In frame 6B machine AA temp is becoming high up to 132.6 degC since last one month while machine is running on Natural gas at a load of 20.1 MW. Due to other machine being in M&I,it is being impossible to change the cooler bundle.
There is no margin left in cooling water. Cooling water is not DM water but we use chemical dosing to reduce scale deposition or corrosion in AA cooling water supply line.
Is there any way to reduce AA temp except cooling water? kindly suggest as it is urgent.
Interesting question but really the answer is, there is no other way, but a few questions :-
1) Is the VTR-2 controlling the AA cooling water wide open? If not, manually open the valve to see if the temperature improves.
2) What is the Air temp. going into the heat exchanger?
3) What is the Compressor Discharge Temp.?
4) What are your cooling water temps?
5) How old is the machine and has the heat exchanger ever been cleaned?
6) What is the ambient temp at your site at the moment?
I'll wait for your reply, Good Luck.
>1) Is the VTR-2 controlling the AA cooling water wide open?
If not, manually open the valve to see if the temperature
Ans- we have provided bypass line (from main supply CW Line to AA cooler supply)of VTR2 so VTR 2 is kept closed manually towards AA cooler and fully open towards main return.Bypass line is supplied with fresh CW so its temp is lower as compare to that of VTR 2 (which is common return line CW of Lube oil coolers).
>2) What is the Air temp. going into the heat exchanger?
Ans- it is to be measured. Will it not be same as compressor discharge temperature which is 330degC?
>3) What is the Compressor Discharge Temp.?
ans- 330degC at CPD =7.4kg/cm2 with load of 21.0MW
>4) What are your cooling water temps?
Ans- while using VTR2 bypass, CW supply temp to AA cooler is 31deg C and that of return is 43degC.
>5) How old is the machine and has the heat exchanger ever
Ans-heat exchanger was replaced last on 1.6.2017.
>6) What is the ambient temp at your site at the moment?
Are you absolutely certain that all air has been bled from the cooling water side of the AA pre-cooler?
If the cooler was replaced in January of this year (2017), what could be the problem with the cooler? Was it a new cooler? Was it refurbished?
Are you absolutely certain there is no condensate in the air side of the AA pre-cooler? (That is, have you opened the shell drain to see if any water (condensate) comes out?)
Hi CSA, I was just about to post something similar. The thing that is very strange from the data sent is the cooling water temp. before and after the cooler, the temp. rise of the water over the cooler seems very small for a machine which is running such a hot AA Temp.
>Are you absolutely certain that all air has been bled from
>the cooling water side of the AA pre-cooler?
ans- yes AA1 drain is checked and no condensate is present.
>If the cooler was replaced in January of this year (2017),
>what could be the problem with the cooler? Was it a new
>cooler? Was it refurbished?
it was a refurbished cooler
>>Are you absolutely certain that all air has been bled from
>>the cooling water side of the AA pre-cooler?
> ans- yes AA1 drain is checked and no condensate is
AA1 drain drains the air side of the heat exchanger. Impossible as it is to believe, if there is air trapped in the cooling water side of the heat exchanger it will greatly reduce the cooler's ability to remove heat from the compressor discharge air.
The question was are you absolutely certain that all air has been bled from the cooling water side of the AA pre-cooler; a later question asked about the shell drain, and I believe that's AA1.
There's usually a manual vent valve somewhere on the water side of the heat exchanger--if not, there should be. Air can, and often does, get trapped in the water side of the heat exchanger.
I agree with glenmorangie--the data is difficult to understand. Are you using a non-contact, infrared "heat gun" to measure the temperature of the cooling water piping going into and out of the heat exchanger?
Are you aware of the fact that the temperature regulating water valve actually has (or should have) a hole drilled in the plug of the valve to prevent the flow of cooling water from being totally shut off to the cooler? So, even if the valve is manually "closed" (flow to the cooler--the "C" port of the temperature regulating valve) there is still a small amount of water that should be flowing to the cooler.
