Engineering studies for cupola melt shops

Engineering studies for cupola melt shops

Computer modeling can establish a roadmap for ferrous foundries seeking to achieve process optimization, cost savings, and future energy savings.

cupola furnace
The melting zone of a cupola furnace, as seen through a tuyere. A cupola’s melting performance and potential for improvement can be significantly enhanced by a comprehensive engineering study that models actual conditions, inputs, and activity.

Two consequences of the current economic recession are that cupola melt shops have begun to take a very close look at their operating costs, while also scaling back their investments in capital equipment improvements. They are realizing that it is essential to reduce overall costs by becoming more efficient, as a key to remaining profitable, or at least to limiting losses as much as possible in this business climate.

The good news is that some economic indicators seem to show the economy is starting to turn around, which could help pave the way for increased budgets for equipment and other capital improvements in 2010, and beyond. In the meantime, many cupola melt shops are turning to engineering studies as a cost-effective way to evaluate their operations, and to develop strategic plans to streamline costs and become more efficient.

Typically a cupola melt system engineering study takes about five weeks to complete. A consultant will start by spending three to four days on site, collecting operating data and talking to the system operators to gain an understanding of furnace and gas-handling system equipment functions. Information is obtained concerning procedures, iron chemistry requirements, operating costs, melt schedules, regulatory requirements, current compliance status, energy demand and cost. Doing this allows the consultant to identify all challenges and needs that are specific to the individual cupola melt shop.

The results of such a study, one that allows a foundry to map a plan for making decisions on future improvements and prevent investment missteps, contain three key elements:

1) It reconciles a foundry’s current operation for accurate and justifiable future predictions;
2) It determines short-term and/or low-cost solutions that optimize the existing operation; and,
3) It maps out a long-term plan that identifies the larger capital investments or process changes to attain a fully optimized melt system with the smallest environmental and energy footprint.

Reconciliation process
The cupola furnace reconciliation process is a computer modeling method that performs a comprehensive energy and mass balance, using well proven thermo-chemistry and metallurgy reaction calculations. Modeling inputs include the chemistry and physical properties of all charge materials, including scraps, coke, alloys and fluxes. Cupola physical dimensions and operating conditions also are used as model inputs, while the energy losses through cupola top-gas, water-cooling systems and slag production are reconciled by comparison to field measurements. The resulting cupola computer model very closely represents the actual cupola operation. Modeling outputs include precise top compositions (%CO, %CO2, %H2, etc.) that are readily used for precise gashandling system engineering.

cupola
Every cupola has different operating parameters, but the modeling process can be tailored to suit the specific conditions of each furnace — and to evaluate the effects of any improvements under consideration.

The cupola model may be used to accurately predict the effects of possible optimization improvements. For example, furnace efficiency, blast rate and coke requirements may be accurately predicted by inputting a different charge recipe.

On the other hand, the model may be used to predict coke and oxygen injection reductions as a result of furnace physical changes, such as stock height or diameter. The modeling process is easily tailored to suit the specific conditions of each operation and may be used to evaluate all possible improvements under consideration. This allows for accurate determination of the cost savings and paybacks for any potential improvement project, and gives a solid basis for cost justification.

The modeling results further allow for long-term planning. A properly performed study will consider and evaluate the efficiency, functionality and suitability of existing equipment to adapt to add-on equipment that will improve waste-gas handling efficiency and recover waste heat from the exhaust gases. Projections may include a strategic staged approach to capital investment that may be implemented over a period of as much as five years, when the system will finally be “complete.” This approach is often possible and allows for deferment of large capital outlays while making improvements along each step of the plan.

A comprehensive approach to planned improvements opens the door to many technologies, including improved heatexchanger design to increase system reliability, improved environmental compliance or waste-heat recovery, in particular, thermal oil waste-heat recovery. The latter allows for effective wasteheat energy and reclamation, and creates many options for plant energy footprint reduction through electric power generation, dehumidification regeneration, air conditioning, domestic water heating and building heating, to name a few. The future implementation of such “add on” energy recovery systems will have the effect of reducing the plant’s reliance on purchased energy, turning the cupola melt system into an extremely efficient melting machine.

Justification process

Cupola physical dimensions
Cupola physical dimensions and operating conditions are used as model inputs, and energy losses through cupola top-gas, water-cooling systems and slag production are reconciled by comparison to field measurements.

Blast air dehumidification is a good example of how the engineering study approach may be used for project justification. The quality benefits, coke savings and improved productivity realized by dry blast air are well established, although only one U.S. cupola foundry currently employs the technology. A recent study of four cupola shops determined payback for blast dehumidification in the range of about nine months to 23 years, depending on operating schedules, annual tonnages, local weather conditions, and the source and type of “drying energy.” An engineered evaluation is essential to understand the process variables and equipment options to make an accurate determination of project feasibility.

In selecting an engineering firm to perform an evaluation, a foundry’s operators must first consider the credibility, engineering capability and experience of the engineering group. Likewise, the engineering firm that’s selected must have a firm command and understanding of all possible proposed equipment options to ensure that future capital investment plans include equipment that is viable and well engineered. When the time arrives to follow a study’s recommendations and authorize system upgrades, nothing can diminish a high ROI faster than poorly designed equipment. Reliability and equipment uptime are crucial for profitability. Low-quality or poorly designed equipment can cause downtime and lost production that reduces profits every minute the plant is out of operation. While some suppliers may quote less expensive equipment, it may not contain the added value that more robust and better-engineered solutions bring to the customer.

With the potential savings in energy, operating costs and capital investments that may be realized as a result of an engineering study, it should be relatively easy for most foundries to justify the comparatively low cost of a study, and to take the first step to savings and improved efficiency. The results of a study allow for decisive, long-term planning by administrators, superintendents and engineers alike; to ensure future optimization and cost savings that will improve the competitive position of the foundries that take this worthwhile first step.


David J. Kasun, P.E. is a senior process engineer at Kuttner North America. Contact him at 262-284-4483, ext. 203; [email protected]
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