Recirculation Of Products Research Articles

The role of heat recirculation and flame stabilization in the formation of NOX in a thermo-photovoltaic micro-combustor step wall

The health and durability of micro thermophotovoltaic systems are contingent upon the level of gaseous emissions of micro combustors regarding their small size, thickness, and compactness. In small combustion devices, the flame stabilization is achieved via conjugated heat transfer from the stabilized flame to the fresh reactant via the step of the micro-combustors. The step could also create a recirculation of products, and a stagnation zone for the fluid, as a result leading to the accumulation of pollutants. In turbulent H2 flame, the main attention is given to the NOX as no other noxious emission, especially carbon emission (CO, CO2, PAH, and VOC), form during the combustion of hydrogen. The existence of NOX in the presence of water, as in the combustion of hydrogen is prevalent, could lead to corrosion in combustor interior walls and other detrimental impacts for the ecosystem. In the presented work, micro-combustion of H2 flame in a cylinder with a step is simulated and the formation of nitrogen oxides is analyzed. The influence of different combustor specifications (equivalence ratio, solid materials) NOX species are discussed and evaluated. Results revealed nitrogen oxides form and accumulate in the vertical step of the microchannel and that the microchannel walls are more prone to the high concentrations of nitrogen oxides. The application of cavity promotes the two-dimensionality of flow, resulting in effective heat transfer from the hot gas to the cavity walls. This not only leads to flame anchoring to the cavity walls but also results in significant NOX.

Sustainability and the circular economy: A theoretical approach focused on e-waste urban mining

Reuse and recirculation of products and materials are the basis of the concept of the circular economy (CE). The CE is an innovative proposal that can result in positive impacts such as reduced demand for raw materials, reduced consumption of basic resources, and job creation, as well as preventing negative impacts resulting from the exploitation and processing of natural resources. Mining is infamous for its potential environmental impact, but mining waste from traditional mining (in the linear economy) may recover material through upcycling techniques, as can urban mining of industrial and post-consumer waste categories (in the circular economy). Urban mining, a form of closed-loop supply chain management, offers an attractive alternative to the management of waste electrical and electronic equipment (e-waste) and, at the same time, as a sustainable way to exploit mineral resources, reduces primary material intake and stimulates the circularity in the supply chain. The present study reviews the main CE solutions for e-waste management, highlighting the importance of recovering and classifying mineral material according to urban mining procedures.

Modeling and simulation of a continuous biomass hydrothermal carbonization process

This work evaluates a continuous biomass hydrothermal carbonization process through modeling and steady state simulation using the UniSim Design process simulator. The reactive process was divided into four stages: biomass hydrolysis, intermediate compounds degradation, aromatics formation, and polymerization process, which make it possible to obtain the solid product or hydrochar. Pure biomass types and their mixtures were compared, considering hydrochar and carbon yields, H/C, and O/C ratios, and their deviation from the batch process. The results of hydrochar yield indicated that biomass with high cellulose content can perform satisfactorily in the proposed model. In addition, the possibility of carrying out the process in reactive stages together with the recirculation of liquid product, allowed a greater yield with respect to the batch process. It is concluded that the proposed model improves the characteristics of the obtained hydrochar compared to its crude biomass, achieving lower proportions of hydrogen and oxygen in the solid product.

Studying the Aerodynamics of the TPP-210A Boiler Furnace When It Is Shifted to Operate with Dry-Ash Removal and Vortex Fuel Combustion

