On-Line Moisture Analysis

A prototype low frequency microwave analyser has been developed to more accurately monitor thick beds of high moisture coal, using low-cost antennas.

The measurement of the moisture content of materials is currently carried out by manual or automatic sampling of product, followed by conventional laboratory analysis by oven drying. Although this procedure enables the moisture content to be routinely monitored, it is frequently too slow for process control purposes. Consequently, there is a strong interest in on-line techniques for the accurate and rapid measurement of moisture in materials carried on conveyors, in chutes and in pipelines.

Microwave-based techniques have emerged over the past 40 years as the dominant technology for on-line measurement of moisture in bulk materials. Although these gauges have proven highly successful, a number of possible improvements have been identified: (1) a reduced cost for the gauge would allow a much wider and diverse application of the technology and (2) better accuracy, speed and dynamic range would allow for the same gauge to be used in a wider range of conditions. A further problem has been that the present commercial analysers are unsuited to the analysis of thick beds of high moisture coal due to their high microwave attenuation.

PROJECT OBJECTIVE

The aim of the on-line moisture analysis project was to develop the next generation of low frequency, on-belt microwave moisture analysers to provide improved performance in a wider range of applications and at a significantly lower installed cost.

FINDINGS

The major findings include:

• The development of a new low frequency microwave (LFM) technique for on-line measurement of moisture utilising:
  • High performance microwave circuitry with improved measurement accuracy (by a factor of 10), around one-tenth the cost of previous systems
  • Compact, low cost antennas that are lightweight and easily installed about a conveyor
• The development of a compact high performance moisture analyser with very high reliability and accuracy through the integration of microwave circuits, digital electronics and a flexible user interface
• A demonstration of the analysis of high tonnage (2,000tph to 10,000tph) coal on the Dalrymple Bay Coal Terminal shiploading conveyors with an overall accuracy of better than 0.3 weight percent moisture at 17 to 19 weight percent moisture. Individual ISO sample increments (~4,000 tonnes typical) were tracked to within 0.1 to 0.2 weight percent moisture.

WHERE TO FROM HERE

The researchers recommend that the technology be developed to commercial prototype stage and that discussions are held with a suitable industrial collaborator for the supply of the product to the wider market.

The researchers believe that only minor further development of the design is required to reach commercial prototype stage and they expect to finalise commercialisation plans by the end of 2001.