Hot Flue Gas Research Articles

Importance of flue gas cooling conditions in particulate matter formation during biomass combustion under conditions pertinent to pulverized fuel applications

Laboratory-scale experiments pertinent to pulverised fuel (PF) combustion are often carried out in drop-tube furnaces (DTFs) at air-fuel equivalence ratios and cooling rate for quenching flue gas that are much higher than those in PF boilers. This paper reports the effect of flue gas cooling conditions on the properties of PM with aerodynamic diameter of <10 µm (PM10) from biomass combustion. This study considers four cooling rates (1000, 2000, 6000 and 20,000 °C/s) and two biomass feeding rates (0.05 and 0.25 g/min) that represents flue gases with significantly-different concentrations of inorganic vapours. The PSDs of PM10 have a bimodal distribution with a fine mode within PM with aerodynamic diameter of <1 µm (PM1) and a coarse mode within PM with aerodynamic diameter of 1–10 µm (PM1–10). All experimental conditions produce PM10 with similar PM1 and PM1–10 yields (∼0.8 and ∼1.6 mg/g_biomass, respectively) and similar coarse mode diameters (i.e. 6.863 µm). However, at a biomass feeding rate of 0.05 g/min, the fine mode diameter shifts from 0.022 to 0.077 µm when the cooling rate decreases from 20,000 to 1000 °C/s, indicating more profound heterogeneous condensation at a lower cooling rate. As the biomass feeding rate increases to 0.25 g/min, the fine mode diameter further shifts to 0.043 µm and at 20,000 °C/s but remained at 0.077 µm at 1000 °C/s though a clear shift of PSD to larger diameters is evident. These are attributed to enhanced heterogeneous condensation and coagulation of small particulates resulting from increased particle population density in hot flue gas. Chemical analyses show PM1 contains dominantly volatile elements (i.e. Na, K and Cl) while PM1–10 consists of mainly Ca. Similar trends are also observed for elemental PSDs and yields. It is also observed that slow cooling of hot flue gas leads to an increased yield of Cl in PM1–10 due to enhanced chlorination of Ca species.

A multiresolution wavelet optimised finite-difference method for simulation of thermal regenerator

The equations demonstrating the heat transfer phenomenon in a thermal regenerator were solved with the finite-difference method (FDM) and the method has been improvised by using wavelets. In the thermal regenerators, hot flue gas enters an initially cold bed, transfer all of its thermal energy in a portion of the bed and leaves at low temperature creating a heat transfer zone which traverses the bed-length with time while establishing the thermal equilibrium on both sides of the zone. The discretization process in conventional FDM takes uniform dense grids for whole domain, however, in actual physical process, the heat transfer happens only in a portion of the domain at a certain time requiring dense grids. Such problems demand a front-tracking method which can adjust the grid pattern according to the temperature-front location for which wavelets are found to be suitable. Wavelets functions have the property of being translated and dilated according to the requirement. An adaptive grid scheme has been developed using wavelets along with the multiresolution analysis. The grid patterns for different forms of Daubechies wavelets i.e. db1, db2, db3, and db4 have been compared. The method based on wavelets has been found accurate and less time-consuming.

Corrosion of duplex stainless steel 2205 in hot flue gas environments produced at advanced oxy-fired pressurized fluidized bed combustion plants

The selection of constructional material of flue gas components is crucial for the successful deployment and long-term safe operation of the newly developed oxy-fired pressurized fluidized bed combustion plants. In this study, the corrosion performance of a candidate steel, duplex stainless steel 2205 (DSS 2205) was investigated in simulated flue gas mainly composed of CO2/H2O/O2/N2/SO2/HCl with a total pressure of 1.50–1.64 MPa at 270−320 °C. The oxidation kinetics of DSS 2205 followed parabolic law, and the formed surface oxide was a double-layer structure with outer Fe-rich oxide and inner Cr-rich oxide. Besides general oxidation, SO2 and HCl-induced pitting also occurred. Increasing temperature led to enhanced general oxidation and accelerated pitting. Extending exposure duration resulted in increased pit density, but did not noticeably affect the maximum pit depth. These results indicate that the steel is a promising candidate for further pilot- and industrial-scale assessments.

Characteristics of HCl Release and SO2/NOx Absorption in Desulfurization Wastewater Evaporation Using Hot Flue Gas

Desulfurization wastewater (DW) can be effectively treated via evaporation using hot flue gas with zero DW discharge. In this study, the characteristics of HCl release and SO2/NO2 absorption were i...

