Flue Gas Duct Research Articles

CO2 Measurement under Different Pressure and Vibration Conditions Using Tunable Diode Laser Absorption Spectroscopy

The greenhouse effect resulting from fuel combustion has drawn growing attention, and CO2 emissions from fossil fuel power stations are one of the main sources of greenhouse gases. It is crucial to monitor the concentration of CO2 in the flue gas ducts of these stations. However, pressure and vibration caused by the combustion of boilers make the measurement of CO2 in flue gas ducts extremely challenging. In this study, tunable diode laser absorption spectroscopy (TDLAS) combined with Wave Modulation Spectroscopy (WMS) was employed to measure the concentration of CO2 under different pressure and vibration conditions in the laboratory. The absorption line of CO2 at the wavenumber 6357.38 cm−1 was recorded under varying pressure conditions ranging from 0 to 1.4 atm, acceleration conditions ranging from 0 to 7.7 m/s2, and a combination of both. Firstly, a negative linear correlation was found between the pressure and the amplitude of the second harmonic, with a maximum relative error of 4.645% observed at a pressure of 1.4 atm. Secondly, the maximum acceleration that the system can withstand was determined to be 7.3 m/s2, as it was not possible to provide a sufficiently low fitting error at higher accelerations. For the combined effects of the pressure and vibration, a dramatic increase in the relative error of amplitude can be observed within the acceleration range of 5.0~6.0 m/s2 while under the pressure conditions of 0.6 atm, 1.0 atm, and 1.4 atm. Moreover, the maximum endurable acceleration decreases with the increase in pressure, which infers that effective measurements can be achieved when the acceleration is below 5 m/s2 within the pressure range of 0~1.4 atm. This suggests that TDLAS combined with WMS possesses a potential for online measuring of CO2 concentrations in flue gas ducts within a certain acceleration range. This work can provide some insights for stable gas detection using TDLAS under varied pressure and vibration conditions.

Potential of V2O5-WO3/TiO2 catalyst usage as the secondary measure for household heating combustion unit

The active substance used in oxidation honeycomb catalysts determined for real flue gas purification usually consists of precious metals such as platinum or palladium, while the most common is the mixture of the two mentioned elements, however high prices and limited availability of these elements encourages producers for the search for new, equally or better effective alternatives. In this study V2O5-WO3/TiO2 honeycomb catalyst was tested during the combustion test with commonly sold manually loaded stove. The catalyst was installed in the flue gas duct at the stove outlet. The experimental comparison of the flue gas composition at the catalyst inlet and at the catalyst outlet was performed. Flue gas sampling took place for whole combustion periods. Relatively high conversion rates by catalyst of CO (up to 87.1%), C3H8 (up to 61.3%) and TSP (up to 17.7%) were reached, which meant that the limit values of Commission regulation for mentioned kind of equipment were met during four, not only one period (in case of non-use of the catalyst). The V2O5-WO3/TiO2 catalyst has a great potential as the secondary emission control device for achieving low mass concentration of the certain pollutants in the flue gas.

Effects of co-combustion Fe-rich mediocre ash coal on slag deposition of Ca-rich Zhundong coal in a 0.4 MW pilot-scale facility

A type of coal with low calorific value and high ash content, locally known as mediocre ash coal (MAC), has been discovered in the interlayer of stratified coals in Jiang Jun Temple area Zhundong district, Xinjiang, China. In order to investigate slag deposition on the convective heating surface during co-combustion of MAC and Wucaiwan Ca-rich Zhundong Coal (WCW), a 0.4 MW pilot-scale facility, with tube panels #1 and #2 located in horizontal flue gas ducts, was constructed. The tube panels were designed to simulate the superheater and reheater of the Π-type boiler. FactSage was utilized to simulate the material balance, whereas the classic models were employed to calculate the slag viscosity. Combustion tests were conducted while maintaining flue gas temperatures (FGT) of 1050∼1100 °C and 900∼950 °C at tube panels #1 and #2, respectively, which were consistent with those observed during sole combustion of WCW. The slags collected from tube panels were analyzed by X-ray fluorescence, X-ray diffraction and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Detector. Furthermore, Computer-Controlled Scanning Electron Microscopy analysis was used to obtain a quantitative characterization of the symbiotic relationship among mineral elements. The study of co-combustion MAC led to the following conclusions: The liquid phase ratio of slag decreased by 44% compared to sole combustion of WCW at 1100 °C. The viscosity was higher than that of sole combustion of WCW from 900 to 1650 °C. Compared to the sole combustion of WCW, the average S, Ca, and Na contents in the slag obtained on the two tube panels decreased by more than 85%, 40%, and 43.5% respectively. Sulfate formation in the slag on the tube panel was significantly reduced at medium to low FGT, and no Na2SO4 and CaSO4 compounds could be detected in the slag. The interaction between Fe-bearing minerals and Si- and Al-bearing minerals during combustion was evidently stronger than that between Ca-bearing minerals and Si- and Al-bearing minerals during combustion. The interaction of Fe with Ca/Na during medium to high FGTs led to a decrease in Si/ Al consumption, thereby increasing their availability for reacting with Ca/Na at medium to low FGTs. As a result, the formation of Na2SO4 and CaSO4 was inhibited.

