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Steam Coil Drum Heater Vs Electrical Coil


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#1 R.Ahmadi

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Posted 19 May 2018 - 01:11 PM

Dear all
what is the difference between steam coil drum heater and electrical coil in design basis of each case?

#2 Art Montemayor

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Posted 19 May 2018 - 01:39 PM

One utilizes utility steam; the other uses generated or purchased electricity.

One employs heat transfer tubes; the other uses electrical resistance elements.



#3 R.Ahmadi

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Posted 25 May 2018 - 04:20 AM

One utilizes utility steam; the other uses generated or purchased electricity.
One employs heat transfer tubes; the other uses electrical resistance elements.

Thank you for your attention, I know the difference, but what I don't know is the criteria of choosing one for special system. Is it chosen fluid-wise or other considerations?

#4 Saml

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Posted 25 May 2018 - 07:13 PM

Usually you use steam because electricity is usually more expensive. Don't take the following figures as exact. They are just order of magnitude examples from top of my head.

 

One

-  A natural gas boiler will have about 80% efficiency. The steam distribution may account for another 5% of losses. So you are getting 75% of the natural gas LHV in your heater.

-  The best combined cycle generators achieve an effiency of about 60% and you have another 6% loss in power transmission from the generator to your site. That is, you get about 55% of the fuel energy.

So, to begin with, you have higher cost of raw energy (natural gas, or other fuel) by about 40%.

 

Two

- The installation cost for a boiler is lower. You can intall a 50 t/h for a few millions.

- That is about 30 MW of heat. You will need to invest about 30 millions for the generation of that electricity. Add to this transmission lines, transformers and control equipment.

 

When you add the two costs, you see that heat in the form of electricity almost never compete with steam

 

 

So basically you go to electricity when you have a combination of conditions:

-  You have few exchangers that don't justify installing a boiler.

-  You don't have access to natural gas, so your options are to burn liquids or solids (more expensive) or purchase electricity.

-  High temperature (above 240 °C) that make you go above 600 psig steam, and you cannot justify installing a hot oil system.

-  You have the possitiliby of operating only when cheap electricity  is available (from wind or hydro) at night and can avoid operating on peak hours.



#5 R.Ahmadi

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Posted 26 May 2018 - 10:35 PM

Saml:

 

thank you for your attention and your answer.

You are true but I want to know the basic criteria for using them generally.  Because in the refinery I am working, I observed both. For example I found that Amin sump drum in GTU equipped with steam heater.  I should also add that the steam boilers and electricity power supply both are available however some sump drums equipped with steam coil the others equipped with electrical coil.



#6 Saml

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Posted 26 May 2018 - 11:44 PM

OK, so from your initial request that was

 

Dear all
what is the difference between steam coil drum heater and electrical coil in design basis of each case?

 

 

We are now talking about a specific case. This is a big advance.

 

Now, please. Not all the people here work in a Refinery so it is almost impossible to figure out the case. What is "Amin sump drum in GTU"? What are "some sump drums"?

 

However that is not the key point. The issue is that your question cannot be answered. As with most of engineering, you will have some rules of thumbs, some guidance, experience, legal requirement, standards, books and other (working) designs to copy from, but you can rarely state a procedure to make an engineering decision. There are too many variables in play.apart from the process consideration. Just to mention without expecting to be exhaustive.

 

- Layout: sometimes the connection is way more expensive that the equipment itself. Steam piping (specially if you also have condensate return) is generally more expensive than wires. So for remote loads (specially small ones), electricity may make sense.

 

- Time (You go for the fastest delivery time, not for what you would like)

 

- Availability (i.e. you have to use used equipment adapted to the new service). Or the boiler is limited. Or the substation transformer is at its limit.

 

- Operability

 

- Reliability and Redundancy (Sometimes having two sources of heat is better)

 

- Political. Say that an agreement was reached with the local goverment that 50% of the material will be purchaed from suppliers in the country. And those sump coils are part of the deal.

 

- Past experience of people involved in the decisions (or stubborness).

 

- Mistakes or Wrong Specs (i.e. you made a lump sump contract without provision for taking operating costs into account for the bidding, and you end up with a lower capital cost option that is more expensive to operate).

 

- Plain corruption. Someone may have a friend that sells electrical equipment. Just keep in mind that this might be the case when you see unexplainable decisions. Obviously, if you have proof or a firm suspicion of wrongdoing, your duty is to report it.

 

 

So, I would suggest that you post the specific cases (duty, fluids begin heated, temperature, pressure, location in the layout, etc), and we may (just may) figure out what criterion was used in each case.

 

Best Regards


Edited by Saml, 26 May 2018 - 11:46 PM.


#7 thorium90

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Posted 27 May 2018 - 04:45 AM

I think the layout as per what Saml wrote is probably the most likely reason. Sometimes it just doesnt make sense to run a steam pipe to a far away remote location just for one consumer. An electric cable is easier and less hassle for the project team to do.



#8 R.Ahmadi

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Posted 27 May 2018 - 02:19 PM

Saml:

 

sorry, my question is related to gas refinery.   Both types of the drum heaters exist in the refinery. There is a steam coil heater in MDEA (Methyl di ethanol Amin) sump drum.  On the other hand, there is a electrical heater in condensate stabilization unit.

I want to know how to choose the heaters generally or based on the fluid? is there any rule of thumb?






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