O&M, Plant Optimization, Water Treatment

Development of a Water Conservation Plan for a Wisconsin Utility

Issue 3 and Volume 122.

Wisconsin Power and Light Company (WPL), a wholly owned subsidiary of Alliant Energy Corporation, submitted a Water Conservation Plan (WCP) under the requirements of Wisconsin Department of Natural Resources (WDNR) Chapter 852 – Water Conservation and Water Use Efficiency. The WCP covered WPL’s existing Riverside Energy Center (REC), existing Rock River Generating Station (ROR), Southern Area Beloit Operations, and future West Riverside Energy Center (WREC), which is planned to be in operation in 2019.

The four facilities on WPL property near Beloit, Wisconsin (collectively, referred to as the Riverside Site). The WCP outlined current and future measures to conserve water at each facility. HDR, Inc. was retained by WPL to aide in the development of the WCP and serves as WPL’s Owner’s Engineer for a variety of projects at the Riverside Site. The WCP was submitted in October 2015 and was approved by the state in June 2016.

Purpose of Plan

The purpose of the WCP was to outline water conservation practices to ensure water conservation and efficiency measures were addressed in accordance with Wisconsin Administrative Code (WAC) Chapter NR 852 for the Riverside Site. The WCP also supported the Application for Water Loss Permit Modification for WPL’s existing REC natural gas combined cycle (NGCC) facility, existing ROR natural gas peaking generation plant, Southern Area Beloit Operations, and the future WREC NGCC facility.

Power block at Alliant’s Riverside Energy Center.

The WCP summarized current water conservation measures in place as well as established potential future measures under consideration for each of WPL’s power generation facilities at the Riverside Site. Building on water conservation measures implemented during plant design and operation of the REC and ROR, WPL evaluated efficiency measures and programs to achieve long-term water conservation practices at each existing facility that may be incorporated into the design of the future WREC.

Background

The future WREC facility is a nominal 650-MW NGCC electrical generating facility, with a planned in-service date of 2019. The existing REC is a nominal 600 MW NGCC facility that has been in operation since 2004. The existing ROR facility consists of demolished generating units and 130 MW peaking units, which are located on the east portion of the ROR property.

An existing horizontal collector well (HCW) provides makeup water to REC, which mainly serves to supply water used in the facility’s mechanical draft cooling tower as well as other miscellaneous water losses that occur during the power generation process. An increased withdrawal from the HCW is proposed for operation of WREC, such that the HCW can provide makeup water to both the future WREC and the existing REC. The increase would result in a water loss averaging more than 2,000,000 gallons per day in any 30-day period above the authorized base level in the existing REC water loss permit. Therefore, under WAC Chapter NR 142.06(1)(b) and in accordance with Wisc. Stat. §281.35, approval for modification of the existing water loss permit is required. The ROR facility withdraws water from the nearby Rock River, where water is used for the facility’s heat rejection system (consisting of a once-through cooling configuration). The only water loss for the Southern Area Beloit Operations is a small quantity of potable water.

All three plants will discharge process wastewater to the Rock River.

Drivers for Water Conservation

Various conservation efforts within WPL are taking place and are being driven by several factors, including the following:

  • Demand for industrial water use is expected to grow over time and it can be reduced through proper water management, efficient utilization of water supplies, minimization of wastewater production, and recycling of various water sources;
  • Desire to conserve natural resources and to promote environmental stewardship; and
  • Requirement to submit a Water Conservation Plan to WDNR in accordance with Wisc. Administrative Code Chapter NR 852.

Goals and Objectives

WPL’s water conservation goals are to conserve, recycle and reduce average day water usage at REC, ROR, the Southern Area Beloit Operations, and the future WREC facilities.

To meet this goal, WPL’s plan included:

  • Complying with WAC Chapter NR 852;
  • Developing strategic planning analysis and implementation timelines in accordance with NR 852;
  • Promoting water conservation awareness to company employees;
  • Incorporating stakeholder input in the evaluation of Water Conservation and Efficiency Measures (CEMs); and
  • Pursuing cost-effective and technically feasible CEMs.

Conservation and Efficiency Measures

In order to develop a water conservation plan, WPL had to implement and/or evaluate water CEMs at the facilities identified as specified by WAC Chapter NR 852, Tables 1 and 2. The driver was to ensure that each plant efficiently utilizes the water supply source that such results in an overall water savings. Water savings would not be gained at the expense of other environmental considerations.

