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Research Papers: Energy Systems Analysis

Modeling Time Variations of Boiler Efficiency

[+] Author and Article Information
Ahmed Rehan

Systems Engineering Department,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: rehan_eme@yahoo.com

Mohamed A. Habib

Department of Mechanical Engineering,
KACST TIC on CCS,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: mahabib@kfupm.edu.sa

Moustafa Elshafei

Department of Systems Engineering,
King Fahd University of Petroleum and Minerals,
KFUPM Box 405,
Dhahran 31261, Saudi Arabia
e-mail: elshafei@kfupm.edu.sa

Iyad T. Alzaharnah

Dhahran Technovalley,
King Fahd University of Petroleum and Minerals,
Dhahran 31261, Saudi Arabia
e-mail: iyadtz@kfupm.edu.sa

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received June 7, 2016; final manuscript received September 23, 2017; published online November 9, 2017. Assoc. Editor: Reza Sheikhi.

J. Energy Resour. Technol 140(5), 052001 (Nov 09, 2017) (15 pages) Paper No: JERT-16-1240; doi: 10.1115/1.4038236 History: Received June 07, 2016; Revised September 23, 2017

Boiler's efficiency is one of the important performance indicators of boiler. To keep track of operation cost, efficiency needs to be calculated with adequate accuracy by employing effective mathematical tools. In this work, a new modification in conventional mathematical formulation of efficiency is presented based on time-varying efficiency using time-varying operational variables of boiler. This modification was accomplished using indirect method of efficiency by applying experimental data of variables for certain time span. Moreover a second-order dynamic model of flue gas temperature (FGT) has been derived to construct the mathematical formulation of efficiency only in terms of available inputs. The resulting input–output-based model proved to be in quite agreement with efficiency calculated from experimental data. After modeling, influence of variations in air to fuel ratio (AFR) and fuel flow rate (FFR) upon efficiency has been discussed and it has been shown that time-varying efficiency covers deeper aspect of dynamic relation between efficiency and other input of boiler especially AFR and FFR. Moreover, it has been established that efficiency interacts with the dynamics of boiler, and in this respect, a dynamic relation between combustion process and boiler dynamics has been constructed via efficiency.

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Figures

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Fig. 1

Fuel composition by volume %

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Fig. 2

CO variation with equivalence ratio (ϕ)

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Fig. 3

Plots of available data and AFR

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Fig. 4

Time variations of flue gas constituents

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Fig. 5

Time variations of AFR

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Fig. 6

Time variations of specific heat of flue gas Cp (kCal/kgC)

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Fig. 7

Plot of hfg (kCal/kgC) of water with time

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Fig. 8

Time variations of losses L1–L4

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Fig. 9

Time variations of losses L5 and L6

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Fig. 10

Time variations of efficiency

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Fig. 11

Control implementation with dynamic efficiency

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Fig. 12

Plot of FFR (SCFH) data

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Fig. 13

FGT plot of model and experimental data

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Fig. 14

Validation plot of FGT using data of second boiler

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Fig. 15

Efficiency model with inputs and outputs

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Fig. 16

Time variations of efficiency using FGT model

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Fig. 17

Efficiency variations with AFR for different loads

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