News. Power Generation 11. ph Control Reduces Acid Consumption in Neutralization Process up to 90 % Perspectives in Pure Water Analytics THORNTON

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1 Power Generation 11 Perspectives in Pure Water Analytics News THORNTON Leading Pure Water Analytics ph Control Reduces Acid Consumption in Neutralization Process up to 90 % THORNTON new instrumentation generated large savings by reducing reagent acid needed to neutralize fly ash slurry and improved reliability of environmental compliance. The process A 500 Megawatt coal-fired power plant on the Ohio River produces massive amounts of fly ash that are carried to a lined 60 acre (24 ha) settling pond as a slurry. The recirculating flowrate to the ash pond runs near 4000 GPM ( LPM) with a ph > 11 due to the soluble combustion products. This water is neutralized with sulfuric acid so the pond water can be recirculated through carbon steel pumps and lines to carry more fly ash from the hoppers. This pond also discharges to the Ohio River during high rainfall events and is subject to regulatory limits. Improvement needed In the past, the acid addition was made by periodic additions from a tanker truck. Without this acid addition, the pumps and lines rapidly scaled, requiring periodic mechanical cleaning. These batch acid additions also produced unsatisfactory mixing and wasted acid as the acid tended to settle to the bottom of the basin and react with the heavily buffered sludge. Acid consumption ran as high as 4000 gallons ( liters) per week and ph of the basin contents varied across its area. ph control system installed To automate the process and maintain more uniform ph levels at all times, a closed loop ph control system was installed. It uses a Mettler-Toledo Thornton ph electrode and housing mounted in a recycle stream. The high flow velocity in that stream keeps the electrode clean and provides rapid response a necessity for good ph control.

2 Transmitter M300. M300 transmitter the heart of the measuring loop A Mettler-Toledo Thornton M300 Transmitter with built-in PID (proportional, integral, derivative) controller provides the readout and control. It is mounted in an electrical box outdoors next to the basin. The M300 analog outputs are configured for both data acquisition for the plant DCS and for the control action. A large metering pump is modulated by the PID analog output and feeds up to 150 GPH (570 LPH) of acid into the turbulent flow. Placement of the acid injection point in a side-stream recycle line was critical as mixing concentrated sulfuric acid with the bulk flow is hampered by its high density and viscosity. Savings realized Once the system was started up, operators quickly realized that the automatic neutralization control was reducing acid consumption by nearly 90 %. This was due to the acid neutralizing only the water layers without it settling down into the sludge. This cost savings quickly paid for the control system. It also gives greater confidence in meeting environmental limits 100 % of the time. Two main benefits of the M300 transmitter Sensor diagnostics The M300 includes continuous sensor diagnostics to detect aging or failed ph sensors which provides added assurance of reliable measurement and control. Automatic buffer recognition For calibration, it provides automatic buffer recognition which identifies the buffer solution being used and automatically corrects for its temperature characteristic. This simplifies calibration and eliminates a source of error, especially where there could be temperature extremes in an outdoor installation such as this. This is just one area where the THORNTON M300 and sensors excel. They are also used to monitor and control make-up water treatment, cycle chemistry, stator cooling, cooling towers and waste water with parameters of conductivity, dissolved oxygen and ORP as well as ph. Publisher / Production Mettler-Toledo AG Process Analytics Im Hackacker 15 CH-8902 Urdorf Switzerland Illustrations Marcor purification US Pure Mettler-Toledo AG Acid Ash pond Ash hopper Subject to technical changes. Mettler-Toledo AG 07/08 Printed in Switzerland. Neutralization of fly ash slurry in a coal-fired power plant. 2 METTLER TOLEDO Power News 11

3 M300 if High Precision is Asked Reliable Measurements of Conductivity and Resistivity Precise measurements of resistivity and conductivity with M300 measuring systems allowed fulfillment of project requirements and prevented breach of contract. General conditions of the project One of the leading engineering companies in China has been developing water treatment operations over the past 20 years. This project consisted of setting up a water treatment system with a capacity of 150 tons / hour. It was planned to apply membrane water-treatment techniques including ultra-filtration, double pass reverse osmosis and electro deionization (EDI). To get the order for this project the engineering company had to consider only suppliers submitted by its customer. Project failed to meet specifications The specifications required a resistivity value of 16 MΩ cm (at 25 C / 77 F) in the EDI facilities during 90 % of the running time. However, tests showed that the resistivity was between 6 to 18.7 MΩ cm which turned out to be a disaster both in terms of profitability and of long term reputation for the engineering company. A very quick solution had to be found! METTLER TOLEDO s experience Trouble shooting showed that due to improper operation salt leakage occurred in one or more EDI modules. The replacement of these modules did not improve the poor results at all. Closer investigations showed that everything corresponded with former successful projects, except the choice of the installed analytical instruments to measure resistivity! It was then decided to contact Mettler-Toledo Thornton to take advantage of their long term experience with these measurements. METTLER TOLEDO solution and customer satisfaction Resistivity measurements using the M300 transmitter from METTLER TOLEDO showed that the resistivity from the produced-water outlet of the EDI facilities to the flow-through cell was very good, and within the range of to MΩ cm. After this experience the analytical instruments for supply-water conductivity and produced-water resistivity were replaced in all three sets of EDI facilities by Mettler-Toledo Thornton M300 measurement systems. Main reasons for measurement errors: 1. Unable to carry out precise and effective temperature compensation 2. Poor rejection of electromagnetic interference by the cable transmitting the conductivity measurement signal 3. Low system measuring accuracy 4. Improper sizing of the conductivity measurement sensor Transmitter M300. METTLER TOLEDO Power News 11 3

