operating instructions - university of...

ECH 4224L Unit Operations Lab I Thin Film Evaporator

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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.


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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.


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Figure 3. Feed control valves, rotameter, and calibrating cylinder.


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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).


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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.


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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.


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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.


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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.


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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.


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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).


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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.


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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.


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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).

operating instructions - university of...

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