Preheater Research Articles

Performance analysis of an efficient waste heat utilization system in an ultra-supercritical coal-fired power plant

With the rise of new energy sources in the power industry, improving the efficiency of coal-fired power plants is essential. Currently, the leading main causes of irreversible energy loss are the energy level mismatches of boilers and turbines. An ultra-supercritical coal-fired power plant thermodynamic system was reconstructed based on the first and second laws of thermodynamics to improve the efficiency of power plants, and an efficient condensate water preheating air integrated bypass flue waste heating efficient utilization system is thus herein proposed. Consequently, high and medium steam turbine extraction flow is returned to the steam turbine to do work, and cold source loss is reduced by increasing the extraction steam flow of the low-pressure cylinder. At the same time, the inlet air temperature in the air preheater is significantly increased by preheating the hot air with condensate water, resulting in a reduced heat transfer temperature difference and significantly improved exergy efficiency. Compared with conventional low-temperature economizer and bypass flue waste heat utilization schemes, the results indicate that the heat transfer exergy efficiency increased significantly from 78.49% to 95.88% in the air preheater, and the heat consumption rate of the turbine generator set decreased by 108.06 kJ/(kW⋅h). The generation efficiency increases by 0.74%, while the standard coal consumption rate decreases by 3.92 g/(kW⋅h). In terms of economic investment, the dynamic payback period is 3.31 years and the net present value is $2.20 M/year. This paper provides an effective energy conservation and emission reduction plan for coal-fired power plants to contribute towards achieving national carbon peaking and carbon neutrality goals.

Thermodynamic analysis of a liquid air energy storage system with off-peak electric heat storage and reutilization

As a large-scale energy storage technology, liquid air energy storage (LAES) can effectively improve the stability and quality of power grid. However, the traditional LAES has low cycle efficiency, high initial investment and low economic benefits. In order to improve the system performance, a LAES system based on off-peak electric heat storage and high temperature preheating of turbine inlet air was proposed. The thermodynamic characteristics of the LAES system were analyzed, and the energy analysis, exergy analysis and economic evaluation were carried out. Combined with off-peak electric heat storage, the power generation during the peak time by the LAES system can be significantly increased, and the economy of the LAES system can be effectively improved with the peak-valley electricity price difference, especially in areas where the price difference is obvious. The results will be beneficial for the application and promotion of the LAES technology.

Identifying the optimum operating conditions for the integration of a solar loop to power an industrial flash dryer: Combining an exergy analysis with genetic algorithm optimization

With the objective to reduce fossil fuels consumption and greenhouse gas emissions, the integration of solar thermal energy into energy-intensive processes represents the most effective solution. This paper investigates the best solar integration scenarios to an industrial dryer unit through an exergy analysis. The exergetic balance for each subsystem is conducted, and a sensitivity parametric analysis was carried out. The optimization using the Genetic Algorithm was then conducted to define the optimum solar operating conditions. The exergetic evaluation showed an important exergy destruction at the dryer and combustion chamber, accounting for 58% and 42% of the inlet exergy flow, respectively. The sensitivity analysis outcomes showed that the exergy efficiency is clearly increased by increasing both drying temperature, decreasing the inlet moisture content, with preheating the combustion air temperature. Considering these variables, the optimization problem enabled enhancing the exergy efficiency by 40% and 30% for the overall process and flash dryer, respectively, when increasing drying temperature to 850 °C, an inlet moisture content of 14.9% and a preheated air combustion of 150 °C. Finally, the solar field could be integrated to the industrial dryer to preheat the ambient air for the combustion chamber to the setpoint temperature of 150 °C.

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.

Study on the condensable particulate matter removal characteristics of air pollution control devices in a Chinese ultra-low emission coal-fired generating unit

Condensable particulate matter (CPM) belongs to PM25. In addition, it is one of PM2.5 main contributors. But CPM emissions are often overlooked in coal-fired power plants. As a result, this paper studies the removal characteristics of (CPM) from air pollution control devices (APCDs) in a Chinese ultra-low emission coal-fired generating unit. The quality and content of flue gas particles, including CPM and filterable particulate matter (FPM), were measured at four points: the selective catalytic reduction (SCR) input, air preheater (APH) inlet, electric precipitator (ESP) outlet, and wet flue gas desulphurization (WFGD) outlet. The removal characteristics of each APCD were studied. Within the scope of this study, it is found that: ® CPM emission concentration accounts for 94.9% of total particle emission concentration, and is higher than the ultra-low particulate matter outflow guidelines for coal-fired power plants in China; ©WFGD has the highest CPM inorganic component removal radio of 97.02%, and ESP has the highest CPM organic component removal radio of 58.46%, among APCDs; ©SO4 2−, NH4 +, F−, and Cl− are the most abundant water-soluble ions in CPM.

