Primary Air Flow Rate Research Articles

Mechanism of Working Fluid Circulation in the Multisource Organic Solid Waste Incinerator

Garbage incineration power generation is utilized to dispose of multi-source organic solid waste. This work constructed a mathematical model for a 750 t/d garbage incinerator to reveal the coupled response between the boiler and furnace sides. Field experiments validated the model, exploring various operating conditions including different loads, fuel blending ratios, primary air, and internal flue gas recirculation (IGR) air flow rates. Increasing the load by 9.1% raised furnace heat exchange by 4.0% but reduced economizer heat exchange by 19.0%. Introducing waste cloth strips and paper mill waste enhanced furnace water-cooled wall heat transfer but reduced economizer heat exchange. A 10.8% rise in primary air flow increased superheater heat exchange by 7.8%. Similarly, a 21.3% rise in IGR air flow increased economizer heat exchange by 9.0%. The temperature rise and enthalpy rise in the superheater were higher when the low calorific value of the fuel was higher. Increasing primary air velocity enhanced heat transfer, raising the outlet temperature of the medium-temperature superheater, necessitating an increase in secondary water spray to adjust the outlet temperature of the high-temperature superheater. This work provides guidance for the design and practical operation of multi-source solid waste incinerators.

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.

Study of the combustion process of liquid off-design fuel in a spray burner device with a controlled supply of primary air

This work studies the process of combustion of liquid off-design fuel (using waste oil as an example) in a jet of superheated water vapor in a spray burner device with a controlled supply of primary air. The average temperature along the vertical axis of the burner device was measured, the composition of intermediate and final combustion products, and heat release were studied when the parameters in the gas generation chamber were varied. It has been shown that changing the primary air flow rate when spraying liquid off-design fuel with a jet of superheated water vapor can additionally influence the flame structure and the level of emissions. And the technology itself can be used to create low-emission burner devices.

Investigating the Characteristics of Pulverized Coal Combustion Using Ansys Fluent: A CFD Study of a 300 kW Swirl Burner

Although the global focus is shifting towards clean energy to replace coal, an immediate technological transition is not yet feasible due to the widespread prevalence of the existing coal combustion technology. The main objective of the present work is to investigate the characteristics of pulverized coal combustion by using Ansys Fluent. This study describes the fluid flow and combustion reactions in the 2D axisymmetric computational fluid dynamics (CFD) model for the 300 kW cylindrical swirl pulverized coal burner. The study was conducted to analyze the combustion process including the volatilization and char combustion models, while varying the ratio of air inlet velocity, and examining the effect of swirl number on pulverized coal combustion. The numerical modeling results for burner′s operating conditions are validated with the steady‐state temperature measurement in the burner. The significant outcome of the associated parameters found that the flame in the burner formed a spiral before converging into the flame line in the main combustion chamber. As a result, increasing the primary airflow rate led to a decrease in the axial temperature in the preliminary combustion chamber and decreasing the primary airflow showed the highest temperature in all three cases. While the secondary airflow increases, the swirling flow will be induced inside the chamber, which affects the highest temperature profile in the preliminary combustion chamber. Changing the tertiary airflow rate did not significantly affect the combustion. However, increasing the tertiary airflow rate improved the completeness of combustion. The swirl numbers also influenced the phenomena of combustion, the volatile released, and combustion reactions which could occur more rapidly with a higher swirl number due to a higher concentration of vortex region. Similarly, the highest swirl numbers resulted in the lowest excess O2 at the exit and the least amount of CO formation.

