PROCESS DESCRIPTION
1. Production Scale
Annual operation day: 300 days
2. Product Plan
2.1 Using dilute Nitric acid and limestone to make Calcium nitrate tetrahydrate.
2.2 The production process
Calcium nitrate mother liquid can be made through the chemical reaction of limestone and dilute Nitric acid. The mother liquid goes through the press filter and the evaporator for being filtered and concentrated. Then, it goes into Calcium nitrate crystallizer for cooling and crystallization. And then it reaches the centrifuge for separation. After being separated, the crystallized Calcium nitrate product is produced.
3. Product Specification
Product standard: HG/T3787-2005, it provides the industry standard of industrial Calcium nitrate product, applies to industrial calcium nitrate. The product is mainly used for steel phosphating solution, pyrotechnic raw materials, and electronics industries. It can also be used as nitrogen fertilizer or soilless cultivation fertilizer.
First Grade technical Indicator
a). Calcium nitrate (calculated on Ca (NO3)2·4H2O) ≥ 99.0%
b). Water insoluble ≤0.05%
c). pH value（50g/L solution） 5.5～7.0
d). Chloride（calculated on Cl） ≤ 0.015%
e). Iron（calculated on Fe） ≤ 0.001%
Note: Calcium nitrate product conforms to the standard HG/T 3787-2005
4. Technical Proposal
4.1 Process Description
Nitric acid and limestone react in the reactor to produce the solution, which is neutralized by lime and then filtered twice to remove solid impurities. After that, the resulting calcium nitrate solution is evaporated for concentration, cooled, and crystallized, separated by the centrifuge. Then, Calcium nitrate product is produced. The process technology is reliable and applicable, and the production safety is high. Wastewater and waste residues can realize utilization of resources.
Besides, emissions meet the latest national standards.
4.2 Device Scale and Annual Operation Hour
Calcium nitrate tetrahydrate: Ca (NO3)2·4H2O
Annual operation Hour: 7200Hours
4.2.1 Configuration of Device
The producing units consist of the preparing of Calcium nitrate solution (Ca (NO3)2) with the reaction of nitric acid (HNO3) and limestone (CaCO3), two-stage press filtration, evaporation, cooling and crystallization, separation, and packing.
4.2.2 Raw Materials, Auxiliary Materials, Fuel and Power
a). Dilute Nitric acid (Containing HNO3 60%): 0.91t/t
b). Limestone (Containing CaCO3 95%): 0.446t/t
c). Steam: 1.0t/t
d). Electricity: 70KWh/t
e). Circulating water: 1.2t/t
f). fresh water 0.1t/t
4.2.3 Brief Introduction to Process Flow
1) Chemical reaction principle
CaCO3+2HNO3+3H2O→Ca(NO3)2·4H2O+CO2
2) Process flow description
Dilute Nitric acid from the storage tank is pumped to the elevated tank. After adding limestone to the Nitric acid reactor, open the valve and slowly add dilute nitric acid to react. After reaction, the solution goes to the circulating tank. When the reaction is finished, the solution goes to neutralization tank. Again, add limestone in the reactor to react.
Filter the crude Calcium nitrate solution to remove insoluble impurities. The clean solution goes to the clean Calcium nitrate liquid tank and is pumped to evaporation unit.
The Calcium nitrate solution adopts double-effect evaporation. First, the solution is preheated with process steam in the preheater. Meanwhile, the process steam is condensed to process condensate. Then through the evaporation and concentration in the second effect evaporator and the first effect evaporator in turn, the concentrated Calcium nitrate solution flows to the crystallizer. After being mixed and cooled, the solution goes to the centrifuge to separate Calcium nitrate crystal while the separated mother liquid returns to the system.