Operation and Maintenance Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers

Transcription

1 October 2005 GE Energy Operation and Maintenance Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers These instructions do not purport to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection with installation, operation or maintenance. Should further information be desired or should particular problems arise which are not covered sufficiently for the purchaser's purposes the matter should be referred to the GE Company General Electric Company

2 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers TABLE OF CONTENTS I. INTRODUCTION... 3 A. Background... 3 II. DESCRIPTION OF SYSTEM... 4 A. Saturation Efficiency (Effectiveness)... 5 B. Evaporation Rate... 6 C. Blowdown (Bleed-off) Rate... 7 D. Makeup Water Rate... 7 E. Water Carryover... 7 F. Water Bypass... 8 III. EVAPORATIVE COOLER COMPONENTS... 8 A. Evaporative Cooler Media... 9 B. Recirculation Pumps and Motors C. Water Distribution System D. Water Draining System E. Flashing and Media Support F. Customer / Purchaser Connections G. Access and Inspection Provisions H. Control, Protection and Convenience Devices IV. EVAPORATIVE COOLER INSTALLATION, OPERATION, AND MAINTENANCE PROCEDURES A. Evaporative Cooler Installation B. Evaporative Cooler Commissioning C. Evaporative Cooler Operation and Maintenance V. EVAPORATIVE COOLER WATER QUALITY AND TREATMENT A. Makeup and Recirculating Water Constituent Limits B. Water Scaling C. Biological Fouling and Other Chemical Treatment...29 D. Water Sampling and Testing VI. REFERENCES

3 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers I. INTRODUCTION Evaporative coolers supplied with General Electric Gas Turbines should provide reliable and trouble free operation for the life of the gas turbine. This document is intended to provide the gas turbine operator with general guidelines and suggestions to ensure proper operation and maintenance of the evaporative cooler. This document is not intended to replace the information provided as part of the Operation and Maintenance (O&M) manual provided by the Evaporative Cooler manufacturer. The scope of this GEK is limited to media type evaporative coolers and the hardware related to such equipment. Gas turbine operators must recognize that if suitable operational and maintenance guidelines are not established and followed, the evaporative cooler and its media may need more frequent maintenance. In the extreme case, the misoperation of the evaporative cooler can result in severe contamination of the gas turbine and have extremely serious consequences in terms of forced outage time needed for maintenance, repair and replacement of gas path components. A. Background Evaporation of water is one of the simplest and oldest methods of cooling air. Even with the sophisticated technology available today, including mechanical chillers, absorption chillers and thermal energy storage systems, evaporative cooling remains a most cost-efficient method for temperature control of the gas turbine inlet air supply. Evaporative cooling can be achieved by several methods. In General Electric gas turbine applications, two forms are typically used: Media type evaporative cooling and Spray type evaporative cooling (commonly known as fogging or SPRITS ). Traditional media type evaporative coolers consist of recirculated water sprayed over an extended surface media mounted downstream from the inlet air filters. As inlet air passes through the water soaked evaporative cooler media, evaporation occurs performing a dual function: 1. Energy in the form of heat is removed from the air by using that energy to evaporate water in the media; and 2. Water vapor content of the air increases due to evaporated water approaching saturation along constant wet bulb lines. These two processes increase the density of the air, which in turn increases the mass flow and output of the gas turbine. 3

4 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers II. DESCRIPTION OF SYSTEM A schematic of an evaporative cooler is shown above. An evaporative cooler is a useful gas turbine option for applications where significant operating time occurs in the warm months, and where low humidity is common. The Evaporative Cooler System is procured as part of the Gas Turbine Inlet Filter Compartment per Model List Item (MLI) A040, and it typically consists of the following components as a minimum: Evaporative Cooler Media Customer/Purchaser Connections Recirculation Pumps and Motors Flashing & Media Support system Water Distribution System Control and Protection Systems Water Draining System Access and Inspection provisions Water Collection (Sump) Tank Lighting and Convenience provision Upper Level Drain pans We will discuss these components in detail in Section III of this GEK document. The function of the evaporative cooler is to increase turbine output by lowering the inlet dry bulb temperature and increasing the air density through the evaporation of water into the inlet airflow. Recirculated water introduced over the top of the evaporative cooler media drains through and wets the media. Filtered ambient air comes into contact with the wetted media where the air is cooled by the heat of evaporation of water. Gas turbine mass flow rate increases due to the lower air temperature and increased water content. Higher mass flow results in increased power output from the gas turbine. When discussing media type evaporative coolers, a couple of key parameters are essential to the proper operation and maintenance of evaporative coolers. These evaporative cooler parameters are: Saturation Efficiency, Evaporation Rate, Blowdown Rate, Makeup Water Rate, Water Carryover, and Water Bypass. 4

5 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers A. Saturation Efficiency (Effectiveness) The performance of an evaporative cooler is based on the ratio of the number of degrees it can cool the air compared to the wet bulb temperature depression. As air passes through an evaporative cooler, the dry bulb temperature is lowered, but the wet bulb temperature remains approximately the same. The dry bulb temperature will then approach the wet bulb temperature as the air is cooled and the relative humidity will rise (due to moisture added to the airflow through evaporation). The entering wet bulb temperature is a function of the entering conditions of the airflow (air dry bulb temperature, ambient pressure or altitude with respect to sea water level, and relative humidity). Since an evaporative cooler operates along constant wet bulb temperature lines, the entering wet bulb temperature determines the maximum amount of cooling that can be achieved. We can define the saturation efficiency of an evaporative cooler as the ratio between the actual amount of cooling achieved (difference between entering and exiting airflow temperatures) and the maximum allowable cooling per the entering conditions (Wet Bulb Depression). The effectiveness of an evaporative cooler may be calculated using the following formula: where: T η = DBE T WBD DBL T = T DBE DBE T T DBL WBE η = Efficiency in percent. T DBE = Entering Dry Bulb Temp T WBE = Entering Wet Bulb Temp T DBL = Leaving Dry Bulb Temp WBD = Wet Bulb Depression, or = T DBE - T WBE 1. Dry Bulb Temperature The temperature as measured by a standard thermometer. 2. Wet Bulb Temperature The temperature as measured by a thermometer that has a water-moistened wick around its bulb. If the air is at a temperature above its dew point, evaporation of water will occur in the wick causing cooling and the reading of a temperature below the dry bulb temperature, the wet bulb and dry bulb temperatures are equal at 100% humidity. The Wet Bulb Depression is the difference between the ambient dry bulb and the wet bulb temperature. The Wet Bulb Depression is the maximum amount of cooling achievable with a 100% efficient evaporative cooler system. 3. Humidity Humidity, which is expressed by the water vapor pressure in air, is controlled by the ambient temperature. Relative Humidity is the ratio of the vapor pressure of water in air compared the 5

