Flue Gas Velocity Research Articles

Pilot-scale study on water and latent heat recovery from flue gas using fluorine plastic heat exchangers

Over the years, in order to enhance the thermal efficiency, coal-fired power plants have witnessed great improvements in water and waste heat recovery. This paper aims to investigate the water vapor and latent heat recovery from the low temperature flue gases exiting a limestone-gypsum wet desulfurization system. A pilot-scale testing system mainly composed of a two-stage fluorine plastic heat exchanger (FHE) was built in a 660 MW lignite-fired power plant in northern China. The additional FHE configuration was first developed and used for water and latent heat recovery based on the condensation mechanism of water vapor. Results showed that the FHE can overcome the shortcomings of the conventional metal heat exchanger, especially when flue gas temperature is below the acid dew point. The recovered latent heat accounted for more than 80% of the total heat recovered from low temperature flue gases, and the heat supply of 92 MWth was achieved. The overall heat transfer coefficient of the FHE reached up to 275 W/(m2•K). The water recovery efficiency increased with an increase in cooling water velocity and a decrease in flue gas velocity. The water recovery efficiency higher than 70% was reached when the flue gas velocity was less than 5 m/s and the cooling water velocity was greater than 0.24 m/s. The highest water recovery efficiency of the two-stage FHE was 85%, suggesting that this technology has a greater application potential in all industrial processes. The recovered water mass from the flue gas by condensation was nearly equal to, or even exceeded, the equivalent mass of supplemental water for the desulfurization system. The good water recovery performance of the FHE device implied that zero water consumption of the desulfurization system could be achieved, which is of great significance for power plants, especially in water scarce regions. This technology will offer an innovative and feasible solution to resolve the issue of water and heat recovery in the highly corrosive conditions.

Fouling characteristics analysis and morphology prediction of heat exchangers with a particulate fouling model considering deposition and removal mechanisms

Fouling of heat exchangers in industrial waste heat recovery is a problem which needs to be solved urgently. In this paper, a numerical investigation on fly-ash deposition and removal processes in tube bundle heat exchangers was conducted for industrial waste heat recovery. This study using a comprehensive fouling model integrated with the CFD framework was carried out with a discrete phase model and a dynamic mesh model in ANSYS FLUENT. First of all, the fly-ash deposition and removal algorithms were developed to establish the judgment criterion of particulate fouling based on the energy balance model and the critical moment theory. Based on this model, then, fouling characteristics with and without removal mechanism were compared. Then fouling processes for different particle diameters and flue gas velocities were simulated. At last, fouling morphology and the effect of fouling on heat transfer performance were predicted. The results indicated that the fouling mass increased almost linearly with time without removal mechanism, but an asymptotic behavior of fouling mass was observed when the removal mechanism was considered. When the number of particles injected from the inlet was specified, smaller particles showed a higher fouling rate. Also, the deposit growth rate decreased with the increase of flue gas velocity. For the particle diameter of 5μm and the flue gas velocity of 6m/s, the thermal effectiveness number was reduced by about 10% after 15min. The paper highlights the fly-ash deposition and removal model and the application of the dynamic mesh method.

Simulation of the absorption of SO2 by ammonia in a spray scrubber

On basis of investigation of the mass transfer coefficient and gas-liquid interfacial area, a mathematical model was developed to simulate the absorption of SO2 by ammonia in a spray scrubber. This model could provide predictions of the desulfurization efficiency at different operating conditions such as pH of solution, velocity of flue gas, liquid-to-gas ratio, SO2 concentration and the height of absorption zone. The calculated desulfurization efficiency of a lab-scale ammonia-based desulfurization system by this model was compared with that of corresponding measured data. The comparison results show that the relative error between the calculated desulfurization efficiency and the measured data is almost within ±32.5%. This fact could be explained as that the velocity of flue gas was not rigorously consistent in the radial direction and the droplets did not descend rigorously along the vertical line, because the diameter of the experimental spray scrubber is small in this study. The relative error between the calculated desulfurization efficiency and the measured values of plant-scale ammonia-based desulfurization system by this model would be smaller than that of lab-scale system. Accordingly, this model would be beneficial for optimizing design and operation of ammonia-based desulfurization system.

