Power Generation Newsletter 13 E Aug09

Transcript

Power Generation Perspectives in Pure Water Analytics 13 News THORNTON Leading Pure Water Analytics Protect Co-generation Plant Equipment by Measuring TOC To fully protect the components of a co-generation plant, it is necessary to continuously monitor both mineral and organic levels of contamination. This requires total organic carbon (TOC) as well as conductivity measurements. Installation In the city of Guaíra in the state of São Paulo, Brazil a sugar and ethanol cogeneration plant is at full capacity producing as much as 20 MW by burning cane in a set of seven boilers. This is sufficient energy to provide electrical power for a city with a population of 40,000. The sugar plant is owned by Colorado Mill, part of the Colorado Group which is a large Brazilian conglomerate company operating in the fields of energy, food, transportation and agricultural equipment. Co-generation process In the power generation cycle of the sugar and ethanol plant, steam is generated to drive steam turbines and to produce power as well as heat for the production processes. The pure condensate water which is recirculated to the boilers is subject to organic contamination. In this plant the main source of this contamination is sugar. Problematic organics During raw sugar production the sugar cane juice is heated, using steam, to remove excess water. The condensed steam from the process is then fed into a series of boilers to regenerate pure steam in the boiler house. If organics contaminate the condensate during the evaporation process this can be catastrophic to the power generation cycle. In the boilers, the organics can be deposited onto the heat exchange surfaces, which significantly reduces their efficiency. Organics can also cause foaming and carryover of other contaminants into the steam, which can corrode expensive turbines. When organics are present in the pure water condensate and are exposed to elevated temperatures in the boilers, partial thermal degradation and oxidation of the organic contaminants occurs. This process produces organic acids which can lower pH and lead to additional corrosion and damage to power generation components. Early quality control of the initial condensate produced from the evaporation process by measurement of key parameters such as total organic carbon, pH and conductivity guards against contamination, subsequent deposits and corrosion. TOC measurement in boiler feedwater Condensate purity is monitored for mineral contamination by conductivity measurements. However, organic compounds like sugar may contaminate the condensate. These organics are generally non-conductive and cannot be detected by a conductivity sensor. For detection of organics they are first converted to a conductive species in pure water. In TOC instrument operation, organics are oxi- dized and produce carbon dioxide which, when dissolved in water, forms carbonic acid, a conductive species which is then measured. In order to detect organic contamination, a Mettler-Toledo Thornton 5000TOC sensor monitors the boiler feedwater. The temperature of the condensate was found to be too high, so a sample conditioning coil was placed at the sensor inlet to reduce the temperature to near ambient conditions. A particulate filter was also placed in the sample line. The 5000TOC sensor is used with the THORNTON 770MAX transmitter, with both mounted on a panel near the sample source. Alternatively, the sensor and transmitter could have been located separately to allow the sensor to be close to the sample for fast response, while the 770MAX transmitter could have been located up to 90 m (300 ft) away in a control panel for convenience of readout and alarm display. An upper alarm limit for TOC of 350 ppb was set on the 770MAX for process control. Limits for both TOC and conductivity were defined for the purposes of controlling the Publisher / Production Mettler-Toledo AG Process Analytics Im Hackacker 15 CH-8902 Urdorf Switzerland Illustrations Mettler-Toledo AG Platte Generating Station Marlee, Avatavat, Silverv | Dreamstime.com Subject to technical changes. © Mettler-Toledo AG 08/09 Printed in Switzerland. 2 METTLER TOLEDO Power News 13 quality of the boiler feedwater, protecting from both conductive and non-conductive contaminants. If TOC exceeds a set point limit, the condensate is diverted to a water treatment tank. In this application the inorganic conductive species limit of 15 µS/cm was chosen. The Colorado Mill plant records of conductivity and TOC measurement showed that organic and inorganic contamination do not always coincide. It is possible for the water to be contaminated with organic compounds without being contaminated with conductive substances. In this application there were several occasions when the water from the power generation plant was sent to the tank for treatment because the TOC level was too high. The in-line TOC measurement is a key monitoring parameter to protect the power generation plant. Why a TOC measurement? TOC is a complementary measurement to conductivity for detection of non-conductive organic substances, e.g. sugar. ■ Sugar in condensate can decompose to organic acids. This leads to a pH drop which causes turbine corrosion. ■ Too much sugar leads to deposition on heat exchange surfaces and decreased efficiency. ■ If TOC exceeds a set point limit, condensate is sent to a water treatment tank. THORNTON 5000TOC sensor Transmitter 770MAX User benefits: Continuous TOC monitoring