Prediction of blade life cycle for an industrial gas turbine at off-design conditions by applying thermodynamics, turbo-machinery and artificial neural network models

A novel method for estimating the rotor blade life cycle of an industrial gas turbine (GT) by the use of artificial Neural Network is proposed in this paper At the first step the blade life cycle is obtained by the use of Larson–Miller method which uses output results of GT performance modeling and blade thermal-mechanical data. Then results of rotor blade life cycle analysis by the above method are compared with results of stress factor curve (which is provided by manufacturers). Comparison of results revealed an average difference value of 9.7 % between blade life cycle estimation by two above mentioned methods. In the next step, by input data such as mass flow rate, temperature and pressure of hot flue gas, the output data such as blade cooling air and turbine shaft rotational speed are obtained from GT modeling. Then blade life cycle are also obtained by Larson–Miller​ method for 811 sample points of GT operating conditions for various ambient temperatures and load ratios. These data are used for neural network training. Results show that life cycle estimated values by neural network method in comparison with life cycle estimated values by Larson–Miller method, had about 4.8% error value in maximum (with 10-4 as mean square error, MSE). Finally, by the use of neural network method, the effects of gas turbine operating and health conditions (at various ambient temperatures, GT load ratios and compressor fouling levels) on blade life cycle are investigated. If we expect to get the nominal power output of clean blade at ISO ambient condition, in ambient temperature range of 15 to 45 ºC, the GG turbine first rotor blade life cycle reduces from 4.85 to 0.07 and in the range of 0 to 7% compressor fouling, turbine blade life cycle reduces from 4.85 to 0.68 years.

Design and development of Slotted Stack‑Petal Pot (SSPP) chimney and its performance analysis over conventional chimney

The conventional chimney structures commonly used in residences and industries are to uplift the hot flue gases from their heating sources to the outside atmosphere by the ‘Stack effect.’ In particular, industrial chimneys are constructed high in order to dilute the composition of flue gases from the discharge point to the point before reaching the ground. Due to the elevated height, these structures face some major issues like dynamic wind stresses, severe thermal fluctuations, occurrence of negative draft, etc. Despite several control measures available, these issues are yet to be resolved. In this study, a new Slotted Stack-Petal Pot chimney which works on ‘Bernoulli’s principle’ was designed, fabricated and analyzed for its performance over conventional chimney. The performance of lab-scale Slotted Stack-Petal Pot chimney on reduction in temperature and emission of CO, improvement in burning rate of fuel, settlement of PM and, dilution of exhaust gas was analyzed and compared with lab-scale conventional chimney. In addition, the distribution of temperature, and pressure and, the velocity profile for chimney prototypes were simulated using ANSYS (FLUENT) software. It is evident that this newly designed SSPP chimney reduces the flue gas temperature up to 90% and the emission of CO by 74%. It also enhances the burning rate of fuel by 50% and the settling rate of particles by 88% and effectively dilutes the different composition of exhaust gas in lab-scale fabricated models. Furthermore, it avoids the negative draft by equal distribution of pressure and uniform uplift of flue gas in chimney prototypes.

Simulation of flow and heat transfer in the duct elbow of an electric arc furnace

One of the common problems of water-cooled panels which is carrying off-gas from Electric Arc Furnace is cracking and punching in their steel bodies due to the high thermal stresses which cause water leakage into the furnace and delaying the production. In this study, heat transfer in the elbow of water-cooled panels was simulated in the steady and transient states using computational fluid dynamics. Hot flue gases of furnace, panel body, and cooling water were simultaneously considered as a computational domain to understand their interaction using conjugate approach. After developing computational grids and applying suitable boundary conditions, the problem was simulated using Ansys-Fluent software. The velocity and temperature contours of cooling water and hot gases for all parts of the computational field were obtained. The results showed that in steady state, the temperature of hot gases decreases about 205 °C within the duct elbow, whereas the temperature of cooling water increases about 8.2 °C. The maximum panels’ body temperature was 90.2 °C, which was occurred in the bends of 180° of water-cooled panel. The results of simulation showed that in the case of replacing the material of panel body by copper, the maximum panels’ body temperature is reduced about 20 K. The simulation results showed good agreements with experimental data.

