Losses and Costs Associated with Coal vs. Natural Gas Firing at Hanes Dye and Finishing

Abstract

Due to decreasing production and rising coal prices, the engineering and management staff at Hanes Dye and Finishing in Winston Salem, NC have been investigating a switch from their current coal-fired boiler to a cleaner, more efficient natural gas boiler for a number of years. For this purpose, a detailed study of the parasitic losses and costs of the current boiler operation is warranted, as well as comparable information on a replacement natural gas boiler system. The Miura brand of boilers is commonly used for this application, and a system of 6 small boilers of similar size was tested at another textile facility in North Carolina.

A study of the current coal-fired boiler yielded a total thermal efficiency of 77.78%, due to stack loss, carbon contained in ash, radiation loss, sootblowing, and blowdown. This efficiency was considerably less than a comparable Miura (natural gas) system which has a total thermal efficiency of 81.91%. In addition, the auxiliary costs involved with boiler operation, such as fuel storage and handling, refuse handling, maintenance, labor, and environmental compliance are over $300,000/year more with the current coal-fired boiler than the Miura natural gas-fired boilers.

Despite these large differences in parasitic losses and costs, coal is still by far the cheaper fuel to fire, based on fuel prices. Coal at Hanes was purchased for an average of $121.53/ton in 2008 ( roughly $4.18/MMBTU), compared to $10.25/MMBTU for natural gas. Altogether, the current boiler operation costs roughly $1,000,000 /year, while a similar Miura system would cost about $1,600,000/year.

While it is not currently economical to switch the boiler operation to natural gas, future factors such as fuel price volatility and increased environmental legislation could make coal more expensive to burn than natural gas. Therefore engineering analysis and economic tools are provided to assist Hanes Dye and Finishing in updating their costs yearly and making an educated decision on whether to switch to natural gas.