Kinetic Energy Recovery from the Chimney Flue Gases Using Ducted Turbine System

An innovative idea of extracting kinetic energy from man-made wind resources using ducted turbine system for on-site power generation is introduced in this paper. A horizontal axis ducted turbine is attached to the top of the chimney to harness the kinetic energy of flue gases for producing electricity. The turbine system is positioned beyond the chimney outlet, to avoid any negative impact on the chimney performance. The convergent-divergent duct causes increase in the flue gas velocity and hence enhances the performance of the turbine. It also acts as a safety cover to the energy recovery system. The results from the CFD based simulation analysis indicate that significant power 34 kW can be harnessed from the chimney exhaust. The effect of airfoils NACA4412 and NACA4416 and the diffuser angle on the power extraction by the energy recovery system using a 6-bladed ducted turbine has been studied with the CFD simulation. It is observed that the average flue gas velocity in the duct section at the throat is approximately twice that of the inlet velocity, whereas maximum velocity achieved is 2.6 times the inlet velocity. The simulated results show that about power may be extracted from the chimney flue gases of 660 MW power plant. The system can be retrofitted to existing chimneys of thermal power plants, refineries and other industries.

Experimental investigation on fluid flow and heat transfer characteristics of a submerged combustion vaporizer

Submerged combustion vaporizer (SCV) occupies a decisive position in liquefied natural gas (LNG) industrial chain. In this paper, a visual experimental apparatus was established to have a comprehensive knowledge about fluid flow and heat transfer performance of SCV. Trans-critical liquid nitrogen (LN2) was selected as alternative fluid to substitute LNG because of safety reason. Some unique experimental phenomena inside the SCV (local water bath freezes on the external surface of tube bundle) were revealed. Meanwhile the influences of static water height, superficial flue gas velocity, heat load, tube-side inlet pressure and tube-side mass flux on the system performance were systematically discussed. Finally, based on the obtained experimental results, two new empirical Nusselt number correlations were regressed to predict the shell-side and tube-side heat transfer characteristics of SCV. The maximum errors between predicted results and experimental data were respectively ±25% and ±20%. The outcomes of this paper were critical to the optimum design and economical operation of SCV.

Experimental and numerical analysis of oil shale drying in fluidized bed

ABSTRACTThe main objective of this work was to experimentally and numerically investigate the Liu Shu River oil shale drying by the means of flue gas in a fluidized bed dryer. Several experiments were performed under different temperatures conditions. The moisture content of oil shale was measured during the experiments. The two-stage drying model was incorporated in computational fluid dynamics (CFD) package FLUENT via user-defined functions (UDF) and utilized for simulation of heat and mass transfer of oil shale drying in the fluidized bed dryer. The simulation results for solid moisture content agreed well with experimental data. The effects of the temperature and velocity of flue gas, initial bed height, and the particle size on the drying characteristics were predicted and analyzed. It is shown that the gas temperature and velocity are the important parameters in the whole drying process. The particle size has more obvious influence in the falling drying period than the constant drying period. The temperatures of gas and solid phases were monitored. It is shown that the so-called “near gas distributor zone” is the most effective heat transfer zone, which agrees well with the calculated value. The system quickly reached thermal equilibrium, characterizing a nearly isothermal bed. The developed model provides a very good demonstration to describe the oil shale drying in the fluidized bed dryer, and may provide important information for design, optimization of operation conditions.