helps to protect turbines from corrosion caused by organic acids. ■ Reducing the risk of deposits forming on heat exchange surfaces leads to higher process efficiency and reduces downtime. ■ Optimized condensate recycling de- ■ The 770MAX multi-channel, multi- creases the costs for fresh water supplies. ■ Low investment and maintenance costs of the Mettler-Toledo Thornton 5000TOC / 770MAX offset more expensive alternatives. parameter transmitter allows simultaneous measurement of complementary pH or conductivity values at a reduced cost. If you want to control TOC at your plant, go to: www.mt.com/TOC Sample Panel Upgrade With Multi-Parameter Instrumentation When replacing an old power plant sample panel and instrumentation, there are many logistics issues to resolve. This upgrade was accomplished Efficient Instrument Replacement smoothly without a plant shutdown thanks to a unique Smart Sensor concept. Need for upgrade The Platte Generating Station, a power plant owned and operated by the City of Grand Island, Nebraska, USA has a 100 megawatt base-load coal-fired unit that was commissioned back in 1982. The plant uses amine and phosphate cycle chemistry in the drum boiler. Analytical measurements are made on demineralized makeup water, boiler feedwater, boiler blowdown, saturated steam and condensate, plus cooling tower water. After a quarter century of operation its cycle chemistry instrumentation and sample panel had aged to the point that replacement was needed. The overall sample panel replacement program was planned to provide state-ofthe-art instrumentation with greater accuracy, more compact components and a few additional measurements. Having ground water as the sample cooling medium has had its good and bad points. The high mineral content of the well water required a cooling water isolation system to reduce scaling of the sample coolers and allow easier cleaning (the isolation system was mounted one floor above the instrumentation). On the other hand, the ground water provided very consistent temperature which eliminated the need for expensive secondary cooling equipment. measure different parameters from up to four sensors, allowed convenient grouping of parameters for each sample within a small panel footprint. Instrument selection Platte Station personnel in discussion with their sample panel manufacturer, Waters Equipment, decided the THORNTON 770MAX instrument platform and sensors would best meet their measurement requirements. This multi-parameter instrument model provided simplicity and uniformity of operation plus minimized spare parts requirements. The ability to Highly accurate temperature compensation, especially for cation conductivity, is particularly important. A sample may be cooled very close to the reference 25 °C but by the time it has passed through a cation exchange cartridge and lengths of sample tubing, its temperature will have been strongly influenced by the air temperature around the panel which is likely to have daily and seasonal changes. The proven The use of sensor quick disconnects also made the 770MAX systems appealing to the maintenance technicians. Appropriate THORNTON Smart Sensors were selected for 13 points, including parameters of specific and cation conductivity, pH, ORP and dissolved oxygen. METTLER TOLEDO Power News 13 3 Best Practice Simplify your process with multi-parameter solutions The continuous stream of data that in-line measurement provides lets you know that your processes are working as they should, and informs you the instant that they are not – helping you maximize production, and saving on lab costs. THORNTON temperature compensation accommodates this much better than other instrumentation. The Smart Sensors maintain their identity and calibration data in imbedded memory for immediate recognition by the 770MAX instrument when they are connected. They also retain much of the configuration data so that if the instrument were ever replaced, the replacement unit would require very little additional configuration. With plug-in sensor patch cords and output signal terminals, any exchange could be accomplished very quickly and only a single instrument is needed as a spare part for four different parameters. Installation Set up of the new panel at Platte Station was unusual in that there was room for it to be installed next to the old sample panel before the old one was removed. This allowed the changeover to be done 4 METTLER TOLEDO Power News 13 smoothly during normal operation of the plant. There was no shutdown. Operation with the new equipment has been very successful with measurement signals going to the plant data acquisition system for convenient monitoring and review. Future requirements Additional need was later identified for measurement of makeup water deionizer regenerant concentrations. The acid and caustic are purchased at high commercial concentrations and must be diluted accurately for efficient ion exchange resin regeneration. In-line measurement will allow continuous monitoring of these concentrations without frequent handling of the hazardous chemicals during grab sample density measurements. Mettler-Toledo Thornton conductivity and multi-parameter instruments provide direct concentration readout and can accommodate both measurements with two sensors and a single 770MAX or M300 Discover more at: www.mt.com/THORNTON instrument. The measurements are temperature compensated specifically for the particular chemical characteristics. Mettler-Toledo Thornton