Preheater Research Articles

Design and Performance Analysis of Air Pre heater for Water Tube Boiler to improve its Efficiency

Air preheater is a heat transfer surface in which air temperature is raised by transferring heat from other media such as flue gas which is coming from boiler exhaust. The paper presents the design of regenerative –air preheater to designed to meet specific performance requirements, using the software application CFD (Computational Fluid Dynamics) / CADD. An analytical study was planned to find out the various heat transfer performance parameters like outlet and inlet air temperature of the air preheater and the boiler, Pressure drop inside the Air preheater and the boiler heat transfer coefficients, heat transfer rate, overall heat transfer coefficient and Velocity of the air and flue gas also Conduction and convection modes of heat transfer were found. These heat transfer parameters are critical in designing and functioning of the air Preheater and to calculate the efficiency of the boiler.

Efficient CO2 capture from lime production by an indirectly heated carbonate looping process

Lime production is associated with unavoidable process CO2 emissions that can only be avoided by CO2 capture technologies. The indirectly heated carbonate looping (IHCaL) is a promising post-combustion carbon capture technology that can be applied to lime plants with high potential for heat and mass integration. In this work, two concepts for efficiently integrating the IHCaL into lime plants are proposed and evaluated. To study and characterize these concepts, heat and mass balances were established, sensitivity analyses were performed, and key performance indicators were calculated by means of process simulations. The results show an increase of 63% in the direct fuel consumption for a highly integrated concept, but almost 30% of the entire heat input can be converted into electric power via heat recovery steam generation. Direct CO2 emissions are reduced by up to 87% when coal is used as fuel in the IHCaL process, but net negative CO2 emissions could be achieved when using biogenic fuels. Critical points for integration are the preheating of the combustion air, the efficiency of the sorbent solid-solid heat exchanger, and the utilization of the sorbent purge as lime product. The developed models and the obtained results will be used to further develop the integration of the IHCaL into lime plants through both experimental and numerical methods.

Development of an Efficient Modelling Approach for Fin-Type Heat-Exchangers in Self-Recuperative Burners

Self-recuperative burners are a common solution for efficient combustion systems in industrial furnaces. Due to the geometric complexity of the recuperators, a detailed CFD simulation is computationally expensive and not feasible for simulation models of burner-integrated systems such as radiant tubes. Especially in the FSI studies of radiant tubes, the temperature of the radiant tube surrounding the burner is decisive for the final results. The exclusion of the recuperator from the simulation models introduces significant uncertainties in the simulations results. The presented paper describes an innovative, efficient approach to model a fin-type recuperator in which the recuperator is geometrically reduced. The resulting acceleration of the numerical simulation makes a fully dynamic modelling of the recuperator in a radiant tube simulation possible. Specifically designed source terms are used to model pressure loss and heat transfer inside the recuperator to match results obtained with a detailed simulation model. The results show deviations in total heat transfer of less than 1.3% with a 98.5% reduction of numerical mesh size. The computational savings enable comprehensive modelling of air preheat for radiant tube simulations and accurately replicate flow and temperature profiles in the recuperator.

Thermodynamic analysis of 100% system fuel utilization solid oxide fuel cell (SOFC) system fueled with ammonia

The system efficiency of solid oxide fuel cells (SOFCs) fueled with ammonia or pure hydrogen always underperforms compared to the SOFCs fueled with carbon-based fuels. Hence, improving the efficiency of SOFCs fueled with pure hydrogen or hydrogen carriers such as ammonia is required to promote hydrogen economy. This study deals with the thermodynamic analyses of SOFC with 100% system fuel utilization configuration achieved by a dead-end anode (DEA) loop. The results are compared with the conventional SOFC configuration with the afterburner setup. It is shown that the energy efficiency and exergy efficiency of ammonia-fueled recirculation system are 12.17% points and 11.39% points higher than the conventional system. Energy balance comparison shows that the reduction in heat loss through exhaust gas is one of the significant factors for improving the system efficiency. The improvement in the exergy efficiency of the recirculation system is attributed to the reduction in exergy destructions in air preheaters and the elimination of exergy destruction at the afterburner. In addition, a parametric analysis and artificial neural network– genetic algorithm (ANN-GA) based optimization are performed to understand the effects of stack fuel utilization, current density, stack operating temperature, radiation loss, the pressure ratio across the membrane, and species removal rate in anode off-gas on system efficiency. The system efficiency as high as 75% lower heating value (LHV) can be achieved by the DEA loop configuration with operating the system at lower stack fuel utilizations.

