Evaluating Local Impacts of a
Utility SCR Retrofit Project
Steven Klafka, PE, DEE
Wingra Engineering, S.C.
A&WMA Conference 2002
Wingra Engineering, S.C.
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Introduction
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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
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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
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Public Service Commission
Department of Natural Resources
Department of Commerce
Village of Pleasant Prairie
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Village Permit Application
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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
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Based on USEPA RMP Comp Model
USEPA Assumptions
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Rail tank car contents lossed in 10 minutes
Toxic endpoint is distance to 200 ppm
Model Results
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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
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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
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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
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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
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ALOHA model
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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
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Comparison with Existing Sites
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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
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RMP includes Process Hazard Analysis
Identifies potential accidents, releases,
frequency, and mitigation methods.
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PHA Results
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Accidents Likely to Once per Year
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Accidents Likely to Occur Once Every 1-4 Years
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e.g. improper closure of after unloading railcar
Maximum release 10 lbs
e.g. truck valves are opened too quickly
Maximum release 10 lbs
Accidents Likely to Occur Once Every 20-75 years
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e.g. railcar derails
Maximum release 148,500 lbs
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NRC Ammonia Accidents
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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
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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
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Aqueous Ammonia and Urea
EPRI reports157 SCR installations in US
Of the 79 site reporting the reagent:
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Anhydrous Ammonia -- 63%
Urea -- 25%
Aqueous Ammonia -- 11%
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Anhydrous vs Aqueous Ammonia
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Anhydrous Ammonia
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Stored as compressed liquid
Immediately evaporates during release
Proposed due to widespread use and low cost
Aqueous Ammonia
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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
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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
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ALOHA use to estimate distance to end point.
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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
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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
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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
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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
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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.
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