Gas Recirculation Research Articles

Numerical investigation of the effect of injection strategy on a high-pressure isobaric combustion engine

High-pressure isobaric combustion adopted in the double compression expansion engine (DCEE) has the prospect to achieve higher thermal efficiency compared to conventional diesel combustion. This work numerically explored the effects of various injection strategies on the combustion and emission characteristics of isobaric combustion. The study developed a mathematical model to predict the injection rate profile. After validations, extensive simulations were conducted with a peak pressure of up to 300 bar – mimicking the high-pressure unit of DCEE. Several major engine design parameters such as the exhaust recirculation gas (EGR) rate, engine speed, injection strategy, and intake pressure were varied and evaluated. The results demonstrated that a higher EGR rate resulted in a higher exhaust loss but a lower heat transfer loss owing to the lower combustion temperature, so the thermal efficiency exhibited a firstly growing and then declining trend. Besides, a higher engine speed generated a higher thermal efficiency due to the shorter combustion duration and thus lower heat transfer loss. Consequently, a peak thermal efficiency of 47.5% was achieved at EGR = 50% and 1800 rpm. The high-pressure cylinder performance can also be improved with an appropriate introduction of the isochoric combustion, but its impact on the whole DCEE setup needs further investigation.

Development of a Combined Plasma‐Matrix Reformer for Solid Oxide Fuel Cell Application

AbstractA novel plasma‐matrix reformer (PMR) was suggested for methane conversion into hydrogen‐rich fuel. To demonstrate the possibility of reforming performance, characteristics of product gas and CH4 conversion were identified according to O2/C ratio, water vapor supply, reformed gas recirculation, and water feed in the recirculation gas affecting energy conversion and hydrogen production. When the reformed gas recirculation and water feed to the recirculation pipe were performed at the same time, hydrogen production and energy conversion efficiency were superior compared to the conventional reforming method. The optimal operating conditions of the PMR were determined. The obtained high energy conversion efficiency and hydrogen selectivity indicated the applicability to solid oxide fuel cell stacks for residential power generation.

Online characterization of operational parameters in an SOFC system with anode‐exhaust gas recirculation by oxygen sensors

AbstractIn solid oxide fuel cell (SOFC) system with anode‐exhaust gas recirculation (AEGR), a part of the depleted anode‐exhaust gas is recirculated and mixed with fresh natural gas prior to entering the reformer, resulting in a high potential of direct current‐efficiencies of up to 65%. However, for SOFC systems, it is of crucial importance to monitor relevant characteristic parameters and keep them within safe and durable operating limits. Such characteristic parameters are oxygen‐to‐carbon‐ratio and fuel utilization, which must not exceed system‐specific thresholds. Monitoring and control of these characteristic parameters is not trivial and a challenging task due to the enhanced system complexity. The authors present an approach and studies for determination and controlling characteristic parameters in an SOFC system with AEGR based on oxygen sensors. Therefore, the oxygen sensors, being a mature and easily available technology, are aimed to be in the fuel gas path at anode inlet and outlet of an SOFC‐stack. Analytical correlations of the output value of oxygen sensors to characteristic parameters and simulative studies on the basis of a reference natural gas composition are shown. Additionally, first results of experimental studies of oxygen sensors in representative gas compositions for the anode inlet and outlet of an SOFC system with AEGR are presented.

Effect of thermal input, excess air coefficient and combustion mode on natural gas MILD combustion in industrial-scale furnace

To promote the application of MILD scheme in furnace, the present work was performed to evaluate the effect of thermal input, excess air coefficient and combustion mode on the MILD combustion at high thermal level (thermal input varies from 600 to 786 kW); meanwhile, the heat from the utilized furnace was extracted by an annular water jacket and a corundum tube was installed in the furnace tube to create the high temperature atmosphere. The results were presented on flow field using numerical simulations and on global flame signatures, temperature/species distribution and exhaust emissions using experiments. Better combustion performance of MILD mode than conventional swirling diffusion combustion mode was verified in the present work. The positive effect of increased thermal input and excess air coefficient on gas recirculation, thermal uniformity and exhaust emissions reduction was observed. In the MILD combustion regime, the switching from nonpremixed to premixed combustion resulted in lower oxygen level and reduced reaction temperature in the combustion region, also much lower NOx emissions and slightly higher CO emission were observed. At 786 kW thermal input, the reaction zone covers the entire combustion chamber; meanwhile, low NOx emission level of 32 ppm@3%O2 are achieved for premixed MILD combustion mode. The MILD regime was established for natural gas fueled furnace with colorless distributed combustion and suppressed NOx and CO emissions.

