Ammonium Hydroxide pumping problems 1

[chasewick]

We are a biotech company with a ammonium hydroxide system. We continually have vapor lock problems that disrupt production. If someone has experience with this application, what would you suggest for improving the process?

 

[hacksaw]

Check with the mechanical engineer who sized the pump. If he is not available, then contact your pump vendor. It is not an unusual problem and is solvable.

Good luck

 

[vanstoja]

Are you putting ammonium hydroxide in water for corrosion control purposes? If so, you can have entrained hydrogen and nitrogen in the water which requires an elevated system pressure,pg, to keep the gases in solution in addition to the water vapor pressure,pv. Entrained gases can choke a centrifugal pump operating in a controlled coolant chemistry system and water cavitation can damage the pump and downstream components of the system. Vapor pressure increases exponentially with water temperature but combined partial pressures of hydrogen and nitrogen gases in water peak around 250F. The minimum pumped fluid pressure at any operating temperature should conservatively be the sum of vapor and gas partial pressures added to the required Net Positive Suction Head (NPSHR) for the pump. You need to know the total concentration of dissolved gases and their proportions along with Henry's Law coefficients for hydrogen and nitrogen to calculate pressures needed to keep dissolved gases in solution. I have Henry's Law coefficients for temperatures to 600F and calculated gas partial pressures for 75-25 and 40-60% compositions of hydrogen-nitrogen if needed.

 

[NVoris]

I provide no answers here. But, I hope that I'll give you some things to think about...

Aqueous ammonia is a particularly maddening beast because ammonia is simply not content to be dissolved into the aqueous phase. As a result, it will jump out at the earliest available opportunity and make your pump's life miserable in the process.

As with all situations that involve dissolved gasses, the vapor pressure of an aqueous ammonia solution is HIGHLY dependant on temperature (19% aqueous is bad, 29% is hella-worse). This is of particular importance in positive displacement pumps that recirculate the pumped fluid back to the suction in order to dissipate heat generation. Unfortunately, my experience has been that the actual amount of heat generated in a PD pump is all but impossible for we mortals to calculate because this calculation involves pump specific parameters that are not readily available.

Also, if your pumps are mag-drive then there is additional heat generated by those insidious eddy currents.

Also, if you have a high point pocket in your pump suction line then you are asking for trouble.

FYI, a plethora of aqueous ammonia information can be found here:

http://www.larocheind.com/Library/lqaa.htm

Good luck.