design operation maintenance instrument ation… · to handle and to control than liquid based...

PROCESS Worldwide 4-201128

With respect to today’s enhancedefficiency and environmental require-

ments, modern processes are often laid-outas ’solids loop processes’. Although havingcertain advantages, they are more difficultto handle and to control than liquid basedprocesses. Examples for such solids loopprocesses are Fluid Catalytic Cracking (FCC)processes in refineries, chemical loopingcombustion or LyondellBasell’s polypropyleneprocess ’Spherizone’. All of these processeshave at least one closed loop where solidscirculate—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 loopmay not be opened, this is in most cases notpossible with conventional instruments as for

Pictures:M

SEMeili

“Panta Rhei—everything flows” said the ancient Greek philosopher Herak-

lit—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 proc-

esses at their optimum, laser backscattering instruments can be important

tools.

DR. RETO T. MEILI

Illumination for ParticlesLaser backscattering provides in-situ measurement of bulk flows

Dr. Meili is the founder and CEO of MSE Meili AG, Schaffhausen/Switzerland.Contact: Phone: +41 (0) 44 / 4 40 55 00; info@msemeili.ch

example balances. Harsh conditions such asgauge pressures or high temperatures, as the40 bar/100°C of the Spherizone process,augment these difficulties.To get a reliable measuring solution for

their closed loop process, LyondellBasellprompted MSE Meili to develop a velocitymeter on the basis of the existing Labasysinstruments. The device should be suited forthe Spherizone process and feature a genuinein-situ measuring solution.

P L U SMagazine • PROCESS worldwide 5-2011 will feature a special on “Powder and Bulk

Handling”.

Online • Further information about this article at process-worlwide.com withInfoClick 2817295

Events • Visit Powtech, the international trade fair for mechanical processingtechnologies and instrumentation (October 11-13, 2011; Nuremberg/Germany).

Laser backscattering is a feas-able method for the continousmeasuring of bulk flows.

A Challenging Task

An accurate insight into the internals of theprocess is necessary for the understandingand further development of the process andalso to operate industrial plants at or at leastnear their optimum conditions. For this pur-pose the bulk flow velocity—a key quantityfor the effective control— is measured. Devel-oping a particle velocity measuring systemfor the Spherizone process was a challengingtask due to its high requirements: The instru-ment needed to be Ex-protected, hold gaugepressures up to 42 bar as well as high tem-peratures. Furthermore, the outer diameter ofthe tip should not exceed 25 mm.After comprehensive tests in a semi techni-

cal unit, the newly developed Labasys ControlEx Bulk Flow instrument was approved byLyondellBasell for industrial Spherizoneplants. During 2008 the first instrumentswere successfully put into production in closecooperation with LyondellBasell.To withstand the required harsh conditions,

the tip of the stainless steel instrument has asapphire window and a double sealing pres-sure barrier. All optical fibres are placedinside the device where they are protectedagainst breakage. Using fibre optics has theadvantage that signals are guided out of therough process environment optically, makingthem insensitive to disturbances. The unitmay withstand high pressures and tempera-tures up to 350°C, since all electronic compo-nents are located in a flame-proof bulb at theback of the instrument.

In-Situ Laser BackscatteringTo measure the particle flow, the Labasys

instruments use laser backscattering. The par-ticles are illuminated by laser light guidedwith optical fibres. A photometer convertsthe backscattered light into electronic signals.From there, the velocities are determinedusing cross correlation methods. The analysissoftware Labasoft Control evaluates about 20

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INSTRUMENTATION/PROCESS AUTOMATION

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PROCESS Worldwide 4-2011 29

variations of the bulk velocity can be ob-served. The instruments also yield valuableconcentration data—at least in qualitativeform—which give direct insight into theinner life of the reactor.By now instruments are in operation in

LyondellBasell’s semi industrial Spherizone

single velocities every four seconds, fromwhich stable mean values are derived.The chart to the right shows typical plant

start-up data of a Spherizone process, meas-ured in the downer. The red points show thetarget quantity velocity. The blue and thegreen markers below show the raw signals ofchannel 1 and channel 2 of the measuringinstrument. These values correspond to thepolymer concentration in the downer, allow-ing for a close observation of the start-upphase: when the plant is started at ca.13:30 h, the filling level rises and the poly-mer particles start to circulate. The velocitiesof the particles falling onto the packed bed atthe bottom of the downer fluctuate stronglyand rise as their density rises, as indicated bythe concentration signals.Slowly the filling level moves upwards and

at about 14:50 h the packed bed reaches theheight of the instrument. From this momenton the velocity of the bulk flow (which ismuch lower and more regular) is measuredinstead of the falling particles: the processreaches stationary conditions and only minor

Process data from the start-up phase of a Spherizone process

plants in Ferrara and Frankfurt and in com-mercial plants in Thailand, Korea and SaudiArabia. A reliable and long-lasting operationwithout costly product interruptions can beassured, as the with Swiss precision engi-neered, manufactured and tested instrumentproved its value well in practice. Or as a su-pervisor of manufacturing platforms of Lyon-dellBasell said: “We are happy with our threeLabasys Control Ex Bulk Flow instruments. Inthe more than two years they were in opera-tion at our plants now, they run perfectly welland delivered important in-situ informationto control our processes efficiently.”These devices are also well suited to moni-

tor velocities and concentrations in othersolids processes—be it in the high concentra-tion ’bulk flow’ or in a more dilute flowrange, be it in a R&D or an industrial produc-tion environment.

THE SPHERIZONE PROCESS

Inside the multi zone reactorThe heart of the Spherizone process is the multi zone reactor. It consists of a riser and adowner, which allows for two fully controlled but separate polymerisation conditions inone single reactor. That makes Spherizone a versatile reactor for polypropylene. Thedowner is filled with polypropylene particles of 2–3 mm diameter, which are movingdownwards slowly. This flow may be described as a ’moving packed bed’ or in otherterminology as ’bulk flow’.

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