Beyond the farm: Making edible protein from CO2 via hybrid bioinorganic electrosynthesis

Beyond the farm: Making edible protein from CO2 via hybrid bioinorganic electrosynthesis

Issues in Formation of Cryogenic Pellets for Fusion Applications

Cryogenic pellets are used for injection into fusion plasmas to add fuel to build up density and replace the ions lost from fusion reactions and imperfect confinement in the plasma. These pellets are formed at cryogenic temperatures with pure hydrogenic isotopes or mixtures of the isotopes. Technology to make these pellets and inject them into plasmas has been under development for many years, and various methods using freezing or desublimation have been shown to produce high-quality solid pellets suitable for injection. The throughput needed and possible impurity content from the necessary recirculation of fusion exhaust gases are two of the key issues to overcome for fusion pellet fueling systems in long-pulse burning plasmas. Here, we describe the technical challenges associated with these issues and the capability of pellet formation extruders to overcome them. Cryogenic pellets of deuterium, neon, and argon are also used in fusion tokamak devices for disruption mitigation in the form of large pellets that can be injected on demand to quickly dissipate the plasma thermal energy through radiation and add significant density in order to prevent runaway electron formation. Here, the issue is not throughput as with the fueling pellets but rather is the time it takes to form pellets of the size needed and the ability to dislodge them immediately on demand when needed to mitigate a disruption. The method used to make these pellets by desublimation is described, and examples related to how pellet size and input gas parameters affect the formation time are provided.

Steam temperature regulation characteristics in a flexible ultra-supercritical boiler with a double reheat cycle based on a cell model

A cell model of double reheat boilers that simplifies thermodynamic calculation was developed to predict the steam temperature characteristics of a flexible 660 MW ultra-supercritical double reheat tower-type boiler. By virtue of the model, the characteristics of steam temperatures under different loads were obtained and the effects of swinging burners, regulating gas dampers, and gas recirculation on the steam temperatures were analyzed based on the 660 MW double reheat boiler. The results showed that the main and reheat steam temperatures had radiation and convective characteristics, respectively. The main steam temperature was found to be more sensitive to flue gas recirculation, whereas reheat steam temperatures were more sensitive to gas damper regulation. The average regulation ranges of secondary reheat steam temperatures were ±32.7 °C and ±8.1 °C for the maximum ranges of dampers and gas recirculation, respectively. This study provided further insights into the steam temperature regulation characteristics of double reheat boilers.

Studies on fluorine-based impurity production in Triple-GEM detectors operated with C[formula omitted]-based gas mixture

One of the primary elements influencing gaseous detector operation is the purity of the gas mixture. Its quality can be undermined by the presence of impurities, already present in the supply gas bottles or that could be created in the gas system or from the detector itself. Gaseous detectors operated with Freon-based gas mixtures are subject to the formation of the products of gas molecules break up, occurring when the gas is exposed to high-rate radiation, and enhanced by the presence of high electric field. The release of highly reactive products could be critical as they could either create polymerized deposits or cause material etching, that could compromise detector performance and accelerate aging processes. Moreover, the operation of gas systems with gas recirculation, nowadays common in many gas systems, could worsen the risk of damage due to possible impurities accumulation. This work focuses on the production of fluorine-based impurities in Triple-GEMs detectors operated with CF4-based gas mixture. Detectors are operated in a LHC-like gas system and exposed to high-rate gamma irradiation thanks to the intense 137Cs source provided by the CERN Gamma Irradiation Facility (GIF++). Impurity production is characterized for different detector operation conditions such as gas mixture, working voltage, input flow rate, and irradiation rates. Furthermore, purifier module operation is validated proving its efficiency in removing Fluoride impurities.