Gasification Burner Performance Test Using Bio-Coal Fuel

Fuel for high-energy solid fuel combustion systems must meet abundant availability, affordability, and environmental friendliness criteria, particularly having low greenhouse gas emissions. One type of fuel that meets these criteria is bio-coal. Gasification burners employ staged combustion techniques that enhance combustion efficiency and reduce the formation of harmful substances, making them more environmentally friendly. This article discusses the performance testing of gasification burners using bio-coal as fuel, with variable primary air flow rates of 25, 30, 35, 40, and 50 m3/hour and biomass percentages in the bio-coal of 25%, 50%, and 75% by weight. The parameters observed are burner capacity, temperature, and CO2 gas emission factor. The experimental results show that increasing the air flow rate from 25 to 35 m3/hour significantly increases burner capacity and temperature, while further increasing the primary air flow rate to 50 m3/hour results in a gradual increase in burner capacity. The experiments also indicate that increasing the biomass percentage in the bio-coal slightly increases burner capacity and temperature due to the similar calorific values of palm pellet and coal used. The gasification burner technology developed by BBP Tekmira has proven to operate effectively within a capacity range of 8 to 20 kg/hour for bio-coal fuel with biomass percentages ranging from 25% to 75% by weight, producing burner temperatures between 805 and 933 degrees Celsius. Using bio-coal for gasification burners has also been shown to reduce greenhouse gas emissions when the biomass percentage in bio-coal exceeds 64%.

Role of Air Staging in a Batch-Type Fixed Bed Biomass Combustor under Constant Primary Air

Staged combustion of biomass is the most suitable thermo-chemical conversion for achieving lower gaseous emissions and higher fuel conversion rates. In a staged fixed bed combustion of biomass, combustion air is supplied in two stages. In the first stage, primary air is provided below the fuel, whereas in the later stage, secondary air is supplied in the freeboard region. The available literature on the effects of air staging (secondary air location) at a constant primary air flow rate on combustion characteristics in a batch-type fixed bed combustor is limited and hence warrants further investigations. This study resolves the effect of air staging, by varying the location of secondary air in the freeboard at five secondary to total air ratios in a batch-type fixed bed combustor. Results are reported for the effects of these controlled parameters on fuel conversion rate, overall gaseous emissions (CO2, CO and NOx) and temperature distributions. The fuel used throughout was densified hardwood pellets.Results show that a primary freeboard length (distance between fuel bed top and secondary air injection) of 200 mm has higher fuel conversion rates and temperatures as well as lower CO emissions, at a secondary to total air ratio of 0.75 as compared to primary freeboard length of 300 mm. However, NOx emissions were found to be lower for a primary freeboard length of 300 mm as compared to 200 mm. An increase in secondary to total air ratio from 0.33 to 0.75 resulted in higher freeboard temperatures and lower CO as well as NOx emissions. The outcomes of this study will be helpful in the effective design of commercial scale biomass combustors for more efficient and environmentally friendly combustion.

Fluoride removal in batch and column systems using bonechar produced in a top-lit updraft drum gasifier and furnace

Hundreds of millions of people are exposed to excessive levels of fluoride in drinking water, predominately in low-resource communities. Activated alumina is recognized as the best available technology for fluoride removal from drinking water by the United States Environmental Protection Agency, but it has substantial economic and environmental costs. Bonechar is a more environmentally friendly and potentially lower cost alternative adsorbent. Here, fluoride adsorption from groundwater (pH 8.1 ± 0.2) by activated alumina was compared with bonechar primarily produced from bovine bones at peak heating temperatures between 400 and 1100 °C in a modular top-lit updraft drum (TLUD) stove (using a bone-wood mixture) and furnace. TLUD and furnace bonechar produced at peak heating temperatures 650–1000 °C and 400–800 °C, respectively, outperformed activated alumina in batch tests (i.e., required smaller doses to achieve 90% fluoride removal). The impact of using bovine versus swine bones to produce bonechar had a negligible impact on fluoride adsorption. A wide range of peak heating temperatures in the TLUD achieved by varying primary air flow rates and fuel selection (e.g., bone-to-wood mass ratios) produced efficient fluoride adsorbents. This finding demonstrates that a TLUD can be a robust, operationally flexible production system. Fluoride removal by TLUD and furnace bonechars showed strong, negative correlations (R2 ≥0.88) with organic matter content. Bonechar pilot column tests indicated that the mass transfer zone was captured (i.e., immediate fluoride breakthrough was not observed) at an empty bed contact time (EBCT) of 5 min, increasing EBCT to 30 min had a minimal impact on adsorption efficiency, and intermittent operation (3–10 d shut-off periods) decreased effluent fluoride concentrations. Furnace bonechars produced at peak heating temperatures 400–700 °C outperformed activated alumina in pilot columns. Differences in adsorption efficiencies in batch and column tests were associated with the linearity of fluoride adsorption. A theoretical model quantifying adsorption linearity with Freundlich 1/n values was able to predict adsorber performance solely based on batch test data.

