fuel lean gas reburn in mineral processing kilns

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» Fifth level

Fuel Lean Gas Reburn in Mineral Processing Kilns

Dung (Edward) LeCadence Environmental Energy

Eric HansenThe Eric Hansen Group

Introduction – Ted T ReeseCadence Environmental Energy




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NOx Formation Mechanisms• Most NOx created by either Thermal or Fuel NOx

• Thermal NOx

• N2(air) + O2 NOx

• Fuel NOx

• N(fuel) + O2 NOx




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NOx Reduction Techniques• Process Control

Reduce excess air and flame temperature

• Process TechnologiesStaged combustionReburn air injectionLow NOx burnerSNCR

Fuel-Lean Gas Reburn Technology




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Fuel Lean Reburn ChemistryFuel-Lean Reburn is the method to inject hydrocarbon fuels in the oxidizing zone at the back-end of the kiln• NOx reacts with hydrocarbon radicals to form reduced

nitrogen species• These nitrogen species react with additional NOx to

form nitrogen gas




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Mechanical Schematic – FLR

Fuel-lean reburn = .CHx + Other Species

.CHx + NOx = .CN + .NH2 + H2O




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Post Combustion Methods for NOx Reduction

• Fuel lean reburning can be used to compete with the post-combustion NOx control technologies such as SNCR

• Cement Industry prefers SNCR as post-combustion NOx control method – WHY?

• SNCR & Fuel Lean Reburn - Goals• Generate NOx reducing species from decomposition of fuel

• Achieve NOx reductions in most economical form

• SNCR uses ammonia based reagents• Fuel Lean Reburn uses oil based reagents




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SNCR

Selective Non-Catalytic Reduction (SNCR)

• Most common reagents are aqueous ammonia and UREA

• Reagents are injected at specific temperature zones

• Targeted temperatures zone between 870C – 1100C

• NOx reduced to nitrogen gas and water

4NH3 + 4NO + O2 4N2 + 6H2O4NH3 + 2NO2 + O2 3N2 + 6H2O




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SNCR Efficiency

• Dependent upon many factors

• Temperature

• Molar ratio of NH3:NOx

• One concern of using SNCR is the ammonia slip level

• Slip occurs when unused ammonia is released at the flue

stack which may potentially create a visible plum stack

• Significant environmental concern to the community




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SNCR Costs

• Plants considering SNCR usage require new storage for reagent• SNCR involves heavy capital expenditures

• New storage equipment required• New permitting required • Annual reagent costs

• Costs only value is reduced NOx

• No other combustion benefit with ammonia use

Unlike SNCR - fuel lean reburn technology may require a much lower capital expenses and very

competitive reagent cost.




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Fuel Lean Reburn Comparison

• Cost of a pure NH3 is approximately $1000 US/ton• Cost of fuel lean reburn reagent such as oil or natural gas is less

Fuel Lean Reburn expected to require lower annual reagent costs and minimum additional storage

cost

• 1 ton of ammonia = $1000• 1 ton of oil = $790• 1 ton of natural gas = $168




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Fuel Lean Reburn Advantages

• Using a hydrocarbon based reagent

• natural gas or oil

• Most cement plants already use the hydrocarbon based

reagents to preheat the kilns during start-up

• A simple connection to supply the hydrocarbon based reagents

at the back end of the kiln

• Lean Fuel Reburn can be done at limited amount of cost to

achieve similar NOx reduction as using SNCR




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Fuel Lean Reburn Possibilities• Fuel Lean Reburn technology is primarily used in the power industry• Cement Industry uses the technology but minimal use• SNCR technology has been more popular compared to FLR

• SNCR poses challenges• High Capital costs• High annual operating costs• Expectation of increased reagent cost (high future demand)• Slip possible with SNCR use - visible stack emission

With documented SNCR costs and challenges,Fuel Lean Reburn method may pose an advantage

over the more common SNCR method




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Challenge to IndustryPerhaps the cement industry should re-examine the possibility of using fuel lean reburn method as a post-combustion NOx reduction before committing to a very expensive SNCR method

Why do cement plants seem to not have a problem with spending millions of dollars to utilize SNCR prior to trying fuel lean reburn?




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Stratified Gasses

• Kiln gasses are stratified at a high degree

• The top of the kiln contains high O2

and high temperature gasses

travelling at high velocity

• The bottom of the kiln contains CO2,

hot meals with much lower temperature

These gas layers never have the opportunity to mix

Getting these gas layers mixed is the key to fuel-lean reburn

(Increased performance by eliminating kiln gas stratification)




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Mixing Technology




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Need for Improved Mixing

• Better cross-sectional mixing in the kiln will allow fuel-lean reburn to mix effectively in the reburn zone for optimum NOx reduction

• Imagine highly stratified kiln gasses coming in contact with the atomized fuel-lean oil reburn. It would be very difficult to achieve well-distributed hydrocarbon radicals in the stratified gas stream to reduce NOx effectively. With additional mixing, hydrocarbon radicals from fuel-lean reburn will have a better chance in contact with NOx

This mechanism may vastly improve the ability to reduce NOx using fuel-lean reburn technology




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MIXING TECHNOLOGY




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Conclusion

In general, fuel lean reburn method may be used as an alternative solution for the post-combustion NOx.

At present, SNCR is widely considered the chosen post combustion method for NOx reduction but it comes with large capital investment and ongoing reagent costs.

The fuel lean reburn method may still not widely adopted as a method of NOx reduction in cement industry, but it appears to deserve a reexamination because it may significantly reduce the customer’s capital and reagent costs while achieving the same or better NOx reduction efficiency than SNCR.




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Fuel Lean Gas Reburn in Mineral Processing Kilns

Dung (Edward) LeCadence Environmental Energy

Eric HansenThe Eric Hansen Group

Introduction – Ted T ReeseCadence Environmental Energy

fuel lean gas reburn in mineral processing kilns

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