operating instructions - university of...
TRANSCRIPT
ECH 4224L Unit Operations Lab I Thin Film Evaporator
1
Operating Instructions
Before operating the thin film evaporator, please be aware of all safety concerns associated with this
experiment:
Burn hazard from the steam lines. Always wear heat-resistant gloves when opening/closing
steam valves. Stay away from steam valves when you are not operating them to avoid an
accidental contact with a hot valve handle. Note: all steam valves in the system are painted red.
Excessive system vibration due to improper operation may loosen bolts on the steam line
flanges, which may lead to discharge of steam at high pressure. Turn off the votator motor
immediately if the system undergoes strong vibrations and ask the lab technician for assistance.
Chemical hazards associated with ethylene glycol (EG). Always wear nitrile gloves when taking
and analyzing feed and product samples.
Potential for large chemical spills due to mistakes during fluid transfer. Make sure to trace the
lines and check that correct valves are opened/closed prior to fluid transfer.
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 2nd floor (see Section 4) and empty the tank sight glasses (see
Section 5).
Go to the 2nd floor and select the tank to be used as a feed source (see Figure 1a). Note that some
of the tanks are used for storage of pure EG. If you are not sure which tank contains feed (i.e., a
water/EG mixture), take samples from ports on the outlet lines of the tanks (see Figure 1b) and
measure the sample concentrations using a tabletop refractometer.
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 1a and
c). Note that some of the valve handles may have been removed to avoid accidental opening of
a wrong valve. All valves with removed handles are closed. Please see the lab technician if
you need to open a valve with a removed handle.
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 suction and discharge valves.
On the 1st 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 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”.
On the 1st floor, check whether the votator level gauge (see Figure 3) reads zero. If not, ask the
lab technician to drain excess fluid from tubing attached to the gauge.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
2
Figure 1. Feed tanks on the 2nd floor: (a) overview, (b) sample port at a tank outlet, and (c) piping around the mixing
pump.
Figure 2. System components near the enclosure for inline refractometers: (a) side view and (b) front view.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
3
Figure 3. Feed control valves, rotameter, and calibrating cylinder.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
4
2. Start-up
Turn on the cooling water for heat exchangers and condensers. There are two main valves for
cooling water: a ball valve located high above ground (see Figure 4) and a globe valve located on
the back of the evaporator stand (see Figure 5).
1. Normally, the ball valve is open. If it is not, open it very slowly to avoid causing
vibrations in the piping.
2. Open the main globe valve for water
3. Ensure that the water valve for the barometric condenser (see Figure 5) is open.
4. If necessary, adjust rotameters for water flows to individual heat exchangers and
condensers (the rotameters are located on the back of the system, see Figure 5).
Figure 4. South side view of the TFE.
Turn on the seal water for the TFE rotor and set it to 1.0 GPM using the rotameter located on the
south side of the TFE system (see Figure 4).
Turn on the electric switch for the votator (see Figure 2).
ECH 4224L Unit Operations Lab I Thin Film Evaporator
5
Figure 5. Back side of the TFE
Figure 6. Steam and air lines.
Preheat the evaporator: slowly open the TFE steam valve (see Figure 6).
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.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
6
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 valve located 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 7.
2. Verify that all three refractometers read the same value. Contact the lab technician if
there is a discrepancy between the refractometer readings.
3. Return the 3-way valves to their original positions to allow the product flow into the
product refractometers.
Important: DO NOT keep feed flowing through the product refractometers for too
long, since it will fill up the product tanks very quickly!
4. Take a feed sample from the feed 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.
Figure 7. 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. This is necessary because, by default,
rotameter is calibrated for water. However, EG is much more viscous than water, which affects
the force balance involved in the rotameter calibration. The rotameter should be calibrated using
the inline calibrating cylinder (see Figure 8). To perform the calibration:
1. Close the feed shut-off valve above the rotameter.
2. Close the calibrating cylinder valve #2 and open the calibrating cylinder valve #1.
3. Adjust the feed control valve to achieve a desired rotameter reading for the flow rate.
4. Wait until the rotameter reading has reached a steady-state.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
7
5. Measure the liquid volume change in the calibrating cylinder during a set period of time
(e.g., 30 seconds). Note that the volume marked on the cylinder is in reverse direction
(i.e., the top of the cylinder is marked as 0). Therefore, use a difference between volume
readings to determine the flow rate1.
