Page 345 - Wastewater Solids Incineration Systems

306 Wastewater Solids Incineration Systems

an isolation valve, quick coupling, flow meter, and check valve. A block and bleed is
provided to prevent oil feed into an offline incinerator if the operator does not
remove the feed gun. The nozzle fits into the annular space of a larger pipe and purge
air is provided to the annular space for cooling.

4.2 Gas Systems
Most systems use natural gas, but some use digester gas or propane for a pilot on the
burner. Gas systems include a valve train assembly that includes pressure-reducing
valves, block and bleed assembly, flow and pressure measurement, and pressure-
regulating valves. Gas is provided to burners or for fluid bed incinerators to gas guns
that inject gas directly to the bed. Regulations require the bed temperature to be
higher than 732°C (1350°F) before direct injection of gas is permitted.
For fluid bed incinerators, gas guns are typically installed at the bottom of the
sand bed, which allows combustion to complete in the bed and not the freeboard.
The gas gun is an injection nozzle that extends into the bed to evenly distribute the
heat. The number of gas guns is dependent on size and can be as high as 16 guns for
large units.
For fluid bed incinerators, the gas supply pressure must be higher than the flu-
idizing air blower maximum discharge pressure to ensure flow. Facilities that replace
a multiple hearth with a fluid bed incinerator typically require a pressure increase.

4.3 Other Fuels
Coal has also been used successfully as an auxiliary fuel for a fluid bed incinerator.
Coal is an inexpensive supplemental fuel that has been used in facilities that are gen-
erating electricity and want to keep a constant heat rate. Coal handling and regula-
tory issues must be considered.