Page 117 - Wastewater Solids Incineration Systems

86 Wastewater Solids Incineration Systems

The central shaft is lined with castable refractory to protect it from high tempera-
tures. The castable refractory is anchored to the metal surfaces by V-shaped stainless
steel anchors welded to the metal surface. Shaft refractory is typically 140 mm
(5.5 in) thick and rabble arm refractory is typically 50 mm (2 in) thick.

9.3.3 Burner Systems
Burners are mounted on steel structures called burner boxes. They may be solidly
bolted in place or have a swing-out feature that allows for rapid cleaning. Burner
boxes are refractory lined and contain a monolithic burner tile composed of either
ceramic or castable refractory. The burner is arranged with an angled hole, typically
convex to allow the burner flame to propagate into the hearth and in the desired
firing axis. Good burner design provides for the burner flame to propagate into the
hearth without impinging on the rabble arms or the sludge bed. The location and
quantity of burners per hearth varies.
Depending on burner type, an MHF can use a variety of fuels including natural
gas, digester gas, fuel oil, and bunker oil. Each burner has connections for main and
pilot fuel(s), combustion air, control piping, flame rod or UV sensor, spark plug, and
sightglass. A description of the auxiliary components associated with burners—
including fuel trains, safety controls, combustion air blowers, and fuel pumps—are
described in Appendix B.

9.3.4 Central Shaft Return Air
Ducts with motorized dampers in the central shaft allow heated air to be either
returned to the furnace as auxiliary heat or to be vented. Control systems allow
adjustment of the amount of air returned to the furnace and vented.

9.3.5 Auxiliary Combustion Air Ports
Earlier MHFs were equipped with auxiliary combustion air ports located on the
walls of lower hearths. These combustion air ports were equipped with manual or
motorized dampers. The desired damper opening was set by the operator, either
locally or remotely, and auxiliary combustion air was drawn into the furnace by the
draft created by the induced draft fan.
Later versions of MHF were equipped with auxiliary combustion air ports on mul-
tiple hearths to allow air to be injected to hotter hearths to control temperatures. These
ports were equipped with motorized dampers that were controlled automatically.