Integration and simulation of solar energy with hot flue gas system for the district cooling application

The worldwide cooling demands are rising drastically. Several causes lead to this scenario such as industrialization, global warming and tropical climate region. This prompts the application of district energy such as district cooling system to fulfill the demands utilizing solar energy for cooling. Hybrid energy systems are sustainable and able to enhance the overall efficiency of the system. The current study provides the feasibility of solar cooling system integrated with the hot flue gases to produce chilled water, which can be scale up later for solar district cooling application. The parametric study conducted by using TRNSYS software to examine the feasibility and potential of integrated solar absorption cooling system. The simulation has been carried out using the feasible parameters of flat plate collector with 5° of collector slope, 15 m2 collector area, and 0.8 m2 tank size for thermal energy storage. The feasibility of the system investigated with respect to the cooling demand of a particular modeled building. It predicted that the room temperature of the building model is lower after the application of the solar cooling system. The case study conducted and simulated based on the weather for Kuala Lumpur, Malaysia.

Pressure drop prediction of ceramic membrane filters at high temperature

ABSTRACT This investigation was performed to predict the pressure drop of ceramic membrane filters at high temperature. Experiments of hot flue gas filtration were carried out to monitor the flow rate, dust concentration, temperature and pressure behavior of the ceramic membrane filters, and the dust states at different temperatures. Based on the Carman-Kozeny's equation and experimental data, a semi-empirical formula was developed for predicting the pressure drop of ceramic membrane filters at high temperature. Results show that high temperature leads to high flue gas viscosity, low filtration efficiency and promotes the sintering of dust cake, which leads to fluctuations in pressure drop which increases at the beginning and then decreases. The highest applicable temperature with lowest pressure drop could be deduced by the semi-empirical formula.

The hydration resistance, evolution mechanism of sol-coated aluminum and its effect on mechanical properties of SiC reticulated porous ceramics

As the key component for porous media burner, the sufficient strength of SiC reticulated porous ceramics (RPCs) is necessary due to the scour of hot flue gas. However, SiC RPCs prepared with template replica method often exhibited serious oxidation and low strength when the foam was burnt out. In the present work, a sol-coated Al powder with high hydration resistance was introduced into the silicon carbide slurry to promote mullite formation in SiC skeleton, meanwhile reduce the SiC oxidation ratio of sample during the heat treatment. Firstly, the silica-sol coated Al with uniform silica-sol was successfully prepared via dip coating to improve the ability of hydration resistance of Al powder. Furthermore, sol-coated Al with spherical morphology improved rheological properties of silicon carbide slurry, including viscosity and rheological behavior. In addition, the evolution mechanism of sol-coated Al in SiC RPCs was revealed. The AlO2(g) and AlO(g) was first formed in the system, thus significantly reducing the SiC oxidation ratio in SiC RPC. The partial pressure of AlO(g) increased with the sintering temperature, the needle-shaped mullite formed at 1300 ○C when it dissolved in the microsilica, while lumpy mullite formed as SiC was the silica source in SiC RPCs. The addition of sol-coated Al was beneficial to optimize the microstructure of SiC skeleton, resulting in higher compressive strength of SiC RPCs.

Application and performance evaluation of desulfurization wastewater spray drying technology

In order to realize zero discharge of desulfurization wastewater, spray drying technology of desulfurization wastewater was used in 2x330MW unit of a power plant. Its principle was to use a rotary atomizer for atomization,and a part of hot flue gas was drawn from the SCR denitrification reactor and air preheater into the drying tower, the heat was used to evaporate the desulfurization wastewater in a spray drying tower. The salt in the waste water was mixed with the dust, which was collected and removed by the electric dust remover. Then the water vapor was mixed with the flue gas and finally enters the desulfurization tower.The field test was carried out under the condition that the unit load was 100% and the amount of desulfurization wastewater treated was 5.1m3/h.The results showed that the hot smoke gas volume of drying tower was about 64896m3/h, The smoke temperature at the inlet and outlet of the drying tower were 335℃ and 205℃ respectively,the moisture content of drying products was only 0.05%. The content of HCl in the flue gas at the inlet and outlet of the drying tower were 55mg/L and 195mg/L respectively, the mass fractions of Cl removal and Cl volatilization in desulfurization wastewater were 87.7% and 12.3% respectively. The increase of Cl content in the dried products had little effect on the utilization of fly ash.

