Secondary Air Flow Rate Research Articles

Experimental and theoretical evaluation of the effect of fluid resistance on the performance of a tubular indirect evaporative cooler

To evaluate the impact of fluid resistance on the performance of tubular indirect evaporative coolers (TIECs), a mathematical model of secondary air channel resistance was developed. An experimental setup was created to study the effects of factors such as secondary air flow rate and water spray flow rate on R2 under actual conditions. The model used the same conditions to analyze how factors like air flow, water flow, and droplet size influenced R2. The relationship between R2 and wet-bulb effectiveness (εwb) was also examined experimentally. The data from the experiments were compared to the model's predictions, showing a maximum relative error of 10 %, confirming the model's accuracy. It was found that R2 and secondary air flow rate (V2) are positively correlated, and εwb increases with R2. The experiments yielded secondary air resistances ranging from a minimum of 548.2 Pa to a maximum of 554.26 Pa. These results are valuable for selecting appropriate fans for the secondary air channel. Additionally, simulations were conducted to predict and calculate energy losses in the secondary air channel under real working conditions, providing a useful basis for future fan selection.

AERODYNAMIC IMPACT OF SECONDARY AIR INJECTION FLOWRATES ON THE MAIN ANNULUS FLOW FIELD FOR A TRANSONIC HIGH-PRESSURE TURBINE STAGE

Abstract In this study, the influence of secondary air blowing on the main annulus flow field of a transonic high-pressure turbine (HPT) was investigated experimentally and numerically. The experimental setup was a single-stage, unshrouded turbine with a blading consistent with modern HPTs. The entire testing campaign was conducted in a full annular, rotating, continuous turbine test rig at the Japan Aerospace Exploration Agency (JAXA), which realized the most faithful matching unrivalled of both the primary and secondary stream similarity parameters to reality. An elaborate secondary air system implemented in the hardware enabled it to mimic all the dominant coolant/purge streams representative of advanced hot sections: the full coverage film-cooling on stator and rotor airfoils, disk wheelspace purge air blown forward and aft of the rotor, and coolant injection through the over-tip casing. Detailed three-dimensional flow field measurements for various secondary air flowrates were performed by traversing a pneumatic thermometric combination probe downstream of the rotor. A complete set of numerical simulations was run concurrently with the testing to determine how well they captured the flow physics, particularly the interaction of the ejected secondary streams with the primary flow. The JAXA in-house code, UPACS, and its best practice settings, based on past verification and validation efforts, were employed and not intentionally tuned to better fit the data.

Multi-Criteria Optimization of a Laboratory Top-Lit Updraft Gasifier in Order to Reduce Greenhouse Gases and Particulate Matter Emissions

Air pollution from combustion processes is harming human health and the environment. To mitigate this, one needs to adopt cleaner energy production methods, in particular, to optimize combustion systems in order to minimize pollutants and increase efficiency. Flue gas analysis and particulate matter (PM) monitoring, starting from the prototype phase, is crucial to minimize and regulate pollutant emissions. This article analyses the emissions of pollutants and particulate matter from a combustion test gasifier working on the Top-Lit Updraft (TLUD) principle in order to optimize functionality and reduce exhaust emissions. Three experiments were performed in which the primary (gasification) air flow rate (GA) was kept constant at 25 L/min, and the secondary (combustion) air flow rate (CA) was adjusted to obtain a CA/GA ratio of 2 (50 L/min), 3 (75 L/min), and 4 (100 L/min) respectively. Based on a multi-criterial analysis, the optimal CA/GA ratio for TLUD combustion is 3, offering a well-rounded performance in output temperatures, PM and greenhouse gases (GHG) emissions, and efficiency, while the CA/GA ratio of 4 has good PM and GHG emissions performance but lower efficiency, and the CA/GA ratio of 2 is the least favorable due to its poor performance in output temperatures, PM and GHG emissions.

