kiln coils & steam traps

[wayne cunliff]

Want to know what type of test you do to test or check them and if any of you use enercon orifice steam traps.  I run a Cleaver Brooks low pressure 15psi boiler feeding two double track kilns ones 65 feet the other is 90 feet, i have been doing checks with a heat gun and im finding dead spots in my coils like 200 degree's on say the top three and bottom and in the middle it would be 80 degree's. There horizontall standing coil's 21' long ten of them in a section three sections high make a zone.  We thought they were old and bad since they have been in there since 1961 so we bought a new one put it in and cut the ends off the old one and it is spot less on the end side.

[MichaelM]

The most reliable way to check a trap is with test valves before and after the trap.  Having said that, the coils are not draining if they are cold at the bottom because steam will have a constant temperature through the coil.  The coils might back up some at start up, so I would test at other times during the schedule - the middle and end.  In the middle of the schedule the control valve is probably mostly open and there is probably enough pressure in the coil to cause it to drain. At the end, when the heat demand is low, the pressure in the coil is less and may not be greater than the pressure on the discharge side of the trap.  Contributing factors are small or long return lines, elevated condensate tanks, and backpressure from other kilns draining into the line or a failed-open trap blowing steam.
I can't really say more without knowing more about the problem and the system.

I hope some folks will comment on their experiences with orafice traps in kilns.

[Joe D]

Another way to test is using a heat gun. With the orifice type traps you will need to develop your information on the temperature differential you should see from the inlet side of the trap to the exiting side.

Michael had some good thoughts on what to look for as far as why your not seeing one area of a set of coils heating. Also each set of coils should be trapped (I could not tell this by what you wrote) because with more than one col feeding into a trap you can get some pressure build up that prevents draining of a coil. With older kilns insure your coils are sloped (check the coil hangers, etc) so the coils can drain.

Last of all make sure you have a trap that can handle the job you want it to do in terms of condensate load, pressures and consistency of load and pressures.

[wayne cunliff]

all of the coil sections have there own traps and it's not the bottom or tops of the coil its the middle its random some coil sections the whole thing is say 220 and some its 3 or 4 in the middle that are say 80 deg iv heard it called short circuit of coils. I have tested them at 25% 50% and 100% with the same out come the grade is good and no bellys. Im currently looking for a steam  specialist that dont mind driveing to riddle to better evaluate are system, if any of you no of any one shoot me a email at kiln@cdlumber.com or just post on here thank you

[Joe D]

Wayne, a good source of a steam specialist may be you trap supplier. They may have one on staff. If not, their competition will. You may have an airlock going on.

[wayne cunliff]

Thank you ill let you know what happens it will be awhile before i can schedule some down time thoe to let some one look at it.

[fbushaw]

I use bucket traps in my kilns. Does anyone have a good idea how often these should be tested? We are currently trying to test, and rebuild or replace atleats every 6 months.

[tanderson]

I also use bucket traps and i look at them once a month by PM's of course if I have a drying problem the traps are one of the first things I check

[Robbie]

Mr. Cunliff,
 
   I believe I will have more questions than I will have any answers for you. What kind of traps are you using? Inverted bucket, ball and float, float and thermostatic, thermodynamic etc. etc? Are they designated for the psi you are using( low pressure )? Do they have an air lock release built into them?
   When you did your checks, did you have your fans on or your kiln doors open? If you just put in some setpoints, you would not get an accurate reading. You need some way to pull the heat off of your coils to get a good "flow" of steam established to check your coils. In your steam system design, are there any Y-strainers? If so, are they being blown down frequently? What about check valves? Does your condensate side of the trap have individual check valves per trap? Are all of your traps feeding back into a single condensate return line and if so, does this go straight back to the Boiler or do you have any condensate return pumps?
   The reason for the questions, is because the whole steam system, from your heat valves to how your condensate can get back to your feed water tank, is imperative to the whole operation of your coils working properly. I've seen a Y-strainer clogged on a steam header and it would not purge the condensate properly. It waterlogged the header and just fed hot water to the kiln. We checked steam traps, y-strainers, check valves and ball valves and finally found our problem outside of the kiln on the distribution header.
   I've also seen the check valves ( bronze swing check ) go bad where they were not seating propely and allowed a backflow back into the trap and binding it up whenever the adjoining kiln would be under a load that shared the same condensate return line. I've seen a steam operated condensate return pump not working and waterloggiing the coils. Also have seen a steam operated condensate return pump used as a reservoir and a pump, with the incoming check valve bad creating a waterlog in the coils. Every time it went to pump, it would push the condensate back into the kilns instead of back to the Boiler. 
   On the other part of your question, we currently have two kilns operating with the enercon fixed orifice traps. We also use Spirax Sarco and Watson McDaniel float and thermostatic traps with the air lock releases as well. All three traps perform very well. We operate at 100 psi on six kilns, 40 psi on five kilns and 15 psi on our Predryer. We check all of our traps, roughly 70 total, about once a year either with an ultrasonic listening device or with a laser thermometer. Our daily checks of our steam traps are to watch the condensate return pumps exhaust. They are steam operated and they produce a small amount of flash steam when they exhaust their motive. When we start seeing more flash coming out of the exhaust, we will go in and check the kilns that feed into that pump. As of current, we have about four bad traps in our Predryer. We initially found that out from the condensate return pump exhaust.
   I hope that this might help you in one way or another. You have a wonderful and great community of knowlege, exempting myself, in this forum with the likes of Mr. Denig, Mr. Duncan, Mr. Milota and all of the other very knowledgable contributors here. If you pick everyones brains and continue to investigate the problems you are having, you will not only find the answer to your problem, you will find you have made an impact in your organization and in this great brotherhood of Kiln Operators. Best wishes to you and when you find the answer to your problem(s), please let us all know. You might be answering some questions that we might have!   