Biosyngas-fueled platinum reactor applied in micro combined heat and power system with a thermophotovoltaic array and stirling engine

Currently, alternative fuels, derived from biomass and urban maximize the overall power output, have been increasingly attracting more attention in the industrial and residential sectors. Micro-combined heat and power (CHP) systems with high energy efficiency have been developed, particularly for the use in remote and rural areas. This study used a micro-CHP system, with a combustion-driven thermophotovoltaic (TPV) cell array and a Stirling engine-driven power system, within which methane and bio-syngas fuels were deployed strategically. This micro-CHP system harvests energy generated through thermal radiation from the reactor surface and harvests thermal energy from hot flue gas. Eventually, the micro-CHP prototype was proven that all energies are converted to electricity, and hot water can be simultaneously supplied. High incandescent surface and high-temperature flue gas of platinum reactor provide the thermal sources for TPV cell array and Stirling engine. The overall efficiency of the micro-CHP system was 35.0% for 50%H2+50%CO, and the generated power included 2.7, 3.5, and 272.1 W from the Stirling engine-driven power system, GaSb TPV cell array, and hot water supply system, respectively. The systematic performance of the micro-CHP system, the combustion features, radiation efficiency, fuel conversion rate, total electricity output, and corresponding overall efficiencies were examined thoroughly.

Techno-economic analysis of ultra-supercritical power plants using air- and oxy-combustion circulating fluidized bed with and without CO2 capture

The adoption of oxy-combustion in a circulating fluidized bed (CFB) producing ultra-supercritical (USC) steam has been investigated to increase energy efficiency and reduce CO2 emissions of coal-fired power plants. This paper presents a techno-economic analysis for 500 MWe USC-CFB power plants with air- and oxy-combustion in the presence of CO2 capture. An amine absorber unit (AAU) and a CO2 processing unit (CPU) were used to capture CO2 in the air- and oxy-combustion power plants, respectively. The air-combustion power plant without CO2 capture (Case 1) showed the highest net electricity efficiency (46%), whereas the introduction of an AAU in the air-combustion power plant (Case 2) reduced the net efficiency to 36%. The net efficiency (39%) of the oxy-combustion power plant with CPU (Case 3) was higher than that of Case 2 owing to the recycling of hot flue gas. The levelized cost of electricity (LCOE) of Case 3 (59 $/MWh) was lower than that of Case 2 (64 $/MWh), which demonstrated that oxy-combustion was advantageous compared to air-combustion in a scenario with CO2 capture. The sensitivity analyses of the electricity price and CO2 credit showed economic situations where Cases 2 and 3 would be profitable.

Quantitative imaging of potassium release from single burning pulverized biomass char particles

The release of potassium from single burning pulverized wheat straw char particles was quantitatively measured using laser-induced photofragmentation fluorescence (LIPF). The char particles were prepared in a drop tube furnace at 1000 °C from wheat straw particles with sizes in the range 224–250 µm. Subsequently, the char particles were injected upward into a hot flue gas flow produced by a premixed CH4/air flame anchored on a McKenna burner. The flue gas had a mean temperature of 1580 K and a mean O2 concentration of 6.5 vol%. The 193 nm laser beam from an ArF Excimer laser was formed into a collimated laser sheet to photodissociate potassium hydroxide (KOH) and potassium chloride (KCl) around the burning char particles, and the signal of the produced fluorescence was captured by a camera. The measurements were conducted for char particles during residence times in the flue gas between 10 and 70 ms. Quantitative data was obtained from a direct calibration of the LIPF signal in hot gas products doped with known amounts of KOH and KCl. The maximum potassium concentration measured surrounding the burning char particles was over 40 ppm. During the oxidation period until 70 ms, the measured potassium release rate remained almost constant at around 0.5 µg/s, with more than 60% of the potassium being released in the form of KOH. The results indicate that the LIPF imaging method can be used to study the potassium release from burning biomass fuels.

Influence of bonding phases on properties of in-situ bonded porous SiC membrane supports

Porous SiC ceramic membrane supports are widely employed in a wide variety of high-temperature applications, such as hot flue gas filtration, porous burners and molten metal filters. Herein, SiC supports, with a porosity of ~37%, were prepared by using low-temperature bonding techniques and the influence of different bonding phases, such as mullite, cordierite and glass, on ambient-temperature flexural strength, hot modulus of rupture (HMOR), thermal shock resistance and oxidation resistance were systematically investigated. The results reveal that the glass-bonded SiC (GBSC) support exhibited the highest ambient-temperature flexural strength of 33.6 MPa, whereas the flexural strength of mullite-bonded SiC (MBSC) and cordierite-bonded SiC (CBSC) supports ranged from 22 to 25 MPa. However, the presence of glass phase deteriorated the high-temperature properties of the support. MBSC support rendered superior mechanical strength at high temperature and self-strengthening in a certain temperature range, such as HMOR improved 47.5% at 900 °C, but HMOR of glass-bonded support was only 57.4% of the ambient-temperature strength. Moreover, MBSC and CBSC supports exhibited better thermal shock resistance than GBSC supports and the critical temperature difference of water quenching for MBSC supports was ~200 °C higher than GBSC supports. In addition, MBSC support rendered superior oxidation resistance and exhibited a weight gain rate of ~0.1% at 1150 °C for 24 h, which is 54.4% and 42.2% lower than CBSC and GBSC supports, respectively.

