Chemical Processing - May 2008 - (Page 13)

FIELD NOTES << Keep plant layout from laying you low spot mistakes before they literally become set in stone on the site At the first site where i worked, AN oPerAtor could see the guts of the plant from the safety of his control room. everything was perfectly laid out. since then, though, i’ve too often seen operators in dark cellars staring at equipment through hazy tV screens. outside the control room, pipes and cables were laid out disorderly; equipment teardown frequently disturbed the normal flow of the plant. here are a few thoughts on improving plant layout. identify equipment with poor reliability or likely requiring frequent attention. decide if spares will be inline or from storage; pumps handling a sticky slurry might be an application where inline won’t work. determine the wind direction, the best escape routes and supply requirements such as where to run a railroad spur. Look at parking, etc. Build from the inside out and then the outside in. if a pipe specification exists, and other leak points; 10) where two-phase flow may exist, avoid rises or allow for traps; 11) put motor control centers as close as possible to control rooms; 12) provide for material storage, for turnarounds, quality assurance, deliveries and routine batch preparation; 13) install air coolers, cooling towers and other equipment affected by heat to take advantage of shade and natural cooling, e.g., the wind normally should flow across the packing in a cooling tower; and 14), most importantly, allow for growth — size utilities, i.e., electricity, compressed air, steam, heating and ventilation, purge gas, fuel and sewers and rail spurs, for future expansions. After the first pass through design, review the layout with operations and maintenance in the same room. if you regularly use contractors such as riggers and crane companies, ask them to check for lifting requirements, scaffolding, removal and replacement of major equipment. several common mistakes often haunt plant designers. foremost are those related to pipe racks. too often, delicate instrument cables are run close above steam piping, parallel to power lines and where they are unshielded from the sun. then, there’re plant expansions. A premium on downtime means that new wires seldom are added to old conduit. this means new wires and new conduit. Good sense dictates filling conduit to a maximum and allowing for future removal and replacement of rotting conduit, terminal strips and pipe. Plan for future tie-ins; one plant had a single shutoff valve in the steam system. i’ve been burned by designs that are blind to insulation needs. design engineers ordering tanks frequently forget to allow for insulation lagging of flanges, manways and instruments — sometimes because these requirements are unknown at the time. however, lack of insulation can pose real risks unless the company enforces a safety standard on surface temperature. operators have been burned to death attempting to squeeze between uninsulated pipe. Another mistake is not considering the rigging of equipment for installation, now and in the future. Plan for trolleys and anchor points in the layout. i remember one project where lugs hadn’t been installed on some spools of a large ceramic-lined pipe. this oversight helped turn a four-day outage into one lasting 10 days. the goal is to design a layout that improves the plant’s operability, safety and production. this requires understanding the needs of mechanics, riggers and operators. CP Dirk Willard, contributing editor dwillard@putman.net May 2008 • 13 Mistakes involving pipe racks should haunt plant designers. establish line sizes from the P&id before attempting a layout; choose the smallest diameter and lightest pipe that will do the job but be wary of waterhammer and pressure drop. once you’ve rated the equipment for reliability and sized the pipe, it’s time to develop the plot plan — keep it simple. Here’s how to cut costs: 1) anchor small equipment to the structure or larger equipment; 2) place equipment on the ground, if possible; 3) install high-maintenance operator-intensive equipment away from high traffic areas; 4) put sampling stations and instruments where operators will be safe; 5) locate the larger equipment and larger pipes and ducts first, then smaller piping and finally conduit, marshalling panels and electrical utilities; 6) create a run for conduit and pipes, usually in the middle of the plant, keeping it above and away from hazardous locations; 7) where possible, construct pipe manifolds and cluster instruments together to maximize serviceability and reduce the number of hazardous (Div. 1) areas; 8) keep pipe and conduit runs as short as possible to avoid problems such as low NPshA, heat losses and signal interference; 9) for a fire-safe design, put pumps and compressors in areas of good drainage and ventilation, away from critical structures, pipe racks and equipment, and minimize flanges www.chemicalprocessing.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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