outsourcing eliminates hazardous regenerant chemicals at TVA

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1 Water Technologies & Solutions technical paper outsourcing eliminates hazardous regenerant chemicals at TVA summary Objectives were established to improve cycle chemistry, to lower the overall cost of treatment, and to meet TVA s Environmental Leadership corporate goal by improving make-up water treatment and condensate polisher performance. This paper discusses the fundamental design criteria and operational results of off-site condensate polishing resin regeneration by service contract. Also presented are how off-site ion exchange resin regeneration is used in combination with new make-up treatment technologies, and outsourced equipment and services, to reduce wastewater discharge of regenerant chemicals and meet the objectives. introduction In 199, Tennessee Valley Authority s (TVA s) Board of Directors established Environmental Leadership as one of the company s primary corporate goals. 1 Regenerant chemicals and the corresponding wastewater discharge were identified as a source for potential adverse environmental impacts. Environmental concerns, along with increasing operational and maintenance costs, lead TVA management to specify the elimination of hazardous regenerant chemicals from TVA fossil plants. This eliminated the use of acid and caustic for the regeneration of ion exchange resins used for condensate polishing and make-up demineralization. Make-up water treatment by service contract (outsourcing) has become commonplace in the electric utility industry. The benefits of improved economics and water quality, allow the utility to refocus resources on power generation and streamline plant performance to remain competitive in a deregulated marketplace. 2, Membrane and electrochemical technologies are leading the charge to eliminate hazardous regenerant chemicals for make-up water production. This combination of electric and pressure driven technologies presents end users the opportunity to process raw water and purify to ultrapure water quality, without hazardous chemicals. Condensate polishing by ion exchange is still the workhorse technology in the industry. Conventional deep bed condensate polishing requires chemical reactivation prior to reuse, which has traditionally been performed at individual generating stations. With requisite chemical regeneration, TVA was presented with a significant challenge to eliminate regenerant acids and caustics in their fossil plants. Temperature and pressure requirements, the low ionic challenge, characteristics of the ionic species, and the nature of potential foulants in a condensate source eliminate the current generation of membrane and electrochemical technologies as an alternative to conventional ion exchange designs. Given that a non-regenerable or disposable bead ion exchange condensate polishing system in a fossil plant is an uneconomical option, TVA s sought to execute the condensate polisher regenerations at an external facility. After evaluating options, Tennessee Valley Authority entered into a Partnering Agreement with SUEZ Power & Water, a global high purity water treatment services company, to achieve these goals. A primary emphasis of this paper is to introduce off-site condensate polishing regeneration services as a qualified alternative for electric utility generators and plant designers to eliminate the negative impacts of on-site resin regeneration. Topics include required modifications to existing TVA equipment, design and operating criteria, improvements in cycle chemistry; other factors Find a contact near you by visiting and clicking on Contact Us. *Trademark of SUEZ; may be registered in one or more countries SUEZ. All rights reserved. Apr-10

2 which affect operational costs and influence the economic decision to outsource off-site regeneration of bead condensate polishing resin. Also presented are the membrane, electrochemical and conventional ion exchange technologies employed by the service company to improve make-up quality, while enabling TVA s fossil plants to become hazardous regenerant chemical-free. expanding outlook Environmental considerations are influencing the way corporations do business. Water intake, recycle/reuse, and wastewater discharge regulations are a prime consideration in planning, permitting, and constructing new power plants. Moreover, existing plant operations are not immune from tightening environmental regulations. There is a growing awareness and examination of individual trace impurities in an industrial discharge stream, which are, or could be, classified as pollutants. As Strauss notes, as the activist political climate for environmental concerns continues to grow, how long will it be before the focus of activist groups shifts from protesting construction of new installations to ongoing operations at existing power plants? 