Customer Brief: SNC-Lavalin

When Severstal North America recently rebuilt one of its blast furnaces, they faced a challenge: the emission control system had to be designed for a casthouse that didn’t yet exist. The project would have been difficult – maybe nearly impossible – without the help of SNC-Lavalin's engineering services and the use of CFdesign.

The redesigned casthouse included a new set of hoods, ductwork, fabric filtration equipment and fans. Under U.S. Environmental Protection Agency (EPA) regulations, casthouse particulate emissions must be controlled with what is called Maximum Achievable Control Technology (MACT). MACT compliance is measured by stack emission concentrations and the opacity of emissions that escape from the casthouse building. The Michigan Department of Environmental Quality (MDEQ) also has established an opacity limit.  The new Severstal casthouse needed to meet both U.S. and Michigan environmental regulations by capturing 98 percent of emissions.

MACT compliance is usually based on actual observations of casthouse operations to determine emission intensities, crosswind speeds and vertical rise rates. But, Severstal could not do that because the rebuilt casthouse was very different in configuration and operation from previous ones.

The solution was to use CFdesign to conduct a comprehensive design study that simulated the new equipment under every conceivable operating condition.

Simulating real-world conditions
After establishing the fundamental geometry and base set of conditions, finding the optimal design was an iterative four-step process:

1. Using initial hood designs and ventilation rates, determine capture efficiencies for tapholes, iron tilters and slag pot areas.
2. If initial hood/ventilation combinations do not achieve the 98 percent emission control rate, revise the geometry of the hood and/or the ventilation rate.
3. Re-run the model with the revised hood/ventilation design.
4. Repeat steps 2 and 3 until acceptable emission control is achieved, then apply the acceptable model parameters to the emission control system design.

Capture efficiency for the casthouse model was computed as the probability that a fume particle generated at each source (taphole, tilter or slag shanty) would be captured by each hood and subsequently drawn through the ductwork to the bag house. The next – and most important – step in the calculation was to determine fume capture percentages for each individual operation.

The entire study entailed dozens of CFD simulations to arrive at an optimal mix of hood configurations and ventilation volumes. In addition to numerical results, CFdesign provided static and dynamic images that created a better understanding of what was occurring during the simulations.

Accurate and cost-effective
“CFdesign proved to be an indispensable analytical method for optimizing design of the emission control system for the Severstal casthouse,” stated Brian Bakowski, Design Engineer at SNC-Lavalin. “It enabled us to successfully establish ventilation volumes, hood configurations and volume distribution profiles for 50 separate operating scenarios for the new blast furnace. All done in three months, without costly physical testing.”

At this time, the new furnace is fully operational and in compliance with the MACT regulations. CFdesign proved to be an accurate and cost-effective method to predict actual performance of the casthouse emission control system under real-world conditions.