6 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers saturated water vapor pressure at the same temperature. Dew Point Temperature of the air is the temperature at which condensation of liquid water may occur. 4. Ambient Pressure The temperature and barometric pressure of atmospheric air vary considerably with altitude as well as with local geographic and weather conditions. The standard atmosphere gives a standard of reference for estimating properties of air at various altitudes. At sea level, the standard barometric pressure is psia [ in. Hg] and the standard temperature is 59 F [15 C]. The temperature is assumed to decrease linearly with increasing altitude while the specific volume increases. The lower atmosphere is assumed to consist of dry air that behaves as a perfect gas. B. Evaporation Rate The evaporation rate is the amount of water that is added to the gas turbine airflow as a result of the energy transfer between airflow and water, and the subsequent evaporation of water into the air. The amount of water evaporated into the air or evaporation rate will depend on the entering ambient air conditions. Factors such as dry bulb temperature, relative humidity, and air ambient pressure determine the maximum amount of water that may be evaporated before air becomes saturated with water. The amount of water evaporated in gallons per minute as the air passes through the cooler can be calculated using the psychrometric chart using the following formula: Evaporation Vair ( WL WE ) ρairvair ( WL WE ) mair ( WL WE ) = = = ρ υ ρ ρ water air water water where: V Air = Actual volumetric flow rate of air (cubic feet of air per minute or CFM) ρ water = density of water (lb water / gal ) at T WBE ρ air = density of air (lb air / ft3 ) at entering airflow conditions W E = Moisture content of entering air (lbs. water/lb. dry air) W L = Moisture content of leaving air (lbs. of water/lb. dry air) m air = Mass airflow rate (lb. dry air / min) at entering conditions ν air = Specific volume of air (ft3/lb. dry air) at entering conditions Similarly, since the evaporation rate is a function of the temperature of the ambient air and airflow, the amount of water evaporated may be obtained from the energy balance equation between air entering and leaving the evaporative cooler media: Evaporation = m air Cp ρ air water ( TDBE TDBL) ρairvaircpairη( TDBE T = HE ρ HE water water water WBE ) where Cp Air = Specific heat of air at T DBE ( btu/lbm- F) HE water = Heat of evaporation of water (btu/lb water) at T WBE For practical purposes, the following version of the energy balance equation is used: Evaporation V = air ( TDBL TDBE ) Vairη( TDBE TWBE ) = 500, ,000 6

7 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers C. Blowdown (Bleed-off) Rate Water always contains a certain amount of dissolved minerals. The process of evaporative cooling removes pure water as vapor from the recirculating flow and leaves behind the solids that had been dissolved in the water when it was added as makeup. Accordingly, enough water must be blown down from the recirculating flow to control the level of these solids and to avoid build-up of insoluble minerals on the pad surface (commonly referred to as scaling ), which results in an increase in pressure drop, and a loss of evaporation area and efficiency. Blowdown is the flow of water that must be continuously removed from the cooler in order to maintain the chemistry of the recirculating water at the design value. It is a function of evaporation rate and the cycles of concentration that can be achieved with a given water quality in the system. Blowdown = (Evaporation Rate) (No. of Cycles 1) The chemistry of the sump is established by determining the maximum cycles of concentration that the makeup water can go through. By definition, the number of cycles of concentration is equal to the number of times that incoming (makeup) water may be recirculated before it is removed (bled) from the system. Two methods are commonly used for controlling blowdown and maintaining the desired chemistry in the sump of the evaporative cooler: Constant flow and Conductivity Control blowdown. D. Makeup Water Rate Makeup water is the water added to the sump of the evaporative cooler to replace the water lost by evaporation into the airflow and the water removed from the sump through blowdown or bleed-off as required. Makeup Rate (gpm) = Evaporation Rate (gpm) + Blowdown Rate (gpm) When conductivity control is used to control blow down, the makeup water required while blowdown is on will be higher than the average identified by the Makeup rate formula. When the blow down is off (Blowdown rate = 0 gpm), the required make up rate will be equal to the current evaporation rate. A high makeup water rate is typically required during startup of the evaporative cooler system in order to ensure enough water is available out of the sump (recirculation) tank during initial wetting of media. E. Water Carryover Water Carryover is the term used to describe water droplets that become entrained in the airflow stream and travel through the Evaporative Cooler Media (Cellulose) and plastic (PVC) Drift Eliminators. Water carryover can be classified into two different categories: Visible and Non-Visible Carryover. Visible Carryover consists of water droplets several microns in diameter that are visible to the naked eye. Visible carryover is often the result of high velocities through the Evaporative Cooler media or incorrect media installation. Non-visible water carryover refers to water droplets that are too small to be perceived by the naked eye. Non-visible water carryover is harder to quantify due to its smaller droplet size. Industry literature suggests that the total drift rate or percentage of drift passing through the drift eliminator as compared to the source water flow is around % depending on source water flow magnitude, drift eliminator angle, and mean air velocity. 7

8 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers F. Water Bypass Water bypass is the term used to describe water droplets that become entrained in the airflow and travel around the drift eliminators and media flashing. It is often the result of manufacturing and/or installation defects such as poor caulking, welding, or gaps in between adjacent pieces of drift eliminators. It is generally characterized by location (sidewalls, module interfaces, structural member, etc.) and relatively large droplet size. III. EVAPORATIVE COOLER COMPONENTS Clean water supplied by the customer enters the lower part of the evaporative cooler section through the Makeup water supply (PC-IE5) connection. Makeup water empties into an evaporative cooler main collection (sump) tank. The level of water in the sump is maintained and controlled by water level switches or transmitters. The water level transmitters control the level in the sump by opening and closing (as required) the makeup water solenoid valve(s). Water in the sump is pumped to a distribution manifold located directly above the evaporative cooler media. The pumps continually recirculate water to the media during operation. Water quantity to the media is regulated via orifices and trim lines for small adjustments to the water flow (based on site specific needs). The distribution manifold evenly wets the media by jetting water through small holes, spaced along its length, into a deflector shield or splash cover. This water enters the distribution pads installed above the media blocks, providing an even distribution of water to the entire top surface of the media blocks. The media blocks are made of corrugated layers of fibrous material with internal channels formed between 8