To reduce the amount of nitrogen oxide emissions and achieve more reliable operation of the TPP-210A boiler, a process arrangement for firing Grade TR Kuznetsk coal that involves using straight-flow burners and shifting the boiler from slag-tap to dry-ash removal is developed. Owing to a large burner downward slope angle and special arrangement of burners and nozzles, four large vertical vortices rotating in opposite directions are produced in the furnace lower part, as a result of which the combustion products dwell for a longer period of time in the burning zone and more complete fuel combustion is achieved. For verifying the operability and efficiency of the proposed combustion arrangement, investigations on a boiler furnace physical model were carried out using a technique for visualizing fuel jets and secondary and tertiary overfire air jets. The fuel jet temperature boundaries in the course of jet propagation in the furnace model are also determined. The study results have shown that staged fuel combustion will be set up with using the proposed arrangement of burners and nozzles. In addition, large vertical vortices produced in the furnace lower part will help to achieve more efficient use of the dry bottom hopper heating surfaces, due to which lower coal combustion product temperature in the furnace upper part and smaller content of combustible products in fly ash will be obtained. Owing to low values of air excess factor at the pulverized coal burner outlet and gradual admission of air into the vortex zone through a few nozzles with intense inner recirculation of combustion products to the jet initial section, staged combustion of pulverized coal and low nitrogen oxide emissions will be secured. Owing to expansion of fuel jets, a rapid growth of mass in the fuel jet is achieved, which is obtained both due to ejection of the jet itself and due to forced admission of hot fuel gases from other jets. Investigations carried out on the physical model have confirmed that the proposed combustion arrangement features high efficiency and that a low content of nitrogen oxides in flue gases is obtained.

The pilot dual-reflux vacuum pressure swing adsorption unit for CO2 capture from flue gas

The results of carbon dioxide separation from real flue gas using the dual-reflux vacuum pressure swing adsorption (DR-VPSA) technology have been presented. The mobile pilot CO2 separation plant consists of two containers: a processing container and a control container. The processing container includes a flue gas treatment section (which comprises dust removal, cooling, deSOx, deNOx, gas drying and compression units), as well as a CO2 adsorptive separation unit. The adsorption unit is made up of four fixed-bed columns, each divided into two sections, operating in a dual-reflux vacuum pressure swing adsorption mode. Two kinds of activated carbon in the total amount of 540 kg were used as the beds filling. The results from the 8-step reference process with no partition of the adsorbers into the upper and lower sections (as one-step separation process with partial product recirculation), and from the 9-step DR-VPSA process (as two-step separation process) with a division of the adsorbers are presented. In the measurement campaign three different feed gas flow rates and five different times of adsorption step were selected to assess their influence on separation results. The results show the optimal parameters of 100 Nm3/h for feed gas flow rate and 300 sec for adsorption step time for both mentioned processes. The 87.5% of purity, 44.6% of recovery, 11.4 kg/(m3 h) of productivity and 978 kWh/MgCO2 of energy demand for gas compression and vacuum evacuation in the case of optimal parameters of 9-step DR-VPSA technology were obtained. Additionally the results from measurement campaign were compared with those reported by other researchers.

Business Models for Circular Economy and Sustainable Development: the Case of Lease Transactions

The purpose of this paper is to discuss the features of leasing as a business model in the circular economy, which is presumed to support sustainable development by product recirculation and driving economic performance. In particular, this study highlights microeconomic benefits for listed Romanian companies, showing that adopting a greener business model, as in the case of leasing, does not penalize firms economically but it is a catalyst for increasing their performance, both in terms of accountancy-based measures (return on assets and return on sales), but also in terms of the subjective perceptions of investors and financial analysts operating on the capital market (proxied by Tobin’s Q and market to book value of equity). Based on 266 observations from companies listed on the Bucharest Stock Exchange (BSE) during 2013-2016, the study uses regression analysis to show that financial performance is higher for quoted Romanian companies that use leasing and renting and that performance is also directly associated with leasing intensity, i.e. the share of the value of the rights to use leased goods in the total value of property, plant and equipment.

Design of two-column batch-to-batch recirculation to enhance performance in ion-exchange chromatography

Preparative liquid chromatography is a separation technique widely used in the manufacturing of fine chemicals and pharmaceuticals. A major drawback of traditional single-column batch chromatography step is the trade-off between product purity and process performance. Recirculation of impure product can be utilized to make the trade-off more favorable. The aim of the present study was to investigate the usage of a two-column batch-to-batch recirculation process step to increase the performance compared to single-column batch chromatography at a high purity requirement. The separation of a ternary protein mixture on ion-exchange chromatography columns was used to evaluate the proposed process. The investigation used modelling and simulation of the process step, experimental validation and optimization of the simulated process. In the presented case the yield increases from 45.4% to 93.6% and the productivity increases 3.4 times compared to the performance of a batch run for a nominal case. A rapid concentration build-up product can be seen during the first cycles, before the process reaches a cyclic steady-state with reoccurring concentration profiles. The optimization of the simulation model predicts that the recirculated salt can be used as a flying start of the elution, which would enhance the process performance. The proposed process is more complex than a batch process, but may improve the separation performance, especially while operating at cyclic steady-state. The recirculation of impure fractions reduces the product losses and ensures separation of product to a high degree of purity.

