CFD Modeling Overview

Benefits of CFD Modeling

  • Reduces costs—CFD modeling allows designers to predict results before installation, avoiding costly errors
  • Saves time—CFD modeling eliminates time consuming on-site trial and error situations and unnecessary costs
  • Provides detailed insights—CFD modeling gives insight into furnace operation that cannot be obtained through testing/measurement
  • Identifies furnace operational problems and solutions
  • Enables pre-installation testing of fuels, equipment, and accessories

Our Experience

CFD modeling is used to: 1) validate the baseline furnace combustion performance and 2) facilitate design of the air pollution control system for a particular unit.

We have developed our own modelling team and capability. The types of models include: 1) non-reacting flow; 2) fuel combustion and reacting flow; and 3) pollutant formation (i.e., NOx, SOx, LOI, CO, etc), with fuel ranging from coal, biomass, oil to natural gas. We have also analyzed a wide range of boiler types from pulverized fuel (p.f.) boilers (tangential or wall-fired) with a wide range of burners to fluidized bed and stoker units. Our models have addressed a variety of chemical-reacting flows associated with fuel combustion and reacting flow:

  • Solid fuel combustion chemistry (devolatilization, char oxidation kinetics)
  • Gas volatiles (i.e. gaseous fuel) combustion
  • CO finite rate chemistry
  • Soot formation chemistry (heavy oil combustion)
  • NOx formation chemistry (thermal NOx, fuel-N conversion chemistry)
  • SOx formation chemistry (SO2 and SO3) and reduction by limestone (CaO+SO2)
  • Urea and ammonia chemistry to reduce NOx
  • Sorbent chemistry for SO2, Mercury, and HCl capture.

RAS’s PhD level experts have modeled over 90 models on a wide variety of boiler configurations:

  • Circulating fluidized bed (CFB)
  • Tangential-fired
  • Wall-fired
  • Cyclone
  • Stoker/grate fired
  • Kilns
  • Various burner types

and fuel types:

  • Variety of coals
  • Biomass
  • Biomass co-fired with coal
  • Waste products
  • Oil
  • Natural Gas
  • Waste and landfill gases

Burner Design and Optimization

Burner design and setting are the keys to flame stability in the boiler. We routinely use CFD to perform parametric analysis to optimize burner design, to retrofit modification solutions, and to set the burner settings for specific boilers.

Model of single burner combustion.

 

CFD modeling shows the change of flame shape when secondary air swirling angle increases from 25° to 60°

 


Furnace Combustion and OFA Design

CFD modeling has been used extensively in furnace combustion with an objective of Low-NOx Burner (LNB) and Over-Fire Air (OFA) design (either traditional OFA or advanced OFA) for a specific boiler with a specific fuel. It is routinely used in our feasibility study as well as detailed engineering phase. The model provides detailed predictions of furnace combustion, heat transfer, and emissions (incl. NOx, CO, LOI, etc). We have used CFD combustion model and designed over 50 OFA systems.

 

Models of a 350-MW tangential furnace combustion between baseline and Advanced OFA. The model demonstrates that while Advanced OFA significantly reduces NOx, the furnace O2 distribution and CO combustion is significantly improved by Advanced OFA high momentum air jets.


SNCR Design and Optimization

CFD modeling can also be used in designing a SNCR system for a specific boiler. As the performance of SNCR system is very sensitive to the furnace temperature, the model helps us determine the number of SNCR injectors and their locations.

Models of furnace temperature (upper), urea injection trajectory (middle) and NOx concentration (lower) of Advanced SNCR system, as applied to a 700 MW boiler.

Model of furnace outlet NOx concentration without urea injection (upper) and with urea injection (lower)


Fuel Switch Combustion Engineering

RAS offers coal-to-gas, and coal-to-biomass fuel switch studies. We have unmatched expertise and extensive experience on biomass cofiring and conversion projects. Our capabilities include:

  • Burner modification or retrofit
  • Evaluate impact of fuel properties on furnace combustion, (e.g., moisture content, particle size, volatile matter content, etc.)
  • Control of slagging and corrosion formation
  • Impact on furnace exit gas temperature and hence steam temperature and boiler efficiency
  • Application of emission control technologies

CFD modeling of coal-to-wood conversion for a 500 MW wall-fired furnace. Modeling shows predicted NOx emissions between coal and biomass with various NOx reduction technologies.

CFD modeling of coal-to-wood conversion for a 500 MW wall-fired furnace. Modeling shows significant combustion differences between fuels and burner settings.


Dry Sorbent/Activated Carbon Injection

Integrated with Proprietary Kinetic Chemistry Submodels

Reaction Analytic Solutions has significant modeling experience and strong capability in design and optimization of Dry Sorbent Injection (DSI) and Activated Carbon Injection (ACI) technology for pollutants removal from flue gas. In addition to Conventional CFD flow modeling, we have incorporated a number of our in-house proprietary sorbent chemistry sub-models, including:

  • Hydrated lime + SO3
  • Hydrated lime + HCl/SO2
  • Trona + HCl/SO2
  • Limestone + SO2
  • Activated carbon + Hg/HgCl2

CFD predictions of SO3 concentration and reduction percentage for a DSI system on a 450-MWe unit for 3 Cases with injection lances.

CFD model to determine injection locations and number of injections to obtain the best coverage of sorbent downstream before airheater inlet.

The following table summarizes the advantages of chemistry-based Advanced CFD modeling versus flow-only (or non-chemistry) Conventional CFD modeling, in terms of CFD outlet and evaluation capabilities. Advanced CFD model provides “real-life” predictions, including not only the mixing and flow related output that a conventional CFD can provide, but also gas species concentration and reduction predictions. Advanced CFD model approach provides a much comprehensive and useful tool for evaluating a number of important design/operating parameters as well as sorbent properties.