9 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers layers. The water flows down by gravity through water channels and diffuses throughout the media by wicking action. Any excess water flows down to the module drain pans before it returns to the evaporative cooler sump where it is recirculated back into the media. An off-season drain valve and piping is provided on the access side of the cooler module for maintenance of the evaporative cooler system. This is required for off-season draining of the evaporative cooler sump as to enable winterization of the system during possible freezing events / seasons. This line can also be used to quickly drain the sump or to enable a manual sump blowdown for troubleshooting of the system. A. Evaporative Cooler Media Two types of Evaporative Cooler Media are normally provided with GE Evaporative Cooler Systems: Cellulose Paper Media and Plastic Drift Eliminators. 1. Cellulose Paper Media Evaporative Cooler media is made of corrugated cross-fluted cellulose material that is impregnated and treated with insoluble anti-rot salts and rigidifying agents. Evaporative cooler media contains alternating 45º and 15º corrugations, held together by resin. Water flows upstream of the airflow through the 45º flutes while air travels through the 15º flutes. Media should be oriented at assembly so that when viewed in elevation, the 45º flutes direct water downward towards the upstream side of the media. The 15º flutes should be oriented downward toward the downstream side of the media. Proper orientation of the media is essential to prevent water carryover into the gas turbine compressor. Evaporative Cooler media is typically marked with a red stripe at the bottom of the upstream side to facilitate correct installation. Nevertheless, it is always helpful to verify orientation using a thin wire inserted into different flutes within a block. 2. Drift (Mist) Eliminators Drift eliminators use inertial forces to separate water droplets from the airflow by forcing air through a number of S-wave channels. As air passes through the honeycomb-like structure, water droplets suspended in the air will impinge on the channel walls. As the droplets impinge and accumulate, they form bigger, heavier droplets that are large enough to fall out of the entering side 9

10 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers of the eliminator without becoming entrained into the flow. Water separated out of the air stream by the mist eliminator blocks drains forward by gravity into the bottom of the cooler into the sump. Moisture separators should be installed so that there are no air leakage gaps between moisture separator panels, at supports, or at the moisture separator perimeter, and oriented so as to drain any captured water droplet runoff to the drain tank / sump (away from turbine airflow). The panels are normally installed into the support structure (flashing) at a 5 to 10-degree slant in order to allow for the water to drip out. B. Recirculation Pumps and Motors Pumps are used to recirculate the water from the sump tank to the evaporative cooler media. Two designs are typically available with GE Evaporative Cooler systems: Single Pump and Dual Pump systems. Dual Pump arrangement requires two (2) separate distribution manifolds per evaporative cooler level. Water is fed by two separate pumps operating at the same time into each manifold from the end near the cooler sidewall to the center of the module. Single Pump arrangement requires each distribution manifold to span the full width of the evaporative cooler module. Water is fed from a single pump located on the main access side of the unit. Pumps draw water from the sump and supply water to the distribution manifolds located directly above the distribution pads and media. Redundant Pumps / Motors are available as an option for Evaporative Cooler Systems provided by GE Energy. Redundant pumps/motors are operated in a lead-lag relationship by the GE Turbine Motor Control Center (MCC). In a lead/lag system, there are two sets of pump(s) and flow switch(es) designated A and B. Either the A or B system may be in operation at any time. When in automatic mode, the same number of pump starts is maintained on each of the A and B systems. When in manual mode, the operator can select operation of either the A or B system. If pump A, does 10

11 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers not respond as requested, the system will automatically initiate pump B to run the evaporative cooler system. Below is a top-level summary diagram of a dual pump evaporative cooler. C. Water Distribution System The Water distribution system ensures that the evaporative cooler media is evenly wet throughout the cooler module. Even wetting is critical to even temperature distribution and performance of the Evaporative Cooler. Water distribution and drain piping may be provided using either plastic (CPVC) or 304/304L stainless steel material depending on customer contract requirements. The water distribution system consists of four main sub-components: Flow Distribution System, Distribution Headers, Splash Covers, and Distribution Media pads. 1. Flow Distribution System A manual valve is provided to regulate and balance the amount of water that is distributed to each of the evaporative cooler distribution headers that saturate the media. Newer designs employ flow balancing orifices and trim lines. A trim line is typically provided in parallel to each orifice that allows for slight adjustments of the flow by turning a manual valve. A flowmeter is also provided in order to measure required flow amount to media. Water Flow to Water Flow to Manual valve with flowmeter Orifice plate with trim line in 2. Distribution Headers The water distribution header is a length of pipe with a number of holes drilled along the top that ejects water upward into the splash cover and wets the media. The header lays either on top of the media and distribution pads or is suspended directly above it. The Evaporation Cooler distribution header may be run as a center fed pipe (with a T connection in the middle) or it can be fed from one side and run the entire length of the module. The header is located toward the front side of the media (air entering side) to reduce chances of water carryover from the downstream side and to deliver water up front where most of the evaporation occurs. Flush valves, plugs or caps are provided at the end of each manifold for cleaning / maintenance needs. 3. Splash Covers The splash cover consists of semi-circular deflector shield that runs the entire length of the distribution header pipe at every horizontal module section. It is used to disperse water from the distribution header jets into the distribution pad and deter water from impinging into the roof of the housing. 11

12 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers 4. Distribution Pads Distribution pads are made of corrugated cellulose based material containing 45ºx45º Cross-fluted channels with reinforced edges to evenly disperse the water across the top cross-section of the evaporative cooling media. They are usually installed directly on top of the evaporative cooler media bank for maximum water transfer efficiency. D. Water Draining System The Evaporative Cooler Water Draining system ensures that all water that does not evaporate returns to the Sump / holding tank where it can be recirculated again back into the media. The water draining system consists of three main sub-components: Upper Level Drain Pans, Drain Lines, and the main collection sump tank. 1. Upper Level Drain Pans Drain pans are used at each of the upper levels in the Evaporative Cooler module to collect the excess water that passes through the media and is not evaporated. Water from the lower modules usually drains directly into the sump tank. Baffle plates are used to completely seal the drain pans in order to prevent any air bypass and possible water carryover under the evaporative cooler media. 2. Drain Lines The drain lines from upper level drain pans to the sump are designed to be fully redundant. Drain lines are normally configured to be outside of the evaporative cooler module or in line with structural support in order to minimize interference with airflow and maximize effective media area. 12