A novel approach to the dry desulfurization process by means of sodium bicarbonate: A full-scale study on SO2 emission and geochemistry of fly ash

The application of Dry Sorbent Injection (DSI) desulfurization with sodium bicarbonate was investigated to reduce SO2 emission from power sector. The sorbent was injected directly into the combustion chamber of the 29 MWth grate boiler, into a non-standard area of high temperature (approximately 700 °C), while generally the DSI method is carried out in the flue gas duct with a temperature below 250 °C. Unique nozzle design for injecting powdery sorbents was implemented and two stoichiometric ratios were tested: NSR = 1.1 and NSR = 3.0. The reduction of SO2 from a base level of 1580 mg SO2/Nm3 to 301 mg SO2/Nm3 at 6% O2 was achieved, resulting in a process efficiency of 81%. The chemical properties of fly ash were determined in terms of its safe storage and potential use according to the principles of the circular economy. Ash formed during the desulfurization process shows a different chemical composition than the reference sample. A significant increase in the concentrations of the following components and parameters was indicated: S, Na, Zn, Cu, As, Mo, Pb, loss of ignition (LOI) and total organic carbon (TOC). The change in chemical composition led to an increase of total dissolved matter (TDS) in water leachate as well as sulphates, chlorides, fluorides, As, PB, Cu and Zn concentrations.

Thermofluidic characteristics for a novel complementary adsorption-absorption post-combustion partial CO2 capture system

A novel complementary adsorption-absorption post-combustion partial CO2 capture strategy was proposed to decrease the energy penalty by integrating the rotary adsorption wheel with traditional chemical absorption process. The finite volume method is used for modeling the adsorption process, and the absorption process is simulated based on the rate-based model and the double-film theory. The techno-economic analyses of the novel complementary system were performed. In the adsorption part, the CO2 concentration of the flue gas can be effectively improved from 5.0%, 10.0% and 15.0% as much as to 17.3%, 27.0% and 33.7%, respectively. By adjusting the flue gas ducts of the adsorption wheel, the flue gas can be concentrated to a CO2 concentration making the absorption process work economically. The performance of the rotary adsorption wheel influenced by different geometrical and operational parameters were investigated. The energy penalty of the chemical absorption part can be significantly decreased. The major equipment cost was dramatically decreased by 48.6%, and the levelized cost of CO2 capture was decreased by 32.3%, when the CO2 concentration in the flue gas was increased from 5% to 20%. In addition, the acceptable investment of the rotary adsorption wheel has been estimated. The smallest acceptable capital cost of rotary adsorption wheel for coal-fired boiler corresponding to one payback year is 3.72 M$.

