Calculating the Cost of Steam
- Knowing the true cost of steam is critical to optimizing processes and boiler efficiency.
- You can determine costs using the steam table method or the direct fuel cost method.
- See Steam Systems from the U.S. Department of Energy for energy-saving tools and resources.
Steam is a critical part of your operations, but what is it really costing you? Understanding the true cost of steam generation and consumption is essential in evaluating process efficiency and economics. It will also help in maintaining boiler systems, optimizing steam production and making capacity improvements.
Getting down to the numbers
The cost of steam generation (in dollars per 1,000 pounds of steam) depends on fuel type and price, boiler efficiency, feedwater temperature and steam pressure.
The Steam Tables published by the American Society of Mechanical Engineers (ASME) are useful for calculating steam costs. According to the tables, 1,073 Btus are required to produce 1 pound of 150-psig saturated steam (boiling point=366°F) — given the availability of 150°F feedwater [857 Btu (latent heat) + (366°F - 150°F, sensible heat) = 1,073 Btu].
Assuming a natural gas price of $8.00/MMBtu and a boiler efficiency of 81 percent, the cost of raising steam is as follows:
You can also determine the cost of steam directly by dividing the amount of steam produced by the amount and cost of fuel used. For example, if a facility produces one million pounds of steam in a 24-hour period while consuming 9,000 gallons of fuel oil at a cost of $2.50 per gallon, you can use these numbers to calculate the cost of steam per thousand pounds:
As these calculations show, the type of fuel has a major impact on steam cost. For each 1,000 pounds of steam produced, natural gas in this case costs about half that of fuel oil ($10.60 versus $22.50).
For more information, see Benchmark the Fuel Cost of Steam Generation from the U.S. Department of Energy.
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