Experimental and numerical investigation of an ultra-low NOx methane reactor

This work investigates a patented novel methane reactor, the Lean Azimuthal Flame (LEAF) Combustor. The combustor operates with non-premixed combustion where both the air and methane enter the combustor volume through small, high momentum jets. The air jets, located at the top of the combustor, are angled to create a swirling flow that mixes with the fuel entering from the bottom of the combustor. The resulting toroidal flow is intended to increase mixing and hot product recirculation within the burner to reduce operating temperatures, increase residence time, and limit the formation of NOx with preliminary emissions levels measured at sub-20 ppm. The main objectives of this paper are to: (i) experimentally characterize the combustor behaviour; and (ii) improve the physical understanding of the combustion process in the system under investigation through the use of numerical simulations. Experiments were performed at various air and fuel flow rates to determine the stability range of the combustor. Direct visualization of the combustion process indicates the formation of a low luminosity stable flame with a toroidal shape. Flame photographs and OH* chemiluminescence images are presented to provide a qualitative comparison of flame structure and reaction zone, as well as to analyse the effect of varying air and fuel flow rate on combustor operation. Numerical simulations were performed using the Large Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) sub-grid combustion model to analyse the flame behaviour within the combustion chamber. The regions around the fuel jet flow in particular were investigated to explore the phenomena of flame lift-off and local extinction in the bottom of the combustor.

CO2-argon-steam oxy-fuel (CARSOXY) combustion for CCS inert gas atmospheres in gas turbines

CO2 emitted from gas turbines in power plants is considered a major contributor to the global environmental damage. Carbon Capture and Storage (CCS) integrated with oxy-fuel (OF) combustion is an advanced and innovative approach that may be used in turbines to reduce these emissions. This method is based on CO2 recycling, however the obstacle to using this recirculation approach in gas turbines is reduction in their performance and reliability.This paper attempts to address the problem in a novel way by investigating theoretically a number of blends that can overcome the performance and reliability issues of pure CO2. These blends, comprising of argon, H2O and CO2, can be used as a working fluid with oxygen and methane as reactants. Additionally, a numerical model for an industrial gas turbine is employed. The aim is to find the optimum blend for complete NOx elimination with a recirculation of products. This study uses 0-D chemical kinetic software (Gaseq), an empirical selection approach with design of experiments and, 1-D chemical kinetic software (CHEMKIN-PRO).Results identify the optimum blend which is numerically assessed in an industrial gas turbine that has been experimentally correlated. The efficiency of this turbine running the selected blend is 1.75–13.93% higher than when running with natural gas/air conditions. This shows the promising use of this blend for a future high efficiency CCS-Oxyfuel approach in gas turbine combustors.

Numerical Investigation of Oxy-mild Combustion of Pulverized Coal in a Pilot Furnace

