Gas Recirculation Research Articles

Ignition delays in diesel combustion and intake gas conditions

Ignition delays in diesel combustion under several intake gas conditions, including different oxygen concentrations changed with exhaust gas recirculation quantities and different intake gas temperatures, were measured for four cetane numbers and three compression ratios in a single-cylinder, naturally aspirated, direct injection diesel engine (bore: 110 mm, stroke: 106 mm, and stroke volume: 1007 cm3). The engine has a common rail fuel injection system which can be set to optional injection timings and has an injector with a needle lift sensor to accurately estimate the injection timing. The intake oxygen concentrations were set by the quantity of exhaust gas recirculation gas, and the intake gas temperatures were changed with a water-cooled exhaust gas recirculation cooler and an electric heater in the intake pipe. Three compression ratios, 16.7, 18.0, and 21.3, were established with three pistons of different cavity volumes. Four fuels with different cetane numbers, 32 (CN32), 45 (CN45), 57 (CN57), and 78 (CN78), consisting of normal and isoparaffins, were examined for the three compression ratios, and the influence of exhaust gas recirculation and intake gas temperature is discussed for 12 combinations of compression ratios and cetane numbers. The results showed that the ignition delay increases linearly with the 1.67 power of the decrease in the intake oxygen concentration changed with cooled exhaust gas recirculation at the same cetane number and the same compression ratio. The ignition delay increases linearly with lowering intake gas temperatures, and the degree of increase in the ignition delay is more significant with lower cetane number fuels and lower compression ratios. Under practical conditions with the intake oxygen concentration between 21% and 11% and the intake gas temperature between 40°C and 100°C, the changes in ignition delays with the intake oxygen concentration are more significant than the changes with intake gas temperature. The ignition delay increases linearly with lowering compression ratios, and the degree of increase in the ignition delay with reductions in the compression ratio is larger in the cases with lower intake oxygen concentrations and lower cetane number fuels. The ignition delays at the higher compression ratios are significantly shorter than with the lower compression ratios in the case of the same in-cylinder gas temperature at top dead center due to higher in-cylinder gas pressures. The degree of increase in the ignition delay with lower cetane numbers is more significant at lower intake oxygen concentrations and lower compression ratios, and the ignition delay decreases linearly with the 0.25 power of the increase in cetane numbers.

Exploring Computational Methods for Predicting Pollutant Emissions and Stability Performance of Premixed Reactions Stabilized by a Low Swirl Injector

ABSTRACTThis article addresses the numerical modeling of NOx emissions and lean blowoff (LBO) limits of confined and pressurized turbulent premixed flames stabilized with a low swirl burner. The study also evaluates existing numerical methods that can be used to predict exhaust pollutant emissions and reaction instability close to the LBO limit. One of the strategies presented in the article consists of establishing a chemical reactor network (CRN), which is a simplified model of the fluid dynamics and energy balance of the system coupled with a detailed reaction mechanism. Since the computing turnaround time for a CRN model is several orders of magnitude less than the simplest computational fluid dynamics (CFD) case, the parameters controlling the pollutant formation and stability of the system can be quickly assessed over the complete flammable range. The results show the value of a simple reactor network as a design tool that can be used to optimize emissions and LBO limits of combustion systems. The parametric analysis examines the most important variables that control the formation of pollutant species (pressure, recirculation of gases, heat losses, geometry variables, air to fuel ratio, and fuel composition). Experiments were carried out at a pressure of 304 kPa using two fuel compositions: natural gas and natural gas enriched with up to 90% hydrogen (by volume). The results obtained with the CRN for NOx and LBO are in good agreement with those observed experimentally and show that, for ultra-low NOx burners, the lowest NOx emissions are concomitant to the onset of instabilities associated with LBO. In sharp contrast, the CFD-based simulations of NOx fail to accurately predict the effect of the fuel composition on the LBO limit. Further analysis of the CRN results show that, at lean conditions and pressures above three atmospheres, NOx is formed primarily through the N2O pathway, regardless of the fuel composition. The CRN model indicates that adding hydrogen to natural gas promotes the production of NOx through the Zeldovich, NNH, and N2O routes while reducing formation via the prompt route. Understanding the relative contributions of each route provides a starting point from which to propose modifications to the system to reduce NOx emissions.