Modelling the Relationships among the Key Factors Affecting the Performance of Coal-Fired Thermal Power Plants: Implications for Achieving Clean Energy

Most countries depend on coal-fired thermal power plants (CTPPs) to meet energy demands. However, the adverse environmental impacts of CTPPs also remain a major concern. As the energy generations from renewable energy resources are still in the developing stage, reliance on CTPPs is inevitable. Hence, the efficiency of CTPPs has to be improved, while decreasing carbon emissions. This study aims to identify and evaluate the key factors that need to be addressed in improving the performance and minimizing the carbon emission of CTPPs. With the literature review and industrial interaction, twenty-four key factors are identified. Next, an integrated approach of the fuzzy analytic hierarchy process (FAHP) and fuzzy decision-making and trial laboratory (FDEMATEL) is used to evaluate the key factors. FAHP prioritizes the key factors and FDEMATEL reveals the relationship among the key factors. Results indicate air preheater leakage, plugging by ash, high levels of air ingress, air preheater secondary fire, and high levels of corrosion as the top five key factors affecting CTPP performance. Based on the outcome, the study offers some implications that may assist the industrial management in taking timely actions in improving the performance of CTPPs.

MILD combustion of co-firing biomass and pulverized coal fuel blend for heterogeneous fuel NO and PM2.5 emission reduction

A sawdust and bituminous coal blend is studied experimentally under MILD combustion conditions, and the PM2.5 emissions of MILD combustion are measured. MILD combustion is established by low-temperature preheated air in a 200-kW pilot-scale furnace. The pilot tests consist of the conventional flame combustion through a swirl nozzle, MILD combustion through symmetrical double straight nozzles, and MILD combustion through an asymmetrical single straight nozzle. Compared to conventional swirl flame combustion, the MILD combustion of the sawdust blend can reduce the fuel-NO emission by at least 45.5%. The results further reveal that the PM2.5 emissions are decreased by over 37%. The burnout rates of the sawdust blend MILD combustion are higher than 95%. Considering the in-furnace distribution, low NO and PM2.5 emissions, and high burnout rate, MILD combustion is an effective way to utilize biomass fuel blends on a large scale. This work extends fuel adaptation of MILD combustion to biomass blends. Compared with previous MILD combustion studies, this investigation further confirms the inhibitory effect of MILD combustion on the formation of fine particles.

Study on the effect of supercritical CFB boiler air preheater and flue gas treatment facilities on sulfur trioxide emission characteristics

The current situation of air pollution in China is very serious, and the control of non-conventional pollutants in addition to conventional air pollutants has received more and more attention. The emission of SO3 in flue gas has attracted widespread attention due to the environmental hazards and equipment problems caused by it, and the study of its emission characteristics and control strategies is the basis for national, local and industry to formulate relevant policies and implement emission control work. The SO3 monitoring and emission control study of a supercritical circulating fluidized bed boiler was carried out based on the controlled condensation method of on-site flue gas sampling, laboratory testing, and instrumental analysis of coal and ash samples, and the synergistic SO3 removal capability of the air preheater and flue gas treatment facilities was explored and summarized. The results showed that the SO3 co-removal rate of the four operating conditions of the test unit ranged from 74.34% to 88.51%, and the highest SO3 co-removal rate (88.51%) was achieved when the SNCR ammonia to nitrogen molar ratio was 1.2 and the slurry pH of the desulfurization system was 5.45 (primary tower) and 6.28 (secondary tower). During the test period, the differential pressure of the air preheater basically fluctuated between 1.245 kPa–1.326 kPa under the operating conditions of working condition 2, with no significant increase. For the same type of unit, the ammonia to nitrogen molar ratio and wet FGD slurry pH can be adjusted to reduce SO3 emissions.