Evaluation of a distributed combustion concept using 1-D modeling for pressurized oxy-combustion system with low flue gas recirculation

Although process modeling of the pressurized oxy combustion (POC) with low flue gas recirculation (FGR) approved a great potential for CCUS cost reduction, there is no globally agreed concept for the boiler design that can satisfy the technical requirements of PC (pulverized coal) boiler operation. In this paper, a new concept for the boiler design and firing configuration based on distributing the combustion into multi-burner levels along the boiler height was evaluated using 1-D modeling. The 1-D model is mainly based on Gurvitch method to deal with radiation exchange between hot flue gases and water walls. Distributing combustion is proved to have remarkable potentials to control the peak flame temperature and heat flux. Two boiler sizes based on 30% and 53% FGR were analyzed which satisfied the critical indexes of the PC boiler operation. Finally, it was shown that distributed combustion concept has good potentials to operate under two abnormal conditions: i) with zero slag thermal resistance on the wall and ii) under low boiler operational load.

Design and application of sensitive thermal energy storage from concrete.

The main objectives of the authors’ current paper include thermal sizing of a regenerative concrete heat exchanger for coupling of the biomass plants and the heat engine like ORC (Organic Rankine Cycles). The main challenge for regenerators is the temperature difference between charging and discharging process. Heat energy charging can be done by hot flue gas or high temperature fluid circulation through solid modules of storage. Optionally heat supply can be obtained by using of electrical energy. The concrete modules contain embedded piping for charging and discharging and definition of the geometric parameters like piping size and distance represented in current work. The application of unsteady heat transfer equations for heat storage description was checked by comparison with experimental and theoretical results. The paper offers equations for evaluation of storage efficiency for different heat transfer coefficient, dimensions of storage and time duration of warming and cooling process.

Preparation of Porous Permeable Ceramic Based on Silicon Carbide for Hot Flue Gas Filtration (Review)

The article presents an analytical review of publications on oxide ceramic binders that are used to prepare porous silicon carbide materials. The most promising ceramic binders are determined and the properties of materials based on ceramic binder data are provided. Mechanisms of modifier action making it possible to reduce the heat treatment temperature by up to 100°C are considered.

Production of porous permeable ceramics based on silicon carbide for filtration of hot flue gases (the review)

The article presents an analytical review of the literature on oxide ceramic binder, which are used to obtain porous silicon carbide materials. The most promising ceramic binders are determined and the properties of materials based on the data of ceramic binders are given. The mechanisms of action of modifiers that reduce the heat treatment temperature to 100 ºС are considered. Ill. 3. Ref. 48.

Exergetic life cycle assessment of hydrogen production from biomass staged-gasification

By combination of life cycle assessment (LCA) and exergy analysis, a modified exergetic life cycle environmental impact model was proposed. The model can quantitatively assess the environmental impacts of resources and pollution by using exergy to measure the deviation degrees of various emissions from the reference environment. Then the comprehensive indicators of resource and environment performance were defined and obtained without introducing subjective weighting factors. Two products of hydrogen (biomass staged-gasification hydrogen (BSGH), and natural gas steam reforming process hydrogen (NGSH)) were evaluated to illustrate the application of the proposed model. The comparison of two products shows that BSGH has significant advantages in both renewability and environmental sustainability. The environment-friendly performance of BGSH mainly exhibits in environment impacts of global warming potential (GWP) and photochemical ozone formation (POF). However, the thermal pollution (TP) of BGSH is slightly larger than that of NGSH. And this indicates that the excessive hot flue gas emissions in BSGH process result in more thermal pollution, and need to be noticed. Furthermore, the sensitivity analysis indicates that the conversion efficiency of tar has a larger influence on total cumulative exergy consumption and environmental index than the combustion efficiency of biomass in the staged-gasification process.