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homework1_f10_sol - October 5 2010 Professor Palazoglu ECH...

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October 5, 2010 Professor Palazoglu ECH 157 Homework 1: Introduction: In the abstract for their book, Introduction to Process Control , Dr. Romagnoli and Dr. Palazoglu define process control in the modern era as “an efficient integration of real -time information management systems with the common regulatory functions to help operate a process safely and efficiently.” [1] In the light of this definition I will examine two common chemical engineering process equipment, a distillation column and a catalytic fixed-bed reactor. To create more continuity in my investigation, I chose applications of each within the petroleum refining industry; specifically, an atmospheric crude tower and a residuum hydrotreater (RDS) unit. For each piece of equipment it is first important to investigate its role within the refinery and general manner of operation. Looking at how the units operate within the whole refinery and at their economic, safety and environmental concerns will help identify the control problems specific to each. Addressing the control problems with the appropriate control strategy can mitigate potential risks and optimize function. The feedback control structure should have an objective that relates to the control problems, clearly using manipulated variables to achieve correct control. [ figure 1 ]
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Control of an Atmospheric Crude Tower: The atmospheric crude unit (a type of distillation column) in a petroleum refinery is the gateway to the rest of the refinery, separating the crude into various cuts to be sent to units in the rest of the refinery for further processing. It has large flow-through and high operating costs due to the magnitude of energy consumed. Crude, containing hydrocarbons as light as methane and as heavy as asphalt, enters the crude tower after being heated in a furnace to about 750F. Entering the distillation column as a mixture of gas and liquid, vapor rises and liquid falls through a series of trays, performing a fractional distillation of the components in the crude [ figure 2 ]. The vapor rises through valves in the bottoms of trays, while the liquid gathers on trays to the level of a baffle then spills along the downcomer to the tray below. Every tray operates on the basis of equilibrium, so on each tray some light hydrocarbons are stripped from the liquid and rise with the vapor while heavy components in the vapor cool and liquefy. Streams can be pulled from various trays in the column with certain properties. The specifications on the products drawn from a column are determined by market demand. Making off-spec product will lose money either due to having to reprocess streams or degrade them to less valuable products. Control is vital since the feed stocks going into a crude unit change weekly, if not more often, requiring altered operating conditions. Considering the significance of the products exiting the crude fractionator, the control objective becomes to maintain constant product properties despite changing feed and the need to alter operating conditions. Good operation of the crude unit can provide millions of dollars in savings.
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homework1_f10_sol - October 5 2010 Professor Palazoglu ECH...

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