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# how can i design the coil for heat transfer

07/21/2008 3:49 AM

we have one line of condensate (temperature-80-90c) which is contaminated so that we can not put directly to boiler feed tank water. its causing to increase tfm of boiler. but i want to transfer heat of condensate to boiler water by passing through coil. how can i design the coil of condensate to fix in a boiler feed tank.tank dimension is 2130mm x 2760mm x 1680mm height.

please advice me with formulas. so that i can use it in future.

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Guru

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#1

### Re: how can i design the coil for heat transfer

07/21/2008 4:09 AM

It would depend on the flow rate in the condensate line.

It would be relatively simple to run it through a length of pipe which dipd in and out of the feed tank. measure the temperate of the condesate coming out. You would then have a rough way of working it out as temperature drop per foot of pipe.

(Yeh everyone I know heat transfer is proportional to temperature difference)

Or to put it another way, in one word 'Experiment'

Del

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#16

### Re: how can i design the coil for heat transfer

10/12/2011 7:42 AM

(Yeh everyone I know heat transfer is proportional to temperature difference)

It called the Second law of thermodynamics. And most everyone here is a law abiding citizen.

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#2

### Re: how can i design the coil for heat transfer

07/21/2008 2:23 PM

flow rate is 10 ton per hour

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#3

### Re: how can i design the coil for heat transfer

07/21/2008 2:36 PM

Oh! That's a somewhate larger volume than I'm used to handling...it makes my sugestion sound a bit silly...

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#4

### Re: how can i design the coil for heat transfer

07/21/2008 10:55 PM

The following link will provide you with just about everything you want to know about calculating heat transfer....

Specifically the section "Defining the Overall Heat Transfer Coefficient"

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/heat-transfer.asp

There is also usable heat energy in the flash steam. A flash heat recovery heat exchanger can be used that will allow you to use the heat energy and re-capture that lost water back into the boiler.

Congratulations on finding the hidden waste energy in your system!

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#5

### Re: how can i design the coil for heat transfer

07/22/2008 4:12 PM

thanks for ur valuable answer can u please tell me that how can i control boiler water total disolve substance

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#6

### Re: how can i design the coil for heat transfer

07/22/2008 4:59 PM

There are two types of boiler blowdown:

- Surface Blowdown

- Bottom Blowdown

Surface blowdown can be done either manually or through using a boiler blowdown controller that blows down based on conductivity, or on a timed interval. In the long run, it is more efficient (reduced therm & water loss) if you perform surface blowdown based on conductivity.

See the following links for further information.

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/the-boiler-house/controlling-tds-in-the-boiler-water.asp

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/the-boiler-house/bottom-blowdown.asp

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/the-boiler-house/heat-recovery-from-boiler-blowdown.asp

Bottom Blowdown - this is regulated by code, so I don't want to get more involved other than to say that this is usually done 1 to 3 x per day (depending on what the boiler manufacturer & code require).

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#15

### Re: how can i design the coil for heat transfer

10/11/2011 10:48 PM

could you gvie me more details?

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#10

### Re: how can i design the coil for heat transfer

07/23/2008 9:40 AM

but as you stated determining the heat transfer coefficient (U) requires iterations. And is the most difficult part.

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#7

### Re: how can i design the coil for heat transfer

07/22/2008 9:09 PM

Hello sandeep lokhande:

I was going to suggest several domestic hot water tanks with coils running through the inside. The water from the boiler heats the coil and then the hot water can be used for whatever you want. Though I have not dealt with the quantities you envisage, you could perhaps link several tanks in series?

Why are you worried about the dissolved chemicals in the boiler water? Just wondered

stay safe

babybear

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#8

### Re: how can i design the coil for heat transfer

07/22/2008 9:51 PM

Re: how can i design the coil for heat transfer

One solution would be to use a horizontal shell & tube heat exchanger and
Route the contaminated condensate through the tubes and boiler make-up water on the shell side, this configuration will make it easier to clean (tubes) or unit if (or when) the tubes gets dirty. This is the most efficient way to get maxium heat transfer. Coils in a tank is not an efficient heat transfer process, designing amount of coils needed, determining Liquid flows, pipe sizes, purchasing and assembling the unit, and cleaning the coils could end up costing more. Purchasing a manufactured heat exchanger to meet your needs (specifications) might be the better choice. DonnieH

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#9

### Re: how can i design the coil for heat transfer

07/22/2008 10:55 PM

This is the formulae for blow-down amount:

A = (S*Q) / (K-S) where:

A [kg/hr] is the blow-down rate

S [μS/cm] is the supply water conductivity

Q [kg/hr] is the steam capacity of the boiler

K [μS/cm] is the maximum allowable conductivity of boiler-water

there is sample control diagrams with different equipments at http//febuda.blogspot.com/iletkenlik-zmleri1-2-3 (blog is not in english but diagramms may be useful)

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#11

### Re: how can i design the coil for heat transfer

07/27/2008 12:01 AM

Are you sure the contanimated condensate return is 10 Tph?

Your Tank works out to be up to 8 Tph.(7' x 9'x5.5' = 2148 gallons=17830 lbs=8.0 T)

What is your process (Textile/Tyre/Rubber/Chemical) ? Why is the return contanimated and from which area & machines?

There is two way of doing:

The first Del's way - You are dumping this condensate anyway so just make stainless steel 316ss L coiling and dump the condensate. Every 6C rise will save 1% gas at the boiler.If the outlet comes down below 30C you made your point else but a second set of coiling/increase the length with the experience.

The second way - Undertaking calculation if it is worthwhile depending on your actual condensate return.

Sandeep Lokhande - CR4 people like Del & others & me are not here to waste our time . You have to be highly technical in posting your questions and data to work out and help you. Do not just shoot out questions for the 'heck oif it'.

How can you have a 10Tph return when you have 8 Tph tank?

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#12

### Re: how can i design the coil for heat transfer

07/27/2008 4:42 AM

hi friends

i am very much sorry about wrong information 10 ton condensate. me i think its ok for example but as a engineer i not suppose to do it i will try to give u right information as possible as. please don't get angry on me

but if u calculate tank capacity in metric it will come around 9.8 ton

and if u go for big units like inch it will give u less capacity

my intension was just to get solution and i got it from dweezle. i am very much thankful for that. please check his solutions. u will find that stainless steel thermal conductivity is only 16W/m degree cel. so that i can not implement this solution.

i m very much impress on your brief bio- i not only use all the brains that i have, but all that i can borrow.-woodrow wilson

i think that is what i m doing. please don't misunderstand me. all cr4 people are not only my friends but they are my mentors. i m getting very nice solutions from them i don't want to miss their solutions. please forgive me for my mistake. please be in touch. because criticism is also important to become a perfect.

thank you very much

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#13

### Re: how can i design the coil for heat transfer

07/27/2008 5:35 AM

I accept your apology , I like your spirits and I like you. I take back everything I said.

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#14

### Re: how can i design the coil for heat transfer

07/27/2008 7:56 AM

thank you

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