The abatement of fine particles from desulfurized flue gas by heterogeneous vapor condensation coupling two impinging streams

A novel process was proposed for fine particles abatement via heterogeneous vapor condensation coupling two impinging steams (TIS) technique in this paper. The essential supersaturation was established by adding steam or humid air into desulfurized flue gas, and the application of TIS technique in this process made the mixture of desulfurized flue gas and humid air or steam more sufficient. The fine particles were enlarged by the heterogeneous vapor condensation and the collision-coalescence in two impinging steams condensational growth chamber (TISCGC), then the enlarged fine particles were intercepted by a wire mesh demister at the top of TISCGC. The results indicated that the enlargement of fine particles in TISCGC was more significant than that of conventional condensational growth chamber (CCGC), thus the fine particle removal performance of wire mesh demister was better. The removal performance of fine particles by this process was influenced by many factors, such as flue gas velocity of opposing jets in TISCGC, additive amount of steam or humid air and the desulfurized flue gas temperature. Under the optimum conditions, the removal efficiency of TISCGC could be increased to 50–60% by using this process.

Performance of a pilot-scale wet electrostatic precipitator for the control of sulfuric acid mist.

The use of a wet electrostatic precipitator (WESP) is often regarded as a viable option to reduce sulfuric acid mist emitted from the wet flue gas desulfurization (WFGD) tower in coal-fired power plants. In this study, a pilot-scale wet electrostatic precipitator equipped with a wall-cooled collection electrode is investigated for the control of sulfuric acid mist from a simulated WFGD system. The results show that due to partial charging effect, the removal efficiency of sulfuric acid aerosol decreases when the aerosol size decreases to several tens of nanometers. Moreover, due to the plasma-induced effect, a large number of ultrafine sulfuric acid aerosols below 50nm formed at a voltage higher than 24kV inside the WESP. The percentages of submicron-sized aerosols significantly increase together with the voltage. To minimize the adverse plasma-induced effect, a WESP should be operated at a high gas velocity with an optimum high voltage. Even at a high flue gas velocity of 2.3ms(-1), the mass concentration and the total number concentration of uncaptured sulfuric acid aerosols at the WESP outlet are as low as ca. 0.6mgm(-3) and ca. 10(4) 1cm(-3) at 28kV, respectively. The corresponding removal efficiencies were respectively higher than 99.4 and 99.9% and are very similar to that at 1.1 and 1.6ms(-1). Moreover, the condensation-induced aerosol growth enhances the removal of sulfuric acid mist inside a WESP and enables a low emission concentration of ca. 0.65mgm(-3) with a corresponding removal efficiency superior to 99.4% even at a low voltage of 21kV, and of ca. 0.35mgm(-3) with a corresponding removal efficiency superior to 99.6% at a higher voltage level of 26kV.

Results of examination of the TGMP-314 boiler superheaters of the power-generating units at Kashira state district power plant using a magnetic ferrite meter

The results of investigating the elemental composition of the scale and the metal of a tube circuit from the austenitic steel grade 12Cr18Ni12Ti are presented. The superheater is part of the high-pressure convection steam superheater of a TGMP-314 supercritical-pressure gas-and-oil-fired once-through boiler that had been operated for a long period of time. A structurally transformed layer, poor in iron, manganese, and chromium and rich in nickel was detected on the outer surface. The layer consisted predominantly of the FeNi3 phase with ferromagnetic properties. The heat-resistance test of the steel in contact with ash that simulated the combustion products of fuel oil showed that the higher the temperature and the longer the test time, the higher the content of the ferritic phase in the layer was. The established pattern of the structural transformations underlies a method for nondestructive control of the thermal nonuniformity and detection of “worst” tube circuits of superheaters from austenitic steel. The magnetic ferritometry complements the conventional selective thickness gauging that does not characterize the condition of the heating surfaces of hightemperature steel grades to the full extend. Data on damageability of high-pressure convection superheaters and low-pressure second-stage convection superheaters with rarefied tube banks of TGMP-314 boilers are presented. The damage is caused by overheating resulting from the nonuniform temperature field at the inlet and by the nonuniform flue gas velocity field in rarefied superheater banks. Sections of the tube circuits from the steel grade 12Cr18Ni12Ti, outlet superheater stages of the TGMP-314 boiler of the power-generating units at Kashira SDPP were examined using an MF-51NTs AKASKAN magnetic ferrite meter. Thermal nonuniformity was established and the “worst” superheater tube circuits were detected. It was shown that the zones with the “worst” and damaged tube circuits coincide. The results of examining the superheaters with the help of a magnetic ferrite meter, of dimensional control, and of metallographic investigation of the samples cut out of the tube circuits are in agreement with each other.

