Linking an annex melter to the existing melters' pollution control system takes pressure off production demands, and saves $62,000 over an independent air filtration system.

Pressure balance is key to a turnkey expansion of the exhaust air filtration ductwork at the Mason, OH, facility of a regional die caster. When growing sales of cast aluminum wheels to the Big Three automakers called for production in excess of 5000 pieces per day, the caster designed an annex to the 275,000 sq. ft. facility, to make room for a third production melt furnace. To marry the new melter to the pollution control system of the original two, the caster turned to process ventilation specialist Kirk & Blum, the company that had designed, built and installed the original ductwork system, in addition to the plant's graphite dust filtration system and 23 rooftop stacks, when the facility was built in 1990.

"The challenge was rebalancing the air pressure," says the client's project engineer. "Because the new melter is located so far from the other two, we hd to double the length of ductwork just to add it to the system. However, all three melters still have to see identical static pressure for the system to work despite the large pressure drop across the new ductwork sections."

The original plan for the annex had assumed that such a rebalance was impossible. The company first asked Kirk & Blum to quote the price for an entirely new and independent system of ductwork, collector and fan supporting only the new melter. Allowing the existing system to support the annex instead saved over $61,000.

Duct resizing

The new melter is located 130 ft. from the closest of the original two melters, which are spaced 60 ft. apart. On the opposite side of the original melters, another 120 ft. of ductwork connects the melters to a baghouse, and to the fan that all of the melters share.

The friction across the 130 ft. of ducting to the new melter added 2.2" w.g. of pressure to the system pressure which required Kirk & Blum to increase the speed and horsepower of the fan to compensate. However, because this change increased negative static pressure throughout the system, thereby increasing air flow, Kirk & Blum also had to retrofit modifications to the original ductwork to ensure continued optimal operation of the existing melters.

Static pressure is proportional to flow cross-section the smaller the cross-section, the higher the pressure. To return each of the melter connections to its proper operating static pressure, Kirk & Blum designed orifice plates to decrease the cross-sectional area of the ducts. Its engineers analyzed the air flow throughout the system, then resized each connection point cross-section to an accuracy of ñ1 sq. in.

Cleaning contaminants

Each melter is open to the system only when it is being cleaned approximately three times per melter per week. Employing a chemical reactant flux, the cleaning process gives off smoke, particulate and fumes. The ductwork carries all of this to the baghouse, which removes the contaminants from the air stream, sending them to drums for disposal per EPA regulations. According to Beach, air reaches the baghouse at 180øF, flowing through it at 17,000 cfm. (The baghouse is also connected to the plant's remelt furnace, which is open even during normal melting, due to contaminants liberated when scrap parts are melted.)

To prevent contaminants from one melter from accidentally being vented into another, Kirk & Blum retrofitted automatic controls to the existing melter electronics, ensuring that no two melters are ever open to the system simultaneously.

When a large die caster had to increase production of cast aluminum wheels to more than 5000 per day, it designed an annex for a third production melt furnace. To link the new melter to the existing pollution control system, process ventilation specialist Kirk & Blum rebalanced the air pressure throughout the system.

Kirk & Blum had to double the length of ductwork in the system to accommodate the new melter. To maintain identical static pressure at all three melters despite the friction this introduced, Kirk & Blum increased the speed and horsepower of the fan, and designed orifice plates to make precise adjustments to duct cross-sections at each connection point.