Exit Gas Research Articles

Co-firing characteristics of wood pellets on pulverized coal power plant

Co-firing testing of the wood pellets was carried out in Pulverized Coal Boiler type tangential firing with a capacity of 315 MWe to determine the effects on the performance, emission, and characteristics of the operational boiler parameters such as mill outlet temperature (MOT) and furnace exit gas temperature (FEGT). Fuel was mixed on stockpile with a fuel composition of 5 % wood pellets and 95 % coal. Fuel was initially filled in four bunkers for each mill operated. The co-firing testing was carried in six hours and the data was collected for four hours after the stabilization period. To observe the further impact on the performance, emission and characteristics of operational boiler parameters, two different fuel (100 % coal fuel and 5 % wood pellet – 95 % coal fuel) were set up through the boiler. The result shows that co-firing by 5 % of wood pellets contributed to the decreasing FEGT by 15 °C from 1,192 °C to 1,177 °C equal to 1.27 % lower than the existing condition. The mill outlet temperature is relatively the same for two types of fuel with mill current slightly increasing by 0.70 Ampere. Emissions of SOx increased by range from 8.22 % to 20.51 %. NOx content in flue gas on the air heater inlet side is almost the same of 310 mg/Nm3 and only an increase of 3.62 % on the air heater outlet side. This test also affected specific fuel consumption which has increased by 4.40 % from 0.556 kg/kWh to 0.580 kg/kWh.

Performance prediction of the tangentially fired pulverised-Coal boiler furnace using a mathematical model and its validation

ABSTRACT A simple thermodynamic model is developed for performance prediction for a tangentially fired pulverized-coal boiler furnace. For this purpose, the furnace is sliced into number of zones of rectangular parallelepiped. These zones are further divided into heat release zones and non-heat release zones. The major sub-routines of the program include framing equations for the definition of the heat release zones, a reasonably approximate flow model to simulate tangential firing, radiation formulation and equations for the calculation of emissivity of CO2 and H2O. A few of the inputs required for this model have been obtained from offline-CFD simulations. The solution for the model’s equations is obtained using the Newton Raphson method. The outputs of the program include the variation of the heat flux along with the height of the boiler furnace and furnace exit gas temperature (FEGT). The influence of operating conditions on the furnace in terms of its performance is also studied. The FEGT predicted using the mathematical model is in fairly good agreement with the site measured data. The model can be used as an effective tool by powerplant operators to optimize the performance of the boiler furnace.

Modified coke breeze distribution in iron ore sintering - a novel technique of reducing energy consumption and improving quality

In normal sintering of iron ore, there is a wide difference in temperature of the sinter bed between top and bottom; i.e. the flame front temperature of the sinter bed gradually increases towards the bottom because the lower part gets longer time for drying and preheating by exit gas. Therefore, the top part may have insufficient fusion and the bottom is excessively fused. Thus, sinter quality may become inhomogeneous and the coke breeze requirement becomes higher than the actual thermal requirement. If it is charged in multiple layers; e.g. higher amount of coke at the top and a lower amount of coke at the bottom, heat will be homogeneously distributed and the actual coke requirement would be lower than the existing. However, no study has been done so far on this. Therefore, the current study explores the possibility of reducing energy consumption in iron ore sintering by reducing the coke ratio from top to bottom without deteriorating the sinter property. 12% reduction in coke breeze rate has been found and the sinter quality has been improved by the use of a triple layer of sinter mix with a lower coke rate towards the bottom. Further, when 5-vol% of oxygen has been enriched in suction gas along with using a triple layer of sinter mix, up to an 18-wt% reduction in coke breeze has been found.