Experimental studies of shell-side fluid flow and heat transfer characteristics in a submerged combustion vaporizer

In this paper, an experimental apparatus was set up to study the two-phase mixture flow and heat transfer over a horizontal tube bundle on the shell-side of the submerged combustion vaporizer (SCV). The influences of the static water height, superficial flue gas velocity and heat load on the heat transfer characteristics were systematically examined. The experimental results revealed some interesting observation of the SCV, such as the circulation flow of water bath accompanying a great deal of gas bubbles and the highly thermal efficiency due to the direct-contact heat transfer between the highly turbulent two-phase mixture and staggered tube bundles. Finally, based on the experimental data, a new dimensionless, semi-theoretical empirical correlation was developed for two-phase mixture convection heat transfer over the staggered tube bundle on the shell-side of SCV. The discussion and correlation provided a framework for designing the SCV.

Investigation of a pilot-scale wet electrostatic precipitator for the control of sulfuric acid mist from a simulated WFGD system

Wet electrostatic precipitator (WESP) was often regarded as an effective countermeasure for sulfuric acid mist emitted from coal-fired power plants. However, recent studies indicate that WESP is an ambivalent measure due to its negative effect of generating ultrafine aerosols, which could lead to non-negligible solvent emission from amine based post-combustion capture (PPC) device. In this study, we attempt to clearly reveal how the key parameters, i.e. operating voltage and flue gas velocity, affected these ultrafine aerosols formation inside a pilot WESP. Our investigations have shown that a large number of ultrafine sulfuric acid aerosols formed in the WFGD process, with a cumulative size distribution (CSD) percentage close to 100% for aerosols below 150nm. With the activation of WESP, size distribution of sulfuric acid aerosol shifted towards smaller size. Especially, the percentages of submicron-sized aerosols were significantly increased with the increase of applied voltage. Our results confirmed that plasma-induced effect inside WESP was mainly responsible for ultrafine sulfuric acid aerosol formation, and indicated that its effect was weakening with increasing flue gas velocity. For further decreasing the plasma-induce effect, the investigated WESP was more suitable for operating at a high flue gas velocity with an optimum high voltage level, which could achieve better effect on energy utilization and aerosol control based on both number concentration and mass concentration. The results indicated that at a high flue gas velocity of 2.28m/s and a specific energy input (SEI) of 2.4kWh/1000m3, the mass concentration of sulfur trioxide and total number concentration of sulfuric acid aerosols at the investigated WESP outlet were as low as ~1.0mg/m3 and ~1041/cm3, respectively.

Conceptual development of an energy recovery from the chimney flue gases using ducted turbine system

An innovative idea of extracting kinetic energy from man-made wind resources (chimney flue gases) with ducted horizontal axis turbine system for producing electricity is introduced in this paper. The turbine system is positioned beyond the chimney outlet, to avoid any negative impact on the chimney performance. The duct acts as a safety cover for the energy recovery system and also enhances the performance of the system. The effect of airfoils NACA4412 and NACA4416 on the power extraction by the energy recovery system using a 6-bladed ducted turbine has been studied using CFD simulation. It is observed that the average flue gas velocity in the duct section at the throat is approximately twice that of the inlet velocity, whereas maximum throat velocity achieved is 2.6 times the inlet velocity. The results from the CFD (Computational Fluid Dynamics) based simulations analysis indicate that a significant power can be harnessed from the chimney exhaust. The system may be retrofitted to existing chimneys of thermal power plants, refineries and other industries. The market potential for this energy recovery system appears to be very high due to abundant chimneys, cooling towers and other man-made air/gaseous exhaust system present globally.

