Due to the absence of any special properties in coal, it cannot be used in iron, steel industry. When the crushed coal is destructively distilled in a closed retort in the absence of air at about 900 - 1000 °C, all the residual substances present in the coal are released in the form of gas, and the residue left in the retort is called coke.
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Process Description
NH3 is produced from coal by moving bed type qualification of coal. For smooth operation of the classifier, the feed is pulverized and passed through a 0.09 mm operating screen. In the feed preparation section, the coal is completed and the raw gas is produced in the gasifier through an assembly of burners. An assembly consists of four burners which are placed horizontally across one another. In each gasifier, 27800 NM2 of raw gas is produced, for maintaining the burner temperature at 700 °C the oxygen reaction is as follows.
C + O2 ⟶ CO2
C + CO2 ⟶ 2CO2
CO2 + H2O ⟶ 2CO2
The composition of elements in the raw gas thus formed is as follows based on volume
CO2 = 13.92%
CO = 34.04%
H2 = 30.24%
Sulphur= 0.26%
Due to high temperature, a lot of ash is formed in the reaction zone of gasification, which is extinguished with water and separated in the control zone. In the mixture chamber, the extinguished ash also goes into the raw gas along with the steam. Therefore, it is very important to separate it from the raw gas.
200 gm NH3 ash is found in the raw gas obtained from the top outlet of the gasifier. To remove this ash, H2O is sprayed from the waste heat boiler and the collided gas is regenerated and saturated with steam at 8 to 10 atm. in the second part of the boiler and heated to about 300 °C.
The gas mixture is sent to the shift converter section from the secondary reformer. First of all, the gas mixture is passed to the shift converter at high temperatures. The shift converter contains feed and CrO3 as catalysts, which converts CO into CO2, now this synthesis gas contains CO2. The absorption solution is stripped to remove CO2.
CO2 is obtained from here and sent to the urea plant. And the absorption solution is sent to the methanator from the absorption tower. Where CO and CO2 are converted into methanene. The methanator contains a highly active Ni-Co catalyst.
After passing the raw synthesis gas through the CO absorption tower and methanator, pure synthesis gas is obtained, which is compressed up to 150 kg/cm2 by the synthesis gas compressor and sent to the ammonia (NH3) synthesis unit.