Combustion characteristics of butanol‐ Jet A‐1 fuel blends in a swirl‐stabilized combustor under the influence of preheated swirling air

Biofuels are carbon-neutral alternative fuels, which have emerged as an important source of energy for the aviation industry to reduce greenhouse gas emissions. Butanol is considered an emerging biofuel with properties that are suited for application in gas turbine engines. It is traditionally produced through the fermentation process of biomass (acetone-butanol-ethanol fermentation). To examine the feasibility of butanol as operating fuel, the combustion characteristics of butanol and butanol/Jet A-1 blends are examined in a lab-scale swirl stabilized burner, with emphasis on the effect of preheating because of the variation of inlet air temperature during flight operation. To rich the constant air temperature to 150°C, the incoming air (main air) is preheated and investigated for various equivalence ratios. Compared to neat Jet A-1, the flames of the butanol/Jet A-1 blends have shown a better effect on global emission characteristics with comparable temperature distribution on adding butanol to Jet A-1. A 50% butanol-loaded blends show a reduction of 29% CO and 24% NOx compared to neat Jet A-1 whereas 30% loading follows a similar trend, and the pollutant emission is slightly higher than the 50% blend case. Additionally, both 30% and 50% butanol blends show a comparable flame temperature distribution, which is higher than neat Jet A-1.

Design optimization of a new supercritical CO2 single reheat coal-fired power generation system

Although supercritical CO2 (S–CO2) coal-fired paper generation systems have been studied broadly in recent years, there is still potential for further energy savings. A new system is proposed to efficiently use the waste heat of both the cooler and the boiler. The new system extends the air preheater surface area, uses the economizer to replace part of the heat load of the high-temperature recuperator, and both the evaporator and precooler are arranged before the cooler. The performance analysis model of the new system is built, and the effects of the economizer split ratio, the main compressor split ratio, and the operation load on the new system performance are investigated. The results show that the new system performance is much better than that of the reference system. Under the design condition, the boiler efficiency and the power generation efficiency of the new system are 96.3% and 49.5%, 1.1% and 2.6% higher than those of the reference system. There exist optimal split ratios for both the economizer and main compressor. The optimal split ratio of the economizer is 10%, and that of the main compressor is 70%. The power generation efficiency decreases with a decreasing operation load.

Experimental investigation of the lift-off height and soot formation of a spray flame for different co-flow conditions and fuels

Since the combustion process in spray flames is a highly complex multi-phase phenomenon, which involves several simultaneous processes such as atomization, vaporization, and chemical kinetics, it is still not fully understood. In the present work, an experimental investigation has been performed for three different hydrocarbon fuels (n-Heptane, n-Decane, n-Dodecane), in order to understand the effect of varying co-flow conditions, fuel mass flow rate, and fuel type on both the flame lift-off height and soot formation. The fuels were injected through a hollow-cone spray injector, with a nominal spray cone angle of 80∘ and orifice diameter of 120μm in an annular non-swirled preheated air co-flow. The flame lift-off height was determined by recording the OH* chemiluminescence, whereas soot formation has been determined through the color diffused back-illumination extinction technique. From the results, it has been observed for a certain fuel that the flame lift-off height is mainly controlled by the co-flow velocity and air co-flow temperature. The results also show that the fuel that yields largest droplet size and that possesses the lowest volatility exhibits the highest flame lift-off height. Furthermore, the results evidence a strong influence of the co-flow velocity on the soot formation. With an increase in co-flow velocity, the flame lift-off height is increased and so the amount of air entrainment, leading to a less rich reaction zone just downstream of the lift-off height, which in turn results in less soot formation. Finally, the comparison among different fuels shows that their differences in soot formation are likely related to fuel sooting tendency. This property, in turn, depends on the fuel molecular structure playing an important role on its determination.

Three-Dimensional Simulation of Leakages in Rotary Air Preheater of Steam Power Plant

One of the major problems of rotary air preheaters (RAPHs) is leakage which has a direct impact on its performance reduction. The purpose of this study is to examine the behavior of different types of leakage in the RAPH and its effects on the performance of overall heat transfer. A real power plant was modeled and simulated using three-dimensional numerical approach. The details found by 3D simulation would give a better understanding of the flow behavior in the RAPH which is very important in the design and maintenance stages of each RAPH. The flow pattern and temperature distribution in clearance spaces of four radial wings and axial sector plates were investigated along with the temperature distribution of the matrix. The results revealed that radial leakage in the hot end had a more negative effect on the performance of RAPH, since in this end, both thermal energy and mass flow of air are wasted together. The effects of each leakage at different clearances were compared and the changes in air and flue gas outlet temperatures due to leakage were discussed. The results were validated with experimental data.

