Energy, exergy and economic analyses on heat pump drying of lignite

Abstract

Evaporative drying of lignite is an energy intensive process. In this study, the heat pump is integrated with a lignite drying system to decrease the energy consumption rate of lignite drying. The performance of heat pump drying is energetically and exergetically evaluated with developed models. Results show that the power consumption rates to dehydrate 1 kg of water from raw lignite in the heat pump drying system without and with lignite preheater are 660.82 and 585.62 kJ (kg H₂O)⁻¹, respectively. Exergetic analysis indicates that most exergy is destructed in the condenser and the evaporator in the heat pump drying. The case of lignite-to-electricity process (i.e., a lignite-fired power plant integrated with heat pump drying) is studied to examine additional benefits of heat pump drying to the downstream industrial processes that consume dried lignite. Thermodynamic and economic models are developed. Net efficiency of the lignite-to-electricity process can be increased by 1.4 and 1.57 percentage points for heat pump drying without and with lignite preheater, respectively. Preliminary economic analysis shows that the integration of heat pump drying without and with lignite preheater can earn additional 1.42 and 1.73 million USD, respectively. The influences of drying system and heat pump parameters are also analyzed.

Keywords:

• Lignite
• heat pump
• thermodynamics
• exergy
• economic

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Ming Liu is an associate professor at the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, China. He received his Ph.D. from Xi’an Jiaotong University in 2013. His research interests include thermodynamic analysis and optimization, drying technology and two-phase flow.

Shan Wang is a graduate student at the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, China. Her research interest is the thermodynamic analysis of lignite-fired power plants and CHPs.

Rongtang Liu is a graduate student at the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, China. His research interests include pyrolysis and drying of lignite, and thermodynamic optimization.

Junjie Yan is a professor at the State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an China. He received his Ph.D. from Xi’an Jiaotong University in 1998. His research interests include enhanced heat transfer, thermodynamic analysis and optimization, steam–water two-phase flow, phase-change heat transfer, and process control.

Additional information

Funding

This work was supported the Natural Science Foundation of China (Grant Number 51776146, 51436006).