10. Ensure the steam boiler is sized large enough to meet the current system consumption and possibly future expansion. Remember: BTUs needed to get feedwater to saturation temperature, and heat loss in piping due to insulation inefficiency.
9. Size steam distribution piping for 6000 FPM velocity below 50 PSIG steam pressure and 8000 FPM velocity for 50 PSIG and above. Remember: lower steam pressure has higher specific volume than higher pressure.
8. Make sure drip legs with drip steam traps are used to remove condensate from steam distribution lines to prevent thermal shock water hammer and poor quality steam delivered to the heat exchanger. Remember: drip legs should be about 2 ft. long and the same size as the steam pipe up to 4” and ½ the size of the pipe above 4”
7. Use equal percentage inherent trim characteristic control valves for process temperature control on steam sized to operate between 20 and 80% open, min to max. Remember: non-linearity in the form of high gain under partial steam load conditions are plotted as the inverse of the =% curve to become close to linear in the installed trim characteristic applied to the process.
6. Use supplemental thermostatic air vents and vacuum breakers (or a single device that does both) on large cavity heat exchangers. Remember: air is an insulator and is detrimental to surface temperature, and vacuum, formed by steam condensing and not replaced with an equivalent volume of steam, prevents the gravity flow of condensate from the exchanger to a steam trap allowing for the potential of thermal shock water hammer and/or internal corrosion.
5. Select the proper steam trap for the application. On modulated steam applications, the F&T (float & thermostatic) steam trap and inverted bucket steam trap are both acceptable depending on performance characteristics desired. Remember: steam traps must 1) stop the flow of steam to allow desired steam pressure to be maintained on the heat exchanger while latent heat is transferred to the process, 2) remove condensate in the heat exchanger simultaneously, and 3) remove non-condensable gases.
4. Ensure the steam trap can provide the capacity at low differential and can overcome static head pressure created by an overhead condensate return. Remember: if that condition can occur, use a mechanical (steam powered) pump as a closed-system in combination with an F&T trap, a double duty type combination device, or a separate open system pump/receiver either mechanical or electric.
3. When the system is operating smoothly and efficiently, look for more ways to increase efficiency by auditing different areas of the generation, distribution, heat transfer, and condensate handling systems periodically and look for opportunities to design and use heat recovery systems. At a minimum, test steam traps once a year for proper operation, but to eliminate the +/- 6 months of lag time between discovery of failed traps at that one moment in time plus the time it takes to arrange and actually repair or replace the steam trap, consider a wireless steam trap monitoring system, at least for the most process-important or highest pressure steam traps that will have the largest steam loss where discovery of failure is within minutes, the system can self-generate a work order, and the repair can be done quickly. One such system utilizes either ISA100 or WirelessHART mesh networks reporting to a measurement, monitoring, and reporting software system designed to manage the system effectively.
2. If you don’t really understand the thermodynamics, proper piping techniques, and potential problems that may occur in your steam system, don’t experiment. Contact someone who has thorough knowledge of steam systems before making that first change.
1. If you do understand your steam heat transfer system, have never instructed someone to “just change out the steam trap, it must be the blame for my system not working correctly since I don’t really know what it does,” then you may be numbered in that new group: “Steam system practitioner, the making of another Prima Donna”.
List courtesy of Steve Huffman, VP of Sales and Marketing, Mead O'Brien.
