Drum Filling

From: Gas turbine Ops [1079] 0 Stars

Date: Thursday, July 15, 2010
Time: 10:06:34 AM
Remote Name: 212.119.85.91

Comments

Hi to All.

We are operating GE 7FA gas turbines with HRSGs as a cogeneration plant. whenever we do the Offline washing of Gs turbines we are doing the 6 hours of natural cooling + 4 hours Forced cooling of the gas turbines.As we dont have any diverter damper the GT cooling will also show effect on the HRSG drum metal temperatures.Forced cooling will be done at a cranking speed of 849 rpm.

We have a limitation of Max. 40 Deg C of difference between the Top and bottom metal temp.During the forced cooling sometimes we are reaching 45 Deg C and we stop the forced cooling that time.

There are two practises we adopted and their results are

1 To fill the drum once to Maximum level and start the forced cooling activity. During natural cooling we will not fill the drum. -- This causes the drum metal temp difference to reach 60 Deg C during forced cooling and wasting time.

2 To fill the drum immediately after reaching the machine barring gear and to maintain in a very close margin during the natural cooling & Forced cooling periods.If we maintain the drum level in a very close range near to the maximum level then this causes the drum metal temp difference to be maintained @ 42 to 46 Deg C during forced cooling.

My doubts are :

1 If we fill the steam drum immediately after the shutdown and maintain the drum level at high levels will there be any effect on HRSG tubing.
2 Some people asked to fill only once and to leave like that.But it causes very high differential temp.
3 Our feedwater incoming temperature will be at 150 Deg C.

Can anyone please explian which is a good practice.

Thanks,
pvrk

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