Topic: Can you offer insight into the reasons for such low heat transfer efficiencies?6 January 2011
Jim Grant Forum Moderator 120 Posts
Re: Can you offer insight into the reasons for such low heat transfer efficiencies?6 January 2011 at 1:29pm
Although I am not familiar with the specific equipment design for the wet phosphoric acid process, the forced circulation evaporator design may have insufficient circulation and/or surface area. This can manifest itself in two ways: 1) velocity and wall shear stress are not high enough to reduce fouling potential. 2) Wall temperature may be high enough to exceed solubility limits of solids with reverse solubility temperature behavior (carbonates for instance).
In general the best approach to systems that may be prone to fouling is to maximize velocity (and therefore wall shear stress) within the constraints of pressure drop and erosion/corrosion and minimize wall temperature. This approach typically will produce a higher power pump and larger exchanger, but will increase the mean time between failures. The Reynolds number of the fluid in the exchanger should also be checked to assure turbulent flow since the viscosity is a strong function of both temperature and concentration of the acid.
harsha vitta Community Member 1 Post
Re: Can you offer insight into the reasons for such low heat transfer efficiencies?21 January 2013 at 8:43am Last edited: 5 February 2013 at 2:32pmIt is obvious that with phosphoric acid solutions having rich of %solids which are easily prone to fouling in heat exchangers , pipes , flash chambers ,condensers etc., Hence before admitting to the evaporators , it is depicting good results as evaporator performance is concerned when we reduce solids content. 1. Maintain high vaccum & low temperature restrict to high temperature operation which reduce supersaturation. 2. Always maintain level above calendria which will not allow the liquid to boil in calendria. 3.Operating under low level which tends to foul heat exchanger easily ( with no sufficient velocity) & as per pump performance characteristics curve.(cavitation) owing to which definetly cause imbalence in pump.