International Journal of Engineering, Applied and Management Sciences Paradigms, Vol. 45, Issue 01 Publishing Month: March 2017 An Indexed and Referred Journal ISSN (Online): 2320-6608 www.ijeam.com IJEAM www.ijeam.com 17 Conventional Control of Continuous Fluidized Bed Dryers for Pharmaceutical Products Gurashi Abdullah Gasmelseed 1 and Mahdi Mohammed 2 1 Department of Chemical Engineering, University of Science and Technology, Khartoum, Sudan [email protected]2 Department of Chemical Engineering, University of Science and Technology, Khartoum, Sudan [email protected]Publishing Date: March 04, 2017 Abstract The dynamic response studies with step disturbances in the manipulated and load variables are investigated. These studies are useful in control system identification schemes for fluidized bed dryer. Both conventional and digital control strategies were developed. Three loops were taken for comparison between the methods of tuning and stability analysis for conventional and digital control, each control loop was treated separately and its transfer functions were developed .In conventional control the characteristic equations were determined and used in Routh array to determine the ultimate gain (Ku), the ultimate period (Pu) was determined by using direct substitution. The OLTF's were used by Root Locus and Bode plot methods using MATLAB software to determine Ku and Pu. It is observed that the three methods of investigating the stability gave optimum and identical parameters Ku and Pu, and they were almost the same. The average values of the ultimate gains and periods were obtained and they were introduced in Zeigler – Nichols table to get the adjustable parameters, however an average was taken to give more précised and correct results. Also the offset was investigated for P-controller, PI-controller and PID-controller. Keywords: Dynamic Response, Fluidization, Drying Control, Automatic Control of Dryers, System Stability and Tuning, Routh Hurwitz, Root Loucs Plot, Direct Substitution, Bode Plot and System Stability. Introduction Drying means the removal of relatively small amounts of water from wet material by the application of heat. Drying is an energy-intensive operation that accounts for up to 15% of the industrial energy usage. Moreover, conventional dryers often operate at low thermal efficiency, typically between 25% and 50%, but it may be as low as 10%. Fluidized bed dryer is used widely in food, metallurgical, chemical and pharmaceutical industry, because of the shorter drying time required and simple maintenance and operation. This type of dryers is based on the phenomena of fluidization. Fluidization is the operation by which solid particles are transformed into fluid-like state through suspension in gas or liquid. When a gas is passed through a layer of particles supported by a grid at low flow rate, the fluid percolates through the void spaces between stationary particles. As the fluid velocity increased, the void age increases, this resulting in an increase in pressure drop on the particles. The pressure drop across the particle layer will continue to increase in proportion to the gas velocity till the pressure drop reaches a constant value that is equivalent to the weight of the particles in the bed divided by the area of the bed, at this point the frictional force between particles and fluid counterbalances the weight of the particles. At this stage the bed is to be incipiently fluidized. Fluid velocity at this point is known as minimum fluidization velocity. With an increase in flow rates beyond minimum fluidization, large instabilities with bubbling, channeling of gas and decrease in pressure drop are observed. Fluidized bed dryers have some drawbacks. Material with a wide particle-size distribution cannot be handled satisfactorily, while at high temperatures the melting and fusing of the material on the grid plate can become a problem. To circumvent these difficulties, dryers, originally developed for grain drying, have been made with conical bottom sections which give a spouted bed rather than a fully fluidized one. Deriving mathematical models can be done by utilizing physical laws to derive a mathematical model, this model must be rigorous enough to give an accurate description of the process. In most cases they obtained models are set of ordinary differential equations with one or more partial differential equation, thus solving them requires powerful mathematical solvers. Drying control is defined as the ability to dry a product to a desired moisture content with acceptable variation. Poor moisture content produces a distribution with a wide moisture content variation, whereas, improved control results in narrow distribution.
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International Journal of Engineering, Applied and Management Sciences Paradigms, Vol. 45, Issue 01
Publishing Month: March 2017
An Indexed and Referred Journal
ISSN (Online): 2320-6608
www.ijeam.com
IJEAM www.ijeam.com
17
Conventional Control of Continuous Fluidized Bed Dryers
for Pharmaceutical Products
Gurashi Abdullah Gasmelseed1 and Mahdi Mohammed2
1Department of Chemical Engineering, University of Science and Technology, Khartoum, Sudan