Energy model-based benchmarking of the drying process in the stenter machine

Stenter machines are used widely in textile dyeing and printing houses for drying and heat setting of fabric. This is one of the most thermal energy-consuming equipment in the textile process. In this paper, the advanced energy model of the stenter machine is developed using primary mass and energy balance equations for ideal conditions as well as standard operating conditions, accounting for various energy losses to understand energy flow. To find out the scope for reduction in energy consumption, energy benchmarking is very important; compared with it, the appropriate energy consumption of a plant can be checked and changed. Furthermore, to eliminate problems such as life, process conditions, and quality of dyeing and printing houses considered during the study, unlike statistical energy benchmarking, in this paper, energy model-based benchmarking is proposed and applied for literature problems. Based on the data given in the literature for conveyor belt, stenter 1 and stenter 2, the specific energy consumption (SEC) for cotton is 4889, 3586, and 4304 kJ/kg of water evaporation, respectively, which is lower than the polywool fabric, having 5185 kJ/kg of water evaporation for another stenter machine. The energy efficiency index (EEI) of conveyor belt dryer, stenter 1, and stenter 2 are 1.56,1.18 and 1.34 for cotton, respectively, and for polywool with another stenter it is 1.92, indicating the polywool process is not energy efficient even polywool do not have bound moisture. Further, Energy flow analysis is carried out for the given stenter and fabric drying process, indicating the highest losses are in the exhaust process even after direct heat recovery by partial recirculation of exhaust gases. By analyzing the energy consumption of stenter machines through energy model based benchmarking and energy efficiency index presents the condition of process and machine from an energy perspective, and energy flow model gives the scope of the energy-saving potential. By using the developed model, the effect of change in atmospheric air temperature and humidity ratio due to season and geographic location on the performance of the stenter machine is investigated and found that there is a variation in performance up to 10% of the total energy required.

Gas mixture quality studies for the CMS RPC detectors during LHC Run 2

Resistive Plate Chamber (RPC) detectors are widely employed in the muon trigger systems of three experiments at the CERN Large Hadron Collider (LHC). They are operated with gas mixture recirculation systems to reduce operational costs and greenhouse gas emissions since their gas mixture is based on C2H2F4, which has a high global warning potential. It is well known that the C2H2F4 molecule can break down under the effect of radiation and electric field. This leads to the creation of several impurities and free fluoride ions (F-), which could accumulate under gas recirculation and potentially attach to the RPC bakelite electrode inner surface. For these reasons, an extensive gas analysis campaign has been performed during LHC Run 2 for the CMS RPC system to verify gas mixture quality and possible accumulation of impurities.During the entire LHC Run 2 period, a gas chromatograph has been used to analyze the RPC gas mixture at different points of the gas system: quality of pure C2H2F4, fresh gas from the mixer, gas at the output of the detectors, and after the purifier module. Several impurities have been found and identified. Few impurities are already present in the C2H2F4 supply, as residuals of the industrial production. Nevertheless, it was found that some of these impurities, as well as others, are created inside the detector gas gap due to the fragmentation of the C2H2F4 molecule under the effects of electric field and radiation.During the 2018 LHC Run several gas analysis points were added to measure the fluoride ions production in different sectors of the RPC detector system. Indeed the products of the C2H2F4 fragmentation do not always recombine and F- species can stay free in the gas mixture. F- analyses were performed on the gas at the output of the detectors both for barrel and endcap regions, where radiation levels and operational conditions were different. In this way, it was possible to correlate the F- production with integrated charge, and gas mixture flow rate. In parallel, the RPC currents have been constantly monitored to look for possible correlations.Fluoride measurements have also been performed at GIF++ to better understand the correlation between F- production, radiation levels and gas volume exchanges.A comprehensive overview of the results obtained from the different types of gas analyses and possible correlation with RPC currents and LHC luminosity will be presented.