Abstract The Conventional coal-fired plants are large contributors to air pollution and greenhouse gas. The combustion generates pollutants such as oxides of sulphur, nitrogen, and carbon as well as fine organic and inorganic particulates. The new technologies able to reduce drastically the pollutant emissions and facilitate to use of coal in an environmentally more friendly way, are commonly known as clean coal technologies (CCT). In this context the CCS technologies play an important role to reduce the CO2 emissions. The only form with truly zero CO2 emissions in existence today is pre-combustion gas separation, namely, the combustion of fuel using oxygen instead of air. It is well known that burning pulverized coal in pure oxygen increases the flame temperatures, thus also increases NOx emissions. Therefore, to moderate the flame temperature and reduce NOx the oxygen is mixed with recycled flue gas (RFG). This approach to reduce CO2 emissions is often called oxy-firing or oxy-fuel combustion. The purified CO2 stream is then compressed and condensed to produce a manageable effluent of liquid CO2, which can be sequestered for storage (CCS) or for use in subsequent processes (CCR). MILD (Moderate or Intensive Low Dilution) or HiTAC (High Temperature Air Combustion) is an innovative combustion technology and probably the most important achievement of the combustion technology in recent years. In MILD combustion the reactions take place in almost the whole volume of the combustion chamber. This leads to temperature and species concentration fields uniform in the chamber. The fuel is oxidized in an environment that contains a substantial amount of inert gases (N2, CO2, H2O) and low oxygen concentrations. This is caused by an internal recirculation of combustion products generated by injecting preheated air jets into the combustion chamber with very high momentum, bringing the temperatures close to the combustion products temperature, reducing the NOx emissions. Because both technologies allow reductions of pollutant emissions, the aim of this work is to demonstrate the advantages of a combination of these two combustion technologies in order to analyze the temperature and specie concentrations field, the CO2 and NOx emissions by means of CFD. The goal is understand if it is possible to combine the MILD combustion and OXY one in order to reduce the NOx emissions, and capture the CO2.

Unsteady-state methanation of carbon dioxide in a fixed-bed recycle reactor — Experimental results for transient flow rate ramps

The utilization of fluctuating renewable electrical energy in chemical processes necessitates the dynamic operation of chemical reactors. One important example is the methanation reactor in the power-to-gas process, where the electrolysis of water is applied for the production of hydrogen, which can be converted into methane via hydrogenation of carbon oxides. The methanation step might be operated dynamically in order to reduce the storage capacity of hydrogen. Therefore, the unsteady-state behavior of the methanation is investigated in the present work. In particular a fixed-bed reactor with product recirculation is considered in terms of the system stability upon dynamic variations of the inlet flow rate. A systematic three-step study based on a steady-state parameter variation as well as load ramps with and without gas recycle was conducted on a lab-scale test facility. Focusing on a reactor system reaching chemical equilibrium, it was found that the reactor behavior is independent of the load change velocity in the investigated range. During the transient variation of the inlet volume flow rate, the temperature response inside the fixed-bed is decelerated compared to the concentration response. The adaption of the product recirculation allows to stabilize the bed temperature, which is unavoidable for a high conversion of carbon dioxide.

The effect of feed overload at secondary coal separation with product recirculation

For coal separation with product recirculation, there is a risk of an excessive increase in the amount of feed. Protection against this effect can be achieved by an adequate control of the recirculated material amount. The paper presents a control analysis and economic results of separation in either one or two jigs. The advantage of a slight jig performance oversizing and application of video monitoring in their control systems were justified.

Production value optimization with intermediate jig product recirculation

The paper describes the result of the production value increase in systems with two and three jigs and recirculation of the interemediate product compared to the output value obtained from a single jig. The increase is greater when the reference ash content in the concentrate is lower.

