Inlet Flue Gas Temperature Research Articles

Performance analysis of a novel power/refrigerating combined-system driven by the low-grade waste heat using different refrigerants

In this paper, a novel power/refrigerating combined-system driven by the low-grade waste heat of the flue gas was introduced. It coupled a transcritical organic Rankine cycle with a vapor compression refrigeration cycle. In order to understand basic characteristics of this novel combined-system, a detailed performance analysis was performed. Results show that the turbine inlet pressure, flue gas inlet temperature and condensation temperature are three important parameters influencing system performance. During the increase of the turbine inlet pressure, the refrigeration capacity and the exergy efficiency exhibit the maximum values. However, with the increase of the flue gas inlet temperature and the decrease of the condensation temperature, both the refrigeration capacity and the exergy efficiency corresponding to the optimal turbine inlet pressure increase. The use of regenerator can improve the system performance and reduce the optimal turbine inlet pressure. Under partial refrigeration load, there is a linear relationship between the electricity output and the refrigeration capacity at a fixed work output from the turbine. The total irreversible loss decreases and the exergy efficiency increases with the decrease of the power ratio. Finally, after screening and comparing various potential working fluids, R134a is recommended as the working fluid of this novel combined-system.

Experimental Research of Flue Gas Simultaneous Desulfurization and Denitrification with the New Gas-Liquid Medium

The flue gas simultaneous desulfurization and denitrification was studied for its feasibility with the new gas-liquid medium by using Ca(OH)2 as absorbent. The effects on key operating parameters were analyzed. They are pH, inlet temperature of flue gas and inlet concentration of air pollution. When pH is almost 5.5-6, and inlet temperature of flue gas is between 110℃ and 120℃, the results show that the removal efficiency of SO2 and NO are above 85% and 80% using rotating biological technology (RDB), respectively, which can satisfy most requirements of industrial scale applications. Besides, When CSO2 is more than 1500 (mg/m3), with the rising of imported pollutant concentration, desulfurization efficiency continues to increasing and denitrification efficiency was growing slowly.

A novel flue gas waste heat recovery system for coal-fired ultra-supercritical power plants

Recovering flue gas waste heat is important in improving power plant efficiency. The most widely method is installing a low-temperature economizer (LTE) after the electrostatic precipitator (ESP) to heat the condensed water, thereby saving the extraction steam from the steam turbine and achieving extra work. The inlet flue gas temperature of the LTE is relatively low, so it can only heat condensed water from low-grade regenerative heaters, resulting in comparatively minor energy savings. After conducting an in-depth analysis of the conventional waste heat recovery system (WHRS), this paper proposes a novel WHRS, in which the air preheater is divided into high-temperature (HT) and low-temperature (LT) air preheaters, and the LTE can be situated between the ESP and the LT air preheater. Through system integration, higher-grade extraction steam can be saved, resulting in greater economic benefits. Results show that the net additional power output can reach 9.00 MWe and using the proposed WHRS can yield net benefits up to USD 2.60 million per year, which is much greater than those of conventional WHRS. Exergy destruction is also reduced from 34.1 MWth in the conventional WHRS to 28.5 MWth in the proposed WHRS.

Experimental study of a zero water consumption wet FGD system

Aiming to the huge water consumption of wet flue gas desulfurization (WFGD), a pilot-scale facility was built and employed to investigate the water consumption with various inlet vapor concentration of flue gas, circulating slurry temperature and inlet flue gas temperature, as well as different desulfurizer, including limestone–gypsum, magnesium, and natrium–alkali. Results show that water consumption decreases with increased vapor concentration in flue gas, while increases with higher temperature of the circulating slurry and the inlet flue gas, and SO2 concentration has a little effect on the water consumption. The water consumption of limestone–gypsum method is the largest, followed by the magnesium method, and the natrium–alkali method has the least water consumption. Meanwhile, critical operating parameters have been found firstly to create a zero water consumption (ZWC) system for all investigated desulfurization methods. For limestone–gypsum, only higher water content lignite can obtain ZWC below 50 °C; While for natrium–alkali, the ZWC system can be built for most of anthracite, bituminous, and lignite coal below 30 °C. Whole research provides considerable guideline for industrial application.