Robbie

[PaulBallard]

Robbie: I liked the thoroughness of your response to Mr Conliff. You walked him through a long list of steps to sleuth out the root cause(s) of his issues.

One of the big challenges we run into with with low pressure kilns is dealing with lift in the return. It is so easy for a modulating system to create a condition where flooding the coils can occur. We have consulted with a lot of sawmills with low pressure and lift in the return and would be happy to share a few of the tricks we've come up with to deal with this nagging situation.

[HencoV]

Well done to all contributors...This is the way forward. To isolate this problem I would firstly check the inlet valve to each heating coil with a heat gun. When the valve is supposed to be 100% open according to the control system, the temperature before and after the valve should be the same. If not, the calibration to your proportionate valve could be out, or it is not opening 100%. Next I would check the temperature before and after the steam trap on the exit side of the heating coil. The temperature before the steam trap should be higher than after the trap, as before the trap, if the trap is in good working condition, temp should only be steam, and after the trap lower because it would be condensate. If temp before and after steam trap is the same AND much lower than after the inlet steam valve, the trap could be faulty or the orifice clogged up. If the heating coils are old, fouling of the inside of the coils could be an issue...this has been addressed by replacing the coils. Remember, a water logged steam heating coil, becomes a "cooling" coil when water logged!!

I would suggest checking the temperature before and after the main steam valved daily, also check the temperature before and after steam traps daily with a heat gun, and record the temps...this way you will immediately spot a faulty steam trap, or problem with calibration on steam inlet valve and steam traps. A steam trap or valve could fail at any time, and opening it only every 6 month could cost you $$$ on extra drying time, over drying of complete load and re-drying of wet boards.

The key to preventative maintenance on the heating system of your kiln is knowing what temperature values are supposed to be when all valves are open, and steam traps functioning 100%, and comparing actual temps to these figures on a daily basis, even if this means having a "maintenance mode" on your control system forcing all valves open for the time it take the operator to check all valves and steam traps with a heat gun.

I don't think the type of steam trap is an issue, as long as it is working, and of course correctly specified for the job. Not 100% sure with orifice steam traps however.. all I know is that the size of any orifice devise is designed/specified according to pressure. The moment pressure varies, as in kilns,  the device may not be operating 100% within it's intended specs...? (I may be wrong regarding orifice tarps however?)

One more thought...if the heating coil was so fouled up that it needed replacing, so could the condensate return line after the steam trap. This heating system is over 50 years old, replacing everything between the steam valve and the condensate return tank could increase overall kiln efficiency to the extend that the improvement could pay for itself in a very short space of time.

....also consider that all heat ex-changers are not "created equally". The heat transfer co-efficient between old and new heat ex-changers may differ considerably, however not as much as originally indicated by Wayne.

Wayne, if you read this...after 2+ years...please share your experience

[PaulBallard]

This is a response to HencoV: "I don't think the type of steam trap is an issue, as long as it is working, and of course correctly specified for the job. Not 100% sure with orifice steam traps however.. all I know is that the size of any orifice devise is designed/specified according to pressure. The moment pressure varies, as in kilns,  the device may not be operating 100% within it's intended specs...? (I may be wrong regarding orifice tarps however?)"

If the orifice of the venturi is sized properly it will work fine through the whole range of the charge modulation (refer below to an expalnation taken from the Technical Discussions section of our Website). I agree with your suggestion that operators become familiar with the temperatures on the Y-strainers of the venturi.

How Matrix Venturis Work with Varying Loads
Large process applications will usually rely on a modulating control valve to vary the load. A modulating valve allows nozzle capacity to vary with pressure differential. When more heat is needed, the control valve opens to increase steam flow, providing greater pressure differential across the nozzle as well as higher nozzle capacity. When demand drops, the control valve closes and pressure and condensate load are reduced.

The range between maximum and minimum flow through a control tends to form a linear relationship such that an orifice size can be found that works for both extremes and everywhere in between without increasing the steam losses to unacceptable levels.  At maximum pressure where there is maximum heat transfer the maximum condensate load is generated. Matrix can size an orifice to handle this pressure and condensate load. Then when the control is modulated to the minimum pressure there is minimum heat transfer which generates the minimum condensate load. The same size orifice used for the maximum load will handle this minimum extreme.

[Grady]

. Remember, a water logged steam heating coil, becomes a "cooling" coil when water logged!!

I have heard this before. I do wonder though, if that zone in a kiln was experiencing a Cooling effect due to water logging, would the DB temperatures in that zone drop and the modulating steam control valve open more to compensate? once the steam valve opens more that should eventually create enough pressure to flush the trap empty.  I only ask this because i have been told the same thing with my kiln setup by a bloke who was trying to sell me bucket traps to replace the float traps we currently use.