Thermal Power Plants In India Research Articles

CO2 concentration retrieval and emission rate estimation over Indian thermal power plants using radiative transfer approach and AVIRIS-NG data

Carbon dioxide (CO2) emissions from thermal power plants (TPPs) are regarded as the primary source of CO2 at the boundary-level atmosphere. The first step toward mitigating these emissions is to improve emission estimation methods at the facility level and establish a reliable emission reporting system. This study aims to establish a transparent and reliable methodology for detecting point source CO2 emissions from TPP and estimating the emission rate released from the stakes of TPP. A remote sensing method continuum interpolated band ratio (CIBR) has been utilized to detect and estimate CO2 emissions over Indian TPPs using Airborne Visible/InfraRed Imaging Spectrometer - Next Generation (AVIRIS-NG) data acquired by the ISRO-NASA joint campaign over India in 2015 and 2018. MODerate resolution atmospheric TRANsmission (MODTRAN) 5.3 radiative transfer (RT) model simulations were carried out for TPP sites to develop a CIBR algorithm for CO2 retrieval. Two AVIRIS-NG short-wave infrared (SWIR) bands were utilized for CO2 concentration retrieval, and the results from each band were compared based on their emission detection capabilities. Comparatively, SWIR-2 (1960–2120 nm) bands show higher sensitivity of CO2 than SWIR-1 (1560–1640 nm). Therefore, we utilize SWIR-2 results for the CO2 retrieval and emission rate estimation. Maximum CO2 emissions of 53.10, 46.36, 96.84, and 53.49 ppmv were detected at Maithon, Dhariwal, Udupi, and Parangipettai TPPs. The study includes one USA-based TPP to compare emission results for validation and test the method in diverse atmospheric conditions. In addition, we compared CO2 estimation results with AVIRIS-NG benchmark data. The simple band ratio method uses only three SWIR bands and operates with minimal computational facility, making it suitable for CO2 retrieval in hyperspectral data. Further, the integrated mass enhancement (IME) method has been used for emission rate estimation using CO2 concentration values from SWIR-2 retrieval results and wind speed at the sites. Yearly 5.96, 6.82, 2.29, and 3.52 Mt emissions were estimated for Maithon, Dhariwal, Udupi, and Parangipettai TPPs, respectively. The emission results have been validated by establishing a relationship between TPP's coal consumption and CO2 emissions. Further, estimated emission rates have been validated with former investigations and the CO2 baseline emission database of India's Central Electricity Authority (CEA) reports. Not having in-situ measurements and uncertainty in wind data may limit the study.

Quantification of climate change-driven water stress on thermal power plants in India

The objective of this work is to quantify the effect of climate change on the intra-annual water stress experienced by thermal power plants in India. The Integrated Environmental Control Model (IECM v11.5) is used to quantify the monthly water withdrawal and consumption for thermal power plants in four different water-stressed states of India. Current water withdrawal range was 2400–5500 l/MWh, and increased during the summer months by as much as 24 % compared to winter months. Simulations for two representative climate change scenarios, namely SSP2 – RCP 4.5 and SSP5 – RCP 8.5, showed 7–18 % increase in water withdrawal as compared to the present. For the state of Rajasthan, future surface water availability, estimated using Budyko's framework, decreased by more than 49 % for both scenarios as compared to present. Power plants in regions analysed will face water deficits during January-May, necessitating careful planning to manage climate change impacts in the future.

Vulnerability assessment of thermal power plants in India under water stress conditions

Vulnerability assessment of thermal power plants in India under water stress conditions

Natural radioactivity assessment of coal combustion residues produced in Indian thermal power plants using high-purity germanium detector

Abstract Huge amount of coal combustion residue (CCR) is being generated in India every year. Since coal contains some natural radionuclides, the CCR may contribute to the enhanced natural radiation background. Hence, it is important to monitor the natural radioactivity levels in Indian CCR samples. The present study aims to estimate the natural radioactivity levels in CCRs produced in Indian thermal power plants. Accordingly, six CCR samples from different thermal power plants were collected and packed to achieve secular equilibrium among daughter products of 226Ra. The samples were counted for activity of gamma radionuclides using high purity germanium detector based high resolution gamma spectrometer. Results show that 40K is the most abundant among analyzed radionuclides, and the lowest was observed for 226Ra. Secular equilibrium was observed between 228Ra and 228Th, whereas no equilibrium was observed between 226Ra and 238U. The activity concentration for 226Ra and its daughter products (214Pb and 214Bi) was found to be similar in CCR sample before and after equilibrium, indicating that progenies are in secular equilibrium in CCR. The X ray diffraction analysis of CCR indicates the presence of aluminosilicate as major fraction, which has potential of trapping of 226Ra and daughter products. The values observed are very low and similar to those observed in naturally occurring radioactive materials such as coal, soil, and sediment, hence are not of radiological concern with respect to human/environment.