Photocatalytic Process of Simultaneous Desulfurization and Denitrification of Flue Gas by TiO2–Polyacrylonitrile Nanofibers

TiO2 nanoparticles were successfully fabricated on electrospun polyacrylonitrile (PAN) nanofibers via the coupling of electrospinning and hydrothermal pathway. A straightforward photocatalysis oxidation process has been developed for simultaneous desulfurization and denitrification of flue gas using the TiO2-PAN photocatalyst. Also, the influences of some important operating parameters, such as titanium loading content of catalyst, flue gas humidity, flue gas flow, and inlet flue gas temperature on removal efficiencies of SO2 and NO were investigated. The results demonstrated that removal efficiencies of 99.3% for SO2 and 71.2% for NO were attained under the following optimal experiment conditions: titanium loading content, 6.78 At %; gas flow rate, 200 mL/min; flue gas humidity, 5%; inlet flue gas temperature, 40 °C. Furthermore, the presumed reaction mechanism of SO2 and NO removal using TiO2-PAN photocatalyst under UV light was proposed.

Numerical modeling and simulation of condensation heat transfer of a flue gas in a bundle of transport membrane tubes

In this paper, a numerical study has been carried out to investigate the heat and mass transfer characteristics of a condensing combustion flue gas in a cross-flow transport membrane tube bundle. The tube wall is made of a porous material that is able to extract condensate liquid from the flue gas. The flue gas investigated consists of one condensable water vapor (H2O) and three noncondensable gases (CO2, O2, and N2). A simplified multi-species transport model was developed for the heat and mass transfer of flue gas. The condensation-evaporation process was simulated as a two-step chemical reaction. The RNG two-equation turbulence model was used for the turbulent flow. The numerical study was conducted within ranges of Reynolds number of 1.0×103–7×104 based on hydraulic diameter of flue gas channel, and 6.4×100–3.3×102 based on inner diameter of the water tube. Flue gas inlet temperature is within the range of 333.2–360.9K. Numerical results were compared with our experimental data. It has been found that the developed multi-species transport model was able to predict the flue gas heat and mass transfer in the tube bundle with fairly good accuracy. The heat and mass depletion levels decrease with the increase of the flue gas Reynolds numbers. A new Nusselt number correlation was developed for flue gas convection in the tube bundle. Detailed results about temperature, mass fraction, enthalpy, and skin fraction factors are also presented and discussed.

Simultaneous Desulfurization and Denitrification of Flue Gas by ·OH Radicals Produced from O2+ and Water Vapor in a Duct

In the present study, simultaneous flue gas desulfurization and denitrification are achieved with ·OH radicals generated from O(2)(+) reacting with water vapor in a duct. The O(2)(+) ions are generated by a strong ionization dielectric barrier discharge and then injected into the duct. Compared with conventional gas discharge treatment, the present method does not need a plasma reaction reactor, additional catalysts, reductants, or oxidants. The main recovered products are the liquids H(2)SO(4) and HNO(3), which can be used in many processes. Removal rates of 97% for NO and 82% for SO(2) are obtained under the following optimal experimental conditions: molar ratio of reactive oxygen species (O(2)(+), O(3)) to SO(2) and NO, 5; inlet flue gas temperature, 65 °C; reaction time, 0.94 s; and H(2)O volume fraction, 8%. Production of O(2)(+) and the plasma reaction mechanisms are discussed, and the recovered acid is characterized. The experimental results show that the present method performs better for denitrification than for desulfurization. Compared with conventional air discharge flue gas treatments, the present method has lower initial investment and operating costs, and the equipment is more compact.