As a part of the evaluation, existing water mass balances were reviewed to determine if any gaps were present. It was found that some water flows were missing in the REC water balance and therefore further plant investigation was required in order to obtain the essential water flows. Once the information was gathered, the water mass balance was updated for the WCP.

“The ROR facility withdraws water from the nearby Rock River, where water is used for the facility’s heat rejection system.”

The team for the development of the WCP consisted of existing WPL plant staff including: plant manager, plant engineers, plant operators, chemistry expert, environmental staff, the WPL new plant development team and HDR. During the process, the existing plant went into an extended outage, which slowed the progress of development of the plan. However, in the end, the team was able to compile the necessary information and get valuable input from the appropriate personnel to finish.

CEMs, NR 852

WAC Chapter NR 852 requires all Power Production (PP) water users applying for a Tier 3 water loss approval to provide documentation showing planned implementation of, or completion of, specified CEMs that do not require retrofitting.

The CEMs in NR 852 that must be considered are broken into two tables: Table 1 indicates the mandatory CEMs that all PP water users must implement and complete; Table 2 indicates the required CEMs that PP water users shall implement that do not require retrofitting, except those CEMs that are not cost-effective or environmentally sound and economically feasible as determined by analysis conducted by the applicant.

NR 852 Table 1 Criteria

The CEMs listed in Table 1 of NR 852 are mandatory measures that a water loss permit applicant must show documentation indicating implementation and completion. The following is a list of the mandatory CEMs in NR 852.04, Table 1 and the required elements for each:

  • PP-1, Water Use Audit

    a. Conduct a water use audit, determine water inflow and outflow from the facility and prepare written documentation of the audit results. Facilities shall identify once-through processes in the audit report.

  • PP-2, Leak Detection and Repair Program

    a. Establish a protocol to repair leaks in a timely manner. Conduct a survey of leaks and develop a corrective action plan.

  • PP-3, Information and Education

    a. Develop and deliver training to educate employees on the implementation of water conservation and efficiency measures at the facility. Information and education materials shall be made available to the department.

  • PP-4, Source Measurement

    a. Measure or estimate all water withdrawals monthly or more frequently to allow for identifying and understanding variability in water use over time.

The mandatory CEMs from Table 1 are discussed in further detail in the following sections.

PP-1, Water Use Audit

WPL continuously monitors water consumption and discharge at the REC and ROR through the following activities:

  • Measures, records, and reports monthly in a Discharge Monitoring Report (DMR) all water that is withdrawn from the groundwater aquifer at REC;
  • Measures and records all water that is withdrawn from the Rock River at ROR;
  • Measures and records all water that is used in water treatment processes at REC; and
  • Measures and records all process wastewater discharge to the Rock River at REC and ROR. REC reports monthly on DMR.

Water from a HCW is used as makeup for the plant cooling system, service water system, and cycle makeup treatment system at both REC and the future WREC. Water will be lost from both plants by way of cooling tower evaporation, cooling tower blowdown, combustion turbine inlet cooling evaporation, and miscellaneous steam system losses. Water is reused within each plant if water quality is adequate for supply requirements. REC recycles oil/water separator effluent and heat recovery steam generator (HRSG) blowdown back to the cooling tower for makeup if quality is acceptable. REC utilizes an existing on-site potable water well for domestic water use and the future WREC facility will install a new potable water well for domestic water needs.

The ROR utilizes Rock River water for once-through cooling in its heat rejection system for turbine lube oil cooling and discharges the same amount of water back to the river. Minimal water is lost through this process. The only water loss from ROR is a small quantity of domestic water that is supplied from WPL’s Beloit Operations Center potable well adjacent to the plant.

Table 1 provides the maximum estimated water withdrawal, water loss and wastewater discharge each year at each facility and the combined facilities flow. WPL used the existing plants’ heat and water mass balances in addition to the WREC design heat and water mass balances to calculate the water flows and evaluate reuse/recycle at each plant. It should be noted that the annual average values are conservatively based on a 100 percent capacity factor for all facilities to ensure there are no operating limitations.

The data presented above was assumed to be a suitable replacement for an actual water loss audit. The water use (withdrawal – discharge) intensity for the combined plants is estimated to be ~217 gallons / megawatt ((10.47 MGD – 3.25 MGD) / (1380 MW x 24 hrs)). This understanding has helped WPL identify measures to minimize water consumption. For instance, REC will be evaluating how they can operate their cooling tower at higher cycles of concentration which will reduce the amount of makeup water supply to the tower.

