Chemical Processing - May 2008 - (Page 41)

< > >> Room for expansion Figure 2. This new cabinet houses a controller and I/O for a portion of the acrylonitrile unit. CPU and power supply modules (upper left) are redundant. times but never affected product, equipment or output. Much of the hot cutover was physically aided by hand jacks and bypasses. I’ve come to believe that every regulating valve should have a bypass if safety isn’t an issue. Hand jacks require too much care with settings to avoid the valve becoming fully opened or fully closed. We cut over the acrylonitrile unit without a process trip. However, failure of an associated ac power device due to a wiring error made after cutover caused a trip, but this wasn’t attributable to the automation or its cutover. Only one element of the former controls remained: a standalone PLC running truck and railcar loading. It was served by two HMIs in a setup that wouldn’t allow the operator to shift from one PC to the other once loading started. These controls were replaced at the end of the project with an HMI that communicates with the PLC over Modbus. This improvement will allow for loading to be controlled from anywhere on the system’s network. Significant benefits The hot cutover provided substantial savings. At our plant, the cost per day in lost acrylonitrile production is roughly $100,000 at today’s product value. A simple trip requires a 1.5-day restart. In addition, we’re gained a number of advantages from the new system: • There haven’t been any control failures due to the automation since conversion. • The plant turnaround in 2010 won’t be complicated or extended by the installation and startup of a new automation system. • The new system’s scalability and flexibility allows www.chemicalprocessing.com us to relatively easily add, enhance and change automation hardware, software and strategies to suit operations. One cabinet has already been fitted with a Modbus TCP/IP card for the fastest communications with Modbus devices. All cabinets have plenty of room for expansion with 20% spare conventional I/O capacity (Figures 2 and 3). Every new cabinet has a Foundation Fieldbus card and power conditioner even though no fieldbus has been installed yet. The adjacent catalysts plant,relies upon field devices very successfully served by Foundation Fieldbus, AS-Interface bus and Profibus DP segments. So, we aim to employ bus connections in the future in our units. • We’re finally using data from HART instrumentation that’s been in place for years. Secondary variables from Coriolis mass flow meters have been especially helpful, plus indications of oscillations in some valves, thanks to position feedback that couldn’t be sensed before. • The DeltaV Analyze tool is helping to identify nuisance alarms, and the system is enabling us to quash such alarms by suppressing a particular parameter alone, not the entire tag. For instance, we temporar- MONITOR VISCOSITY SIMPLY Sense Motor Horsepower with Universal Power Cell EASY INSTALLATION • No holes in tanks or pipes • Away from sensitive processes VERSATILE • One size adjusts for motors, from small up to 150 HP • Works on 3 phase, fixed or variable frequency, DC and single phase power SENSITIVE • 10 times more sensitive than just sensing amps CONVENIENT OUTPUTS • For meters, controllers, computers 4-20 milliamps, 0-10 volts CALL NOW FOR YOUR FREE 30-DAY TRIAL 888-600-3247 WWW.LOADCONTROLS.COM http://WWW.LOADCONTROLS.COM http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - May 2008

From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor WirelessHART signals a change at plants Avoid costly fabrication mistakes Watch out with variable speed pumping Hot cutover boosts control system migration Plant InSites Process Puzzler Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - May 2008

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