3.1 INTRODUCTION
The gas turbine assembly contains five sections they are:
1. Air inlet system.
2. Compressor section.
3. Combustion System.
4. Turbine section.
5. Exhaust duct.
This section describes how the gas turbine operates and the interrelationship of the major components as shown in Fig.(3.1)
3.2 DESCRIPTION OF THE GAS TURBINE UNIT IN CAIRO NORTH STATION
The gas turbine unit in CNS consists from the following systems
:
3.2.1 Air Inlet System
Air quality can have an enormous impact on gas turbine performance and reliability and is heavily influenced by the surrounding environment in which the unit is installed. Furthermore, within any given location, the quality of air can change dramatically over a year‘s time or, in some situations, within hours. Poor air quality leads to compressor fouling. The output of a turbine can be reduced significantly in cases of extreme compressor fouling.
In order to meet full potential in performance and reliability, and make each Unit adaptable to a variety of air conditions, it is necessary to treat the air entering the turbine to remove contaminants. The self-cleaning filtration system easily and efficiently removes airborne particles of 10 um or greater that generally cause significant erosion and compressor fouling when present in sufficient quantities. Air temperature can also have a significant impact on gas turbine performance. An inlet cooling system is a beneficial option for applications where significant operations occur during times of warmer temperatures combined with low relative humidity.
Cooler air is denser, resulting in a higher mass flow rate to the compressor. This results in an increase in turbine output and efficiency. Noise pollution is a concern associated with the inlet system. Gas turbine operation generates a significant amount of noise in the inlet duct. This noise is attenuated, to levels necessary to meet regulations, through the use of a silencer installed as part of the ductwork. For a general overview of the inlet system arrangement, refer to the Inlet and Exhaust Flow Diagram and the Control Air Schematic Piping Diagram. These are located in the Operation and Maintenance manual in this section. Fig. (3.2) show the air inlet system.
3.2.1.1 The Air Intake Main Parts are as the following:
The air intake main parts are as the following:
1. Air Intake Filter House
Filter house normally designed to have large shape so to make sure that the pressure drop across it will minimized (each 10 mbar pressure drop will reduce turbine power by 1%), it contains air filters, air entrance guide vanes & the implosion doors as shown in Fig. (3.3)
2. Filter Element
Air entering compressor must be filtered from any dust or residues that may enter compressor, cause fouling which reduce compressor efficiency, the use of series of filters instead of one big filter is more because design, erection complexity are reduced, also if pressure drop in air intake increases, a set filters can easily be removed instead of removing the hall big filter as shown in Fig (3.4)
3. Air Intake Silencer
Due to the high speed of air entering air intake filter house, a large noise level will produced & silencer must be used to reduce noise level. The silencer contain sound absorbent baffles & these baffles are covered with perforated sheets & filled with high quality heat& moisture resistance mineral wool, this mineral wool is covered by a glass fiber which gives an additional mechanical protection for the absorbent material as shown in Fig.(3.5)
4. Filter Element Purging System
As air passes through filter elements for a long period, the filters become dirty & thus the pressure drop across them will increase, to overcome rapid increase in pressure drop either filter elements is replaced with new elements or air filter must be purged. The filter purging system is compressed air that provided from separate air compressor, if the pressure drop across any one of the filters raw increase to more than normal limit, these compressor will start to provide compressed air for clearing these filters. The compressed air will released via small holes on the air lines located behind each filter, there are solenoid valves that operate with respect to each raw of filters to release that compressed air. Fig (3.6) Compressed air lines for filters purging and pulse air outlet can be seen Pulse air header pressure us 7.5 bar and each pulse has a pressure of 3 bar.
Compressed air releasing process will done by pulsing ,so some time filters cleaning system may named as pulse air system ,complete purging process may take 84 pulses (30 minutes duration ) and the cleaning process will start from top of the air intake to the bottom so that we avoid dust to sucked again by upper filter raw.
5. Activation of Pulse Air System
Pulse air system aim is to clean the dirty filters & to do so there are two ways to activate this system which are:
a- high pressure drop across filters raw signal
b- High ambient air relative humidity signal (humidity > 80% signal)
a- high pressure drop across filters raw signal
During gas turbine on load, the control system will monitor air intake filter house pressure drop via two pressure sensors:
First sensor is to measure air pressure before and after filters raw (this sensor activates pulse air system). Second sensor is to measure air pressure drop across air
intake filter house (this sensor not activates pulse air system & it is associated with gas turbine protection only) as shown in Fig. (3.7). The second sensor indicate very high pressure drop, a gas turbine trip will initiated by the following steps:
1-As air intake pressure drop increases, the air pressure after silencer decreases, this will create a local vacuum area,
2-Due to the vacuum inside air intake filter house, the implosion doors (4 to 6 doors) will be sucked in
3-There are limit switch on each door so for any door reach full open position, this mean that the limit switch will send open signal which will initiate gas turbine trip to protect gas turbine from operating with air intake filter house is blocked.
Implosion doors are designed to make sure that the pressure inside air filter house is equalized to the atmospheric pressure to avoid air intake damage. If the gas turbine on load, normally pulse air system will activated only due to pressure drop signal High ambient air relative humidity signal (humidity > 80% signal) .
There is humidity sensor on air intake filter house entrance to measure ambient humidity, if humidity is raise to 80%, a signal will go to activate pulse air system, and complete purging process may take 168 pulses (1 hour duration), this is to insure dry filter & avoid condensation which may block the filters during gas turbine
.
6. Operation
Normally pulse air system activated by humidity sensor only when the unit is off load, pressure drop sensor will not sense any pressure drop because air is not entering inside filter house at high speed.