Investigation into the operation of an autothermal two-section subbituminous coal fluidized bed gasifier

Using a newly developed experimental setup, the features and advantages of an autothermal single-casing atmospheric subbituminous coal fluidized bed air-blown gasifier, combining a combustion and gasification section, and mixing the dispersed phase (inert material, char) and heat exchange between them through an annular transfer device, have been revealed. To increase the efficiency of the gasifier, an experimental-computational method was developed find the conditions for optimal operation, combining changing the annular flow’s geometry and regulating the primary air for gasification. A simple and reliable multizone thermodynamic calculation model makes it possible to predict the composition of char and syngas in the gasification section with acceptable accuracy. This method confirmed that a two-section fluidized bed gasifier can provide efficient gasification of solid fuels and is suitable for use in small-scale cogeneration plants. Syngas with a heating value of 3.6–4.5 MJ/m3 and CGE of 38.2%–42.3% was obtained in the experimental setup without optimizing the primary air flow rate. With optimization, the indicators increased to the heating value of syngas of 5.20–5.34 MJ/m3 and CGE of 42.5%–50.0%. With heat regeneration of 0.8, CGE increases to 70%.

An Approach to Analyzing and Comparing the Cooling Performance of Two Indirect Evaporative Cooler Designs

Abstract Energy-efficient air cooling systems are always in demand. Direct evaporative coolers are energy-saving and have low cost, but in hot and humid areas, they produce an almost uncomfortable environment. Alternatively, modified indirect evaporative coolers with different technical configurations can produce better thermal output. This paper presents a simple thermodynamic approach developed to analyze, for comparison, the behavior of conventional and regenerative indirect evaporative coolers that comprise different process structures. The analysis is based on the energy balance of the coolers to consider which is more applicable for further modification. Similar performance cross-flow heat exchangers with separate air washers are adopted for both units. The two coolers are subjected to the same general summer operating conditions. The results showed that the conventional indirect evaporative cooler provided better cooling performance in terms of all thermal comparison parameters. The supply temperature trend in regenerative indirect evaporative cooler (RIEC) is higher by 23.4–34.1%, while its effectiveness is lower by 26–56% compared to that of the conventional indirect evaporative cooler (CIEC). The cooling capacity of CIEC is always higher at any air ratio value. At an equal secondary air flowrate where the primary air flowrate of RIEC is 25% more than that of CIEC, CIEC still generates lower air supply temperature and its effectiveness is higher. Thus, CIEC deserves priority attention for further development and additional improvement of performance.

SIREN – smart ventilation for infection risk mitigation and HVAC energy efficiency: a case study amid the COVID-19 pandemic

The COVID-19 pandemic has underscored the need for effective ventilation control in public buildings. This study develops and evaluates a smart ventilation control algorithm (SIREN) that dynamically adjusts zone and system-level HVAC operation to maintain an acceptable COVID-19 infection risk and HVAC energy efficiency. SIREN uses real-time building operation data and Trim & Respond control logic to determine zone primary and system outdoor airflow rates. An EnergyPlus and CONTAM co-simulation framework was developed to assess its performance across various control scenarios and US climate zones. Results show that SIREN can flexibly control infection risk within a customized threshold (e.g. 3%) for every zone, while traditional controls cannot. At the building level, SIREN’s HVAC energy consumption is comparable to a fixed 70% outdoor airflow fraction scenario, while its infection risk is lower than the 100% outdoor airflow scenario, illustrating its potential for safe and energy-efficient HVAC operation during pandemics.

