Propane Dryer-Inlet Water Content

If your water content at inlet is 2 kg/hr, then it is 568 ppm.

Total flow = 3,520 kg/hr

1,000,000/3,520 = 284

2 kg/hr x 284 = 568 parts

3,520 kg/hr x 284 = 1,000,000 (million)

I wonder if water is soluble in propane so that at the given conditions, saturation is about 300ppmW. (I.e., part of the water to be removed is dissolved, part is free.)

Do you also know what type of MOLSIV is used ( size in Angstrom = e.g. 3A ) and how much is in their container?

Need more info:

Normally the propane releases its water when burnt - do you burn it? - do you heat up the MOLSIV to regenerate it? Is it a 2 cycle unit - (2 tanks ?)

The water content at the end is only function of what type MOLSIV and the cycle system, considered the tank is big enough, the density - packing - with too small tanks is critical. ( 3A can produce 0.1 ppmV )

Wonder why they quote in weight.

Dear dvmdsc...

Molecular sieve quantity quoted by the 2 bidders is different....because moisture content at inlet is different....i can check the grade of desiccant from them but size in angstrom seems difficult...but yes...dynamic adsorption capacity considered by 650 ppm vendor is 12% and 325 ppm vendor has considered 7%.

We do not burn the propane, but we pass the propane through a vessel filled with this desiccant vessel which adsorbs moisture from it...when this desiccant becomes saturated, we regenerate it by passing hot propane, (heated by a electric heater)...

Molecular sieve quantity quoted by the 2 bidders is different....because moisture content at inlet is different...

I do not agree with you for above statement. You have specified Inlet conditions: Flow rate= 3520 kg/hr (max.), operating P & T= 24.4 kg/cm2(g) & 38 Degree C, water content= 2 kg/hr. This condition can not be changed by bidders. Have you asked your bidders about basis of arriving at different ppm? Have you asked your bidders about basis of arriving at different dynamic adsorption capacity?

Dear pradeep,

This question was posted here by me, the moment after i received the offers. Currently we in progress of technically evaluating the 2 bidders.

Yes i did discussed about diference in dynamic adsorption capacity(DAC), and it was due to different grade of desiccant as quoted by them. As we have not specified any particular grade but only the name as 'molecular sieve; as desicant, hence whatever dynamic ad. capcity they are giving i have to accept it as i cant reject a bid solely on the basis of different DAC.At the same time i have asked both bidders to give me the past references where they have used the same DAC adn the equipment is working fine for some period without any major repair work required.

But my basic question was to find the ppm content at inlet in order to compare the same wat 2 bidders have quoted, which mikerho has explained.

As soon as i come to know about the differences of ppm for both bidders, i"ll post it here.

As Mikerho has commented at #1, ppmW is 568. Safe side the bidder took 650, it's OK.

Other bidder has considered as saturated+325. it means 2 kg in 3520 kg propane is more than it can hold at saturated condition at inlet temperature and pressure. If it is so then it contains free moisture which can be removed by just installing a separator or knock-down vessel to reduce load on driers to just half. So please go through the properties of propane and calculate how much water it can hold at saturated condition at inlet temperature and pressure.

"So please go through the properties of propane and calculate how much water it can hold at saturated condition at inlet temperature and pressure."

Pls clarify how to calculate this...

Mayank, I tried in internet, didn't get solubility of water in propane. Everywhere I'm getting solubility of propane in water which is not the case here. For air it is easily available. I remember, long back I have seen seen this information for many gases in "Handbook of Chemical Engineering" by Perry. You can calculate theoretically also, but you have to look out for its formulae. If I happen to go library, I will try. You can also ask your bidders, it may be at their finger tips.

After discussion with both bidders the situation for propane dryer is as follows:

Bidder-A: ppm @ inlet considered: 650 ppm

Bidder-B: ppm @ inlet considered: 325 ppm + saturated....

Actually this bidder-B has considered a coalescer at inlet which is removing about 300 ppm at inlet and balance about 325 is being considered at vessel (filled with desiccant)...So basically this bidder is designing the complete dryer package taking advantage of inlet coalescer...and hence he is arriving at lesser size of desicant filled vessel.

Bidder B is logically very right, but wat happens if coalescer needs maintenance for filter element cleaning..in that case, i have to by pass the coalescer and pass the inlet stream of 650ppm water content to 325 ppm designed vessel...which is not suitable...

Hence the only case in which i can accept bidder-B is if he provides a standby coalescer and hence 1 coalescer will always be under operation...And of course we are going to use pressure gauges/manual changeover valves to achieve the same

While bidder A has not used a coalescer and is designing the desiccant vessel for 650 ppm and hence is arriving at a higher size...

Now i have ask bidder-A to use inlet coalescer (1working+1standby) to arrive at lesser cost of dryer package in line with bidder-B..