4 Today s reality is that hazardous chemicals and wastewater issues are in the spotlight, and industry will bear more pressure to reduce wastewater generation at the source, or to implement costly end-of-pipe treatment. The current trend is to shift major decisions affecting the environment away from the plant s environmental engineer and senior management to the Board of Directors. This shift in decision-making is driven, in part, by the fact that current and future environmental liabilities are reported on a company s balance sheet, and thus can adversely affect the ability of a business to attract investor capital. Indeed, as we have one eye focused on improving water quality for high-pressure steam generation systems, we must also look at how these improvements will affect current and future wastewater discharge requirements. TVA s corporate decision to eliminate regenerant chemical use and wastewater discharge represents a proactive leadership role in environmental matters. This decision may also position the utility to mitigate any adverse effects of uncertain future wastewater discharge regulations. condensate polishing To drive the power producing turbine and generator, copious volumes of water are converted to steam which expends its energy in the turbine, is condensed in a heat exchanger (condenser) and returned to the boiler or steam generator. In facilities with supercritical high pressure boilers, once-through steam generators (OTSG), nuclear generating stations (PWRs and BWRs), and a greater number of high pressure drum boilers, this condensate must be polished to remove trace contaminants to achieve the required purity before it can be recycled. 5 Ion exchange technology, using powdered resin or deep bed systems, accomplishes this purification by removing particulate and non-ionic matter by adsorption or mechanical filtration, and exchange of dissolved ionic material. The design objectives of condensate polishing systems are to protect the steam generator from a condenser leak, and produce a reliable, high quality treated return condensate. While the powdered resin is discarded after use, the deep bed system requires chemical regeneration before reuse and is the subject of further discussion. The commercial dates for TVA s eleven fossil plants range from the early 1950s to the early 1970s. 6 Condensate polishing equipment was not included with any of TVA s drum-type fossil units, while all of the OTSG designs are equipped with condensate polishing equipment. The four (4) TVA fossil generating stations (six (6) generating units) with deep bed condensate polishers are: 1. Bull Run Fossil, Clinton, TN 2. Colbert Fossil, Tuscumbia, AL. Cumberland Fossil, Cumberland City, TN 4. Paradise Fossil, Drakesboro, KY All polisher designs include naked mixed beds. The four plants did not use any special techniques or equipment to improve resin separation. At Paradise and Colbert Fossil, the resins were backwashed, separated, regenerated, mixed and rinsed in one vessel. Cumberland and Bull Run Fossil used conventional external separation and regeneration equipment. In the external design, exhausted beds are transferred from the service vessel to a Page 2

3 separation vessel, where the cation and anion resins are classified into individual components. The anion portion is transferred into another vessel for caustic regeneration, while the cation resin typically undergoes an acid regeneration in the separation vessel. The regenerated resins are then re-mixed and transferred to clean storage or returned to service. external regeneration, very external Off-site regeneration requires the exhausted bed be moved into resin storage vessel, or transferred directly to a transportation unit for delivery to SUEZ s centralized regeneration facility located in St. Peters, MO. It is obvious that the service contract does not eliminate the requirement for condensate polisher chemical regeneration, but it does shift the chemical storage, handling, regeneration, and wastewater discharge to an external location. Of course, like a power plant, a service company must meet current and future wastewater discharge regulations. But a properly positioned service provider can alleviate these issues by location in an area with the infrastructure and treatment technology to handle ion exchange regenerant wastes. In addition, consolidation of TVA s regeneration requirements at its St. Peters plant enabled SUEZ to design and install advanced wastewater treatment technologies specifically engineered to process impurities from condensate polisher regenerations. regeneration facility The St. Peters Regional Plant, located 15 miles northwest of St. Louis, MO, began operation in January 1999 (Figure 1). The 48,000-square foot facility has more than 25,000 square feet dedicated to ion exchange resin processing and regeneration. Figure 1: St. Peters Regional Plant Exhausted resins are physically inspected on arrival at the regeneration facility prior to processing. The purpose of this inspection is to obtain a gauge on the required cleaning, if the presence of crud or other resin foulants is detected. The exhausted resin is then transferred from the transportation vehicle to resin cleaning equipment. This equipment is custom designed and built to optimize results from SUEZ s proprietary physical and chemical resin cleaning procedures. Segregated separation equipment and proprietary separation techniques minimize resin cross contamination, which is the most important step to minimize ion leakage and achieve a high purity effluent. The separated cation and anion segments are transferred to dedicated cation and anion regeneration vessels for chemical reactivation. After regeneration to the H /OH cycle, the resins are mixed and transferred to clean resin storage, or directly to the transportation vehicle. + - An inventory of replacement resin is maintained at the service provider s facility to adjust to the correct volumetric resin ratio before regeneration. resin selection Simplicity, consistency, and the flexibility to service multiple generating stations; all are reasons TVA elected to standardize on one condensate polishing resin manufacturer and type. Standardization also enabled the service company to avoid maintaining an inventory of multiple manufacturers and resin types. TVA selected a uniform particle size (UPS), 10% DVB, cellular strong acid cation resin, and a macro porous, Type 1, strong base anion resin (Rohm and Haas Amberjet 1500 and Ambersep 900, respectively). This resin combination facilitates separation by the difference in terminal settling velocities between the cation and anion resin. A 1:1 volumetric resin ratio (approximate 2:1 equivalent ratio: cation to anion) is the service charge delivered Page