Water washing of torrefied biomass products for effective replacement of coal in Indian thermal power plants

Water washing of torrefied biomass products for effective replacement of coal in Indian thermal power plants

Characterisation of coal and its combustion ash: recognition of environmental impact and remediation.

Energy generation from coal poses an environmental drawback due to the abundance of some potential hazardous elements (PHEs). A few PHEs (As, Sb, Cu, Mn and Zn) are noticed in the coal collected from thermal power plants of India. Among them, As and Sb are depleted while Cu, Mn and Zn are enriched in fly and bottom ash. The short- and long-term exposure of these PHEs into the ecosystem by emission, deposition and leaching causes environmental contamination as well as pollution and health hazards. The water-leaching experiment shows that these elements have feeble mobilisation tendency and low risk. The bioavailability test reflects that bio-uptake of these PHEs into the human system may be the origin of several diseases. Proper storage and recycling of the large amount of fly and bottom ash are a serious concern of thermal power plants. Chemical characterisation of ash, including elemental mapping by scanning electron microscope, calculated enrichment ratio (ER) and relative enrichment index (REI) values, as well as lab-scale water-leaching experiments predict that combustion residues of the studied power generating unit are safe for utilisation in construction, geotechnical and even in agricultural sectors. Chemical characterisation and pre-treatment of ashes before utilisation are urgently required to prevent any possible contamination. Regular scrutiny of emission control device, proper management of ash disposal and frequent utilisation are the keys for clean energy generation. A deep chemical and physical analysis of coal from power plants prior to utilisation is the primary task for sustainable energy generation from environmental aspect.

Techno-Economics and the Identification of Environmental Barriers to the Development of Concentrated Solar Thermal Power Plants in India

India is endowed with a lot of solar radiation as a result of its location. The Indian government therefore intends to maximize the usage of its solar energy resources through the development of solar power plants across the country. The concentrated solar power plant (CSP) is one of the technologies that rely on solar energy for its electricity generation. The type of condenser model in the CSP technology has the potential to affect its techno-economic viability. In this paper, a 100 MW solar tower power plant (STPP) with two different condenser models, i.e., the dry-cooled STPP and wet-cooled STPP models, are studied using the System Advisor Model (SAM) at six different geographical areas in India. The study employed the optimization of the thermal energy storage and the solar field size to identify the minimum levelized cost of electricity (LCOE) for all six locations. Results from the simulation show that the LCOE will range between 13 and 17 cents/kWh under the optimization conditions for the STPP dry-cooled condenser model, while that of the wet-cooled condenser model will range between 12.40 and 12.96 USD cents/kWh for the study locations. It was also observed that the optimized solar multiple (SM) for the dry-cooled STPP model ranges between 1.4 and 1.8, whereas that of the wet-cooled model ranges between 1 and 1.8. The study identified Bhopal as the best location for installing the STPP plant for both condenser models. In addition, this paper also discusses major potential barriers and government policies that are needed to develop CSP technologies in India. The outcome of the study is expected to help both government and other stakeholders in decision making and policy formulation for the sector.

Laboratory and Field Evaluation of Stabilized Fly Ash as an Alternative Material for Sustainable Pavements

Thermal power plants in India produce a large quantity of fly ash, which is harmful to the environment. Underutilization of fly ash and the scarcity of natural minerals have created the need for an unusual construction strategy to prevent huge waste dumps on valuable land and to preserve fast-depleting resources. A study was conducted to determine the efficacy of lime-stabilized fly ash blended with quarry fines as flexible pavement subbase materials. The laboratory investigations were conducted to determine compaction characteristics, unconfined compressive strength, California bearing ratio (CBR), and durability to obtain the optimal quarry fines, fly ash, and lime (QFL) mix. The durability of QFL mixes was studied using 12 wetting–drying cycles. Using the strength and durability criteria specified by the Indian Road Congress, the optimum mix proportion of 40Q:60F+3L was determined. Pavement analyses were performed using the IITPAVE program. The QFL mix was observed to be superior to conventional granular subbase (GSB) layer material in terms of service life and cost-effectiveness. A field investigation was carried out on trial test sections constructed using the optimum QFL mix and GSB in the subbase layer of pavement. Field dry density and dynamic cone penetrometer (DCP) tests were performed on the compacted subgrade and subbase layers to assess the desired quality assurance in the construction of test sections. The early structural performance assessment of pavement sections using a falling weight deflectometer (FWD) test indicated that QFL could effectively replace conventional GSB.