Experimental and Numerical Study on the Fluid Dynamics and Exergetic Performance of the Heat Exchanger in an Industrial Corn Drying System

The heat exchanger is the key component of an industrial drying system. The present work introduced a novel tube heat exchanger into a corn drying system. To fully understand the heat exchange process and optimize the heat exchange performance of the heat exchanger, numerical simulation, exergy analysis and economic analysis methodologies were adopted to analyze the comprehensive performance of the heat exchanger. The fluid dynamics as well as the exergy performance of the heat exchanger under different flue gas velocities (3, 5 and 7m/s) and different ambient air relative humidities (80%, 85% and 90%) were investigated. The results showed that there are two strong turbulences causing the huge pressure drop at the last two stages of the flue gas duct, while there are two insufficient heat exchange areas on both sides of the heat exchanger; thus, the corresponding improvement recommendations were proposed in the present work. The values of the Re and Nu were found to vary in the range of 1256.275–2210.554 and 21.337–32.415, respectively. The average heat transfer coefficients were ascertained to be above 8.274 kW·m−2·K−1, while the pressure drop of the ambient air was ascertained to be under 16.138 Pa. Moreover, the exergy analysis revealed that the heat exchanger experiences sustainable development (SI < 2), and the exergy efficiency is above 11.461%. The main results may provide some references for further optimizing the heat transfer performance of the heat exchanger.

Investigation of velocity distribution in channels and chambers of the electrostatic precipitator at TPP Nikola Tesla Unit A1

To achieve the optimum dust removal performance of an electrostatic precipitator, the flue gas should be distributed uniformly over its vertical cross-section. The flow in the upstream flue gas ducts has a significant influence on the downstream gas distribution in the chamber of the precipitator. This paper presents the results of homogeneity assessment of velocity distribution in the ducts and vertical cross-sections of the electrostatic precipitator of Unit A1 at the Nikola Tesla thermal power plant in Obrenovac. The measurements confirmed that the reconstruction of the vertical chamber at the front of the precipitator, which was carried out during the overhaul in 2020, effectively solved the problem of the original asymmetric arrangement of the vertical flue gas ducts. Nevertheless, the analysis revealed poor homogeneity of the flow field through the chambers. Therefore, additional measures must be taken to increase the dust removal efficiency of the precipitator.

Multifaceted Analysis of Landfill Gas Use for Energy Purposes

This paper assesses the use of gas from a landfill located in Kiełcz for energy purposes, considering energy, environmental and socioeconomic aspects. The literature review contains information on waste management methods in various regions of the world and the legal acts regulating them. The reference was also made to the methods of degassing landfills and the methods of reducing pollutants from this process. The research methodology describes, among other things, the method of measuring exhaust gas quality and temperature or gas composition. This section also presents the catalyst that was used as a reducer of flue gas emissions. The use of a catalyst in the flue gas duct allowed for the reduction in CO emissions by 85%, NOX by 53%, SO2 by 95%, and PM by 82%. For the socio-economic analysis, formulas and quantities were given that allow for the parameterization of profits. Three leading indicators were selected, i.e., the impact of the energy produced on the producer, the reduction in greenhouse gases, and the responsibility for the product. The section of results graphically presents the efficiency of using the catalyst. This part also contains a summary table of the socioeconomic analysis on the basis of which the social profit index SROI was determined, which amounted to 7.57. This analysis may be helpful for landfill managers/owners who may consider the potential commercial use of landfill gas for energy purposes, as well as for governments, which, amid the current global fuel crisis, can benefit from this analysis and include the use of landfill gas in their energy transition strategies.

Mathematical model of a power boiler operation under rapid thermal load changes

Due to the current need for coal-fired power units to cooperate with renewable energy sources, they should be characterized by a high flexibility of operation. An in-house mathematical model of a natural circulation power boiler was developed to analyse whether such cooperation is possible. A new method to simulate the heating of several surfaces located parallel in one flue gas duct is proposed. The correctness of the results obtained using the developed model was verified experimentally. A test was performed in a fossil fuel-fired power plant involving a rapid increase in the steam mass flow rate at the boiler outlet. The model verification consisted of comparing the measured and computed temperature and mass flow rates of the fluids at several boiler locations. To estimate the accuracy of the results obtained using the developed model, relative errors and root-mean-square errors were calculated. The small values of these errors indicate the correctness of the results obtained with in-house developed computation methods. The mathematical models presented in this study can be used in power unit simulators. In particular, they can be applied to create in-house models of other power boilers intended for cooperation with renewable energy sources under fast-changing loads.

