Mechanical Vapor Re-Compression

You may have seen the term Mechanical vapor compression or re-compression. It is basically the compression of vapors. The main difference is the general compression is used for gases not for vapors while this term is used for compression of vapors.

You know the difference in VAPOR & GAS...I am not going to cover it here.

The term is derived mainly from the compression of steam evaporated from the evaporators. It seems that the need got generated from the large scale desalination plants where very large amount of water is to be evaporated economically. So some brilliant chemical / mechanical engineer (I don't know him) thought about the use of some compression device so that evaporated steam it self can be used for heating purpose. It can be visualized from the diagram below.





The short description of the process is as below.

1. Unheated wastewater is fed to the liquid vapor separation tank (1) and is heated to a boil by the electric heating element (6).

2. Recirculation pump begins circulating heated water through the main heat exchanger (2) and back into the separation tank (1).

3.Steam flows up through the mist pad (8) to inlet side of vapor compressor (4).

4.Compressed steam from vapor compressor (4) is forced through the steam side of main heat exchanger (3) giving up latent heat to the counter flowing water from the separation tank (1).

5.High temperature distillate flows out of the main heat exchanger (3) to feedstock heat exchanger (7) giving up sensible heat to feedstock wastewater.

6.Upon reaching steady state, cold feedstock wastewater is fed at a constant rate through the feedstock heat exchanger (7) to raise temperature before feeding to recirculation loop.

7.Concentrate is periodically discharged based on temperature, conductivity or time from separation tank (1) to concentrate tank (9) through residue pump (10).

Benefits of MVR
The beauty of MVR is that by putting in a fraction of energy into comprssor, we can recover entire latent heat of steam. Thus it can produce a COP of >15. Though it has got many limitations but the economy ratio of 15 (Simply understand it this way - that one MVR evaporator is equal to 15 Multi Effect Evaporators running on successive levels.)

I will try to show one practical example with calculations in the next post as & when I get some more time from my schedule.

Work On it NOW....

Get Free Updates: *Please click on the confirmation link sent in your Spam folder of Email*

Continue to read this post...

Collapse this post back.

Drive Through ATM

Here is another truth....
Drive through ATM is a new concept & may be popular soon in Europe & then in the rest of the world.

The story goes like this....

A sign in the Bank Lobby reads: "Please note that this Bank is installing new "Drive-through" teller machines enabling customers to withdraw cash without leaving their vehicles. Customers using this new facility are requested to use the procedures outlined below when accessing their accounts. After months of careful research, MALE & FEMALE procedures have been developed. Please follow the appropriate steps for your gender."


MALE PROCEDURE

1. Drive up to the cash machine.
2. Put down your car window.
3. Insert card into machine and enter PIN.
4. Enter amount of cash required and withdraw.
5. Retrieve card, cash and receipt.
6. Put window up.
7. Drive off.

FEMALE PROCEDURE

1. Drive up to cash machine.
2. Reverse and back up the required amount to align car window with the machine.
3. Set parking brake, put the window down.
4. Find handbag, remove all contents on to passenger seat to locate card.
5. Tell person on cell phone you will call them back and hang up.
6. Attempt to insert card into machine.

7. Open car door to allow easier access to machine due to its excessive distance from the car.
8. Insert card.
9. Re-insert card the right way.
10. Dig through handbag to find diary with your PIN written on the inside back page.
11. Enter PIN.
12. Press cancel and re-enter correct PIN.
13. Enter amount of cash required.
14. Check makeup in rear view mirror.
15. Retrieve cash and receipt.
16. Empty handbag again to locate wallet and place cash inside.
17. Write deposit amount in check register and place receipt in back of checkbook.
18. Re-check makeup.
19. Drive forward 2 feet.

20. Reverse back to cash machine.
21. Retrieve card.
22. Re-empty hand bag, locate card holder, and place card into the slot provided.
23. Give appropriate one-fingered hand signal to irate male driver waiting behind you.
24. Restart stalled engine and pull off.
25. Redial person on cell phone.
26. Drive for 2 to 3 miles.
27. Release Parking Brake

JUST A JOKE............

Get Free Updates: *Please click on the confirmation link sent in your Spam folder of Email*

Continue to read this post...

Collapse this post back.

How True...???

Few lines, which are true for those whosoever read them. Here they are.....Tell us your comments what do you feel ??....??....??

1. Whenever I find the key to success, someone changes the lock.


2. To Err is human, to forgive is not a COMPANY policy.


3. The road to success??.. Is always under construction.


4. Alcohol doesn't solve any problems, but if you think again, neither does Milk.


5. In order to get a Loan, you first need to prove that you don't need it.


6. All the desirable things in life are either illegal, expensive, fattening or married to someone else.


Read More.....



7. Since Light travels faster than Sound, people appear brighter before you hear them speak.


8. Everyone has a scheme of getting rich?.. Which never works.


9. If at first you don't succeed?. Destroy all evidence that you ever tried.


10. You can never determine which side of the bread to butter. If it falls down, it will always land on the buttered side.


