Emissions Control

REI takes an integrated approach to pollutant emissions from combustion sources. We continue to innovate and develop new models and modeling tools in the areas of NOx, SO2, and mercury. We put our modeling tools to work for clients, solving problems in a variety of industrial applications. REI has modeled over 100 different utility boilers firing a range of fuels including coal, oil, gas, biomass, syngas, TDF and blends of these fuels. Types of systems modeled include arch-fired, cyclone-fired, roof-fired, tangential-fired, turbo-fired and wall-fired units. REI’s primary expertise is in pollutant formation (e.g., NOx control), but we also have experience with furnace performance and operational impacts. REI is also involved with developing next-generation models to evaluate the performance of Air Pollution Control Devices (APCD) downstream of boilers. A major focus here is the behavior of mercury, sulfur oxides and particulates as combustion products move from the boiler to the stack. Components studied include SCR, ESP, scrubbers and baghouses.  In addition to the utility industry, REI provides research and consulting services for industrial furnaces (including applications in the steel, aluminum, and glass industries), incinerators, rotary kilns, smelters, and stokers.

REI also has extensive experience with on-site experimental programs in the area of emissions control.  From program planning to demonstration management and data analysis, REI’s skilled engineers can help in every stage of a testing campaign.  REI has investigated emission control from lab-scale up to pilot- and full-scale demonstrations.


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REI advises clients on a wide variety of NOx control technologies. We use our CFD and other modeling tools to predict emissions in utility and industrial boilers for integrated NOx control:

  • Low NOx burner
  • Staging, Overfire Air (OFA), ROFA
  • Burner Optimization and Balancing
  • Flue Gas Recirculation (FGR)
  • Gas and Coal Reburning
  • Fuel Lean Gas Reburning (FLGR)
  • Selective non-catalytic reduction (SNCR)
  • Rich-Reagent Injection (RRI)
  • Fuel Blending and Switching
  • Biomass and Syngas Co-firing

Water_Wall_Corrosion_in_T-fWhen we evaluate NOx control strategies, we do more than prediction NOx emissions. REI has the tools and expertise to look at aspects of NOx control that affect operation and performance of combustion systems, including:

  • Unburned Carbon-in-ash (LOI)
  • Waterwall Wastage and Corrosion
  • Deactivation of SCR Catalyst
  • CO Oxidation
  • Fouling and Slagging
  • Fuel Efficiency
  • Furnace Heat Transfer

In some coal-fired boilers, corrosion rates can be dominated by by the presence of reducing gases (CO and H2S) or by the deposition of ash or char containing partially reacted material (sulfur and carbon). Accordingly, REI has modeled the evolution of sulfur species in the combustion zone.

The evolution of SO3 in the backpass of a coal-fired boiler impacts both operation (air heater fouling, low-temperature corrosion) and emissions (visible plumes). REI uses models for SO2 oxidation to predict production of SO3. Detailed CFD modeling of injection of calcium and magnesium for SO3 control in the backpass has also been carried out.

The impact of SO3 on mercury control has also been studied using REI’s mercury process model, MerSim.  SO3 is known to interfere with mercury capture by activated carbon (or unburned carbon in fly ash). SO3 condenses out of the gas phase as H2SO4 when temperatures drop below the H2SO4 dew point. Most power plants operate at flue gas temperatures above the dew point to avoid corrosion. However, many particle surfaces or equipment surfaces may be below the dew point. H2SO4 condenses on the surfaces and on unburned carbon, removing sites for mercury oxidation and absorption.

Sulfur emissions have also been studied in other applications, such as copper smelting.

REI has extensive expertise in mercury behavior, from mercury control technology assessments to compliance strategies and prediction of mercury emissions.  With in-house mercury measurement equipment, REI can provide mercury testing support from lab-scale to pilot- and full-scale demonstrations.  REI’s mercury process model, MerSim, can be used to evaluate potential operating changes or technology additions to predict changes in mercury emissions.  Custom models for new technologies are also possible.  REI can also provide Computational Fluid Dynamics Modeling to asses mixing and distribution for sorbent injection.

Mercury Control Assessment can include:

  • Detailed plant analysisHg2
  • Planning, oversight, and review of measurement campaigns to characterize current mercury emissions and removal of mercury by existing air pollution control equipment
  • Screening and recommendation of appropriate mercury control technologies
  • Experimental evaluation of control strategies: pilot and full-scale demonstration
  • Predictive evaluation of control strategies using detailed process simulations
  • Hg control demonstration planning, management, and analysis
  • Thorough understanding of mercury measurement techniques and mercury mass balance
  • Comprehensive CFD modeling to address mixing and distribution issues
  • Analysis of specific coal sources to determine if the plant can maintain compliance if fuels are changed
  • Assessment of current and future compliance status to determine if existing equipment can be tuned to improve mercury reduction
  • Evaluation of pollution control device impacts on plant mercury emissions to determine how planned Air Pollution Control Devices (APCD) changes will impact current emissions

REI Advantages

  • Leader in modeling mercury chemistry
  • Independent, third-party assessment
  • Experts in control technologies and compliance strategies

REI has developed expertise in CO2 Control technologies, particularly oxy-combustion. In oxy-combustion, fuel is burned with a combination of pure oxygen and recycled flue gas instead of air. This provides a high quality CO2 stream that would be ready for sequestration or use in enhanced oil recovery activities. REI has extensively studied retrofitting a typical coal-fired boiler for oxy-combustion. The different combustion environment present during oxy-combustion leads to difference in gas volumes, gas heat capacities, flame ignition, radiative heat transfer, particle and acid gas clean up requirements, and potential deposition and fouling issues.

REI has investigated:

  • Burner Performance
  • Char oxidation
  • Aerosol Formation
  • Slagging & Fouling
  • Corrosion
  • Soot Formation
  • Radiative Heat Transfer
  • Mercury Speciation and Emission