Chittatosh Bhattacharya - Academia.edu (original) (raw)

Papers by Chittatosh Bhattacharya

Journal of Energy Resources Technology-transactions of The Asme, Aug 11, 2008

Pulverizers play a pivotal role in coal-based thermal power generation. Improper coal fineness or... more Pulverizers play a pivotal role in coal-based thermal power generation. Improper coal fineness or drying reflects a qualitywise deterioration. This results in flame instability, unburnt combustible loss, and a propensity to slagging or clinker formation. Simultaneously, an improper air-coal ratio may result in either coal pipe choking or flame impingement, an unbalanced heat release, an excessive furnace exit gas temperature, overheating of the tube metal, etc., resulting in reduced output and excessive mill rejects. In general, the base capacity of a pulverizer is a function of coal and air quality, conditions of grinding elements, classifier, and other internals. Capacity mapping is a process of comparison of standard inputs with actual fired inputs to assess the available standard output capacity of a pulverizer. In fact, this will provide a standard guideline over the operational adjustment and maintenance requirement of the pulverizer. The base capacity is a function of grindability; fineness requirement may vary depending on the volatile matter (VM) content of the coal and the input coal size. The quantity and the inlet temperature of primary air (PA) limit the drying capacity. The base airflow requirement will change depending on the quality of raw coal and output requirement. It should be sufficient to dry pulverized coal (PC). Drying capacity is also limited by utmost PA fan power to supply air. The PA temperature is limited by air preheater (APH) inlet flue gas temperature; an increase in this will result in efficiency loss of the boiler. Besides, the higher PA inlet temperature can be attained through the economizer gas bypass, the steam coiled APH, and the partial flue gas recirculation. The PA/coal ratio, a variable quantity within the mill operating range, increases with a decrease in grindability or pulverizer output and decreases with a decrease in VM. Again, the flammability of mixture has to be monitored on explosion limit. Through calibration, the PA flow and efficiency of conveyance can be verified. The velocities of coal/air mixture to prevent fallout or to avoid erosion in the coal carrier pipe are dependent on the PC particle size distribution. Metal loss of grinding elements inversely depends on the YGP index of coal. Besides that, variations of dynamic loading and wearing of grinding elements affect the available milling capacity and percentage rejects. Therefore, capacity mapping is necessary to ensure the available pulverizer capacity to avoid overcapacity or undercapacity running of the pulverizing system, optimizing auxiliary power consumption. This will provide a guideline on the distribution of raw coal feeding in different pulverizers of a boiler to maximize system efficiency and control, resulting in a more cost effective heat rate.

International Journal of Innovative Research in Engineering & Management, 2017

The case study is related to an assessment of derating of power generation capacity of 75 MWe nam... more The case study is related to an assessment of derating of power generation capacity of 75 MWe nameplate capacity units due to unavailability of high pressure (HP) heaters of a pulverized coalfired power generating station in India. The generation capacity of the said Power Plant units, which were commissioned since the 1960s onward, was deteriorated due to trouble in the regenerative feed water heating system. The power generating station was consisting of three 75 MWe BTG units and the generated steam from any of the three similar 320 TPH boilers may be fed to any one of 75 MWe turbo generators through available crossover connections. The study summarizes the results of the series of calculation on collected in-situ data to evaluate the performance and efficiency deterioration due to fall in final feed water (FW) temperature at boiler inlet, as per the provisions of standard thermodynamic 1st law based cycle efficiency evaluation practices. The erosion in IP turbine blades degrades the back pressure on the high-pressure turbine with aging and thereby degrades last HP Heater shell pressure resulting degradation in FW temperature. Bypassing HP heaters affects the same way along increasing condenser losses. Cycle heat rate loss is also inevitable due to emergency drip operation, turbine gland steam leakage, makeup water flow in the condenser. These findings discuss the impact on unit heat rate with reference to design and operating data of 75 MWe generating units while HP Heaters were available and the same were partly or fully unavailable causing performance deterioration.

