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Benefit of lower condenser temperature on Turbine 1
- Thread starter Ivan69
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YOU SHOULD CONSULT THE ORIGINAL EQUIPMENT MANUFACTURER BEFORE EFFECTIVELY RERATING YOUR MACHINE.
You have a few steps that must be completed in trying to assess the effect of lower condenser cooling water. What I describe is valid for a turbine without controlled extraction flows (different from "bleed" flows to f/w heaters) of steam to some process applications. For typical power generation applications, the turbine is a "straight condensing" configuration.
Use performance curves for your condenser to predict condenser pressure at the new cooling water temperature.
Turbine exhaust flange pressure = (Condenser pressure) + (Condenser trunkline losses)
New turbine exhaust pressure implies a new "available energy", AE, across the turbine. AE is the isentropic change in enthalpy from the inlet conditions to the exhaust pressure.
The simplest approximation is to assume that the flow reduction is inversely proportional to the increase in AE. However, this ignores possibly significant changes to the efficiency of the turbine's last stage, and increased pressure drop within the exhaust casing.
As the exhaust pressure drops, the volume flow through the last stage will increase, and the last stage efficiency (and hence the overall turbine efficiency) will change. If we assume, for conversation's sake, that the efficiency is now at its maximum, the higher volume flow will decrease the last stage efficiency, and diminish the flow savings. In any case, the higher volume flow will require a higher pressure drop through the exhaust casing, to the turbine flange. What this means is that only part of the increased AE is actually used by the turbine; some of it is needed to push the flow out of the exhaust casing.
There are also lower limits of exhaust pressure for safe operation of the last stage. Although changing the cooling water temp. alone will typically not give you great changes in condenser pressure...
YOU SHOULD CONSULT THE ORIGINAL EQUIPMENT MANUFACTURER BEFORE EFFECTIVELY RERATING YOUR MACHINE.
You have a few steps that must be completed in trying to assess the effect of lower condenser cooling water. What I describe is valid for a turbine without controlled extraction flows (different from "bleed" flows to f/w heaters) of steam to some process applications. For typical power generation applications, the turbine is a "straight condensing" configuration.
Use performance curves for your condenser to predict condenser pressure at the new cooling water temperature.
Turbine exhaust flange pressure = (Condenser pressure) + (Condenser trunkline losses)
New turbine exhaust pressure implies a new "available energy", AE, across the turbine. AE is the isentropic change in enthalpy from the inlet conditions to the exhaust pressure.
The simplest approximation is to assume that the flow reduction is inversely proportional to the increase in AE. However, this ignores possibly significant changes to the efficiency of the turbine's last stage, and increased pressure drop within the exhaust casing.
As the exhaust pressure drops, the volume flow through the last stage will increase, and the last stage efficiency (and hence the overall turbine efficiency) will change. If we assume, for conversation's sake, that the efficiency is now at its maximum, the higher volume flow will decrease the last stage efficiency, and diminish the flow savings. In any case, the higher volume flow will require a higher pressure drop through the exhaust casing, to the turbine flange. What this means is that only part of the increased AE is actually used by the turbine; some of it is needed to push the flow out of the exhaust casing.
There are also lower limits of exhaust pressure for safe operation of the last stage. Although changing the cooling water temp. alone will typically not give you great changes in condenser pressure...
YOU SHOULD CONSULT THE ORIGINAL EQUIPMENT MANUFACTURER BEFORE EFFECTIVELY RERATING YOUR MACHINE.
anotheroldguy
Chemical
If you have liquid ring vacuum pumps (typically two-stage) backing up the surface condenser the reduced temperature of the condenser water will also enhance the capacity of these vacuum pumps. The reduced vacuum pump ring water partial pressure allows a larger condensible load to be extracted from the system.
Typically the condensor cooling water serves as the ring water in the liquid ring vacuum pump. This causes the vacuum pump effciency to track the condenser water temperature.
Be careful if the pumps are of the 'flat-sided' design however and not 'conically ported' as changes in the ring water flow can lead to mechanical problems in the vacuum pumps. Surges in ring water to flat-sided pumps can cause a sort of 'cavitation'; the pump can stall and the shaft can be snapped.
Typically the condensor cooling water serves as the ring water in the liquid ring vacuum pump. This causes the vacuum pump effciency to track the condenser water temperature.
Be careful if the pumps are of the 'flat-sided' design however and not 'conically ported' as changes in the ring water flow can lead to mechanical problems in the vacuum pumps. Surges in ring water to flat-sided pumps can cause a sort of 'cavitation'; the pump can stall and the shaft can be snapped.
Just read this post, and ANOTHEROLDGUY's response, which has led me to a question: What exactly are the problems in using flat-sided vacuum pumps?.......these pumps are confounding me....also, What are the overall advantages of conical ported pumps as compared to flatsided designs? Do you have the names of any great reference books on vacuum pumps and vacuum systems? Thanks for any help!
Regards,
SASC
Regards,
SASC
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