Methods for reducing nitrogen oxide emissions in steam generators of thermal power plants

Main problem: Ensuring environmental safety of thermal power plants by reducing emissions of harmful substances, in particular nitrogen oxides. When all types of fossil fuel, including solid fuel, are burned, nitrogen oxides are formed in the boilers of TPPs. The sources of their formation are air nitrogen and nitrogen- containing components of the organic matter of the fuel. As you know, they adversely affect the health of humans, plants and animals. Therefore, it became necessary to consider and analyze methods to reduce these emissions. Purpose: To review and analyze various ways to reduce nitrogen oxide emissions and propose a new scheme for reducing these emissions by recirculating flue gases. Methods: This is achieved due to the fact that in the known method for purifying the flue gases of steam generators from nitrogen oxides by lowering the temperature in the furnace of the steam generator by supplying flue gases with a temperature below the temperature in the furnace of the steam generator, it is proposed that the flue gases be fed into the furnace of the steam generator after ash cleaning. At the same time, as a result of the supply of recirculated gas cooled after filtering and passing through the main smoke exhauster into the combustion chamber, having a temperature of 110-170 °C, in comparison with the initial version, a greater decrease in temperature in the furnace of the steam generator occurs, which in turn leads to a decrease in the flue gases of oxides nitrogen, since the chemical reaction of their formation goes with the absorption of heat. Results and their importance: The technical result at the proposed method of cleaning from nitrogen oxides is to reduce the consumption of electricity by eliminating the collateral wear of the recirculation gas duct, due to the cleaning of time gases from ash (a requirement of the rules of technical operation of PTE).

Comprehensive studies on alcohol using port fuel injection facilitated with spark plug engine

Abstract The spark ignition engines are universally used for automobile applications as a result of their consistent performance and economy. Regarding SI engine utilization in such applications global issues are concerned like NOx, HC, CO. Alternative fuels are the fuels of present and future. More and more vehicles are switching to alternative fuels worldwide. Usage of different fuels also reduces emissions which has further pushed demand for eco-friendly fuels. during this direction interest is concentrated on reducing formation of NOx & PM.Exhaust Gas Recirculation (EGR) may be a technique to attenuate NOx and smoke emission. the foremost reliable alternative possibility to deal with critical emissions is to use oxygenated fuels like ethanol, butanol and ether etc. which are renewable. Experimental investigations are performed out on one cylinder four stroke petrol engine producing an influence output of 5.2 kw In this experiment ethanol blends are used alongsideconventional gasoline. The blends used are 75% Ethanol 25% petrol, 50% Ethanol 50% petrol, 75% petrol 25% Ethanol alongsidethis performance parameters like ignition timing, Brake thermal efficiency and Emissions like HC, CO, NOx are monitored.

The effect of mixing rate and gas recirculation on biological CO2 methanation in two-stage CSTR systems

In-situ biological CO2 methanation (BM) in a biogas reactor by the addition of H2 is an attractive low-cost biogas upgrading process, as it does not require investment in a new reactor and can be incorporated into existing biogas plants. On the other hand, maintenance of stable reactor performance during in-situ BM is challenging due to factors such as high H2 partial pressure and CO2 depletion which may lead to an increase in pH. Thus, BM that uses two-serial connected continuous stirred tank reactors (CSTRs) could be an option. For such a process set-up, the second reactor acts as an upgrading reactor (UR) and a secondary CH4 producer for slow-degrading substrates such as straw and manure. In this study, improvement of the BM process was attempted by varying the mixing speed and gas recirculation to enhance hydrogen transfer to the liquid phase of the UR. The experiments showed that the mixing speed and gas recirculation had a significant effect on BM in CSTRs. CH4 production from BM was highest at 170 rpm, but the total CH4 production fell above 140 rpm due to reduced production of CH4 from the manure substrate. The CH4 production rate from CO2 and H2 conversion was further enhanced as the output gas was recirculated at 12.20 mL min−1. Further gas recirculation above 12.20 mL min−1 did not improve BM.

Characterization of RPC detectors with LHC-like background radiation and new eco-friendly gas mixtures

Resistive Plate Chamber (RPC) detectors are widely used at the CERN LHC experiments as muon trigger thanks to their excellent time resolution. They are operated with a gas mixture containing C2H2F4 and SF6, both greenhouse gases with a very high global warming potential. The search of new environmentally friendly gas mixtures is advised to reduce GHG emissions and costs as well as to optimize RPC performance. Several recently available gases with low GWP have been identified as possible replacements for C2H2F4 and SF6. In particular, HFO-1234ze has been studied as a possible replacement for C2H2F4 and several gases like Novec fluoroketones, C4F8O and CF3I were tested as a replacements of both C2H2F4 and SF6. The RPC detectors have been tested in laboratory conditions and few selected mixtures were tested at the CERN Gamma Irradiation Facility, which provides a high energy muon beam combined with an intense gamma source allowing to simulate the background expected at HL-LHC . The performance of RPCs was studied at different gamma rates in a presence of muon beam by measuring efficiency, streamer probability, rate capability, induced charge and cluster size. The studies are being carried on by operating RPCs under gas recirculation with the selected gas mixture and exposed to the intense gamma radiation of GIF++ for evaluating possible long-term aging effects, gas damage due to radiation and compatibility of LHC gas system with new gases.