4 to each facility. TVA s resin selection was based on empirical data: what resins give the best results in field performance in their units. delivery vehicle The bulk resin is moved between TVA sites and the regeneration facility by a Heil tank type trailer (Figure 2), co-designed by TVA and SUEZ. The unit has volume capacity of 1500 ft (42 m ), but highway weight limitations restrict transport volume to approximately 1200 ft (4 m ). Isolated compartments permit the unit to carry a mixture of clean and dirty resin without intermixing. These compartments allow one trailer to service one or more plants in a single trip. Isolated compartments also enhance resin transfer and aid in complete resin removal. Figure 2: Transportation Vehicle Each compartment is equipped to receive air or water pressure (or both) to fluidize and move the resin. A custom underdrain design facilitates resin movement, and allows the sluice water from a dirty bed to drain to waste. The prototype Heil trailer was purchased and transported by TVA. required modifications bulk storage Storage capability for both clean and dirty resin is a practical requirement at the power plant for off-site condensate polishing regeneration by service contract. The required holdup volume of both exhausted and regenerated resin is an important plant decision. The bed exhaustion schedule, response record of the service provider, regeneration, and transportation time and the total resin float volume all merit consideration to determine the required storage capacity for each plant. Page 4 Economics and risk assessment also play a major role to determine the required safety margin to protect against a condenser leak. Undoubtedly, spare charges of regenerated resin stored at the owner s facility provide the best protection against unexpected problems. TVA operates with a minimum one spare charge of regenerated resin onsite per operating unit. At least one additional bed is in transportation or regeneration at the service provider s regeneration facility. As is typical, the plants originally had little condensate resin storage capacity. To achieve the desired storage volume, TVA retrofitted existing vessels, and installed new storage vessels. resin transfer Design changes were required for the transportation vehicle loading and unloading area, referred to as the transfer area. Plant modifications include a supply of the following to the boundary of the transfer area: Pressurized demineralized water Pressurized oil-free plant air Transfer piping for regenerated resin Transfer piping for exhausted resin Wastewater piping SUEZ personnel trained TVA plant operators in pneumatic and hydraulic transfer techniques to sluice resin to and from the transport trailer and the appropriate storage vessels. Transfer distances are 00 to 400 feet (91 to 122 meters), at up to 100 feet (0 meters) elevation. The typical time to unload a trailer is one to two hours, including set-up. paradise condensate polisher system Commissioned in 196, TVA s Paradise Fossil Plant has 625 MW generating capacity, using two (2) cyclone-fired Babcock & Wilcox subcritical 2,400 psi OTSG s. The full-flow deep bed condensate polisher system consists of: x 100% vessels; 2400 gpm (545 m /h) per vessel 100 psi ASME 00 ft (8 m ) bed volume per vessel 2 x 00 ft (8 m ) clean storage vessels 2 x 00 ft (8 m ) dirty storage vessels Oxygenated feedwater treatment (OT) is regulated between ppb at the boiler feedwater pumps,

5 with ammonia and oxygen treatment chemicals added to the OTSG feed. The average ammonia challenge to the condensate polisher is 0.1 ppm at a ph between results at paradise TVA has always practiced tight cycle chemistry at Paradise Fossil Plant. The strict criteria for taking a bed out of service remained unchanged after initiation of contract regeneration services in 1998: Sodium (Na + ) 0.5 ppb Specific conductivity 0.1 micromho/cm To establish and maintain a routine off-site regeneration schedule, the service company exchanges one (1) bed per week. Two regenerated beds are maintained in clean resin storage at Paradise Fossil as an additional safety factor for the two-unit generating station. Average bed throughput has increased over percent after commencement of off-site condensate polishing (Figure ). Since establishing routine service, only one (1) bed was removed from service because of control set points. The balance of the beds has been changed out according to schedule (e.g. they could have run longer than 120 million gallons). loading to avoid bed stratification and the complete removal of exhausted resin from the service vessels (to avoid the dreaded heel affect) is also crucial in the production of low sodium demineralized water, not to mention reliably producing parts per trillion sodium. Table 1: Typical Polisher Effluent Quality economic influences Transportation distance and bed throughput are two influential factors in the operational expense of offsite condensate polisher regeneration services. While the former can be considered a constant (Figure 4), bed throughput is influenced by many different factors: Quality requirements Operational cycle (H + /OH - vs. NH 4 +/OH - ) Ionic loading (boiler chemistry and condenser leaks) Deep bed design (SAC/MB vs. naked MB) Particulate (crud) load and other potential resin foulants Figure : Off-site condensate polishing The most important factor in achieving low contaminant levels is the diligence of qualified equipment operators in handling the resins, both at the generating stations and the off-site regeneration facility. The effluent quality detailed in Table 1 is a reflection of the high efficiency separation, cleaning and chemical regeneration techniques performed by the service provider. TVA personnel are highly trained and skilled in resin transfer. Precautions in vessel Figure 4: Mileage to Regeneration Plant Page 5

