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Case Study | November 2013

Coke Dry Quenching: An innovative step in operational excellence

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.

Innovation par excellence has always been the driving force for the ways and means of improved environmental performance, energy efficiency and productivity at Tata Steel. In this process it has come up with numerous means of innovative, indigenous as well as heterogeneous technology that has paved the way forward for a new technological wonder. These new technologies have changed the way the industry views aspects of environmental benefits and energy conservation.

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.

The model project, to promote energy conservation, has been carried out inside Tata Steel Works by New Energy and Industrial Technology Development Organisation (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 has 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. The 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 majorÆs philosophy of care for the environment.

Process of Coke Dry Quenching
Tata Steel introduced the new technology of Coke Dry Quenching in 1989. Tata Steel has seven batteries that generate about three mt of coke per annum. Previously all the coke was wet quenched by water where the sensible heat of the coke was lost and huge amount of water would be wasted. With this installation, almost 37 per cent of the coke is dry quenched, which not only helps in moving ahead in sustainable methods but also in improved quality of the coke. CDQ is a counter current solid-gas heat exchange operation, where a nitrogen enhanced mixed gas is moving upwards in between a packed column 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 carriage, 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 pressurised for re-supplying it to the cooling chamber.

Advantages
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 and improved coke properties in the coke helps in efficient blast furnace operation: With 100 per cent CDQ, carbon rate reduces by 12kg/thm (14kg/thm coke rate). Blast furnace productivity increases by 2.8 per cent.   
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