Методы определения эффективной высоты трубы при учете рассеивания выбросов в рабочей зоне производств

Introduction. In order to determine the height of the rise of the polluted substances above the source of the pollution, it is important to know the exact distribution of the gas plume. Problem Statement. The determination of the dust concentration in the working area of asphalt concrete plants should take into account the assessment of the concentration of harmful substances in the working area of the asphalt concrete plant. The study is the analysis of methods for determining the effective height of the pipe, taking into account the dispersion of emissions in the working area. Theoretical Part. The paper considers the dependences of the estimation of the initial rise of the gas jet, proposed by Berland, Holland, Briggs, and the specialists of the Tennessee Valley. The value of the initial rise of the impurity jet depends on the moment of the amount of gas movement, the thermal power of the wind speed carrying the jet, and the conditions of thermophoresis. The paper presents the comparative graphs of the calculation of the level of the initial rise of the gas jet at different rates of gas exit from the pipe and constant wind speed. Conclusion. The method of taking into account the initial rise of the heated gas jet gives us better convergence in the calculations of the maximum surface concentrations of harmful substances and in the estimation of distances to them.

Contributions of Boudouard reaction to NO electrocatalytic reduction by Fe-loaded carbon materials in the presence of O2

The effects of solid carbon on NO electrocatalytic reduction in the presence of O2 content, as low as can be found in a gasoline engine, were investigated. Tubular solid-state fuel cells filled with Fe-loaded carbon materials (Fe-loaded activated carbon, Fe-AC, and Fe-loaded carbon black, Fe-BC) were fabricated for electrochemical reduction in the configuration of LSM as the cathode, NiO-YSZ mixed powder as the anode, and YSZ as the electrolyte. A moderate NO removal efficiency of 60% and maximum peak power density of 0.035 W cm−2 were achieved for Fe-AC in the presence of 1% O2, whereas no such performances were detected in the case of AC. Following TGA-MS and in-situ analyses of exit gases from the anodes, it can be concluded that Fe-loaded carbon materials promote CO formation in Boudouard reactions by utilizing excess oxygen transported from the cathode, which is capable of alleviating the impact of oxygen on NO removal while also enhancing electrical performance. The formation of CO contributes to the reduction of both concentration polarization loss and activation polarization loss at both electrodes.

Effect of different turbulence model on prediction of lean blowout limit for micro gas turbine combustor

ABSTRACT This paper aims to present turbulence modelling results of methane/air combustion in a micro gas turbine combustor. Modelling studies were carried out with different turbulence models to evaluate Lean Blowout (LBO) performance on the micro gas turbine combustion chamber by using a commercially available computational fluid dynamics code. Turbulence models implemented in this study are k-epsilon standard, k-epsilon RNG, K-epsilon realisable, k-omega standard, and k-omega SST. A two-dimensional axisymmetric 3 kW swirl stabilised micro gas turbine combustor model was built to investigate the impact of various turbulence models on the prediction of LBO behaviour of the combustor fuelled with methane. Performance evaluation of these models was executed by calculating the average exit gas temperature (AEGT) that have been used for predicting the blowout conditions. Results obtained from this study were validated with experimental results. Numerical results showed that two-equation turbulence models give consistent simulation results with experimental results employing trend and value. Standard k-epsilon was found to give consistent simulation results with experimental data.

Effect of combination of fabric material layers in reducing air pollution

Air pollution is a global issue for many years. However, in developing countries, this is a major concern which is affecting the health of the people. Industrialization, less awareness among people, increased number of vehicles and no major actions taken so far drastically increased the pollution levels in the air. Increase in pollution, in turn, increases the number of airborne diseases. The existing filtration mechanism is complex and costly. This hinders their application in industries. The present work addresses this issue by designing a low cost multi-layered filter system. The critical parameters considered are selection of materials, number of layers and the arrangement of layers of different materials. Selected materials are High-Efficiency Penetration Air (HEPA) fabric, Cotton, fibreglass, nylon, polypropylene and non-woven polyester fabric. The best combination of the arrangement order found is HEPA, Cotton, Fibreglass, Nylon, non-woven polyester and poly-propylene respectively. Experiments are conducted with single layer and combination of the materials with 6, 12 and 18 layers using a specially designed test chamber. The exhaust gas of a two-stroke engine is taken as an input source of pollution. As a single filter, of all the selected materials, fibre glass material shows the highest reduction in CO, HC, CO2 and increase in O2. As the pollution is reduced the O2 percentage is more in the exit gases after filter. Polypropylene shows highest % reduction of Nox. Filter with 6/12layers shows unsteady filtration. Filter with 18 layers shows maximum and steady filtration of the pollutants CO, CO2, HC, NOx; 74.5%, 70.6%, 76.66%, 72.66% respectively.

