Boiler

A boiler including first means defining a primary combustion zone,

• second means defining a combustion gas receiving zone disposed above said primary combustion zone,
• passage defining means disposed between said first and second means for connecting said primary combustion zone and said combustion gas receiving zone,
• coal burning means disposed at the lower end of said primary combustion zone and including means for injecting coal into said primary combustion zone, spreader means for distributing said coal across the lower end of said zone, and air delivery means for delivering combustion air upwardly into said primary combustion zone and through said spreader means,
• combustion means disposed adjacent the upper end of said primary combustion zone for delivering combustion air and a fluid fuel to said primary combustion zone, said combustion means being located below the passage defining means and is constructed and arranged for projecting fluid fuel and combustion air downwardly and inwardly into said primary combustion zone and in a direction which intersects said spreader means for producing a flame which extends into said zone and backwardly up through passage defining means into said combustion gas receiving zone whereby heat will be generated in said primary zone when either or both of said coal burning means or combustion means are operated,
• first water tube means disposed in said combustion gas receiving zone,
• second water tube means disposed in said primary combustion zone and disposed to be heated directly by said coal burning means or said combustion means,
• and third water tube means distinct from and interconnecting said first and second water tube means so that circulation therebetween will occur when said combustion means or said coal burning means are operated.