Development of a neural network model predictive controller for the fluidized bed biomass gasification process

In this study, an advanced controller for the fluidized bed biomass gasification (FBG) process is proposed. The controller is based on the model predictive control method, utilizing a long short-term memory neural network to accurately predict the controlled variable in the FBG process. Then, employing a gradient-based optimization algorithm, it optimizes the inputs to achieve the desired control objective. The controller specifically aims for temperature regulation in three spatial regions (fluidized bed, freeboard and outlet), using primary air, secondary air, and biomass flow rates as input variables. Open-loop simulations are used to fine-tune the controller's parameters (prediction and control horizon). For unbiased controller testing, a computational fluid dynamics (CFD) model of the FBG process is also developed, which is integrated with the controller in a closed-loop system, simulating real-process feedback for performance evaluation. The proposed controller effectively maintains temperatures (steady state error < 1.5 %) at desired set points (800–900 °C) with a short prediction horizon of 24 time steps, reducing response time to under 5 s, making it suitable for real-time FBG process control.

Biomass energy conversion in a gasifier for injera baking mitad application

The performance of gasification for Injera baking was explored in this study, as well as the effects of moisture content, and primary and secondary airflow rates. Primary air is used in the reactor of a biomass gasifier, which creates syngas that is burned by secondary air on the mitad's bottom side. An average temperature of averaged 185°C at the center and 170°C away from the center was observed; the size of the cone determines the temperature distribution on the metal surface. The reactor's narrower cone diameter allowed for a greater temperature only in the center and a more variable baked Injera eye appearance. The cone diameter has been reduced to 0.15 m of the mitad diameter to improve the temperature distribution on the mitad surface. The gasifier temperature is 800°C when the air/fuel ratio is 5.8 kg/kg and the moisture content of the wood is 16%. Gasification is improved by heating the primary air and changing the air-fuel ratio. The findings revealed that pre-heated air is more efficient for gasification and saves money on baking and fuel. Fuel efficiency (0.45) and time savings (0.12) were discovered in the new gasifier. Between gasification temperatures of 650 and 800°C, an effective Injera baking temperature (170–185°C) on the mitad surface was attained. Following the tests, the average specific wood fuel consumption (1.414 g/kg), char residue (317 g), and average Injera baking time were calculated. For each test of one baking cycle, this was found at the burning rate capability of both stoves, which is 6 kg/hr. Therefore, the fuel consumption and burning rate of fuel are depending on the amount of airflow rate.

Development and validation of a dynamic flowsheet model for a 350 MWe supercritical circulating fluidized bed boiler

The circulating fluidized bed (CFB) boiler is highly recommended in peak shaving for its wide load regulating range compared with the pulverized coal (PC) boiler. However, the research on dynamic flowsheet model of the CFB boiler is quite limited due to its complex flow regime. In this paper, both steady state and dynamic flowsheet model of a supercritical 350 MWe CFB boiler was developed based on Aspen Plus and Aspen Dynamics software coupled with comprehensively user defined combustion kinetics and heat transfer coefficient with FORTRAN subroutines. This model was then validated by the operating data of the 350 MWe supercritical CFB boiler. Based on this model, the dynamic characteristics of three typical step signal disturbances, coal flow rate, primary flow rate and secondary air flow rate, were further analyzed to provide theoretical references to dynamic operation. Also, the quantitative relation between the stabilization time and step signal amplitude was calculated. The calculated dynamic characteristics demonstrates that the heat distribution does not vary much after adding step signal disturbances of coal flow rate, primary air flow rate and secondary air flow rate. The step signal disturbance of secondary air flow rate has less influence to the CFB boiler system compared with that of primary air flow rate. The superheated steam temperature is more sensitive to step signal disturbances compared with reheated steam temperature. The higher step signal amplitude results in longer stabilization time. Above all, this dynamic flowsheet model can not only be used to conduct dynamic behavior prediction and analysis but also provide transfer functions to the further development of CFB automatic control system.