Assessment of the Applicability of Ca-Based Sorbents for Arsenic Removal from Flue Gases

Arsenic is one of the most hazardous compounds released into the atmosphere from coal conversion processes. One possibility to limit its amount in the flue gas is to inject dusty sorbents directly into the flue gas duct. The aim of this study was to analyze the removal efficiency of gaseous forms of As on selected Ca-based materials, with a focus on sorbents based on waste materials versus traditionally used sorbents. Coal combustion byproducts, waste (such as filter cake, fly ash, and gypsum), sedimentary rocks (dolomite and limestone), and chemical reagents like Ca(OH)2, Fe2O3, and Mg(OH)2 were examined in the quartz retort in a heated furnace where the temperature of the sorbent bed was 120 °C. The source of Asgas was the direct combustion of coal at 1200 °C. Among the tested materials, calcined limestone, calcined dolomite, Fe2O3, Mg(OH)2, and Ca(OH)2 were the most effective (removal efficiency: 85–98%). In the case of waste materials, the highest efficiency was obtained for filter cakes. However, because of their high content of toxic elements, they could be used as sorbent only after thermal preparation at 250 °C. Furthermore, the analyses showed that an increased Ca concentration in the sorbent may promote Asgas adsorption more than the development of the sorption surface area.

Comparison of Selected Technologies to Improve the Quality of Exhaust Gases from Landfill Gas Combustion

This paper presents the results of research on exhaust gases from landfill gas combustion. The measurements were carried out in a reclaimed landfill in Kiełcz (a passive degassing system based on gas flare). The research concerned the effects of selected exhaust gas purification technologies (platinum catalyzer on a ceramic carrier, molecular sieve, copper(II) oxide) for the quality of exhaust gases, and their particulate matter content. This paper aims to indicate which catalytic systems are most suitable for this gas type and their most efficient positioning in the flue gas duct. Due to increasingly stringent emission standards, the outcomes presented in this article could be helpful for landfill owners who wish to avoid paying fines for not complying with applicable limits. The measurements were carried out using a flue gas analyser, a particulate matter analyser fitted with a probe, and four thermocouples connected with the data recorder. The research outcomes determined the percentage reduction of pollutant emissions into the atmosphere (CO, NOx, and particulate matter) using catalysts. The potential benefits of using catalysts in landfill gas combustion systems due to their operating temperature ranges are discussed.

Modeling and Optimization of Surface Roughness of Epoxy/Nanoparticles Composite Coating

In power plants, flue gases can cause severe corrosion damage in metallic parts such as flue ducts, heat exchangers, and boilers. Coating is an effective technique to prevent this damage. A robust fuzzy model of the surface roughness (Ra and Rz) of flue gas ducts coated by protective composite coating from epoxy and nanoparticles was constructed based on the experimental dataset. The proposed model consists of four nanoparticles (ZnO, ZrO2, SiO2, and NiO) with 2%, 4%, 6%, and 8%, respectively. Response surface methodology (RSM) was used to optimize the process parameters and identify the optimal conditions for minimum surface roughness of this coated duct. To prove the superiority of the proposed fuzzy model, the model results were compared with those obtained by ANOVA, with the coefficient of determination and the root-mean-square error (RMSE) used as metrics. For Ra, for the first output response, using ANOVA, the coefficient-of-determination values were 0.9137 and 0.4037, respectively, for training and prediction. Similarly, for Rz, the second output response, the coefficient-of-determination results were 0.9695 and 0.4037, respectively, for training and prediction. In the fuzzy modeling of Ra, for the first output response, the RMSE values were 0.0 and 0.1455, respectively, for training and testing. The values for the coefficient of determination were 1.00 and 0.9807, respectively, for training and testing. The results prove the superiority of fuzzy modeling. For modeling the second output response Rz, the RMSE values were 0.0 and 0.0421, respectively, for training and testing, and the coefficient-of-determination values were 1.00 and 0.9959, respectively, for training and testing.

Numerical Simulations in SCR systems with Emphasis on Uniform Flow at the Catalyst Inlet

Selective Catalytic Reduction (SCR) is one of the most widely used technologies for reducing emissions from diesel engines, which are widely used in the energy world. This technology is very complex, and it is not currently possible to address all aspects of it comprehensively. This study focuses on trying to improve the distribution of the exhaust stream at the catalyst inlet using models which represent the most common geometric distributions. Four types of geometries are selected, complemented by a fifth design, which is used as a reference, to find the maximum achievable values of the parameters under study. In this case, mainly the uniformity index is addressed, which indicates how uniformly the selected variable is distributed over the particular area. The study presents possible modifications of the flue gas duct which will be generally applied.

