MinnesotaSlinger
Mechanical
- Feb 13, 2008
- 23
In a system I'm working on, we will have a 4" superheated steam line for approx. 6000 pph at 500 F and 100 psig going from a header to the point-of-use (a heat exchanger---the plant has no saturated steam distribution system). Near the connection to the header, there will be a manual gate valve. This valve will be normally open except when needed as an isolation. As steam goes toward the source from that valve, it will slope upward. Near where it will be used, we will have an automated ball valve that acts as the shutoff valve to initiate and stop steam flow. Immediately downstream of the ball valve, I will install the control valve, which is a globe valve. Shortly beyond that point, steam will enter the HX.
I'm curious about the two sections of pipe between the three valves and want to know what I have to do for safe operation, shutdown, and start-up with the two sections:
1. Looking at the long section from the manual gate shutoff valve up to the automated ball shutoff valve, I am thinking I should have a condensate drip pot with a drain valve on it at the base of the run, just downstream of the manual gate valve. I'm not sure there would be any reason for a steam trap off of this condensate pot since there should be virtually no condensation in the line during operation. However, when that valve is shut, steam in the line would condense and drain back toward the valve. There would then be a slug of subcooled condensate sitting on the one side of the gate valve while the other side has superheated steam in the header. Therefore, I would think the condensate pot should be drained before the gate valve is opened to avoid a dangerous mixture of steam and condensate were the valve opened without draining out condensate first. Am I getting anything wrong here? Supposing I have a condensate pot with a drain, is there any size that the pot would need to be? I'd plan on using a 4"x4" tee, but would I need additional volume in the pot? And how big would the drain line need to be? Do I need additional accessories besides a 4"x4" tee, a reducer to the drain line size, the drain line run with a valve and removable cap? (Of course, the drain line and components would be insulated.)
2. As for the second section, if I have a short section (say, just a couple feet) between the ball valve and the control valve, do I need to slope it toward one of the two valves, or can it be perfectly flat? And do I need to do anything to trap or drain that line? The control valve isn't designed to be a shutoff valve, but it may act as one nevertheless, so I expect that this section of pipe could retain condensate (albeit not much). And to ensure safe and effective operation, would there be a reason to open either the automated ball valve or, by a small amount, the automated control valve ahead of the other in the startup programming sequence and also the shutdown sequence?
For both sections, besides being concerned about condensate forming in the lines during shutdown, I also am wondering about vacuum forming in the line. I would imagine it would eventually form a saturated mixture at the ambient temperature of the plant, which would be a vacuum. Is there anything to be concerned about with that? I'm guessing not really, but I hadn't really thought much about this before now.
I realize my question is long, so thank you for taking the time to read it. If you have any wisdom you can share with me, I'd appreciate it.
I'm curious about the two sections of pipe between the three valves and want to know what I have to do for safe operation, shutdown, and start-up with the two sections:
1. Looking at the long section from the manual gate shutoff valve up to the automated ball shutoff valve, I am thinking I should have a condensate drip pot with a drain valve on it at the base of the run, just downstream of the manual gate valve. I'm not sure there would be any reason for a steam trap off of this condensate pot since there should be virtually no condensation in the line during operation. However, when that valve is shut, steam in the line would condense and drain back toward the valve. There would then be a slug of subcooled condensate sitting on the one side of the gate valve while the other side has superheated steam in the header. Therefore, I would think the condensate pot should be drained before the gate valve is opened to avoid a dangerous mixture of steam and condensate were the valve opened without draining out condensate first. Am I getting anything wrong here? Supposing I have a condensate pot with a drain, is there any size that the pot would need to be? I'd plan on using a 4"x4" tee, but would I need additional volume in the pot? And how big would the drain line need to be? Do I need additional accessories besides a 4"x4" tee, a reducer to the drain line size, the drain line run with a valve and removable cap? (Of course, the drain line and components would be insulated.)
2. As for the second section, if I have a short section (say, just a couple feet) between the ball valve and the control valve, do I need to slope it toward one of the two valves, or can it be perfectly flat? And do I need to do anything to trap or drain that line? The control valve isn't designed to be a shutoff valve, but it may act as one nevertheless, so I expect that this section of pipe could retain condensate (albeit not much). And to ensure safe and effective operation, would there be a reason to open either the automated ball valve or, by a small amount, the automated control valve ahead of the other in the startup programming sequence and also the shutdown sequence?
For both sections, besides being concerned about condensate forming in the lines during shutdown, I also am wondering about vacuum forming in the line. I would imagine it would eventually form a saturated mixture at the ambient temperature of the plant, which would be a vacuum. Is there anything to be concerned about with that? I'm guessing not really, but I hadn't really thought much about this before now.
I realize my question is long, so thank you for taking the time to read it. If you have any wisdom you can share with me, I'd appreciate it.