6. Close the cylinder valve #1 to stop flow into the cylinder.
Note: The calibrating cylinder has a small hole near its top. The purpose of the hole is to
maintain atmospheric pressure in the cylinder to prevent blockage of flow by compressed
air. Always monitor the level in the cylinder during calibration and make sure that
the level never reaches the hole near the top (to prevent spills). Always use the ball
valve (cylinder valve #2) and not the feed control valve to stop the flow into the
cylinder. Closing the control valve takes some time and the cylinder may overflow
before the valve is fully closed.
7. Drain the cylinder into the bottoms tank by opening the cylinder valve #2.
8. Repeat this procedure for several flow rates covering the entire range of the rotameter
readings.
9. Plot a calibration curve, i.e. a curve relating the rotameter reading with the actual flow
rate.
10. If the liquid level in the product tank is too high, return the content of the bottoms tank to
the feed tank (see Section 4).
Figure 9. Feed control valves, rotameter, and calibrating cylinder.
1 In addition to the volume scale, the calibrating cylinder has a flowrate scale. Do not use the flowrate scale, since it
assumes a different calibration procedure.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
8
Make sure that the calibrating cylinder valves are closed and the feed shut-off valve is open (see
Figure 9).
Use the feed control valve to set a desired feed flow rate for your experiment.
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.
Open the steam injector valve (see Figure 4) 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 10) to set the desired
system vacuum pressure.
Figure 10. Vacuum gauge and vacuum valves.
3. While the system is running:
Measure and record product concentration and temperature every 5 minutes (for both the top and
bottom products).
o The product concentration is measured by inline refractometers. Don’t forget to convert
Brix % to ethylene glycol concentration!
o 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.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
9
Periodically measure the flow rate of steam going into the steam injector. Use the vortex
flowmeter installed on the steam injector line for this purpose.
Periodically check temperatures at the outlets of the heat exchangers and condensers. Adjust the
cooling water valves, if necessary.
Periodically check the votator level gauge (see Figure 3). It is important to avoid accumulation of
the liquid at the bottom of the votator, since it may damage the rotor blades. If you observe an
increase of the level, purge the bottom of the votator by creating a pressure difference between
the votator and the product tanks. To do that, close the vacuum valves (see Figure 10) on the
product tanks and slightly close the steam injector valve (see Figure 4). Open the vacuum valves
and return the steam injector valve to its original position after purging is complete.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
10
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 2nd floor while
other group members should remain on the 1st floor. Liquid transfer requires communication between
the 1st and the 2nd floors. Please use 2-way radios (available in the control room) for this purpose.
On the 2nd floor:
Make sure that
1. The 2nd floor return valve is open (see Figure 11).
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 2nd floor
(see Figure 11). 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.
Wait for a signal from the 1st floor.
Once you receive a signal, open the “deadman” valve on the return line (see Figure 11). 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 11. Product return and DI water lines near the feed tanks on the 2nd floor.
On the 1st floor:
Close the feed valve.
Close the steam injector valve and wait for vacuum pressure to return to zero.
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 12).
ECH 4224L Unit Operations Lab I Thin Film Evaporator
11
Verify that the valve at the discharge of the return pump is open (see Figure 12).
Figure 12. Product tanks, return line, and return pump.
Inform the person on the 2nd 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 12). 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.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
12
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 13).
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 13. 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 valve2, which
will prevent the liquid level in the sight glass from reaching the liquid level in the tank.
2 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.
ECH 4224L Unit Operations Lab I Thin Film Evaporator
13
6. Shut down
Close the TFE steam valve. Keep the steam mains valve open at all times (see Figure 6). This is
necessary for automatic condensate purge from the steam line.
Keep the feed valve and the steam injector valve open for several minutes. The liquid flowing through
the evaporator will help condense steam remaining in the evaporator jacket. Keeping the steam
injector valve open will allow some of the steam to be condensed by the barometric condenser. You
should see reduction in the steam pressure on the gauge shown in Figure 6.
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 4 and Figure 5).
Pump the liquid contained in the product tanks back to the feed tank on the 2nd floor (see Section 4).