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Evaluating Local Impacts of a Utility SCR Retrofit Project

Steven Klafka, PE, DEEWingra Engineering, S.C.A&WMA Conference 2002

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Introduction

Wisconsin adopted SIP for new 1-hour ozone air quality standard

Required NOx reductions at utilities in southeastern Wisconsin

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Pleasant Prairie Power Plant

WEPCo operates the Pleasant Prairie Power Plant in southeastern Wisconsin.

Two 600 megawatt coal-fired boilers. To comply with new NOx limitations, WEPCo

proposed SCR retrofit of one boiler. SCR system would use anhydrous ammonia

as the reagent. Proposal included ammonia storage tanks,

and equipment for rail and truck deliveries.

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Pleasant Prairie Power Plant

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Review by State Agencies

Public Service Commission Department of Natural

Resources Department of Commerce Village of Pleasant Prairie

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Village Permit Application

Application for conditional use permit.

Description of SCR system. Three 30,000 gallon storage tanks. Rail and truck delivery. Risk Management Plan (RMP). Off-site consequence analysis.

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Worst-case Release Scenario

Based on USEPA RMP Comp Model USEPA Assumptions

Rail tank car contents lossed in 10 minutes

Toxic endpoint is distance to 200 ppm Model Results

Toxic endpoint predicted to be 6.9 miles Affected population of 124,568 people

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Area of Worst-Case Scenario

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Alternative Release Scenario

More realistic accident scenario. Assumed fracture in loading line from rail car. Based on USEPA RMP Comp Model. Toxic endpoint predicted to be 0.3 miles. Affected population

13 residences 100 WEPCo employees 200 employees at nearby businesses Public Safety Dispatch Center and Police

Department

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Area of Alternate Scenario

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Issues Considered by Village

More realistic evaluation of risk. Comparison with existing storage sites. Identification of potential accidents. Anhydrous ammonia accident history. Availability of alternative reagents.

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More Realistic Evaluation of Risk

ALOHA model Tool of local emergency planning

coordinators. Allows changes in release rate,

meteorology, and toxic endpoint.

Worst-case and alternative SCR release scenarios repeated using ALOHA model.

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RMP Comp and ALOHA Models

ReleaseScenario

RMP CompResults

ALOHAResults

Worst-Case 6.9 miles 3.4 miles

Alternate 0.3 miles 0.1 miles

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Comparison with Existing Sites 11 existing anhydrous ammonia

storage sites in Kenosha County. Proposed SCR storage is twice

current largest site. Proposed SCR storage and two

existing sites potentially affect > 100,000 people based on worst-case release.

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Evaluation of Potential Accidents

RMP includes Process Hazard Analysis

Identifies potential accidents, releases, frequency, and mitigation methods.

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PHA Results Accidents Likely to Once per Year

e.g. improper closure of after unloading railcar Maximum release 10 lbs

Accidents Likely to Occur Once Every 1-4 Years e.g. truck valves are opened too quickly

Maximum release 10 lbs Accidents Likely to Occur Once Every 20-75

years e.g. railcar derails Maximum release 148,500 lbs

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NRC Ammonia Accidents Releases > 100 pounds reported to

National Response Center (NRC) Since 1992, five anhydrous NH4

spills. Since 1993, nine aqueous NH4 spills. Since 1990, 118 unspecified NH4

spills.

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RMP Ammonia Accidents

15,436 RMP filed with USEPA 7,540 anhydrous storage sites 656 reported anhydrous NH4 releases No industry breakdown for NH4

releases Of 1,911 releases, 6 attributed to

fossil fuel generation facilities.

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Alternative SCR Reagents

Aqueous Ammonia and Urea EPRI reports157 SCR installations in

US Of the 79 site reporting the

reagent: Anhydrous Ammonia -- 63% Urea -- 25% Aqueous Ammonia -- 11%

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Anhydrous vs Aqueous Ammonia

Anhydrous Ammonia Stored as compressed liquid Immediately evaporates during release Proposed due to widespread use and low cost

Aqueous Ammonia Stored as liquid Atmospheric temperature and pressure Upon release, forms liquid pool then

evaporates Eliminated by WEPCo due to higher costs

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Increase Cost of Aqueous Ammonia

Aqueous has higher reagent costs, requires a larger tank farm, more frequent deliveries.

Estimated cost increase for aqueous ammonia is $740,000 per year.

Cost increase to WEPCo customers is $ 0.00007 per kw-hr or 0.1% (Unit

2).

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Anhydrous vs Aqueous Release

Scenario Anhydrous Aqueous

Worst-Case 3.4 miles 0.06 miles

Alternate 0.07 miles 0.06 miles

ALOHA use to estimate distance to end point.

USEPA Evaporation Calculator for aqueous.

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Village Response to SCR Project

Anhydrous ammonia reagent posed a significant risk to local population.

Compromised emergency response capability due to proximity of Public Safety Dispatch Center and Police Department.

Informed WEPCo that Conditional Use Permit would not be issued to the SCR project unless a less hazardous reagent than anhydrous ammonia were used.

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Influence of September 11th

September 11th terrorist attacks occurred during review of SCR project.

Increased awareness of vulnerability due to hazardous materials storage.

Provided additional incentive to identify a less hazardous reagent.

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WEPCo Response to Village

Prior to the public hearing on Condition Use Permit, WEPCo informed the Village it would agree to use an alternative to anhydrous ammonia such as aqueous ammonia.

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Conclusions

Use of anhydrous ammonia as an SCR reagent poses risk to a local population due accidental releases.

After September 11th, there is greater awareness of public vulnerability due to the storage of hazardous materials.

Alternative reagents such as aqueous ammonia are more expensive but result in lower potential risk.