The benefits of a mid-route exhaust gas recirculation system for two-stage boosted engines

Exhaust gas recirculation is a widely known technique applied in internal combustion engines for controlling the combustion process and harmful emissions. The recirculation of gases can be achieved either by delivering burnt gases from upstream of the turbine to downstream of the compressor (short-route) or by taking the exhaust gas from downstream of the turbine and deliver to upstream of the compressor (long-route). Although long-route system is preferred for highly boosted engines due to the higher exhaust gas recirculation availability at low engine speeds, it lacks a fast response time during transient performance compared to the short-route system. This article examines the potentials of introducing an alternative exhaust gas recirculation route which can be applied in two-stage boosted engines. The proposed mid-route exhaust gas recirculation system, applied in a gasoline engine, combines the benefits of the long routes and short routes. The system provides high exhaust gas recirculation rates at all engine speeds while the transport delay in the case of transient operation is relatively short. The potential of a hybrid exhaust gas recirculation system combining mid-route and long-route exhaust gas recirculation is examined and various components’ (i.e. compressor, turbine and coolers) sizing and transient performance studies are performed to understand the trade-offs of the system. It was demonstrated that mid-route could provide high exhaust gas recirculation particularly at high- and low engine speeds. A combination of mid-route and long-route exhaust gas recirculation can provide maximum exhaust gas recirculation rates at all speeds with a maximum fuel consumption penalty of 1.4% at engine speeds below 2500 r/min. The reduction in exhaust gas recirculation response time was of the magnitude of 50%, while the faster exhaust gas recirculation purging time combined with the smaller turbine implemented dropped the load tip-in response time by 25%. The coolers’ sizing study revealed that a long-route exhaust gas recirculation cooler is unnecessary, whereas the mid-route exhaust gas recirculation cooler can also be omitted when the flow is delivered prior an intercooler with a 25% larger cooling capacity than of the baseline engine.

Dual-Stage Drying Process of Lignite Using Pilot Scale Coal Rotary Dryer

ABSTRACTIn conventional rotary drying process, lignite is fed into the drum with rotary-valve feeder and hot flue gas is injected concurrently at the bottom of the feeder. It is called single-stage drying since lignite is passed through one-step drying process. This study presents dual-stage drying process in which the primary dried coal is reintroduced into the rotary drum which results in secondary dried coal. Its effect on particle size distribution and total moisture at various feed mass flow rates ranging from 325 to 500 kg/h were investigated. The results show that total moisture of lignite decreased significantly for both single-stage (23.9%) and dual-stage drying (11.7%) without any spontaneous combustion even at excessive temperature as high as 188°C. Recirculation of flue gas creates less oxidative air which ranged from 16.5% to 19.7% inside the rotary drum. Standard deviation of moisture content implies that dual-stage drying process is able to reduce variation in moisture content which means better drying consistency.

On the effect of injection timing on the ignition of lean PRF/air/EGR mixtures under direct dual fuel stratification conditions

