Compute the first ammonia charge

[luissandoval]

Hi everyboby:

I have a NH3 liquid overfeed system and i don't sure how can i compute the ammonia charge? the system has the following components:


Low pressure receiver @ -42ºC
Low pressure receiver @ -37ºC
Suction line accumulator @ -5ºC
High pressure receiver
Evaporators
Condensers

I need to know the basic rules for compute the ammonia charge.

I hope that someone can help me.

Best Regards

Luis.

[jaysephus]

personal stuff sorry

[US Iceman]

Calculate the volume of each component or pipe for the phase (liquid or vapor). Volume X Density = Mass. Mass is mass, so if you do each temperature requirement and then add the totals together you should be very close.

For the pressure vessels, vertical orientation will be the easiest. For horizontal, the easiest method is to assume the vessel is half full of liquid, which is usually the recirculators. Half full is how the maximum capacity is defined, so I think it's reasonable to use this for holdup volume.

If you get into trying to calculate the incremental volumes of horizontal vessels you will make yourself crazy doing the trig!

[luissandoval]

So much thanks guys

I'm thinking to do the following calculate:

V total = V low presure tanks * 0.5 + Suction line acumulator *0.5+ High presurre vessel * 0.5 + V evaporators + V condensers + V liquid feed line + V wet return line*0.25 ( i don't sure of this if the flow rate is 4)


Is it Ok ?

Obviusly i' m going to consider the evaporating temperature and if the refrigerant is liquid or vapor for compute the mass.

Luis.

[gwapa]

luissandoval
Luis as US Iceman had pointed out you should compute in mass (kg,lb)
hear some teorical aspect
v=vf+X*vfg
v= specific volumen of the mixture
X=mg/mt (quality of mixture)
vf= specific volume of liquid
vg=specific volumen of gas
vfg= vg-vf

You should figure out in kg or lb
So, the mass (kg) will be

m= V(volumen)/ v (specific Volumen)
Ejem
if a tank is half full
mg= Volumen of gas / specific volumen of gas =Vt/2*vg
ml= Vlumen of Liquid/ specific volume of liquid =Vt/2*vl
mt=Vt/2*(vg+vl)

in any case you could look in the mollier chart (P-h) the x,vg and vl values
hope it can help
best regards
GWAPA

[samiam]

I concurr - calculate the volumes/mass on the components that make up the whole system.

[luissandoval]

Ok guys tha's right maybe i'dont explain you very good i'm goint to compute in mass but my question is about levels in tanks i don't sure if the levels in each tank and wet suction line are good someone could tell me if is it ok??

Luis.

[US Iceman]

For the tank liquid level you have to make an assumption where the liquid level will be during normal operation.

For the wet suction line remember this: the volume of gas can be high, but the mass is low. For liquid, it is the opposite. The mass of liquid returning to the vessel will be small. If you look at normal overfeed rate (which is the recirculation rate - 1) calculate the amount of mass coming out of each evaporator for gas and liquid for a given evaporator capacity. Then for each evaporator operating at that temperature you can use a ratio per capacity and add it all up.