GENERAL
Gas turbine performance and reliability are a function of the quality and cleanliness of the air entering the inlet to the turbine. Therefore, for most efficient operation, it is necessary to treat the atmospheric air entering the turbine by filtering out contaminants. It is the function of the air inlet system with its specially designed equipment and ducting to modify the quality of the air under various temperature, humidity, and contamination situations to make it more suitable for use by the gas turbine.
Hot exhaust gases produced by combustion in the turbine are cooled and attenuated in the exhaust system ducting before being released to atmosphere. These exhaust emissions respect certain environmental standards of cleanliness and acoustic levels depending on site location. The noise generated during gas turbine operation is attenuated by devices built into the inlet and exhaust sections which dissipate or reduce the acoustical energy to an acceptable level.
AIR INLET SYSTEM
The air inlet system consists of an integrated, high efficiency self cleaning fil ter house, support structure, inlet ducting system with acoustical silencer, trash screens, and an inlet plenum leading to the compressor section of the turbine. The elevated ducting and filter house arrangement provides a compact system and minimizes pickup of dust concentrations found near the ground level.
All external and internal surface areas of the inlet system are coated with a protective inorganic zinc primer with epoxy overcoat, stainless steel or hot dipped galvanized for corrosion protection.
The general arrangement of the inlet compartment with respect to the gas turbine inlet plenum is shown on the mechanical outline drawings.
INLET COMPARTMENT
The inlet filtration compartment is provided with weather hoods for filter ele ment protection. The filter system consists of numerous single-stage, high-efficiency, moisture resistant element pairs mounted on vertical grid plates. The filter elements are contained within a light gauge sheet-metal enclosure which has been specially designed for proper air flow management and weather protection. The filter elements are connected to a common clean air plenum which terminates in an outlet flange which connects to the inlet ducting system.
The reverse-pulse type self-cleaning system is initiated either manually or when the filter elements become laden with dust and the pressure drop across the filter media reaches a predetermined value (as measured by a differential pressure switch). The elements are cleaned in a specific order, controlled by an automatic sequencer.
The sequencer operates a series of solenoid-operated valves, each of which controls the cleaning of a small number of filters. Each valve releases a brief pulse of high pressure air. This pulse shocks the filters, causing a momentary reverse flow, disturbing the filter cake. Accumulated dust breaks loose and falls into triangular shaped hoppers. The cleaning cycle continues until enough dust is removed for the compartment pressure drop to reach the lower differential pressure switch set-point.
INLET DUCTING AND SILENCING
The inlet ductwork system contains the compressor noise silencing, and con nects the inlet compartment with the compressor inlet plenum. It consists of an acoustically lined transition duct, lined ninety degree elbow (with trash screen), and eight feet of parallel baffle silencing and unlined ducting with a flexible joint to complete the air flow path to the filter house
ducting downstream of the silencer are of similar construction. The vertical-parallel baffle configuration was specifically designed to eliminate the fundamental compressor tone, and Attenuate noise at other frequencies as well. There is a stationary stainless steel trash screen within the elbow which can be accessed for cleaning and inspection through a removable access panel.
EXHAUST SYSTEM
The exhaust system is that portion of the turbine in which the gases used to power the turbine wheels are redirected through the exhaust plenum and the silencer modules, into the exhaust stack and released to atmosphere. The exhaust system includes the exhaust plenum outlet expansion joint, transition duct, silencer modules, transition duct, and the exhaust stack. Exhaust temperature thermocouples are mounted in the aft wall of the exhaust plenum to sense ex haust temperatures and input these values to the MARK VI TMR control system.
EXHAUST PLENUM
The exhaust plenum is the beginning of the exhaust duct, receiving the gas flow from the exhaust diffuser. It consists of a box, open at each side and at the top, which is welded to an extension of the turbine base. The exhaust plenum is connected to the exhaust frame assembly with flex-plate expansion joints. The open sides and top of the plenum are covered with a wrapper whose purpose is to enlarge the plenum volume and force the exhaust gases to one side and into the exhaust ducting. The wrapper is supported by the foundation mounted pedestals
EXHAUST EXPANSION JOINT
The exhaust system expansion joint compensates for the thermal expansion of the exhaust ductwork system. The expansion joint is located between the exhaust plenum and the exhaust transition duct.
EXHAUST TRANSITION DUCT (FIRST)
The transition duct is a horizontal section of ductwork which is located down- stream of the first expansion joint. The first transition duct in the ductwork sys tem provides an enlarging flow path from the exhaust plenum to the silencer modules.
EXHAUST SILENCER MODULE
The exhaust silencer module for this exhaust system is located in the horizontal duct run just downstream of the transition duct. The exhaust silencer module is acoustically designed to attenuate the sound of the exhaust gases. This is done using a parallel batt silencer concept. This arrangement of silencing media provides for maximum required attenuation of both low and high frequency sound to meet site requirements.
EXHAUST TRANSITION DUCT (SECOND)
The transition duct is a horizontal section of ductwork which is located down- stream of the silencer modules. The second transition duct in the ductwork system provides a decreasing flow path from the silencer modules to the exhaust stack inlet.
EXHAUST STACK
The exhaust stack is designed to release exhaust gases to atmosphere well above the machine baseline and at a proper plume velocity for optimal dispersion of exhaust gas particles. The exhaust stack is a round piece of vertical ductwork which is self supporting from the machine baseline.
VENTILATION SYSTEM
The accessory, turbine and load coupling compartments are pressurized and cooled by ventilation fans (9-C-12608XA/B) installed in the pressurized and cooled ventilation ducting after the inlet
The ventilation system consists of two separate fans driven by their respective motors (9-CM-12608XA/B); one fan provides ventilating air during normal turbine operation. The other operates as a stand-by fan and starts when, for any reason, the temperature inside the turbine compartment increases and reaches the set point of the RTD.The ventilating air exits from the turbine and coupling compartments through the upper opening of each compartment.
Two types of dampers are foreseen for the safety of the ventilation system:
a) gravity dampers, positioned in the filter chamber, held open by the fans of the ventilation system;
b) Manual dampers positioned on the inlet/outlet ducts of the ventilation sys tem; they are closed automatically by the fire fighting system, by the pressure of the CO2 discharge.
GAS DETECTION SYSTEM
Three gas detectors are provided on the Gas Turbine. These are located inside the turbine compartment.
Two set points are provided on each gas detector (set on the control of each gas detector, located on the UCP), one for 30% LEL (alarm indication on Mark VI CRT) and one for 60% of LEL (trip executed by Mark VI panel).