Investigating the impact of flow rate and moisture content for different concentration of liquid desiccant solution

The desiccant air conditioning system consists of two processes, namely cooling and dehumidification, in which the air temperature and humidity are controlled in order to provide comfortable thermal conditions. A typical system includes a dehumidifier, indirect evaporative cooler, and regenerator. The desiccant is selected depending on its ability to absorb water vapor present in the air. In this study, calcium chloride solution was used as a desiccant for the desiccant solution regeneration process, and a flat plate solar collector was employed. Different variables, such as the primary air flow rate, desiccant flow rate, and the concentration of the desiccant solution, were changed during the experiments. The impact of these variables on the performance parameters of the desiccant system such as moisture removal rate, moisture efficiency, enthalpy efficiency, sensible heat ratio, and the mass transfer coefficient was studied. The obtained results revealed that as the solution concentration and the flow rate of primary air increase, the moisture removal rate, sensible heat ratio, and mass transfer coefficient increase. A particular value of inlet primary air flow rate (0.18Kg/s), an increase in the inlet concentration of calcium chloride solution from 0.85 to 0.95 leads to a rise in moisture removal rate, sensible heat ratio, and mass transfer coefficient of (1.1 _1.65) g/s, (0.18-0.25), and (0.01075-0.0123) m/s respectively. While at a certain inlet concentration of a desiccant solution (0.95), increasing the inlet primary air flow rate from 0.1Kg/s to 0.18Kg/s leads to an increase in the moisture removal rate, sensible heat ratio, and mass transfer coefficient o (0.94-1.26) g/s, (0.24-0.26), and(0.0038 -0.011) m/s respectively.

On the diagnosis of a fouling condition in a kraft recovery boiler: combining process knowledge and data-based insights

Fouling is still a major challenge for the operation of kraft recovery boilers. This problem is caused by accumulation of ash deposits on the surfaces of heat exchangers in the upper part of the boiler over time. The first consequence is the reduction of steam production due to loss of heat transfer and, finally, the shutdown of the boiler due to clogging. The present work investigated the operational condition of a modern kraft boiler under a critical fouling condition. This boiler had even faced a manual cleaning due to a clogging event. This analysis combined process knowledge, plant team experience, and a data-driven approach, given the complexity of the process. In this sense, historical data covering this critical period of operation were collected. After a cleaning procedure, they were used to obtain a predictive neural network model for the flue gas pressure drop in the boiler bank, which is an indirect measure of ash deposit accumulation. Once validated, it was used for sensitivity analysis, with the aim of quantifying the effects of the model inputs. Five variables out of eighteen accounted for nearly 60% of the total effect on pressure drop. Namely, primary air temperature (21.6% of the total effect) and flow rate (11.1%), black liquor flow rate (9.9%) and temperature (8.4%), and white liquor sulfidity (8.6%). The analysis of these results mainly suggested an excess of carryover, which composes the ash deposits. Recommended actions to mitigate the fouling condition involved adjustments to the primary air system before the more drastic solution of reducing the boiler load.

Mixing Characteristics and Flow Fields Optimization of Primary Air for Coal Mill

This paper mainly focuses on the problems of inaccurate measurement of the primary air flow rate in a coal-fired power plant. The feasibility of improving the uniformity of flow fields and temperature fields by installing double-layer arch cool air distributor and mixed flow matrix was analyzed by the method of numerical simulation. The results show that, the relative standard deviation of the wind speed measurement section of optimization model decreased from 18.7%~18.4% to 9%~9.1%, compared with the original model. Similarly, the relative standard deviation of temperature measurement section also decreased from 15%~14.6% to 1.3%~1.4%. The study suggests that this mixed flow fields equalization solution can effectively enhance the mixing of cool and hot primary air, and can improve the uniformity of the mixed air flow fields, thereby improving the accuracy and reliability of primary air measurement.

