Page 257 - Wastewater Solids Incineration Systems

Incinerator Operations 219

may have built up within the incinerator, the induced draft fan should be operated to
maintain negative draft. The time required to purge the incinerator of combustible
gases varies based on the size of the incinerator. Thirty minutes is generally suffi-
cient; however, in some cases a facility’s insurance agency may require a specific
purge time. Before purge, ensure that all safety limits are met and all equipment is
operable. In addition, the center shaft cooling air should be on before burner startup.
To begin heating up the incinerator, the operator should place all of the burner
pilots online. If the burners do not have pilots, the operator will proceed to the next
step and light only one burner on low fire. After approximately two hours, the oper-
ator should light the burner located on the lowest hearth that has burners on low fire.
Using the burner controller, the operator will increase the temperature at a rate of
approximately 10°C (50°F) per hour until the burner controller is at 50%.
After one hour with the burner controller at 50%, the operator should reduce
the burner controller to low fire and start another burner located on the same
hearth. The operator should maintain both burner controllers at low fire. When the
temperature stabilizes, the operator will start one burner located on the next
higher hearth on low fire. The two burners and pilots located on the lower hearth
should then be shut off.
When the temperature in any location within the incinerator reaches 260°C
(500°F), the operator should start rotating the center shaft at 0.5 rpm. The operator
should continue to increase the temperature on the higher hearths as done on the
lower hearths. The operator will follow these procedures upward through the incin-
erator from hearth to hearth and burner to burner until all of the burners located on
the highest hearth are on low fire. The operator will use the burner controllers to
increase the temperature by 10°C (50° F) per hour.
When the temperature in any location within the incinerator reaches 538°C
(1000°F), the operator should increase the rate of internal incinerator heating to 38°C
(100°F) per hour until the internal temperature reaches 593°C (1100°F). The operator
should allow the temperature to stabilize for three to four hours at 593°C (1100°F).
This temperature stabilization is necessary because when the temperature within the
incinerator first reaches 593°C (1100°F), only the surface of the refractory is at 593°C
(1100°F). By maintaining the temperature at 593°C (1100°F) for several hours, the core
temperature of the refractory will also be raised to 593°C (1100°F). This ensures evap-
oration of all moisture from within the refractory and provides the heat necessary to
start combustion of the feed cake. As previously noted, an internal temperature
higher than 593°C (1100°F) may be required before combustion can occur. The cold