PP-2, Leak Detection and Repair Program

WPL actively performs on-site walkdowns to monitor the water use throughout both the existing REC and ROR facilities and to identify any leaks that may develop. To minimize leaks, WPL actively manages the facility by replacing and/or repairing damaged or degraded plant piping system components as necessary. However, WPL plans to modify their existing “Leak Detection” protocol within the next 12 months to improve upon and formally document the existing monitoring program. The program will include items such as who will perform the leak surveys, frequency of surveys, instructions for surveyors, corrective action plans, and will establish a maintenance schedule if a repair is required.

The future WREC will adopt a similar leak detection and repair program as REC.

PP-3, Information and Education

WPL currently trains employees on plant operations and procedures at REC and ROR including information regarding operation of the plant water systems. As a result of the study, the plant plans to develop, implement, and provide additional informational materials for specific site training to continue to educate its employees on water conservation and efficiency measures. This training will be incorporated into plant employee training.

The future WREC plant plans to incorporate the same water conservation training and materials as identified above.

PP-4, Source Measurement

As previously noted, WPL monitors the water withdrawal and wastewater discharge on a daily basis at the REC and ROR. The future WREC plans to have flow monitoring incorporated into the design of the plant. WPL uses this information to understand the water use variability over time and to identify when changes may have occurred. The information will also be useful to trend water usage which will help WPL develop and implement water conservation measures to incur water savings.

When WPL develops and implements future CEMs for the Riverside Site, a monitoring plan for the implemented CEMs will be developed to assess the impact to the facility water use.

“WPL actively manages the facility by replacing and/or repairing damaged or degraded plant piping system components.”

NR 852 Table 2 Criteria

The stipulations of NR 852 requires that the CEMs identified in NR 852 Table 2 must be evaluated and potentially retro-fitted into the existing facilities at the Site. The following is a list of the Table 2 CEMs and the required elements for each:

  1. PP-R1, Cooling Towers

    a. Conduct an evaluation of the existing cooling tower system operation. The evaluation shall review all phases of cooling tower operation including the amount of water used for makeup and release as blowdown, water quality characteristics, treatment application and chemicals used, metering, use of automated monitoring and controls, repair and maintenance schedules and procedures. A complete evaluation will consider the installation of sub-meters to the cooling tower makeup water line. Installation of any new cooling towers shall incorporate the measures identified in PP-R1.

  2. PP-R2, Sub-measuring

    a. Implement sub-measuring to account for water usage in specific processes to determine water use and loss in a process and to identify additional water efficiency goals.

  3. PP-R3, Steam Systems

    a. Implement steam system conservation by assessing the system operation and maintenance. Repair system leaks, maximize condensate recovery, and install continuous blowdown heat recovery.

  4. PP-R4, Water Reuse

    a. Conduct a technical assessment to evaluate the feasibility of water reuse. Implement water reuse projects identified by the assessment and allowed under current state law.

  5. WPL performed an analysis of these CEMs from a technical, economical, and environmentally sound standpoint. WPL has maintained the best practices and will continue to do so on an ongoing basis into the future. The following subsections describe the Table 2 CEMs, the required elements associated with each CEM, and how WPL evaluated and implemented each CEM into the facilities.

    PP-R1, Cooling Towers

    The team conducted an evaluation of the existing REC cooling tower system in operation for the WCP. The team’s evaluation reviewed all of the required elements and considered the installation of sub-meters to the cooling tower makeup water line. The installation of the new cooling tower at WREC will incorporate the required elements in PP-R1 (i.e. treatment, use of metering, automated controls, etc).

    The team evaluated how they could operate their cooling towers at REC and WREC at higher cycles of concentration which would reduce the volume of makeup water supply to the tower as well as the volume of wastewater discharged from the plant. The following sections summarize the results of the evaluation.

    Cooling Tower Treatment

    The existing REC plant currently operates the cooling tower between 4-5 cycles of concentration (COC) with untreated well water fed as makeup to replace losses due to evaporation, drift and blowdown.

    However, in order to improve water conservation at the REC plant, the cooling tower would have to operate at higher COC. Two options were evaluated as a part of the WCP in which the cooling tower could increase its COC: 1) Pre-treat the well water (cooling tower makeup) with a cold lime softening system to reduce the hardness concentrations or 2) Treat the circulating water flow in a side-stream cold lime softening system to reduce the hardness concentrations.