Gas R&D on gas recirculation and recuperation for the Resistive Plate Chamber detectors

Resistive Plate Chamber (RPC) detectors at the Large Hadron Collider (LHC) experiments are operated with a gas mixture containing C2H2F4 (R134a) and SF6. These gases are used because they allow to achieve specific detector performance. However, due to their high Global Warming Potential (GWP) they are currently subject to a phase down policy that started to affect the market with price increase and it may cause a decrease in their long-term availability. To minimize these risks, four different strategies have been identified for optimizing their usage. As immediate actions and where possible, during the LHC Long Shutdown 2 (LS2) the RPC gas systems will be upgraded to cope with new detector requirements and, in parallel, extensive campaigns for fixing leaks at detector level will be performed. Since R134a dominates the greenhouse gas consumption, the development of a R134a gas recuperation plant is going to be the next step and it might have an important positive impact on the overall optimization process. Recently a prototype system was tested with encouraging results. For future long-term detector operation, R&D studies are ongoing for finding “green” alternatives to the currently used gases. Unfortunately, new gases developed by industry as refrigerant fluids are not behaving as the R134a in particle detectors which makes the replacement for present experiments difficult. The last strategy consists in the possibility of using industrial plants for the disposal of greenhouse gases by decomposition in harmless compounds. This solution avoids the emission in the atmosphere but it does not optimize the gas usage and problems like gas availability and price for detector operation might become the challenge in the coming years due to the greenhouse phase down policy.

Effect of the Primary Air Ratio on Combustion of the Fuel Preheated in a Self-preheating Burner

ABSTRACT The experiments with λ p (ratio of the primary air flow to the theoretical combustion air) were launched on a bench-scale coal preheating combustion test rig. The effect of λ p on operating characteristics of the self-preheating burner was investigated in detail. Besides, the combustion characteristics of the high temperature preheated fuel and NOX emission were discussed. The results showed that with increasing λ p, the temperatures in the self-preheating burner climbed and the main compositions of the coal gas (excluding N2) were CO, H2, CO2, and CH4. When λ p is 0.35 and 0.43, the conversion ratios of carbon, fixed carbon and volatile matter were both above 50%. The high combustion temperatures at the preheating fuel nozzle exit were caused by the rapid ignition of the coal gas and the recirculation of the high temperature flue gas. The unburned carbon content of the fly ash was slightly increased with the increase of λ p and the combustion efficiencies were all higher than 98%. No significant HCN was detected during the experiments, indicating that NH3 was the major precursor of NOX. On one hand, with the increase of λ p, more fuel-N was released during the preheating process, resulting in more fuel-N conversion to N2 and NH3. On the other hand, increasing λ p could elevate the combustion temperatures in the self-preheating burner, which would affect the heterogeneous reduction of NOX on the char surface in the DFC. Therefore, the exit NOX emission was the lowest for λ p was 0.35.

Повышение энергоэффективности и экологической безопасности судовых паровых котлов

The article focuses on the methods of reducing nitrogen oxide emissions that are important to consider and apply in operation of ship boilers and thermal power plants, along with other activities aimed to protect the environment. Nitrogen oxide emissions can be restrained by using the technological (primary, in-process) operations. Flue gas recirculation is the most popular method of restraining nitrogen oxide emissions in oil-gas boilers, reducing the temperature and nitrogen oxide concentration in flue gases. Besides affecting the environment, the combustion products recirculation greatly lowers the technical and economic performance of the boiler by decreasing its performance that is why using the method remains limited. There has been described the scheme of flue gas recirculation in the ship auxiliary boilers that ensures reduction of nitrogen oxide emissions and increase in efficiency of boiler furnace. It has been proposed to combine steam and carbon dioxide fuel conversion with power combustion and thermochemical heat regeneration. Thermodynamic feasibility of combustion product recirculation in ship auxiliary boiler has been given. Using the power and stoichiometric analyses of reference liquid fuel combustion, the possibility of fuel conversion has been illustrated for the case when both fuel and recirculation gases are supplied into reburning zone of the furnace. The calculations determine air oxygen ratio for reburning and oxidative zones, flue gas recirculation factor and furnace efficiency change at thermochemical heat regeneration. The study results are proposed to use in non-stoichiometric and staged fuel combustion.