Comparison of PMtotal, PM10, PM2.5, NOx, and SO2 Emission Factors from Coal-fired Power Plants per Load Change

For two bituminous coal-fired power plants with 500 MW and pulverized coal combustion type, the concentration of PMtotal, >PM10, PM2.5-10, PM2.5, NOx, and SO2 was measured, and their emission factors were calculated through field measurement. The measurement points started from the boiler downstream and continued to the air pollution control devices (APCDs) that are installed in series, namely, the selected catalytic reduction system (SCR), air preheater (APH), electrostatic precipitator (ESP) and wet flue gas desulfurization system (WFGD). The measurement was performed at one point for more than three times by using the Korean standard method for air pollutants. However, all measurement points, except for the stacks, were not representative of the standard test method. In addition, the PM concentration was too high to reduce the collection time due to isokinetic sampling. There is a limitation of how representative the measurement results can be. During the field measurement period, the power production rate of the two coal-fired power plants was 91.6% and 79.2% in the P-1 and P-2, respectively. Moreover, in the P-2, with a low power production rate, the concentration of PMtotal, PM10, PM2.5, and NOx was found to be low, and the emission factor calculated by dividing the measured concentration value by the fuel usage was also estimated to be low. Such results are due to the coal combustion chamber and various types of APCD being operated at a lower-load condition than the design capacity. In turn, the number of pollutants generated was less, and the removal efficiency of the pollutant became high. However, it was found that the concentration of SO2 generated and the emission factor are more significantly affected by the sulfur content of the coal than the load factor change. To this end, reducing the operation load of the coal-fired power plant improves the combustion efficiency and APCDs performance and decreases the emission factor, resulting in more reduction of the air pollutants than that based on the simple calculation.

Experimental investigation on combustion and emission characteristics for heavy fuel and used motor oils blends in a free-flames burner

The main objective of this experimental investigation is to evaluate the feasibility of heavy fuel (HFO) and used motor (UMO) oils blends combustion in a free-flames burner installed in an isothermal oven. Temperature and chemical products of the combustion process are reported for mass percentages blends from 25% to 100% UMO (UMO25, UMO50, UMO75, and UMO100). For these tests, a burner with preheated oil blends and a primary and secondary air injection system are considered. Firstly, pure heavy fuel oil (HFO100) combustion is tested on its thermal effect as a baseline, recording emission factors for gaseous and solid emissions. Then, fuel blends are tested using secondary air injection regulated for minimal CO emissions. Overall results show that: i) flames radiation heat transfer for fuel blends are higher than for HFO100, ii) combustion efficiencies increase in the range of 48.8% to 63.5% for UMO25 and UMO100, respectively, and iii) exergy balance with a preheated air combustion shows the highest value for UMO100. Finally, this study suggests that used motor oils as fuel have a potential application in free-flames combustion process.

Investigations on the thermal performance of a novel thermal energy storage unit for poor solar conditions

A novel thermal energy storage unit (TESU) that can store the heat from lower solar radiation during daytime and preheat air in winter during nighttime for areas with poor solar resources is proposed. To achieve an efficient operation of this TESU for poor solar conditions, this study proposed a structure that innovatively combines tube bundle and spiral tube heat exchangers to enhance heat transfer with paraffin wax as the phase change material (PCM). The thermal performance of the TESU is then evaluated by experimental measurements and a three-dimensional Computational Fluid Dynamics (CFD) model. The numerical modelling provides details of the solidification behavior of the PCM and the two heat transfer processes - thermal heat extracted from PCM and the effective discharging process. Results show that the pure conduction model can suitably describe the solidification process of PCM. The possible maximum amount of heat extraction of 4.68 MJ can be achieved during the discharging process in 20h. Moreover, an air outlet temperature of 11.5 °C is considered the lowest effective temperature. The effective heat extraction efficiency is about 89.74% till the lowest effective temperature is reached.