Flue Gas Simultaneous Desulfurization and Denitrification with Urea in Spouted Bed

Simultaneous desulfurization and denitrification removes SO2 and NOx from flue gas in one unit and only uses one absorbent. Using urea as absorbent removing SO2 and NOx in semi-dry spouted bed has the enormous developmental potential and wide foreground for it overcomes two shortages of wet process such as the amount of urea is large and the waste water is difficult to handle. The chemical absorption mechanism and thermodynamics of SO2 and NOx with urea were studied, the operating condition optimization of spouted bed was determined through several repeating experiment, the effects of some important operational parameters such as molar ratio of urea and gaseous pollutant, inlet temperature of flue gas and approach to adiabatic saturation temperature on SO2 and NOx removal efficiency were analyzed. The results provide a foundation for the commercial scale application of simultaneous desulfurization and denitrification technology.

Experimental Investigation of Sintering Flue Gas Desulfurization with Steel Slag Using Dry CFB Method

SO2 Emission of sintering flue gas accounts for more than 70% of total SO2 emission of steel industry. The purpose of this paper was to use steel slag for desulfurization of sintering flue gas. Based on traditional circulating fluidized beds (CFB) for flue gas desulfurization (FGD), a new dry digestion CFB-FGD process was developed. The new process eliminated the traditional digestion procedure, and the functions of the reactor include preliminary dust collection, digestion and desulfurization. An pilot CFB installation with maximum flow rate of 8000 Nm3/h for flue gas desulfurization was established. The desulfurization effects of calces, converter slag and blast furnace slag were investigated under the following experimental conditions: temperature of inlet flue gas, 150 °C; temperature of outlet flue gas, 75 °C. Relative humidity, 13%; flue gas flow rate, 6800 Nm3/h; Ca/S ratio, 1.2. The results showed that all of the desulfurization agents had desulfurization capability and the desulfurization efficiency of calces was the best, followed by converter slag and blast furnace slag. The removal efficiency of steel slag ranged from 75% to 82%. Considering solid waste utilization, the application of steel slag in desulfurization using dry CFB has a promising future.

Removal of fine particles by heterogeneous condensation in the double-alkali desulfurization process

Removal of fine particles by heterogeneous condensation in the rotating-stream-tray scrubber was investigated experimentally for the double-alkali desulfurization process in this paper. A supersaturated vapor phase, necessary for condensational growth of fine particles, was achieved in the SO 2 absorption zone and at the top of the scrubber by adding steam in the gas inlet, between the pieces of rotating-stream-tray and above the desulfurization liquid inlet of the scrubber, respectively. Fine particles grew in size by vapor heterogeneous condensation with the particles acting as nucleation centers. Then the condensational grown droplets were removed efficiently by the desulfurization liquid and a high-efficiency demister. In order to optimize the removal process, the influences of temperature of inlet flue gas and desulfurization liquid, steam addition method and amount of steam added on the particle removal efficiency were presented. The results show that a few fine particles could be removed in the rotating-stream-tray scrubber. The removal efficiency can be significantly improved for various steam addition cases, and the improve performance is related to the method and the amount of steam addition. Particle removal efficiency with steam added between the pieces of rotating-stream-tray is higher than that of else steam addition cases.

Simultaneous Desulfurization and Denitrification from Flue Gas by Ferrate(VI)

An innovative semidry process has been developed to simultaneously remove NO and SO₂ from flue gas. According to the conditions of the flue gas circulating fluidized bed (CFB) system, ferrate(VI) absorbent was prepared and added to humidified water, and the effects of the various influencing factors, such as ferrate(VI) concentration, humidified water pH, inlet flue gas temperature, residence time, molar ratio of Ca/(S+N), and concentrations of SO₂ and NO on removal efficiencies of SO₂ and NO were studied experimentally. Removal efficiencies of 96.1% for SO₂ and 67.2% for NO were obtained, respectively, under the optimal experimental conditions, in which the concentration of ferrate(VI) was 0.03 M, the humidified water pH was 9.32, the inlet flue gas temperature was 130 °C, the residence time was 2.2 s, and the molar ratio of Ca/(S+N) was 1.2. In addition, the reaction mechanism of simultaneous desulfurization and denitrification using ferrate(VI) was proposed.

