By Robert T. Taylor, Jr.

Introduction
Business is competition and competitive market pressures are now present in the evolving power generation marketplace. In this environment, the company that can produce the lowest cost power and sells the most power makes the most profit and wins “the game.” Contract water treatment services are one tool power companies are turning to reliably meet their water treatment needs and increase their competitive position in the marketplace. Water treatment service providers have evolved from emergency mobile demineralizer suppliers to solution providers that can offer a flexible platform to integrate mobile or fixed membrane and media technologies optimized to meet site-specific client needs.

Water treatment service contracts present the power generation industry with the opportunity to eliminate upfront capital outlay for equipment and transfer operational and performance risk to an expert in the field. Service contracts also offer clients the flexibility to continually optimize their water treatment system for changes in demand for treated water quality or quantity, to change treatment designs to incorporate future water treatment technologies as they evolve and meet site-specific environmental requirements. This article classifies water treatment service contracts for demineralized (DI) water into four categories and presents the associated design, economic and operational advantages to power plant designers, constructors, owners and operators.

Service contract categories
Service contracts for high purity water production can be structured for terms between one to 15 years for continuous, seasonal or emergency use. Service contracts in the power industry typically range in flow capacity between 50 to 1,000 gpm and designs can employ all mobile equipment, building/container enclosed fixed equipment, or a combination of fixed and mobile equipment to meet client needs. Equipment designs used by leading global service providers to meet the variable needs of the power industry can be generically classified into four categories:

  • Mobile trailer-mounted demineralization;
  • Mobile trailer-mounted primary treatment (RO) and mobile demineralization;
  • Fixed primary treatment (RO) and mobile demineralization;
  • Fixed primary treatment (RO) and primary demineralization (EDI) and “exchange” demineralization polishing.

In each class, the assets used to produce the treated water are service-provider owned (on the service provider’s balance sheet), with consumables and replacement parts normally provided by the service company. While client operation and monitoring of mobile demineralizer equipment is typical, skilled service provider operational support for membrane treatment technologies is required for the service provider to assume operational risk and offer system performance guarantees.

Mobile trailer-mounted demineralization
Mobile trailer-mounted ion exchange demineralization has reliably serviced the power industry for the last 40 years. In the early years, mobile demineralizers were primarily used as a “911 service” or emergency support for capital equipment failures. Today, new combustion turbine (CT) plant designs use mobile demineralizers as the facility’s sole water treatment plant. It is common for simple cycle combustion turbine (SSCT) designs to use mobile demineralizers to meet their full complement of DI water needs for power augmentation (fogging and evaporative cooling) and oxides of nitrogen (NOx) control. Combined cycle combustion turbine (CCCT) makeup designs in some cases also use mobile demineralizers as a facility’s sole water treatment plant. The most common drivers are water restrictions for consumption or discharge, or eliminating the use of thermal processes for zero discharge.

Mobile demineralizer advantages
Treatment with mobile demineralization eliminates capital investment in a rarely used asset, simplifies plant design and construction and frees operational resources to focus on power production. Designs using mobile demineralizers present advantages to CT power plant developers in that no industrial wastewater discharge permit is required because a mobile demineralizer is a true zero discharge treatment system (liquid and solid). Eliminating industrial wastewater generation and discharge can help mitigate local community concerns and facilitate CT plant developing and permitting. The most successful new plants designed for mobile demineralizer treatment involve consultation with the service supplier in the design stage to address required footprint and utilities, instrumentation for monitoring plant operational responsibilities and most importantly, to provide adequate demineralized water storage tank volume.

Mobile primary treatment (RO) and mobile demineralization
This “integrated mobile services” capability is available due to the expanded range of technologies available on a mobile platform from leading global service companies. Mobile primary treatment is conventionally reverse osmosis (RO) and the supporting pretreatment equipment (i.e. filtration, softening, activated carbon, etc.) and chemicals. The integration of mobile demineralizers (DI) with mobile pretreatment enables service providers to deliver a complete mobile water treatment system to process raw river water into high purity demineralized water.

RO technology, in combination with mobile demineralization, presents advantages to improve treatment economics on water sources typically greater than 200-300 ppm total dissolved solids (TDS). The mobile RO-DI design can be favored over mobile DI for those installations with one or more of the following characteristics:

  • Continuous water demand at the design flow.
  • Wastewater discharge/treatment capabilities to handle the RO reject.
  • Medium to high TDS supplies.
  • Ion exchange treatment alone cannot meet specification (TOC).

In general, this integrated mobile platform presents advantages to clients that need continuous DI water production for a defined period of time, typically for one peak season (winter or summer peak). Integrated mobile services require longer advanced notice and prescheduled service, because RO equipment is a limited rolling stock inventory item and requires more preparation time by the service provider. The service supplier must be able to predict and schedule tangible business to present the most favorable economics, manage equipment inventory and commit to equipment availability. Integrated mobile services for peak power facilities or for seasonal supplemental support for coal-fired stations typically include a minimum service period commitment.

Integrated and mobile demineralizer services discussed above have been presented from the perspective of supporting ongoing plant operations. It is important to note that these mobile capabilities are also critical to support plant startup, commissioning and steam blow requirements for the new combined cycle combustion turbine fleet. Like the leading regulated and unregulated power generators, the major engineer, procure and construct (EPC) firms have signed system-wide agreements to secure priority equipment availability status with the leading service provider to meet critical startup schedules.