The ignition characteristics of lean primary reference fuel (PRF)/air/exhaust gas recirculation (EGR) mixture under reactivity-controlled compression ignition (RCCI) and direct duel fuel stratification (DDFS) conditions are investigated by 2-D direct numerical simulations (DNSs) with a 116-species reduced chemistry of the PRF oxidation. The 2-D DNSs of the DDFS combustion are performed by varying the injection timing of iso-octane (i-C8H18) with a pseudo-iso-octane (PC8H18) model together with a novel compression heating model to account for the compression heating and expansion cooling effects of the piston motion in an engine cylinder. The PC8H18 model is newly developed to mimic the timing, duration, and cooling effects of the direct injection of i-C8H18 onto a premixed background charge of PRF/air/EGR mixture with composition inhomogeneities. It is found that the RCCI combustion exhibits a very high peak heat release rate (HRR) with a short combustion duration due to the predominance of the spontaneous ignition mode of combustion. However, the DDFS combustion has much lower peak HRR and longer combustion duration regardless of the fuel injection timing compared to those of the RCCI combustion, which is primarily attributed to the sequential injection of i-C8H18. It is also found that the ignition delay of the DDFS combustion features a non-monotonic behavior with increasing fuel-injection timing due to the different effect of fuel evaporation on the low-, intermediate-, and high-temperature chemistry of the PRF oxidation. The budget and Damköhler number analyses verify that although a mixed combustion mode of deflagration and spontaneous ignition exists during the early phase of the DDFS combustion, the spontaneous ignition becomes predominant during the main combustion, and hence, the spread-out of heat release rate in the DDFS combustion is mainly governed by the direct injection process of i-C8H18. Finally, a misfire is observed for the DDFS combustion when the direct injection of i-C8H18 occurs during the intermediate-temperature chemistry (ITC) regime between the first- and second-stage ignition. This is because the temperature drop induced by the direct injection of i-C8H18 impedes the main ITC reactions, and hence, the main combustion fails to occur.

Effect of Gas Recycling on the Performance of a Moving Bed Temperature-Swing (MBTSA) Process for CO2 Capture in a Coal Fired Power Plant Context

A mathematical model of a continuous moving-bed temperature-swing adsorption (MBTSA) process for post-combustion CO2 capture in a coal-fired power plant context has been developed. Process simulations have been done using single component isotherms and measured gas diffusion parameters of an activated carbon adsorbent. While a simple process configuration with no gas re-circulation gives quite low capture rate and CO2 purity, 86% and 65%, respectively, more advanced process configurations where some of the captured gas is recirculated to the incoming flue gas drastically increase both the capture rate and CO2 purity, the best configuration reaching capture rate of 86% and CO2 purity of 98%. Further improvements can be achieved by using adsorbents with higher CO2/N2 selectivity and/or higher temperature of the regeneration section.

Influence of the technique for injection of flue gas and the configuration of the swirl burner throat on combustion of gaseous fuel and formation of nitrogen oxides in the flame

How the points at which the flue gas was injected into the swirl burner and the design of the burner outlet influence the formation and development of the flame in the submerged space, as well as the formation of nitrogen oxides in the combustion products, have been studied. The object under numerical investigation is the flame of the GMVI combined (oil/gas) burner swirl burner fitted with a convergent, biconical, cylindrical, or divergent throat at the burner outlet with individual supply of the air and injection of the gaseous fuel through tubing. The burners of two designs were investigated; they differ by the absence or presence of an inlet for individual injection of the flue gas. A technique for numerical simulation of the flame based on the CFD methods widely used in research of this kind underlies the study. Based on the summarized results of the numerical simulation of the processes that occur in jet flows, the specific features of the aerodynamic pattern of the flame have been established. It is shown that the flame can be conventionally divided into several sections over its length in all investigations. The lengths of each of the sections, as well as the form of the fields of axial velocity, temperatures, concentrations of the fuel, oxygen, and carbon and nitrogen oxides, are different and determined by the design features of the burner, the flow rates of the agent, and the compositions of the latter in the burner ducts as well as the configuration of the burner throat and the temperature of the environment. To what degree the burner throat configuration and the techniques for injection of the flue gas at different ambient temperatures influence the formation of nitrogen oxides has been established. It is shown that the supply of the recirculation of flue gas into the fuel injection zone enables a considerable reduction in the formation of nitrogen oxides in the flame combustion products. It has been established that the locations of the zones of intensive fuel burnout and generation of nitrogen oxides do not coincide over the flame length, and the ambient temperature has a significant impact on the combustion stability at low values and on the concentration of nitrogen oxides in the combustion products at high values.

