Industrial Flowmeter for Pneumatically Conveyed Bulk Solids

During the last four years, members of the Institute of Electrical Measurement and Measurement Signal Processing were engaged in the development of flowmeters for the field of pneumatic conveying applications for gas-solids flows. The essential task of such a flowmeter is the measurement of the prevailing material velocity and the material concentration, parameters with which the mass flow can be determined. Among the realised sensor principles, the developed capacitive cross-correlation flowmeter turned out to be by far the most reliable and cost- effective principle. In the course of this Translational Research Program, a transfer shall be undertaken from results of intensive and successful basic research towards an industrial flowmeter for pneumatically conveyed bulk solids, as can be found in numerous industrial, agricultural or pharmaceutic applications. Based on the insights gained in practical testing of our prototype sensor under industrial conveying conditions, several improvements of the technology are required for the flowmeter: The program is scheduled for two years and comprises the design and the evaluation of two different excitation strategies for the sensor front-end as well as a fundamental improvement of the circuitry in terms of measurement rate. It is furthermore necessary to develop suitable calibration strategies for the mass flow determination and enhanced reconstruction methods for the material velocity and material concentration. A cost- effective, industrial flowmeter furthermore requires an implementation of the cross-correlation function calculation on a digital signal processor instead of a personal computer. For every critical development step, the sensor will be tested at the facilities of the national research partner. The final testing and evaluation of the flow sensor will be carried out at the Centre for Bulk Solids and Particulate Technologies, University of Wollongong, Australia.

The material velocity and mass flow of fluids and gases through pipes and tubes can be measured reliably and with sufficient accuracy for most industrial applications. For gas-solids flows (e.g. pneumatically conveyed bulk solids, where material is taken through a pipeline by means of a gas flow), the determination of these parameters is still a challenge and a current topic in industry and science. This sort of flow is very common in industrial processes since material such as coal or sand, and products such as cornflakes or plastic pellets are pneumatically conveyed in a variety of applications. Reliable measurement approaches for material velocity and mass flow will help to make industrial processes safer and more efficient, increase product quality and reduce energy consumption (i.e. CO 2 reduction). In the course of the TRP project L355, two measurement principles - one based on a cross- correlation principle and one on a grid-structured spatial filtering principle - have been developed towards a sensor prototype that can be used in industrial conveying processes. The capacitive measurement setup used for both approaches basically consists of an array of flexible electrodes mounted on the outer surface of a non-conducting pipe section as well as an evaluation circuitry that meets the requirements for operation under harsh environmental conditions to be found in industrial production processes. The material motion in a pipe and the ratio and distribution of granular material and gas is determined by means of the sensor. One of the main advantages of the innovative measurement principle is that the parameters of interest can be obtained from outside the pipe without the necessity of exposing the device to the abrasive material flow. The control and evaluation circuitry developed for this sensor is a versatile platform and is well suited for different and quickly varying flow patterns. The applicability of the sensor principle and the versatile measurement hardware could also be shown for other transportation processes than pneumatic conveying, such as screw conveying of wood pellets or flow measurement of liquid hydrogen. Since material moisture is a crucial parameter in bulk materials handling, methods and practical applications have been investigated for online moisture determination. The main output of the project is a versatile and easy to install prototype flow meter for gas-solids flows that has been presented to public e.g. at Austrian Research 2010 Exhibition. The work has been documented in more than 30 scientific papers and three granted patents. The project supported the scientific development of the project team and contributed to finish two habilitation theses and one PhD thesis.