Influence of flue gas parameters on conversion rates of honeycomb catalysts

• The most important parameter was the flue gas temperature at the catalyst inlet. • Average conversion rate of carbon monoxide was 69% in case of catalyst Cat A. • Average conversion rate of carbon monoxide was 96% in case of catalyst Cat B. • There was no dependence between C 3 H 8 conversion rate and observed parameters. • Tested manually operated stove is suitable for retrofit by catalysts installation. In this study, two honeycomb catalysts with palladium and platina-palladium as active elements were used for an oxidation of products of incomplete combustion such as carbon monoxide (CO) and propane (C 3 H 8 ) contained in flue gas produced by a small-scale stove. Catalysts were installed into the flue gas duct right behind the flue gas outlet of the wood log, and pellet stove. During the tests, the conversion rates of unburned pollutants were observed according to volume fraction of oxygen in the flue gas, space velocity of flue gas, temperature of flue gas at the catalysts inlet, and mass concentration of oxidized pollutants at the catalysts inlet. The CO conversion rates ranged between 37% and 95.4% (69% in average) in case of Cat A and 51.4% and 99.9% (96% in average) in case of Cat B. In terms of C 3 H 8 conversion rate, Cat B proved higher effectiveness (25% in average), than Cat A (4% in average). The most significant parameters were determined. The significant influence of combustion phase on C 3 H 8 conversion rate was observed in case of manually loaded stove.

Proposal Of Simplified Way of Applying Wind Load on Circular Cross-Section

Wind action on circular cross section was described in many publications. It finds an application for flue gas ducts, pipelines, silo or chimneys. This study concentrate on elements with diameter greater than 1m. There are well recognized analytical solutions of static calculation with uses Fourier-series for wind distribution. Although during last 10 years numerical methods of solving problems get more popular, especially among young engineers. For surface structures ability of analytical finding internal forces disappears, and Finish Element Method substitutes analytical calculation. Modelling of wind load in FEM programs cause several problems. Using wind load distribution proposed in Eurocode 1-4, or from laboratory test, it is usually necessary to divide circular cross-section into 32 up to 72 rectangular elements. Applying load in that way is the most accurate method to imitate wind load in FE model. From the other hand that take much time, and requires preparing data about distribution before modelling. Applying wind on complicated model, with many independent parts of piping, for at least 2 load cases cause faults and slows down work. This paper shows and compares a few proposal wind load models for numerical calculation. Those models were built to obtain accurate internal forces in compare to Eurocode procedure. Proposed models offers simplification of Geometry in numerical model, and saves of time. It also helps to make FE mesh become independent from structural nodes, lines or divisions. This paper concern on one case of one Reynolds number, with refers to 2m wide cylinder, wind velocity of 22m/s and surface roughness of steel plate – 0,05 mm. This paper compares different wind load distributions, in terms of required number of division of model, time consuming, precision of results. Author selected one proposal load distribution, with give equivalent internal forces as wind load distribution obtained from Wind Flow simulation (for example CFD method). Proposed model is useful for structural engineers and statics in offer stage of project. With some safety factor it can be also used as wind load as case for detailing cylindrical structures.

Numerical Analysis on the Flue Gas Temperature Maintenance System of a Solid Fuel-Fired Boiler Operating at Minimum Loads

Currently, energy policy is associated with the increase in the share of renewable sources in systemic energy production. Due to this trend, coal-fired power units must increase their work flexibility. Adapting a coal power plant to work with a lower load often causes the issue of maintaining the temperature before the selective catalytic reduction (SCR) installation at a sufficiently high level. This paper presents a CFD analysis of the mixing area of two flue gas streams before the SCR installation with various methods for mixing flue gas streams. The novelty of the work is mixing the flue gas streams of different temperatures using a flap shape developed by the authors. A series of numerical simulations were performed to develop the location and method of introducing the higher temperature gas, obtaining a uniform distribution of the exhaust gas temperature. The simulation scheme was applied to a series of geometrical modifications of the boundary conditions. The tested solution using only a single, straight flap in the flue gas duct allows the amplitude to be reduced from 298 K to 144 K. As a result of the research, a mixing flap design was developed to reduce the initial temperature amplitude of the flue gas streams from 298 K to 43 K.

