26-12-2012, 02:37 PM
Laboratory Instruction Manual for Boiler Simulation Unit
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Introduction
A boiler is a closed vessel in which water or other fluid is heated under pressure. The fluid or steam is then circulated out of the boiler for use in various processes or heating applications.
Boilers can be divided into three types. First, the fire-tube boilers are those with the heat source inside of the tubes, and the water to be heated is outside. Second, the water-tube boilers are those with the heat source outside of the tubes, and the water to be heated is inside. Third, primitive boilers are traditional boilers, the inefficient type where there are no tubes and the fire heats one side of the water container. Figure 1 shows a fire-tube boiler and a water-tube boiler [1]. Boiler construction started in the 17th century. The first water-tube boiler was built in 1804, and the first fire-tube boiler was built in 1811 [2].
Unit Layout
The boiler simulation unit that we use is built by G.U.N.T. company of Germany. The model is ET 860. The unit layout is shown in Figure 3. The plexiglass tank is modeled after the water chamber. The clarity of the tank allows observers to observe water level inside of the tank. The burner unit simulates the actual burner, but there is no actual flame. Since there is no actual flame, compressed air is supplied to simulate steam pressure, and drain water regulatory valve at the bottom of the tank can be opened to drain some water to simulate the water lost due to evaporation. The plexiglass tank is not airtight, so the compressed air is supplied to the pressurized copper chamber to which the manometer, the pressure switch, the pressure limiter, and the safety valve are attached. The switch cabinet contains various alarms, timer, and power switches. With fifteen switches, the error triggering circuit, attaching to the switch cabinet, can trigger fifteen different errors that are used to train the operators to solve problems.
Level Monitoring Sensors
Three level sensors are connected to three level switches. The level sensors are inside of the tank, whereas the level switches are on the switch cabinet. Figure 4 shows a picture of all three level sensors.
• Regulated level sensor number 1-5 is used to regulate the feed water pump. There are four electrodes, but only the middle two electrodes are used as minimum and maximum level sensors. When the water level reaches the minimum level, the pump is turned on. When the water level reaches the maximum level, the pump is turned off. No alarm is triggered. This level sensor can be activated and deactivated by the level switchnumber 1-5 on the switch cabinet. During normal operation, the level switch number 1-5 is turned on.
• Low-water level sensor number 1-7 is used as a precaution in case the level sensor number 1-5 malfunctions. If the water level reaches the level sensor number 1-7, the burner is shut down to prevent damage to the chamber. The red “low water” alarm located on the switch cabinet and the “low water” alarm located on the level switch number 1-7 on the switch cabinet are both lighted.
• High-water level sensor number 1-8 is used as a precaution in case the level sensor number 1-5 malfunctions. If the water level reaches the level sensor number 1-8, the pump is shut down to prevent water overflow. The “high water” alarm on the level switch number 1-8 on the switch cabinet is lighted.
Burner Unit
The burner used in this simulation unit is modified from an actual commercially available oil burner used in boilers for domestic hot water. As the operation of the burner is simulated, the operating state of the burner can be recognized from the noise of the burner fan and the display on the burner housing. The display on the burner housing is shown in Figure 6.
Operating Indicators and On-Off Switches
Burner operating indicator (7) illuminates when the pump is working, so does the pump operating indicator (8). The burner on-off switch (9) is used to turn on the burner and the pump changeover switch (10) is used to turn on the pump. There are two states for the pump changeover switch, stage 1 is for normal operation and stage 2 is for test operation. In normal operation, the pump starts and stops according to the water level sensors in the tank, and in the test operation, the pump always works, disregarding the water level sensors.
At the bottom right of the switch cabinet, there are a master switch (12) and an emergency stop switch (13). The master switch is used as a main power switch for the whole system and the emergency stop switch will shut the whole system down when pressed.
Time Control Device
The time control device (item 11 of Figure 7) is an electromechanical timer relay. The time setting is made on a rotary knob. A black trailing pointer indicates the time set, while a red pointer runs from the time set back to 0. Ten minutes prior to expiration, an acoustic signal is output as a pre-alarm. When the point position 0 is reached, the relay automatically shuts down the system; at the same time the “time out” alarm is signaled on the switch cabinet. Acknowledging the “time out” alarm by pressing it sends the red pointer back to where the black pointer is and the timing restarts.
When in operation the boiler must regularly be checked by a boiler attendant. At the latest every 2 hours the boiler attendant must ensure that the system is in correct working order. The boiler attendant must then operate the time control device. If this control device is not operated, the system automatically shuts down.