Catalytic Decomposition of Nitrous Oxide for Use in Hybrid Rocket Motors

In recent years, there has been significantly increased interest in using nitrous oxide as an oxidizer in hybrid rocket motor systems. The attraction of nitrous oxide is its low relative toxicity and high vapor pressure, potentially enabling self-pressurizing systems. Its decomposition is highly exothermic with a large energy barrier, typically requiring high temperature (700°C) to achieve appreciable decomposition rates. One solution is to use a catalyst to enable decomposition at significantly lower temperatures. This Paper uses a commercially available rhodium-based catalyst in a custom test cell to decompose nitrous oxide at temperatures well below the uncatalyzed self-sustaining decomposition temperature. This Paper also demonstrates that decomposition using the tested catalyst is direct to and at all temperature ranges observed and is incomplete with residual present at lower temperatures. Further, this Paper couples our test cell with a counterflow burner to ignite and burn hydroxyl-terminated polybutadiene fuel with the decomposed nitrous oxide and evaluate performance via fuel regression rate at a variety of conditions. The fuel autoignites when the gas exit temperature reaches 750°C, and regression rate is shown to increase with both mass flux and temperature.

Optimization of separated overfire air to reduce NOX emissions under combustion stability for the retrofit of a 500 MW tangentially pulverized coal boiler

Retrofitting of an aging 500 MW tangential coal-fired boiler with high pollutant emissions in South Korea was investigated to achieve low nitrogen oxide (NOX) emissions and high combustion efficiency. This study evaluated and analyzed the combustion and emission characteristics of five arrangements to optimize the position and direction of a separated overfire air (SOFA) installation using a computational fluid dynamics (CFD) simulation. The results show that the air injection of SOFA at the center of the boiler wall causes substantial obstruction of the rising airflow below, causing unstable combustion behavior in the boiler, and increasing the amount of unburned carbon (UBC). However, combining the wall injection with corner SOFA helps reduce the formation of NOX and has the effect of promoting the burnout of UBC. For the direction of the wall injection under combined conditions, a clockwise airflow helps to reduce the formation of NOX with increasing UBC. Otherwise, the counter-clockwise airflow weakens the flow rate of the ascending airflow, increasing the residence time of unburned particles, increasing the coal burnout rate, and increasing the furnace exit gas temperature (FEGT). Among the five SOFA arrangements studies, this study recommends Case 4, which has a clockwise wall SOFA (30%) with corner SOFA (70%). This case has the best performance in terms of combustibility, NOX emission, UBC, and FEGT. The proposed condition was verified through a field test, and the results indicate that NOX emissions decreased from 169 ppm to 57 ppm, the UBC content decreased from 3.64% to 0.7%, and the boiler efficiency increased by 2%.

Modeling of Third Party Access Tariffs and Portfolio Gas Purchases of CCGTs in the Self-Unit Commitment Problem

The structure of the operational costs of gas fired units (GFU) in real power systems is much more complex than what standard unit-commitment (UC) models consider in the state-of-the-art formulations. On the one hand, when a generation company owning several GFUs procures its gas -either totally or partially- at the gas spot market, the final fuel price will depend on the total gas purchases. This fact couples the operation of all the GFUs as it is impossible to build individual cost functions for each generator. On the other hand, as any other gas consumer, the generation company has to pay the gas Third Party Access (TPA) tariffs. The generation company must contract in advance the monthly TPA capacity for each gas exit point and depending on such decision, the final variable cost of the GFUs will be different. This paper states the importance of modeling properly both issues and presents a novel mathematical formulation that can be embedded in a self-UC model. The presented example case highlights the benefits of the proposed formulation.

