Operation & Maintenance of Power Plants
Maximising turns Te increasing concentration of minerals which is a result of water evaporation in cooling towers creates difficulties for heat exchange processes. Mineral deposits (scaling) in the pipes of heat exchangers affects their heat transfer performance. Bacteria too can produce organic residues (fouling), which also compromise process efficiency. Te continual automatic measurement and control of pH, ORP, conductivity, alkalinity, hardness, corrosion and other factors avoid these problems. Te use of an automated controller with integrated networking capabilities – like Bürkert’s new multi-channel mxCONTROL 8620 – in combination with the necessary analytical sensors, valves, flow transmitters and switch’s, allow a normal conductivity only controlled cooling tower to go from a two turn system (ratio between water in and water out of a cooling tower) to a seven or eight turn system. Tis increased number of turns means less water is required to remove the same amount of heat from the plant. Some water stressed regions have taken note of this and are even offering financial incentives for plants to upgrade their controller in an effort to conserve water.
Fig. 2. Bürkert´s mxCONTROL 8620 can be used in general process and chemical control applications such as cooling towers, boilers, dead end or cross flow membrane filtrations systems. It saves time and space by allowing parameterization and data logging of a wide number of control variants via an SD card slot, serial interface or USB connection.
added periodically over a two week window. It is often the case when biocide chemicals are added, loop conductivity increases. Tis being the case, it is some times beneficial to bleed to a conductivity set point that is lower then normal. Tis is called the Biocide PreBleed Setpoint. To prevent bleeding expensive chemicals to drain, an internal interlock prevents the bleed valve from opening while chemicals and biocides are added to the system even if high conductivity set points are reached. In addition, a time delay ’lock out’ prevents the bleed valve from opening for a predetermined period of time after the chemical is added to ensure that the added biocide has maximum effective contact time in the system to kill all unwanted organics.
Cooling system corrosion is another unwanted expense factor. Accurate pH and conductivity readings cannot always guarantee a low corrosion environment throughout the system. A corrosion sensor is often connected to the control unit. If a predetermined corrosion limit is reached, the control unit will shut down the pH dosing module and energize the general alarm alerting local maintenance to investigate. In addition, corrosion inhibitor chemicals can be added based on a feed water ratio automatically.
Automated all-rounder With the development of mxCONTROL 8620 – a state-of-the-art modular multichannel control system – Bürkert responded to the trend for full automation and cost saving. By allowing parameter setting of a wide number
Te central control unit regulates the feed of chemicals that prevent corrosion, scaling and fouling processes. Biocides for example are added over a predetermined period of time as determined necessary during an initial water analysis. An example of chemistry cost savings is the Biocide pre-bleed function. Continuous monitoring and effective control of biocides provide greater protection from harmful bacteria. Biocides preventing legionella, algae and other bacteria, are
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of control variants via an SD card, serial interface or modem connection, the mxCONTROL 8620 saves time, space and equipment costs in cooling towers, as well as in boilers, dead end and cross flow membrane filtration systems. With the launch of the mxCONTROL, users no longer have to select a model type that fits their specific application. Instead, via customised software and a standard SD card, the number of control variants is unlimited, making the mxCONTROL a true ’one-size-fits-all’ solution. Te mxCONTROL 8620 is specifically designed for seamless integration into countless chemical or process control applications. Its modular design integrates multiple, customer-selectable inputs and outputs (4–20mA, Pt100, digital, relay and transistor), combines these with various control parameters resulting in dozens of flexible configuration possibilities. In addition to normal chemistry control, the 8620 can also integrate control of a large number of traditional process variables such as pressure, temperature and level, removing the requirement in many automated systems for external devices to cover the same functions. Understanding the needs of the water treatment users, and combining these with the processing power of the mxCONTROL, has led to the introduction of intelligent control of the water parameters that significantly reduces waste by avoiding unnecessary or untimely dosing and bleeding-off.
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