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BIA-Brukerstyrt innovasjonsarena

Effective Handling of Bulk Solids with Focus on Reduction of Erosion and Scale Formation

Alternative title: Effektiv håndtering av pulver for å unngå slitasje (erosjon) og for å hindre dannelse av belegg

Awarded: NOK 12.7 mill.

Project Number:

247789

Project Period:

2015 - 2019

Funding received from:

Subject Fields:

Erosion and scale formation can cause major challenges in process industry (e.g., metal and mineral industry) where bulk solids are handled. The objective of the research project, 'Effective Handling of Bulk Solids with Focus on Reduction of Erosion and Scale Formation', was to improve the understanding of the scaling and erosion mechanisms and to develop online measurement methods for monitoring of both phenomena. The project was coordinated by SINTEF Industry and the partners were the University of South-Eastern Norway, Hydro Aluminium, GE Power Norway, and Omya Hustadmarmor. Project findings: Two PhD studies have been formulated under the project, one on scaling and one on erosion. In the PhD study on scaling, four different methods for online monitoring of scaling in pneumatic conveying systems were tested. Two most promising methods, heat pulse monitoring and active acoustic chemometrics, were selected for further testing. Both methods depend on calibration against reliable reference measurements of scale growth, and therefore a reference method based on laser imaging of scale inside a pipe was developed. A full-scale industrial test campaign was conducted in an aluminium smelter. During the campaign, active acoustic chemometrics and laser imaging method were used in combination to monitor scale growth in a test pipe in a pneumatic conveying system. A scale growth curve describing the scale progression during the measurement period was developed, showing periods of increasing and decreasing scaling rate. A multivariate data analysis was conducted to reveal any correlation between process data and meteorological data measured during the test campaign and the changes in the scaling rate. The results indicated that variations in some of the process parameters could be linked to variations in scale growth. The findings were presented in the PhD thesis of Ingrid B. Haugland, entitled "Monitoring of Scaling in Pneumatic Conveying Systems", published by University of South-Eastern Norway in 2018 and several scientific publications. An ultrasound vibration system was attached to a pipe in a pneumatic conveying system for secondary alumina to investigate whether vibration could prevent or reduce scaling. Visual inspection after a period of 6 months indicated less scaling in the pipe segment where ultrasound vibration system was installed. Other types of scaling typically observed in the production of calcium carbonate products were also investigated. The scale deposits often form during handling of very fine mineral powders, when the conveying air is very dry and in areas of high turbulence. Samples of scale deposits from a production plant have been characterized by SEM and RAMAN spectroscopy to investigate the morphology and the elemental composition of the deposits. The analysis of particle cross-section revealed that eggshells are most likely formed by compression of many fine-grained particles into relatively large particles. Measurements of electrostatic charge of fine CaCO3 particles at different levels of relative humidity showed that electrostatic charging tends to decrease as powder moisture content increases. Visual observation showed that at low levels of humidity, the powder has a higher tendency to stick to surfaces and this in combination with high particle impact, could trigger formation of eggshells. Preliminary lab tests with fine CaCO3 powder carried out using a sand-blast type erosion tester and dry compressed air indicated that eggshells could be created on a solid surface by particle impact and long enough exposure time. SEM analysis showed that the eggshell particles from the plant and the particles created in the lab using the erosion tester had a very similar structure, indicating that the tester reproduces well what happens at the plant. In the PhD study on erosion, lab tests using a sand-blast type erosion tester were conducted with steel wall materials and calcium carbonate as the erodent material. Preliminary tests showed that impact erosion is highest at low angles and thereafter decreases with increasing impact angle, which is characteristic for ductile materials. The effect of particle size on erosion was dependent on the selected impact angle (30 or 90 deg). The eroded craters on the surface of the target material were analysed by surface profilometry to estimate the penetration depth and to obtain 3D profiles. An experimental design was performed to study the effect of selected variables, incl. impact angle and velocity, particle size, temperature, particle concentration and the amount of solid mass. The results show that impact angle and velocity have the highest influence on erosion, followed by temperature and particle size. Recently, the active acoustic chemometrics method, used above for online monitoring of scaling, has been successfully tested for online monitoring of erosion in a pneumatic conveying system with promising results.

The project has contributed to development and testing of novel online measurement methods. Scaling in pneumatic conveying systems was for the first time monitored in real industrial settings with promising results. Preliminary tests indicated that the method based on acoustic chemometrics could be also suitable for online monitoring of erosion. These methods could be used for development of more effective process control and/or development of a system for predictive maintenance to help determine when maintenance should be performed.

Erosion and scale formation can cause major challenges in some industries where bulk solids are handled. In aluminium production, the main raw material is alumina, which is converted to aluminium by smelting. In the first step, alumina passes through a dry-scrubber to remove fluoride emissions from aluminium smelters. The fluoride-enriched alumina is then fed into the smelters and converted to aluminium. Alumina is highly abrasive powder that can cause significant wear of equipment. In addition, the process equipment used for the fluoride-enriched alumina is often hampered by formation of scales, i.e., fouling of process equipment. This may have severe consequences for the economic and potentially environmental performance of smelters. In production of calcium carbonate based products, some of the raw materials, especially dolomite and calcium carbonate with high content of hard mineral contamination like silica, are abrasive and their handling can cause frequent wear of conveying equipment. This leads to frequent shutdowns due to repair or exchange of pipeline elements and substantial maintenance costs. On the other hand, some of the raw materials handled, have a tendency to stick inside the pipelines. The fouling deposits detached from the surface of equipment contaminate a finely granulated product, causing severe quality issues. We need to improve our understanding of the scaling and erosion mechanisms and to develop online monitoring systems in order to control both phenomena. With better knowledge of the most influencing parameters, maintenance schedules can be optimized as well as more effective process control solutions and improved equipment designs can be developed. The project is coordinated by SINTEF AS with University of South-East Norway, the Light Metals Research Centre in New Zealand, and Loughborough University in UK as the R&D partners. The industrial partners are Hydro Aluminium, GE Power Norway, and Omya Hustadmarmor.

Funding scheme:

BIA-Brukerstyrt innovasjonsarena