Co-gasification of woody biomass with organic and waste matrices in a down-draft gasifier: An experimental and modeling approach

In this paper an extensive experimental campaign about the co-gasification of virgin wood biomass with organic and waste matrices in a full-scale downdraft air gasifier is presented. In particular, wastes from cherry processing, plastic wastes, sewage sludges and hazelnut shells were co-gasified with biomass adopting different mixtures. The syngas composition was continuously measured in order to assess the gasifier behaviour and performances using these mixtures. Results obtained mixing biomass with other feedstocks up to 60% (by mass) showed that the downdraft gasifier adopted, characterized by a patented internal air distribution system, was able to maintain a good gasification performance in terms of syngas lower heating value (LHV) (>5.18 MJ/Nm3), syngas flow rate (>400 Nm3/h) and cold gas efficiency (>71.9 %).A pseudo-kinetic model of the gasifier using Aspen Plus® code was developed as well. The model, calibrated with the experimental data, proved to fit the syngas composition and physical properties with satisfying accuracy. The numerical model confirmed its usefulness in predicting the performance of the gasifier as the operating parameters vary and clearly highlighted that secondary air flow and preheating of the gasifying air are effective ways for the enhancement of the cold gasification efficiency, which can reach values around 80%.

Laser-Based, Optical, and Traditional Diagnostics of NO and Temperature in 400 kW Pilot-Scale Furnace

A fast sensor for simultaneous high temperature (above 800 K) diagnostics of nitrogen oxide (NO) concentration and gas temperature (T) based on the spectral fitting of low-resolution NO UV absorption near 226 nm was applied in pilot-scale LKAB’s Experimental Combustion Furnace (ECF). The experiments were performed in plasma and/or fuel preheated air at temperatures up to 1550 K, which is about 200 K higher than the maximal temperature used for the validation of the developed UV NO sensor previously. The UV absorption NO and T measurements are compared with NO probe and temperature measurements via suction pyrometry and tuneable diode laser absorption (TDL) using H2O transitions at 1398 nm, respectively. The agreement between the NO UV and NO probe measurements was better than 15%. There is also a good agreement between the temperatures obtained using laser-based, optical, and suction pyrometer measurements. Comparison of the TDL H2O measurements with the calculated H2O concentrations demonstrated an excellent agreement and confirms the accuracy of TDL H2O measurements (better than 10%). The ability of the optical and laser techniques to resolve various variations in the process parameters is demonstrated.

Performance studies on mixed-mode forced convection solar cabinet dryer under different air mass flow rates for drying of cluster fig

A Mixed-mode Forced Convection Solar Cabinet Dryer (MFCSCD) is designed for the maximum harnessing of solar radiation. It utilizes the direct heat from solar radiation through glass cover as well as preheated air from two solar air heaters (SAHs) fixed in series having a double pass. The experimental research works were performed in the metrological conditions of Guwahati, India. The drying performance of MFCSCD was analyzed under different air mass flow rates in terms of specific moisture extraction rate (SMER), pickup efficiency, and dryer efficiency for the drying of cluster fig. Further, a thin layer drying kinetics analysis was carried out to find the best suited mathematical model for representing the drying behavior of cluster fig in MFCSCD and open sun drying. Cluster fig dried from moisture content (MC) of 5.67 to 0.08 kg/kg on a dry basis in 7.0, 8.0, 8.5, and 9.5 h at airflow rates of 3.72, 2.76, 1.8, and 1.08 kg/min, respectively, whereas it took 14 h to attain the same moisture level under open sun drying. The experimental results showed higher dryer and pickup efficiencies and SMER at 3.72 kg/min air flow rate. The quality analyses of solar and sun-dried were carried out to estimate the total phenolic content, antioxidant activity, and rehydration ratio.

Numerical simulation of a novel regenerative heat exchanger with combined sensible–latent heat storage matrix

A new rotary regenerative heat exchanger with combined sensible–latent heat storage matrix was proposed. A local thermal non-equilibrium model with three energy equations for fluid, sensible heat storage material, and latent heat storage material in the porous matrix was developed. Rotary regenerative air preheaters (RAPHs). The RAPHs with combined sensible–latent heat storage matrix (CRAPH), with sensible matrix (SRAPH) and with latent heat storage matrix (LRAPH) were comparatively evaluated according to their thermal and economic performances. The temperature distributions of sensible and latent heat storage materials in the matrix exhibit different characteristics. The latent heat storage material that undergoes a phase change process during charging or discharging can greatly buffer the temperature swings of fluid and sensible heat storage material, especially under lower rotating speed conditions. Even if a small amount of latent heat storage materials were added to the sensible heat storage matrix, the efficiency of RAPH can be greatly improved.

