Page 220 - Wastewater Solids Incineration Systems

186 Wastewater Solids Incineration Systems

bin vibrators or activators, ash dust filters, and material-level measurement equip-
ment. Problems with ash bins include bridging and uneven distribution of accumu-
lated ash. Bridging is caused when portions of the stored ash achieve enough struc-
tural strength in combination with the bin sidewalls to support ash accumulation
above while allowing free flow of ash from below. Moisture in the ash, which can
accumulate from diurnal temperature and humidity changes, increases the proba-
bility of bridging. Bridging reduces usable bin capacity and complicates its emp-
tying into the transport container or vehicle. Bridging can be reduced through the
use of bin vibrators or activators or pulsed air jets.
Level measurement devices that contact ash are prone to failure because of the
hostile environment. Load cell sensors and noncontact ultrasonic level sensors have
been used successfully where the specific density of the ash is known and is consis-
tent. However, this instrumentation does not replace routine inspections and manual
soundings of ash bin levels. The greatest operational success is achieved through pro-
grams that include the following:
• Frequent operator inspection,
• Frequent unloading of ash bins before maximum storage levels are reached,
and
• Daily tracking of generated and disposed ash quantities.

The storage vessel size should be based on the quantity of ash that is to be pro-
duced and frequency of removal.

3.2.2.2 Dry Ash Conditioners
Ash conditioners are mechanical devices designed to facilitate wetting of ash before
discharge to a truck or roll-off container. They may consist of a helical screw con-
veyor or dual screws or a rotary conditioning drum, and may include service water
addition nozzles, baffling, scrapers, and associated drives and isolation gates.
Dry ash conditioners must be properly maintained to perform effectively and
equipment drives must be sufficiently sized for wetted ash conditions. These load-
ings can be significantly higher than loadings imposed by dry ash alone. Control of
service water flow requires frequent operator attention because of changing ash wet-
ting characteristics and dry ash flow rates from the ash storage bins.
Conditioning water can contribute significant added weight to the ash to be trans-
ported. This added weight translates into increased vehicle trips and tipping fees at
commercial landfills. Added water accounts for as much as 30% of the conditioned