Falling Utilization Factor of Thermal Power Plants in India and Its Financial Impact

Thermal power plants in India are operating under very low Utilization Factors. The average national Utilization Factor of coal based thermal power plants was 77.5 % % in 2009-10 which has come down to 53.37 % in 2021-22. Many studies and reports indicate that, in the business-as-usual situation, average Utilization Factor may drop to 40% in next 2-3 years. This situation has arisen partly because of substantial injection of renewable energy in the grid. Since the renewable energy provides intermittent supply, thermal plants have to dance to the tune of renewable energy in order to sustain the grid stability. These thermal plants have to therefore ramp-up and ramp-down load several times a day. It is one of the major causes for overall low Utilization Factor. The situation is now putting immense technical and financial pressure on the thermal plants. Regulators, policy makers, power plant developers, lenders and other key stakeholders need to take notice of it. In this paper, we explore the direct financial impact on the Profits / Return on Equity (ROE) of thermal power plants under these circumstances. We find that under the regulated tariff regime, thermal power plants may see a reduction in Return on Equity (ROE) to the tune of 26 % if average Utilization Factor drops from a level of 90 % to 35 %.

Estimation of Fly ASH Availability in a Thermal Power Plant for Cement Manufacturers

The Indian coals are having 25 to 45% ash content and huge quantity of fly ash is being generated every day in the Indianthermal power plants. The fly ash so generated are being disposed by dry or wet mode from the power plant. The fly ashdisposed in dry mode is lifted by the cement manufacturers and the fly ash disposed in wet mode is unattended. Mostof the quantity of fly ash is collected in the ESPs. The particle size of fly ash collected in ESPs is finer compared to the flyash collected in other parts of the power plant. For this reason the cement manufacturers prefer the fly ash from ESPs.The quantity of fly ash collected in the ESPs is not directly measurable on everyday basis as there are no well proveninstrumental methods. Also the quantity of fly ash collected in ESPs fluctuates every day due to the varying load factorand coal quality. However, it is important to estimate the quantity of fly ash collected by ESPs on everyday basis so thatthe proportion of fly ash lifted by the cement manufacturers and the fly ash sent to the ash pond will be known. Presentlypower plants do not have a method to estimate the exact availability of fly ash and it is being theoretically calculated fromthe design value that the 80% of the total ash is fly ash and in that a fixed proportion (about 70% of total fly ash generated)is collected in the ESPs. However, the actual generation of fly ash would be different and this is influenced by the type ofcoal used, fineness of the input coal particles, boiler operating conditions, load factor, age of the power plant, etc. Thisuncertainty leads to disputes between cement manufacturers and the utility if there is a penalty clause in the agreementfor not completely lifting the available fly ash (as theoretically calculated by the utility). In view of this it is imperative toformulate acceptable methods for determining the actual quantity of fly ash collected in the ESPs on daily basis. In thepresent work, a simple methodology was developed to quantity the average fly ash collected in ESPs in a 210 MWe coalfired power plant on every day basis through site measurements and routine power plant data. The amount of fly ashdisposed in dry and wet mode has also been estimated through this method.

Impact of India's power purchase agreements on electricity sector decarbonization

A large number of Indian thermal power plants are tied under power purchase agreements with distribution companies. However, the existing energy models do not account for these ‘take or pay’ contracts for investigating climate policies. In this context, this paper investigates the impact of these power purchase agreements on power sector operations, cost of electricity and emissions from the Indian power sector. An optimization model was developed for this study with 620 coal, 239 gas, 21 nuclear and 686 hydro units with technology and operational characteristics to analyze electricity dispatch for power sector. The operations of thermal power plants were analyzed with and without power purchase agreements, and low carbon policy scenario. The scenarios are compared for power plant operations, cost of electricity, stranded assets, and emissions. The results show that there is a significant cost advantage for plants covered under power purchase agreements which favors the operations of older inefficient power plants in baseline scenarios. In addition, the representation of power purchase agreements raises the cost of electricity by 26 percent. A change in operating strategy from least cost to least emissions with a lower demand growth scenario can mitigate 24 percent emissions. The cost of carbon abatement is 268–277 USD/tonne for policy scenarios. Options like renegotiation of power purchase agreements can be considered to mitigate emissions.