A Tale Told Thrice: Hawthorne, Doctorow, and the Intertextual Imagination

Since John Barth's famous essay on Literature of Exhaustion, it has become commonplace to say that we live in an age characterized by a constant recirculation of products. Thanks to twenty-first-century information technologies, the possibilities for the global dissemination of information and contents have become more ubiquitous and instantaneous than ever, and technologies have assumed the guise of global facilitators of exchange and democratic participation. At the same time, these developments raise questions about the effects of a potentially infinite electronic repository on processes of communication, remembering, and community-building, all of which depend on modes of selection. (2) Moreover, while technological changes facilitate the virtual circulation of contents as never before, increasingly severe and aggressively pursued copyright laws are turning a growing amount of materials, knowledge, and information into the of a limited number of individuals and companies. As Stanford professor of law Lawrence Lessig puts it, [t]here has never been a time in our history when more of our 'culture' was as owned' as it is now (12). And even though copyright owners might fight a losing battle when it comes to controlling the dissemination of film and music on the Web, trends in copyright law make obvious the discrepancy between the idea(l) of a worldwide network that facilitates global sharing and the contemporary status quo. (3) Questions regarding the desirability and feasibility of a democratic circulation, accessibility, and, perhaps most important of all, (re-) utilization of materials also bear in major ways on the contemporary literary field. (4) Over the past decades, the book market has witnessed a proliferation of rewritings, sequels, prequels, and so-called bio-fictions that mirrors the trend toward sharing, appropriating, and recycling preexisting materials facilitated by the Web, while at the same time fostering a debate about which parts, and which aspects, of our heritage may be worth preserving and how this heritage affects the imagination. (5) Along with the proliferation of fan fiction on the Web, the success of recent spinoff novels such as Michael Cunningham's The Hours (1998), Geraldine Brooks's March (2005), and Sena Jeter Naslund's Ahab's Wife (1999) indicates the popularity of this type of fiction with both authors and readers, the prominent role that popular and narratives play for the individual and collective imagination, and the considerable amount of economic and symbolic capital involved. (6) However, the writer who decides to retrieve and recycle materials of the past straddles a dangerous line. Such ventures often conflict with contemporary conceptualizations of intellectual property and copyright laws, and may therefore have considerable legal consequences. (7) Moreover, by appropriating well-known, and often canonic, materials of the (literary) past, rewritings also invite comparisons with their pre-texts. In such assessments, aesthetic and moral criteria are often conjoined: For example, a perceived lack of aesthetic mastery or complexity of the rewriting is typically seen as the result of a lack of originality and a debasing economic interest on the side of the literary recycler, as opposed to the pre-text's author's creative genius. (8) What such approaches to the phenomenon tend to disregard are the specific agendas and implications of acts of rewriting, which range from an apparent wish for participation and continuation on the part of readers to an exploration of the continued impact of cultural texts (Assmann, Texte 232) on the community, including the perceived need to reconsider the implications of formative narratives along the lines of race, class, gender, and sexuality, to name but a few. In other words, by rewriting literary classics, contemporary authors also attempt to re-conceptualize the imagined community that serves as a basis for identification. …

Chemistry reduction for modelling flameless combustion of ethylene

Flameless combustion is a novel combustion technology able to ensure high combustion efficacies with low pollutant emissions thanks to the dilution of reactants, usually achieved through recirculation of combustion products. The technology has been successfully applied in several processes and has been found to be able to handle a large variety of fuels, including low grade fuels, industrial by-products and hydrogen. Further development of this innovative combustion technology would benefit of Computational Fluid Dynamics (CFD) tools; however, modelling flameless combustion is much more challenging than conventional flames, because of the strong coupling between turbulent mixing and chemical kinetics. In particular the chemical kinetics plays a fundamental role, even though there no common opinion on the degree a mechanism can be reduced. Some useful works may be found on flameless burners fed with methane, but there is lack of information on different fuels. The present work describes the numerical modelling of an ethylene jet flame issuing in a hot coflow burner, emulating flameless combustion and fully characterised in literature, with the scope of investigating the potential for chemistry reduction in the context of flameless combustion. A Principle Component/Variable Analysis is used to investigate the most important species in the chemical mechanism and subsequently a dimension reduction technique based on the Rate-controlled constrained-equilibrium (RCEE) principle is applied to the detailed mechanism to be coupled to the CFD code, in order to make simulations more affordable. Results indicated that the use of Principle Component/Variable Analysis leads to a good choice of the variables to be retained as results with the reduced scheme were found to be consistent with those obtained with the full mechanism.

Definition of rational modes of operation of baking ovens

The flue gas temperature is one of the main variables that are most sensitive to changes in load in industrial ovens. This temperature in turn is associated with the loss of heat from the flue gases. The last value determines the change in fuel consumption, not directly related to the load. Therefore, the problem of determining a rational oven load is reduced mainly to establish the exact or approximate relation tf1=f(G).The authors is studied the work at alternating mode of ovens with recirculation of combustion products - the most common type of baking ovens. In these furnaces load increase leads to an increase of tf1, and decrease - to decrease of tf1.Increasing the temperature of the flue gas with increasing of oven productivity is explained by the fact that productivity causes a corresponding change in the heat flow to the working chamber of the oven. This change is due to increased fuel consumption and increasing the initial temperature of the heating gases. The growth in the total enthalpy heat transfer ΔQ gas determines the increase of them, which leads to increase of tf1.Thus, the change in heat flow into the working chamber is caused by a change in the temperature difference of the heating gases. The calculations show that the change in different modes of temperature difference, calculated as the difference between the average temperature of the heating gas and the walls of the working chamber by the law of convective heat transfer, well reflects the change under the same conditions.The obtained research can be applied to bakeries, at installation and after repair of baking ovens in order to obtain high-quality products with minimal cost of fuel-energy resources.

