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Vol. 25, No. 1, February 2006

Technololgy Spotlight logo

This column features helpful information, innovative equipment, systems and applications utilities around the nation can use to save energy and improve service.

Insulating process steam systems

When steam distribution and end use equipment is uninsulated, or under-insulated, you have a constant loss of energy. Considering soaring energy prices and the fact that installing insulation is generally relatively inexpensive, insulation projects can be very cost-effective.

The first step is to conduct an insulation appraisal at your facility. An appraisal identifies current energy losses, estimates dollar savings from reducing losses, determines total installed costs and provides management with the information necessary for making sound, economic energy decisions.

Estimating potential savings

The main factors influencing the amount of energy lost include steam pressure and temperature, process fluid temperature, ambient temperature, surface area or pipe length, equipment orientation, resistance to thermal heat losses and wind speed.

To determine the energy savings from insulating a surface or length of pipe, contrast the heat loss from the bare surface with the heat loss after the surface has been insulated. The optimum or “economic insulation thickness” depends on fuel cost, boiler or heater efficiency and the cost of purchasing and installing the insulation type suitable for your application.

One example of dollar savings

Consider a chemical plant with 150 feet of uninsulated 8-inch diameter outdoor pipe with a process temperature of 400°F, a natural gas cost of $8/MMBtu, and a boiler efficiency of 80 percent. The annual heat losses, assuming constant operation, are:

Annual Energy Loss = 150 feet x 3,350 MMBtu/year/100 ft = 5,025 MMBtu/year

The potential dollar savings, assuming that the insulation applied reduces heat losses by 90 percent, are:

Annual Savings = 0.9 x 5,025 MMBtu/year x $8/MMBtu / 0.8 = $45,225/year

For a detailed calculation of energy losses from outdoor steam distribution piping, use the free 3E Plus software. Sponsored by the North American Insulation Manufacturers Association, the program calculates the most economical insulation thickness for conditions input by the user.

Other benefits of adding insulation

Insulation performs multiple functions including:

  • Reducing heat loss (or heat gain for chilled water or refrigeration systems)
  • Minimizing temperature reductions along distribution pipe runs
  • Limiting surface temperatures for personnel safety and protection
  • Preventing condensation on cold surfaces
  • Reducing damage to equipment from chemically corrosive atmospheres or from fire
  • Providing sound attenuation

Insulation jacketing or protective coverings used in certain applications may serve additional functions:

  • Weather barriers
  • Vapor retarders
  • Mechanical abuse protection
  • Hygienic (toxicity, hygroscopicity or tendency to absorb water vapor from the air)
  • Appearance

 Selecting and specifying insulation

Insulation comes in various types (fibrous, cellular, granular) and forms (e.g., rigid boards, blocks, sheets and pre-formed shapes; flexible sheets, blankets, cements and foam). Available insulation materials include calcium silicate; fibrous or cellular glass; mineral fibers including rock and slag wool, expanded silica or perlite; elastomeric (foamed resins combined with elastomers); foamed plastics; refractory fiber insulations and insulating cements.

Process systems requiring insulation fall into three application temperature ranges:

  • Low temperature range (-100°F to 60°F) – refrigeration, cold/chilled water piping and commercial heating and cooling systems.
  • Intermediate temperature range (61°F to 600°F) – low-pressure steam and hot water piping, and process equipment (such as dryers, reactors, converters, reformers, fractionation and stripping columns, and distillation towers).
  • High temperature range (601°F to 1,500°F) – power generating equipment, turbines, exhaust systems, high pressure and/or superheated steam piping, furnaces and ovens.

Special systems with process fluid temperatures below -100°F are called "cryogenic" systems while systems operating above 1500°F are termed "refractory."

Selection factors

Base your insulation selection on application temperature range, combustibility, absorptive properties, sound control qualities, thermal shock resistance, structural and compressive strength, density, chemical resistance, impact and thermal shock resistance, resistance to ultraviolet light, resistance to fungal or bacterial growth, fire retardancy and combustibility and, of course, thermal properties and resistance to heat loss.

Thermal properties are a primary consideration. The “k-factor” or thermal conductivity is based on the number of Btus per hour that pass through a 1-inch square block of insulation given a 1°F temperature difference between the inside and outside surfaces. Materials with low k-factors have superior insulating qualities. The R-value, or thermal resistance of a material, measures the material’s ability to retard heat losses—higher R-values mean reduced heat losses.

To assist industries in selecting insulation and to identify companies that manufacture and supply products that conform to different ASTM insulation specifications, the National Insulation Association has produced the Guide to Insulation Product Specifications.

Publications

Insulate Steam Distribution and Condensate Return Lines (pdf)

Install Removable Insulation on Uninsulated Valves and Fittings (pdf)

Steam System Survey Guide (pdf)

Improving Steam System Performance: A Sourcebook for Industry (pdf)

Call the Power Line at 1-800-769-3756 for further technical assistance or submit your questions on-line. You may also find many other resources on steam system efficiency on Western’s Energy Services Web site.

 

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