The Turning Point in Indian Environment

The human life in the earth may be continued without water for few days, without food for few weeks. However the human life in the earth may not be continued for few minutes without air. Air comes under. 24 ? 7 in our human system. In such condition, air plus sulphur dioxide is harmful to respiratory system which leads to premature deaths and reduction in life expectancy. It is a big shock to the nation that India becomes the highest emitter of sulphur dioxide of the world, surpassing the China. It is not a encouraging trend for us. Under these circumstances MOEF and CC has notified the norms for various pollutants including sulphur dioxide emission from thermal power plants in December 2015. The norms cover various size plants for various periods with various levels of emission, with a timeframe of two years as implementation schedule. This notification is a correct notification in correct direction, but with some time delay. This notification has put about 1800000 MW in study mode, mainly of coal fired units in nature. The sulphur dioxide emission may be well controlled by installing flue gas desulphurisation (FGD) system in boiler flue gas path. By injecting lime in the flue gas path, sulphur dioxide is converted to calcium sulphite and then by reacting with oxygen, it is converted to calcium sulphate. Thus the flue gas is purified from sulphur dioxide. India has to import this technology. Technology transfer is a difficult task especially on commercial terms. This article narrates the various happenings in the country after the publication of notification.so that the reader gets the overall picture in single presentation. The implementation of the flue gas desulphurisation (FGD) system in Indian thermal power plants as early as possible, may improve the environment prevails in the country. This paper deals with various issues related to Sulphur dioxide emission and reduction measures.

Biochar production from crop residues, its characterization and utilization for electricity generation in India

Post COP-15, the push is to reduce coal dependence for electricity generation and GHG emissions from the national electrical grid. Phasing out coal-based thermal power plants (TPPs) does not favour India's economic and social interests. Therefore, it becomes imperative to make coal-based power plants clean. Biochar derived from crop residues has been considered a clean fuel and an economical substitute for coal. The present study investigated the biochar potential of crop residues from rice, wheat, maize and sugarcane cultivation, accounting for 89% of total agro production, for coal replacement in TPPs using primary & secondary data and ArcGIS for mapping agro-residue collection point and TPP. Results show that biochar produced from the identified agro resources in the temperature range of 400 °C–500 °C are suitable for cofiring with coal. 121 MT surplus residues of the selected crops could produce 40 MT biochar having 90 TWh electricity generation potential. Biochar produced from surplus residues is equivalent to 69 MT of coal, about 11% of coal consumed annually in Indian TPPs. Also, biochar cofiring could reduce 165 MT annual CO2 emissions from coal-burning in TPPs, about 14% of CO2 emissions by the energy sector and 7% of overall CO2 emissions by India. Techno-economic analysis showed that the infrastructure development & operation cost for the biochar conversion facility is in the range of 2–3 USD/MWh, which is significantly lower than that of the new biomass to electricity generation facility (43–53 USD/MWh). The results would provide baseline data for policy decisions to avoid net GHG emissions from TPPs, and site identification for additional infrastructure to develop alternative clean fuels for India's coal-based TPPs.

Analysis of coal ash samples from thermal power plants of India for their gallium content using NAA and EDXRF techniques

Coal fly ash (CFA) is an important secondary source for the recovery of gallium (Ga) which has a high potential for its wide applications in many strategic fields such as cellular communications and direct broadcast satellite.Various coal fly and bottom ash samples obtained from thermal power plants located in different parts of India were investigated for their gallium content using NAA and EDXRF techniques. The concentration of gallium in NIST SRM 1633b CFA is not available in NIST certificate and hence was established using k0 based IM-NAA method along with the other certified elements like As, Ce, Co, Eu, Fe, K etc. In addition, the gallium concentration in the NIST SRM was also obtained by relative NAA using Ga2O3 as a standard towards the validation of IM-NAA. Using the NIST SRM, the gallium content in the ash samples of Bituminous coal collected from South Central and Eastern India was found to be from 17.2 to 47.9 mg/kg whereas the same was 6.3–33.3 mg/kg for the ash samples of Lignite coal collected from the South-Central India and Western India. The gallium concentrations obtained by NAA in coal ash samples were compared with another non-destructive assay technique, i.e. EDXRF and the results are found to be in good agreement. These samples were proved to be a potential secondary source of gallium, available in India.

