5 replies to this topic

[Tejinder Singh]

I have installed an economiser on a 2MW steam boiler and it was designed for 80% boiler load but the client is ruuning on 40-50% boiler load. After installation my client has informed me that he has noticed water hammering in the economiser when boiler shuts down. There is no water hammering when the boiler is running. The outlet temperature of the economiser is below the saturation temperature so there is no flashing in the economiser. I would really appreciate if someone can give me some advice how to fix it or what could be causing the hammering.

Thanks is advance

[Ajay S. Satpute]

Hi,

 

I guess more info. (PFD, P&ID, datasheet) would help for problem comprehension.

 

Thanks.

 

Ajay

[Tejinder Singh]

Hello Ajay,

 

Thank you for your reply.

Please see attached design sheet I donot have a P&ID.

The boiler has on/off pump and when pump start after the shut down then the hammer occurs for 5 mins.

Do you think installing a solinoid valve on economiser to relief the pressure in feed water tank can fix the problem?

 

Regards

Tejinder

Attached Files

•  Taura at 80% load.xls   29.5KB   21 downloads

Edited by Tejinder Singh, 31 October 2013 - 09:54 PM.

[thorium90]

I dont agree that flashing is not happening. The water hammer is a clear indication that it is flashing. Can you attach the DCS screens? your excel sheet does not tell us what are the conditions you observe and where the conditions are taken from.

 

If the problem only occurs when the boiler is shut down, then what temperature is your client looking at? If the boiler is not running, then a low outlet temperature is not indicative.

 

I would suggest you either drain the economizer during shutdown or open some vent line.

 

Otherwise, use a thermal gun to confirm the temperature at the location, not rely on a transmitter installed at another location that does not reflect the true temperature. This will be more effective troubleshooting.

[katmar]

Why is this question in the Student Forum?  Is this a real problem, or an artificial one posed by your professor?

 

The data sheet assumes that the flows are at the design rates.  They will not apply when the boiler shuts down.  As soon as the fuel (oil or gas) is shut off there will be virtually no boiling and the water flow through the economiser will decrease abruptly.  However, it is normal in boilers for the fans to be on timers so that air continues to flow through the boiler to remove any gas and to cool the boiler.

 

You therefore have the situation where the water flow has decreased to almost zero, but the gas flow is still high and although the gas temperature will decrease quickly there will be a period where it is still above 100°C while it removes the heat built up in the boiler and ducting.  If you have not taken some precuations then it is almost certain that you have flashing in the economiser at this time. For example, you could link a bypass valve to the fan timers so that at shut down the water flow continues through the economiser but is recycled back to the boiler feed water tank rather than filling the boiler.

[breizh]

http://www.kirsner.org/index.html

 

Consider this resource , in particular the part related to boiler.

 

Hope this helps

 

Breizh

Edited by breizh, 02 November 2013 - 03:51 AM.