Waste heat recovery analysis in a vertical riser with air–sand: hydrodynamics and heat transfer

In the current global endeavor of energy conservation, waste heat recovery is a key contributor and deserves more focused attention. Process industries demand high energy inputs and often generate high-temperature exit gases, which can potentially be considered as secondary energy sources. If such waste heat is recovered, considerable savings in the net energy demand is possible. This report, based on this objective, details the outcome of an experimental study conducted in a vertical riser where solid particles, through a co-current contact with hot air, recover the energy content of the gas. Fabricated experimental setup is a prototype of suspension preheater (riser–cyclone combination) used in a modern-day cement industry. Data relevant to hydrodynamic and heat transfer patterns are collected as not much information is available in the literature on these aspects. Empirical correlations for acceleration length and heat transfer coefficient in dimensionless form, are reported and are recommended for not only cement but for diverse other industries, where waste heat recovery is possible.

Waste cooking oil as an efficient solvent for the production of urea precursor ammonium carbamate from carbon dioxide

AbstractCarbon sequestration and utilization are currently gaining attention as they help to reduce the emission of greenhouse gases in the atmosphere. This study explores the possibility of using carbon dioxide as a feedstock for the production of ammonium carbamate, a precursor molecule for urea production. Waste cooking oil was used as the indispensable nonaqueous medium for the formation of pure ammonium carbamate. This makes the process completely ecofriendly and cost‐effective. A continuous process of ammonium carbamate production at 20°C results in 88.86% consumption of carbon dioxide. The highest yield of ammonium carbamate was achieved at an NH3/CO2 ratio of 2.5. A three‐stage setup was also found to increase the yield of ammonium carbamate. The reusability of oil after each cycle was checked and it was found that the formation of the product is comparatively less compared to the previous cycle. Lower yield was observed when the same experiment was carried out with fresh oil (sunflower oil). The exit gas from the process was found to be rich in ammonia that can be further used for the production of struvite, a phosphate fertilizer. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Temperature and CH* measurements and simulations of laminar premixed ethylene jet-wall stagnation flames

New experimental 2D measurements are reported to characterise the flame location, shape and temperature of laminar premixed ethylene jet-wall stagnation flames when the equivalence ratio, exit gas velocity and burner-plate separation distance are varied. Bandpass-filtered optical measurements of the CH* chemiluminescence were used to provide information about the shape and location of the flames. Thin filament pyrometry (TFP) using a 14 µm diameter SiC filament was used to make line measurements of the temperature to reconstruct the full 2D temperature field for the first time in premixed, jet-wall stagnation flames. The comparison of CH* measurements with (intrusive) and without (non-intrusive) the presence of the SiC filament showed that the filament resulted in minimal disturbance of the flame when the filament was placed downstream of the flame front. However, the flame was observed to attach to the filament, resulting in more significant disturbance, when it was placed upstream of the flame front. The flames were simulated using both 1D and 2D models. The 2D simulations were used to provide estimates of the velocity, kinematic viscosity and thermal conductivity required to calculate the gas temperature from the TFP data. The 1D simulations showed excellent agreement with the experimentally observed centreline quantities, but required the strain boundary condition to be fitted in order to match the experimentally observed flame location. The 2D simulations showed excellent agreement without the need for any fitting, and correctly predicted the flame shape, location and temperature as the experimental conditions were varied. A comparison of the set of simulated temperature-residence times along different streamlines showed relatively uniform distributions within each flame. However, the most uniform set of temperature-residence time distributions did not correlate with the flattest flame.

Analysis of an electrochemical compressor stack

Electrochemical compression (ECC) of gases offers advantages over conventional mechanical compression such as higher efficiency and noiseless operation. However, ECC performance can be affected by back-diffusion of the gas across the membrane which is exacerbated at high pressures. Practical systems employ multiple cells in a stack configuration to achieve higher flowrates and gas pressures. Here, we analyze two different stack configurations in order to understand their influence on gas throughput and exit pressure in the presence of back-diffusion. Both the stack configurations examined here are connected electrically in series such that the external voltage applied to the stack terminals is divided equally across each individual cell. On the other hand, the flow of gas within the stack can occur either in parallel or in series. Accordingly, we name these stack configurations Electrically in Series/Flow in Parallel (ESFP), and Electrically in Series/Flow in Series (ESFS). The ESFP configuration can deliver higher gas throughput but at limited pressures, whereas the ESFS configuration can deliver higher pressures but at lower flowrates. A theoretical performance analysis has been conducted for both configurations to gain insights into the compressed gas flux, pressure rise, back diffusion, and efficiency. Furthermore, it is also possible to design a hybrid configuration that combines both parallel and series flow aspects to deliver flow and pressure that is optimized for a given application.

