Hot Corrosion & Erosion Problems in Coal Based Power Plants in India and Possible Solutions – A Review
Vikas Chawlaa*, Amita Chawlab, D. Puric, S. Prakashc , Prema G. Gurbuxanid and Buta Singh Sidhue
Mechanical Engineering Department, F.C.E.T. Ferozepur-152002, India Chemistry Department, Govt. Brijindra College,Faridkot-151203,India c Metallurgical & Materials Engineering Department, I.I.T. Roorkee, Roorkee-247667, India d Chemistry Department, Smt. C. H. M. College,Ulhasnagar-421003,India e Dean (Academics), P.T.U., Jalandhar-144001,India b
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ABSTRACT Hot corrosion and erosion are recognized as serious problems in coal based power generation plants in India. The coal used in Indian power stations has large amounts of ash (about 50%) which contain abrasive mineral species such as hard quartz (up to 15%) which increase the erosion propensity of coal. Hot corrosion and erosion in boilers and related components are responsible for huge losses, both direct and indirect, in power generation. An understanding of these problems and thus to develop suitable protective system is essential for maximizing the utilization of such components. These problems can be prevented by either changing the material or altering the environment or by separating the component surface from the environment. Corrosion prevention by the use of coatings for separating material from the environment is gaining importance in surface engineering. Keywords: Hot corrosion, erosion, Thermal spraying (TS), Physical vapour deposition (PVD), Chemical vapour deposition (CVD), Nanostructured coatings.
1. INTRODUCTION The attainment of high temperatures has been important in the development of civilization for many countries . Structural materials in many front-line high technology areas have to operate under extreme conditions of temperature, pressure and corrosive environment . So, Materials
Vikas Chawla et al
degradation at high temperatures is a serious problem in several high tech industries. Gas turbines in aircraft, fossil fueled power plants, refineries, and petrochemical industries, and heating elements for high temperature furnaces are some examples where corrosion limits their use or reduces their life, considerably affecting the efficiency . World-wide, the majority of electricity is generated in coal-fired thermal plants, in which the coal is burned to boil water: the steam so produced is expanded through a turbine, which turns a generator . The steam at the low pressure exit end of the turbine is condensed and returned to the boiler. Coal is a complex and relatively dirty fuel that contains varying amount of sulfur and a substantial fraction of non combustible mineral constituents, commonly called ash . The coal used in Indian power stations has large amounts of ash (about 50%), which contain abrasive mineral species such as hard quartz (up to 15%), which increase the erosion propensity of coal . The vast technical literature available is evidence that corrosion and deposits on the fireside of boiler surfaces or in gas turbines represent important problems . Metals and alloys may experience accelerated oxidation when their surfaces are coated by a thin film of fused salt in an oxidizing gas. This mode of attack is called hot corrosion, and the most dominant salt involved is Na2SO4 . High temperature degradation is one of the main failure modes of hot-section components in the gas turbines, so an understanding of this high temperature oxidation is very necessary . Solid particle erosion (SPE) is a serious problem for the electric power industry, costing an estimated US$150 million a year in lost efficiency, forced outages, and repair costs . Erosive, high temperature wear of...