Low-Cost Solar Collectors to Pre-Heat Ventilation Air in Broiler Houses

The objective of the study was to evaluate the effect of a low-cost solar collector to pre-heat ventilation air in commercial broiler buildings on supplemental heating demand and air quality during the cold season. Six black fabric-based solar collectors of 36 m2 each were installed on the south-facing rooftop of a broiler house. The solar collectors provided fresh warm air into the house during the ON cycle of minimum ventilation and during the OFF cycle of minimum ventilation when the temperature under the collectors met certain criteria. The daily cumulative duration of solar collectors in operation averaged 125 and 133 min during the first two or four weeks of brooding in the fall and winter flocks, respectively. When in operation, the solar collectors were able to raise up to 20 K above the ambient temperature, reducing fuel usage by 7% in the fall and winter flocks. The greatest challenge of solar collector utilization was the collectors providing less than half of ventilation air during daytime due to not enclosing the fresh air inlets. The limited airflow capacity and limited activation of the solar collectors due to the existing minimum ventilation scheme is another reason for low heating fuel savings.

Manufacturing of a Granular Fertilizer Based on Organic Slurry and Hardening Agent

The manufacturing of a granular fertilizer based on organic slurry (OS) and sorptive materials aims to enhance the circular economy. This article describes a technology that was conceived after appraising the chemistry of the anaerobic digestate and wood ash and the synergies of combining both materials. The information available in the literature about similar materials such as cattle slurry and lime was also considered to build a better understanding of the underlying science. The processes and machinery designed were optimized from the points of view of energy and material consumption, cost of storage, transportation and land application. The system was sized to process 1 tonne of OS (97% moisture) in a 10 h batch-shift, consuming 140 kg of wood pellets and 0.55 kW of electricity for the fan blowing preheated air. The results of the market research allowed us to reach the most economically viable routes for the commercialization of granular fertilizers. Based on the financial study, an initial investment of GBP 20,000 is needed to successfully implement the value proposition and business plan. The wide adoption of the composite fertilizer improves the management of the OS and reduces the contamination of air, soil, and water derived from intensive agricultural practices.

TP 78 An Interactive Genetic Algorithm and Machine Learning approach for validating the effect of preheated air combustion on fuel consumption of oil-fired industrial furnace

This paper presents an interactive approach of Genetic Algorithm and Machine Learning being used as tool for optimizing the Fuel Consumption of oil-fired rotary furnace operating with 20% preheated excess air. The author has attempted to solve a crucial problem of optimizing fuel consumption in ferrous foundries. Based on experiments carried on a self-designed and developed 200 kg rotary furnace in a foundry, it was found that crucial operating parameters like preheated excess air not only affects the flame temperature and melting rate but also significantly the fuel consumption An attempt has been made to establish a correlation between fuel consumption as output parameter and all others as input parameters It is expected that this model may prove practically beneficial for industry by estimating the effect of input process parameters for predicting the fuel consumption The results of Genetic Algorithm and Machine approach correlates with the experimental results

Air flowrate and particle size effect on gasification of arecanut husk with preheated air through waste heat recovery from syngas

Gasification of arecanut husk (AH) was performed in a downdraft gasifier with preheated air through waste heat recovery. The effect of air flowrate (20–40 L/min) and AH particle size (<2–10 mm) on gasification performance was studied using response surface methodology. Gasifying air was preheated to 190–230 °C from the waste heat of syngas. Air flowrate was found to have a greater influence on gasification characteristics than particle size. Under optimized conditions (31 L/min and < 2 mm), the CO (%), H2 (%), CO2 (%), CH4 (%), Yg (m3/kg), and ηcg (%) were 21.92, 14.72, 12.62, 2.75, 2, and 62.07, respectively. Further, the effect of air preheating was investigated at the optimized conditions. Air preheating improved the performance of AH gasification by increasing the CO, H2, and ηcg by 17.38, 22.42, and 15.4%, respectively. This study shows that recovering the waste heat of syngas is a promising option for enhancing gasification performance.

