Laser Backscattering Laser Backscattering Provides In-situ Measurement of Bulk Flows

Editor: Dominik Stephan

“Panta Rhei — everything flows” said the ancient Greek philosopher Heraklit — and although he did not consider bulk flow processes, their importance for the industry is immense. Measuring flow rates in a moving particle flux, at high temperatures or gauge pressure, is a difficult task. To run such processes at their optimum, laser backscattering instruments can be important tools.

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Laser backscattering is a feasable method for the continous measuring of bulk flows. (Picture: MSE Meili)
Laser backscattering is a feasable method for the continous measuring of bulk flows. (Picture: MSE Meili)

With respect to today’s enhanced efficiency and environmental requirements, modern processes are often laid-out as ’solids loop processes’. Although having certain advantages, they are more difficult to handle and to control than liquid based processes. Examples for such solids loop processes are Fluid Catalytic Cracking (FCC) processes in refineries, chemical looping combustion or LyondellBasell’s polypropylene process ’Spherizone’. All of these processes have at least one closed loop where solids circulate — be it in fluidized or in bulk form.

It is often important to measure the solids flow rate in such a loop in-situ. Since the loop may not be opened, this is in most cases not possible with conventional instruments as for example balances. Harsh conditions such as gauge pressures or high temperatures, as the 40 bar/100 °C of the Spherizone process, augment these difficulties.

To get a reliable measuring solution for their closed loop process, LyondellBasell prompted MSE Meili to develop a velocity meter on the basis of the existing Labasys instruments. The device should be suited for the Spherizone process and feature a genuine in-situ measuring solution.

A Challenging Task

An accurate insight into the internals of the process is necessary for the understanding and further development of the process and also to operate industrial plants at or at least near their optimum conditions. For this purpose the bulk flow velocity — a key quantity for the effective control — is measured. Developing a particle velocity measuring system for the Spherizone process was a challenging task due to its high requirements: The instrument needed to be Ex-protected, hold gauge pressures up to 42 bar as well as high temperatures. Furthermore, the outer diameter of the tip should not exceed 25 mm.

After comprehensive tests in a semi technical unit, the newly developed Labasys Control Ex Bulk Flow instrument was approved by LyondellBasell for industrial Spherizone plants. During 2008 the first instruments were successfully put into production in close cooperation with LyondellBasell.

To withstand the required harsh conditions, the tip of the stainless steel instrument has a sapphire window and a double sealing pressure barrier. All optical fibres are placed inside the device where they are protected against breakage. Using fibre optics has the advantage that signals are guided out of the rough process environment optically, making them insensitive to disturbances. The unit may withstand high pressures and temperatures up to 350 °C, since all electronic components are located in a flame-proof bulb at the back of the instrument.