13 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers 3. Main Collection (Sump) Tank The function of the sump tank is to collect and store the water for recirculation. Most arrangements utilize a single sump located below the bottom module (away from the airflow stream) to maximize effective media area. A non-reducing, manual valve / gate valve is provided to fully drain the sump without residual puddling of collected water for Off-season system drain and to aide in maintaining extreme bleed-off requirements. An overflow standpipe or weir is provided in the sump tank. When the water level inside the tank is too high, it will flow over the standpipe or weir and drain to the plant drain system from the main drain purchaser s connection (PC-IE7). The overflow standpipe is located a few inches higher than the prescribed maximum operational water level. E. Flashing and Media Support Flashing is required in order to eliminate water bypass into the gas turbine airflow path. Flashing at the top of any bank of media is configured to bite into the side of the media to assure that any water running down the face of the media is redirected back into the media and does not become loose water that can enter the air stream. Media (Top) Media (Bottom) Installation guidelines for Evaporative Cooler Media flashing Similarly, flashing at the base of any bank of media flares out to assure that all water running down the upstream or down stream face of the media is redirected back into the media and never contacts the outboard side of the flashing. Flashing at the sidewalls is designed to prevent water from flowing downstream along the interface of the evaporative cooler sidewall and the outside edge of the evaporative cooler media. Flashing and baffles are designed to completely seal off any potential airflow paths in order to reduce risk for water bypass. Evaporative Cooler media will vary in weight depending on media dimensions, amount of water retained during operation, and general condition of the media (new, old, heavy deposits, etc.). The evaporative cooler media supporting system has been designed to provide full support to all evaporative cooler media (dry, wet, new and clean, old and scaled, etc.) and any applicable hardware (distribution headers and splash cover) that might be resting on top of it. 13

14 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers F. Customer / Purchaser Connections Two (2) flanged stainless steel purchaser / customer connections are provided on the sump for water supply and drainage of the Evaporative Cooler System. These connections are labeled PC-IE5 and PC-IE7 respectively and are normally located on the access side of the Evaporative Cooler module. The Makeup Water Supply (PC-IE5) is provided with makeup water solenoid(s) that regulate incoming water flow and prevent overflooding of the sump tank. The main Evaporative Cooler Drain line (PC-IE7) contains a manual butterfly valve with a limit switch. The limit switch on the valve provides a signal to the Turbine Control System that enables the evaporative cooler to run only when the drain valve is full open. This drain line should be closed only during off-season periods when the evaporative cooler sump tank is fully drained as to prevent air bypass. A loop seal downstream of the drain line connection is also required to prevent dirty air bypass into the clean air side of the gas turbine inlet system. 14

15 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers G. Access and Inspection Provisions The Evaporative Cooler Module is typically provided downstream of the filter module (clean air side) of the gas turbine inlet compartment (MLI A040). Access to the main inspection / maintenance walkways via a lockable door on the upstream side of the module. Access from level to level is through internal ladders or stairs and doors. Access to the Filter House Clean Air Plenum and downstream side of the drift eliminators is provided via a bolt-on access hatch. Windows are provided for inspection. Two windows are provided on the access hatch to allow for water carryover / bypass inspection during Evaporative Cooler commissioning and routine checks. The windows are installed so that one person can hold a light in one window and look through the other window simultaneously while inspecting the downstream side of the drift eliminators and the clean air plenum for any presence of water. Some evaporative cooler designs are available with an internal walkway (accessible through an access hatch or door) in between the Cellulose Evaporative Cooler media and the Drift Eliminators for enhanced inspection ability and performance. Other designs may have an access manway (hobbit door) that transverses the media and drift eliminator banks. H. Control, Protection and Convenience Device Devices used in the evaporative cooler system are typically wired to the Evaporative Cooler Junction Box (JB78A). The following control, protection and convenience features are currently provided with the Media Type Evaporative Coolers: Blowdown Control, Water Level Control, Temperature Control, Motor Control & Protection, and Water Carryover Control. 1. Blowdown Control System Due to the isolated locations of some of the installations and the limited water sources often available, the use of the evaporative cooler to condition inlet air for the gas turbine results in some of very challenging water control requirements. The use of high mineral content waters can result in scale formation in the media, which decreases the efficiency of the cooler and increases the static pressure drop. Conversely, the use of very high purity water can result in corrosion problems and may have a destabilizing effect on the evaporative cooler media. Blowdown is required for all recirculated water evaporative cooling applications. 15

16 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers a. Constant Flow (Manual) Blowdown Control The simplest form of blowdown control is to set a valve on the pressure side of the recirculating pump to continuously discharge a constant flow of water to drain. Water may also be drained from the sump directly. Installing a flow meter at the point of blowdown will help operators monitor and set the blowdown rate. The amount of water discharged in this method is normally calculated using the highest evaporation rate for a given geographical location. b. Electronic Conductivity Blowdown Control Since evaporation rates fluctuate throughout the year due to changes in ambient temperature and humidity, the set point for manual blowdown needs to be changed periodically to accommodate seasonal changes in evaporation rates. Seasonal fluctuations in evaporation rates can be accommodated automatically, by controlling the blowdown, based on the conductivity of the recirculating water. This is accomplished by installing a conductivity controller in the system. It continuously measures the conductivity until the measurement surpasses the desired set point. It then opens a solenoid valve and blows down water until the conductivity is back within control range. Sump water conductivity is measured using two Conductivity Sensors (Device Codes 96AC-22, -23) that each sends a signal to the Turbine Control System (TCS). Two sensors are provided for redundancy to ensure proper and accurate function. The turbine control system uses these signals to control the blowdown system solenoid valve. The number of desired concentration cycles determines the high conductivity setting of the sensors. The number of cycles of concentration is the ratio between supply makeup (evaporation + blowdown) and drain (blowdown) water flow 16