6 Boiler pressure and limitations on feedwater contaminants dictate quality requirements. OTSG units require full-flow polishing to control contaminants and maintain ultrapure feedwater quality. There is a strong interconnection between effluent quality and the resin bed ionic form. The H + /OH - cycle results in the highest effluent quality and achieves maximum protection from a condenser leak, albeit at the sacrifice of bed throughput if not run past the ammonia break. For a given target effluent sodium and chloride concentration, higher resin conversion + rates are required for operation in the NH 4 /OH - cycle; thus, the benefit of longer bed runlengths is offset against increased chemical consumption and cost. TVA operates their condensate polishers in the H + /OH - form, and does not run past the ammonia break. steam cycle chemistry and feedwater treatment determine the ionic challenge to the polisher system in the absence of air ingress and condenser leaks. Paradise practices oxygenated feedwater treatment (OT) with ammonia to control ph. Ammonia represents the major cationic load on the polisher because it volatizes with the steam and returns in the condensate. Cycle chemistry and ph influence the ionic challenge to the resin and affect bed throughput, thereby influence economics. resin fouling leads to reduced bed throughput and a higher bed exchange frequency. In the absence of a lead cation bed or pre-filtration, particulate is deposited directly on the mixed bed resin. If severe, crud loading can cause a bed to be taken out of service on pressure drop before full utilization the operational capacity. Difficult resin separation, resin fouling and reduced capacity all can result from crud loading. It is well known that corrosion byproducts from the boiler and steam cycle components apex after idle periods. During unit start-up, disruption of passive metal layers and corrosion products can result in these high crud loads. TVA protects the polishing resin from high crud loading at unit start-up with coated pre-filters. Fouled resin can also result from sealant or lubricant leaks, and contamination due to system maintenance. Regardless, abnormal crud loads or other resin fouling mechanisms will cause laborious scouring and extended cleaning procedures and may dictate elevated regenerant levels to restore resin operational capacity. Therefore, avoiding resin fouling and requests for partial deliveries saves on the cost of treatment. rise of the membrane processes Condensate polishing is one determining factor in feedwater purity; the second is make-up water treatment. One can argue the most exciting developments in water treatment are the new technologies applied in current make-up systems. The development and advancement of membrane separation processes have fathered these new generation treatment technologies. Today, there are membrane processes available to replace classic treatment technologies for virtually every component in a water treatment system. Not only can membrane processes produce superior water quality (used alone or in combination with chemically driven technologies) they also offer the opportunity to process raw water to ultrapure quality, with no regenerant chemicals. The total cost of ownership analysis for a water treatment system has evolved to include contract services versus capital purchase, and conventional chemical versus electrochemical and mechanical membrane purification technologies. Although still valuable, fading are the days of solely relying on spreadsheet calculations to indicate the system with the lowest cost of ownership to determine equipment selection. Environmental considerations are commanding a larger role in the decision process, dictating wastewater concerns be evaluated along with economics. make-up demineralization TVA performed such an analysis to decide how to meet its demineralized make-up water requirements. The details of this analysis have been presented in prior work. 7 TVA selected a hybrid combination of TVA owned equipment and contract services to meet the make-up requirements for five (5) of TVA s eleven fossil facilities. Necessary design modifications and unexpected and unbudgeted cost overruns for the capital equipment resulted in an estimated cost to produce demineralized make-up water 0% to 60% higher than the fixed cost quoted by the service provider. TVA has since entered into a Partnering Agreement with the service provider to build, own, operate and maintain (BOOM) the high purity demineralized water make-up systems for the remaining six (6) fossil plants, and TVA s three () nuclear plants. Page 6

