September 30, 2008

Just Time Pass.....

Just Time Pass....
Some fun facts from another blog called tellmewhyfacts

  1. Venus is the only planet that rotates clockwise.

  2. Elephants are the only animals that cannot jump.

  3. Google receives about 200 million search queries each day.

  4. The first owner of the Marlboro company died of lung cancer.

  5. Russia has the most movie theaters in the world.

  6. Canada is an Indian word meaning "Big Village"

  7. Pearls melt in vinegar.

  8. The Eiffel Tower has 1792 steps.

  9. Each king in a deck of playing cards represents a great king from history. Spades - King David, Clubs - Alexander the Great, Hearts - Charlemagne and Diamonds -
    Julius Caesar.

  10. If a statue in the park of a person on a horse has both front legs in the air, the person died in battle; if the horse has one leg front leg in the air, the person died as a result of wounds received in battle; if the horse has all 4 legs on the ground, the person died of natural causes.

  11. Honey is the only food that does not spoil. Honey found in the tombs of Egyptian pharaohs has been tasted by archaeologists and found edible.

  12. Guinness Book Of Records holds the record for being the book most stolen from Public Libraries.

  13. Donald Duck comics were banned in Finland because he didn't wear pants.

  14. If you can see a rainbow you must have your back to the sun.

  15. There are only four words in the English language which end in '-dous': tremendous, horrendous, stupendous, and hazardous

  16. The colder the room you sleep in, the better the chances are that you'll have a
    bad dream.

  17. No piece of paper can be folded more than 7 times.

  18. The term Cop comes from Constable on Patrol, which is a term used in England.

  19. More steel in the US is used to make bottle caps than to manufacture automobile

  20. Humans and dolphins are the only species that have sex for pleasure.

  21. Last one added from my side for my Indian friends.

  22. There are only two Hindi words which end on -dook; Sandook & Bandook. - Tell me the third one if you Can

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September 23, 2008

Process Checklist for Energy Saving in Distillation

Distillation operations have been branded as high energy users. An estimate says 3-5% of the total energy used in the United States was for distillation.

Therefore it is necessary for process engineers to have a ready check list for energy saving in distillation columns. In this post we are suggesting a list for process side. This does not include general recommendations for utilities.

Here is the Process Check List.
  1. What is present energy usage per unit of production? Keep electrical energy and mechanical energy separate from heat energy. Keep separate usage of steam at different pressures. Don't forget to include energy used for auxiliaries such as
    instrument air, vacuum pumps or cooling water.

  2. What is present energy usage per unit of production by competitors? If lower usage, why?

  3. Are foremen and operators sufficiently skilled and trained to incorporate energy conservation techniques in their job duties?

  4. Can product purity be lowered, thereby reducing column reflux and reboiler heat duty?

  5. Can column operating pressure be allowed to float with ambient conditions with subsequent reduction in reflux and reboiler heat duty?

  6. When column is operated at production rates below the economic production rate, is reflux flow reduced to maintain same reflux ratio and lower reboiler heat duty?

  7. Can circulation in the main process e.g. in absorber - stripper combination be reduced.

  8. Is feed stream at optimum temperature to maximize separation and reduce column heat duty requirements.

  9. Is location of feed to column at optimum position?

  10. Can column internals be replaced with more efficient design?

  11. Can additional trays be installed in stripping or rectification sections of column to improve separation, thereby reducing heat duty requirements?

  12. Can an impurity be withdrawn from column to improve separation?

  13. Can the technique of pasteurization be used on existing column, thereby eliminating further separation operations?

  14. Is it economically feasible to convert column operation to a heat pump or vapor recompression cycle?

  15. Can control system be updated to automatic control with an economic payout and subsequent savings in energy requirements?

  16. Can steam supply pressure be allowed to float ?

  17. Are exchangers used in heat recovery maximizing the available heat recovery, considering economics? Will additional exchangers or revisions in the flow scheme improve heat recovery?

  18. Has a procedure been developed for deciding when to remove exchangers that are used in heat recovery service for cleaning? Procedure is based upon economics.

  19. Can excess heat from other process units within the plant be used in this process unit?

  20. Is heat being recovered from column pumparounds at the highest temperature level? Are pumparounds at best tray locations for heat recovery and column separation?

  21. If column operates at high overhead temperature, has heat recovery from overhead being maximized by using two stage condensation and cooling?

  22. Can control valves be resized for less rangeability, but still maintain required system control? Benefits are reduced pressure drop and power loss across the new, larger control valve.

  23. a. If production is to be increased by installing another column, can present column be cascaded with new column to save energy?

  24. Can columns in the distillation train be resequenced to improve separation, production and reduce energy usage?

  25. Can a vacuum pump replace a steam ejector at an energy saving and economic benefit?

You can add more if you have done something else.

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September 16, 2008

Excel Sheet For Steam Leak Calculation

One of the most talked about energy wasters is steam leakage from "bad" steam traps and leaking fittings. Steam traps are blamed for being inefficient or worn out and causing as much as 10% of the generated heat from steam to be lost. Is this true or just a sales method to sell more traps? It turns out that steam leaks cause a significant energy loss.

