Method for controlling temperatures in the afterburner and combustion hearths of a multiple hearth furnace

In a method of incinerating combustible waste in a multiple hearth furnace containing a series of superimposed hearths which comprises feeding the combustible waste at the upper end of the furnace and passing the waste downward through a series of combustion hearths, supplying air to the combustion hearths to combust the waste material, and discharging the inert solid products of combustion at the lower end of the furnace, while the gaseous products of combustion flow upward countercurrent to the flow of waste material through the hearths and into an afterburner to remove the malodorous gases and/or pollutants, said afterburner being located after the uppermost waste handling hearth, the improvement wherein the temperatures of the afterburner and individual combustion hearths of the multiple hearth furnace are simultaneously controlled by:

• (A) splitting the waste feed between (1) the uppermost waste handling hearth and (2) the hearth directly below the uppermost waste handling hearth in such proportions as to control the temperature of the afterburner to a temperature within preselected limits;
• and
• (B) controlling the supply of combustion air to the individual combustion hearths in sufficient quantities so as to operate the combustion hearths at a temperature at or below a preselected maximum temperature;
• wherein said steps (A) and (B) are synchronized in response to the temperature of the afterburner and also in response to the temperatures in the individual combustion hearths by (I) controlling the temperature of the uppermost waste handling hearth below temperatures which would result in thermal stress of the furnace parts beyond safe operating limits and yet high enough to maintain the temperature of the afterburner within preselected limits to remove malodorous exhaust gases, and (II) controlling the temperatures of the combustion hearths by supplying air to the individual hearths in amounts sufficient to control the temperatures of said individual hearths at temperatures at or below preselected maximum temperatures, which temperatures are below that which would cause thermal stress in the furnace parts.