Scaling Considerations in All-Iron Flow Batteries

In recent years, the deployment of renewable energy sources, development of smart grid technology and advances in electrified transportation have resulted in a surge in markets for large-scale stationary energy storage. Several factors contribute to the demand for large-scale energy storage, including capital costs of managing peak demands, integration of renewable energy sources and investments needed for grid reliability. Although hydroelectric is one of the most common types of energy storage, flow batteries offer a much more desirable alternative, due to scalability and location flexibility. A number of studies and demonstration projects have been carried out in the field of flow batteries, in particular with the vanadium [1,4], and iron/chromium[2-4] chemistries and these and other systems are in the first stages of commercial deployment. In this presentation we will discuss the scale-up an all iron flow battery, focusing on two issues in particular, flow distribution and hydrogen generation/recombination. Flow distribution is a scaling concern in all flow battery systems both on a cell to cell level within a stack and within an individual cell. This investigation utilizes the all iron chemistry to investigate the effects of flow distribution within a single cell on cell performance and the pressure drop associated pumping costs of achieving a more even flow distribution within a cell. These effects are considered in the context of transitioning from a 50cm2 lab scale cell to a 1100cm2 commercial scale prototype. An optimization can be achieved between flow uniformity and pumping losses. Hydrogen evolution is a parasitic reaction in many chemistries that can have a significant effect on lifetime. We have developed a simple in-tank system that captures and re-oxidizes hydrogen to maintain electrolyte stability and demonstrated this concept on a laboratory scale.[5] This investigation looks into scaling considerations and their effect on the hydrogen recombination system. Specifically, the relationship between head space, gas recirculation and the effectiveness of the reactor are considered. [1] G. Codina, J. Perez, M. Lopez-Atalaya, J. Vasquez, and A. Aldaz, J. Power Sources, 48, 293 (1994). [2] S. Takahashi and T. Hiramatsu, J. Power Sources, 17, 55 (1986). [3] M. Futamata, S. Higuchi, O. Nakamura, I. Ogino, Y. Takada, and S. Okazaki, J. Power Sources, 24, 137 (1988). [4] M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mjalli and M. Saleem, J. Electrochem.Soc., 158, 8 (2011). [5] S, Selverston, R. F. Savinell and J. S. Wainright, J. Power Sources., 324, 674, (2016).

Nitrogen oxides emissions from the MILD combustion with the conditions of recirculation gas

ABSTRACTThe nitrogen oxides (NOx) reduction technology by combustion modification which has economic benefits as a method of controlling NOx emitted in the combustion process, has recently been receiving a lot of attention. Especially, the moderate or intense low oxygen dilution (MILD) combustion which applied high temperature flue gas recirculation has been confirmed for its effectiveness with regard to solid fuel as well. MILD combustion is affected by the flue gas recirculation ratio and the composition of recirculation gas, so its NOx reduction efficiency is determined by them. In order to investigate the influence of factors which determine the reduction efficiency of NOx in MILD coal combustion, this study changed the flow rate and concentration of nitrogen (N2), carbon dioxide (CO2) and steam (H2O) which simulate the recirculation gas during the MILD coal combustion using our lab-scale drop tube furnace and performed the combustion experiment. As a result, its influence by the composition of recirculation gas was insignificant and it was shown that flue gas recirculation ratio influences the change of NOx concentration greatly.Implications: We investigated the influence of factors determining the nitrogen oxides (NOx) reduction efficiency in MILD coal combustion, which applied high-temperature flue gas recirculation. Using a lab-scale drop tube furnace and simulated recirculation gas, we conducted combustion testing changing the recirculation gas conditions. We found that the flue gas recirculation ratio influences the reduction of NOx emissions the most.

Displacement of the Ingnition Furnace in the Iron Ore Sintering with Re-Circulation of Waste Gases

In search of new technologies for the iron ore sintering process, the re-circulation of waste gases in the process can provide some advantages in relation to the conventional process. For such study, a sintering multi-phase model was used for the assessment of the re-circulation of waste gases in the process. Five cases of re-circulation of waste gases in the sintering process were analyzed, always aiming at a stable operation in the process. The results of the simulation indicate an enlargement of the combustion front with the re-circulation of the waste gases and the possibility of existing a reduction of the solid fuel consumption. As a result, there was an increase of the calcium-silicate fraction, providing a sinter reducibility improvement, apart from the reduction of the emission of CO2 and PCDD/Fs in the sinter machine.

