Coal Gasification Plant and use of by-products, Angul
Direct-reduced iron (DRI), also called sponge iron is produced from direct reduction of iron (in the form of lump, pellets or fines) by a reducing gases produced from natural gas or coal. This reduction takes place in the temperature range 800- 1050 degrees C when reducing gases; mainly Hydrogen and Carbon-monoxide; react with the iron oxides to produce iron. The degree of metallization, defined as the extent of conversion of iron oxide into metallic iron, is 92-96% in a typical DRI process. This high percentage of metallization makes DRI a highly suitable input for steel making. The specific investment and operating costs of DRI plants are low compared to integrated steel plants and are more suitable for many developing countries where supplies of coking coal are limited. This holds true for India where most of the coking coal has to be imported.
Natural Gas based DRI is a highly efficient technique of manufacturing sponge iron that creates less environmental impact - However the challenge in this manufacturing technique is the availability of natural gas. At JSPL’ Angul site the DRI – BF- Electric Arc Furnace route has been adopted for steel making. The hurdle of non-availability of natural gas at Angul site was overcome by an innovation. A Coal to Gas Plant was set up at Angul. It uses high ash coal available in the vicinity of the site and converts it into Synthetic Gas or SynGas. It is the first plant of it’s kind in India and the 2nd in the world.
At Angul the Syngas produced contains methane, carbon monoxide, carbon dioxide, hydrogen and water vapour from coal, water and air by gasification process. This process has a lesser impact on environment as compared to coal combustion process – the CO2 emitted in the process is entirely absorbed back in to the process and the Hydrogen Sulphide emitted is entirely converted into Sulphur production.
The setting up of Syngas plant required a very large initial investment and it had a long gestation period of three years. It ensures energy efficiency and reduced environment impact in the long run.
In addition, all the 7 by –products of the Syngas plant are being recycled through internal use or by sale to external parties. This ensures health and safety of employees as well as local communities and environmental protection.
This one of it’s kind project faced numerous risks and challenges from the first day but they were overcome with innovative ideas and out-of-box thinking. A list of these risks and how they were overcome:
Rectisol Naptha – This is produced in the rectisol unit (No. 8 in the diagram above)when raw Syngas is washed by cold methanol to remove lighter hydrocarbons (“naphtha”), CO2, HCN and volatile sulphur components. Naptha is used in petrochemical industry and in the chemical industry for solvent (cleaning) applications.
Phenols and Phenolic Pitch – When raw Syngas is cooled, gas liquor is produced. Gas liquor, consisting primarily of water, is transferred to Phenosolvan unit where it is subjected to a liquid – liquid extraction process in which diisopropy ether or DIPE is used as solvent (No 6 in diagram above).Phenols are used in production of plastics. Phenolic pitch is used as fastening material in manufacturing of mineral plates.
Ammonia – The dephenolised gas liquor is transferred to the Ammonia recovery unit. Ammonia is used to produce fertilizer, household cleaning products, refrigerator coolants, medicine and even cosmetics.
