Page 339 - Wastewater Solids Incineration Systems

300 Wastewater Solids Incineration Systems

system needs to be designed to discharge a higher pressure than the fluidizing
blower. Multiple-hearth furnaces (MHFs) are typically fed at the top.

2.1 Cake Pumps
There are two types of cake pumps used. The most common is the high-pressure
piston pump because it is able to develop nearly 6895 kPa (1000 psi) of material pres-
sure and can convey material up to 152.4 m (500 ft), depending on the solids charac-
teristics. In general, the drier the cake, the more difficult it is to pump. For shorter
distances, a progressing cavity pump may be considered.
2.1.1 High-Pressure Piston Pump
The high-pressure piston pump consists of a hydraulic unit, auger feeder, and pump.
The hydraulic unit uses a pump to develop hydraulic pressure which is used to
operate the auger feeder and pump. The auger feeder has two screws that convey the
solids from a collection bin to the pistons. Because the feed and fill connections are
near the discharge, poppet valves are used to control the fill and discharge cycle of
the pistons. High-pressure piston pumps are available with one or two discharge
connections. Because most incinerators have two feed points, the cake pumps typi-
cally are equipped with two discharge connections with independent piping systems
to the incinerator. The advantage of a two-pipe system is that the solids and heat are
more evenly distributed, resulting in smaller temperature gradients within the incin-
erator. A photograph of a high-pressure piston pump is presented in Figure B.1.
The sizing of the cake pumps needs to be based on the maximum and minimum
feed rates anticipated. The operator typically has control over the timing of the dis-
charge but not the volume. If the pump is too large, the volume may overwhelm the
incinerator and cause temperature gradients.
2.1.2 Flow Measurement
Cake pumps can have two types of flow measurement: a pulsating flow meter or a
proprietary system that measures the volume displaced. Both systems have been cal-
ibrated to within 5% accuracy.
2.1.3 Pipeline Lubrication System
For high-pressure applications, a lubrication pump, injection ring, and pressure
sensor are added to minimize the pressure. The system is designed to start on high
pressure and inject a thin film of water along the interior of the pipe to reduce fric-
tion losses. The water can reduce by 50% the operating pressure of the piping system.