Evaluating Local Impacts of a Utility SCR Retrofit Project

1
Evaluating Local Impacts of a Utility SCR
Retrofit Project

• Steven Klafka, PE, DEE
• Wingra Engineering, S.C.
• AWMA Conference 2002

2
Introduction

• Wisconsin adopted SIP for new 1-hour ozone air
  quality standard
• Required NOx reductions at utilities in
  southeastern Wisconsin

3
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.

4
Pleasant Prairie Power Plant
5
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

10
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.

12
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
Release Scenario RMP Comp Results ALOHA Results
Worst-Case 6.9 miles 3.4 miles
Alternate 0.3 miles 0.1 miles
14
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 gt 100,000 people based on
  worst-case release.

15
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

17
NRC Ammonia Accidents

• Releases gt 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

21
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).

22
Anhydrous vs Aqueous Release

• ALOHA use to estimate distance to end point.
• USEPA Evaporation Calculator for aqueous.

Scenario Anhydrous Aqueous
Worst-Case 3.4 miles 0.06 miles
Alternate 0.07 miles 0.06 miles
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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.

25
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.