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Special Report | May 2014

Power generation through waste heat recovery

The project involved undertaking a major modification work in the existing sinter machines to make it suitable for hot air intake. However, despite several challenges from execution to implementation, Precision Engineering Corporation with the help of Japanese engineers has completed the project in April. Rahul Kamat provides a detailed project report.  

Rashtriya Ispat Nigam Limited (RINL) and Vishakhapatnam Steel Plant (VSP) have recently commenced a 20.6 MW sinter cooler waste heat recovery based power plant through waste heat recovery from both the straight line coolers of sinter machines 1 & 2, each of 312 sq. m. area.

 

The waste heat recovery system essentially consists of the cooler hood and hot waste gas duct to recover the hot air discharged from the cooler, the dust catcher to remove the dust from hot air, the boiler to recover sensible heat from the hot air, the circulation fan to circulate comparatively cool air or gas for cooling sinters and recovering the waste heat through boiler and finally the turbine generator to convert the steam into electricity.

 

The project is being executed in accordance with the Memorandum of Understanding (MoU) for the model project for sinter cooler waste heat recovery system duly executed between New Energy and Industrial Technology Development Organisation (NEDO) of Japan and the Ministry of Steel (MoS), Ministry of Finance (MoF) - Department of Economic Affairs, both under the Government of India and RINL. JP Steel Plantech Co. (SPCO) has provided basic engineering for complete plant and equipment and will also supply boilers, auxiliaries, turbine generators and associated auxiliaries.

 

Precision Engineering Corporation (PEC) has been entitled to carry out the mechanical balance of payment work which includes the following:

 
     
  • Detailed design and engineering preparation of detailed fabrication drawings based on more than 900 basic drawings provided by SPCO and preparation of detailed specifications for bought out items.
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  • Fabrication of technological structure for boiler and other equipment; of ducting up to 4.7m x 6.6m in size; mechanical equipment such as dust catcher and multiclones; a total of 2,800 tonnes of steel.
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  • Designing and supply of a number of ancillary equipment such as ACVS, Compressed Air System, EOT of 20 t handling capacity, electric hoists, dust pneumatic system, dampers and expansion joints all bought out items.
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  • Erection, testing and commissioning of all the items under BOP package as well as BTG and circulation fans.
 

Major challenges

 

The project involved undertaking a major modification work in the existing sinter machines to make it suitable for hot air intake. Since sinter machines are continuously supplying sinter to blast furnaces, getting shutdowns of sinter machines for any modification work was extremely difficult. "As modification of sinter machines was one of the most critical items for the successful commissioning of the plant, we had to plan several one day shutdowns during the entire duration of the project," says Puneet Agrawal, Executive Director, Precision Engineering Corporation.

 

He adds: "Before each shutdown careful and detailed planning was done to ensure maximum productivity during the shutdown period."

 

Another major challenge in the project was to work with the Japanese engineers, who had a very high standard of project management as well as quality. A detailed project schedule was drafted upfront in consultation with the Japanese and was modified during the course of the project as and when deemed necessary. The entire fabrication activity was thoroughly checked and approved by the Japanese before the work was finished and PEC managed to finish the tasks to their utmost satisfaction, at times even brought out improvements to the originally proposed Japanese design.

 

"One of the other major challenges in the project was fund and timeline management," Agrawal said.

 

The project, by its very nature, required extensive interaction with a number of vendors. This included vendors for procurement, for fabrication as well as for erection and commissioning. Detailed procurement plan was drafted considering the sequence of erection and was procured accordingly. Procurement action was taken strictly in line with the production plan in order to minimise the fund involvement and to limit the number of simultaneous vendor interactions.

 

As was the nature of the project, a number of activities were identified during the execution of the project, which were neither foreseen nor accounted for in the original pricing. In the best interest of the project and to ensure timely completion, the activities were all taken up immediately without waiting for the approval of financial implications. This meant significant infusion of funds in order to keep the pace up.

 

Approvals

 

The primary approval that was required was from the Directorate of Boilers, Andhra Pradesh. Thorough documentation and engineering calculations were submitted for the boiler, piping and other IBR accessories.

 

The other major approval was required from the Japanese engineers who had conceptualised and designed the entire plant. The approval of compliance to the design was critical to get the desired parameters of operation of the plant. Prior to the start of commissioning activities, approval from Inspector of Factories was required under Factory Acts & Rules for risk assessment and safety regulations. Also approval from Central Electricity Authority (CEA) was required for commissioning of all electrical equipment.

 

Consultants involved

 

The project consultant for the plant owner was MECON Limited. The consultant was involved from the point of drafting of project technical specifications to bid evaluations and thereafter at the time of project execution. The complete responsibility of carrying out inspection related to this project was entrusted to Projects & Development India Limited.

 

A number of bought out items were sourced from reputed vendors, including expansion joints from Keld-Ellentoft, dampers from IndFans, EOT from Anupam Industries, compressor from Kirloskar, valves from Weir-BDK & Audco, pipes from ISMT, JSW; multiclone from CK Airtech. Apart from this, the air conditioning and ventilation system and the dust pneumatic system was designed and supplied in-house. Other major fabricated or assembled items supplied by PEC include feed hopper, dead plate, dust catcher, ducting system and structural items.

 

Technology used

 

While a number of waste heat recovery systems exist on the sinter cooler today, the unique aspect of this project is to generate power using this waste heat. The technology of the project is rather unique and is being implemented in India as a model project. The success of this project could lead to a number of similar installations in India. The technical challenges overcome in the design include the following:

 
     
  • Extraction of hot gases at 700°C efficiently, with proper sealing to limit the losses.
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  • Transporting of hot gases to outside the sinter plant without loss of thermal energy.
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  • The complete gas circulation system is a closed loop system wherein hot air from top of sinter coolers is extracted and fed into the boilers and cold air from boiler is again recirculated to sinter cooler for cooling of sinters. In the process, power is generated and also because of recirculation of cold air into the sinter cooler, cooling fans required to cool sinter are switched off, thereby reducing power consumption.
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  • De-dusting of the gas before feeding it to the boiler or recirculating into the cooling system.
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  • Generation of steam at desired temperature and pressure using the hot gases, the waste heat boiler for this purpose was designed and supplied by JFE Engineering of Japan and is the most critical component of the plant.
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  • Generation of 20.6 MW power from the available steam generated by the boiler, the TG/Condenser was supplied by JFE Engineering of Japan.
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  • Cooler hood erection was done in 8 parts for ease of erection during one day shutdowns.
 

Transportation

 

Transportation was tricky for the project since a wide variety of heavy and large equipment had to be transported. Some of the large equipment included TG, condenser, pressure part modules, steam drum, EOT and multiclone. Furthermore, the fabricated equipment such as cooler hoods, feed hopper, dead plate, ducts of 6.6m x 4.6m in size were to be transported. These items were fabricated in smaller pieces, trial-assembled in shop, transported and finally reassembled at site to overcome the challenges with transportation. The cutting plans were made by PEC, which were then reviewed and approved by MECON as well as the Japanese technology provider.

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