Microwave moisture levelling of lucerne chaff

Abstract

This project has seen the development of a low cost method of microwave drying of lucerne chaff prior to packaging and distribution. Lucerne has long been used as a high protein food source for livestock in particular for horses fed in the form of a dry chaff. The process of harvesting the lucerne is complicated by the long drying times prior to baling. This requires that the weather remains fine and no rain occurs during this period, as rain on the cut lucerne causes loss of colour and higher than target moisture contents which has the effect of poor shelf life and loss of colour.

By exploiting the drying capability of microwave heating a low cost prototype was designed to reduce the moisture content of the lucerne post chopping down below 10% whilst maintaining the green colour. The designed system consists of seven individual magnetrons providing 1.2kW each of heating power to the chaff on a conveyor belt moving at 0.5m/s. Individual cavities were designed so as to allow the conveyor to move product through the system whilst avoiding adverse interactions occurring between the individual magnetrons. The constructed system has been constructed and trialled at Putaruru Lucerne and has clearly demonstrated the concept. On one trial the lucerne chaff moisture content was reduced from an unstable 14% down to 9% which substantially extends the shelf life of the end product. This system also means that the lucerne can be baled days earlier at a much higher moisture content removing the current issues around weather stability