Flame characteristics and NO emission in methane/air-air counterflow premixed flames with applying FIR and FGR

Numerical study was conducted to grasp flame characteristics and NO emission behaviors in CH4/air-air premixed counterflow flames with applying Fuel induced recirculation (FIR) and Flue gas recirculation (FGR) with CO2 and H2O by varying global strain rate and the ratios of FIR and FGR. Chemical effects of additional CO2 and H2O via FIR and FGR were analyzed through comparing flame characteristics and NO behaviors from real species (CO2 and H2O) with those from their artificial species (XCO2 and XH2O) which have the same thermochemical, radiative, and transport properties to those for the real species. The results showed that flame temperature and NO emission with FIR varied much more sensitively than that with FGR. Those varied little via FIR with CO2 and H2O as well as XCO2 and XH2O. However, those varied complicatedly by chemical effects of added CO2 and H2O via FGR. In particular, there is a critical ratio of FGR below which NO emission index can be larger than those without applying FGR. Detailed analyses for them were made and discussed.

Effect of atmosphere reaction and heating rate on the devolatilization of a Colombian sub-bituminous coal

This work studies the combined effect of heating rate and reaction atmosphere on the devolatilization of sub-bituminous type A coal (SubbA coal). Non-isothermal thermogravimetric analysis (TGA) was performed on SubbA coal undergoing pyrolysis. Mass loss dataset was fit to a lumped kinetic model using two different model-free fitting methods (FWO and Vyazovkin). Meaningful differences were obtained in devolatilization kinetics under N2 (traditional combustion) and CO2 (oxy-combustion process with gas recirculation). Through TGA it was found that at low heating rates, the pyrolysis mass loss rate is higher in N2 than in CO2. Based on the activation energy distribution, CHN analysis on residual char, and tracking the evolution of products in gaseous phase during devolatilization in CO2, it was demonstrated that at temperatures higher than 660°C, CO2 reacts with the formed char. This gasification reaction becomes a controlling stage of the thermochemical transformation in CO2. Additional pyrolysis experiments were conducted in a fast-heating hot plate reactor (HPR) with 2mm particles in N2 and CO2 using heating rates between 50°C/s and 1200°C/s. These higher heating rates are similar to those of fluidized beds. In the HPR experiments, devolatilization is more intense for CO2 than N2. Differences arising from the two environments are likely caused by the different thermal and diffusive properties of both gases.

Analysis of a gas system with a recirculation of the flue gases and carbon dioxide capture

EU regulations in the field of climate policy imposes strict limits on the emission of pollutants. In addition, there are ongoing work on systems to CO2 capture, which is considered a major cause of global warming on Earth. During gas combustion emits significantly less pollution and carbon dioxide which ifs their advantage. However, because of the limited CO2 emission it is possible to introduce the uptake of said compound by chemical absorption, predisposed to be used for the coal-fired plants. Low concentrations of carbon dioxide in the exhaust gas can be increased by using exhaust gas recirculation system of a gas turbine, while reducing energy consumption during capture. In addition, the second topic discussed in the article relates to the use of hydrogen fuel for gas system. It has been shown that hydrogen admixture injection for natural gas affect considerable reduction emission carbon dioxide. This article presents the change in the operating parameters of the combined cycle with installation of CO2 capture and exhaust gas recirculation. Built a mathematical model of the system using the code of Ebsilon Professional and performed parametric calculations. In the report, there was conducted an analysis of the dependence of the change of LHV of gaseous fuel which is a mixture of natural gas and hydrogen for proper work of the gas turbine installation. The built model and obtained results are useful in the analysis of combined cycle systems integrated with separation of carbon dioxide from the flue gas.

