Production process of calcium ammonium nitrate

Background and overview

Calcium ammonium nitrate is an agricultural ammonium nitrate modified chemical fertilizer containing nitrogen and calcium. High-quality nitrogen with good physical and chemical properties has a wide application area, which can increase the yield of various crops. In terms of market development There are dual concerns about cost and price. Many countries abroad (especially Western Europe) have begun to use it widely in the 1980s, and both production technology and agricultural application effects have matured.

Property

Calcium ammonium nitrate is a compound fertilizer composed of ammonium nitrate and calcium nitrate, with a yellow-brown granular solid in appearance. Domestic calcium ammonium nitrate products include ammoniated calcium nitrate [5Ca(NO3)2·NH4NO3·10H20] and calcium ammonium nitrate (nNH4N03·CaC03). Due to the presence of calcium element, the nitrogen content of calcium ammonium nitrate is lower than that of ordinary ammonium nitrate, and the nitrogen content of typical products is 14.5%, 0.5% or 26.5%. 0% (mass fraction, the same below). The hygroscopicity of calcium ammonium nitrate is lower than that of ordinary ammonium nitrate. Taking calcium ammonium nitrate with a nitrogen content of 20.5% as an example, its hygroscopicity is 2% to 3% lower than that of ammonium nitrate, but its agglomeration is only that of pure ammonium nitrate. 1/2.4-1/3.0. Calcium ammonium nitrate with nitrogen content less than 22% has no risk of explosion, and nitrogen content ≥ 26% has risk of explosion; at the same time, due to the improvement of the defect of poor thermal stability of ammonium nitrate, it is not easy to cause fire and damage during storage and transportation. Causes an explosion, and is a nitrate nitrogen fertilizer that is safer than ammonium nitrate. Nitrogen in fertilizers exists in two forms: ammonium nitrogen and nitro nitrogen. Nitro-nitrogen can be directly absorbed by crops, but ammonium-based nitrogen cannot, and must be converted into nitro-nitrogen by microorganisms in the soil before it can be absorbed by crops. Ammonized calcium nitrate contains more than 90% nitro nitrogen, and the rest is ammonium nitrogen

In calcium ammonium nitrate, nitro nitrogen and ammonium nitrogen each account for 50%. Compared with urea, although the nitrogen content of calcium ammonium nitrate is low, its use effect is no less than that of urea. All nitrogen in urea exists in the form of ammonium nitrogen, which must be converted into nitro nitrogen before it can be absorbed by crops, and the loss of nitrogen during storage and use is relatively large. In addition, calcium ammonium nitrate also has the characteristics of convenient storage, safe and reliable product performance, and neutrality to soil.

Production process

The main production method of calcium ammonium nitrate in China is the mixing method of ammonium nitrate and calcium carbonate, which adopts tower granulation, basically using the original ammonium nitrate device to produce calcium ammonium nitrate.

Ammonia and nitric acid are neutralized in the second stage to obtain an ammonium nitrate solution, and then evaporated to a mass fraction of 96% to 99% in the second stage, mixed with calcium carbonate fine powder for spray granulation (or drum granulation), and after granulation The finished product is obtained by drying, cooling, screening and coating in a rotary kiln.

(1) Neutralization

Ammonia and nitric acid are neutralized, and the concentrated part is the same as the general ammonium nitrate production method, and will not be repeated. The evaporation pressure and temperature of the second stage should be controlled, which are 0.017 MPa and 175 ℃ respectively, and the mass fraction of ammonium nitrate after evaporation is 96.0% to 97.5%.

(2) Mixed

The concentrated ammonium nitrate melt is mixed with limestone powder with a particle size of 20-40 bucket m in a certain proportion in two mixing tanks with agitators. It is sent to the top of the granulation tower for spray granulation. A radioactive concentration detection device is set at the outlet of the ammonium nitrate and calcium carbonate mixing tank to adjust the amount of calcium carbonate added.

(3) Granulation

The mixed solution of calcium ammonium nitrate is pumped to the high-level tank at the top of the granulation tower, and the rotary granulator of the artificial granulation tower relies on the potential difference to flow. The granulator is a conical multi-L nozzle with a taper of 30. , the hole diameter is more than 1 mm, the hole spacing is 10 mm, the nozzle height is 500 mm, and the speed is 300 r/min. There is a scraper in the nozzle, and the scraper and nozzle rotate at different speeds to clean up debris and prevent nozzle blockage. The granulator is equipped with a lifting device, and each granulator has 2 sets of granulators, 1 set for cleaning and standby, and 1 set for running production.

(4) Conditioning

The calcium ammonium nitrate granules coming out of the granulation tower are first dried in the rotary drying furnace, and the water content is reduced to 0.3%, and then fluidized cooling and vibrating screening are carried out. The fine powder with a particle size less than 1 mm is returned to the mixing tank. The granules are sent to the powder coating barrel for coating and powder coating. The powder dressing agent is limestone powder, and the particle size is less than 2 bucket m accounting for 60% to 70% (mass fraction). The powder coating agent is added from the mouth of the powder coating tube, and amine oil (0.35 MPa) is sprayed in the middle of the powder coating tube, and the finished product is sent to the warehouse for packaging and storage. Calcium ammonium nitrate (the mass fraction of nitrogen, calcium and moisture are 26.0%, 11.0% and 0.3%, respectively, and the mass fraction of particles with a particle size of 1 to 4 mm accounts for more than 95%