Effect of fluid field on the eco-friendly utilization and recycling of CO2 and dyes in the waterless dyeing

Abstract During the supercritical waterless dyeing, ineffectual separation of dye powders from carbon dioxide often occurs with the gas random motion in the separator, which easily causes gas recontamination in the final separation and recycling period. In this work, a novel separator structure was designed, which greatly helps to enhance the separation efficiency. The flow field characteristics of carbon dioxide in the improved separator were investigated using numerical simulation. Numerical results showed that the regular rotating airflow, quasi-forced vortex and quasi-free vortex of carbon dioxide appear in the separator vessel. The total pressure loss at 200 L/h is 0.98 Pa, which is much smaller than the prototype separator. Furthermore, the enhanced separation efficiency of 9.96 %, 8.82 %, 13.24 % and 13.24 % is obtained for the dye particle sizes from 0.5 µm to 2 μm in the improved separator, which displays a better separation performance. The minimum cycle number which exists at the gas exit is 15654. Separation mechanism of carbon dioxide and dyes in the the supercritical dyeing was also proposed.

Fossil Natural Gas Exit – A New Narrative for the European Energy Transformation towards Decarbonization

This paper discusses the potential role of fossil natural gas (and other gases) in the process of the energy transformation in Europe on its way to complete decarbonization. Mainstream conventional wisdom has it that natural gas, perhaps in combination with other gases, should maintain an important role in the energy mix, first, as a “bridge fuel”, and then through a gradual transition toward decarbonized gases. This is most comprehensively rolled out in three consecutive discussion papers by Jonathan Stern from the Oxford Institute for Energy Studies (2017b, 2017a, 2019). Based on an in- depth assessment of the ambitious climate targets of the EU and the subsequent need for far-reaching decarbonization, as well as on results from energy system modeling, a contrasting result emerges, where the disappearance of fossil natural gas and its corresponding infrastructure is the next logical step of the transformation process in Europe. The lack of an economic perspective for nuclear power and the absence of a plausible deployment of large-scale carbon-dioxide removal technologies (CDR) imply that natural gas has no “sweet spot” any longer in the decarbonization process. In other words: Fossil natural gas is no longer part of the solution to the challenge of climate change, but has become part of the problem. Over the last years, the phasing out of natural gas in Europe has already started, and will continue until its complete phase-out, most likely in the 2040s, i.e. only two decades from now. The decline of natural gas in Europe has implications for the short- and longer-term aggregate and sectoral energy mix, but also for the future of the lumpy infrastructure, that has been developed over the last decades for a growing market. Today, investments into natural gas infrastructure are likely to produce stranded assets, as we show in three concrete cases: The € 10 bn. investment into the North Stream 2 pipeline are not necessary to assure European supply security, nor to make a return on investment; projects of new LNG terminals on the shore of the German North Sea (Brunsbuettel, Stade, Wilhelmshaven) lack a business case; and new natural gas power plants are likely to be unprofitable. The paper proposes to replace the dominant narrative (“natural gas in decarbonizing European energy markets“) with what we consider a more coherent narrative in the context of decarbonization: Fossil natural gas exit.