Numerical investigation on the influences of swirling flow to thermal efficiency enhancement of an LPG-energy saving burner

This study investigated a swirling flow in household LPG burners and its effects on thermal efficiency enhancement. Modified from a typical energy-saving burner (EB), a newly invented swirling flame energy-saving burner (SEB) was built and tested both experimentally and numerically. Computational Fluid Dynamics (CFD) simulations were employed to investigate the flow inside the SEB with an inclined angle of 50° and a swirl angle of 15° as well as the flow inside the EB. The computational results were used to calculate the heat conversion efficiencies, which were then compared to the experimental values obtained from the water boiling test (DIN EN 203-2 standard). Additionally, the simulations provide data on the combustion temperature, the turbulence intensity, and the secondary air flow rate. This detailed information clearly confirms that the swirling flow does increase the maximum combustion temperature and the net heat flux into the vessel, directly enhancing the heat conversion efficiency and thus increasing the thermal efficiency. According to the simulations, the heat conversion efficiency of the SEB is around 3.44% greater than that of the EB, while the experiments show that the SEB gives approximately 2.75% higher thermal efficiency than that of the EB. The future expectation is that the heat conversion efficiency can be used to predict the increase in thermal efficiency. With this method, the commercial design of the energy-saving burner can be improved.

Gasification of N-rich fibreboard in an air-blown fluidized bed reactor: A study on the fate of tars, NH3 and HCN during oxidative mild Hot Gas Filtration

Wood wastes, such as Medium Density Fibreboard (MDF), are interesting low-cost fuels for gasifiers. The present study examines the effect of oxidative Hot Gas Filtration (HGF) on gasification indicators and pollutants (tars, NH3 and HCN) of producer gas. Pellets of N-rich MDF were gasified in an air-blow bubbling bed reactor at 800 °C coupled with a downstream HGF unit equipped with multilayer metallic filters and operated at mild temperature (400–600 °C). The fate of pollutants was assessed by complementary analytical techniques (HPLC, UV-fluorescence, GC/MS-FID and wet chemical methods for N-compounds). The deposit of the filter was also sampled after gasification trials and characterised by SEM-EDX.For the reference tests, conducted without the HGF unit, tar concentration was 6.5 g/Nm3 (dry gas, benzene-free) while, 43% of Fuel Bounded Nitrogen (FBN) was converted to NH3 and 4% to HCN. Oxidative HGF tests showed that secondary reactions inside the HGF unit undergo in homogeneous (gas-gas) and heterogeneous (gas-solid) phase. At a relatively high secondary air flow rate brought in the HGF unit, the severe oxidation of the dust cake particles led to irreversible melting, aggregation and sintering phenomena of ash deposits on the surface of the filter, as well as, to a drop of 49% in the tar yield. Overall, this work demonstrates that the addition of secondary air inside the HGF unit should be carefully tailored in order to minimise the exothermic oxidation of dust cake particles and, to promote long-term operation of the filter.

Effect of the staged secondary air on NOx emission of pulverized semi-coke flameless combustion with coal preheating technology

Coal self-preheating combustion technology has been proved its potential on NOx reduction. This study adopted the technology to mainly investigate the effect of the staged secondary air on NOx emission with two different types of coaxial jet nozzles. Besides, the difference between flameless and flame combustion of the high temperature preheated fuel was also discussed. After being preheated, more than half of nitrogen was released to coal gas, and the released N was mainly converted to N2. It was confirmed that flameless combustion of the preheated fuel (coal gas + coal char) could be easily realized in a coaxial jet triple channel straight nozzle, and (1) the down-fired combustor was transparent without visible flame fronts; and (2) compared with flame combustion, NOx emission was far lower, and the lowest was 50.8 mg/m3 (@6% O2). By comparing the temperature eigenvalues, it was impossible to effectively distinguish between flameless and flame combustion of the preheated fuel. However, it could still be found that T′ (normalized temperature fluctuation) and δT (difference between the maximum temperature and the inlet temperature of the preheated fuel) of flame combustion were always higher than that of flameless combustion, and the differences were enlarged as increasing R12 (ratio of the inner secondary air flow rate to the external secondary air flow rate). With the increase of R12, the exit NOx emission increased first and then decreased whether it was flameless or flame, and the best R12 for NOx emission was about 1.

