Experimental evaluation of forced circulation crystallizer performance in production of sugar crystals
Authors: Farahbod Farshad 
Published: February 2019

Operating conditions of forced circulation crystallizer, which is equipped with a condenser, are investigated in this research. The results can be used as tally rules for design and process optimization. The effect of operating pressure, operating temperature, and cooling water flow rate on the performance of forced circulation crystallizer as an industrial type of evaporators is evaluated in this research. Moreover, the relationship between the amounts of produced sugar crystal, acidity, distilled water, sugar crystal size, and energy consumption in the heat exchanger has been investigated, experimentally. Finally, the relationship between the concentration of sugar in liquor and related density is measured in this article. The experimental results show, with increasing operating temperature from 87.1 to 91.6 °C, the density of outlet liquor from the crystallizer decreases from 1,122.37 to 1,121.48 kg/m3. In addition, 6.24 kWh as the minimum amount of energy consumption is obtained at a temperature of 27.3 °C. Results show that the difference between feed temperature and heat exchanger temperature is between 5.9 and 9.8% for different cooling water flow rates.

Practical applications

A forced‐circulation crystallizer operates under reduced pressure. A high recirculation rate through the external heat exchanger is used to provide good heat transfer and minimize encrustation. The crystal magma is circulated from the lower conical section of the evaporator body through the vertical tubular heat exchanger and reintroduced tangentially into the evaporator below the liquor level to create a swirling action and prevent flashing (sudden evaporation). Feedstock enters on the pump inlet side of the circulation system. Product crystal magma is removed below the conical section. Its purpose is to concentrate nonvolatile materials such as organic compounds, mineral sugars, acids, and bases. Totally, a forced circulation evaporator utilizes a heavily recirculated heat exchanger with suppressed boiling. Moreover, it is typically used for fouling or crystallizing products. A high liquid rate combined with induced turbulence deters scaling on the heat transfer surfaces. Totally, the forced circulation crystallizers apply in food industries. Some of the industries, which are related to the forced circulation crystallizer, are mineral ingredients companies, chemical companies, and feed industries. The main applications of forced circulation crystallizer are as follows: (a) suitable for material with bigger concentration ratio, higher viscosity, and easily crystallization; (b) widely used in the evaporation and concentration of water phase solution or organic phase solution, in food, pharmaceutical, chemical, biological engineering, and other industries; (c) widely used for the evaporation and concentration of tomato sauce, malt dextrin, starch, sugar, glucose, lysine, inositol, fructose, oligosaccharides, peptides, and so on; (d) compact structure and convenient operation, ideal evaporator for treating corn syrup, tomato paste, and industrial sewage; and (e) for the production of chemical and petrochemical compositions such as phosphoric acid, ammonium sulfate, soda, sodium sulfate, and gelatin, urea.