11CO2 positron emission imaging reveals the in-situ gas concentration profile as function of time and position in opaque gas-solid contacting systems

The in situ analysis of industrial processes, mostly conducted in opaque equipment is difficult. Whereas previously the positron emission technique was successfully applied to study the flow and mixing in gas–solid and liquid–solid systems using radio-active tracer particles, research on imaging a radio- active tracer gas is scarce.The present paper demonstrates the use of a fully three-dimensional (3D) Positron Emission Tomography (PET) in imaging the adsorption of 11CO2 tracer gas, while validating the measurement by conventional exit gas analysis. It will be demonstrated that PET can be used to measure the kinetics of high-pressure CO2 adsorption in situ, including the essential breakthrough and mass transfer zone characteristics. Such high-pressure operation is characteristic of pre-combustion CO2 capturing processes. It is expected that this work will foster further studies of gas–solid systems of adsorption, gas–solid catalysis, gas–solid hydrodynamics, and processes where the gas–solid interaction is of primary importance.

Comparison of the Photoautotrophic Growth Regimens of Chlorella sorokiniana in a Photobioreactor for Enhanced Biomass Productivity

Microalgae have a wide industrial potential because of their high metabolic diversity and plasticity. Selection of optimal cultivation methods is important to optimize multi-purpose microalgal biotechnologies. In this research, Chlorella sorokiniana AM-02 that was isolated from a freshwater lake was cultured under various high photosynthetic photon flux density (PPFD) conditions and CO2 gas levels in standard Bold’s basal medium (BBM). Furthermore, a wide range of nitrate levels (180–1440 mg L−1) was tested on the growth of C. sorokiniana. Microalgae growth, pigment concentration, medium pH, exit gas composition, as well as nitrate, phosphate, and sulfate levels were measured during an experimental period. The preferred high PPFD and optimal CO2 levels were found to be 1000–1400 μmol photons m−2 s−1 and 0.5–2.0% (v/v), respectively. The addition of nitrate ions (up to 1440 mg L−1) to the standard growth medium increased final optical density (OD750), cell count, pigment concentration, and total biomass yield but decreased the initial growth rate at high nitrate levels. Our findings can serve as the basis for a robust photoautotrophic cultivation system to maximize the productivity of large-scale microalgal cultures.

Assessment of Combustion and Gasification Behavior in a Bubbling Fluidized Bed Reactor: A Comparison between Biomass with and without Chemical Additives

During the storage of biogenic materials for energy utilization, destructions by microbial attacks are inevitable. Besides material degradation, self-ignition of wood chip piles also occurs consistently. Treating the feedstock with, for example, mineral additives such as Dolomite can inhibit the microbial destructions, though such treatment may affect the thermochemical conversion of the fuel particles. This study therefore demonstrates the effect of mixing 4 wt % calcium hydroxide with wood chips used as feedstock in a 20 kW (fuel input) bubbling fluidized bed reactor. The reactor consists of a 100 mm (inner diameter) cylindrical column with 1.0 m height, where both gasification and combustion modes can be applied. Six different tests within equivalence ratios of 0.1–1.1 are conducted, and in each run, both fluidization behavior and quality of the product gas at different reaction temperatures (750–900 °C) are analyzed and compared with the results from wood chips of the same particle size but without the additive. The results show that there is no significant difference in the product gas composition, but evidence shows that the chemical additive impacts on the bed pressure drop over the equivalence ratio tested. The gasification window is increased and the energy value of the product gas is higher with a lower hydrogen content. During the combustion, both the exit gas temperature and oxygen concentration are lower, suggesting that additional light molecules such as water vapor are released during the conversion of biomass mixed with additive.

Measuring the rotational temperature and pump intensity in molecular alignment experiments via high harmonic generation.

We demonstrate a method to simultaneously measure the rotational temperature and pump intensity in laser-induced molecular alignment by the time-resolved high harmonic spectroscopy (HHS). It relies on the sensitive dependence of the arising times of the local minima and maxima of the harmonic yields at the rotational revivals on the pump intensity and rotational temperature. By measuring the arising times of these local extrema from the time-resolved harmonic signals, the rotational temperature and pump intensity can be accurately measured. We have demonstrated our method using N2 molecules. The validity and robustness of our method are tested with different harmonic orders and by changing the gas pressures as well as the distance between the gas exit and the optical axis. Moreover, we have also demonstrated the versatility of our method by applying it to CO2 molecules.