Development and Validation of a Dynamic Flowsheet Model for a 350 MWe Supercritical Circulating Fluidized Bed Boiler

The circulating fluidized bed (CFB) boiler is highly recommended in peak shaving for its wide load regulating range compared with the pulverized coal (PC) boiler. However, the research on dynamic flowsheet model of the CFB boiler is quite limited due to its complex flow regime. In this paper, both steady state and d ynamic flowsheet model of a supercritical 350 MWe CFB boiler was developed based on Aspen Plus and Aspen Dynamics software coupled with comprehensively user defined combustion kinetics and heat transfer coefficient with FORTRAN subroutines. This model was then validated by the operating data of the 350 MWe supercritical CFB boiler. Based on this model, the dynamic characteristics of three typical step signal disturbances, coal flow rate, primary flow rate and secondary air flow rate, were further analyzed to provide theoretical references to dynamic operation. Also, the quantitative relation between the stabilization time and step signal amplitude was calculated. Above all, this dynamic flowsheet model can not only be used to conduct dynamic behavior prediction and analysis but also provide transfer functions to the further development of CFB automatic control system.

Analysis of vegetable oil mixture combustion in a conventional 50 KW thermal energy installation

This work presents the combustion results of a vegetable oils blend in a low-pressure auxiliary air fluid pulverisation burner (o emulsion burner). This blend was prepared from soy and sunflower refined vegetable oils (54.4%) and sunflower and rapeseed crude vegetable oils (45.4%). The influence of varying the fuel flow rate, the secondary airflow rate as well as the fuel preheating temperature on combustion, performance and pollutant emissions was studied. Additionally, a comparison between the combustion results obtained from this mixture of vegetable oils and those previously obtained in combustion for pure vegetable oils was also carried out. For all of the conditions tested, the vegetable oil mixture combustion performance exceeded 77% and NOx emissions were extremely low (<60 ppm). In the established optimal operating conditions: un-preheated vegetable oil and Amid airflow rate, CO emissions were virtually negligible (5–17 ppm), regardless of the fuel flow used. The pollutant emissions and the combustion performance of the vegetable oils blend are comparable to those obtained in the combustion of refined soybean, sunflower and rapeseed oils, all of them with a high percentage of unsaturated fatty acids (mainly oleic and linoleic).

Study on Airflow Migration and Rock Dust Pollution Behavior in TBM Construction Tunnel

When tunnel boring machines (TBMs) are used to construct tunnels, large quantities of rock dust are produced, affecting the working environment of construction personnel. To explore ways to improve the air quality in tunnels, this study employed a numerical simulation to investigate controlling rock dust via tunnel ventilation systems. The results showed that when the secondary compressed airflow rate (Q2) was set to 4–11 m3/s, the rock dust produced could be controlled within a range of 77.2 m from the tunnel face. When Q2 = 8 m3/s, the rock dust diffusion distance (LD) reached a minimum of 42.7 m, and the rock dust concentration around the operating region (CW) was approximately 30.1 mg/m3. To explore the further enhancement of dust suppression performance in a tunnel, a numerical simulation was conducted on rock dust diffusion in the tunnel when Q2 was fixed but the exhaust airflow rate (QC) was set to different values. According to the numerical simulation results, when QC = 15 m3/s, the rock dust produced could be effectively controlled at the front of the tunnel with a length of 14.6 m, i.e., the rock dust could be most effectively suppressed.