Modification of rotary air preheater toward achieving extended life-span utilizing porous media approach: A case study

The main goal of this study is to achieve the extended operating life of the rotary regenerative air pre-heater (Ljungström) of Bandar Abbas power plant by modifying operational parameters by decreasing the corrosion. To achieve this goal, a three-dimensional CFD simulation of the Ljungström is carried out, utilizing the thermal non-equilibrium porous media model. Temperatures are validated against measured data from the power plant with a maximum relative error of 5.54% on the Celsius scale, and mass flow rates are validated with a maximum relative error of −5.25%. The effect of the Ljungström key parameters including the rotational speed, cold layer material, inlet air/flue gas temperature, and mass flow rate, are analyzed in presence of leakages and neglecting it, using porous media approach. The leakage effect is investigated considering radial and axial/peripheral clearances. Finally, a simulation is performed by applying feasible improved parameters extracted from the above analyses considering the effect of all parameters together in presence of leakages, which shows a 6.14% improvement in the Ljungström effectiveness, reducing the total leakage to about one-third of the actual model and eliminating any corrosion.

Study on the feasibility of the micromix combustion principle in low NOx H2 burners for domestic and industrial boilers: A numerical approach

The purpose of the present investigation is to explore the feasibility of applying the micromix combustion principle (MCP) to design low NOx burners using 100% H2 as fuel for domestic and industrial boilers. Previous investigations studying the MCP on stationary and aero gas turbine applications, showed low NOx emissions without flashback risk, which represent the two main issues when burning 100% H2. Since boiler burner operating conditions differ from gas turbine combustors, the present paper studies the MCP through CFD calculations under re-defined conditions for domestic and industrial burners, adapting the energy densities, air-fuel equivalence ratios and pre-heated air temperatures. A reference geometry was built to validate the selected numerical models with experimental results from literature. Afterwards, burners were re-dimensioned following an existing geometry-scaling methodology. The obtained results evidenced that MCP characteristics were still maintained for the defined cases, keeping low NOx values between 4 and 14 ppm. The numerical results were also validated through experimental NOx measurements in a laboratory scale micromix burner prototype. In order to assess the benefits of using hydrogen micromix burners in domestic and industrial boilers, the present work includes a final discussion with practical design considerations. The present study lays the groundwork for complementary experimental research work, which is being carried out in laboratory-scale prototypes.

Semisupervised dynamic soft sensor based on complementary ensemble empirical mode decomposition and deep learning

Noise, redundancy, and dynamic characteristics in industrial process data have been regarded as the key factors that affect the measurement accuracy of data-driven soft sensors. In this paper, a semi-supervised dynamic soft sensor is proposed to capture the dynamic characteristics of data while removing noise and redundancy within the data, thus ensuring improved accuracy. Complementary ensemble empirical mode decomposition and isometric feature mapping are combined to reduce noise and redundancy. A semi-supervised deep learning model is designed to capture the dynamic characteristics. Compared with traditional soft sensors, the effectiveness and superiority of this method are verified via an experiment using an air preheater of a power boiler. The proposed method achieves the lowest MAE of 0.1745 and the highest correlation coefficient of 0.9969. Compared to methods without data preprocessing, the MAE of the preprocessed soft sensor decreases by 22.28% on average, while the correlation coefficient increases by 0.24% on average.

Numerical and experimental analysis of parallel-pass forced convection solar air heating wall with different plenum and absorber configurations

PurposeOver the recent years, solar energy has received outstanding attention from researchers. Solar energy applications and related large-scale projects are increasing to meet growing global energy demand as an economical, non-polluting and renewable energy source. The purpose of this study is investigating different plenum and absorber configurations of solar air heating wall (SAHW) experimentally and numerically.Design/methodology/approachIn this study, various configurations of SAHW have been numerically simulated to determine the most effective design. According to the simulation results, two SAHWs with various plenum thicknesses have been fabricated and tested at different conditions.FindingsNumerical simulation results indicated that parallel-flow SAHWs exhibited better performance in comparison with other placements of absorber plate. Regarding to the experimentally attained results, the highest thermal efficiency was reached to 80.51%. Also, the average deviation between experimentally and numerically obtained outlet temperature is 5.5%.Originality/valueConsidering the obtained results in the present study, designed SAHW has admissible efficiency to be used in various industrial and residential applications such as; air preheating, space heating and drying.

Design and Analysis of Actual Soot Cleaning System for Fire Tube Boiler

Soot blowers are used to control a boiler with high power to release dirt from the heat transfer surfaces towards the gas. They are additionally accustomed to gas pass closure. They are mechanical devices used to clean gas side boiler ash and deposits online on a periodic basis. They dictate To get rid of the ash deposited on the coil and improve the heat transfer power, the operating medium through the nozzle against the soot or ash deposited on the heat transfer surfaces on the boiler. Sort the blowers in boilers in many places such as water walls, super heaters, economists and air preheaters. Watch for heat transfer soot blowers and efficiencies do not improve. Therefore, the design and analysis of soot burners can effectively increase boiler power in power plants.