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.

Experimental study of condensation characteristics and operation strategies of induction radiant air-conditioning system

To study the operation and condensation characteristics of an induction radiant air-conditioning system as a novel system that combines induction ventilation and radiant air conditioning, the characteristics of convection and condensation of an indoor terminal device radiant induction unit were studied. The mass transfer coefficient, condensation temperature, and condensation rate were analyzed experimentally. The time required to achieve a steady state indoor thermal environment was collected. The results indicated that the primary airflow rate and temperature mainly affected the mass transfer coefficient, condensation temperature, and condensation rate. When the indoor thermal environment reached a steady state, the heat transfer performance of the radiant induction unit was mainly affected by the primary air temperature. When condensation occurred, the primary airflow rate had a greater influence on the condensation rate. The start-up and response performances of the system were better than those of a traditional radiant air-conditioning system. In the condensation condition, reasonable control strategies maintain the primary air temperature and adjust the primary air flow rate, which can ensure sufficient heat transfer and stabilize the indoor thermal environment faster.

Modeling Study on Non‐Uniform Lateral Distribution in Large‐Scale Circulating Fluidized Bed Boilers

AbstractWith the development of the circulating fluidized bed (CFB) combustion technology, the cross‐sectional area of the boiler furnace increases gradually, making the lateral non‐uniform distribution in the furnace more prominent. To investigate the flow field inhomogeneity in the furnace, a two‐dimensional mass balance model was established in this work, and the lateral solid concentration deviation was adopted to evaluate the degree of the flow field inhomogeneity. Afterwards, the effect of four factors on the lateral non‐uniform distribution was examined. It turned out that the lateral profile of the primary air flow rate had a much greater influence than that of the coal feeding rate.

Experimental Investigation of Thermal Performance Parameters of Drying Air Unit with a Different Flowrate of Liquid Desiccant Solution

Liquid desiccant air-conditioning systems remove directly the latent load from moist air and remove indirectly sensible load of this air by using an indirect evaporative cooling process. The liquid desiccant must subsequently be regeneration once again with a low-grade heat source like solar energy. In this study, calcium chloride solution was used as a desiccant. For the desiccant solution regeneration process, a flat plate solar collector was employed. Different variables, such as the primary airflow rate and desiccant flow rate, were changed during the experiments. The impact of these variables on the performance parameters of the desiccant systems such as moisture removal rate, moisture efficiency, enthalpy efficiency, sensible heat ratio, and the mass transfer coefficient was studied. The obtained results revealed that as the flow rate of primary air increases, the moisture removal rate, sensible heat ratio, and the mass transfer coefficient increase. For example, from 0.006 m/s to 0.0125m/s when the mass airflow rate increased from 0.1 kg/s to 0.18 kg/s.

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.

Effect of air flow rate and temperature on the atomization characteristics of biodiesel in internal and external flow fields of the pressure swirl nozzle

In this study, the flow and spray of biodiesel in the swirl atomization nozzle were analyzed. The influence of primary air flow rate and temperature on the atomization characteristics in the internal and external flow fields of biodiesel was discussed through simulation and experiments. The velocity of biodiesel in the nozzle and mixing chamber were symmetrically distributed. With increasing primary air flow rate, the maximum speed area increased and the shape of the turbulent kinetic energy of biodiesel changed from columnar to funnel. When the primary air flow rate increased from 10 to 30 L/min, the Sauter mean diameter, (SMD, d32) decreased from 95 to 28 μm, and when it increased to 50 L/min, d32 changed slightly. With increasing fuel temperature, the spray velocity increased and the particle size gradually decreased, while the particle size of each interval remained almost unchanged over 45 °C. Therefore, the best primary air flow rate and temperature for the swirling atomization of biodiesel were 30 L/min and 45 °C. It was determined that the increase in air flow rate and temperature promoted the development of atomization flow field and the breaking of droplets in biodiesel, thus optimizing the swirling atomization of biodiesel.