Application of multi-response robust parameter design for performance optimization of a hybrid draft biomass cook stove

A novel design of a hybrid draft biomass cook stove was proposed, constructed and tested for 54 combinations of five important parameters viz. Inlet area ratio, Fuel surface to volume ratio, Pot diameter, Secondary air flow rate, and Pot gap. The combined effects of these factors on the stove performance parameters such as overall efficiency (ηo), CO emissions and PM2.5 emissions were estimated. The data obtained by executing designed experiments (CCD) on the stove prototype was fitted to independent second-order models using RSM. The fitted models were further used to predict the stove performance for different combinations of the five factors. The analysis revealed that the prototype cannot achieve energy performance better than Tier 2 level and ηo greater than 30%. However, the hybrid draft enabled the prototype to achieve Tier 4 level performance in CO and PM2.5 emissions. Desirability function coupled with the fitted RSM models was used for robust parameter optimization of the stove performance to maximize efficiency, minimize emissions and propagation of error. The robust parameter optimization resulted in the best possible overall stove performance of ηo = 26.54%, CO/MJd = 2.249 g/MJ and PM/MJd = 34.67 mg/MJd obtained at the control factor levels of Ms = 1.74 g/s and Pg = 14 mm.

Biomass Gasification in a Bubbling Fluidized Bed Reactor

The effect of secondary airflow rate and particle size on the combustion temperature inside a bubbling fluidized bed reactor were reviewed. The experiments were carried out for four-particle sizes with different secondary airflow rates. From the results, it was evident that the secondary airflow rate has a more substantial impact on the temperature of the freeboard zone. The temperature profiles show that the maximum temperature is achievable when the magnitude of secondary airflow rate is lower than that of the primary airflow rate. It was concluded that the desired maximum temperature could be achieved regardless of the particle size through the optimum secondary airflow rates.

Household Biomass Gas Stove Performance and Exhaust Gas Emission

This work focuses on the design of the household biomass gas stove which is suitable for the lifestyle of the Thai northern people. In addition, the performance and exhaust emission of the stove - updraft gasifier - was design per the community requirement were evaluated. The stove consists of a combustion chamber – a primary chamber - and a secondary chamber with the primary and secondary air inlet of 0.016 and 0.002 m2, respectively. Moreover, the flow rate of primary air and secondary air was 0.456 and 1.340 kg/s, respectively. The performance of the stove was analyzed by the water boiling test technique and the emission of exhaust gas was evaluated with a fuel gas analyzer. The result indicated that the thermal efficiency of the stove was 44.84%. The specific fuel consumption was 0.029 kg/kg of water. Comparing the designed stove with the traditional clay brazier stove, the performance of the designed stove was higher than the traditional stove. The emission comparison between the designed household biomass gas stove, the traditional stove and the Thai exhaust gas emission standard indicated that both stoves released NOx and SO2 which are less than the standard whereas CO emission of the designed stove conformed to the standard. This work confirmed that the efficiency and the exhaust gas emission of the designed stove are better than the traditional stove. Therefore, this household biomass gas stove could replace the conventional stove

Effect of air flow rate and secondary air jets on the operation of TLUD gasifier cookstove

ABSTRACTThe current article presents experimental results of the operation of top-lit updraft (TLUD) gasifier cookstove. The independent variables for the experiments are secondary airflow rate, the ratio of the secondary to the primary air flow rate, and the secondary air jet velocity. Based on the mass, temperature, and gas measurements the stove performance variables like effectiveness, combustion efficiency, AF, and power are calculated. The results show that varying the secondary airflow rate and jet velocities affect the fuel consumption rate for the flow rates considered. Combustion efficiency is relatively constant around 98%. Increasing the secondary air decreases the CO emission. Effectiveness starts to saturate beyond AF of 10. Useful power is found to be a strong function of secondary air.

