6/21/02 DOE NETL Pittsburgh 2002 1

SNCR System

Design, Installation, and

Operating Experience

David Wojichowski, Principal

De-NOx Technologies, LLC
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The Basic Process

• SNCR is a gas phase reaction between

ammonia radicals and NO to form N2

and water in the absence of a catalyst.

• Strong Temperature Dependence

NH2- + NO +1/2O2 N2 + 2 H2O
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The First Patent

• First patented by Exxon for use on

combustion effluents in 1975, using

ammonia.

• Established required temperature range

and stoichiometry/performance.

• Patent expired in 1990.
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Other Patents

• EPRI was soon thereafter granted a

very similar patent , using urea, in

1980.

• EPRI furthered the art by patenting

SNCR in excess of 2000 degrees F in

the absence of oxygen.

• Commercialized in the late 80’s.

• The original two EPRI process patents

have expired as well.
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The Perfect World

• In laboratory conditions (insulated

tubular reactor with perfect mixing and

unlimited residence time), NOx

reduction greater than 90% has been

demonstrated.

• Ideal Conditions – Temperature of

1800F, Residence time greater than 0.5

seconds.
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"Perfect World" SNCR @NSR=2

-20

0

20

40

60

80

100

1318 1408 1498 1588 1678 1768 1858 1948 2038 2128

Temperature (F)

% NOx Reduction

0.2 sec 0.4 sec 0.6 sec 1.0 sec
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The Real World

• Rapidly declining temperatures

• Access limitations

• Imperfect mixing

• Liquid evaporation time delay

• Load swings

• Operator indifference

• Carbon Monoxide

• Ammonia Slip is Important
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Closest to Perfect

• Waste Incinerators, Wood/Bark Boilers,

CFB’s, some PC Boilers.

• All are characterized by reasonable

furnace plan dimensions, well defined

gas profiles, and adequate residence

time prior to first convective surface.

• Common performance is 50% reduction

at NSR = 1.0 and ammonia slip L.T. 10

ppm.
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"Real World" SNCR @NSR=2

-20

0

20

40

60

80

100

1318 1408 1498 1588 1678 1768 1858 1948 2038 2128

Temperature (F)

% NOx Reduction

0.2 sec 0.4 sec 0.6 sec 1.0 sec

Optimum

Injection

Location
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Ammonia Process

• Simplest and least expensive*

approach.

• Gaseous injection.

• Anhydrous ammonia has lowest

delivered cost.

• Storage and Handling issues.

• Low boiler corrosion risk.

* - Assumes typical tank/containment.
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Urea Process

• Liquid Reagent, with or without

atomization.

• Higher reagent costs, but friendlier

chemical.

• Equivalent performance and

stoichiometry.

• More difficult to distribute reagent

equally.

• Local boiler corrosion common.
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Design Considerations

• Heat or Dilute

• Load Range

• Injector Location

• Injector Number, Location, and Sizing

• Controls

• On-Site Urea Dissolver?
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Economic Summary

• Installed Cost – Utility scale $5-10/kW

• Installed Cost – Industrial $15-20/kW

• Negligible Outage Costs

• Operating Cost - $500-750 per ton NOx

removed using urea
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Optimization

• The more injectors the better.

• Use flat pattern nozzles if possible.

• Check flow balance once per day.

• Secondary dilution water quality is an

issue.

• Pull and inspect injectors once per

week.

• Generic reagent works fine.
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Operational Issues

• Corrosion

• Detached Plume Formation

• Air Heater Pluggage

• Nozzle Failure
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Corrosion

• Localized corrosion at liquid injected

SNCR facilities is a problem.

• Generally located in immediate vicinity

of injector ports, or on opposite walls of

narrow boilers.

• Especially problematic for fuels with

high chloride and sulfur.
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LOCALIZED CORROSION
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Short Term Corrosion Fixes

• Reduce liquid impingement

• Extended wall injectors

• Higher air pressure/flow

• Lower water flow

• Inconnel overlay
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Long Term Corrosion Fix

• Evaporate solution prior to injection.

• OTA (Once Through Ammonia) System

– Patent Pending.

• Simpler, Cheaper, Smaller.

• Demo in 2002.
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Plume Issue

• Quite common in non-scrubbed flue gas

• Most often detached from the stack

• Caused by condensation/combination at

lower temperatures.

• Ammonium chloride, ammonium

bisulfate, +?
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Plume Suppression

• Slip reduction – keep less than 10 ppm

• Nozzle orientation/operation key.

• Get good stack and operational data.

• Ammonia monitors recommended for

non-scrubbed facilities.
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Not so fast

• Detached plumes can be difficult to

diagnose and solve.

• Plumes observed at near zero slip

• Plumes not observed at high slip

• Not obvious from manual sampling

analysis.
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Air Heater Plugging/Corrosion

• Ammonium Bisulfate is a liquid above

300F

• Sticky material - difficult to remove.

• Not a problem with low sulfur fuels

• Again, minimize slip

• Another good reason for an ammonia

monitor.
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Injector Burn-out

• High Temperature Corrosion

• Erosion

• High alloy with heavy wall thickness

• Interchangable lances
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Combination Technologies

• Very compatible with combustion

controls.

– Low NOx Burners

– OFA Injection

– Gas Reburning

• NOx reduction approaching that of SCR

at lower capital cost - $30/kW, 60-80%

reduction.
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SNCR Summary

• Mature Technology

• Fuel Indifferent

• Low cost alternative for first 50%

reduction.

• Easily retrofitted

• Compatible with combustion

modifications for High NOx removal