Vacuum Low but Condenser Exhaust Steam Pressure High

I

Thread Starter

instrumentTH

I have issue about exhaust steam pressure high, cannot build up vacuum condenser. For detail:

1. Combine cycle power plant 2 unit of GT (I will call GT-A 40MW and GT-B 40MW) 1 unit of ST (40 MW).

2. Found this issue after minor inspection GT and ST (first minor inspection).

3. Now, operated with open cycle due to some problem about Steam turbine.

4. For start with GT-A can build up condenser vacuum normally (-0.95 barg) at 5 MW.

5. But for start with GT-B cannot build up condenser vacuum (vacuum -0.80 barg) higher than permissive setting to control load (-0.85 barg) at 5 MW.

6. For HP steam can control by De-super-heat but IP not have.

For more detail,

1. I found that Exhaust steam temperature of GT-B (60 C) higher than GT-A (40 C). and then I found temperature after IP bypass of condition start with GT-B higher than GT-A around 10C.

2. During Start GT-A found that between pipe line of IP main steam bypass valve of unit B (IP stop valve bypass and IP control valve bypass of unit B are close) are vacuum (-0.5 barg) and we sure that IP bypass valve passing.

3. I found that IP main steam pressure of GT-A pressure below than GT-B (bypass valve of GT-B open more than GT-A) but temperature are nearly.

So, for my opinion I think may be cause below

1. Exhaust steam temperature high due to spray de-super-heat after valve bypass abnormal (sprat pattern not good).

2. IP bypass control valve passing.

3. Main steam condition (Pressure, Temperature, Flow).

4. Exhaust temperature of GT.

I like to know other opinion please advise me.

1. What is the cause of this problem and how to solution?

2. If I try to manual mode for control spray water after bypass, what is effect?

3. and If I try to manual open exhaust hood spray what is effect, and it can be reduce exhaust steam temperature or not?

4. If IP bypass valve of other unit passing it's possible cause of vacuum low?

5. How about the relation between vacuum and exhaust temperature (from bypass directly)? Vacuum is lead effect to temperature of exhaust temperature is lead effect to vacuum?
 
I

instrumentTH

Please Correct detail as below

Topic: Vacuum Low (or Condenser Exhaust Steam Pressure High)

For more detail,

3. I found that IP main steam pressure of GT-B pressure below than GT-A (bypass valve of GT-B open more than GT-A) but temperature are nearly.
 
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