Mud Drum Heater Coil Question
Mud Drum Heater Coil Question
(OP)
I have a water tubed boiler with a superheater that produces 400-psi steam at 650 deg F. There are currently 3 boilers at the plant. One boiler supplies the steam, another boiler is on hot standby, and another boiler is on what I call cold standby. The difference between cold and hot stand by is on hot standby the rapid mix burner is fired once per shift where the boiler on cold standby isn't fired. The hot standby boiler is more of a back up if the boiler producing steam trips offline. A lead/lag/standby operation.
All boilers have a mud drum heating coil. The boiler that is used for cold standby has the inlet boiler feedwater valve closed and the outlet superheater valve closed when in cold standby. The superheater inlet/outlet vents are closed. The mud drum heater coil was designed for 400-psi at 650 deg F. However, there is a low pressure steam line going to the mud drum heating coil at 150-psi at 230 deg F. There is a heat transfer process between the low pressure steam inside the mud drum heating coil and the water in the mud drum and water tubes and superheater tubes. On a perfect day there will be 40 to 70 psi of positive pressure in the tubes.
When the feedwater is closed off and superheater steam outlet is closed I am pulling a vacuum in the tubes with the steam condensing to water. I believe the inlet/outlet superheater vents need to be cracked open partially since there is some small amount of pressure in the boiler. What consequences do I have with those vents being closed? Will these cause possible vacuum conditions in seals or gaskets in valves, drums, etc? possibly damage seals/gaskets?
All boilers have a mud drum heating coil. The boiler that is used for cold standby has the inlet boiler feedwater valve closed and the outlet superheater valve closed when in cold standby. The superheater inlet/outlet vents are closed. The mud drum heater coil was designed for 400-psi at 650 deg F. However, there is a low pressure steam line going to the mud drum heating coil at 150-psi at 230 deg F. There is a heat transfer process between the low pressure steam inside the mud drum heating coil and the water in the mud drum and water tubes and superheater tubes. On a perfect day there will be 40 to 70 psi of positive pressure in the tubes.
When the feedwater is closed off and superheater steam outlet is closed I am pulling a vacuum in the tubes with the steam condensing to water. I believe the inlet/outlet superheater vents need to be cracked open partially since there is some small amount of pressure in the boiler. What consequences do I have with those vents being closed? Will these cause possible vacuum conditions in seals or gaskets in valves, drums, etc? possibly damage seals/gaskets?





RE: Mud Drum Heater Coil Question
Doug
RE: Mud Drum Heater Coil Question
RE: Mud Drum Heater Coil Question
You can increase the heat to the mud drum coils which I doubt will work.
Is your boiler manufacturer still in business? Some PV's designed for high pressure aren't necessarily well designed for vacuum and especially deep vacuum.
If you open the vents, then you will bring air into the boiler internals which will accelerate corrosion.
Unless you can absolutely isolate the air/flue gas side of the boiler (think guillotine dampers) you won't be able to prevent the steam inside the boiler tubes, etc. from condensing and even then you might have to add more heat. Not only are you faced with the potential for internal corrosion, but if you are located in a climate where the ambient goes below the dew point often, you are sweating on the outside of all the boiler surfaces shortening their lives too.
rmw
RE: Mud Drum Heater Coil Question
All in all, this is what the manufacturer suggested. Having a drum vent cracked would minimize air leakage from valves, gaskets, and seals. Since there is some positive pressure in the boiler it would prevent air from coming in the vent...
What do you take on this?
RE: Mud Drum Heater Coil Question
rmw
RE: Mud Drum Heater Coil Question
Aerated feedwater is INCREDIBLY corrosive. Please don't try to Lay-Up a boiler without either inhibiting the feedwater/condensate left in the tubes, or inerting the vapor space in the tubes and steam drum.