Combustion characteristics of biodiesel fuel in high recirculation conditions

The potential of biodiesel as an alternative fuel for various applications leads to an investigation to understand the combustion characteristics of pure and blended biodiesel. The concept of internal recirculation of combustion products is employed in a high swirl and low emission burner to reduce emissions. Due to high boiling point (613K) and SMD (37μm) of biodiesel, air preheating with minimum temperature above the boiling point of biodiesel is considered. Air at different temperatures of 623, 673 and 703K is injected tangentially. Swirl flow pattern in the combustor creates the central low pressure zone due to vortex breakdown and improves the recirculation of combustion products. Results in improved mixing and high residence time of reactants. Biodiesel is blended with diesel to reduce the surface tension and viscosity and improve the combustion characteristics. Literature has little consensus on NOx emissions from the combustion system operating with biodiesel. Therefore, the present study aims to reduce the thermal NO formation through the concept of exhaust gas recirculation. The CO, HC, NOx emissions and soot-volume fraction from biodiesel (100B0D), 50% blending (50B50D), diesel and kerosene are compared at different air preheating temperatures. A drastic reduction in emissions is observed in 50B50D as compared with pure biodiesel.

Recirculation of combustion products in the heating channels of coke furnaces

The recirculation of combustion products in the heating channels of coke ovens is considered. The influence of recirculation on the temperature distribution over the height of the channel walls is assessed.

Experimental and Numerical Research of a Novel Combustion Chamber for Small Gas Turbine Engines

New combustion chamber concept (based on burner JETIS-JET Induced Swirl) for small gas turbine engine (up to 200kW) is presented in this article. The combustion chamber concept is based on the flame stabilization by the generated swirl swirl generated by two opposite tangentially arranged jet tubes in the intermediate zone, this arrangement replaces air swirler, which is very complicated and expensive part in the scope of small gas turbines with annular combustion chamber. The mixing primary jets are oriented partially opposite to the main exhaust gasses flow, this enhances hot product recirculation and fuel-air mixing necessary for low NOx production and flame stability. To evaluate the designed concept a JETIS burner demonstrator (methane fuel) was manufactured and atmospheric experimental measurements of CO, NOx for various fuel nozzles and jet tubes the configuration were done. Results of these experiments and comparison with CFD simulation are presented here. Practical application of the new chamber concept in small gas turbine liquid fuel combustor was evaluated (verified) on 3 nozzles planar combustor sector test rig at atmospheric conditions results of the experiment and numerical simulation are also presented.

Efficiency of Small Scale Manually Fed Boilers —Mathematical Models

This study reviews test results for a biomass-fired hot water boiler with a nominal boiler thermal power of 120 kW. In the experiments, prismatic wheat straw bales were used as biomass. The impact of the quantity (220, 290, 360 and 430 m3 h−1) of inlet air fed to the boiler firebox was continuously monitored. This was to examine the influence of the quantity of inlet air and recirculation (0, 16.5 and 33%) of combustion products on the boiler thermal power and boiler energy efficiency. Thus, the following mathematical models and formulas were presented: correlation between boiler thermal power and bale residence time; bale mass loss during the combustion process; correlation between boiler energy efficiency and bale residence time. Mathematical models were obtained by using experimental data and by applying nonlinear regression analysis. Adjustment evaluation of mathematical models with experimental data was performed based on the determination coefficient, t-test and F-test. Increase the amount of air throughout the firebox produced boiler thermal power increase and bale residence time decrease. It was shown that combustion products recirculation of 16.5% partly improved boiler characteristics, while the recirculation of 33% did not, comparing with the case without recirculation.