Wear Protection
Metal matrix composite technology
Ken Birchett, PE destaca una solución para mejorar el elemento de esmerilado para toda la vida útil, para centrales térmicas a carbón en la India.
Ken Birchett, PE umreißt eine Lösung zur Verlängerung der Lebensdauer von Mahlteilen für mit Kohlestaub betriebene Wärmekraftwerke in Indien.
Ken Birchett, PE outlines a solution to improve the grinding element lifetime for pulverised coal-fired thermal power stations in India.
I Fig. 1. Xwin Grinding Rolls.
ndia possesses some of the largest coal reserves in the world. As a result coal is an important natural resource for India and an important consideration for electrical generation and generation sufficiency.
Today India’s electrical generation from coal accounts for almost 60 per cent of the total generation. As a growing economic power with a large population India faces the daunting challenge of mitigating the severe deficiencies that currently exist between demand and supply and must plan rapidly for additional generation capacity to service current and future growth expectations of its national economy. As a result there is a critical need for new blocks of reliable power to be added to the Indian electrical grid. To achieve these requirements it is expected that India will increase its power output over the next several decades by more than 3-5 times its current production. Much of the planning for this new generation is based on coal-fired thermal power plants grinding coal to a specific fineness and transporting the pulverised coal to the furnace for spontaneous combustion. In face of this daunting challenge to enhance generation capacity another complexity is added because the Indian coal reserves are typically the most abrasive coals in the world having a low
calorific value and high ash content. Te calorific value of Indian coal typically ranges from 2,500-4,500kCal/kg (4,497–8,095Btu/lb). Te ash content in the coal generally ranges
from 35-50 per cent with the silica in the ash ranging anywhere from 45-60 per cent. Te ash and the silica contained in the ash offers no heating value but, being an integral part of the coal, must be processed as part of the pulverisation process. For pulverised coal-firing this translates to the need for higher quantities of pulverised coal in order to achieve the required furnace heat input resulting in greater wear on the pulverising equipment, fuel lines and furnace components. Of particular importance to pulveriser operation are the grinding elements for which lifetimes in India, because of high ash and silica, are measured in hours instead of months or even years in other less abrasive locations. Proper operation and condition of the grinding elements is a critical component to efficient mill operation. Tis coupled with proper control and distribution of primary air (PA) is critical to pulveriser performance and has a direct impact on all aspects of downstream operations and performance. Te grinding rolls or tires are particularly susceptible to abrasion wear because of their location in the mill relative to the pulverised coal/air stream; being in the direct path of the PA and entrained pulverised coal. Depending upon the distribution, the direction and the magnitude of the PA velocity vectors the greater the potential impact of abrasion wear on the roll. Likewise the higher the ash content and the higher the silica content in ash the greater the effect of abrasion wear on the roll. It is thus no wonder that the grinding element lifetimes in Indian coal-fired power plants are measured in running hours. As a result a strong need exists for grinding elements with better wear resistant properties. Mono-metal high chromium alloys and high chromium hard-surfaced products do not provide sufficient wear resistance to adequately serve the market needs in India. A recent case in point is a power station located in the state of West Bengal in eastern India in which the coal’s average heating value is 3,600Kcal/kg (6,476Btu/lb) with an
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