7 Membrane based separation technologies included in the service provider s make-up systems include: Microfiltration (MF) Reverse Osmosis (RO) Gas Transfer Membranes (GTM) Electro deionization (EDI) The service provider s DeltaFlow* system is the primary make-up system design serving the TVA system. The DeltaFlow system combines three membrane separation technologies: RO, Liqui-Cel* GTM* and E-Cell* EDI into a continuous, reliable ultrapure water treatment system. Moreover, the DeltaFlow system can produce <5 ppb dissolved oxygen by adding catalytic chemical deoxygenation or multiple-pass GTM for nuclear plant make-up specifications. Kingston make-up system The Kingston plant had a 17-year-old conventional three-step ion exchange make-up system. Problems with the 00 gpm (68 m /h) dual-train demineralizer included inconsistent regenerations and effluent quality, resin fouling, hazardous regenerant chemical leaks, and high operational and maintenance costs. Hot water was used to elevate the anion resin bed temperature during caustic regeneration. Hot water supply problems almost caused an explosion when the hot water tank overheated and melted all lined piping in contact with the unit. During the last year of operation, a leaking regenerant valve contaminated five (5) units with caustic when both fail-safe conductivity shutdown features malfunctioned. between ppm TDS, and 10-0 NTU. Effluent quality is typically <1 NTU. The service provider s design includes ion exchange softening and activated carbon as pretreatment to the DeltaFlow system. Ion exchange softening beds provide media filtration to remove any trace suspended solids, and exchange divalent, and trivalent scale forming cations for sodium. The granular activated carbon beds provide polishing filtration and dechlorination. This combination of pretreatment steps allows the DeltaFlow system to produce ultrapure water, and requires no chemical feeds. The make-up system was fabricated and delivered by the service company in self-enclosed equipment housings. TVA requested this containerized design to eliminate the need for a supplemental system during the demolition of the bulk chemical storage tanks and the demineralizer system. Containerized equipment also offered TVA rapid start-up and operation, and an easy transition phase between the two systems. In the containerized design, all electrical wiring and interconnecting piping were prefabricated and tested at the service provider s facility. Upon arrival at the Kingston plant, TVA just had to hook up electrical feeds and connect the external piping, and the system was ready for service. TVA selected a containerized equipment design at half of the outsourced make-up systems, the balance being building enclosed. Figure 5 illustrates the make-up water quality improvement after commencement of the service provider s make-up system at Kingston Fossil Plant. results at Kingston The 00 gpm (68 m /h) DeltaFlow system began service in August To meet the higher pretreatment requirement with RO systems, TVA upgraded the existing inclined tube clarifiers to increase performance and durability. The plastic tubes were replacing with stainless steel inclined tube settlers. The wood baffles and supports were replaced with HDPE. An in-line turbidity analyzer and level/flow indication instrumentation were added to better monitor performance and maintain effluent quality. The raw water to the clarifier is a mixture of the Tennessee and Clinch rivers, which typically varies Figure 5: TVA, Kingston Fossil Make-up Quality Conventional ion exchange is still required in the production of ultrapure water. The current generation electrochemical demineralization technologies are not capable of consistently producing the make-up water quality required by Page 7

8 high pressure steam generating systems. The micromho/cm specific conductivity and <5 ppb silica (as SiO 2 ) effluent quality is achieved by conventional mixed bed ion exchange polishing of the EDI product water, with off-site chemical regeneration. conclusion On the eve of deregulation and with the growing use of gas turbines to generate electricity, power plant operators are challenged to develop and implement methods to reduce costs and remain competitive in the generation industry. In addition to cost considerations for water treatment, a company may better position itself for the future by evaluating the influence of current and future wastewater discharge regulations on the proposed treatment scheme. TVA identified hazardous regenerant chemical use and wastewater discharge as potential operational and environmental economic liabilities. Water treatment service contracts can offer advantages to system suppliers and plant designers by presenting alternatives to conventional water treatment designs. Membrane technologies and offsite resin regeneration services can eliminate bulk hazardous chemical storage tanks, transfer equipment, the maze of valve trees, and large waste neutralization basins. All can translate into a smaller real estate requirement and a less capitalintensive project. The use of contract services for off-site condensate polishing resin regeneration and make-up water treatment allowed TVA to eliminate regenerant chemical storage, handling, and wastewater discharge at all their fossil plants. This improved water quality and economics, supported TVA s corporate Environmental Leadership goal, and allowed the utility to refocus resources on efficient power production. Although no single approach provides all the answers, outsourcing water treatment services can provide economic, operational, and environmental advantages to existing power plants. footnotes 1. Bartley, G.L., Capital and Service Contract Reverse Osmosis Systems at TVA s Fossil Plants, 57th International Water Conference Proceedings, Pittsburgh, PA, October 1996, pp Miller, W.S., Make-up Water Treatment by Service Contract, 55th International Water Conference, Pittsburgh, PA, October Painter, J.C., Benefits of Non-capital Make-up Systems, NUS Make-up Water Treatment Seminar, Clearwater Beach, FL, June Strauss, S.D., Water Treatment, Power, June 199, pp Ibid 6. Bartley, G.L., Capital and Service Contract Reverse Osmosis Systems at TVA s Fossil Plants, 57th International Water Conference Proceedings, Pittsburgh, PA, October 1996, pp Ibid. Page 8