Operating Instructions

Transcription

1 Operating Instructions Before operating the thin film evaporator, please be aware of all safety concerns associated with this experiment: Burn hazard from the column and steam lines, Chemical hazards associated with ethylene glycol. 1. Preparation for Start-up Make sure that the product tanks and their sight glasses are empty. If necessary, pump the tank content to the feed tanks on the 2 nd floor (see Section 3) and empty the tank sight glasses (see Section 4). Go to the 2 nd floor and select the tank to be used as a feed source (note that some of the tanks are used for storage of pure EG). Mix the content of the selected feed tank o Make sure that all valves are closed except the inlet and outlet valves for the selected tank, the main outlet valve, and the suction and discharge valves of the mixing pump (see Figure 1). o Turn the mixing pump on by using a switch on the electric panel o Turn the mixing pump off after about 10 minutes. Close the pump suction and discharge valves. Figure 1. Feed tanks on the 2 nd floor (left) and piping around the feed mixing pump (right). On the 1 st floor, check that the enclosure for the inline refractometers is pressurized (see Figure 2). The enclosure is required to be pressurized by clean dry air to ensure that there are no flammable 1

2 gases near electronic equipment contained in the enclosure. If pressure in the enclosure is too low, the low pressure alarm will go off. If this happens, adjust the air valve on the enclosure control panel until the pressure gauge indicates Safe. Figure 2. System components near the enclosure for inline refractometers: (a) side view and (b) front view. 2

3 2. Start-up Turn on the cooling water for heat exchangers and condensers by slowly turning the main water valve shown in Figure 3. Make sure that the water valve is fully open. If necessary, adjust rotameters for water flows to individual heat exchangers and condensers (the rotameters are located on the back of the evaporator stand). Figure 3. South side view of the TFE. Turn on the seal water for the TFE rotor and set it to 2.5 GPM using the rotameter located on the right side of the TFE system (see Figure 3). Turn on the electric switch for the votator (see Figure 2). 3

4 Figure 4. Steam and air lines. Preheat the evaporator: slowly open the blue TFE steam valve (see Figure 4). 1. Make sure to wear a heat-resistant glove the steam line is hot! 2. It is important to open the valve slowly to prevent thermal shock to the system. The gap between the rotor blades and inner walls of the evaporator is very narrow (0.75 mm) and thermal shock may cause distortion of the system. 3. Start with opening the steam valve so that the steam pressure is approximately 5 psi. 4. Continue to slowly open the valve so that the pressure changes at a rate of about 20 psi per minute. 5. Stop when the steam pressure reached 75 psi. Open the main feed valves located on near the power switch (see Figure 2). Check calibration of the inline refractometers by briefly sending feed flow through all of three them. 1. Use the 3-way valves located below the refractometer enclosure (see Figure 2) to change direction of the flow. Direction of the flow is indicated by the short end of the valve handle, as shown in Figure Verify that all three refractometers read the same value. 3. Return the 3-way valves into their original positions to allow the product flow into the product refractometers. 4. Take a feed sample using the sample port shown in Figure 2a. 5. Measure the sample composition using the tabletop refractometer and compare the result with the measurements of the inline refractometers. 4

5 Figure 5. 3-way valve with the short end of the handle pointing (a) to the right and (b) to the left. The dashed red lines indicate the path of the fluid flow corresponding to the position of the valve handle. On the first day of the lab: Calibrate the feed rotameter; use the feed control valves to adjust the feed flow rate (see Figure 6). Use the feed control valves to set a desired feed flow rate for your experiment. Figure 6. Feed control valves and rotameter. Important: Never feed liquid into the evaporator without the rotor turning. Doing so may cause: 1. Uneven heating around a stationary rotor, which may cause deformation of the rotor. 2. Accumulation of liquid in the process area, which will generate an extra resistance to the rotor when it starts turning, which may damage the system. 5

6 Open the steam injector valve (see Figure 3) to generate vacuum in the system. Do this slowly to avoid shocking the system with a rapid pressure change. 1. Make sure to wear a heat-resistant glove! 2. Use the pressure gauge located above the product tanks (see Figure 7) to set the desired system vacuum pressure. Figure 7. Vacuum gauge. 3. While the system is running: Measure and record product concentration and temperature every 5 minutes (for both the top and bottom products). o o The product concentration is measured by inline refractometers. Don t forget to convert Brix % to ethylene glycol concentration! The product temperature should be read using a thermocouple reader. Make sure that the thermocouple type displayed by the reader is K. If it s not, press the TYPE button on the reader until K is displayed. Record liquid level in the product tanks every 5 minutes After reaching a steady-state, measure the flow rate of the steam condensate using the bucket and stopwatch method. 6

