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Product category: Power Industry Process News
News Release from: ABB Automation Tech (Instrumentation + Automation) | Subject: AW600
Edited by the Processingtalk Editorial Team on 16 October 2006

Water quality control in power
generation

Groundbreaking technology for monitoring contaminants in water-intensive industrial processes such as power generation has been incorporated in the latest ranges of water analysers from ABB

World population crossed the six billion mark in June 1999, according to the US Census Bureau This means that the earth's population is over 3.5 times the size it was at the beginning of the 20th century, and roughly twice its size in 1960

This explosive growth has created an unprecedented demand for energy, leading to further exploitation of the planet's already limited natural resources.

The surge in energy demand can only be met through the adoption of sustainable production practices and a drive to achieve higher levels of efficiency [References 1, 2].

To achieve greater efficiencies in power generation processes, the ABB AW600 is providing advanced monitoring of the chemical composition of the steam-water cycle.

Recognizing the need to conserve resources, ABB is committed to the development of energy efficient products and processes that yield a reduced environmental impact over their complete life cycles.

The next generation of instrumentation products from ABB is embracing global environmental challenges, while capitalising on the significant business efficiencies brought about through the company-wide Common Components Development process.

The critical role of water quality measurement in power generation.

In the power generation process, water is heated in boilers and converted to steam, which is used to drive turbines and generator sets to produce electricity.

Many different fuel types may be used to generate electricity, but the production of huge quantities of steam in the energy conversion process is universal.

For example, a typical fossil-fuel power station converts around 650 tons of water into steam per hour, in each of four 160 MW boilers.

This represents around two million tons of water usage per month.

With such a large throughput of water in the steam-raising process, the chemical quality of the water used is critical [Reference 3].

Even the smallest concentration of contaminant or minor excursion in water chemistry can have serious and expensive consequences in relation to performance, reliability, efficiency and safety.

Analytical measurements are essential therefore, to monitor contaminants and to minimise corrosion in the steam generating plant.

Water quality monitoring in power generation represents a core market for ABB and is addressed through a comprehensive range of chemical measurements.

Silica, second only to carbon as the most prevalent element in the lithosphere, and phosphate, used as a pH reagent to limit corrosion, are two of the many such substances that must be monitored closely in boiler feedwater and condensate.

Even the smallest concentration of contaminant or minor excursion in water chemistry can have serious and expensive consequences in relation to performance, reliability, efficiency and safety.

Silica is a naturally occurring substance that is difficult to remove from water.

At high temperatures and pressures it is volatile, and is carried over with the steam and deposited unevenly on the superheater tubes and turbine blades.

Silica forms tenacious deposits that are very hard and resemble porcelain.

Even small amounts of silica can cause significant loss of power generation efficiency and result in serious mechanical damage.

Minor leaks in the condenser can also contribute to silica contamination in the steam-water cycle.

Constant monitoring of silica at a number of points in the steam-water cycle is critical to prevent boiler and turbine damage.

Phosphate, on the other hand, is added to the water in some power stations to control the pH tightly throughout the steam-water cycle, thus minimising corrosion through -acid or caustic attack.

It too must be monitored constantly to avoid expensive corrosion in the steam-raising tubes.

The cost of poor water quality.

Water chemistry problems lead to corrosion failure, super heater fouling and/or chemical deposition on turbine blades.

This results in efficiency losses and ultimately, plant downtime, which in turn contributes to increased electricity generating costs.

A one-week boiler shutdown in a typical power station, caused by an acute water chemistry excursion leading to corrosion and chemical deposition, is estimated to cost around US$4 million (US$0.2 million for repairs and chemical cleaning, and US$3.8 million for lost production capacity).

A catastrophic failure resulting from poor water quality would take even more time and money to repair.

It is not easy to estimate the value of good water-quality control through chemical measurements, but the following data, from US fossil fuel power utilities, reported in the mid-1980s, are still relevant today [Reference 4].

Around half of forced power generation outages are corrosion related.

More than US$3 billion per year in operation and maintenance costs is due to corrosion and chemical deposition.

More than 10 percent of the cost of electricity is due to corrosion related costs.

For a 100 MW unit, a one percent loss in efficiency represents around US$150,000 annually in increased operating costs.

The AW600 Silica Analyser.

The new AW600 analysers for silica and phosphate are the most advanced water quality analyzers in the market today.

Taking into account the current issues and future challenges facing power plant operators, the AW600 has a low environmental impact throughout its life cycle.

It also delivers the lowest cost of ownership of any comparable water quality analyser.

Asset management features and communication capabilities designed into the product help deliver greater efficiencies in the power generation cycle.

What customers get is a high quality water analyser that allows them to control the process, achieve cost and reliability targets, manage assets (plant and instrumentation) and ensure compliance with local and international regulatory controls.

Customers also realise significant cost savings through lower reagent and consumables costs, and lower service costs.

Owing to the simplicity of design and low maintenance requirement of this analyser, the skill level of operators can be downgraded.

With state-of-the-art communication capabilities, internal diagnostics, preventative maintenance functions and data trending routines, all incorporated in the AW600, customers can streamline business processes by only committing resources when required, or at pre-scheduled times.

Advanced communications and diagnostic features in the AW600 Analyzer allow the plant operator a high degree of instrument control and asset management capability.

