Boiler Condensate Return Basics February 24, 2016

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1 Boiler Condensate Return Basics February 24, Explain what you mean by saturated steam. A: Saturated steam is really saturated water which has been heated to the point where no additional Btu s are absorbed without the water changing state and becoming a vapor. When this pound of water, now steam, condenses, it gives off its latent energy, and becomes water again, and that is the condensate we want to capture. The hotter, the better! 2. Is it always possible to recover TDS controlling blowdown and save energy? A: It s always possible to save energy in this way, but the amount of the blowdown and frequency will dictate the payback potential, and if it equals a legitimate ROI. It s certainly worth looking at. 3. Isn t it possible to avoid stall by properly selecting the right trap with an adequate minimum static head; avoiding the use and cost of a power pump? A: Absolutely this is possible, but many times there is insufficient height (2.3 feet/pound) to provide the differential (static head) required at low loads for the trap to properly function. The last thing you want is for the heat exchanger to flood. 4. What is the maximum distance (not to exceed) for drip pocket placement in a straight length of pipe? A: Never more than 300 feet. 5. You mentioned condensate transfer pumps not having sufficient NPSH What s that? A: NPSH stands for Net Positive Suction Head which means the amount of static head required on the pump inlet at specific duty points including operating temperature, pumping rate and discharge pressure (TDH). Insufficient head will result in pump cavitation which reduces the pumping rate and tears up the pump. 6. Can you review the flash steam calculation again? A: Say you have condensate coming out of a process at 150# saturated and it is discharging into a 15# condensate line. You go to a steam table and note the sensible Btu s at 150# (338) and the sensible Btu s at 15# (218). Subtract the two (120) and divide that result by the latent Btu s at 15# (946). It will be about 13%.

2 7. Is it possible to have differential water hammer in a condensate line? A: Absolutely! As the amount of condensate increases, and the pressure differential increases as a result of higher pressure feeder lines discharging into the common condensate line, differential water hammer can result, potentially causing severe destruction. Remember, 7000 feet per minute velocity is about 80 MPH and a gallon of water weighs over 8 pounds 8. Should neutralizer kits be used to improve piping life? A: This answer really needs to come from a qualified water treatment expert. 9. How much is a cubic foot of condensate? A: One cubic foot contains approximately pounds of water. 10. Will the Condensate Return System eliminate the need for an Economizer? A: No. The economizer is used after the condensate has returned to the boiler feed system (vented receiver or deaerator), and then is pumped through the economizer to pick up additional heat from the boiler stack before the water is introduced into the boiler, saving additional energy. 11. We have a Machamer System for condensate return. We find ourselves not getting rid of condensate well enough, and our pressure vessels on the corrugator get water logged quite easily. What is the issue with the Cochran Pump/Machamer System that allows this to happen? A: If all of your steam traps on the corrugator are properly functioning (not fouled or plugged), the siphon tube is in its proper place with good working flexible joint(s), the return lines are properly sized for the pressure drop and amount of flash steam in the bi-phase line, and the boiler s operating pressure has not been raised or lowered, the pumping system should work properly. Is the Cochrane pump system piped to a modulating feed valve? If so, is this working properly? If not, it could be causing the condensate to back up because the pump is not allowed to fully discharge. What I m referring to here is a Cochrane balanced pumping system with no electric motor driving the pump to get the water in the boiler. 12. Can periodic blowdown of steam traps and strainers prevent or reduce water hammer? A: Possibly, if the trap is not fully closed after evacuating the condensate and (steam) blow through is occurring causing over pressurization of the condensate line which could lead to both thermal and differential water hammer.

