How is steam efficiently used?

While steam is the most efficient way of distributing and transferring heat energy, the equipment used must be designed and maintained properly to realize the benefits of that efficiency.

07/02/2013


According to the U.S. Dept. of Energy (DOE), over 45% of all the fuel burned by U.S. manufacturers is used to produce steam. This statistic may sound high, but steam is used to heat raw materials, cook and condition foods and beverages, treat semi-finished products, process oils and chemicals, and even extract oil from the ground. It is also a power source for equipment, as well as for building heat and electricity generation. But steam, and the water it’s made from, is not free. It costs more than $20 billion annually to feed the boilers generating the steam.

So, doesn’t it make sense to make that steam and use it as efficiently as possible?

While steam is the most efficient way of distributing and transferring heat energy, the equipment used must be designed and maintained properly to realize the benefits of that efficiency. The problem is, very few steam users know how efficiently their boilers are running, let alone the efficiency of the steam system installed in their entire plant.

To increase a steam system’s efficiency, the DOE recommends that users:

  1. Determine the efficiency of their steam generation system, based on steam output/fuel input
  2. Determine how much steam they use and how much it costs to generate this steam
  3. Optimize excess air in their boiler to increase steam generation efficiency
  4. Maintain clean fire-side and water-side boiler heat transfer surfaces
  5. Optimize boiler blowdown to reduce total dissolved solids (TDS) in the boiler system
  6. Optimize their boiler control system to optimize steam generation efficiency
  7. Ensure that an effective water treatment system is in place.

While items No. 3 through No. 7 are tackled to some degree in most boiler houses, many do not have real-time data for actual efficiencies or how much it really costs to produce the steam. Conversely, because this data isn’t available, plants are unaware of the money that could be saved by implementing a few changes to their steam systems.

The benefits of monitoring boiler and steam system efficiencies

In the U.S., most plant boilers operate with a fuel-to-steam efficiency of 75% to 85%. This results from stack losses, poor controls and set-up, blowdown losses, losses due to radiation of heat from the boiler, and poor heat transfer due to scaling. The rest of the steam system can then lose up to an additional 30% of energy due to insulation losses, steam leaks, blowing steam traps, flash steam losses, and lack of heat recovery from condensate. Many of these losses can be easily fixed once you know the problem exists. This is where a boiler and steam system efficiency monitoring system can help.

  • It will provide percentage figures for fuel-to-steam efficiencies for each boiler, with being data logged over time. This can immediately flag opportunities to improve boiler performance. For example, it’s possible to see the immediate effects of adding an economizer or changing from manual to automated TDS blowdown control. It allows boilers in a plant to be compared with each other and predicted efficiency figures from manufacturers. It also flags new problems with the boiler. Perhaps blowdown was missed or there’s a problem with the deaerator tank because the feedwater temperature has dropped resulting in a drop in the measured efficiency.

  • It will provide the steam system efficiency for the entire plant which can also be data logged over time. This allows a comparison to be made against industry benchmarks and between plants. For example, let’s say there are two identical plants, Plant A and Plant B. Their system efficiency figures differ greatly: Plant A’s efficiency is 20% higher than Plant B because at Plant A they have just fixed all of their leaking traps—a 7% efficiency improvement—and started recovering heat from all of their blowdown and flash steam—a 13% efficiency improvement.

  • It will provide the cost of producing steam for each boiler and for the plant. Of course, once you know the cost of the steam produced you can estimate the losses you may have when compared to other boilers, plants and benchmarks. This data can then easily be used to help justify system improvements to reduce overall costs.

Courtesy: Spirax Sarco

Content provided by Spirax Sarco, originally published in Steam News Magazine.



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