已知锅炉燃烧产物飞灰可燃物<img src="https://nimg.ppkao.com/2019-04/xiaotian/2019041513530517116.jpg?sign=7c39c21e0e2feee8a13f400a1a68c1e3&t=62d6e857" />，燃煤收到基灰分<img src="https://nimg.ppkao.com/2019-04/xiaotian/20190415135328754.jpg?sign=6e23e7664cccd49ee4a95dd66871a27f&t=62d6e857" />，燃煤低位发热量<img src="https://nimg.ppkao.com/2019-04/xiaotian/2019041513533711586.jpg?sign=0a6ccac0546e0292d2bed230aaa64e77&t=62d6e857" />，飞灰占燃总灰分的份额<img src="https://nimg.ppkao.com/2019-04/xiaotian/2019041513535493085.jpg?sign=d6e6f9d8955ff65f15e1a326e230eb06&t=62d6e857" />（锅炉效率每下降1%，煤耗增加3.5g/kWh）。求飞灰可燃物对煤耗的影响。