LPG PRODUCTION 1

[padovano]

my refinery produces LPG which is a mixture of Buatane and propane. The "light" gases coming from the top of the column are been used like fuel gas. This light gas is mainly propane. For some time now, we have been producing LPG with a vapour pressure of around 6 bars. We would like to raise it to about 7 Bars.(max=7.5bars). The present operating pressure and temperature is 23 bars and 98°C repectively. I would like to know if somebody has ever tried optimising LPG by reducing the temperature or increasing the pressure which are the more likely things to do. Where there any consequences,like more sulphur compounds etc. I am in a tropical region. The ambient temperature is 31°C.

 

[EmmanuelTop]

Is your condenser partial (like it seems to be) or total? By mentioning "light gases", I can think only of the vapor phase in reflux drum.

If you want to raise the content of C3 in your liquid LPG product, you should go for higher operating pressure in the tower, accompanied by higher temperatures of both tower top and bottoms, in order to maintain bottoms product within specification and not to loose C4 from the overhead product. It is simple material balance. Since you mentioned that you are located in tropical region, the option to reduce temperature (and certainly this must be followed by pressure reduction), it doesn't seems to be viable solution; the condensing capacity increases with increasing operating pressure. Furthermore, if this column operates close to the design point, pressure reduction could push you closer to the flooding regime.

There is only one way to get this information: run the tower with different operating parameters and watch for the outputs. If you have some modeling software, it can serve you as a guidance in determining the optimum values.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[dcasto]

I'd modify EmmanuelTop's post. By raising the tower pressure, the top temperature should stay the same and depending on the composition of the feed, the bottom temp may go up somewhat or even drop.

But after reading the post, I have to question why you running the tower at such a high pressure. It looks like you want the product to be 7 bar at 35 C, so if you run the tower at say 10 bar, the top condensor temperature would be 40 C, giving you enough temperature difference above ambient.

The bottom temperature would drop too.