Fixed primary treatment (RO) and mobile polishing
Like mobile primary treatment, fixed primary treatment is conventionally RO and the supporting pretreatment equipment and chemicals. Fixed primary treatment can be favored over integrated mobile systems for installations with one or more of the following characteristics:

  • Plants that operate in the winter and summer peaking seasons.
  • Custom engineered pretreatment equipment is required for primary treatment.
  • Baseload operations (with mobile demineralizer polishing in service year-round).

For seasonal operations, the fixed primary treatment design gives the ability to rapidly produce demineralized water, because the fixed equipment is already onsite with utilities connected and eliminates mobile pretreatment equipment preparation, delivery, setup time and charges. The only mobile component is the mobile demineralizer, which is simply delivered to the plant to produce demineralized water on an as needed basis when the power plant is dispatched for generation. This asset-light design for fixed equipment (compared to category four) minimizes installed assets “on the ground” to produce demineralized water. Contracts are set up with a fixed fee to cover equipment amortization, plus a variable charge for operations, process chemicals and mobile demineralizers. As the fixed assets are light, contracts generally have a lower percentage of fixed costs, with a higher variable percentage compared to asset-heavy systems with the same flow capacity. The low fixed costs are attractive to CT plants that operate in both winter and summer peak because, during off-peak or non-operational seasons, use of mobile equipment allows removal and cost savings.

The fixed primary treatment design with mobile DI polishing is also successfully used for plants with base load operation and plants that require customized pretreatment designs to treat challenging water sources, such as tertiary municipal wastewater. Economics for baseload service are influenced by cost centers such as water quality (TDS) and proximity to the service provider’s regeneration facility. This fixed primary treatment design with mobile trailer-mounted demineralizer polishing is in current service at numerous fossil and nuclear facilities throughout the world.

Fixed primary treatment designs can also use offsite regenerated naked mixed bed polishers to polish RO permeate. Trailer polishing designs however offer performance advantages and reduced operational risk to industry over the use of naked mixed bed polishers. If there is a problem or failure of the RO system, the RO unit can be partially or completely bypassed with feed sent to the mobile demineralizer with no deterioration in effluent quantity. Naked mixed bed polishers carry a higher operational risk, because they do not have ample ion exchange capacity to provide this level of redundancy.

Fixed primary treatment (RO), primary demineralization (EDI) and mobile polishing
This design is more asset-heavy, as a large percentage of the treatment equipment is fixed and remains at the facility for the contract term. Fixed components can consist of pretreatment processes, RO, gas transfer membranes (GTM®) and electrodeionization (EDI). The mobile component is polishing demineralizers, conventionally 40-80 cubic foot mixed bed vessels, which are transported for chemical regeneration at a remote facility.

The economics of this design can offer a lower evaluated cost per unit volume ($/kgal) for facilities with continuous baseload operation. Asset-heavy designs have a high percentage of fixed costs for capital recovery, consumables and operations, with a smaller variable fee percentage charged during DI production. As with fixed primary treatment designs in category three, typical contract terms for this asset-heavy design are five to 10 years. In both categories, use of standardized equipment designs for the fixed equipment enables service providers to present favorable economics for contract terms as short as five years. This capability is not available with custom engineered equipment because these assets cannot be readily redeployed and all costs for this equipment are recovered over the contract term.

Although mobile trailer-mounted equipment is not used in daily operation with this design, the importance of mobile demineralizer and integrated mobile services capabilities should not be overlooked. When considering a service supplier, an important question to ask is: How will that supplier ensure performance guarantees for water quantity and quality when problems occur? Suppliers may offer guarantees, but that piece of paper will not help their system produce one extra drop of water when there is a partial or complete system failure. True service companies have a global backup fleet of mobile equipment to stand behind and meet their performance guarantees.

Conclusion
Power companies are using contract water treatment services to reliably meet water treatment needs and increase their competitive position in the marketplace. Available design options with combinations of fixed and mobile equipment offer clients flexibility to continually optimize their water treatment system for changes in treated water quality or quantity demand and to change treatment designs to incorporate future water treatment technologies as they evolve. With water treatment service contracts, clients can devote their capital, operational and managerial resources to profitably producing power and transfer accountability and risk for water treatment operations and performance to an expert in the field.

Mobile water treatment services offer economic and operational advantages to power plants by eliminating the need to commit operational manpower and upfront capital for water treatment assets when the need is variable due to changing, seasonal or market conditions. Mobile services can also simplify and expedite plant construction and permitting, allow zero discharge and eliminate onsite hazardous regenerant chemical delivery, handling, storage and discharge.

About the author
Robert Taylor is the corporate development director at Ionics Inc., working with Ionics’ clients to develop Build-Own-Operate solutions for a variety of industrial water requirements. He has over 15 years of experience in industrial water treatment, having held several technical and marketing positions with Ecolochem, Inc., which was acquired by Ionics in early 2004. Taylor holds a B.S. in chemistry from Randolph Macon College, and is a member of AWWA, ACS and AIChE. He has authored and presented several technical papers at various industry conferences and is a member of the Advisory Council of the International Water Conference.

 

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