There should be labels on the three ports of the temperature regulating valve: "E" for Entry (this is where the incoming cooling water to the valve enters the valve body); "C" for "Cooler" (this is where the cooling water is directed to the heat exchanger (the "cooler") by the valve); and "B" (this is where the flow that does NOT go to the cooler is re-directed back to the cooling water system. The valve is not a full open/full closed valve; it regulates flow as necessary to control the temperature of the air leaving the air side of the heat exchanger.
We don't know if the unit has its own cooling water system heat exchanger (a "fin-fan" cooler), or if it gets it cooling water from a plant cooling water system. If the temperatures of the cooling water into and out of the heat exchanger are accurate then it might be there is too much "residence" time of the cooling water in the heat exchanger, which might mean it's not really doing it's job of cooling very well. Most "self-contained" cooling water systems have orifices in the piping to try to limit flow-rate as necessary to help with effective cooling.
There is usually, or should be, a temperature gauge at the inlet to the Main Atomizing Air Compressor. This would be the same temperature as the outlet of the atomizing air pre-cooler.
The absolute limit of the temperature of the air entering the Main Atomizing Compressor is 300 deg F (approx 149 deg C). This is the maximum inlet air temperature the compressor is designed to receive; higher temperature can decrease the internal clearances of the compressor (which runs at a VERY high RPM!) and can cause catastrophic failure and be very dangerous of anyone is standing near the accessory gear or accessory compartment when it fails.
The atomizing air temperature regulating valve is to be set for approximately 225 deg F, and that is to ensure there is no moisture condensing in the heat exchanger, which can get pushed along into the inlet of the Main Atomizing Air Compressor which can also cause catastrophic damage (just like a "slug" of water can cause an operating steam turbine).
Does the unit have two L.O. heat exchangers? If so, are both of them in service? If not, what are the positions of the manual valves of the out-of-service cooler (there should be a manual cooling water inlet valve and a manual cooling water outlet valve on each cooler)?
It doesn't seem likely, but it could be that the gasket on the cooling water "head" of the heat exchanger could be improperly installed or broken, allowing cooling water to flow directly from the inlet of the cooler to the outlet of the cooler (again, the data don't seem to support that--but it has happened many times at many sites, AND we don't know the temperatures are being monitored/taken).
The absence of water (condensate) in the AA1 drain does make it seem like there is not excess cooling water flow--which would cause humidity in the compressor discharge air to condense in the shell--which is NOT desirable.
Cooling water system pressure should be less than CPD, so cooling water should NOT leak into the heat exchanger. Which brings up the possibility that hot air from the air side of the heat exchanger is leaking INTO the cooling water flow and heating up the outlet cooling water of the heat exchanger somehow....
Please write back with more information as you work towards a resolution of this problem!
>Are you using a non-contact, infrared "heat gun"
>to measure the temperature of the cooling water piping going
>into and out of the heat exchanger?
yes i am using the IR temp gun.
>Does the unit have two L.O. heat exchangers? If so, are both
>of them in service? If not, what are the positions of the
>manual valves of the out-of-service cooler (there should be
>a manual cooling water inlet valve and a manual cooling
>water outlet valve on each cooler)?
ANs--yes one of the LO cooler (CW supply and return fully open) is in line and another one(CW supply and return fully closed) is stand by.
I can't provide the information regarding cooler end cover gasket and cooler tube choking etc until we shut down the machine.
We tried the following things but no effect was found:
a) Switched ON both the turbine compartment vent fans so that AA cooler shell outer surface get cool.
b) Also exposed cooler bundle and AA compressor suction line to plant air separately .(although it was risky)
What are we left with:
a) Can we inject some CW at higher pressure than normal CW through cooler CW supply drain? will it help in de-choking of cooler tubes? Will it help in better cooling?
b) Can we expose the AA cooler shell outer surface to water spray continuously ?