In general you can find many references where steam losses from different leak sizes at different steam pressures are listed. An example shows that a 1-inch union was found leaking at a loss of $3000 per year. The repair cost was $50 or a six day payout. So the point is whatever be the size of leaks or whatever be the pressure of steam the payback is generally in days compared to high fuel cost now a days.

If condensate is recovered, leaking traps can cause an excessive return temperature and cause failure of the condensate return pumps. Severe water hammer can occur
as hot steam contacts condensate that has cooled below the temperature of the steam

The leakage rate can be easily calculated by using general orifice equation.

Q = K x d^2 x H^0.5

Example template sheet in Excel is attached herewith for your easy use. In the said example steam of 34 bar can have a leakage rate of 17.0 Kg/hr from 1 mm hole. This is equal to Rs. 95000 / year in fuel loss. Normal repair cost can be only few thousand Rs. resulting in payback of few days/months. Therefore a regular survey of such leakage systems is necessary for every process plant.

Download Excel Sheet Here

The following steps are recommended for saving energy in your steam condensate distribution system and starting an effective steam energy management program:
  • Develop an estimate of the cost of steam leaks based upon your plant costs similar to other articles or references. A method for demonstrating visually to plant people what these losses are can be made.

  • Run a survey, recording all leaks, size, cost, and location.

  • Check the operation of all installed disc traps used for drips and steam tracing. If found leaking, consider replacing with a more efficient type trap. Before replacing, check installation design and confirm trap size (not over or undersized).

  • Check installation and operation of steam traps used on equipment using the sound detection method, the pyrometer method, or the glove method. The installation should be checked for proper trapping. Items checked include strainer, check valve, back pressure, orifice, and inert gas venting. Improper venting can cause a severe reduction in heat transfer rate.

  • Check vent valves on steam jacketed equipment and kettles for proper operation (removal of inerts without steam loss).

  • Start a preventative maintenance program to maintain the steam distribution system in excellent condition. If manpower is not available in maintenance, you can have the operating people maintain a simple log for their area of responsibility.

  • Steam trap manufacturers will be happy to furnish information to assist in your energy saving program to reduce steam losses, but use your own economic costs to decide whether to replace, repair, or redesign the system.

  • It is always beneficial to collect condensate at different pressures in different flash drums to recover flash steam
  • .
  • Also connect each high pressure drum liquid to subsequent low pressure drum

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September 09, 2008

Expansion Tank Sizing for Thermic Fluids

The design of the expansion tank in a liquid phase heat transfer system using Thermic fluids or other organic fluids is an important parameter in the total system’s successful operation.

It is important to design an expansion tank correctly as it can result in lower maintenance, lesser failure, low downtime, higher onstream factor etc.

The main function of the expansion tank in a heat transfer system is to provide
for fluid expansion, which can be greater than 25% of its original volume depending on the fluid used and the operating temperature.

Since the tank is usually installed at the highest point in the system, it also can serve as the main venting point of the system for excess levels of low boilers and moisture which may accumulate in the heat transfer fluid. The highest point installation also creates positive head pressure to the pump’s inlet, providing flooded pump suction with uninterrupted flow of fluid to the user station. A simplified drawing showing a suggested positioning of the expansion tank in a heat transfer system is given below.

The expansion tank should be sized so that it is 25% full at ambient temperature and 75% full at normal operating temperature. This sizing should cause positive fluid pressure to the pump’s suction side during system startup and should minimize the
vapor space in the tank during normal operation.

Fluid expansion between two temperatures can be calculated by dividing the fluid’s density at the lower temperature by the density of the fluid at the higher temperature — i.e., the density of Therminol® 66 at 40°F is 8.47 lb./gal. and changes to 6.72 lb./gal. at 600°F. Thus the expansion of Therminol 66 is 8.47/6.72 = 126% of the original volume at 40°F when heated to 600°F.

Therefore, an expansion tank for a 1,000-gallon Therminol 66 system operating between 40°F and 600°F should be sized for 260 gallons of expansion. Since this expansion represents 50% of the tank volume (the volume between 25% and 75% full), the expansion tank should be 520 gallons in size.

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September 02, 2008

Easily calculate LMTD orally

You may feel frustrated when somebody suddenly ask you about LMTD for the given heat exchange condition. That time you feel screamed if you do not have calculator with you.

Also, when you just begin using your calculator somebody answered the LMTD value and you feel surprised & wonder how he did it so quickly?

Now you can also do it.

LMTD can easily be calculated manually by the difference of airthematic means of fluid temperatures. Got it or Not....NO Problem. Here is an Example.

Suppose Hot fluid is entering at ~140°C & leaving at ~110°C. So its Airthmatic mean is 125°C.

Now if Cold fluid is entering at 40°C & leaving at 60°C its mean (average) is 50°C

Now the difference of two mean i.e. 125 - 50 is 75°C.
So your LMTD should be ~75°C.

Let us check it with conventional formula.
Hot side difference = 140 - 60 = 80°C
Cold side diff = 110 - 40 = 70°C

So LMTD = 10 / Ln(80/70) = 74.88°C

So an error of <0.2%. Usually it is less than 1%.

Hope all of you find it useful.

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