A Thermal power plant of 3000 MW capacity needs 55000 - 60000 MT of coal per day to meet its generation demand. Quality of coal is a challenge for coal handling plants in Indian thermal power plants.
Indian Coal generally contains impurities in the form of shale stones and hard boulders. In the first stage of a coal handling plant, coal crushers ( also known as coal granulators) are used to break large size coal pieces into smaller granules or lumps. These coal crushers are equipped with arrays of ring hammers rotating freely on shafts and the coal is crushed between the rotating hammers that convert the larger coal pieces into granules. Traditionally these ring hammers are made of cast steel with high manganese content and due to the high wear and tear inherent of this application, these ring hammers have to be replaced at regular intervals. Thus they constitute an important element of the overall spares and maintenance cost of coal handling plants. Due to the presence of stones, boulders and other hard impurities in the coal, these cast steel ring hammers , premature wear as well as breakage ( metal fracture) is commonly observed in Indian coal handling plants.
This not only increases the replacement cost of ring hammers but also leads to severe consequential damage of other allied parts like shaft, guide plates, and housing leading to long outages and break downs. Other than this, high vibration & noise during operation is also observed at coal crushing machine.
To overcome such issues, a major power plant, joined hands with Bharat Forge and initiated development of suitable forged ring hammer for its coal crusher. Bharat Forge analysed the failure mode of existing cast steel ring hammers s and proposed appropriate alloyed steel grade for the forgings. Joint trial commenced on one coal crushing machine by replacing cast hammers with alloy steel forged hammers since October 2013.
After three months, on January 2014, joint inspection was done at site and data was meticulously recorded for weight reduction, cracks etc. Based on the wear pattern, the power plant officials predicted that the forged ring hammers could last for additional 9 months. Cost benefit analysis of forged versus cast hammers was also done and it was found that payback period of these forged hammer is 5 months. Considering the expected life of nine months, four months additional cost benefit is achieved. At the time of printing this article, eight months have passed and during monthly review inspection, it has been observed that there is no significant wear of these forged hammers. Most importantly, there is no breakage or metal fracture of the hammers thus significantly reducing expensive downtime of both the coal handling plant as well as downstream coal pulverizing mills. At the current rate of performance, it can be predicted that the service life of forged ring hammers from Bharat Forge can be more than twelve months which could increase the cost benefit period from 5 months to 7 months.
A comparison table between cast ring hammers and special forged hammers from Bharat Forge is enclosed.On the back of this successful trial with forged ring hammers, the largest thermal power producer in the country has decided to horizontally deploy forged hammers across all their coal handling plants.Bharat Forge is also engaged with private and state owned thermal power plants for adopting forged ring hammers in their coal handling plants and will be pleased to offer this value added solution to interested power producers.
The author of the article is Naresh Kumar Sharma, AVP Sales, Bharat Forge
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