17 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers rates. Maximum allowed constituent limits for makeup and recirculation water are set forth by the Evaporative Cooler Water Quality document GEK S Recirculating back to tank Blowdown C JB78A /TCS C Blowdown discharge from The Blowdown Solenoid Valve(s) (Device Code 20AC-X) is a two-position three-way valve (as shown above) that either directs the blowdown into the drain system for blow down or recirculates the water back into the sump. This is required to provide a constant flow through the blow down line and eliminate fluctuations in the flow from the evaporative cooler recirculation pumps. The three-way blowdown valve is normally provided on a pressurized distribution line from the recirculation pump(s). A flow meter is provided upstream of the solenoid valve to calculate the amount of blowdown water. 2. Water Level Control System A differential Water Level Transducer (Device Code 96AC-21) is used to measure the water level and monitor for abnormal conditions in the reservoir (sump) tank. The turbine control system uses this information to control the Makeup Water Solenoid Valves (device codes 20AC-21 and 20AC-32) to control the sump water level. The makeup water solenoid valves are in series and are redundant as a safety measure. The entire evaporative cooler system will be shut down if water level reaches an unacceptable level (too high or too low), or no signal is received from the transducer. A Drain Line Shut Off Valve Limit Switch (Device Code 33AC-1) for the main drain line (PC- IE7) butterfly valve provides a signal to the Turbine Control System enabling the evaporative cooler to run only when the drain valve is fully opened. It is also used to verify that the drain is closed when the sump tank is empty during off-season / extended shutdown period to prevent dirty air bypass. This is a protection feature to both the evaporative cooler and the gas turbine. A sloped transition piece oriented as to drain water away from the compressor inlet bellmouth is also provided. 3. Temperature Control System A Low Temperature Limit Switch (Device Code 26AC-1) is supplied with GE Evaporative coolers and mounted upstream of the evaporative cooler media to monitor ambient air temperature as it enters the cooler section and media. It is used to restrict evaporative cooler operation and to initiate a pump shutdown by the turbine control when the ambient temperature drops below 60ºF due to icing concerns. Humidity Sensors (Device Code 96TD-X) and temperature transducers provided downstream of the evaporative cooler monitor for icing conditions at the compressor inlet bellmouth. Inlet Air Ambient Thermocouples (Device Code 17

18 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers AT-ID-X) are also available upstream of the evaporative cooler module for monitoring of ambient air temperature. 4. Motor Control and Protection System One set of pumps is provided to power the circulation of water from the sump tank to the evaporative cooler media. The pumps are driven by Totally Enclosed Fan Cooled (TEFC) Motors (Device Code 88AC-X) with rated operational voltage as required per the local electrical system rating. Each pump motor is provided with a separate Overload Relay (Device Code 49AC-x) and a local Pump Disconnect (Device Code 8AC-x). The overload relay protects the motor from thermal overloads while the local disconnect electrically disconnects both the motor feed and the motor heater feed when so required. Multiple pump motors share local disconnects for safety and convenience. Motor Heaters (Device Code 23AC-X) are provided with each motor to protect against moisture damage. A low Flow Switch (Device Code 80AC-x) is provided for each motor/pump set. The switch provides a signal to the turbine control system to initiate an alarm and/or pump shutdown when the water flow drops below the normal operating setting or to verify pump startup in redundant pump arrangements. 5. Lighting and Convenience Outlet Provisions Lighting (Device Code AL-32) is provided on the upstream side of the evaporative cooler module section. The Light Switch (Device Code ASW-14) is accessible from the outside the evaporative cooler module normally next to the bottom level access door. A Convenience Outlet (Device Code AR-20 or AR-21) is also provided at the same location for maintenance. 6. Water Carryover Detection System New designs incorporate a Water Carryover Detection System provided in order to detect water carryover past the drift eliminator stage. The carryover detection system consists of a blind box located at grade level and attached to the support steel columns located underneath the Inlet Compartment (MLI A040). Drain couplings (number dependant on evaporative cooler size) are provided on the filter house transition and manifolded into a single connection to the blind box. Dams are provided in the filter house transition to aide in directing the water to the drains. The blind box contains two independent Level Switches (Device Code 71AC-12, -13) that are wired back to the Evaporative Cooler Junction Box (Device Code JB-78A). The flow switches will send a warning signal to the turbine control room once the water has reached a predetermined level. In addition, a manual drain valve and a sight tube/window are provided with the carryover detection system so that an operator is able to check the system s health by opening the valve and validating visually if there s any water inside. The complete list of electrical devices used in the evaporative cooler system is provided below. Electrical characteristics for each device will vary depending on local electrical system requirements (60 Hz versus 50 Hz service). 18

19 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers Device Name 8AC-X 20AC-X 20AC-21 20AC-32 23AC-X 26AC-1 33AC-1 49AC-X 71AC-12 71AC-13 80AC-X 88AC-X 96AC-21 96AC-22 96AC-23 Description IV. EVAPORATIVE COOLER INSTALLATION, OPERATION, AND MAINTENANCE PROCEDURES The correct installation, setup and checkout of the evaporative cooler are critical to its operation, and particularly to the prevention of water carryover (drift) of liquid droplets in the gas turbine airflow path. The installation instructions provided by the manufacturer of the evaporative cooler need to be followed to ensure the health of the gas turbine. In addition, all evaporative coolers shall undergo commissioning per the GE Evaporative Cooler Commissioning procedure prior to initial start up and, during service, a minimum of once a year, at the beginning of the evaporative cooler use season. A copy of the evaporative cooler commissioning procedure is available in the gas turbine Operational and Maintenance (O&M) manual. Please contact GE Energy Services for copies of the latest commissioning procedure (as applicable). A. Evaporative Cooler Installation Turbine Inlet Air Evaporative Cooler Pump Motor Disconnect(s) Turbine Inlet Air Evaporative Cooler Water Blowdown Solenoid Valve(s) Turbine Inlet Air Evaporative Cooler Make-Up Water Solenoid Valve Turbine Inlet Air Evaporative Cooler Redundant Make-Up Water Solenoid Valve Turbine Inlet Air Evaporative Cooler Motor Space Heater(s) Turbine Inlet Air Evaporative Cooler Low Temperature Switch Turbine Inlet Air Evaporative Cooler Drain Line Valve Position Switch Turbine Inlet Air Evaporative Cooler Pump Motor Overload(s) Turbine Inlet Air Evaporative Cooler Carryover Level Switch Alarm Turbine Inlet Air Evaporative Cooler Carryover Level Switch - Shutdown Turbine Inlet Air Evaporative Cooler Water Flow Switch(es) Turbine Inlet Air Evaporative Cooler Pump Motor(s) Turbine Inlet Air Evaporative Cooler Sump Water Level Transducer Turbine Inlet Air Evaporative Cooler Conductivity Sensors Turbine Inlet Air Evaporative Cooler Conductivity Sensors 96TD-X Turbine Inlet Air Humidity Sensor (MLI A041 / A122) AL-32 ASW-14 AR-21 Turbine Inlet Air Evaporative Cooler Compartment AC Lighting Turbine Inlet Air Evaporative Cooler Compartment AC Lighting Switch Turbine Inlet Air Evaporative Cooler Compartment Convenience Outlet During installation, the following items should receive special attention: Media and Distribution Pads, Drift Eliminators, Water distribution piping, Flashing and Baffling, Gasketting and Cleanliness. The following items need to be addressed as a minimum to ensure proper installation of the evaporative cooler system: 1. Cellulose Media Blocks And Distribution Pads Correct media orientation is critical to the operation of the evaporative cooler system. If the media is installed backwards it will result in water carryover. Water will travel downwards from the top of the media stack through the 45-degree flutes while air will travel through the less restrictive 19

