Bhubaneswar: Achieving high standards in innovation has been the driving force for improved environmental performance, energy efficiency and productivity at Tata Steel. The steel major has always aimed to raise the bar in delivering the best to its customers. In this process it has come up with numerous innovative, indigenous as well as heterogeneous technologies that have paved the way forward for other technological wonders in the industry. These new technologies have changed the way the industry views aspects of environmental benefits and energy conservation in its overall operations.
It is in this journey of Operational Excellence that Tata Steel introduced the model of Coke Dry Quenching (CDQ) of its Coke ovens # 5, 6 & 7 in order to promote energy conservation and add to the industrial environmental benefits. The implementation of the Coke Dry Quenching (CDQ) technique helps in reduction of carbon emissions, energy and water consumption and aids in power generation in the operational processes at Tata Steel.
Speaking on the implementation of this state of the art technology, Mr. Ashok Kumar, Chief Technology Officer, Process, Tata Steel said, “We at Tata Steel have always endeavored for innovations in technology which propel our production and underscore our proposition in promoting energy conservation and industrial environmental benefits. The technology of Coke Dry Quenching is a step in that direction and is an extension in implementing ourbest practices in production of steel and conserving energy.”
The model project on CDQ, to promote energy conservation has been carried out inside Tata Steel Works by New Energy and Industrial Technology Development organization (NEDO) in collaboration with the Ministry of Steel, Government of India, Ministry of Finance of India and Ministry of Economy, Trade and Industry of Japan. Nippon Steel Engineering Co. Limited of Japan and Tata Steel Ltd. India have jointly constructed a Coke Dry Quenching facility for Coke ovens # 5, 6 & 7. The project came into operation in August 2011. The Plant recovers the sensible heat of hot coke by using circulating gas and feeds the recovered heat into the boiler to generate utility steam. Coke Dry Quenching is a benchmark in excellence in Operations on the environmental front as it prevents wastage of water and energy in the form of steam. This innovation has helped in conserving water, a scarce resource to a great extent in the operational lines inside the plant. The benchmark novelty stood as a pioneer in technology which remains an extension of the steel major’s philosophy of care for the environment.
Process of Coke Dry Quenching:
Continuing in its journey of leadership in pioneering the stamp charge battery operations in India, Tata Steel introduced the new technology of Coke Dry Quenching in 1989. Tata Steel has seven batteries that generate about 3 million tons of coke per annum. Previously all the coke was wet quenched using water where the sensible heat of the coke was lost and huge amount of water would be wasted. With this installation, almost 37% of the coke is dry quenched which not only helps in moving ahead in sustainable methods but also assists in improving quality of the coke. CDQ is a counter current solid-gas heat exchange operation, where a nitrogen enhancedmixed gas is moving upwards in between packed columns of coke pieces with an exchange of thermal energy. Thermal energy is extracted from the heated gas and the residual gas is re-circulated within the system with some additional make up gas to maintain desired composition.
• The hot coke (about 1000-1050oC) from coke ovens is transported to the CDQ facility in bucket carriages, pulled by an electric locomotive.
• The bucket is lifted by crane to the top of the chamber and dumped into the pre chamber by a charging facility.
• The hot coke descends through the cooling chamber, exchanging heat with the circulating cooling gas which is introduced from below. It is cooled (below 200oC) and released through the discharging device.
• Circulating gas heated to 930oC in the cooling chamber is passed through the primary dust catcher to remove coarse dust and is then supplied to the boiler. The boiler uses the heat energy to generate steam which is used elsewhere in the plant.
• The circulating gas after passing though the boiler attains a temperature of about 170oC. It is then passed through the secondary dust catcher to remove fine dust particles and sent to the circulating gas blower where it is pressurized for re-supplying it to the cooling chamber.
Advantages of the technology:
Improvement in Coke properties leading to operational efficiency:
Coke strength after reaction or CSR is an index which gives us an idea about the strength of the coke in hot conditions (as it descends down to the hot zone in an operational Blast furnace). With CDQ , CSR is increased by 1 point (from 64.5 to 65.5)
M 40 tells us about the tendency of the coke pieces to break into smaller pieces. It is also a measure of coke strength in cold conditions. With this data we find that there is an approx. increase of 1.5 to 2 points. Negligible moisture & improved coke properties in the coke helps in efficient Blast furnace operation: With 100% CDQ, carbon rate reduces by 12kg/thm (14kg/thm coke rate). Blast furnace productivity increases by 2.8%.