Sudden Dropoff in heat transfer : Steam coil
Sudden Dropoff in heat transfer : Steam coil
(OP)
All,
I would appreciate any ideas or thoughts you may have regarding a phenomenon I am experiencing.
A large vessel with 6,000 gallons of a water/grain mixture (a mash cooker) has a steam coil supplied with 20,000 lbs/hr and the supply valves is ~ 30% open.
The vessel starts at 170 degrees with the intent of inducing a boil...at just over 200F the steam flowrate drops off drastically (down to 10,000 lbs/hr) while the supply valve opens to 100% attempting to make setpoint.
The pressure in the vessel is 14.7 psia.
The weird part is that this only occurs when using grains from the 2007 crop year. Can there be something in the fluid mixture that suddenly changes the heat transfer across the coil? There is no burnt residue on the coil when the vessel is emptied.
I would appreciate any ideas or thoughts you may have regarding a phenomenon I am experiencing.
A large vessel with 6,000 gallons of a water/grain mixture (a mash cooker) has a steam coil supplied with 20,000 lbs/hr and the supply valves is ~ 30% open.
The vessel starts at 170 degrees with the intent of inducing a boil...at just over 200F the steam flowrate drops off drastically (down to 10,000 lbs/hr) while the supply valve opens to 100% attempting to make setpoint.
The pressure in the vessel is 14.7 psia.
The weird part is that this only occurs when using grains from the 2007 crop year. Can there be something in the fluid mixture that suddenly changes the heat transfer across the coil? There is no burnt residue on the coil when the vessel is emptied.





RE: Sudden Dropoff in heat transfer : Steam coil
Just a thought!
RE: Sudden Dropoff in heat transfer : Steam coil
What is the steam condition at the entry to the coil?
Where does the steam go when it exits the coil? What is the pressure there?
What type of controller?
Does the controller have "recipes" for different products, grains, etc.?
RE: Sudden Dropoff in heat transfer : Steam coil
What is the steam condition at the entry to the coil? Slightly superheated, 70 psig
Where does the steam go when it exits the coil? What is the pressure there? Into several, properly functioning, bucket traps. There isn't a pressure indicator downstream of the coil.
What type of controller? PLC with a PID loop controlling the valve off the steam flow meter.
Does the controller have "recipes" for different products, grains, etc.? No. For this portion of the cycle the set point for the controller is the same for all recipes.
RE: Sudden Dropoff in heat transfer : Steam coil
Just an idea that came to mind...
On a similar application, I used a steam injection nozzle with success.
RE: Sudden Dropoff in heat transfer : Steam coil
Regards
Stonecold
RE: Sudden Dropoff in heat transfer : Steam coil
RE: Sudden Dropoff in heat transfer : Steam coil
Either you have "classic" heat exchanger
"stall", or the 2007 crop has some kind of bizarre agricultural curse on it. Have you really experimented with crops from other years ? How about crops grown with farm subsidies from the Bush administartion... Is this really and truly a viable variable...??
In HX stall, the coils get flooded with condensate, the little controler goes wide open, trying its best to do its job, but to no avail...heat transfer from condensate to the mash is just not as good as from saturated steam...
The classic solution is to install a "fair size" drain pot at the bottom of the coil and allow the steam trap to draw from the new pot
htt
Let us know your final decision and tell us more about condensate drainage
-MJC
RE: Sudden Dropoff in heat transfer : Steam coil
RE: Sudden Dropoff in heat transfer : Steam coil
Offshore Engineering&Design