Analysis of the Influence of Partial Blockage of Air Preheater on Boiler Combustion and Its Countermeasures and Causes

Analysis of the Influence of Partial Blockage of Air Preheater on Boiler Combustion and Its Countermeasures and Causes

Experimental and computational fluid dynamics simulation of performance analysis of steam generators of boilers

Poor air temperature in modern power plants is one of the main reasons for the increase in unit temperature and the deterioration of boiler performance. The main problem of the air preheater is the leakage of air on the side of the gas flue and thus lead to improper thermal performance. Thehigh ash content in Indian coal also adds to the problems associated with air tube heating. Air preheaters are designed to meet the operational requirements with consideration of the most impact parameters. heat transfer, leakage and pressure reduction. In the current work the performance of the air-conditioning heater is being tested with the help of the computational fluid dynamics (CFD)Fluent 14.0 analysis tool.

Energy harvesting in diesel engines to avoid cold start-up using phase change materials

In diesel engines, a significant amount of energy is wasted to the environment by the exhaust gases and coolants. In this study, a new design of the exhaust waste heat recovery (WHR) heat exchanger is proposed to preheat the intake air before supplying it into a diesel engine at the cold start-up conditions. The heat exchanger is designed of ribbed plates containing paraffin wax phase change material (PCM). This PCM is used to store the thermal energy coming out from the engine during the operation for later use in cold start-up conditions. A numerical model is developed and validated with the experimental results in the literature. The effect of different design conditions along with various operating conditions is evaluated. The influences of ribs height and spacing, engine rotational speed, and intake air temperature on the thermal energy storage were evaluated. Based on the results, it can be concluded that the highest thermal performance was obtained at a rib gap of 90 mm and a rib height of 7.5 mm. Through the warming-up process, in less than 1 min, the cold intake air temperature can be increased from 273 to 302.2 and from 283 K to 300.7 K. This results in overcoming the cold start-up difficulties, specifically in icy weather, and delivers preheated air to the engine after 1 min.

Performance Analysis of a Waste-to-Energy System Integrated with the Steam–Water Cycle and Urea Hydrolysis Process of a Coal-Fired Power Unit

An innovative hybrid energy system consisting of a waste-to-energy unit and a coal-fired power unit is designed to enhance the energy recovery of waste and decrease the investment costs of waste-to-energy unit. In this integrated design, partial cold reheat steam of the coal-fired unit is heated by the waste-to-energy boiler’s superheater. The heat required for partial preheated air of waste-to-energy unit and its feedwater are supplied by the feedwater of CFPU. In addition, an additional evaporator is deployed in the waste-to-energy boiler, of which the outlet stream is utilized to provide the heat source for the urea hydrolysis unit of coal-fired power plant. The stand-alone and proposed designs are analyzed and compared through thermodynamic and economic methods. Results indicate that the net total energy efficiency increases from 41.84% to 42.12%, and the net total exergy efficiency rises from 41.19% to 41.46% after system integration. Moreover, the energy efficiency and exergy efficiency of waste-to-energy system are enhanced by 10.48% and 9.92%, respectively. The dynamic payback period of new waste-to-energy system is cut down from 11.39 years to 5.48 years, and an additional net present value of $14.42 million is got than before.

Investigation on the ammonia emission characteristics in coal-fired power plants of China

The coal-fired power plants in China have basically completed the upgrade and transformation for the ultra-low emission, and the reduction in traditional pollutant emission is significant. However, excessive ammonia emission has become one of the major concerns due to its adverse effects on environmental protection facilities and atmospheric environment. In this paper, four typical coal-fired power plants which have completed the ultra-low emission retrofits were measured on site to investigate the whole process emission characteristics of ammonia. The ammonia in the flue gas was classified into the gaseous ammonia, the filterable ammonia or the total ammonia, based on different sampling systems. Besides, the ammonia in the captured fly ash, desulfurization slurry, desulfurization wastewater, and gypsum was also analyzed to provide a quantitative overview of ammonia emission. Results showed that there was only gaseous ammonia detected at the outlet of SCR devices. Most gaseous ammonia was converted into filterable ammonia when it passed through the air preheater. Filterable ammonia, the predominant form of ammonia that made up about 65% to 95% of the total ammonia, could be effectively captured by the dust removers, with over 80% of it being removed. Higher ammonia concentration was measured from the fly ash collected in the rear storehouses. The concentration of ammonia emitted at the WFGD outlet was less than 0.5 mg/Nm3, with no more than 0.3 mg/Nm3 being discharged after the further removal by WESP. Discharging with the captured fly ash was the main pathway for ammonia emission, which should be considered in the further pollution control in coal-fired power plants.