Gas-side fouling, erosion and corrosion of heat exchanger for middle and low temperature flue gas waste heat recovery

With the ongoing emphasis on the efficient use of energy, much effort is put on the development and application of various heat recovery technologies. Heat exchangers play an important role in energy transfer and utilization and are widely used to recover waste energy from different kinds of heat sources in many fields such as energy and power engineering, petroleum and chemical engineering, air conditioning and refrigeration, aviation and aerospace, etc. In the heat exchangers for waste heat recovery, the gas-side fluid mediums usually are unclean and corrosive. The problems of fouling, erosion and corrosion of heat exchangers in the middle and low temperature flue gas-side caused by the high ash content, viscous and corrosive components are inevitable, and how to effectively solve the problems has been the subject of much research in recent years. In this paper, the researches of fouling, erosion and corrosion characteristics in middle and low temperature flue gas heat exchangers are reviewed. The causes and influence factors are discussed. Firstly, the fouling mechanisms of heat exchangers are introduced and the existing theoretical models, empirical models, and numerical methods of particle transport, impact and deposition are reviewed. The ash fouling characteristics of 6-row tube heat exchangers are presented and the effects of flue gas velocity, particle diameter, spanwise tube pitch, longitudinal tube pitch, tube shape and geometry conditions on fouling rate are discussed. Both decrease of the longitudinal tube spacing and increase of spanwise spacing can effectively reduce the deposition of particles. The geometry of elliptical tubes can fulfill this requirement for fouling reduction with smaller longitudinal spacing and larger spanswise pitch. The feasibility of using oval tube is explored for the fouling reduction. Compared with the circular tube arrangement, the deposition rate of the elliptical tube was decreased by 68.8%. Secondly, the existing erosion mechanisms, theories and methods are introduced. Different erosion models, including the model advantages and disadvantages are also summarized. The dynamics behaviour of the entrained solid particles in the flow and the deformation of the tube surface due to erosion are presented. The effects of particle diameter, particle mass flow rate and fluid Reynolds number are discussed. Among the three parameters, fluid Reynolds number has the most important effect on the erosion of tube surface. Erosion mainly occurs at the first part of the single tube surface. Thirdly, the existing mechanisms, theories and methods of corrosion characteristics of heat exchangers are introduced. Then a coupling numerical model, developed in author’s previous research, is discussed to predict the condensation characteristics of sulfuric acid vapor on heat exchanger surfaces. The corrosion risk can be reduced by decreasing the water vapor concentration and increasing the flue gas temperature. The effects of operating parameters and geometry conditions on the sulfuric acid condensation and corrosion characteristics are also discussed. A correlation of Sh number of sulfuric acid versus fin geometries for a 10-row tube bundle is provided. In order to reveal the anti-corrosion characteristics of different materials and the coupling mechanisms between the fouling and dewpoint corrosion, the online water-cooled test system and laboratory static sample test system on the corrosion characteristics of heat exchangers are introduced. Some dewpoint corrosion resistant steels are presented. The mechanism of dewpoint corrosion is revealed, the relationship between the thickness of corrosion layer and wall temperature is discussed and the coupling mechanisms between the fouling and dewpoint corrosion are also discussed. The corrosion products are composed of the ash and acid reaction products in the outer layer, iron sulfate in the middle layer, and iron oxide in the inner layer. The innermost layer is the main corrosion layer. Finally, the research needs and prospect of fouling, erosion and corrosion research are discussed. Hope to solve the problems of designing the anti-fouling, anti-erosion and anti-corrosion heat exchangers, and promote the development of efficient utilization technologies in middle and low temperature flue gas heat exchangers.

Mathematical modeling of and parametric studies on flue gas recirculation iron ore sintering

A relatively more comprehensive 1D mathematical model, compared to previous models, is proposed for flue gas recirculation sintering (FGRS). The proposed model considers multiphase theory, eight major reactions significantly affected by the input gas conditions, and various heat transfer processes within/between different solid and gas phases. Characteristic size distributions of materials including coke, limestone and dolomite are used to correct the reaction rates of key sub-models, as well as specific kinetic parameters determined via thermogravimetric analysis instead of empirical values. Geometric changes caused by the reactive and melting factors are described in improved manners. This model is validated by contrasting the modeling results and the measured data from sinter pot tests. Parametric studies show FGRS technology can significantly enhance combustion characteristic within sinter bed, meaning to increase maximum temperature and melt fraction, improve the uneven distribution of heat. Therefore, the quality of sintered ore can be improved. However, the slightly reduced flame front speed deserves further attention. The velocity of input flue gas exerts the most significant effect, followed by O2 concentration, and then, temperature. The operating parameters of FGRS must be carefully determined. Three measures, which still require further investigations, can be proposed to optimize the process.