Examining Contamination of Arsenic in Soil Around Thermal Power Plant at Dadri in India

Coal fired thermal power plant (TPP) serves as point source releasing hazardous heavy metals in the environment contributed from burning of coal for electricity generation. This causes altered physicochemical properties of soil. Arsenic (As) is highly toxic in nature which gets transferred to the soil environment by varied pathways. The present study attempts to measure the physicochemical properties and arsenic contamination in soil around a coal fired thermal power plant in India for two consecutive years (2017-19). The soil pH, moisture, conductivity, water holding capacity, nitrogen, phosphate, potassium, manganese, iron and arsenic were measured in six villages located within 0-10km around TPP. Results suggest soil from the villages to be slightly alkaline with good water holding capacity and soil moisture. The soil was manganese deficient however the levels of nitrate, phosphate and potassium were similar to that of agricultural soil suggesting negligible impact of TPP on soil quality in the region. Low arsenic contamination (though within permissible limits), at site 4 (Piyawali) located within 0-5 km and in windward direction from TPP was noted. Traces of as was also measured at site 2 (Jarcha) and site 3 (Khatana) which were within 5-10 km of TPP and in the windward direction. Results indicate that arsenic from the emissions migrate with the wind to Jarcha and Khatana whereas it directly falls and retains at Piyawali which is in the leeward direction. Thus, a significant relation between movement of arsenic and the position of the village, distance and direction of wind with respect to TPP is evident. The soil pollution index (Pi) for arsenic revealed the Pi values to be <1 in all seasons suggesting that though arsenic is present in the soils of the villages near the thermal power plant, it may not be contributing largely towards the pollution in the soil. Application of zinc to bind arsenic electrostatically in the soil matrix is therefore recommended to mitigate arsenic or growing of non-edible or energy rich crops will be helpful. Moreover, power plants be geared for arsenic containment measures to minimize input of arsenic in soil environment.

Modeling Challenges for Improving the Heat Rate Performance in a Thermal Power Plant: Implications for SDGs in Energy Supply Chains

Rapid industrialization and the increased use of consumer electronic goods have increased the demand for energy. To meet the increasing energy demand, global nations are looking for energy from renewable sources rather than non-renewable sources, to adhere with the sustainability principle. As energy from renewable sources is still in the experimental stage, there is a need to use available energy sources optimally. Considering this, the present study aims to identify, evaluate, and reveal the interrelationship among critical challenge factors in improving the heat rate performance of coal-fired thermal power plants. The study identifies twenty critical challenges through a comprehensive literature review. Then, to evaluate the identified critical challenges, the grey-DEMATEL (Decision Making Trial and Evaluation Laboratory) technique is used. For evaluating the challenges, this study conducts an empirical analysis in a thermal power plant in India. The findings reveal that air preheater leakage, coal flow balancing, and air heater air outlet temperature are the top three critical challenges hampering the thermal power plant’s performance. Additionally, fourteen challenges come under the cause group, while eight challenges come under the effect group. The findings of the study can assist industrial managers in overcoming problems in their thermal power plants. The results can also guide the development of a robust and reliable framework for mitigating these challenges.

Direct single-step synthesis of phase pure zeolite Na–P1, hydroxy sodalite and analcime from coal fly ash and assessment of their Cs+ and Sr2+ removal efficiencies

Combustion by-products of coal from thermal power plants cause environmental pollution; efforts are made to develop techniques and green processes that could reduce the waste volume and convert the waste to useful materials. Synthesis of phase pure zeolites from coal fly ash and its use as adsorbent and ion exchangers to remove Cs+ and Sr2+ from simulated nuclear waste solutions is the focus of the current study. Zeolite Na–P1, hydroxy sodalite and analcime were synthesized from fly ash obtained from an Indian thermal power plant by using hydrothermal method. Zeolite synthesis conditions were optimized by studying the effect of concentration of NaOH solution, homogenization time, hydrothermal temperature and time. The zeolite phase formation, surface morphology, thermal stability studies were carried out by XRD, SEM, TG-DTA techniques; specific surface area was determined by BET analysis. Crystalline pristine zeolite Na–P1 was prepared from fly ash on reaction with 1 M NaOH at 150 °C. Similarly, hydroxy sodalite and analcime were also synthesized from the fly ash by hydrothermal reaction with 3 M NaOH at 150 °C and 5 M NaOH at 200 °C respectively. The removal efficiencies of synthesized zeolites were investigated with aqueous simulated nuclear waste solutions containing Cs+ and Sr2+. The adsorption capacities and cation exchange capacity (CEC) of zeolite Na–P1, hydroxy sodalite and analcime for Cs+ and Sr2+ ions were demonstrated. The results show the adsorption capacity of Na–P1 for Cs+ is 39.3 mg/g and for Sr2+ is 92.48 mg/g respectively and is a better adsorbent than analcime and hydroxy sodalite.