Seawater scrubbing desulfurization: A model for SO2 absorption in fall‐down droplets

AbstractAn unsteady model of SO2 absorption in fall‐down spherical seawater droplets is presented, focused on marine diesel engine exhaust gas scrubbing. The model evaluates the amount of sulfur dioxide absorbed by a single droplet, with given initial velocity, diameter, and alkalinity, falling counter‐flow with respect to the exhaust gas stream. Kinematics of the droplet, heat exchange, and evaporation has been considered, taking into account internal circulation. Neutralization of absorbed sulfur species in the droplet has been modeled with a global and fast reaction mechanism. Transport equations for species inside the droplet have been solved on a nonuniform computational grid, which is regenerated at every time step to account for droplet diameter reduction. The single‐droplet model has been incorporated in a simple scrubber plug‐flow model, to evaluate the desulfurization efficiency and the seawater supply rate under realistic marine engine exhaust gas desulfurization conditions. The influence of flue gas inlet temperature, flue gas velocity, initial droplet size, and velocity on the scrubbing process were investigated. Results of this model are valuable for judging the feasibility and operating costs of this SO2 scrubbing technique compared with alternative methods. © 2011 American Institute of Chemical Engineers Environ Prog, 2011

Experimental study of fine particles removal in the desulfurated scrubbed flue gas

Droplets growth by heterogeneous condensation of water vapor as a preconditioning technique for the removal of fine particles from flue gas was investigated experimentally in a wet flue gas desulfurization (WFGD) system using spray scrubber as scrubber. The supersaturated vapor environment was achieved by adding water vapor into the particle growth region, which was above the liquid phase inlet in the desulfurization tower. Fine particles grow in size by vapor heterogeneous condensation with the particles acting as nucleation centers, and then the grown droplets are removed efficiently by a high-efficiency wire mesh demister. The results show that particle number concentration decreased significantly by application of heterogeneous condensation of water vapor in the WFGD system. The influence of initial particle number concentration, temperature of inlet flue gas and desulfurization solution, amount of steam added on the removal efficiency of fine particles is presented. The removal efficiency of fine particles decreased with increasing the initial particle concentration. Anyway, heterogeneous condensation in combination with a WFGD system is a highly efficient technique for the separation of fine particles from the desulfurized flue gas.

Experimental study on titanium heat exchanger used in a gas fired water heater for latent heat recovery

Abstract In general, latent heat recovery is usually accompanied by the corrosion of the heat exchanger, which is caused by the strongly acidic condensate when the temperature of the flue gas is lowered below the acid dew point. The present study has been conducted to investigate the heat and mass transfer characteristics in a titanium heat exchanger with excellent corrosion resistance used for waste heat recovery with the condensation arranged in a gas fired water heater. In addition, the thermal efficiency of the gas fired water heater was evaluated based on the net calorific value at the maximum rated output during latent heat recovery from the exhaust flue gas. Parametric studies were conducted for the flue gas flow rate, inlet temperature and mass flow rate of the supplied water, respectively. Different arrangements of the tubes of the heat exchanger including in-line and staggered configurations were investigated. The experimental results indicate that the thermal efficiency of the gas fired water heater with a latent heat recovery (LHR) heat exchanger was enhanced by about 10% compared with conventional instantaneous water heaters, i.e., water heaters without heat recovery. In addition, in terms of the Nusselt number and the Sherwood number, the heat and mass transfer performance of the staggered tube bank type were approximately 50% and 10% higher than that on the in-line tube bank type when the Reynolds number of the flue gas was 103.

