Industrial Utility Efficiency

# Steel Forging Facility Maximizes Investment in Compressed Air System

When a company is considering making an investment of more than a million dollars in system upgrades, it is crucial for them to review all options to get the best return. By exploring energy efficiency impacts throughout the entire compressed air system, vendors can propose projects resulting in both a larger sale for them and increased financial benefits for their customers, while still meeting capital expenditure guidelines. This “best of both worlds” scenario was evident when a foundry in the Midwest was evaluating options for replacing its steam system used to drive the plant’s forging hammers.

Steam hammers have proven to be invaluable in many industrial processes, especially the steel forging business. Yet steam systems are not energy efficient, as modern forging hammers are driven either hydraulically or with compressed air. This particular steel forging foundry knew it was time to contact its maintenance vendor for help when the company realized it was facing nearly \$660,000 in deferred maintenance. ### Analyzing the Existing System The vendor and the foundry’s plant engineer worked together to evaluate the existing system. It was determined the aging equipment would need to be replaced in the next 5 years. They were also able to calculate current annual operating costs. They calculated fuel, electric, water, and other miscellaneous costs using the approach described below: Fuel Costs • Assuming 1,101 British thermal units (BTUs) produce one pound of steam, and there are 1,000,000 BTUs in 1,000 cubic feet (MCF) of natural gas (at 100% efficiency), 66.1 MCFs produce 60,000 pounds of steam (the rated capacity of the boiler and the amount needed to drive the hammer system) each hour. • At run hours of 3,000 per year, 66.1 MCF * 3,000 hours = 198,000 MCFs used per year. • At \$6.50/MCF (cost of fuel), the fuel cost is \$430 per hour, or \$1,288,950 per year.

Electric Costs

• The system water pumps are 300 horse power (hp) total. Converted to kilowatts (kW), 300 hp * 0.746 kW/hp = 223.8 kW.
• At \$0.0854 per kilowatt-hour (kWh), the cost of electricity, operating 3,000 hours per year, (3,000 hr/year * 0.854 \$/kWh * 223.8 kW), the electricity cost is \$57,390 per year. Water Costs • Water usage is make-up water for the steam boiler. This amount (10,666 gallons per hour) was measured by the vendor. • This amount is reduced by 10% (or multiplied by a factor of 0.9), assuming 10% of the water is returned back to the boiler as condensate. • At \$4.50/1,000 gallons (cost of water), 10,666 gallons/hour * 0.9 * \$4.50/1,000 gallons * 3,000 hours = \$129,600, the annual cost of water used by the system.

Miscellaneous Costs

• Annual boiler certification: \$24,000 • Water treatment chemicals: \$29,000

### Switching from Steam to Compressed Air

The plant only needed steam production for 2,700 hours annually. However, the boilers ran an extra 300 hours each year during start up. A compressed air system driving the hammers would only need to run 2,700 hours. Therefore, the cost per hour of productivity of the existing system was \$590. And, despite the plant having a variable load, the existing system was constantly producing the same volume of output, resulting in wasted energy. The vendor knew from experience that electrically driven compressed air systems typically produce around 100 cubic feet per minute (cfm) at approximately 20 kW, or 0.2 kW per cfm. Therefore, knowing that the plant required a maximum of 25,000 cfm, the operating cost of a new system would be no more than \$427 per hour¹ — a savings of \$163 per hour over the current system (or \$440,000 annually). Based on operating costs alone, the natural solution was a switch to an electrically driven compressed air system to drive the hammers.

At this point, the plant engineer asked for a proposal for a new system.

### Meeting the Customer’s Financial Requirements

The foundry has capital expenditure guidelines that require any capital project have a simple pay back (SPB) ² of five years or better. To meet this requirement, the compressed air vendor proposed a complete system with an installation cost of \$3,910,000. The package included: • Five 1,500-hp, water-cooled centrifugal compressors • A 3,000 gallons per minute (GPM) cooling tower • Heat of compression (HOC) desiccant air dyers • All accompanying controls • A 120-by-60-foot unheated building to house the equipment Using the actual cubic feet per minute (acfm) load profile determined during the existing system assessment, the vendor was able to calculate the energy and water savings of the new system. In addition to the \$660,000 savings in deferred maintenance, the vendor-proposed system (Table 2) would provide annual energy and water savings of \$780,000 (nearly a 50 percent reduction from their current annual operating costs) and meet the SPB requirement of five years. The proposed system was estimated to result in an hourly operating cost of \$302, assuming 2,700 operating hours per year.

##### ² Project cost divided by project annual savings.

Tim Stearns is a Senior Energy Consultant with Efficiency Smart, a division of the Vermont Energy Investment Corporation. He can be reached at tstearns@efficiencysmart.org. For more information, visit www.efficiencysmart.org