4 Measurement of Organics in Power Plant Waters TOC Instrumentation in Power Plant Water Detection of organic contamination is critical in the power industry in achieving the purest water possible. THORNTON TOC instrumentation ensures accuracy and fast response in real-time measurements. Costly problems Organic contamination can foul resins in make-up and condensate deionizers and require more frequent resin cleaning and replacement. It can break down to organic acids that lower the ph of early condensate and cause turbine corrosion. It can also deposit along with other contaminants onto heat exchange surfaces and significantly reduce efficiency. Additionally, it can cause foaming in boiler drums and increase carryover of other contaminants into the steam. Organics are a concern in plants where any of these problems occur, and accurate, on-line measurement of TOC concentration is the first step in its reduction. Improvements Mettler-Toledo Thornton has developed on-line TOC instrumentation based on high intensity ultraviolet oxidation of a continuously flowing sample. Organics are oxidized to carbon dioxide, and conductivity measurements are made both upstream and downstream of the UV lamp. The first measurement accounts for any conductive contaminants already in the sample while the second measurement detects the increased conductivity due to added carbon dioxide. The conductivity measurements and their difference are compared using a correlation curve to produce a consistent TOC measurement. Make-up and steam-water Measurements TOC measurement of make-up water is a straightforward process capable of detecting residual surface water organics or DI resin breakdown products. On the other hand, measurement of TOC in the steamwater cycle is not as simple as in make-up water. Most cycle chemistry treatments raise the ph with ammonia to a range near 9. If the sample was run directly through the direct UV oxidation TOC instrument, the carbon dioxide produced by organics oxidation would be neutralized by the ammonia, the conductivity would not increase, and TOC could not be determined. The measurement cannot be made directly. For this reason, it is necessary to take the sample after a cation exchange column, the same as for cation (or acid) conductivity measurement. In fact, Thornton s 5000TOC sensor also provides the cation conductivity measurement. The sample after cation exchange will have the ammonia removed and the ph lowered so that additional carbon dioxide adds to the conductivity and TOC can be METTLER TOLEDO Power News 11 4

5 Sample inlet Pressure control valve Conductivity sensor (1) UV oxidation Conductivity sensor (2) Flow sensor Flow control valve Oxidized sample outlet Flow path of a direct conductivity TOC sensor The THORNTON 5000TOC and 770MAX platform ensures analytical accuracy, fast response and reliability, and can help determine in real-time if organics are being reduced in your system. Transmitter 770MAX. THORNTON 5000TOC sensor. determined reliably. It is necessary to use high grade cation exchange resin that is fully rinsed and does not contribute organics of its own. THORNTON solution The THORNTON 5000TOC Sensor and 770MAX Transmitter provide excellent results on cycle chemistry samples when used with this kind of sample conditioning. The THORNTON 5000TOC and 770MAX platform ensures analytical accuracy, fast response and reliability, resulting in real-time determination if organics are being reduced in your system. Key benefits of the THORNTON 5000TOC sensor Continuous flow design provides rapid TOC response with complete oxidation No gases or reagents to handle, store or replace and no moving parts minimize routine maintenance and service requirements Smart sensor design reduces installation and setup time Real-time continuous monitoring for precise data trending and better process control Wide dynamic operating range meets the needs of pure and ultrapure water applications Two TOC measurement points with one 770MAX instrument for cost-effective installation Compact NEMA 4X rated enclosure for demanding industrial environments Meets ASTM D5173 standard test method for on-line TOC monitoring Conductivity sensor and measurement calibration are traceable to NIST and ASTM Link for further information This article is based on the Mettler-Toledo Thornton white paper: Measurement of Organics in Power Plant Waters. To read the full text of this paper, and other readings on the importance of conductivity measurements in pure water applications, please visit: METTLER TOLEDO Power News 11

6 Process Analytics Product Catalog New Edition 08 / 09 Available Get an overview of the latest INGOLD and THORNTON products available for your process application with the new product catalog 08 / 09. The catalog offers comprehensive overview on product features and specifications, benefits and recommended application areas, order details and much more for process analytics measurement solutions. The product catalog covers complete measuring solutions for the parameters: ph Dissolved oxygen and O2 in gases Ozone Dissolved CO2 Conductivity Turbidity TOC Flow The featured product range includes: Electrodes / sensors Housings Process connections Transmitters / analyzers Cleaning and Calibration systems Cables Accessories Order your copy of this useful desk tool today! Mettler-Toledo AG Process Analytics Im Hackacker 15 CH-8902 Urdorf Switzerland Visit for more information