TM 10--3510--221--10
0005 00--1
HEATING SYSTEM THEORY
OF OPERATION
0005 00
HEATING SYSTEM
The heating system provides hot thermal fluid to the water recycle system for boiling water and to heat exchangers in
the washing/drying systems for drying laundry. Heating system operation consists of the following sub--operations.
THERMAL FLUID HEATING
An oil--fire heater is used to heat the thermal fluid that is circulating through the heating system. Ambient air is drawn
into the heater by the burner blower (M301). The blower consists of a squirrel--cage wheel driven by an electric
motor. A fuel pump, connected to the external source of JP--8, is also driven by the blower motor. When the blower is
on it pushes air through the heater outer chamber into the burner chamber. As the air flows from the outer chamber to
the burner chamber, it is preheated for maximum efficiency. The air gap created by routing the inlet air through the
outer chamber creates a barrier that eliminates the need to insulate the burner chamber while also reducing the
heater exterior surface temperature. This eliminates potential burn hazards to personnel and allows rapid cooldown
of the heater after shutdown. When air reaches the burner chamber it is mixed with the fuel and ignited. Ignition of
the fuel/air mixture occurs when two electrodes located in the burner chamber are energized with 10, 000 volts. This
high voltage is provided by the ignition transformer that is controlled by the flame programmer. As the hot air flows
through the burner chamber the coil filled with circulating thermal fluid is heated. The exhaust air is then vented from
the top of the heater through an exhaust stack. Operation of the burner blower and fuel pump are continuous when
the heating system is on. Ignition is turned off by the flame programmer once combustion is established. There are
times during laundry operations that the still is not being used. When this occurs the control system will turn the
heater on and off as necessary to maintain the required dryer air temperatures. This is accomplished by turning off
the burner blower and de--energizing fuel solenoid valves (FV300 and FV301). When combustion is required the
control system will provide a call for heat signal to start the burner blower and fuel pump. Once the flame programmer
verifies the blower is operating and fuel pressure is available it will energize the fuel solenoid valves and apply power
to the ignition transformer.
THERMAL FLUID CIRCULATING
The hot thermal fluid is circulated through the heating system by the thermal fluid pump (M300). The thermal fluid
pump is a centrifugal type pump driven by a electrical motor. When the thermal fluid exits the heater coil it is pumped
through the heat exchangers in the drum drying ducts. The thermal fluid then passes through the heatplates in the
still and is returned to the heater. As the temperature of the thermal fluid rises the thermal fluid will expand. To
compensate for this expansion the heater contains an expansion tank. When the thermal fluid is at ambient
temperature the expansion tank will be approximately one--third full of thermal fluid. As the heating system reaches its
maximum operating temperature the level in the expansion tank will rise to approximately two--thirds full. A vent is
provided at the top of the expansion tank to bleed air pressure from the system as the thermal fluid expands. A relief
valve is installed in the thermal fluid line at the outlet of the heater. This valve prevents the pressure of the thermal
fluid from exceeding safe operating pressures in the event of a control system failure.
