The Cost of Steam Systems: Make Sure to Add All the Factors
by Taryn Hardes, on Tue, Jan 29, 2013 @ 09:01 AM
Fuel cost and boiler efficiency are key elements, but they tell less than half the story
Depending on the system, condensate may be getting to the tank through several different return systems at different pressures. Active management can lower costs considerably. Learn about Steam and Engineering Services available from Swagelok Energy Advisors »
What does a steam system cost? It's not always an easy question to answer. However, knowing the numbers will help you operate your plant more efficiently.
The specific answer will be a little different for each system. Fuel cost is an obvious factor. Operating steam pressure is another: The lower the pressure, the lower the cost. The percentage of make-up water will make a difference too. It has a lower Btu content than condensate return. Finally, there's the matter of boiler efficiency, which can vary with load demand and firing rate. If you have that information, you can make the simplest of calculations, called the unloaded steam cost. That's basically the amount of steam produced, and the cost of fuel required to produce it.
Let's start with the simplest kind of system: one boiler, a single type of fuel, and one operating pressure. In this example, we'll assume steam is being generated at 100 psig and is being returned to a deaerator tank operating at 10 psig. We'll peg the fuel cost at $9.50 per MMBtu, and the boiler efficiency at 85 percent. (For the specific equations used for these calculations, visit Swagelok Energy Advisors.) The unloaded steam cost, then, is $10.96 per 1,000 pounds.
If we don’t bring any condensate back and we use 100% make-up water, then we lose all the sensible energy that is in the condensate and we have to bring the make-up water up to the steam temperature before we can make steam at a given pressure. This extra energy we are putting in costs money. If we keep all the other variables the same, the cost of producing the same 1000 pounds of steam rises from $10.96 to $12.50, a difference of $1.54 per 1000 pounds. If our boiler is producing 50,000 lbs/hr the annual savings is over $600,000!
A wider look
An even more sophisticated calculation is to figure out the loaded cost of steam. In addition to the costs we've already considered, we add the cost of electricity, chemicals, water and sewer service, emissions payments, labour costs, waste disposal, maintenance and new projects. Once they are all factored in, the true cost of steam can easily come to twice as much as the unloaded steam cost.
It's a tough assignment to take on without any help. That's why Swagelok Energy Advisors stand ready to help you. Once you know the correct cost of steam, you can more accurately assign the true cost to various production areas for accountability, evaluate the economics of proposed improvement projects, and set a benchmark for optimizing the steam generation system.
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