A techno-economic appraisal of parabolic trough collector and central tower receiver based solar thermal power plants in India: Effect of nominal capacity and hours of thermal energy storage

To increase the share of solar thermal power in the energy mix, deployment of large capacity plants with the provision of thermal energy storage can be an attractive option subject to their techno-economic feasibility. In this paper, an attempt has been made to assess the effect of the nominal capacity and the hours of thermal energy storage on the techno-economics of solar thermal power plants in India. Based on two commercially proven solar concentrating technologies (parabolic trough collector and central tower receiver) and two condenser cooling technologies (wet-cooled and dry-cooled), three solar thermal power plants i.e., wet-cooled parabolic trough collector, dry-cooled parabolic trough collector and dry-cooled central tower receiver have been considered in the study. For the analysis, four different nominal capacities (50 MW, 100 MW, 150 MW and 200 MW) for parabolic trough collector based plants and three nominal capacities (50 MW, 100 MW and 150 MW) for central tower receiver based plants along with seven different values of hours of thermal energy storage (0, 3, 6, 9, 12, 15 and 18 h) have been considered. The capital cost has been estimated based on inventory of materials based approach. The estimated values for the levelized cost of electricity are highest for dry-cooled parabolic trough collector based plants (higher by 26% and 33%, respectively than the estimated values for wet-cooled parabolic trough collector and dry-cooled central tower receiver based plants). Further, the economy of scale was also observed in estimating capital expenditure with an increase in nominal capacity and hours of thermal energy storage. From the viewpoint of the project developer, for the same capital expenditure, wet-cooled parabolic trough collector based plants (without thermal energy storage) of higher nominal capacities are observed to be techno-economically more viable as compared to relatively smaller nominal capacity plants with significant hours of thermal energy storage. On the contrary, for central tower receiver based plants, it is techno-economically advantageous to increase hours of thermal energy storage in an existing lower nominal capacity plant compared to planning a higher nominal capacity central tower receiver based plant without storage.

Efficiency of Indian Thermal Power Plants and Suspended Particulate Matter: Findings Across Technological Assumptions and DEA Models

Suspended particulate matter (SPM) emissions from coal-based thermal power plants (CTPPs) cause respiratory illness. However, this has not been given its due importance in the efficiency assessment of CTPPs. This study contributes to the literature by incorporating suspended particulate matter in the benchmarking exercise for Indian CTPPs. In such a study, the theoretical assumptions regarding pollution generating technology or the choice of evaluation tool may impact the ranking of CTPPs. To draw robust inferences, we present a comparative study of two alternative microeconomic approaches (joint and by-production technologies) and two types of data envelopment analysis tools (graph–hyperbolic and directional distance function) applied on two representative samples of Indian CTPPs. Results indicate that Indian CTPPs are moderately inefficient. Choice of technological assumption or data envelopment analysis model does not impact the ranking of CTPPs. Ownership and plant load factor play vital roles in determining inefficiency, and impacts of these factors remain stable across models. JEL Classifications: C61, D22, Q40, Q50

Hot corrosion behaviour of CNT-reinforced ZrO2-Y2O3 composite coatings on boiler tube steel at 900°C

PurposeIn Indian thermal power plants, the main cause of boiler tube failure is the presence of molten sulphates and vanadates, which deteriorate the tube material at high temperatures. To combat the hot corrosion failure of metals, thermal spray technology is adopted. This study aims to investigate and study the effect of hot corrosion behaviour of carbon nanotube (CNT)-reinforced ZrO2-Y2O3 composite coatings on T-91 boiler tube steel in a molten salt environment at 900 °C for 50 cycles.Design/methodology/approachA plasma spray technique was used for development of the coatings. The samples were exposed to hot corrosion in a silicon tube furnace at 900 °C for 50 cycles. After testing, the test coupons were analysed by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and cross-sectional analysis techniques to aid understanding the kinetics of the corrosion reaction.FindingsCNT-based reinforced coatings showed lower weight gain along with the formation of protective oxide scales during the experimentation. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.Originality/valueIt is pertinent to mention here that the high temperature behaviour of CNT-reinforced ZrO2-Y2O3 composite on T-91 steel at 900°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at elevated temperature.