instrumentation has been found to be fully applicable for most in-line analytical measurements in the power plant, including cycle chemistry, makeup water treatment, stator cooling, wastewater, cooling towers and scrubbers. For more information, go to: www.mt.com/770MAX Calibration System for Conductivity Sensors Ensuring Precise Performance of Conductivity Sensors To ensure your process water is as pure as it should be, use of highly accurate conductivity measurement equipment is vital. The Autoloop ensures your THORNTON conductivity sensors are operating reliably and precisely. Avoiding corrosion In thermal power generation, pure steam is the bloodstream that transfers heat energy to produce electricity. Steam and water are in contact with some of the most expensive components of the plant at conditions that can cause corrosion, erosion, deposition and scaling. Proper water quality and treatment are essential to efficient and safe operating conditions. The most reliable measure of water quality is conductivity in all its forms: specific, cation (acid) and sometimes degassed. EPRI, VGB, Eskom and other guidelines place great emphasis on conductivity limits in each part of the steam / water cycle as well as the quality of the makeup water going into the cycle. THORNTON, a leader in conductivity THORNTON has been a leading producer of conductivity sensors for UPW applications for decades. A significant part of our success has been due to the development and use since the early 1990s of Autoloops; a series of UPW recirculating systems used as internal calibration tools for conductivity sensors. In fact, other instrument manufacturers come to Mettler-Toledo Thornton for the sensors and certification they need to calibrate their own equipment. brated simultaneously. This flexibility in calibration translates into faster cycle times to THORNTON customers for sensors returned for recalibration. Calibration facility Our Production and R&D teams designed the latest Autoloop system for the test and calibration of all new and in-field UPW conductivity sensors manufactured by THORNTON. The Autoloop is constructed from state-of-the-art materials to enhance the reliability of the calibration process and to protect against possible contamination or undesirable influences. The Autoloop has a rigorous cleaning and calibration procedure which is designed to guarantee THORNTON sensor accuracy and traceability to meet and exceed the highest industry standards. Proper calibration of the conductivity cell and embedded temperature sensor is essential to the accuracy and compliance of any conductivity measurement system. With support from the Autoloop, MettlerToledo Thornton continues to set the global standard for precision, calibration and traceability of conductivity sensors. Production calibration At the completion of each sensor calibration, a unique certificate and identification bar code are automatically printed. Each calibration certificate provides all cell constant and temperature factors for the sensor with traceability to both NIST temperature and ASTM D1125 and 5391 conductivity standards. Discover more at: www.mt.com/Cond The Autoloop is actually comprised of two separate recirculating water systems. In both loops, multiple testing modules are used in parallel so that sensors of various designs and cell constants can be cali- METTLER TOLEDO Power News 13 5 The THORNTON Solution One Transmitter for Multi-Parameters for TOC, pH, Conductivity, DO … THORNTON solution Wide range of instruments for your processes … Mettler-Toledo Thornton is the market leader in critical ultrapure and pure water analytics. Our 770MAX instrument is a multiparameter meter with a broad range of measurement sensor options. The in-line 5000TOC rapidly detects organic contamination in real time. As well as TOC, THORNTON produces sensors for monitoring pH / ORP, DO2  / DO3, conductivity, flow and pressure. Flow Sm ■ 770MAX multi-parameter transmitter ar t ■ 5000TOC sensor for continuous Total Organic Carbon measurements ■ pH for ultrapure water applications ■ 2-electrode, 4-electrode and inductive conductivity sensors pH / ORP DO2 / DO3 6 METTLER TOLEDO Power News 13 THORNTON benefits ■ All-in-one supplier with sensors for all your pure water analytics needs ■ Multi-parameter transmitter capabilities saves panel space and lowers costs per parameter ■ 5000TOC Pressure / Tank level Transmitter 770MAX allows a real-time TOC measurement, in-line, all the time ■ No Sm gases or reagents to handle, store or replace for TOC sensor; absence of moving parts minimizes routine maintenance ar t ar t Sm Sensor technology offers “Plug and Measure” communication from sensor to transmitter Sm ar t ■ Smart ■ Sterilizable sensors designed for exceptionally long lifetime Conductivity TOC METTLER TOLEDO Power News 13 7 Get in-line with METTLER TOLEDO Boiler Blowdown Conductivity Measurement Without Sample Cooling Measuring conductivity in-line using THORNTON’s new High-Tem­ perature High-Pressure Boiler Conductivity Sensor can help to reduce the need for boiler shutdown, cleaning and repairs, and can save significant money over time. Simultaneously, continuous measurement and control conserves energy and treatment chemicals by eliminating excessive blowdown going to waste, while also minimizing corrosion and scaling compared with manual measurement and control. www.mt.com/THORNTON Mettler-Toledo AG Process Analytics Im Hackacker 15 CH-8902 Urdorf Switzerland www.mt.com/pro Visit for more information