20 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers (preferred) path of the 15-degree flutes. Media should be oriented at assembly so that when viewed in elevation, the 45-degree flutes direct water downward toward the upstream side of the media. The 15-degree flutes should be oriented downward toward the downstream side of the media. A red stripe is typically added at the bottom of the evaporative cooler media blocks for ease of installation. However, it is recommended to double check correct orientation by carefully inserting a 12-inch straight length of round-nosed weld rod (or similar device) into alternate air and water corrugation flutes. Gaps in excess of 1/8 are not allowed between adjacent pieces of evaporative cooler media or between media and module sidewalls. End pieces are typically field cut to ensure a tight fit in between media blocks and against module sidewalls. Media shall be inspected for damage on the upstream and downstream side (when looking in the direction of airflow) and replaced accordingly. Damage on the upstream side is not considered as critical as damage on the downstream side barring large indentations in the media that are several layers deep or wide. However, damage on the downstream side can result on unrestricted wicking of water, which can overwhelm the drift eliminators, and result in water carryover. Damage on the downstream side of the media requires immediate replacement of the blocks to ensure proper operation. Distribution pads provided on top of the media blocks ensure even water distribution from the headers and splash cover across the evaporative cooler media top surface. Distribution pads are smaller than media blocks (2-inches thick) and feature 45ºx45º cross-fluted channels with reinforced edges for handling and ease of installation. 20

21 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers 2. Drift Eliminators Drift Eliminators must be installed as to allow for draining of water droplets through the S-shaped channels in the direction opposite to airflow. Complete interlock (0.50-inch nominal and 0.25-inch minimum) is required between adjacent pieces of drift eliminator panels. The last piece of drift eliminator panel is cut to interlock with the adjacent piece and fit tightly against the module sidewall on the cut side. A yellow line is typically provided at the upstream and bottom edge of the drift eliminator panels for ease of installation. Drift Eliminators shall be inspected for damage after installation, and prior to operation. Separation between layers within a panel is common when drift eliminators are left exposed to sunlight and UV rays for long periods of time. Since drift eliminators play a pivotal role in the elimination of water carryover and/or bypass, it is imperative that damaged pieces be replaced immediately. 3. Water Distribution Piping Water distribution piping shall be verified to meet the installation drawings and instructions provided by the inlet filter house supplier. Correct orifice sizes and locations are critical to the operation of the evaporative cooler system. Bore sizes are mechanically stamped on each orifice. As a general rule, the larger bore size corresponds to the upper level distribution manifold. The smaller bore size corresponds to the bottom distribution manifold. Orifices on the blowdown line (connecting back to the sump tank or drain) are exempt from this general rule. Sump strainers and in-line strainers provided upstream and downstream of the pumps should be inspected to determine whether they are missing, damaged, or unlined. Inline strainers provided downstream of the Makeup water supply line (PC-IE5) also need to be inspected (where applicable). Inline-strainers protect solenoids, pumps, flowmeters, and distribution manifolds from becoming clogged with particulates that would affect their function. Flowmeters shall be inspected, cleaned and calibrated as appropriate to ensure accurate flow readings. Distribution headers shall be inspected to ensure the water spray holes (0.125-inch holes on top of the manifold) are oriented at the 12 o clock position in order to spray up directly into the splash cover. This is ideally done prior to media installation / replacement as it is difficult to inspect 21

22 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers these holes while the media is still in place. Newer systems employ a removable splash cover for added convenience. 4. Flashing and Baffling Flashing at the top of any bank of media is configured to bite into the side of the media to assure that any water running down the face of the media is redirected back into the media and does not become loose water that can enter the air stream. Flashing on top of the media banks (at distribution levels and/or intermediate trays) shall be configured to bite at least 0.25 inches into the media to ensure sealing. Media (Top) Media (Bottom) Installation guidelines for Evaporative Cooler Media flashing Similarly, flashing at the base of any bank of media flares out to assure that all water running down the upstream or down stream face of the media is redirected back into the media and never contacts the outboard side of the flashing. Flashing that does not confirm to these guidelines may be carefully bent back into position to maximize efficiency (depending on amount of deflection). Flashing at the sidewalls is designed to prevent water from flowing downstream along the interface of the evaporative cooler sidewall and the outside edge of the evaporative cooler media. Caulking (Sikaflex 221 or similar as approved by GE Engineering) may be used to seal off any potential water bypass locations or non-conforming flashing. Caulk should be applied to a clean and dry surface as per the manufacturer s recommendations. Baffles are designed to completely seal off any potential airflow paths in to prevent water bypass and highest efficiency. 22

