6 replies to this topic

[Pronab]

Two air blowers are running with saturated steam at 34 barg. Before entering to the steam turbine, steam comes from the high pressure (HP) steam header followed by a KOD. Any condensate build-up in the KOD is drained to steam condensate (SC) header via a steam trap. Most of the HP steam comes from the boiler drum to the HP steam header network saturated at 34Barg. HP steam import from upstream supply at 40 barg via a let done valve PV-740 and maintain at 34 Barg and any extra steam in the HP steam header is let down to low pressure (LP) steam via another letdown valve PV-743 which set point is 0.5 barg more than PV-740. LP steam header pressure maintain at 5 barg. KOD is equipped with HH level switch, which will trip the running blower in case of HH level activate. Letdown valve PV-740 is clamped at 15 %( valve will minimum open 15% all the time to avoid any steam condensate in the line).
Problem: whenever one blower start, several times other running blower KOD level reach to HH and trip the blower. Anyone experienced the similar phenomenon and can someone help how we can overcome the problems.

Thanks in advance.

[Pronab]

Please see the attached sketch for the said problem which I forget to upload..

Regards.
Pronab

Attached Files

•  Drawing.xlsx   13.4KB   29 downloads

[DB Shah]

Kindly give detail sequence-
Normal operation-1 turbine running ??
Turbine steam draw
PV 740 flow and opening
Boiler A & B steam generation
PV 740 flow and opening
Levels in KOD


Operation change - second turbine started
Turbine steam draw
PV 740 flow and opening
Boiler A & B steam generation
PV 740 flow and opening
Levels in KOD
WHen you start 2nd turbine do you observe any substantial fall in HP steam header pressure

[Pronab]

Please see the answer below:

Kindly give detail sequence-
Normal operation-1 turbine running ??- BOTH TURBINE RUNNING
Turbine steam draw - NO FLOW METER.
PV 740 flow and opening - MINIMUM 15% ALL THE TIME TO AVOID IMPORT LINE CONDENSATION. MAXIMUM DEPENDS ON CONSUMPTIONS.
Boiler A & B steam generation- 65 MT/HR @ NORMAL CONDITION. 35 BARG PRESS@ SAT.
PV 740 flow and opening-
Levels in KOD - NORMALLY ZERO( ALMOST)

Operation change - second turbine started

Turbine steam draw- NO FLOW METER HOWEVER MAY BE 20 MT/HR.
PV 740 flow and opening- OPENING INCREASE TO MAINTAIN PRESSURE.
Boiler A & B steam generation- 65 MT/HR @ NORMAL CONDITION.
PV 740 flow and opening-
Levels in KOD
WHen you start 2nd turbine do you observe any substantial fall in HP steam header pressure - YES HP STEAM HEADER PRESSURE DROP ( 0.5 TO 1 BARG ).


Hope you will find the senario.
Thank you for your time.

[DB Shah]

Dear Pronob,
By mistake I asked PV740 data again in my reply, it should be PV 743 opening.
As I understand the scenario is-
One tubine operating, 65 MT/hr total steam generation from Boiler A&B, one turbine steam consumption is 20MT/hr. Hence you are exporting 65-20 = 45 MT/hr of steam through PV743. All the time your header pressure is 35 Barg (0.5 Bar higher than PV740 set point)

Now you start second turbine, header pressure falls by 1 Barg & level in KOD rises fast.

I will suggest you to open & check steam trap bypass valve at-
1. PV 740 upstream
2. Between PV 740 & first KOD tapping
for condensate accumulation

Another question , do you face KOD level high when one boiler trips?
{I have come across such issue in (different configuration).}

[Pronab]

Yes, whenever one boiler trip, there is level build-up in KOD and even reach to HH level and trip of the turbine. Opening of PV-743 depends of steam production and consumption.

Regards.

[DB Shah]

Dear pronob,

As suggested in my earlier post -

{
I will suggest you to open & check steam trap bypass valve at-
1. PV 740 upstream
2. Between PV 740 & first KOD tapping
}

I envisage condensate accumulation in your HP header (PV740 line) as I donot doubt condensate carryover from boiler. The scenario I presume is - the HP header (PV740 15% open) is stagnant. The steam generated in boilers is in excess and let down to LP header. The header all the time operates as 0.5Bar higher than PV 740 set point (Kindly confirm). You need to keep HP header live by continues flow through it.
Kindly open the drain and confirm if there is condensate in HP header? You need to eliminate the cause one by one and arrive at root cause.