无码在线观看调教亚洲无码,国产高清无码在线观看一区,国产黄色在线自慰,日韩无码亚洲专区,无砖码永久免费视频在线

六、 Classified by fuel or energy used

1. Solid fuel boiler: burning solid fuel such as coal; 2. Liquid fuel boiler: burning liquid fuel such as heavy oil; 3. Gas fuel boiler: burning gaseous fuel such as natural gas.