Analysis of Chemical Reaction Kinetics Behavior of Nitrogen Oxide During Air-staged Combustion in Pulverized Boiler

Because the air-staged combustion technology is one of the key technologies with low investment running costs and high emission reduction efficiency for the pulverized boiler, it is important to reveal the chemical reaction kinetics mechanism for developing various technologies of nitrogen oxide reduction emissions. At the present work, a three-dimensional mesh model of the large-scale four corner tangentially fired boiler furnace is established with the GAMBIT pre-processing of the FLUENT software. The partial turbulent premixed and diffusion flame was simulated for the air-staged combustion processing. Parameters distributions for the air-staged and no the air-staged were obtained, including in-furnace flow field, temperature field and nitrogen oxide concentration field. The results show that the air-staged has more regular velocity field, higher velocity of flue gas, higher turbulence intensity and more uniform temperature of flue gas. In addition, a lower negative pressure zone and lower O2 concentration zone is formed in the main combustion zone, which is conducive to the NO of fuel type reduced to N2, enhanced the effect of NOx reduction.

Experimental investigation on the thermal performance of heat recovery system with gravity assisted heat pipe charged with R134a and R410A

The purpose of this study is to investigate the thermal performance of heat recovery system with gravity assisted heat pipe charged R134a and R410A working fluids and also determine the usefulness of heat pipe bundle system in heat recovery applications. For this purpose an experimental test rig was designed and built. Series of experimental tests were carried out by varying the flue gas temperature (75, 100, 125, 150 and 175 °C), flue gas velocity (1, 1.5, 2 and 2.5 m/s) and cooling water flow rates (1, 2, 3 and 4 l/min). Values of the overall effectiveness of the heat pipe heat recovery system are shown to vary with the flue gas velocity, as expected, but the results also allow the prediction of effectiveness variation with the variation of the flue gas temperature. Effectiveness of the heat pipe for both working fluids R134a and R410A has been varied averagely between 35.6% and 57.7% with a good agreement with the published results. Quantitatively, it is found that R134a working fluid is 14% more effective than R410A in heat pipe bundle system.

Estimation of uncertainty of mean velocity of flue gas in a conduit as determined by the traverse method within the gravimetric measurement of particulate concentration

In gravimetric measurements of dust emissions from industrial technological plants, the required mean gas velocity in a conduit is often determined by Pitot traverse method. It is commonly seen as a method giving good approximate values of mean gas velocity, although the actual rate of this approximation is not considered in the analysis of measurement results. It was seen that there was a need to establish what magnitude of error might occur in practice due to the small number of measurement points and typical non-uniformity of the gas velocity profiles in conduits of rectangular cross-section. The calculations were based on the concept of treating a measurement plane as one consisting of a set of elementary planes. The elementary gas velocity profiles in these elementary planes were simulated, the mean velocity for these profiles were calculated based on point velocity values, and the measurement uncertainty of this mean velocity determined. This uncertainty results in the uncertainty of the mean velocity across the entire measurement plane. It appears that, depending on the number of measurement points and gas velocity profile non-uniformity, the value is not small and is of the order of several percent, and hence needs to be taken into account in the budget of the combined uncertainty of mean velocity, which in turn contributes to the uncertainty of gas volumetric flow rate and dust pollutant mass flow rate.

