4 replies to this topic

[pankaj shah]

I am designing 5 tons/hr crystallizer for Potassium Nitrate . This will be done by evaporation of 5,500 kgs/hr of water. Crystallizer will be Oslo evaporative type with external heat exchanger.The temperature to be maintained in crystallizer is 60*C so that effective crystallisation takes place.Cold water at 30*C is available at site.

Any idea on the size of vaporizer chamber?
Any other idea about this type of crystallizer?
Can this be done in a single crystallizer or battery of crystallizer may have to be operated?

Pankaj,India

[breizh]

Hi ,
Did you try Google?
http://www.google.co...iw=1147&bih=636

Hope this helps
Breizh

[kkala]

Besides the web data suggested by breizh, following notes might be of further help.
1. Operations in a local fertilizer plant (1976-81) included a phosphoric acid evaporator, concentrating phosphoric acid from 30% to 50% P2O5 w/w. One single stage, forced circulation evaporator (of rather small size); with cooling water condenser, Cl free water ring vacuum pump, steam heater just upstream of circulating pump. Evaporated water 1/0.30 -1/0.50 = 1.33 ton H2O / ton P2O5. Evaporation capacity not remembered, but more than 5.5 ton/h of water (more than 4.1 ton/h P2O5 passing from evaporation).
2. Oslo evaporator - crystallizer is assumed as in http://www.niroinc.c...rystallizer.asp, not being in principle far from mentioned evaporator.
3. From the usual three ways of KNO3 preparation (http://en.wikipedia....tassium_nitrate, Production), the neutralization of HNO3 and KOH is assumed, occurring in a vessel separate from crystallizer.
4. One Oslo evaporator - crystallizer can evaporate 5500 kg/h of water, based on (1) above. The classifying section should have sufficient residence time T for crystal growth and homogenization; T is not known to me; but even if T=24 hr, size would not be a problem due to small feed rate (5 ton/h of crystals + mother liquor).
5. Neglecting boiling point elevation of KNO3 solution at present, steam tables suggest an operating pressure of 0.20 bara for the temperature of 60 oC (if the solution was pure water). Thus steam density=0.130 kg/m3, water density=983 kg/m3, steam volumetric flow=5500/0.130=42300 m3/h=11.75 m3/s.
5.1. Liquid entrainment should not happen in vaporizer chamber, so allowable gas velocity has to be 0.035*SQRT(983/0.130) = 3.0 m/s, or lower (Coulson & Richardson, Chemical Engineering, Vol 6, Pergamon 1983, Chapter 10.9 Gas-liquid separators). Resulting cross section of (vertical) vaporizer chamber = 11.75/3.0 = 3.92 m2, that is diameter = 2.3 m or higher. Disengagement height from liquid level to top = 2.3 m or higher.
5.2 Above estimates are rough approximations. Perry (Chemical Engineers' handbook, 7th edition, 1998, Section 11, Subsection "Evaporators, Vapor - Liquid separation" presents a not so clear formula for allowable velocity.
6. Having no familiarity with this crystallizer type, I can only say that way of scale cleaning has to be assessed before order; crystals of fertilizer (NH4)2SO4 were separated here by use of centrifuges.

Note: Since KNO3 solution has to be at 60 oC after the boiling point elevation, produced steam will be superheated. For boiling point elevation see [url ]http://www.chemistry...Properties.html[/url].

Edited by kkala, 12 November 2011 - 03:15 PM.

[Dawood]

Hi

 

I am required to design Crystallizer for an upcoming project. Can you please recommend books for Desiging Crystalizers.

[breizh]

Consider Perry's chemical engineers' handbook (chapter 18th) .

Google should be an option .

 

Breizh 

Edited by breizh, 04 March 2013 - 06:24 AM.