Investigation on a new lignite predrying power generation system combined with a front air heater

Abstract

Many lignite-fired power plant are built near the coalfields located in high latitudes where the winter is cold and long. The front air heater is generally installed to protect the rotary air preheater from low-temperature corrosion, which increases the amount of low pressure extraction steam reducing the thermal efficiency of steam cycle. A new combined power generation system integrating the lignite predrying system, the heat regenerative system and the front air heater was proposed to obtain better energy matching and to improve the system adaptability to low temperature regions. The new system can not only provide sufficient heat source for the lignite dryer and the front air heater but also comprehensively utilize the heat of the dryer exhaust and extraction steam under different ambient temperature conditions and lignite dryness requirements. The effects of the lignite drying degree and the ambient temperature on power plant performance were analyzed. The boiler efficiency of new lignite predrying power plant is higher than that of the conventional lignite-fired power plant by about 4.4%. As the lignite dryness changes from low to high, the working mode of new system is switched from mode B to mode C once the lignite dryness is above 0.14 kg·kg⁻¹ at an ambient temperature of −30 °C.

Keywords:

• Lignite drying
• front air heater
• power plant
• waste heat recovery

Additional information

Funding

This work was financially supported by China Postdoctoral Science Foundation (Grant No. 2018M643643).