(1) The clear citric acid mash sent from the filter press section is pumped into the neutralization tank and neutralized at 80 °C. Calcium carbonate is sent to the workshop through a closed conveyor, and is dispersed and put into the neutralization tank by the stepless speed regulation feeding screw to prevent the local concentration from being too high and make the neutralization and precipitation reactions uniform;
(2) After passing the end point test, the calcium citrate suspension is discharged into the belt filter, and the solid calcium citrate is separated from the suspension. In order to meet the dual requirements of the production technology of corn raw materials and dried potato raw materials, the belt filter for neutralization adopts a specific lengthening and strong washing type, and the operation of raw materials is flexible, so as to meet the requirements on the neutralization and affination and the index control of finished products during the production of crude raw materials;
(3) Use hot water or acid hydrolyzate for size mixing. The concentrated sulfuric acid is pumped from the acid-base station, and then metered into the acid-base tank with calcium citrate at 80°C to form a suspension of calcium sulfate and citric acid, which is sent to the acidolysis belt filter for filtration. The cleaning liquid, namely the acid hydrolyzate, is collected for size mixing. The calcium sulfate is transported to the slag yard for comprehensive utilization, and the citric acid is acidly hydrolyzed and sent to the refining section.
(1) Ion exchange and decolorization
The citric acid liquid is pumped from the temporary storage tank to the separation and purification process, through the cation exchange tower, anion exchange tower and activated carbon decolorization tower. The separation and decolorization processes remove the anions and cations that affect the quality of the finished product and accelerate the corrosion of the equipment, and the anion and cation resins need to undergo pickling and alkaline washing for regeneration treatment, and the refined mother liquor of citric acid after ion exchange is sent to the evaporation process.
(2) Evaporation and crystallization
Before the purified solution enters the evaporation section, fine resin particles in the supernatant are removed by fine filtration. The finely filtered solution is preheated by a heat exchanger and sent to a double-effect vacuum concentrator to be concentrated to a specific concentration, and then transferred to a vacuum crystallizer or a low-temperature crystallizer for crystallization. Determine the product (monohydrate product or anhydrous product), and then separate the citric acid crystal grains from the liquid phase, and the liquid phase is placed in the mother liquor storage tanks at all levels after separation. According to the ion exchange concentration of impurity, it is sent to re-evaporative reflux to the pretreatment process for purification, and the crystal is sent to the dryer.
(3) Drying and packaging
The wet citric acid grains separated from centrifuge machines are sent to the fluidized bed dryer, and the drying process is carried out by controlling dry air, temperature and cooling air volume according to the production type. And the citric acid after drying is discharged through the treatment of wet cyclone separator. The dried citric acid grains are transported to the screening machine through the conveying device, and the unqualified grains are screened and separated, and then returned to the crystallization system after being dissolved. The finished citric acid is quantified, packaged, and stored.