Computational investigations of low-emission burner facilities for char gas burning in a power boiler

Various variants for the structure of low-emission burner facilities, which are meant for char gas burning in an operating TP-101 boiler of the Estonia power plant, are considered. The planned increase in volumes of shale reprocessing and, correspondingly, a rise in char gas volumes cause the necessity in their cocombustion. In this connection, there was a need to develop a burner facility with a given capacity, which yields effective char gas burning with the fulfillment of reliability and environmental requirements. For this purpose, the burner structure base was based on the staging burning of fuel with the gas recirculation. As a result of the preliminary analysis of possible structure variants, three types of early well-operated burner facilities were chosen: vortex burner with the supply of recirculation gases into the secondary air, vortex burner with the baffle supply of recirculation gases between flows of the primary and secondary air, and burner facility with the vortex pilot burner. Optimum structural characteristics and operation parameters were determined using numerical experiments. These experiments using ANSYS CFX bundled software of computational hydrodynamics were carried out with simulation of mixing, ignition, and burning of char gas. Numerical experiments determined the structural and operation parameters, which gave effective char gas burning and corresponded to required environmental standard on nitrogen oxide emission, for every type of the burner facility. The burner facility for char gas burning with the pilot diffusion burner in the central part was developed and made subject to computation results. Preliminary verification nature tests on the ТP-101 boiler showed that the actual content of nitrogen oxides in burner flames of char gas did not exceed a claimed concentration of 150 ppm (200 mg/m3).

Thermodynamic Model for Updraft Gasifier with External Recirculation of Pyrolysis Gas

Most of the thermodynamic modeling of gasification for updraft gasifier uses one process of decomposition (decomposition of fuel). In the present study, a thermodynamic model which uses two processes of decomposition (decomposition of fuel and char) is used. The model is implemented in modification of updraft gasifier with external recirculation of pyrolysis gas to the combustion zone and the gas flowing out from the side stream (reduction zone) in the updraft gasifier. The goal of the model obtains the influences of amount of recirculation pyrolysis gas fraction to combustion zone on combustible gas and tar. The significant results of modification updraft are that the increases amount of recirculation of pyrolysis gas will increase the composition of H2and reduce the composition of tar; then the composition of CO and CH4is dependent on equivalence ratio. The results of the model for combustible gas composition are compared with previous study.

Selective conversion of carbon monoxide to hydrogen by anaerobic mixed culture

A new method for the conversion of CO to H2 was developed by anaerobic mixed culture in the current study. Higher CO consumption rate was obtained by anaerobic granular sludge (AGS) compared to waste activated sludge (WAS) at 55°C and pH 7.5. However, H2 was the intermediate and CH4 was the final product. Fermentation at pH 5.5 by AGS inhibited CH4 production, while the lower CO consumption rate (50% of that at pH 7.5) and the production of acetate were found. Fermentation at pH 7.5 with the addition of chloroform achieved efficient and selective conversion of CO to H2. Stable and efficient H2 production was achieved in a continuous reactor inoculated with AGS, and gas recirculation was crucial to increase the CO conversion efficiency. Microbial community analysis showed that high abundance (44%) of unclassified sequences and low relative abundance (1%) of known CO-utilizing bacteria Desulfotomaculum were enriched in the reactor.

THE FORMATION OF BENZ(A)PYRENE IN THE COMBUSTION OF FUEL OIL IN THE BOILER FURNACE

The analysis of the parameters influencing the rate of formation of benz(a)pyrene combustion of fossil fuels in power plants. Established the functional dependence of the influence of net calorific value of fuel oil at the conditions of generation of benz(a)pyrene in the combustion chamber of the boiler. The methods of calculating the benz(a)pyrene content in the flue gases taking into account the influence of heat applied to the active combustion zone with the fuel, air, gas recirculation and moisture (water or steam) characterizing the mechanism and intensity of the combustion process of fuel oil. The heat of combustion of the fuel determines the mechanism of the process of generation of benz(a)pyrene. The presence of heavy hydrocarbons contributes to greater release of carcinogens and worst environmental conditions of the combustion process. Therefore, for meaningful emissions reductions benz(a)pyrene combustion of heavy fuel oil needed to conduct research on burnout and low-grade alloreactive fuel, especially when using high sulfur content of fuel oils and fuel oils with high content of heavy hydrocarbons.

