Effect of hydrothermal treatment on co-combustion of paper sludge with coal: thermal behavior, NO emissions, and slagging/fouling tendency

ABSTRACT

In this study, the effect of hydrothermal treatment (HTT) on co-combustion of paper sludge with subbituminous coal was investigated. The paper sludge was treated by the hydrothermal pilot plant at a temperature of 197°C and a pressure of 1.9 MPa for 30 min. Thermal degradation during co-combustion was studied by thermogravimetric analysis. When burning hydrothermally treated paper sludge (HTT-PS) with coal, multiple decomposition behaviors were observed. The ignition temperature of the mixture was reduced since the paper sludge was more reactive than coal. NO emissions performance was tested by a batch-type fixed bed combustor. Results showed that the NO emissions could be reduced by 26–31% and, therefore, the mixture of coal and HTT-PS yielded lower NO emissions compared to the original mixture. NO conversion of HTT-PS was also lower. X-ray photoelectron microscopy suggested that HTT dissolved or protonated amide and simultaneously condensed the nitrogen functional compounds resulting in lower NO emissions. The ash composition of paper sludge was positively altered by HTT and slagging and fouling indices of HTT-PS were improved.

KEYWORDS:

• Paper sludge
• hydrothermal treatment
• co-combustion
• NO emissions
• slagging and fouling

Acknowledgments

The authors acknowledge Prof. Toshihide Baba and Dr. Ken Motokura from the Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, for XPS measurement. Mr. Areeprasert was financially supported by the Faculty of Engineering, Kasetsart University, Thailand. The authors gratefully acknowledge Dr. Kriengkrai Suksankraisorn and Mr. Korakoch Phetdee from the Siam Cement Public Company Limited for the substantial support.

Disclosure statement

No potential conflict of interest was reported by the authors.