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Offloading And Venting Emmisions

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#1 AbhinavK


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Posted 03 April 2007 - 06:15 AM

Hi, I posted this topic in the Student forum first but thought it's more relevant to this forum.

I am working on a design project to design a scrubber for a bromine storage tank. The scrubber gets bromine laden vapour from venting the bulk tank at the start of the off-loading operation and from venting the iso-tanker at the end of the off-loading operation. The bulk tank remains pressurised at aroung 4 bar using air. Before filling the bulk tank with bromine from the road tanker, it needs to be vented first. I calculated the amount of bromine that will flow to teh scrubber during venting using two different methods. I got different results so am confused which one is right.

The vapour pressure of Bromine at 20C is 22756 N/m2.
In the first method, I calculated the mole fraction of bromine in the vapour at STP to be

y = 22756/101300 = 0.22
Therefore 0.22m3 bromine will be present in every cubic meter of headspace available. As 1 mole of any substance occupies 22.4 litres, therefore 220 litres of bromine is equivalent to 9.82 moles.
9.82 moles of Bromine = 9.82 x 159.81 = 1569.47g = 1.5kg.
As the tank is pressurised to around 4 bar therefore according to Boyle’s law, PV=constant, amount of bromine that will flow to the scrubber is 0.375kg per cubic meter of head space available.
Volume of the bromine bulk storage tank is 13.5m3.
Therefore amount of bromine flowing to the scrubber while venting the bulk tank = 13.5 x 0.375 = 5.06kg

Volume of iso-tanker (from which the bromine is transferred) = 6m3.
Therefore the amount of bromine flowing to the scrubber while venting the iso-tanker = 6.7 x 0.375 = 2.25kg

In the second method, I used the ideal gas equation.
Calculating the mole fraction of bromine in vapour, y=Vapour Pressure of bromine /Total system pressure = 22756/400000 = 0.056
Therefore 0.056m3 bromine will be present in every cubic meter of headspace available.
Using ideal gas equation,
400000 *0.056 = n*8.314*293
n= 9.19 moles = 1.4kg emission/m3 of head space available.
Therefore total emission from bulk tank = 18.9 kg
Total emission from iso-tanker = 9.3kg

I don't know which one is right. In the first one I calculated for STP and then adjusted for extra pressure. I know that the pressure will drop down as the tank will get vented but I'm told to ignore that and calculate the emission using 4 bar.

I tried to use the software TANKS on EPA website but that does not have bromine. I have provided a detailed description. Hope you can help? Thanks

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