Modelling and experimental study on agglomeration of particles from coal combustion in multistage spouted fluidized tower

An experimental platform of spray agglomeration has been designed and built for removing small fly ash particles (PM 10) from coal combustion. Agglomerating model of fine particles during the spray process was developed by combining rapid coagulation theory and analysis of the interaction between droplets and particulates. Systematic experiments were conducted in multistage spouted tower using several kinds of agglomerant solutions. The influencing factors such as surfactant, pH value, flow rate of agglomerant solutions and inlet flue gas temperature were analyzed. SEM was used to analyze the microstructure of the aggregation. Based on this model, coagulation rate constant was calculated and the influences of original parameters were observed. The spray agglomeration mechanism of particles can be analyzed from both macroscopical and microcosmic aspects. Preliminary results are presented and discussed in this work. Final results indicate that the special shape of multistage spouted fluidized tower has significant influences on the effect of agglomeration. The findings from this work will be helpful to form the basis and provide guidance for further studies on the control of fine particles such as PM 2.5 or even smaller ones.

Agglomeration of particles during coal combustion in multistage spouted fluidized tower

An experimental platform of spray agglomeration has been designed and built for removing small fly ash particles (PM10) from coal combustion. Systematic experiments were conducted in a multistage spouted tower using kinds of agglomerant solutions. The particle concentration increases greatly from the first stage to the second stage of the tower. With the increase of flue gas flow rate the oscillation of impulse signal response curves increases and the internal circulation of the tower intensifies. The influencing factors such as the surfactant, PH value, flow rate of the agglomerant solutions and inlet flue gas temperature were analyzed. SEM was used to analyze the microstructure of the particles. Final results indicate that the special shape of a multistage spouted fluidized tower has significant influences on the effect of agglomeration. The findings from this work will be helpful to form the basis, and provide guidance for, further studies on the control of fine particles such as PM2.5 or even smaller.

Modeling of SO 2 removal in fabric filter

Fabric filters are involved in most semi-dry flue gas desulfurization process and represent ability of SO 2 removal. SO 2 removal efficiency in fabric filter after a semi-dry scrubber is investigated. Experimental results showed that SO 2 inlet concentration has little effect on SO 2 removal efficiency, SO 2 removal efficiency increases as flue gas inlet temperature increases and relative humidity affects SO 2 removal efficiency significantly. The kinetic model based on shrinking core theory has been presented. It is found that, in the beginning, when calcium hydroxide conversion ratio is less than 0.3, SO 2 removal process is mainly controlled by chemical reaction (Model-2); and when calcium hydroxide conversion ratio is greater than 0.3, SO 2 diffusion through product layer is rate limiting (Model-3). The experimental results in fabric filter are successfully correlated by Model-3.

Evaluation of the Performance of Various Amine Based Solvents in an Optimized Multipurpose Technology Development Pilot Plant

Abstract The overall goal of this work was to show experimentally using a CO 2 capture plant of reasonable capacity the contributions of plant and solvent optimization to minimizing the steam requirement. Experimental studies were conducted in an optimized CO 2 capture pilot plant to evaluate the performance of RS-1 solvent and 5 molar aqueous MEA. The first objective was to test a highly improved plant configuration that can minimize both the amine circulation rate and the steam requirements below the values reported in the literature for a desired CO 2 recovery. The second objective was to show the superior performance of RS-1 relative to 5 molar MEA. Both these strategies were aimed at reducing the steam requirement without increasing the size or complexity of the CO 2 capture plant. The pilot plant used for the tests was the highly optimized multi-purpose technology development plant at the International Test Center for CO 2 capture which processes 186 Nm 3 /h of flue gas to produce CO 2 with a nominal capacity of 1 tonne per day. This plant has 12-inch ID for the absorber and stripper columns. The inlet flue gas temperature was 40 ∘ C while the CO 2 concentrations in the flue gas were 4 and 8% based on exhaust gases obtained respectively from a natural gas turbine-natural gas boiler combination, and a natural gas boiler. The results show that for flue gas containing 4 and 8% CO 2 for a 90% recovery or absorber efficiency, the steam duties using our optimized plant configuration were respectively 2.03 and 1.43 kg steam/kg CO 2 for MEA as compared to industry and literature values based on conventional plant configuration in the range of 1.9 to 2.5 kg steam/kg CO 2 depending on the CO 2 concentration in the flue gas. When RS-1 solvent was used, the steam duties using the optimized plant configuration were respectively 1.74 and 1.35 kg steam/kg CO 2 which showed improvements over the corresponding performance of 5 molar MEA. It was interesting to observe that with a completely modified and optimized process configuration, the heat duty using RS-1 was 1 kg steam/kg CO 2 . These results show that in order to minimize steam requirements in a post combustion CO 2 capture amine plant, there is the need to optimize both the plant process configuration and the solvent.

