Waupaca Foundry: Cupola Furnace Blast Air Dehumidification Improvement

Background

Waupaca Foundry – Plant 5.1 in Tell City, Indiana is one of seven foundries in North America operated by Waupaca Foundry, a Hitachi Metals Group company that produces gray and ductile metal castings for transportation, off-highway, and other industrial sectors. The plant melts approximately 400,000 tons of gray iron per year using cupola furnace technology. To achieve efficiency gains in the cupola melting process, the Tell City plant installed a desiccant wheel to remove water vapor from ambient air before blast preheating in the recuperator tower. This desiccant cupola blast air drying system was installed to offset the impact of humid blast air, which increases the plant’s consumption rate of coke per unit of iron melted.

The benefits and cost savings for cupola blast air dehumidification are well established and significant, especially in humid climates. This project has significant energy savings and environmental impact, which contributes towards achieving Waupaca’s sustainability goals. Coke represents 50% of the energy used at Waupaca Foundry, and the melting process consumes 65% of the total energy at each facility. High humidity levels can cause multiple performance issues that lead to higher energy consumption per unit of iron melted. These issues include reduced melt rates, reduced combustion temperatures, reduced carbon pickup, and elevated thermal oil heat loads increasing exhaust volume to the emission system.

Solutions

Because of its high energy footprint, optimizing the energy efficiency of the cupola furnaces is important for Waupaca Foundry. The desiccant blast air drying system reduces blast humidity to levels as low as 7 to 10 grains of water per pound of dry air. The resulting annual reduction in coke consumption and cupola efficiency gains are significant—1.19 lbs. of coke reduction per pound of moisture removed—allowing a reduction of 2.5% of total coke usage and representing savings of nearly 17,000 MMBTU and $335,000 per year. Regeneration of the drying wheel is accomplished by using reclaimed waste heat, provided by the thermal oil cooling system. This process minimizes operating costs and provides the most positive energy balance and environmental benefit.

The engineering project was developed as part of a collaborative effort by the cupola manufacturer, the dehumidifier manufacturer, and the Tell City plant’s engineering team. From April 2019 to March 2020, the installed blast air dehumidification system removed 1 million pounds of water from the blast-air, providing the following benefits:

Improved cupola melting efficiency by 3%
Reduced Coke usage by 2.5% per year, which equals 656 tons or nearly 17,000 MMBTU
Energy cost savings of $335,000 per year
Avoided 1,804 CO2-tons (1 %) of GHG emissions
Reduced plant’s total energy usage by 0.7%

The project cost was $1.3 million and the simple payback of this project was 3.8 years. Once blast-air dehumidifiers systems are installed across the company’s portfolio of plants, the upgrades are projected to save Waupaca Foundry approximately 126,500 MMBTU and $2.5 million of energy costs annually. This would avoid the emission of 13,650 tons of CO₂-equivalent.

Other Benefits

Company-wide, Waupaca Foundry melts 2.5 million tons of iron per year; 80% of this total achieved with cupola furnaces. The installation of the blast air dehumidifier at the Tell City plant has allowed Waupaca Foundry to verify theoretical values of coke reduction and cupola efficiency increases. Using this information, Waupaca Foundry can estimate the annual savings of coke by using dried blast air at the remaining cupola furnace plants. This helped the corporate energy team to develop a Long-term Cupola Energy Investment Plan to standardize energy efficiency best practices across all cupola operations. The plan considers the expansion of the blast-air dehumidification system as well as other energy projects, including maximizing waste heat recovery; development of a cupola energy dashboard; and the installation of variable frequency drives on large blower motors.

The upgraded dehumidification system also offsets the detrimental impact of humid blast air in the melting process, which allows cupola-operating conditions to remain more stable throughout the year. This not only reduces coke usage but also impacts the ratio of melt to coke productivity. To capture additional savings from blast air dehumidification, Waupaca Foundry has defined an aggressive installation plan to be completed by 2025. The second unit is planned to be commissioned by the end of 2020 at Plant 23 in Waupaca, WI.

Waupaca Foundry: Cupola Furnace Blast Air Dehumidification Improvement

ANNUAL ENERGY USE

ANNUAL ENERGY COST

ANNUAL WATER USE

ANNUAL WATER COST

ANNUAL PLANT ELECTRICITY USE

ANNUAL PLANT ELECTRICITY COST

IN BUILDING ENERGY USE

IN BUILDING ENERGY COST

ACROSS NETWORK USE

ACROSS NETWORK COST

ANNUAL EMISSIONS

USE

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Waupaca Foundry: Cupola Furnace Blast Air Dehumidification Improvement

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