    Both treatment systems detailed above were studied for application at REC. The results of the study found that both systems would provide minimal economic and environmental benefits. Both treatment systems have high capital and operational costs and do not remove specific water constituents. One drawback of utilizing a softening treatment process to remove hardness from the cooling tower circulating water is that it will allow other constituents (i.e. phosphorus) to enter the tower and cycle up. This means that the tower blowdown would be more concentrated with constituents that were not treated for in the softening process. The cooling tower blowdown for both REC and WREC would be discharged to a combined outfall. The combined wastewater discharges will have a total maximum daily load (TMDL) mass loading rate limit of 0.65 lb/day of total phosphorus after WREC is operational, the same limit that REC currently has. In order to meet the total phosphorus wastewater discharge permit limit at the outfall, a wastewater treatment system would have to be installed at REC to remove phosphorus. The wastewater treatment system would also be expensive to install and there would be no economic or environmental advantage to operate the system.

    Since REC is a part of the overall Riverside Site, it was determined by WPL that the future WREC would include raw water pre-treatment cold lime softening system on 100% of the cooling tower makeup to increase the COC in the future cooling tower to a minimum of 8 COC. The pre-treatment system at WREC would also treat service/fire water in order to reduce overall Riverside Site water usage and wastewater discharge. WREC will also include a wastewater treatment system that would reduce total phosphorus to the necessary level such that the combined discharges in the outfall will not exceed 0.65 lb/day of total phosphorus.

    Circulating Water Chemical Program

    The chemicals currently utilized for circulating water treatment at REC include the following:

  • 12.5% Sodium Hypochlorite
  • 93% Sulfuric Acid
  • Polymer/Dispersant
  • Scale/Corrosion Inhibitor

The circulating water chemical treatment program is evaluated frequently by WPL and their chemical vendor to ensure that circulating water quality and cycles of concentration are appropriate to meet wastewater discharge requirements. The current program achieves an optimal COC within the cooling tower. The cooling tower chemistry is maintained by blowing down when the specific conductivity reaches 2,800 uS/cm.

Cooling tower at Alliant’s Riverside Energy Center.

Flow Metering

The cooling tower well water makeup, quench water, and blowdown streams all have flow metering devices that are tracked in the plant distributed control system. Each of these meters has an associated flow control valve which is adjusted based on specific process parameters.

During the team’s evaluation of the REC cooling tower, the plant currently uses secondary makeup water sources. These include: HRSG Blowdown Drain Sumps, Oil/Water Separator Clean Effluent, Clean Chemical Building Sump, and Clean Water Treatment Building Sump. All of the secondary makeup water sources do not have flow metering.

The existing flow metering within the system allows WPL to have real-time data to make rapid operational changes to conserve makeup water flow and minimize cooling tower blowdown.

Automated Monitoring and Controls

The cooling tower fans are operated to have the outlet circulating water temperature approach the ambient temperature. The remaining cooling tower system, including the makeup and blowdown streams, is fully automated and includes the necessary controls to conserve water. The cooling tower makeup flow control valve is automatically adjusted based on cooling tower basin level, measured by an ultrasonic level transmitter, and the blowdown flow rate. The makeup water valve is equipped with an adjustable opening stop to limit flow to 4,000 gallons per minute. The blowdown has a flow meter and flow control valve that is automatically modulated based on online monitored blowdown water quality (specific conductivity setpoint).

Repair and Maintenance Schedules and Procedures

Inspection of the cooling tower basin, tower structure, cooling tower fans and fill material occurs on a routine basis throughout the year. Routine repair and maintenance of the cooling tower is scheduled during planned outages. WPL tracks all repair and maintenance activities through a logged work order list.

However, when an emergent repair is required for a cooling tower component during normal operation, WPL completes the repair in a timely manner.

A major renovation project was recently completed on the REC cooling tower. In the fall of 2016, the tower was overhauled with provisions for plume abatement technology. Internal and external modifications were completed to reduce the visible plume emitted from the top of the tower. Overall, the renovation will produce minimal water savings.

The remaining facilities at the Riverside Site also incorporate cooling systems. The ROR has a once-through cooling system which does not include a cooling tower; thus all of the water withdrawn from the Rock River is returned with minimal water loss.

The future WREC wet, mechanical draft cooling tower installation will incorporate the measures identified in PP-R1. Various other measures are being evaluated and could be potentially implemented. The design of the cooling tower includes a cold lime softening pre-treatment system to minimize fresh water consumption and will also have plume abatement.

PP-R2, Sub-measuring

Sub-measuring is defined as flow monitoring within the subsidiary water systems of the plant. At both REC and ROR, the team evaluated and considered implementation of sub-measuring on major water lines where it was not already installed to account for water usage in specific processes. This activity would provide both plants the ability to focus on internal process water flows and may facilitate further re-use/recycle of water within each facility to increase water efficiency. Flow monitoring devices are currently used on the REC cooling tower makeup water line and elsewhere throughout the facility. Sub-measuring is currently performed at wastewater discharge sample points.