Descriptive Statistical Analysis of Vegetable Oil Combustion in a Commercial Burner to Establish Optimal Operating Conditions

This article studies the combustion of refined sunflower, virgin sunflower and virgin rapeseed oils in a low-pressure auxiliary air fluid pulverization burner in order to establish the optimal operating conditions. The influence of varying the type of vegetable oil, fuel flow rate and secondary airflow rate in the combustion process was analyzed. These three factors are independent in the combustion process, which means having to carry out numerous assays, combining the various factors with one another. Given the amount of variables to be optimized and the existence of three factors, a statistical approach is adopted to help interpret the results obtained and to evaluate how each factor influences the combustion results. Optimal combustion is determined based on three criteria, minimum pollutant emissions (CO, NOx and CxHy), maximum combustion performance, and minimum excess air. The result of this study showed that airflow was the principal factor affecting emissions, whereas for combustion performance, both factors (airflow and fuel flow) were determinant. In general, admissible combustion performances were obtained, with CO and NOx emissions below permitted levels. The best combustion performance was achieved under conditions of maximum fuel flow and minimum airflow rates.

Development of Subair Technique for Combustibility Enhancement and NOx Reduction in a Pulverized Coal-Fired Boiler.

In this work, subair injection was proposed to improve the combustibility and NOx emission in a 500 MW tangentially fired coal boiler. The location of injection ports was determined based on the coal particle trajectory and its effect was investigated numerically. The flow rate of subair was set to 0, 5, and 10% of the total combustion air. The secondary air flow rate was decreased appropriately to ensure that the total quantity of combustion air remained constant. The over-fire air was not adjusted to retain the effect of an air-staged combustion. The simulation results showed that the subair improved the combustibility of coal particles originating from burners A and B in the lower part of the furnace. Particles from other burners were not affected significantly. In addition, this method achieved reduction of NOx by 6.3 and 13.2% when the subair accounted for 5 and 10% of the combustion air, respectively. This reduction was attributed to the decrease in the peak temperature as a result of a wider combustion region. The proposed subair technique improved the coal combustibility and reduced the NOx emissions successfully in the furnace.

Calculation of the Parameters of Combustion Products of Sewage Sludge

The problems associated with the use of existing thermal installations for the incineration of sewage sludge and the design of new structures are considered. The results obtained by calculating the chemical and phase equilibria are presented. Recommended optimal ratio of primary and secondary air flow rates with its step-by-step approach.

Optimization of combustion characteristics of palm kernel-based biofuel for grate furnace

Grate firing is one of the main competing technologies in biomass combustion for steam and electricity generation. Ash generated in the furnace during combustion process would greatly reduce the boiler thermal performance and may lead to unscheduled shutdown. The focus of this study is to optimize the combustion characteristics of the mixture of palm kernel shell (PKS) and selected additives (Al2O3, MgO and CaO) to develop a fuel mixture of low ash yield and higher heating value (HHV). D-Optimal Design under Cross Methodology of Design Expert (6.08) was employed to mix the components alongside various particle sizes. The mixed samples were ashed in a muffle furnace (848 K) to a constant weight and their HHV were determined using Ballistic Bomb Calorimeter. Combustion test based on optimized PKS additive mixture was conducted with a 5 kW grate furnace from which the effects of varying the ratio of primary to secondary air flow rate on temperatures and flue gas compositions from the furnace were measured. The ash obtained after combustion process was characterized using X-ray diffraction (XRD) for the purpose of identifying the mineral phase compounds that are present in PKS and PKS-additive ash. The optimum composition obtained for the process was 2.5, 0.0, 5.0, 92.5% and 5.50 mm for additives (Al2O3, MgO, CaO), PKS and particle size, respectively. The composition resulted in lowest ash yield (0.56%) and HHV (20.64 kJ/g). The coefficient of determination (R2) (0.7951 and 0.7344) and least-square errors (0.19 and 0.024) of the prediction model indicated a close fitness to the experiment results obtained for ash yield and HHV. Primary to secondary air ratio of (40:60) recorded maximum temperature (1058 K), minimum level of CO (285 ppm) and 6% oxygen. XRD results showed excellent interaction between PKS and additives. The appearance of potassium-alumino silicate (KAlSiO4) in the PKS-additive ash prevented the release of potassium chloride which has the ability to increase ash deposition and corrosion.