11. Anything dropped on the floor will roll over to the most inaccessible corner.


12. As soon as you mention something?? if it is good, it is taken?. If it is bad, it happens.


13. He who has the gold, makes the rules ---- Murphy's golden rule.


14. If you come early, the bus is late. If you come late?? the bus is still late.


15. Once you have bought something, you will find the same item being sold somewhere else at a cheaper rate.


16. When in a queue, the other line always moves faster and the person in front of you will always have the most complex of transactions.


17. If you have paper, you don't have a pen??. If you have a pen, you don't have paper?? if you have both, no one calls.


18. Especially for engg. Students----
    If you have bunked the class, the professor has taken attendance.


19. You will pick up maximum wrong numbers when on roaming.


20. The door bell or your mobile will always ring when you are in the bathroom.


21. After a long wait for bus no.20, two 20 number buses will always pull in together and the bus which you get in will be more crowded than the other.


22. If your exam is tomorrow, there will be a power cut tonight.

Get Free Updates: *Please click on the confirmation link sent in your Spam folder of Email*

Continue to read this post...

Collapse this post back.

Pressure Swing Distillation - Use it Economically - 2

In the last post we discussed a bit about azeotropes & refreshed ourselves on basics.

So basically because of deviations from ideality (Raoult's Law), liquid mixtures form azeotropes.

Now, the phase envelope at different pressure suggest that the azeotropes shift due to change in pressure and this is our best tool to be utilized in the industry instead of going for extractive distillation where other solvent is used to carry over more of one component than other thus breaking the azeotrope.

Let us understand the conventional azeotropic distillation system, its basic, benefit & limitation.

The conventional method of separation of binary azeotropes have been through addition of another solvent to shift the equilibrium by forming ternary azeotrope. This is called azeotropic distillation.

The common example is to separate ethanol & water using cyclohexane. The ternary azeotrope of 7% Water, 17% Ethanol & 76% Cyclohexane boils off at ~62 C. So in the binary azeotrope of 95.6 % Ethanol and 4.4% Water, just enough cyclohexane is added to remove the water in 7 to 76 ratio which removes all water with some ethanol leaving almost pure ethanol at the bottom.

For example - For 100 Kg of ethanol azeotrope (means 4.4 Kg water) requires 4.4 x 76 / 7 = 47.8 Kg of Cyclohexane. This will carry all water i.e. 4.4 kg of water, 47.8 Kg of cyclohexane & 10.7 Kg Ethanol.

So WHAT????????????

This is just an example of azeotropic distillation where it can be used effectively, but just think if the azeotrope of ethanol water is say 60:40 in place of 95.6 & 4.4. Will it be possible by same system of cyclohexane let us see...

In this hypothetical case, 40 Kg water requires 434 Kg of cyclohexane & how much ethanol it will carry....97 Kg. SO It is not possible because all ethanol is also carried to top distillate & practically no separation.

So now you have fair idea about the benefits & limitations of azotropic distillation.

Therefore, I would like to explain something more which is more beneficial.

Pressure Swing Distillation
As explained earlier, the azeotrope composition varies with change in pressure. This can be understood from the following diagram.



In the above figure, you can clearly see that the azeotrope point is shifting towards right side at high pressure.

So if let us say point B = 30% of component A is at azeotrope now this mixture if pressure is raised will become point C at high pressure & then distillation can continue to point D of another azeotrope at that higher pressure.

So now if I again subject point D to same low pressure then it will become point E at low pressure but distillation can continue. So I can achieve 100% of component A.

This can be applied to any system without any issue and you have following benefits.

1. You do not need any third component.
2. You do not need two more columns for removal of solvent - one for solvent removal from light component & one for solvent removal from heavy component.
3. So more hardware cost.
4. So more energy cost also.
5. PSD (Pressure Swing Distillation) is very simpler to design.
6. No losses of components.
7. No Bulk quantities handling hence very low cost of operation.
8. Many more.........I am not in a mood to loist down all.

Now I will give you one practical example.....which I personally handled.
Ethanol & Ethyl acetate also forms azeotropes & I came across one such system with large quantities. So instead of considering Az Disitll I used PSD.

In this case, We came across an Az mix of ~69% Ethyl acetate (EA) & 31% Ethanol (EtOH). When we ran Aspen Simulation for PSD, we fixed the pressure of first column as 5.5 Bar (After Optimization) & 300 mm Hg for second column.

Now feed was sent to first column & we could recover EA from bottom as 99.9% pure and top was fed to vacuum column at 300 mmHg pressure. Here we coul dseparate 99.9% EtOH from bottom again. the top cut from second column was recycled to first column and thus there was no loss.

I also used it for separation of cyclohexane, EA & EtOH separation later on & my experience shows that slight moderate pressures of 2 to 5 bar can change azeotropes significantly.

So now on try to use it for your benefit & get the recognition from your Boss.

Get Free Updates: *Please click on the confirmation link sent in your Spam folder of Email*

Continue to read this post...

Collapse this post back.