The coal‐fired power generation efficiency and minimization of loss of fuel energy for low-rank c... more The coal‐fired power generation efficiency and minimization of loss of fuel energy for low-rank coal is essentially integrated to pulveriser performance. In this book, the merit of proposed concept of PFGR© arrangement has been established on the fact that, drying capacity of the milling system of a sub-critical PC fired power plant may be enhanced from rated allowable maximum gross raw coal moisture drying to higher percentage low-rank raw coal moisture drying without compromising the coal throughput capacity of the milling system while a fuel switching is done from mill selection coal having a gross coal ash-moisture less than gross ash- moisture of available low-rank coal. The present study has been established on the fact that there is a tangible reduction in above referred low-rank coal consumption and reduction in equivalent CO2 emission along a steam cycle heat rate incentive and simultaneously a substantial amount of boiler exhaust waste heat energy is recovered per kg of co...

ASME 2011 Power Conference, Volume 1, 2011

Coal bound moisture is a key issue in pulverized coal fired power generation. Coal being hygrosco... more Coal bound moisture is a key issue in pulverized coal fired power generation. Coal being hygroscopic, accumulates considerable surface moisture with seasonal variations. A few varieties of coals are having unusually high inherent as well as surface moisture that affects the pulverizer performance and results lower thermal efficiency of the plant. A proper coal drying is essential for effective pulverization and pneumatic conveyance of coal to furnace. But, the drying capacity is limited by available hot airflow and temperature of hot primary air. Even, use of high-grade coal for blending would not provide the entire useful heat value due to moisture, when used for matching power plant design coal parameters. Besides, the inefficient mining, transportation, stacking and associated coal fleet management deteriorates the “as fired” coal quality affecting cost while purchased on “total moisture and gross heat value” basis. Partial devolatilisation of coal in a controlled heating process...

Indian Journal of Power and River Valley Development, 2021

There were quick and successive failures of economiser tubes in a four years old cold cyclone cir... more There were quick and successive failures of economiser tubes in a four years old cold cyclone circulating fluidised bed 135 tph boiler in a short span of three months. Advance inspection and failure analysis, change in operational practices were used to get the boiler running at full load at the earliest possible time. This paper presents details of the process of inspection, maintenance, operation and failure investigation carried out for the economiser tubes of the boiler. The failure of the economiser tubes was due to external corrosion of the tubes furnace fire side due to presence of sulphur in coal, accompanied by localised erosion by high levels of alpha-quartz in coal ash.

The pulverizer plays a pivotal role in coal based thermal power generation. The improper coal fin... more The pulverizer plays a pivotal role in coal based thermal power generation. The improper coal fineness or drying reflects a quality-wise deterioration. This results in flame instability, unburnt combustible loss, and a propensity to slagging or clinker formation. Simultaneously, an improper air-coal ratio may result in either the coal pipe choke or the flame impingement, an unbalanced heat release, an excessive FEGT, overheating of the tube metal, etc, resulting on the reduced output and excessive pulverizer rejects. In general, the base capacity of the pulverizer is a function of coal and air quality, conditions of grinding elements, classifier and other internals. The capacity mapping is a process of comparison of standard inputs with actual fired inputs to assess the available standard output capacity of the pulverizer. In fact, this will provide a standard guideline over operational adjustment and maintenance requirement of the pulverizer. The base capacity is a function of grin...

The techno-economic aspects of coal drying with cost effective waste heat recovery mechanism is o... more The techno-economic aspects of coal drying with cost effective waste heat recovery mechanism is one of the challenging issues faced while using lignite or high ash brown coal for direct combustion in coal fired thermal power plant. Coal being hygroscopic in nature, re-adsorbs considerable moisture even after conventional drying post wet coal washing condition affecting boiler performance. Particularly moisture in coal affects the pulverization where pulverized coal (PC) firing is adopted. In this paper the impact of coal moisture on useful heat value for PC fired steam generation is evaluated for some typical steam coals so that related change in direct firing coal throughput can be estimated for application of suitable online coal drying mechanism. This assessment can be further used to determine usefulness of pre-combustion coal drying methods like integrated drying and partial coal gasification method, particularly for coal processed through dry or wet coal washing to improve the...