Analyzing the possibility of constructing the air heating system for an integrated solid fuel gasification combined-cycle power plant

Combined-cycle power plants operating on solid fuel have presently been implemented only in demonstration projects. One of possible ways for improving such plants consists in making a shift to hybrid process circuits of integrated gasification combined-cycle plants with external firing of solid fuel. A high-temperature air heater serving to heat compressed air is a key element of the hybrid process circuit. The article describes application of a high-temperature recuperative metal air heater in the process circuit of an integrated gasification combined-cycle power plant (IGCC). The available experience with high-temperature air heating is considered, and possible air heater layout arrangements are analyzed along with domestically produced heat-resistant grades of steel suitable for manufacturing such air heater. An alternative (with respect to the traditional one) design is proposed, according to which solid fuel is fired in a noncooled furnace extension, followed by mixing the combustion products with recirculation gases, after which the mixture is fed to a convective air heater. The use of this design makes it possible to achieve considerably smaller capital outlays and operating costs. The data obtained from thermal and aerodynamic calculations of the high-temperature air heater with a thermal capacity of 258 MW for heating air to a temperature of up to 800°C for being used in the hybrid process circuit of a combined-cycle power plant are presented.

Effects of Equivalence Ratio on Asymmetric Vortex Combustion in a Low NOx Burner

This study presents a combustor with high combustion efficiency and low emissions. The flow field in a combustion chamber is significant in achieving good fuel–air mixing. The experimental and computational results of the temperature and emission of a vortex combustor are presented. Air enters into the combustor in a tangential direction relative to the combustor axis to produce vortex flow, which facilitates the recirculation of hot gas near the fuel nozzle for enhanced mixing. Propane is injected in the direction of the combustor axis at variable mass flow rates to produce variations in the equivalence ratio. The temperature measured along the center line of the combustor. The lowest temperature is measured under rich conditions first and then under lean and stoichiometric conditions. The trend of the combustor temperature at varying equivalence ratios is reproduced well in the simulation despite the increasing temperature near the inlet. An expected trend of NOx is measured at the outlet where the lowest NOx is produced by the rich combustion first, followed by the lean and stoichiometric combustion. The relative NOx emission at different equivalence ratios is reproduced well in the simulation, although the magnitude of the NOx emission is reduced. As indicated by the calculated number of swirls, the combustion under rich conditions produces about 15% more swirls near the nozzle compared with that under stoichiometric conditions as a result of the low combustor temperature. Moreover, such rich conditions produce a more uniform temperature inside the combustor than lean and stoichiometric conditions.

Recovery of ammonia and sulfate from waste streams and bioenergy production via bipolar bioelectrodialysis

Ammonia and sulfate, which are prevalent pollutants in agricultural and industrial wastewaters, can cause serious inhibition in several biological treatment processes, such as anaerobic digestion. In this study, a novel bioelectrochemical approach termed bipolar bioelectrodialysis was developed to recover ammonia and sulfate from waste streams and thereby counteracting their toxicity during anaerobic digestion. Furthermore, hydrogen production and wastewater treatment were also accomplished. At an applied voltage of 1.2 V, nitrogen and sulfate fluxes of 5.1 g NH4+-N/m2/d and 18.9 g SO42−/m2/d were obtained, resulting in a Coulombic and current efficiencies of 23.6% and 77.4%, respectively. Meanwhile, H2 production of 0.29 L/L/d was achieved. Gas recirculation at the cathode increased the nitrogen and sulfate fluxes by 2.3 times. The applied voltage, initial (NH4)2SO4 concentrations and coexistence of other ions were affecting the system performance. The energy balance revealed that net energy (≥16.8 kWh/kg-N recovered or ≥4.8 kWh/kg-H2SO4 recovered) was produced at all the applied voltages (0.8–1.4 V). Furthermore, the applicability of bipolar bioelectrodialysis was successfully demonstrated with cattle manure. The results provide new possibilities for development of cost-effective technologies, capable of waste resources recovery and renewable energy production.