3 13. What is the determining factor in selecting a FT or a thermodynamic trap and is it based on condensate load? A: Suggest you go to our website (cleaverbrooks.com) and under archived webinars, find the Boiler Steam System Supply Basics webinar (November 2015). All the popular traps are reviewed with their respective pros & cons. Then, depending on your particular situation you can begin evaluating your best option. 14. How does cold make-up water impact the operation of the boiler feed water system? A: Two problems with this: One, you reduce the feed water temperature, and for every 10 degree drop you lose 1% in efficiency. Two, the colder water entering the boiler could thermally shock it causing pressure vessel issues such as cracking of tube ligaments and boiler tube failure. In both of these cases I m referring to a firetube boiler. 15. How can someone identify how much condensate is being returned? A: You need to install a steam flow meter and a water meter to first determine the amount of steam going out to the system. This steam is water in vapor form. There are 8.3 pounds per gallon of water. Next with your water meter, you determine how much water you are taking in to make up for the condensate lost if there is any. If there is makeup, the difference from the steam out converted to gallons minus the gallons of makeup is your answer. In many cases where steam is not lost to the process, the amount of condensate returned is 75 85%. 16. In the diagram for a steam powered trap, there was a second steam trap downstream of the steam powered trap. What is the purpose for installing back to back steam traps? A: The power steam pump is only in play when the modulating steam valve controlling heat to the process is closing. This causes a loss of differential on the downstream trap. When this occurs, the steam power pump begins to fill and evacuates the condensate through the downstream trap which has lost its differential until the steam modulating valve goes full open again. 17. When is discharging condensate from a MP system into a LP pumped condensate return line ok? A: It s OK if the resultant effluent coming from the medium pressure line is properly flashed off or diffused into the LP line, and the LP line is sized properly to accommodate any remaining flash while not exceeding the pressure drop tolerance. Remember too, the condensate pump only pumps liquid so all flash has to be gone at this point.

4 18. How high should the column of steam from the vent of the receiver be? A: If you are talking about venting flash steam through the roof the steam plume height will vary based on the pounds of flash being evacuated and the size of the vent line. Regardless, this is very wasteful. 19. How should low pressure condensate return and high pressure condensate return systems be combined when feeding back to a common boiler? A: The high pressure line should probably go to a flash tank where the flash steam can either be vented or recovered as explained in the program today. It would then be taken to the low pressure line where it should be diffused into the common return. Refer to today s program again for the criteria which needs to be considered for properly sizing this common return line. 20. Please explain again how CO2 is formed from the condensing process. A: The carbon dioxide I was referring to enters the feed system from the carbonate and bicarbonate alkalinity entering in from the raw makeup water. Once heated, it turns to carbon dioxide, a non-condensable gas, now carried along with the steam. When the steam condenses, the CO2 combines with the condensate and forms carbonic acid (H2CO3). 21. Can you have Steve explain the Float & Thermostatic trap after the Pressure Power Pump again, specifically how the pressure differential works when there are differences in the condensate loads. A: See question #16 above. 22. Do high pressure condensate receivers negate the use of steam traps? A: Absolutely not. The trap is there to trap steam and evacuate the hot condensate. Without the trap you would be blowing live steam through your condensate return line causing all sorts of problems and considerable energy waste. 23. How do you recommend connecting different pressure condensate lines together into one header if the boiler plant is far away in another building? A: You have a couple possibilities: One, take the condensate into a single medium to high pressure line (if this is what you have), sized for the blended effluent which will be a combination of liquid and steam (bi-phase). Based on the pressure now in the line (provided it s constant), size the line to account for the line transport loss and bring it directly to the DA or a high pressure receiver using the motive force exerted at the inlet of each trap. Two, bring the high pressure condensate into a flash tank or flash tank/recovery system before going to a low pressure common return with an adequately sized condensate pump to deliver the hot condensate back to the boiler room.

5 24. How do you size vertical condensate line that discharges into main header? A: It is all about the differential pressure through the trap and the height of your vertical condensate line above the trap s outlet. For every 2.3 feet you have 1# of pressure you have to overcome. Then, depending on the size of the vertical pipe, and the flow rate through it, there will be some friction loss, but this will be minimal if the pipe ID is not too small. 25. Do you recommend sloping the main condensate line before the main condensate pump and if so how much slope? A: A good rule of thumb is about 1 per 10 feet.