity and steam availability; more stable ESJ (Evaporator Supply Juice) brix which produces more stable evaporator performance; consistent final bagasse moisture and quality.