Journal of Engineering for Gas Turbines and Power

The steam consumption in a turbine within an operating pressure range determines the effectivenes... more The steam consumption in a turbine within an operating pressure range determines the effectiveness of thermal energy conversion to electric power generation in a turbo-alternator. The low pressure (LP) stage of the steam turbine produces largest amount of steam to shaft-power in comparison to other stages of turbine although susceptible to various additional losses due to condensation of wet steam near penultimate and ultimate stages. The surface deposition in blade is caused by inertial impaction and turbulent-diffusion. With increasing blade stagger angle along the larger diameter of blading, the fractional deposition of wet steam is largely influenced by blade shape. From this background, the aim of this work is to predict the effect of mathematical models through computational fluid dynamics analysis on the characterization of thermodynamic and mechanical loss components based on unsaturated vapor water droplet size and pressure zones in LP stages of steam turbine and to investi...

International Journal of Energy Technology and Policy, 2016

Economic advancement in current climate change scenario need to address two key concern of the na... more Economic advancement in current climate change scenario need to address two key concern of the nation. An immediate action is vital for a long term sustainable carbon dioxide emission reduction plan along gradual improvement of energy intensity over Indian industrial economy to pave the way for national Energy Security. Energy intensive sectors of the Indian economy is still driven by volumes of production rather than cost of production more focusing on the bottom line of profit. Affordable, cost effective and less polluting energy availability can create sustainable, technically feasible development, and changes in metal, mining, manufacturing, service industries, transport and agricultural sectors to minimise the impact of climate change with less emission potential. Reliable electricity and primary energy supply is key for growth and socioeconomic development and in a country like India the options of affordable fuels are more confined to bio-mass or coal, both in domestic and industrial sectors. With the deregulation of Indian Power sector since 90 s steam cycle coal thermal power plants has experienced a rapid growth. This deregulated growth is primarily through the hands of independent power producers (IPP) and CPSUs. These power producers have promulgated both a growth in new power production and a shift from coal to multi fuel fired conventional steam plants to gas fired combined cycle power plants and the recent trend to go for high efficiency supercritical technology as already envisaged by Ultra Mega Power Projects. But still the customers have no say for a failure to supply power by the power distribution companies. There is no penalty for unavailability of quality and contractual power supply, neither the customers are rewarded for reducing their own consumption. Bio-mass sourced from forestry, animal husbandry and agricultural residue is still a favourite low-cost fuel option to rural India followed by abundant supply of coal as fuel in east, central, west and southern parts of India. Coal is predominantly available primary energy resource other than untapped resource of thorium and annually available solar radiation. At the same time, there is a growing belief that the use of fossil fuel and the consequent release of greenhouse gases are mainly responsible for the observed global warming trend. Hence there is a challenge ahead for adapting new efficient technological input for clean, alternative energy for replacing or minimising the use of the fossil fuels and promoting energy efficient appliances and processes to elevate end use efficiency. As such, increasing users end power cost, decreasing fuel quality and tightening global and national environmental standards are putting pressure to adopt advance environment friendly technologies to push a low carbon economy, together with renewable and advanced nuclear technologies, such that environment friendly clean and green energy is available for the well-being of the present and to sustain the need of future generations. Coal is fuelling about 56% of electricity generated in the country and at a consumption growth rate of 5%; it can sustain estimated domestic need till 2050. Therefore, India s choice of energy security particularly the electric power demand is only achievable with advanced coal and alternative energy utilisation technologies with a reduced carbon footprint for the country. After all, we need to have a clear sky initiative to visualise the appearance of rainbow in the horizon, once again!! Introduction: Total population of India in 2006 was 1.1 billion and likely to be 1.2 billion in 2011 and expected to be stabilised at 1.6 billion