Capacity Mapping for Optimum Utilization of Pulverizers for Coal Fired Boilers

Pulverizers play a pivotal role in coal-based thermal power generation. Improper coal fineness or drying reflects a qualitywise deterioration. This results in flame instability, unburnt combustible loss, and a propensity to slagging or clinker formation. Simultaneously, an improper air-coal ratio may result in either coal pipe choking or flame impingement, an unbalanced heat release, an excessive furnace exit gas temperature, overheating of the tube metal, etc., resulting in reduced output and excessive mill rejects. In general, the base capacity of a pulverizer is a function of coal and air quality, conditions of grinding elements, classifier, and other internals. Capacity mapping is a process of comparison of standard inputs with actual fired inputs to assess the available standard output capacity of a pulverizer. In fact, this will provide a standard guideline over the operational adjustment and maintenance requirement of the pulverizer. The base capacity is a function of grindability; fineness requirement may vary depending on the volatile matter (VM) content of the coal and the input coal size. The quantity and the inlet temperature of primary air (PA) limit the drying capacity. The base airflow requirement will change depending on the quality of raw coal and output requirement. It should be sufficient to dry pulverized coal (PC). Drying capacity is also limited by utmost PA fan power to supply air. The PA temperature is limited by air preheater (APH) inlet flue gas temperature; an increase in this will result in efficiency loss of the boiler. Besides, the higher PA inlet temperature can be attained through the economizer gas bypass, the steam coiled APH, and the partial flue gas recirculation. The PA/coal ratio, a variable quantity within the mill operating range, increases with a decrease in grindability or pulverizer output and decreases with a decrease in VM. Again, the flammability of mixture has to be monitored on explosion limit. Through calibration, the PA flow and efficiency of conveyance can be verified. The velocities of coal/air mixture to prevent fallout or to avoid erosion in the coal carrier pipe are dependent on the PC particle size distribution. Metal loss of grinding elements inversely depends on the YGP index of coal. Besides that, variations of dynamic loading and wearing of grinding elements affect the available milling capacity and percentage rejects. Therefore, capacity mapping is necessary to ensure the available pulverizer capacity to avoid overcapacity or undercapacity running of the pulverizing system, optimizing auxiliary power consumption. This will provide a guideline on the distribution of raw coal feeding in different pulverizers of a boiler to maximize system efficiency and control, resulting in a more cost effective heat rate.

Availability analysis of post-combustion carbon capture systems: Minimum work input

This paper describes the availability analysis of a generic, post-combustion carbon capture plant. The analysis first establishes the minimum work input required in an ideal plant with a flue gas inlet temperature equal to the sink temperature. The analysis shows that the ideal work input is surprisingly low and that, roughly equal amounts of work are required to first separate and then compress the CO2 contained in a typical flue gas stream. The analysis is then extended to include the effects of variable inlet temperature and extraction efficiency. This extended analysis shows that there is a considerable quantity of available energy in the flue gas of a normal power station. Indeed, in principle, carbon capture is theoretically possible without any external work input for fuels of low carbon/hydrogen ratio such as heavy fuel oil and natural gas. When burning coal, the minimum work input would be significantly reduced if the flue gases' availability were utilized. The final section of the paper compares the actual work input of a variety of carbon capture schemes found in the literature, with the minimum work input for an ideal process. This comparison shows that the techniques presently found in the literature have a low second-law efficiency.