Influence of vertical burner tilt angle on the gas temperature deviation in a 700 MW low NOx tangentially fired pulverised-coal boiler

In the present paper, computational fluid dynamic modelings were established to research a newly presented re-heat steam temperature deviation solution on the basis of FLUENT 6.3.26 considering a 700MWe tangentially fired pulverised-coal boiler, which confronted with severe flue gas and re-heat steam temperature deviation. The model was solidly validated by grid independence test and comparison with the experimental data obtained from a series of on-site measurements. Upon reliable validation, the model was further used to investigate the forming mechanism of re-heat steam temperature deviation as well as the influence of burner tilt angle on it. The conclusions mainly include (1) Residual swirling flow in the upper furnace caused the flue gas velocity and temperature deviations in crossover pass. For a typical anticlockwise tangential firing system, the flue gas velocity and temperature were lower in left part of crossover pass. The deviation of flue gas further generated the convective heat transfer imbalance of final re-heater, therefore, the temperature deviation of re-heat steam was severe. (2) Tilting the burner upward can effectively reduce the intensity of residual flow as well as the flue gas deviation degree. The +11° tilt angle of burner was relatively optimum considering the flue gas deviation and final re-heater overheating potential. Specifically, the intensity of residual swirl flow dropped 44% with burner tilting upward for +11°. Practical operation of boiler demonstrated that the reheat steam temperature deviation was reduced from 22°C to 10°C in this case. (3) When the tilt angle of additional air (AA) was bias set, the flow field of upper furnace was changed. Consequently, the residual swirl flow intensity and the flue gas deviation were reduced considerably. On-site measurements indicated that the combination of tilting burner upward for +11° and setting the bias of AA tilt angle for 10° can further reduce the re-heat steam temperature deviation to 4°C.

Application of an empirical model in CFD simulations to predict the local high temperature corrosion potential in biomass fired boilers

To gain reliable data for the development of an empirical model for the prediction of the local high temperature corrosion potential in biomass fired boilers, online corrosion probe measurements have been carried out. The measurements have been performed in a specially designed fixed bed/drop tube reactor in order to simulate a superheater boiler tube under well-controlled conditions. The investigated boiler steel 13CrMo4-5 is commonly used as steel for superheater tube bundles in biomass fired boilers. Within the test runs the flue gas temperature at the corrosion probe has been varied between 625 °C and 880 °C, while the steel temperature has been varied between 450 °C and 550 °C to simulate typical current and future live steam temperatures of biomass fired steam boilers. To investigate the dependence on the flue gas velocity, variations from 2 m·s−1 to 8 m·s−1 have been considered. The empirical model developed fits the measured data sufficiently well. Therefore, the model has been applied within a Computational Fluid Dynamics (CFD) simulation of flue gas flow and heat transfer to estimate the local corrosion potential of a wood chips fired 38 MW steam boiler. Additionally to the actual state analysis two further simulations have been carried out to investigate the influence of enhanced steam temperatures and a change of the flow direction of the final superheater tube bundle from parallel to counter-flow on the local corrosion potential.

Influential parameters on ultrafine particle concentration downwind at waste-to-energy plants

A numerical investigation on the parameters influencing the ultrafine particle concentrations downwind an incinerator plant has been carried out on a three-dimensional full scale model. The simulation was based on a modified version of the k–ε turbulence model in order to take into account the thermal buoyancy effect of the plume, and reproducing a stable and neutral atmospheric boundary layer by setting appropriate values of velocity, turbulent kinetic energy and turbulent dissipation rate. The ability of the model to reproduce and maintain a stable atmospheric boundary layer was evaluated by analyzing the turbulent characteristics of the flow along the domain. A parametric analysis made on the basis of different plant operational, environmental, and flue gas treatment parameters was carried out in order to evaluate the impact of incinerator plants on the background concentration of ultrafine particles. The evaluation was made at 5km downwind the chimney in a breathable area, showing that the most significant impact is due to the flue gas treatment section, with a variation on the background concentration up to 370% for a plant hypothetically working without controls on ultrafine particles emission. Operational and environmental parameters determine variations of the concentrations ranging from 1.62% to 4.48% for the lowest and highest chimney, from 1.41% to 4.52% for the lowest and highest wind speed and from 2.48% to 4.5% for the lowest and highest flue gas velocity, respectively. In addition, plume rise evaluation was carried out as a function of wind speed and flue gas velocity from the chimney.