in 2050. Its population is just next to China in the world with 1/6 th of the globe. Total land area is 32.88 million ha (2.3% of world land area) and seventh largest in the globe. This constitutes 11.7% of world s arable area (2 nd largest agriculture area in the world) and having 95 million ha irrigated land cover (highest in the world with 21.8% of world s irrigated land cover).Withdrawal of water is mostly as groundwater or fresh surface water (5% of world s freshwater resources). The total forest cover is 76.87 million ha (23.4% of total land area) which is 10 th most forested nation in the globe. This forest cover is enough to neutralise 9.31% of our total annual emissions of 2000 and balance 6.5% of estimated emission in 2010. Total utilisable surface water available is 690 km 3 and utilizable ground water is 396 km 3. Total annual water availability is 1112 billion m 3. The estimated annual water requirement based on projected population growth with national average consumption would be 694-710 billion m 3 in 2010; 784-843 billion m 3 in 2025 and 973 1180 billion m 3 in 2050. Almost 80 per cent of the rainfall occurs during the monsoon period. Further, there is considerable variation in the rainfall from one region to another. The average annual rainfall of India is about 1,170 millimetres; but it varies from less than 100 millimetres in the western part of Rajasthan to over 10,000 millimetres near Cherapunji in Meghalaya. The flow in peninsular rivers are dependant mostly on annual rainfall. During 1950 to 2002, Irrigation potential has increased from 22 to 95 million hectare and food production from 50 to 200 million tons. With projected population growth, food grains requirement will be 450 million tons by 2050, For which irrigation potential has to be increased to 160 million hectares (Maximum irrigation potential possible from conventional projects 140 M ha). The irrigation component of Bharat Nirman aimed at creation of additional irrigation potential of 10 million hectare (Mha) in four years from 2005-06 to 2008-09 to sustain national food security plan. Most of the river basins in India will be deficit by 2025 i.e. per capita availability will reduce to less than 1,000 m 3 which may advance for Himalayan snow-fed rivers with increment of Global warming rate. Total CO 2 emission from India in 2006 was 1510 million tons CO 2 eq. (ORNL-USA). It ranks 3rd in emission with 1342 MT CO 2 eq. average emission per year since 2005. But India s total emission contribution stands around 4% compared to more than 16% each by US and China of total global emission. However on per capita basis it stands at 140 th position with 1.9 tons/person/year with worldwide average 5.6 tons/person/year (UNDP Human Dev. Report :2007-08).The current report suggests per capita emission in India stands at 1.1 tons/person/year compared to 20+ tons from US and 10+ tons from most of the OECD countries. The global emission from fossil fuel burning in 2005 was 27136 Mt of CO 2 eq. and India s share was 1147.46 Mt. Again, the fossil fuelled sectors account for around 61 per cent of total national emissions (as on 2004) followed by agriculture sector (28% of total emission as estimated by MoEF in 1994). For fossil fuels, coal combustion had a dominant share of emissions, amounting to around 64 per cent of all fossil-fuelled energy emissions (as on 2004). In 2004-05 total power generation in India was 590158 GWh resulting to equiv. CO 2 emission of 462,192,140 MT. [CEA, 2006]. Fossil fuels account for 80% of global primary energy consumption. 35% and 24% of world s consumption is sourced from oil and coal respectively (2007). The global total primary energy supply and consumption was 11433.92 Mtoe and 7911.7 Mtoe respectively in 2005. Fossil fuels account for 68% of energy consumption in India; coal and oil supply 37% and 25% of total energy consumption followed by 30% from biomass resources. India s total domestic energy production in 2005 was 419.04 Mtoe supplemented with equivalent energy import of 121.6 Mtoe, amounting total primary energy supply of 537.31 Mtoe (4.7% of world s TPES) which grew at a compound rate of 3.4% since independence. The electricity consumption in 2005 was 525.93 TWh (3.1% of world s electricity consumption). As predicted, India is the 3 rd largest energy consumer in the world. The demand for primary energy will increase to 1,836Mtoe to meet the projected GDP growth of 8% per annum by 2031-2032, (4 x demand of 2003-04). The share of commercial energy grew from 28% in 1950 to 70% in 2004 as a result of industrial growth. Commercial energy requirements would also be around 1,651Mtoe by 2031-32 (5 times of 2003-04). The annual per capita total primary energy supply in India was (27% of world s average) only 490 kgoe (compared to 1320 kgoe in China and the world average of 1,780 kgoe.) in 2005 with 480 kWh/per person (compared to 1802 kWh in China and the world average of 2596 kWh)

ASME 2006 Power Conference, 2006