[nertil1]

In our thermo course, we have a design project where we have to estimate the cost of running a boiler, heat exchanger and a series of flash evaporators for a day. Could someone point me in the right direction to where I can find this information out?

Thanks

[nertil1]

Nobody knows?

[Montemayor]

The answer(s) is simple - but it all depends on how well you have studied and learned the Themodynamics taught to you in your course.  You haven't even let one day go by and you are already prompting for an "answer" to your project.  The answer is going to take a little bit longer than a couple of days - especially when we haven't even received a clue as to what you have been assigned to burn in your boiler as fuel.  Additionally, your thread title, "saltwater project design cost", has nothing to do with what you described as the general scope of work.  What function does saltwater play in the boiler design?  Or is it in the evaporators?  And if so, what are you producing in the evaporators?  I mention just some of the questions that will be forthcoming since you haven't furnished very much basic data except generalities.  Therefore, generally speaking you can start your project by defining the size and capacity of your main energy source: the boiler.  Use stoichiometry to calculate the steam generated to use in the evaporators.  For that you must know the amount of product you are going to produce - which you haven't stated either.

Once you know the steam to raise, you also can size the evaporators and the fuel handling facilities for the boiler.  In order to start the project you should generate a Process Flow Diagram (PFD) of the facilities described in your scope of work.  With the PFD you generate a heat and material balance for the process.   With the results of the heat and material balance you generate a Piping and Instrumentation Diagram (P&ID).  Using the P&ID, you can estimate the piping and related equipment costs - both capital and installation.  From the capacities of the major equipment, you then estimate the capital and installation costs.  Once you have all the capital investment costs, you depreciate the investment and knowing the cost of operating the facilities (you have to calculate the fuel, chemicals, labor, and all other fixed and variable costs) you can then factor out what it cost to operate the facilities for one day or one year.

I hope that this rough and general explanation helps to give you an idea of what is in store for you.

Lots of luck, and good calculating.

[nertil1]

Actually I was just hoping for a website that could help me find that information out but I do see your point. I was just in a little hurry and din't have time to write the specifics. This is the flow diagram for the whole process.

http://img84.imageshack.us/my.php?image=80773876xj3.jpg

I have calculated all the streams as following (I'm not sure if they're correct or not.
The following assumption were made:The stream with brine leaving the evaporator is 95% brine
The quality of the steam leaving the heat exchanger is 90%
I also assumed that an equal amount of vapor leaves each flash evaporator, but I'm pretty sure thats not correct

The saltwater coming in the heat exchanger: 1.6439E7 kg/day
The brine stream leaving the evaporator: 599578.2188 kg/day
I then did an energy balance around the heat exchanger to get how much saturated steam was entering the heat exchanger and I got:2.251E9 kg/day
I then did a balance on the boiler to figure out how much heat was required to heat the water from 20C to 140C sat'd. I got: 4.36E14 kJ/day


If someone can give me some advice or check my work, I would appreciate it.
thanks a lot

[nertil1]

I also have a quick question. Can you guys give me some tips as to how I can improve this whole desalination process. One thing I was thinking of was maybe adding another evaporator to get more fresh water from the brine. I was also thinking of adding a rankine cycle with an econimizer. Anybody have any other ideas?

thanks a lot