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By Brent J. Thomas
Monsanto’s plant in Soda Springs, Idaho, produces elemental phosphorus, or P4. Most of the P4 is sent to other Monsanto facilities in Luling, La., and Camacari, Brazil, to make PCL3, the primary ingredient for Roundup herbicide. The remainder ends up in a variety of products including foods, cleaners, water treatment, flat-panel televisions, oral care products, paints and coatings, and pharmaceuticals. Specific applications of Soda Springs elemental phosphorus include the manufacture of Skydrol hydraulic fluids for aircraft, Phos-Chek fire retardant for fighting forest fires and Dequest water purifier.
The process of manufacturing elemental phosphorus begins with mining the phosphate ore from the Rasmussen Valley mine thirty miles north of Soda Springs. The ore is trucked to the site on Monsanto’s private highway and stockpiled.
The ore is fed to a rotary kiln, much like a cement kiln, 325 ft long and 16 ft in diameter, rotating at about 3.5 rpm. Organic material is burned out of the ore, and nodules are formed. The nodules are then mixed in batches with quartzite and coke and fed to one of three electric arc furnaces. The three furnaces combined consume approximately 150 megawatts of electricity. The phosphorus leaves the furnaces as an off-gas and is condensed for shipment.
The furnace process at Soda Springs is a dynamic one that requires sophisticated controls. Monsanto began using Fisher’s PRoVOX distributed control system (DCS) in the early 1980s. By about 1996, Fisher had become Emerson, and development of the DeltaV control system had begun.
Figure 1. A PB4Y fire bomber drops Phos-Check on a brush fire. The bright red retardant fades in the sun and eventually decays into fertilizer.
Monsanto began putting an emphasis on Six Sigma practices in 2001 and an emphasis on alarm management in 2002. Both corporate and local teams were formed to assess the state of the alarm systems within Monsanto and define a path forward to develop an effective, efficient alarm methodology and system. The local team decided to apply the new methodology to one furnace first to get a feel for what we were up against. This furnace was due for conversion to DeltaV and presented some opportunities for improvement.
How to analyze the present state and how to improve the situation were the biggest questions. The answer to both was the DMAIC (Define, Measure, Analyze, Improve, Control) methodology model of the Six Sigma process. After two years of work. Monsanto arrived at a firm alarm philosophy and had corporate-wide standards for analysis, improvement and key performance indicators (KPIs).
The first step in the analysis was to ask, just what is an alarm system and what should it look like?
Figure2. Typical control room alarm boundaries and appropriate d operator responses.
Our alarm problems came down to these:
We used the Six Sigma cause-and-effect fishbone diagram to investigate the possible causes of our alarm problems. We found that while we did a good job of selecting and maintaining instrumentation, our methods were the root cause of the alarm system state—we had no philosophy or guidelines for configuring alarms.
At this point, we applied the Six Sigma DMAIC system to the problem. First we developed an alarm management philosophy and selected alarm metrics (the Define phase). Then we assessed the present alarm system (Measure/Analyze phases). We reduced the number of nuisance alarms (Analyze /Improve phases). We rationalized alarms by need and priority (Improve phase). Then we developed an alarm configuration database (Improve – Control phases). Finally, we will implement knowledge-based alarming where appropriate.
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