23 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers 5. Gasketting A modular concept has been adopted in the design of the inlet filter house and evaporative cooler system. This modular design allows for similarity and configuration options between multiple designs. Bolted gasketed joints are provided throughout the inlet system in order to prevent dirty air bypass and allow for air management between modules. Neoprene (closed cell) gaskets are used at all dirty-to-clean air bolted joints (external joints) as well as module-to-module connections. It is essential to the integrity of the inlet system that all gaskets and bolted joints are installed correctly as to minimize the risk of dirty air and/or water contaminating the clean air side of the gas turbine. Prefilters and Final filters need to be installed tight against the retaining frame or tubesheet in order to ensure a positive seal between the dirty and clean air side. Gasket use and presence shall be verified to meet the installation drawings and instructions provided by the inlet filter house supplier. It is recommended to seal off external gasketed joints with a caulk profile on the outside as a redundant sealing method for the clean air side. Missing gasketting can be corrected by use of rope gasket or caulking depending on size. The use of correct caulking profile and application procedures is critical. While applying caulk, one must ensure that the surface is clean and dry as to ensure good caulk adhesion to the receiving surface. Caulking (Sikaflex 221 or similar as approved by GE Engineering) may be used to seal off any potential air bypass locations or nonconforming bolted gasketed flanges. 6. Cleanliness It is important to remember that the evaporative cooler system and associated hardware inside the filter house resides in the clean air side of the gas turbine. Thus, it is extremely important that critical steps be taken to ensure the integrity of this location. After installation is complete, it is important to do a walkthrough inspection throughout the entire filter house in order to ensure that all equipment has been installed as per the manufacturer s 23

24 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers recommendations. Damage to painted or galvanized surfaces shall be repaired with appropriate coating protection in order to not compromise corrosion protection of the hardware. Any surface corrosion to stainless steel components or galvanized or painted surfaces (from carbon steel crosscontamination) needs to be removed from the clean air path. Debris in the upper level drain pans and sump tank shall be removed from the evaporative cooler as to prevent clogging of system drains. All surfaces downstream evaporative cooler media and transition (clean air plenum) shall be cleaned or repainted as appropriate to facilitate inspection of the clean air side and trouble for water bypass / carryover location. Inspection windows in the evaporative cooler door and access hatch shall be clean and free of damage (scratches, cracks, etc.) to allow for a clear view of the gas turbine clean air side surfaces. Any objects that are brought in for inspection and maintenance of the evaporative cooler shall be tracked, accounted for, and removed prior to operation. Any loose hardware shall be tightened, secured or removed from the clean air side of the gas turbine to minimize risk of Foreign Object Damage (FOD). B. Evaporative Cooler Commissioning All evaporative coolers shall undergo commissioning per the GE Evaporative Cooler Commissioning procedure prior to initial start up and, during service, a minimum of once a year, at the beginning of the evaporative cooler use season. A copy of the evaporative cooler commissioning procedure is available in the gas turbine Operational and Maintenance Manual (O&M). The basic overview of the procedure includes the following steps: 1. Water Quality Confirm suitability of makeup water per Water Supply Requirement for Gas Turbine Inlet Air Evaporative Coolers GEK Establish frequency of sampling and testing for makeup water and sump quality. See Section V of this document for details. 2. Device Testing and Calibration Verify installation of evaporative cooler, and inlet filter house components. Test and Calibrate evaporative cooler devices to ensure operation after installation or extended shutdown period. 3. Evaporative Cooler Flow Testing Evaporative Cooler Flow test with gas Turbine off to verify flows to evaporative cooler media and appropriate settings of water distribution system devices. Followed by another Evaporative Cooler flow test with the gas Turbine On (typically around 4 hours) to verify proper draining capability of the system during operation and shutdown. 4. Evaporative Cooler Shutdown and Inspection Inspection of Evaporative Cooler during and after turbine shutdown to look for signs of water carryover and bypass. Look for signs of over flooding of upper level drain pans and/or sump tank. Please contact your local GE Energy Services representative for copies of the latest commissioning procedure and/or evaporative cooler O&M manual as applicable. C. Evaporative Cooler Operation and Maintenance During checkout and operation the following items should receive special attention: Media Wetting, Distribution and Blowdown Water Flow rates. The following items need to be addressed (as a minimum) to ensure proper operation and longevity of the evaporative cooler system and its components: 24

25 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers 1. Media Wetting Uneven water distribution will cause too much water flow to one section of the pad and not enough water to another. Wetting of cellulose media may be verified through visual inspection by means of the internal access platforms and ladders provided on the upstream side of the cooler media. Even and uniform wetting of evaporative cooler media is required regardless of configuration except for some minor dry streaks at the center and/or at the ends evaporative cooler modules. Isolated dry streaks may be caused by accumulated debris inside of the distribution header and can be easily corrected by regular maintenance and use of the flushing valves located at the end of each Distribution header. Random and excessive streaking throughout the evaporative cooler media can be attributed to either a high degree of blockage on the distribution header spray holes or issues with media wetting. Media wetting issues typically manifest themselves in the form of water carryover or bypass downstream of the media. Therefore, it is imperative that this media be replaced as soon as a media wetting issue is identified by qualified personnel. 2. Distribution Water Flowrates Depending on the evaporative cooler arrangement, a single horizontal module (level) may be serviced by either a single pump feeding from one side or collectively by two pumps from both sides of the module. Regardless of how many manifolds feed the evaporative cooler horizontal module (level), the total water flow rate to the media will be only driven by the depth of the individual evaporative cooler pad and the resulting top surface area of media. Single face (on left) and Arrowhead filter house (right) arrangements are shown below for reference. General Electric evaporative cooler designs typically utilize 12-inch deep cellulose media pads. These pads have been proven historically to provide a good balance between saturation efficiency, and pressure drop both of which affect performance of the gas turbine. Per manufacturer s wetting guidelines, a 12-inch deep media pad requires 1.5 gallons of water per square foot of top media 25

