Computational Modeling of Pulverized Coal Fired Boilers by Vivek V. Ranade and Devkumar F. Gupta
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Computational Modeling of Pulverized Coal Fired Boilers by Vivek V. Ranade and Devkumar F. Gupta


1. Introduction.

2. Toward the Computational Modeling of Pulverized Coal Fired Boilers.

3. Kinetics of Coal Devolatilization and Combustion: Thermogravimetric Analysis (TGA) and Drop Tube Furnace (DTF)

4. CFD Model of a Pulverized Coal Fired Boiler.

5. Reactor Network Model (RNM) of a Pulverized Coal Fired Boiler.

6. Application to Practice.

7. Summary and the Path Forward.


Pulverized coal fired boilers have been and will be the mainstay of coalbased power generation worldwide. Such pulverized coal boilers are complex chemical reactors comprising many processes such as gas-solid flows, combustion, heat transfer (conduction, convection, and radiation), and phase change simultaneously.

Conventional pulverized coal fired boiler designs have been continuously improved upon and even today new combustion technologies are being developed. Improving the efficiency of pulverized coal (PC) fired boilers has been the focus of considerable efforts by the utility industry since it leads to several benefits (reduced emissions and consumption of coal per MWe). Typically, a one percent improvement in overall efficiency can result in a nearly three percent reduction in CO2 emission. Efficiency of these PC boilers depends on several issues such as flow and mixing, inter-phase and intra-particle heat and mass transfer, and homogeneous and heterogeneous reactions. Some specific issues are critical in determining overall efficiency of such boilers.

These are coal composition (proximate and ultimate analysis), characteristics of pulverized coal particles (shape and size distributions), reactivity of coal (devolatalization and combustion kinetics of coal), boiler design and configuration (size and shape of combustion chamber, burner design, number and locations of burners), excess air used, mixing of air and coal, flow mal-distribution, generation of fly and bottom ash particles, radiative heat transfer, heat recovery, and so on. Any efforts in improving the effective operating efficiency of these boilers therefore rest on fundamental understanding and control of the underlying flow, mixing, heat transfer, and reactions.

Computational modeling offers an excellent way to develop such fundamental understanding and to develop an ability to optimize boiler performance. However, through our interactions with industry, we realized that there is insufficient help available to practicing engineers for harnessing state-of-the-art computational modeling tools for complex, industrial boilerlike applications. Many boiler engineers either consider the complexities of industrial PC boilers impossible to simulate or expect miracles from off-theshelf, commercial modeling tools. These two diverse views arise because of inadequate understanding about the role, state of the art, and possible limitations of computational modeling.

This book is aimed at filling this gap and providing a detailed account of the methodology of computational modeling of pulverized coal boilers. The book attempts to develop and discuss an appropriate approach to model complex processes occurring in PC boilers in a tractable way. The scope is restricted to the combustion side of the boiler. The rest of the components of PC boilers are outside the scope. Even for the combustion side, the scope is restricted to the burner/excess air entry points to the exit of flue gases (and fly ash) from the heat recovery section. Milling and conveying of coal particles as well as further processing of flue gas beyond heat recovery sections (electro-static precipitators and so on) are beyond the scope of the present work.

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