Design & Operation Considerations for Condensate Polishing A.Govindan*, R.Rajkumar Siemens Water Technologies *corresponding author: Siemens Water Technologies, Colorado Springs , CO, USA Phone:+1(719) 550 2025 Email: [email protected]

ABSTRACT : This paper briefly explains the need for Condensate Polishing and its benefits. It then goes on to discuss in detail the extremely crucial aspects of polisher internals design, key design criteria and resin separation technology which play a pivotal role in determining performance of the Condensate Polishing system efficiency of the power plant.

consequently having an impact on the entire steam cycle

Keywords FullsepTM, Resin cross-contamination, Inlet distribution, Bottom collection system, CFD, simulation, inlet distribution

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BACKGROUND Globally, the demand for electricity is set to grow faster than any other form of energy. Demands are expected to rise almost 70% from 2010 to 2035, or 2.2% year on average. Over 80% of this growth is anticipated to come from non-OECD countries with China and India contributing almost half of this demand. Bulk of the projected capacity additions is expected to come from coal and gas fired power plants and wind power as illustrated below. Coal Fired generation dominates as the main fuel source in non-OECD countries (~40%). The average thermal efficiency of coal fired power plants increases from 39% in 2010 to 42% in 2035 as advanced plants including supercritical, ultra-supercritical and integrated combined cycle (IGCC) designs are expected to be built. By 2035, almost 20% of these plants are likely to have these advanced designs.

Source: International Energy Agency (IEA) World Energy Outlook 2012

China continues to contribute the largest increase in coal fired generation, accounting for over two-thirds of the Global increase. By 2035, China accounts for 46% of the global coal fired generation up from 38% in 2010. India is expected to overtake the United states as the second largest generator coal fired power generation by 2035. In ASEAN, Key growth countries such as Vietnam, Indonesia, Thailand and Malaysia have majority of their future power generation from Coal Fired power plants. In essence, Coal fired power generation continues to be a major part of the fuel mix Globally and Condensate Polishing attributes as a critical component in these plants to ensure availability, reliability and assist in achieving optimum performance.

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INTRODUCTION: Condensate is formed after steam from a boiler has gone through a turbine to produce electric power and is condensed in the condenser by the cooling water. Condensate may also include heater drains or drips from staged heaters used in the steam cycle loop. This condensate is collected in the condenser/hotwell and eventually reused after it undergoes a series of staged heaters and deaerators in the pre-boiler system to produce steam again as illustrated in Figure 1. Demineralized make-up water is also added to the condenser above the cooling tubes to gain partial de-aeration. This make-up water is usually 1% of the condensate flow rate in Utility boilers. Ammonia or amines for pH correction are added after the Condensate Polisher.

Figure 1 Condensate Polishing in a Steam cycle loop

Condensate flows in GPM(Gallons Per Minute) in Coal fired boilers is usually estimated at 10xMW rating of the turbine. Various boiler designs that require Condensate Polishing are illustrated in Figure 2.

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Natural / controlled circulation boilers upto 2800psig

Once through supercritical w/o intervening drum for blowdown

Condensate Polishing

Once through subcritical w/o drum >2800psig

Advanced combined cycle boilers (HRSG) > 1800psig

Figure 2 Various types of boilers that need Condensate Polishing

Condensate Polishing has a long history of usage from the early 1950s in Fossil & Nuclear fueled power generating stations . Prior to this period, boiler pressures were below 1500psig and that the condensate was not Demineralized. The makeup was Demineralized and blended with the condensate, which did not pose any problems. With Boiler pressures surging to almost 1800psig, turbine fouling was soon evident and reported in the late 1950s. Deposits of sodium, carbonates copper, iron, silica and salt in some cases were reported resulting in loss of turbine efficiency. Further in the present framework of a renewed global power generation growth cycle in the fossil fueled plants having super critical & Ultra super critical boilers and thermal cycles employing AVT or OT regimes , demands on the purity of condensate returning to the boiler are extremely high. While the underlying technology for Condensate Polishing has not changed over the years, there have been continuous improvements to address specific challenges faced by Utilities. Figure 3 illustrates some of these key developments over the years.

Figure 3 Developments in Condensate Polishing since the 1950s

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Condensate Polishers are resin based ion exchange systems that are designed to meet the challenge of purifying very large quantities of water contaminated with low levels of dissolved minerals and suspended matter that reduce the efficiency of thermal cycle and degrade metal components. The major dissolved contaminants range from sodium, chloride, silica and sulphate while the suspended contaminants are typically oxides of iron and copper. Condensate Polishers maintain cycle purity and efficiency by controlling the effects of corrosion transport, condenser tube leakages etc. The polishers also need to be designed to allow the power plant to continue operating with a minor tube leakage that might otherwise require an immediate outage. For the most part, Condensate Polishing can be broadly divided into two categories. One being deep bed polishers which use either Mixed beds/separate beds of Cation and Anion. Deep beds have been used independently without any pre or post treatment, called as “naked beds” and in some cases used with physical filtration technologies for efficient removal of suspended contaminants. The second type called as Precoat filters essentially consists of the use of very fine particle size media (cation and anion resins as well as inert fibers) that are used to coat the septum type filter elements. These septa are normally tubular with the most common wrapping being continuously wound yarn or plastic or metal wire. EVALUATING THE NEED FOR CONDENSATE POLISHING Most of the advanced coal fired power plants utilizing supercritical and ultra-supercritical technology mandate the use of Condensate Polishing. In the past, many utilities and engineering perform an economic analysis for the justification of use of Condensate polishers. The flowchart below provides a graphical representation of the steps necessary to evaluate and justify the use of Condensate Polishers.

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OT Chemistry

Yes

No SCC