By bestowing our first-ever Plant Innovation Award, the staff at Chemical Processing are honoring significant improvements to existing operating facilities by the insightful engineers who run these plants on a daily basis. We received 13 nominations from companies in various sectors: chemicals, pharmaceuticals, petrochemicals, power generation and food processing.
We thank the five members of our editorial board who judged the entries: Vic Edwards, Aker Kvaerner, Houston; Tim Frank, The Dow Chemical Co., Midland, Mich.; Ben Paterson, Eli Lilly and Co., Indianapolis; Roy Sanders, PPG Industries, Lake Charles, La.; and Jon Worstell, Shell Chemical, Houston.
Our judges gave their highest rankings to:
• Jim Sturnfield, South Charleston, W.Va.-based senior specialist for The Dow Chemical Co., Eli Maldonado, Houston-based commercial manager, Dwight Pesek, process control technician, James Morgenroth, technical adviser, Rodney Hodde, production leader, and Seadrift Energy System Operations for implementing the G2 expert system from Gensym Corp., Burlington, Mass., in conjunction with Visual MESA, a closed-loop optimizer, from Nelson and Roseme Inc., Walnut Creek, Calif., at Dow’s Seadrift, Texas, site.
• Geovanna Nazario, principal engineer, Adalberto Maldonado, manufacturing manager, Diana Santiago, senior principal engineer, Marylin Roque, technical services engineer, Diana Rodriguez, documentation manager, and Carlos Santiago, lead instrument technician for Baxter Healthcare Corp., based in Guayama, Puerto Rico, for using model predictive control (MPC) from Emerson Process Management, St. Louis, in conjunction with statistical process control (SPC) to eliminate failed acetone batches by improving operation of an acetone recovery column. Francisco Feito, director, and Ruben García, director, sponsored this project (Figure 1).
Dow gets an energy boost
Last year, Dow Chemical saved $1.75 million at its Seadrift petrochemicals plant by reducing overall energy demand, including electricity and natural gas, due to the use of G2 and a closed-loop optimizer. Sturnfield estimates 2005 savings could reach $3 million resulting from increased natural gas prices, as well as other changes that have been made at the plant.
G2 is an object-oriented expert system software platform that captures operations expertise in the form of rules, procedures and models to infer production conditions and make supervisory control decisions. It reduces the amount of programming required to run the optimizer for the many possible operating conditions that exist at a site that produces a variety of products.
After trying several open-loop optimizers to improve operation of the cogeneration plant, a team led by Sturnfield decided to switch to a closed-loop optimizer, which would require less input from the operators. Visual MESA and G2 were installed in 1997. However, the optimizer was initially run in open-loop mode. As the system was debugged by Dow personnel, Sturnfield says they started closing loops, beginning with the heat-recovery steam generators (HRSG) and steam turbines (Figure 2).
The team’s efforts then turned toward implementing the system on cogen units at two other sites. The focus returned to the Seadrift site in 2002 when the scope of the project was expanded to include a new cogen unit. This necessitated additional training for the operators so they would trust the system and not turn it off when they felt the system’s recommendations were incorrect.
For example, the optimizer recommended running the turbines at partial load, but the operators were concerned that the hydrogen-rich fuel fed to the turbines might flash back and force a shutdown. The operators were encouraged to bring such problems to the attention of the engineers, who then used G2 to implement guidelines to the optimizer on the relationship between fuel richness and the limitation on partial loading of the gas turbine (Figure 3).
Once staff started seeing the value of the optimizer, use of the system increased; during a four-month period, the amount of on-stream time the system ran in closed-loop mode increased from less than 10% to more than 90%. During the past two years, the optimizer has run in closed-loop mode for more than 98% of the time.
“We are looking to use G2 to maintain the whole system,” Sturnfield says. “The degrees of freedom we have for operating the plant are affected by decisions that were made yesterday,” so he is analyzing the results from G2, which will help Dow implement it in other parts of the cogen plant, as well as at other sites. Sturnfield is also working toward integrating the optimizer and G2 with advanced control of the cogen unit.
Our judges were impressed by the immediate results the system provided. “This is a good example of what can be achieved through optimization of the overall work process for faster/better decision-making,” Frank says. Edwards adds, “This is [a] significant plant improvement through advanced process control.”
Another recognizes the value of optimizing energy resources. “While many chemical manufacturing facilities have cogen units, they are not operated as an integral part of the site, thus many of the possible gains are not realized,” Worstell says. “As we enter another period of world energy shortage, cogen can help ease the impact if its operation is optimized with respect to the operation of its parent facility.”
Baxter doesn’t stand still
Last year, engineers at Baxter improved operation of an acetone recovery column (the Xc still) through use of MPC. The throughput and quality of acetone increased and failed batches were eliminated, thereby making it unnecessary for Baxter engineers to spend time documenting and investigating off-spec material.