Sub-Measuring at Rock River Generating Plant

The Rock River plant has water flow monitoring at the inlet and outlet of the non-contact once-through cooling system as well as a water meter for domestic water usage.

WPL continuously monitors water consumption and discharge at ROR through the following activities:

  • Measures and records all water that is withdrawn from the Rock River at ROR;
  • Measures and records all process wastewater discharge to the Rock River at ROR;
  • Measures and records all domestic water supply to ROR.

All once-through cooling water that is used for the peaking plant is returned to the Rock River. There are no other water users at the ROR, so no additional sub-measuring was considered as a part of this evaluation.

Sub-Measuring at Riverside Energy Center

Flow monitoring devices are currently used in REC and are reported in a monthly DMR as previously noted. The water supply is used for makeup to the service water treatment system, cycle makeup water treatment system and the cooling tower makeup. Sub-measuring is also performed on Wisconsin Pollutant Discharge Elimination System (WPDES) discharge sample points 101 and 102.

The following REC water streams have sub-measuring devices to monitor flow rate: Domestic Water Supply System, Raw Water Supply System, Cycle Makeup Water Treatment System, Demineralized Water System, and the Wastewater System. Additional sub-measuring was considered for each recycle (secondary) cooling tower makeup source within REC, but it would be costly. Therefore, the plant relies on sump pump design flow rate, pump stroke and pump run time. Based on this information, flow rates were determined and total volume was calculated.

The evaluation showed that the existing plants are adequately measuring water flow. The future WREC facility has implemented sub-measuring flow monitoring on major internal water lines and is designed such that high water efficiency is maintained throughout the plant.

PP-R3, Steam Systems

WPL staff conducted site investigations to walkdown the steam systems at the existing facilities; HDR did not participate in these activities. WPL found that REC currently has heat recovery steam generator (boiler) continuous blowdown condensate recovery incorporated in the plant and also indicated that the future WREC plant will incorporate it as well. Steam traps are also incorporated throughout the various steam systems within each plant so that as condensate is formed, it is captured and returned to the condensate system. HRSG blowdown is also captured and recycled to the cooling tower to minimize water loss from the system. WPL considers steam leaks very serious and a hazardous environment for plant employees, so they are repaired in a timely manner.

The future WREC facility will have similar steam conservation methods implemented into the operation and maintenance of its steam systems as noted above. This is not applicable to the existing ROR facility as it does not have a steam system in operation.

PP-R4, Water Reuse

As a result of the assessment, the team found that the REC plant has been designed and constructed with efficient water reuse measures.

The WREC plant will incorporate water reuse methods that are cost effective or environmentally sound and economically feasible. Heat recovery steam generator blowdown and water treatment system wastewater streams (reverse osmosis reject) are planned to be routed to the WREC cooling tower basin to be reused in the cooling tower to reduce well water supply requirements. Other water reuse opportunities will be evaluated (such as stormwater capture/treatment, landscape irrigation and roadway wash-down) based on the water quality characteristics of the various internal water streams.

Additional water treatment equipment may be required such that the identified reuse streams can be utilized for other purposes. If found to be feasible from an economic and technical standpoint, WPL will consider implementing water reuse options in addition to what is already planned for the future facility.

PP-R4 is not applicable to the existing ROR facility since the only process water used is for once through cooling. For this application, the cooling water taken from the Rock River is returned to the river.

Closing

The water conservation plan for the Riverside Site was approved by the WDNR in June of 2016 and since that time, WPL has implemented water conservation and efficiency measures at each facility, including in the design of the future WREC plant. This progress WCP will serve as the guiding framework for water conservation and management at the REC, ROR, Southern Area Beloit Operations and WREC facilities. The WCP may evolve over time based on continued investigation and evaluation of current and future conservation efficiency measures to align with WPL’s sustainable focus at the Riverside Site.

Josh Prusakiewicz is a chemical engineer for HDR, Inc., where he serves as project manager and lead/staff engineer. Robert Kasch is a water treatment specialist at Alliant Energy, focusing on process water and waste treatment streams. Heidi Gauthier is senior generation system specialist for Alliant Energy in Wisconsin. John Lee is senior engineer and a specialist at Alliant Energy, focused on power plant cycle chemistry, chemical utilization and water treatment. Phong Nguyen is senior engineer and a thermal performance engineer at Alliant Energy, specializing in HRSG thermal performance engineering.