EVALUATION OF OXYGEN ENRICHMENT EFFECTS ON DISTRIBUTION COMBUSTION MODE IN A LABORATORY-SCALE FURNACE

Colourless distribution combustion is a developing method that involves circulating a product gas internally or externally, generally with air preheating. Even in high-energy consumption processes, combustion emissions, especially NOx, are dramatically reduced through this technique. In this study, the nonpremixed combustion of methane-air mixtures with different concentrations of oxygen ranging from 21% to 27% is investigated under the distribution combustion mode in a laboratory-scale furnace. ANSYS Fluent 18.2 software is used for numerical calculations. The eddy dissipation concept (EDC) model is chosen for the combustion involving detailed chemical kinetic mechanisms for turbulent flows. The GRI-Mech 2.11 detailed kinetic mechanism is used to model methane-air mixture combustion, including nitric species for NOx predictions with 49 species and 279 reactions. The results obtained demonstrate that the oxygen-enrichment affects flame characteristics, such as flame temperature, length, and diameter, and pollutant emission levels. Increasing the oxygen concentration from 21% to 23%, 25%, and 27% results in increase in the flame temperature from 1759 to 1798, 1834, and 1869 K, respectively. Furthermore, as the flame lengths increase, the diameters of the flame become more prominent than for normal air combustion. Regarding pollutants, oxygen enrichment reduces CO emissions and causes CO2 and NOx emissions to increase gradually.

Physical Processes in the Thermal Vacuum System

Physical processes occurring during dehydration of heterogeneous materials in a thermal vacuum system have been analyzed. It has been demonstrated that the thermal-vacuum method provides dehydration and simultaneous wet-stock dispersion due to thermal diffusion, shock-wave and ionization effects, thereby leading to formation of novel-type nanodispersed material at minimum energy input. In recent years the intensification of production processes, as well as the solution of energy- and resource-saving problems have taken on great significance. For the sake of dehydration working-cycle improvement, combination of several process procedures in a single installation is used, resulting in both the intensification of the production process and the reduction in capital expenditures. There are the facilities, where the simultaneous use of mechanical grinding operation and the drying process is practiced. In this case, a preheated air is used as a drying agent, and this considerably increases the energy demands of the technological process. This phenomenon is attributed to the impact action and friction of material particles against grinding surfaces of the mill, to the appearance of new surfaces at crushing, and also, to the dust-gas mixture turbulence in the mill working area. That requires substantial power consumption and prevents from obtaining the product with desirable indicators, in particular, the with dispersion and moisture content, which substantially affect the quality of materials produced from fine-grained products. The analysis of fine grinding methods has shown that the most rational method of material grinding is the combination of impact loads. The impact loads facilitate the structure destruction of wet stock, while the abrasion loads acting in the field of high turbulent flows lead to the material destruction. The aim of the present work has been to define the physical processes in the thermal vacuum system, which can efficiently provide dehydration along with simultaneous dispersion of wet material, yielding a dried and ground feedstock in a short span of time.

Experimental Demonstration of Nitric Oxide Measurement at Elevated Temperature in the Coal-Fired Boiler Exhaust

Oxides of Nitrogen (NOx) are among the most critical pollutants, leading to a variety of environmental concerns. This paper describes the demonstrates a high-temperature Quantum Cascade Laser-based (QCL) probe-based system for in-situ measurement of the pollutants in the flue gas. The system demonstrates a sensitivity of less than one ppm and a fast system response time of 60 seconds at high temperature (>300°C) and high dust-load (70 g/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) flue gas from a coal-fired boiler. The system uses a pulsed 2f wavelength modulation spectroscopy technique for the NO concentration measurement at the core. The paper also elaborates on a novel optical design using hollow-core fibres to couple the laser and launch the laser beam into the measurement zone. A unique fibre cooling mechanism was adopted to shield the fibres from excessive temperatures. The filter arrangements and shielding mechanism on the measurement chamber prevent the dust from entering the measurement zone and maintain the stoichiometry of the flue gas during measurement. The probe was tested in a lab setup at 300°C for its sensitivity, response time and linearity. Field-test demonstrates designed performance and repeatability in a coal-fired power plant at an air-preheater (APH) inlet. The gas temperature was below 350°C. In conclusion, this paper demonstrats the useof a QCL based probe for in-situ gas concentration measurement in harsh conditions.