Readily Constructed Glass Piston Pump for Gas Recirculation.

The recirculation of gases in a sealed reactor system is a broadly useful method in catalytic and electrocatalytic studies. It is especially relevant when a reactant gas reacts slowly with respect to residence time in a catalytic reaction zone and when mass transport control through the reaction zone is necessary. This need is well illustrated in the field of electrocatalytic N2 reduction, where the need for recirculation of 15N2 has recently become more apparent. Herein, we describe the design, fabrication, use, and specifications of a lubricant-free, readily constructed recirculating pump fabricated entirely from glass and inert polymer (poly(ether ether ketone) (PEEK), poly(tetrafluoroethylene) (PTFE)) components. Using these glass and polymer components ensures chemical compatibility between the piston pump and a wide range of chemical environments, including strongly acidic and organic electrolytes often employed in studies of electrocatalytic N2 reduction. The lubricant-free nature of the pump and the presence of components made exclusively of glass and PEEK/PTFE mitigate contamination concerns associated with recirculating gases saturated with corrosive or reactive vapors for extended periods. The gas recirculating glass pump achieved a flow rate of >500 mL min–1 N2 against atmospheric pressure at 15 W peak power input and >100 mL min–1 N2 against a differential pressure of +6 in. H2O (∼15 mbar) at 10 W peak power input.

Impact of Reaction Chamber Geometry on the Particle-Residence-Time in Flame Spray Process

Production of functional nanoparticles and nanoscaled powders is a key process in several recent industrial applications. In this work, the flame process in nanoparticle production in sprays is analyzed. Specific focus is on the flow behavior, the temperature distribution, and the residence-time of particles in the hot (reactive) regions in a flame spray reactor that are analyzed by numerical simulations using computational fluid dynamics techniques. The role of the co-flowing gas rate provided to the flame spray reactor and its effects on the spray behavior, flame morphology, and particle properties in an enclosed atmosphere is highlighted. The influence of different operational conditions on the reactor temperature and temperature-residence-time distribution of gas and particles is investigated. It is found that providing a reduced co-flowing gas rate to the flame spray reactor favors the recirculation of hot gas, and, consequently increases the residence-time of particles in the high-temperature regions. The numerical results of particle diameter and gas-phase temperature are compared to some existing experimental data.

Performance studies of RPC detectors with new environmentally friendly gas mixtures in presence of LHC-like radiation background

RPC detectors are widely used at the CERN LHC experiments as muon trigger thanks to their excellent time resolution. They are operated with a Freon-based gas mixture containing C2H2F4 as well as some amount of SF6. Both C2H2F4 and SF6 are greenhouse gases with a very high global warming potential. The search of new environmentally friendly gas mixtures is necessary to reduce greenhouse gas emissions and costs as well as to optimize the RPC performance. Several recently available gases with low global warming potential have been identified as possible replacements for C2H2F4 and SF6. More than 60 environmentally friendly gas mixtures have been investigated on 2 mm single-gap RPCs. The RPC detectors have been tested in laboratory conditions and at the CERN Gamma Irradiation Facility, which provides a high energy muon beam combined with an intense gamma source allowing to simulate the background expected at HL-LHC . The performance of RPCs were studied at different gamma rates with the new environmentally friendly gases by measuring efficiency, streamer probability, rate capability, induced charge, cluster size and time resolution. To finalize the studies, the RPCs are now operated under gas recirculation with the selected new gas mixture and exposed to the intense gamma radiation of GIF++ for evaluating possible long-term aging effects, gas damage due to radiation and compatibility of LHC gas system with new gases.