We are operating a large Ammonia Urea Complex in Pakistan. Following are details of Steam Turbine driving Boiler Feed Water pump at our expansion unit.
Type - Single stage impulse with one nozzle ring, one ring of reversing blades and two rows of moving blades
Following are permissible steam inlet and exhaust operating parameters;
Inlet Pressure (bar gauge)
Inlet Temperature (0C)
Exhaust Pressure (bar gauge)
As per OEM
At normal conditions with 37.3 bar gauge inlet pressure, 380 0C inlet temperature and 3.43 bar gauge exhaust pressure turbine will deliver 1742 KW at 23040 Kg/Hr steam consumption with 215 0C exhaust temperature. Refer to attached Annex-I for steam flow diagram at normal conditions.
At most unfavorable conditions with 36.3 bar gauge inlet pressure, 3750C inlet temperature and 3.92 bar gauge exhaust pressure the turbine will deliver 1935 KW at 26510 Kg/hr steam consumption with 220 0C exhaust temperature. Refer to attached Annex-II for steam flow diagram at most unfavorable conditions.
Power requirement of boiler feed water pump to produce desired flow is 1742KW @2985RPM; which is same as nominal power of the turbine; hence turbine is undersized for the application. Refer to attached Annex-III for specification sheet of the turbine.
Turbine is able to meet power requirement of the pump after initial startup following a cooling cycle, however its performance deteriorates with the passage of time. Following is the comparison of operating parameters of the turbine;
Steam inlet Pressure
Steam Inlet Temperature
Exhaust Steam Pressure
Exhaust Steam Temperature 0C
Turbine Steam Consumption
Parameters of Start-up after a cooling cycle
Parameters after 02 months of operation
As per my understanding, increase in exhaust temperature of this type of turbine is a clear indicative of its performance degradation. Interestingly, performance of the turbine is restored after a cooling cycle of 10~12 hrs without doing any maintenance work. This abnormal behavior of the turbine is exhibited every time after a cooling cycle. The turbine has been overhauled several times but no abnormality is ever found in its internals.
It would be a great favor if anyone advise us on following points;
- What can be the possible reason for this gradual increase in exhaust temperature of the turbine? Why the exhaust temperature and steam consumption restored after a cooling cycle?
- Is this performance degradation with time related to overloading of the turbine?
Thank you in advance.