To improve the flexibilities of coal-fired boilers

the subcritical and supercritical front and rear wall opposed coal-fired boilers and subcritical and ultra-supercritical tangentially coal-fired boilers are selected as research objects to carry out experiments. Through low load running test of three boilers and variable load disturbance test of one boiler

the control characteristics and regulating quality of main parameters during low load and variable load running of four typical coal-fired boilers are compared and analyzed. The results show that

the lowest load of stable combustion of boilers with different structures without oil can reach 17%Pe~25%Pe. The boiler with large capacity has better performance of steady combustion with the lowest load. The main steam pressure

main steam temperature and reheat steam temperature decrease rapidly with the load reduction of boilers. As the boiler load decreases

the excess air coefficient increases

and the increment of fuel NO_x is much larger than that of thermal NO_x

causing the change trend of NO_x concentration is generally opposite to that of boiler load.