The gas turbine assembly contains five sections they are:
1. Air inlet system.
2. Compressor section.
3. Combustion System.
4. Turbine section.
5. Exhaust duct.
This section describes how the gas turbine operates and the interrelationship of the major components as shown in Fig.(3.1)
3.2 DESCRIPTION OF THE GAS TURBINE UNIT IN CAIRO NORTH STATION
The gas turbine unit in CNS consists from the following systems
:
3.2.1 Air Inlet System
Air quality can have an enormous impact on gas turbine performance and reliability and is heavily influenced by the surrounding environment in which the unit is installed. Furthermore, within any given location, the quality of air can change dramatically over a year‘s time or, in some situations, within hours. Poor air quality leads to compressor fouling. The output of a turbine can be reduced significantly in cases of extreme compressor fouling.
In order to meet full potential in performance and reliability, and make each Unit adaptable to a variety of air conditions, it is necessary to treat the air entering the turbine to remove contaminants. The self-cleaning filtration system easily and efficiently removes airborne particles of 10 um or greater that generally cause significant erosion and compressor fouling when present in sufficient quantities. Air temperature can also have a significant impact on gas turbine performance. An inlet cooling system is a beneficial option for applications where significant operations occur during times of warmer temperatures combined with low relative humidity.
Cooler air is denser, resulting in a higher mass flow rate to the compressor. This results in an increase in turbine output and efficiency. Noise pollution is a concern associated with the inlet system. Gas turbine operation generates a significant amount of noise in the inlet duct. This noise is attenuated, to levels necessary to meet regulations, through the use of a silencer installed as part of the ductwork. For a general overview of the inlet system arrangement, refer to the Inlet and Exhaust Flow Diagram and the Control Air Schematic Piping Diagram. These are located in the Operation and Maintenance manual in this section. Fig. (3.2) show the air inlet system.
3.2.1.1 The Air Intake Main Parts are as the following:
The air intake main parts are as the following:
1. Air Intake Filter House
Filter house normally designed to have large shape so to make sure that the pressure drop across it will minimized (each 10 mbar pressure drop will reduce turbine power by 1%), it contains air filters, air entrance guide vanes & the implosion doors as shown in Fig. (3.3)
2. Filter Element
Air entering compressor must be filtered from any dust or residues that may enter compressor, cause fouling which reduce compressor efficiency, the use of series of filters instead of one big filter is more because design, erection complexity are reduced, also if pressure drop in air intake increases, a set filters can easily be removed instead of removing the hall big filter as shown in Fig (3.4)
3. Air Intake Silencer
Due to the high speed of air entering air intake filter house, a large noise level will produced & silencer must be used to reduce noise level. The silencer contain sound absorbent baffles & these baffles are covered with perforated sheets & filled with high quality heat& moisture resistance mineral wool, this mineral wool is covered by a glass fiber which gives an additional mechanical protection for the absorbent material as shown in Fig.(3.5)
4. Filter Element Purging System
As air passes through filter elements for a long period, the filters become dirty & thus the pressure drop across them will increase, to overcome rapid increase in pressure drop either filter elements is replaced with new elements or air filter must be purged. The filter purging system is compressed air that provided from separate air compressor, if the pressure drop across any one of the filters raw increase to more than normal limit, these compressor will start to provide compressed air for clearing these filters. The compressed air will released via small holes on the air lines located behind each filter, there are solenoid valves that operate with respect to each raw of filters to release that compressed air. Fig (3.6) Compressed air lines for filters purging and pulse air outlet can be seen Pulse air header pressure us 7.5 bar and each pulse has a pressure of 3 bar.
Compressed air releasing process will done by pulsing ,so some time filters cleaning system may named as pulse air system ,complete purging process may take 84 pulses (30 minutes duration ) and the cleaning process will start from top of the air intake to the bottom so that we avoid dust to sucked again by upper filter raw.
5. Activation of Pulse Air System
Pulse air system aim is to clean the dirty filters & to do so there are two ways to activate this system which are:
a- high pressure drop across filters raw signal
b- High ambient air relative humidity signal (humidity > 80% signal)
a- high pressure drop across filters raw signal
During gas turbine on load, the control system will monitor air intake filter house pressure drop via two pressure sensors:
First sensor is to measure air pressure before and after filters raw (this sensor activates pulse air system). Second sensor is to measure air pressure drop across air
intake filter house (this sensor not activates pulse air system & it is associated with gas turbine protection only) as shown in Fig. (3.7). The second sensor indicate very high pressure drop, a gas turbine trip will initiated by the following steps:
1-As air intake pressure drop increases, the air pressure after silencer decreases, this will create a local vacuum area,
2-Due to the vacuum inside air intake filter house, the implosion doors (4 to 6 doors) will be sucked in
3-There are limit switch on each door so for any door reach full open position, this mean that the limit switch will send open signal which will initiate gas turbine trip to protect gas turbine from operating with air intake filter house is blocked.
Implosion doors are designed to make sure that the pressure inside air filter house is equalized to the atmospheric pressure to avoid air intake damage. If the gas turbine on load, normally pulse air system will activated only due to pressure drop signal High ambient air relative humidity signal (humidity > 80% signal) .
There is humidity sensor on air intake filter house entrance to measure ambient humidity, if humidity is raise to 80%, a signal will go to activate pulse air system, and complete purging process may take 168 pulses (1 hour duration), this is to insure dry filter & avoid condensation which may block the filters during gas turbine
.
6. Operation
Normally pulse air system activated by humidity sensor only when the unit is off load, pressure drop sensor will not sense any pressure drop because air is not entering inside filter house at high speed.
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