Operating and Control Points of Carbonizer

1. The production strength of a carbonizer is an important indicator. It is generally expressed with the utilization factor of the gross carbonation volume, its unit (by sodium carbonate) is m3.d, production strength multiplies with the tower volume equals to the production capacity of the tower. 

Relationships between the three can be expressed by the following formula: W=BV, Wherein, W – Production capacity of the tower (by sodium carbonate) t/d; V—Volume of the tower, m3 B – Production strength of the tower (by sodium carbonate) t/ (m3.d)

Obviously, when the volume of the tower is certain, the production capacity of the tower determines the size of the production strength. Factors affecting the production strength also include operating conditions affecting reaction and reaction speed in addition to the structure performance of the tower, such as the concentration and temperature of the reactants, gas pressure, liquid column height inside the tower, as well as the cooling area and heat transfer efficiency of the tower. Due to restrictions of automation level, these conditions in China are mainly controlled, adjusted and used by man and DCS operating systems currently. Therefore, the improvement of production strength depends on whether the operator and management personnel can fully master the performance features of the tower, make prosper use of all conditions and fully dig all potentials of the equipment.

Basic Operating and Control Principles: First, don’t jut pay attention to reaction time but not to time required by crystal nucleus for normal growth, thereby reducing crystallographic particle size and resulting in deterioration of filtering and firing conditions; Second, don’t just speed up alkali production time regardless of residence time necessary for ammoniacal brine carbonation, thereby reducing NaCl conversion rate while increasing the consumption of various materials and energy; Third, don’t ignore the performance and characteristic restrictions just for momentary or short-term high yield, which may lead to shortened normal alkali production cycle, increase of tower change, or even disorder of tower change order, and bring undue production fluctuations and losses.

According to practical experience, the average production strength of carbonating tower expressed with volume utilization factor is1.0-1.2 sodium carbonate (m3.d) generally. The determination of suitable production strength indicators (including cleaning tower) under different conditions should be based on data summarized through specific exploration and practice.

2. The concentration of NaCL and free ammonia in ammoniacal brine of the inlet tower should be higher and the ratio of NH3 and CL- should be kept between 1.13 and 1.18.

The higher the concentration of NaCL and free ammonia in the ammoniacal brine, the more complete the chemical reaction proceeds and the more NaHCO3 is generated, but the ratio between NH3 and CL- should be certain, that is 1:1. In the carbonation process, about 10% - 13.5% ammonia in the ammoniacal brine is brought out by tail gas exhausted from the tower top (if the air temperature at the tower top is low, the amount of NH3 brought out is less; or, it will more). So, the ratio of NH3 and CL- in the ammoniacal brine should be high. Ammoniacal brine contains 99-103tt free ammonia, 88-90tt CL-. If the content of free ammonia is low, the conversion rate of NaCL will be low; if the content of free ammonia is too high, the concentration of CL- and the NH3 conversion rate will be reduced, and “tower blocking” will occur in the carbonation alkali making tower. Because lots of surplus NH4 and HCO3 form crystallization and block the inner wall, cap and cooling tube of the tower.