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Newsletter 2006 issue 3 |
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Blowing Off Steam is a Waste of Energy
With the legwork of a MnTAP intern, Rock-Tenn developed an insulation plan for steam and condensate lines.
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MnTAP intern Steffen Springborn investigated nearly 20,000 feet of steam and condensate lines. |
Papermaking is energy intensive. According to the U.S. Department of Energy the pulp and paper industry is the third-largest user of fossil fuels in the U.S. industrial sector, spending about $6 billion per year on energy.
Rock-Tenn Company, a recycled paperboard mill in St. Paul, has been working to lessen the bite of its energy bills. Its electricity use dropped approximately six percent after installing over 200 variable speed drives on pumps and some fans. When the Xcel Energy High Bridge power plant shared its plan to convert from coal to gas power, eliminating the paper mill's source of steam, the mill redoubled its energy efficiency efforts to prepare for bringing its own steam system online.
The company has reduced its thermal energy use from steam by 31 percent since it began installing its new steam system. Insulating steam and condensate lines is saving $171,000 in energy use annually. The company has also instituted a steam trap management plan.
Steam and condensate lines
The company’s steam lines transport heat energy to run
electrical generators and dry paper as it progresses through
the paper machine. After transferring its heat, the steam condenses into warm water which is returned to the boiler via condensate lines to be turned into steam again.
Often in older production facilities, such as Rock-Tenn’s 1908 paper mill, steam and condensate lines were not insulated because energy used to be inexpensive.
Of the nearly 20,000 feet of steam and condensate lines, only a small fraction were uninsulated, primarily the condensate lines. But these provided significant heat recovery opportunity. Uninsulated lines at the mill lost millions of Btus annually—enough heat to keep 350 homes warm through a Minnesota winter—at a cost of $190,000.
Because Rock-Tenn did not have enough staff time to investigate 20,000 linear feet the company requested a MnTAP intern to help. The intern researched steam and condensate line insulation and found that heat loss could possibly be reduced by 90 percent.
“Our need required more legwork than we had resources to accomplish,” said Gary Myhrman, Rock-Tenn plant engineer. “The MnTAP intern could dedicate 100 percent of his time to walk the pipes and do the calculations.”
The intern gathered data from CAD prints, interviews with plant personnel and plant walkthroughs. Using the 3E Plus Insulation Thickness Computer Program developed by the North American Insulation Manufacturers Association, the intern determined the optimal thickness of insulation for the condensate and steam lines and developed a cost/benefit analysis. As a result of the intern’s work, the company changed its insulation standard for the steam lines and set a standard for the condensate lines, commented Myhrman. The mill is nearly complete with its phased-in plan to insulate all lines.
Steam trap management
The company mapped, numbered and catalogued all of its 1,000 plus steam traps and established a leak program. A staff technician checks all of the traps once a year to ensure they are functioning properly. Condensate return levels are monitored in order to flag steam losses and keep leaks under control.
A consultant helped the company determine if the traps had the proper orifice size. If openings are too small water can backup into the pipes, decreasing performance; too large, the trap can lose steam after it drains water and if traps get stuck open even more steam/energy is lost. Oversized traps are being retrapped for better sizing and improved design efficiency.
Benchmarking data from the Recycled Paperboard Technical Association shows the average unreturned condensate as 18 percent. With condensate losses as low as 12 percent, Rock-Tenn’s steam line is now one of the most efficient in the business.
Beyond the bottom line
In addition to the economic impact at Rock-Tenn, reducing energy use alone from insulating the pipes has an estimated annual environmental impact of reducing five million pounds (2,500 tons) of carbon dioxide emissions from coal burning to generate the steam. Carbon dioxide is a greenhouse gas associated with global warming.
See the complete Rock-Tenn intern project summary.
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