26 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers area (1.5-gpm H20/ ft2). As a general rule, the following formula may be used to estimate the water flow rate to each level of evaporative cooler media. Distribution Flow Rate (gpm) = 1.5 x Module width (feet) / Number of Pumps These values shall be verified via the flowmeters provided with the evaporative cooler system. The table below highlights the required Distribution header flows based on the specific filter house arrangement. Gas Turbine Arrangement PG Model Series Filter House Module width** Single Pump Header Flow Dual Pump Header Flow 7EA Single Face PG feet 54 GPM 27 GPM 7EA Arrowhead PG7121 N/A N/A 35 GPM 7FA Single Face PG feet 66 GPM 33 GPM 7FA Arrowhead PG feet N/A 42 GPM 7FB Single Face PG feet 66 GPM 33 GPM 9FA Single Face PG feet 90 GPM 45 GPM * 9FB Single Face * PG feet 90 GPM 45 GPM Please note that these values are based on the approximate width for the evaporative cooler module and filter house. These dimensions may vary slightly depending on inlet filter house (MLI A040) vendor. Arrowhead filter houses employ dual pump systems due to their arrangement. It is important to point out that regardless of ambient air conditions (altitude, pressure, temperature or relative humidity), the water flow rate to the cooler media will not change regardless of location and / or season of evaporative cooler operation. Under extremely dry conditions, the water flow to the media may be increased to ensure proper wetting throughout the media bank, however this is done in very rare occasions and always under operator supervision / surveillance as to not compromise the evaporative cooler system and gas turbine. New Design Evaporative coolers are provided with orifice plates and flow meters on distribution line in order to guarantee adequate flow to the cellulose media. Excessive water flowrates to the distribution headers will result in oversaturation of the evaporative cooler media pads and potential risk of water carryover and/or bypass. 3. Blowdown (Bleed-Off) Water Flowrates As discussed in the previous section, excessive water flows can have very adverse effects on the performance of the evaporative cooler due to water carryover and/or bypass. Conversely, providing less than adequate flow to the evaporative cooler media can result on decreased efficiency, and increased formation of solids (scaling) that will severely limit media life and performance. The water used in an evaporative cooler typically contains dissolved solids, which can be capable of both scaling (rendering ineffective) the cooler media and causing turbine corrosion. The mediascaling problem is addressed by constantly and uniformly over-wetting (flushing) the media and limiting the number of effective concentration cycles of the water through bleed-off and make-up (constant dilution). Various methods of controlling blowdown are used to maintain the desired cycles of concentration in the evaporative cooling system. Evaporative rates (and required blowdown) fluctuate constantly due to outside temperature and humidity. The exact amount of blowdown will depend on the ph, alkalinity, hardness, intensity of evaporation, and overall chemistry of the Makeup water source. 26

27 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers Gas Turbine Frame Size PG Model Series Airflow rate Evaporation flow rate Distribution flow rate Total Pump flow rate MS7001EA PG lb/s 40 GPM 170 GPM 210 GPM MS7001FA PG lb/s 60 GPM 200 GPM 260 GPM MS9001FA PG lb/s 90 GPM 270 GPM 360 GPM Please note that these values are based on the approximate dimensions for the evaporative cooler module and filter house. These dimensions may vary slightly depending on inlet filter house (MLI A040) vendor. These values apply to single face evaporative arrangements only. New Design Evaporative coolers are provided with orifice plates and conductivity controllers on the blowdown line in order to guarantee adequate bleed-off to the evaporative cooler system drain. Electronic conductivity control allows for less waste of cooling water by directing water back to the sump tank once the conductivity in the sump tank is back to within allowable limits. Blowdown on units not equipped with electronic conductivity control shall be adjusted periodically during the evaporative cooler running season depending on expected water evaporation rates and makeup water quality (maximum number of attainable cycles). 4. Other Maintenance Considerations At no time shall any of the cooling water flow outside of the areas designated for its containment within the evaporative cooler. Sump water level and pan water levels shall be verified to be within the supplier s allowed limits (refer to the vendor s Operation and Maintenance for details). All drains and associated piping shall be inspected on a regular basis to remove any debris that may prevent proper draining. All internal and external piping shall be checked for leaks and replaced / repaired as appropriate. Heavily fouled or damaged areas in the evaporative cooler media are often a source of carry over. Heavily fouled media should be replaced. Major damage to the media requires the entire pad to be replaced while minor damage should be cut out and smoothed off to reduce risk of water carryover and/or bypass If any visible water (carryover, bypass, flooding, etc.) is found downstream of drift eliminators during Commissioning or Regular inspection, please contact GE Energy Services for full assessment of situation, and recommended corrective action. V. EVAPORATIVE COOLER WATER QUALITY AND TREATMENT Water Scaling resulting from typical Evaporative Cooler operation presents one of the major concerns in Evaporative Cooler operation. Water Scaling on the media will adversely affect both saturation efficiency (evaporative cooling effectiveness) and pressure drop (gas turbine efficiency). For this reason, it is extremely important that we keep strict water quality requirements and establish rigid guidelines for media maintenance and water monitoring in order to ensure proper operation of the evaporative cooler. Such Guidelines are established and discussed in detail in the Water Supply Requirement for Gas Turbine Inlet Air Evaporative Coolers document (GEK ). The Water Supply Requirements document (GEK ) is intended to help the customer in the choice and treatment of water for the evaporative cooler. The use of suitable water is essential in minimizing carryover, preventing corrosion and scale formation and in obtaining the expected service life and performance from the evaporative cooler. If suitable water treatment guidelines are not established and followed, the evaporative cooler and its media may need more frequent maintenance and/or replacement. Furthermore, poor water quality and/or the misoperation of the cooler can result in severe contamination of the gas turbine and have extremely serious consequences in terms of forced outage time needed for maintenance, repair and replacement of gas path components. 27

28 O&M Recommendations for Media Type Gas Turbine Inlet Air Evaporative Coolers In the evaporative cooler, there are three main goals for a water treatment programs: 1. Prevention of corrosion from carryover of solid contaminants into the gas turbine. Carryover into the gas turbine can result in corrosion and fouling in both the compressor and turbine sections. 2. Prevention of fouling, scaling, corrosion and media deterioration in the cooler. Scale build-up will foul the media, affect operating efficiency and reduce the service life of the media. Corrosion will reduce the service life of the framing, sumps, piping, and support systems. 3. Prevent microbiological infestation that can foul the media and affect operating efficiency. It can also produce spore formation, objectionable odors, reduce the service life of the media, and induce corrosion in the system piping and sump. A. Makeup and Recirculating Water Constituent Limits Due to the isolated locations of some of the installations, and the limited water sources often available, the use of the evaporative cooler to condition inlet air for the gas turbine results in some very challenging water control requirements. The water available ranges from brackish, with extremely high mineral concentrations to demineralized water. The evaluation of the water supplies to be used in the evaporative cooler should be done as early as possible. All the critical factors as listed below, which bear on suitability, must be considered in making a choice. The following table contains the Makeup and Circulating water limits for media type evaporative coolers as described in GEK The Circulating water limits are based on the maximum levels allowed for each constituent on the clean air side of the gas turbine. They are driven by the makeup water chemistry and number of cycles allowed. B. Water Scaling Scale formations occur when soluble salts are deposited from the recirculating water due to evaporation. Three main problems are associated with scale formation in evaporative cooling units: Uneven airflow and water distribution which can lead to water bypass and carryover, Increase in system pressure drop due to plugging of the cellulose media, and decreased effectiveness due to reduced evaporation surface area. 28