Improving the thermal efficiency of balanced flue gas space heaters currently marketed in Argentina

The most widely used home heating appliances in Argentina are the balanced flue gas space heaters. The reasons for this choice may be found in their affordable cost and in the comfortable and secure indoor environment generated (i.e., indoor air is not employed for combustion while flue gas is discharged outside). However, the units that are currently marketed have an important disadvantage: their relatively low thermal efficiency. Measurements made in our laboratory for a balanced flue gas space heater with independent inlet (for the fresh air) and outlet (for the flue gas) ducts, yielded values of around 73% for the maximum power (2.9 kW), while for the minimum power (1 kW) are reduced to 61%. Those values are directly related to the outlet temperatures of the flue gas stream of about 400 °C and 240 °C for maximum and minimum powers, respectively. In this context, it is of major interest to develop and implement alternatives to improve the thermal efficiency of such type of devices.In a previous contribution we proposed to employ a heat exchanger (designed ad-hoc) to take advantage of the relatively high enthalpy of the flue gas to preheat the fresh inlet air. This alternative was implemented in a balanced flue gas heater and encouraging results were reached, as the discharge temperature of the flue gas stream could be considerable reduced, but certain limitations arose, which are revisited in this article.The aim of this contribution is to present the advances in the design and manufacture of a new heat exchanger applicable to a different type of balanced flue gas heaters. The results obtained in the test-runs are reported and analyzed. It is anticipated that a remarkable improvement in the thermal efficiency was achieved.

Operational tests of an electrostatic precipitator reducing low dust Indexed by: emission from solid fuels combustion

The article presents the continuation of the research aimed at designing, manufacturing and selecting the operating parameters of the electrostatic precipitator for household applications. The tests were carried out in the laboratory and real conditions. The object of the research was a pre-production prototype of the electrostatic precipitator installed in the flue gas duct of a single-family building. The source of exhaust gases was a coal-fired, low-temperature water heating boiler with a nominal power of 21 kW (old generation boiler-year of production: 2007). The obtained results showed that the adopted design of the electrostatic precipitator enables the reduction of dust emissions generated in the combustion of solid fuels in households at relatively low operating costs.

Mechanical hazards to stack coatings

The use of a wet stack requires protective coatings to prevent corrosion of the inner surface of flue gas ducts. The corrosion may arise in result of flue gas cooling below the dew point as well as in presence of hygroscopic and deliquescent salts. Different technologies are used to serve this purpose, such as composite coatings. This paper presents the mechanical and thermal resistance testing of the ARC 982 composite coating. The testing was comprised of:•assessment of specimen bending at a specific angle in terms of the occurrence of coating exfoliation,•assessment of the probability of metal exposure due to the impact of tools on the coating,•assessment of the effect of welding in the area without the composite on the state of the coating.The results of the performed tests prove that both bending (even at a small angle) and a hammer impact may lead to composite coating cracking and exfoliation from the metal plate. They also prove that if coated metal plates are welded in some conditions, the allowable temperature for the ARC 982 material may be exceeded.

Reduction of mercury emissions from combustion processes using electrostatic precipitators

The article presents the results of laboratory and industrial tests on the reduction of mercury emission from coal combustion in power boilers. In laboratory conditions, the influence of the quantity of unburned carbon (UBC) in fly ash on the collection efficiency has been studied. The obtained results confirm that the higher content of unburned carbon in fly ash improves its ability to accumulate Hg and promotes the reduction of mercury emission downstream of the electrostatic precipitator by capture of particulate-bound mercury - Hg(p). In industrial tests, the possibility to add selected additives to oxidize the metallic mercury has been studied. The key feature of this solution is the oxidation of metallic mercury by injecting dedicated oxidizing additives into the flue gas duct upstream the electrostatic precipitator (ESP), and using fly ash as an adsorbent for mercury compounds. The use of the proposed solutions can contribute to the reduction of mercury emission. In some cases, it can ensure compliance with regulatory requirements of mercury concentrations in the flue gas without the need to build expensive mercury control installations.