7 4. Recycling products After an experimental run is complete, it is necessary to recycle the content of the product tanks back to the feed tank. In order to do this, at least one of the group members should go to the 2 nd floor while other group members should remain on the 1 st floor. Liquid transfer requires communication between the 1 st and the 2 nd floors. Please use 2-way radios (available in the control room) for this purpose. On the 2 nd floor: Make sure that 1. The 2 nd floor return valve is open (see Figure 8) 2. The inlet valve for the feed tank is open (see Figure 1). Important: there is a line for deionized (DI) water next to the return line on the 2 nd floor (see Figure 8). Make sure to open the valve on the return (and not the DI water) line. The DI water line should be used by the lab technician only. Figure 8. Product return and DI water lines near the feed tanks on the 2 nd floor. Wait for a signal from the 1 st floor. Once you receive a signal, open the deadman valve on the return line (see Figure 9). In order to keep this valve open, it is necessary to hold on to its handle. Once the handle is released, the valve returns to the closed position. Monitor the level of the feed tanks while the fluid is being transferred. If you see that one of the tanks is overflowing, release the deadman valve. Figure 9. Deadman valve on the return line (2 nd floor). 7

8 On the 1 st floor: If the system is in operation, reduce the vacuum pressure to below 8 in Hg. This is required for proper operation of the return pump (see below). Open the main return valve located next to the power switch (see Figure 2) and the return valves located next to the product tanks (see Figure 10). Figure 10. Product tanks, return line, and return pump. Inform the person on the 2 nd floor that you are about to start the return pump. Make sure that they are ready to open the deadman valve before turning the pump on. The return pump is air-operated. Turn it on by opening the on/off air valve located next to the return pump (see Figure 10). Adjust the air control valve so that the pump makes about 2 clicks per second. Once the tanks are empty, close the return valves and turn off air supply for the return pump. 8

9 5. Taking a product sample or emptying sight glass while the evaporator is under vacuum Note: This procedure should only be performed if one of the inline refractometers is faulty. The purpose of this procedure is to take a sample that can be analyzed using a desktop refractometer. Close the sight glass valves (see Figure 11). o This isolates the sight glass from the product tank Open the vent valve on the sight glass o This lets atmospheric air into the sight glass Open the sample port valve and take a sample (or drain the sight glass completely) Figure 11. Product tank. After the necessary amount of fluid is taken from the sight glass: o Close the sample port valve o Close the vent valve o Reestablish the connection between the sight glass and the tank: Slightly open the bottom sight glass valve. Slowly open the top sight glass valve until it is fully open. This will return the sight glass to the same pressure as the tank and, if the tank is not empty, you should see liquid filling up the sight glass. Slowly open the bottom sight glass valve until it is fully open. o It is important to follow this procedure for reestablishing connection between the sight glass and the tank. Opening the valves out of order or too quickly may result in a fast and turbulent flow from the tank to the sight glass, which will activate a check valve 1, which will prevent the liquid level in the sight glass from reaching the liquid level in the tank. 1 The purpose of the check valve is to prevent a large spill in case the sight glass is broken. A broken sight glass will lead to a fast flow from the tank to the sight glass and will activate the check valve, thus preventing spilling the entire content of the tank. 9

10 6. Shut down Close the blue steam valve. Keep the steam mains valve open at all times (see Figure 4). This is necessary to for automatic condensate purge from the steam line. Keep the feed valve open for several minutes. The liquid flowing through the evaporator will help condense steam remaining in the evaporator jacket. You should see reduction in the steam pressure on the gauge shown in Figure 4. Wait until the steam pressure has reduced to about 5 psi. Close the steam injector valve. Close the feed valve and wait until the flows into the product tanks stop. Turn off the votator motor. Turn off cooling water for the heat exchangers and condensers and the seal water for the TFE rotor (see Figure 3). Pump the liquid contained in the product tanks back to the feed tank on the 2 nd floor (see Section 4). 10