Data handling, storage and security allow the user to perform entirely new tasks and functions, to extract greater value from process data and even to automate certain reporting tasks.

The new, modular design of the AW600 eliminates some of the frustration previously experienced by users and service personnel when undertaking routine maintenance tasks, troubleshooting or repairs.

AW600 and the environment.

The positive environmental aspects and product life cycle cost benefits of the AW600 are significant, especially when compared to contemporary analysers.

The AW600 consumes around one-fifteenth of the volume of reagents used in conventional analysers.

This results in lower reagent costs and less waste.

The weight and volume of materials used in the construction of the AW600 analyser has been reduced by about 60 percent.

The new design complies with the latest WEEE and RoHS directives, using environmentally friendly materials, designed for easy dismantling and cost-effective -recycling.

Service intervals have been extended to 90 days - about three times longer than currently needed for the maintenance of competitor's measurement instruments.

Alongside this, service times have been reduced by two-thirds, yielding significant savings in service costs.

Considerable thought has gone into adding user-friendly features.

For instance, viewing instrument status remotely via the Internet and using SMS instant messaging whilst on the move precludes the need for frequent service visits.

Even inadvertent spillage of potentially harmful chemical reagents is guarded against by incorporation of secondary containment measures in the analyser design.

Design considerations.

Of all requirements, reliability and accuracy of measurement were paramount.

Over and above that, the design team has taken an exacting and complex analytical chemistry and packaged it into a simple-to-operate modular product.

Where reliability and accuracy risks were considered high, such as in the reagent transport system, well-established technologies were employed.

In those areas where the technical risks were lower, bespoke solutions were developed on the basis of significant breakthroughs.

For example, the videographic user-interface, optical sensing module and internal diagnostic sensors were three areas where technical innovation was needed to deliver value-generating functionality.

The design team met the challenge of significantly reducing manufacturing costs and lead time by creating a modular design, in which the primary parts and sub-assemblies were constructed so as to streamline the manufacturing process.

The emphasis was on elimination of labour-intensive steps, purchasing of pre-tested parts, and sourcing of materials from low-cost countries.

To achieve this aim, more than 80 percent of the material content has been sourced from China and the Far East.

A significant design goal was to utilise a high percentage of components from the ABB Common Components Programme.

The advanced HMI, common software framework and common fieldbus device were all created within the Common Components Programme.

The AW600 electronics enclosure was also developed as a Common Component that will be used for future ABB Instrumentation products.

All of the major AW600 modules (electronics unit, wet section components and wet section enclosure components) will also be used in future analytical products, thus saving significant development investment.

It was considered of prime importance that the AW600 deliver additional value to the customer, beyond that of basic analytical measurement.

This value-addition was accomplished by the creation of a hugely powerful graphical user interface (GUI), the ABB advanced HMI common component.

The GUI is based on the newly released SM500F Graphical Recorder hardware.

The application firmware is specifically written to give the user a more comprehensive visualisation of the measurement of interest, the status of the instrument and in-context information about the process or application.

For example, the user can monitor up to six process streams and review historical data and instrument events as graphical trends or tabular data.

The AW600 also allows the user to save data via a number of optional levels of security to a Secure Digital (SD) card for later review and reporting.

A further benefit of the SM500F module is its ability to update instrument firmware as product improvements, newer features and additional measurands are added to the platform.

A battery of internal diagnostic sensors within the AW600 is used to monitor the real time status of the instrument.

Information, such as measurement time remaining, based upon reagents and standard solution liquid levels can be assessed and alarms pre-set to alert the user, when replenishment of consumables is needed.

Internal flow and liquid level sensors monitor pump efficiencies and notify the user, when preventative maintenance is deemed necessary, so that future failure can be averted.

Regular automatic calibrations and compensation corrections can be set up to reassure the user that the measurement is valid at all times.

Communications.

The very latest communication capabilities are included in the AW600 analyser.

Profibus DP-V13 provides cyclic bus connectivity to the latest ABB Distributed Control System, the System 800xA.

Further advanced communications are provided with e-mail messaging and Internet connectivity via an Ethernet module.

An associated PC software application allows the user to interrogate the AW600 in real time from a desktop PC or from a laptop using mobile technology.

Users can receive updates and status information on their mobile telephones using the SMS text messaging service provided via a GSM module.

Future adaptations will allow the user to operate and configure the AW600 using the wireless capabilities of a mobile computing device, such as a PDA or Pocket PC.

The AW600 instrument platform.

The silica and phosphate analysers represent just the first two products to be released from the new AW600 platform.

Future water quality analyzers based on the AW600 will include numerous applications for potable water and wastewater.

They will be targeted at core markets, such as power generation, municipal water and chemical processes.

This article was provided by Eric D'Costa of ABB Analytical Instruments Stonehouse, UK for the ABB Review.

References.

[1] A Bursik: Power Plant Chemistry 1 (1999) 5, 16 "19".

[2] A Bursik: Power Plant Chemistry 4 (2002) 1, 18 "21".

[3] A Whitehead, R.G Rowe: Power Plant Chemistry 2 (2000) 8, 471 "477".

[4] J.A Matthews: Power Plant Chemistry 3 (2001) 4, 203 "208".

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