Enginuity 2009

Flare minimization: Simulations increase savings and safety

Ku-Yen LiLamar University researchers Ku-Yen Li (right) and Qiang Xu (below) are pioneering work in dynamic simulation that is already saving the chemical industry money, protecting the environment and improving plant safety.

Through their efforts in flare minimization, Li, professor of chemical engineering, and Xu, assistant professor of chemical engineering, along with departmental colleagues are exploring a new paradigm that is proving profitable for chemical plant start-up operations.

In 2000, Li first sought to apply the rapidly improving capabilities of dynamic computer simulation to the challenges of unsteady-state plant operations found during start-up operations. His first inclination was to address the industry’s air quality challenge caused by flaring, but it quickly became apparent that flare minimization would benefit a plant’s bottom line by saving valuable feedstock and increase safety as well. At that time, computer modeling was just becoming good enough to use and fast computing was becoming more available, Li said. He presented his ideas to regional industry more than a dozen times, each time not only sharing but also gathering more ideas on how to address industry’s needs.

Flaring is crucial to plant safety, but excessive flaring emits huge amounts of volatile organic compounds (VOC) and some are highly reactive VOCs (HRVOCs). Both the EPA and Texas Commission on Environmental Quality (TCEQ) have made clarion calls for source reduction in the interest of public health. Li and Xu’s research was initially funded by the EPA along with the Texas Air Research Center and the Texas Hazardous Research Center.

Li’s interest in start-up simulation with the goal of flare minimization began at an ethylene conference where he asked how many chemical engineers present were using dynamic simulation in any way in their plants. He found only a few plants used the process, none used it in a systematic way and no one had any real confidence in dynamic simulation as a predictive tool.

“We have developed a methodology that uses a series of verifications based on the steady-state (normal) operation data, then converts it to the dynamic model found at start-up,” Li said. “Rather than blindly running new operation procedures, dynamic simulation can show you where things can get out of control or out of the acceptable range. It shows you how to avoid problems during plant startup.”

Plant-wide dynamic simulation is based on the integration of rigorous process models, plant design data, piping and instrument flow diagrams, industry experience and data collected from the historian of a Distributed Control System (DCS). "We used that data to verify and fine tune the model," Li said.

“Every plant is unique,” Li said. “A model set up for one plant cannot be used for another plant; however, the methodology used to develop accurate models can be applied everywhere.”

Qiang XuEven with a typical seven-year cycle for turn-around, perhaps more frequently in an active hurricane season, it can be a challenge for some plants to assemble teams with a lot of start-up experience. Knowing what to do all depends on human experience—and experience leaned at one plant may not translate well to another process or plant, Li said. That increases risk and is one reason “start-up is a nightmare for plant managers.” Even with gathering as much experience as is available, start-ups don’t always reach steady state as planned.

“Sometimes plants have to shut down and then try again,” Li said. “So they burn a lot of raw materials, costing a lot of money, and, even with the best flaring, add significantly to the problem of source emissions.”

The first real-world application of the flare minimization simulation came with the start-up of the Lyondell olefins plant’s recovery section in 2003. For that to take place, Li needed to convince not only the top echelon, but also the chief operation engineers in the start-up committee. When Li was presenting simulation results to that committee, “one of the long-time experienced engineers almost jumped up as he remembered from his experience . . . he started mumbling ‘that doesn’t have C3C4 so the temperature should be lower.’” He arrived at the same solution the flare minimization simulation had suggested, and a key convert was won, Li said.

Since the Lyondell experience, simulations have successfully run at the recovery section of Huntsman Chemical’s ethylene plant, PDGlycol plant’s ethylene oxide reaction section and, the largest challenge to date, BASF’s ethylene complex. As experience grows, the simulation has continued to show improvement. “BASF worked out even better than the other three projects,” Li said.

The aging infrastructure of the American chemical industry contrasts sharply with newly minted plants in Asia. It is much easier to develop accurate simulation models in new plants with modern DCS systems, said Li, who has presented his simulation methodology at conferences in China and Taiwan. There is tremendous opportunity for growth both domestically and internationally, Li said.

“This is a powerful tool for industry,” Li said. “We are delivering a method that saves plants money, cuts pollution and increases safety.”