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Prediction of inlet SO2 concentration of wet flue gas desulfurization (WFGD) by operation parameters of coal-fired boiler

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Abstract

Circulating fluidized bed (CFB) boilers with wet flue gas desulfurization (WFGD) system is a popular technology for SO2 removal in the coal-fired thermal power plant. However, the long response time of continues emission monitoring system (CEMS) and the hardness of continuously monitoring the coal properties leads to the difficulties for controlling WFGD. It is important to build a model that is adaptable to the fluctuation of load and coal properties, which can obtain the SO2 concentration ahead CEMS, without relying on coal properties. In this paper, a prediction model of inlet SO2 concentration of WFGD considering the delay between the features and target based on long-short term memory (LSTM) network with auto regression feature is established. The SO2 concentration can be obtained 90 s earlier than CEMS. The model shows good adaptability to the fluctuation of SO2 concentration and coal properties. The root-mean-squared error (RMSE) and R squared (R2) of the model are 30.11 mg/m3 and 0.986, respectively. Meanwhile, a real-time prediction system is built on the 220 t/h unit. A field test for long-term operation has been conducted. The prediction system is able to continuously and accurately predict the inlet SO2 concentration of the WFGD, which can provide the operators with an accurate reference for the control of WFGD.

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Data availability

The datasets analyzed during the current study are not publicly available for the sake of safety and privacy of power plant related, but are available from the corresponding author on reasonable request.

Abbreviations

A :

Ash content of the coal, %

bc :

Bias vector of the cell output

bf :

Bias vector of the forget gate

bi :

Bias vector of the input gate

bo :

Bias vector of the output gate

Ca/S:

Moler ratio of Ca and S

c t :

Cell output at moment t

FBT:

Temperature at bottom of furnace, °C

FMT:

Temperature at middle of furnace, °C

FNP:

Furnace pressure, Pa

FOT:

Flue gas temperature, °C

FTT:

Temperature at top of furnace, °C

f t :

Forget gate e at moment t

h t :

Hidden state of the LSTM cell at moment t

i t :

Input gate at moment t

MSP:

Main steam pressure, Pa

n :

Number of sample

OCF:

O2 concentration in the flue gas, %

o t :

Output gate at moment t

PAF:

Primary air flow rate, m3/h

R 2 :

R Squared

RMSE:

Root-mean-squared error

SAF:

Secondary air flow rate, m3/h

Sash :

Weight fractions of sulfur in the ash, %

SCF:

SO2 concentration in the flue gas, mg/m3

Scoal :

Weight fractions of sulfur in the coal, %

TCF:

Total coal feeder rate, t/h

tanh:

Tanh function, \(\mathrm{tan}h\left(x\right)=({e}^{x}-{e}^{-x})/({e}^{x}+{e}^{-x})\)

W c :

Weight of the cell output

W i :

Weight of the input gate

W o :

Weight of the output gate

W f :

Weight of the forget gate

x t :

Input vector at moment t

\({y}_{i}\) :

SO2 concentration measured by CEMS

\({\widehat{y}}_{i}\) :

Predicted SO2 concentration

\(\overline{y}\) :

Average value of measured SO2 concentration

\({\Delta }_{r}{G}^{o}\) :

Standard Gibbs free energy change of reaction, kJ/mol

\({\eta }_{\mathrm{SR}}\) :

Sulfur retention percentage, %

\(\sigma\) :

Sigmoid function, \(\sigma \left(x\right)=1/(1+{e}^{-x})\)

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Funding

This work is supported by the National Key Research and Development Plan (2022YFC3701500) and the Fundamental Research Funds for the Central Universities (2022ZFJH004).

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Authors and Affiliations

  1. State Key Laboratory of Clean Energy Utilization, State Environmental Protection Center for Coal-Fired Air Pollution Control, Zhejiang University, Hangzhou, 310027, China

    Zhongyang Zhao, Qinwu Li, Yuhao Shao, Chang Tan, Can Zhou, Haidong Fan, Chenghang Zheng & Xiang Gao

  2. Jiaxing Research Institute, Zhejiang University, Jaixing, 314000, China

    Can Zhou, Chenghang Zheng & Xiang Gao

  3. Jiaxing Xinjia’aisi Thermal Power Co., Ltd, Jiaxing, 314000, China

    Lianming Li

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  1. Zhongyang Zhao
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  2. Qinwu Li
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  5. Can Zhou
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Contributions

Zhongyang Zhao: conceptualization, investigation, methodology, visualization, validation, writing — original draft, writing — review and editing. Qinwu Li: validation, methodology. Yuhao Shao: investigation, methodology. Chang Tan: investigation. Can Zhou: investigation. Haidong Fan: investigation. Lianming Li: validation. Chenghang Zheng: conceptualization, supervision, Writing — review and editing, funding acquisition. Xiang Gao: conceptualization, supervision.

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Correspondence to Chenghang Zheng.

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Zhao, Z., Li, Q., Shao, Y. et al. Prediction of inlet SO2 concentration of wet flue gas desulfurization (WFGD) by operation parameters of coal-fired boiler. Environ Sci Pollut Res 30, 53089–53102 (2023). https://doi.org/10.1007/s11356-023-25988-5

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