Radiant Syngas Cooler Research Articles

Numerical simulation of ash deposition behavior in radiant syngas cooler coupled with impact surface temperature

Radiant syngas cooler (RSC) is a crucial heat recovery device for entrained-flow coal gasification technology. However, ash deposition in an RSC can severely affect operating efficiency and safety. An ash deposition model coupled with the impact surface temperature was established based on the ash particle deposition morphology. The effects of different operating conditions on ash deposition characteristics are discussed. The simulated data agreed well with the industrial data. The results indicate that ash particles were primarily deposited in the collision deposition zone. The maximum deposition thickness of radiation screen and cylinder membrane wall is 9.82 mm and 1.88 mm, respectively. The ash deposition hindered heat transfer process and the highest heat flux was observed in the middle part of the RSC. Ash deposition around 5.3 m increases significantly with an increase in the inlet syngas temperature. Increasing the load increased probability of ash particle collision and the area of influence.

Influence of syngas components and ash particles on the radiative heat transfer in a radiant syngas cooler

Radiant syngas cooler (RSC) is widely used as a waste heat recovery equipment in industrial gasification. In this work, an RSC with radiation screens is established and the impact of gaseous radiative property models, gas components, and ash particles on heat transfer is investigated by numerical simulation method. Considering the syngas components and the pressure environment of the RSC, a modified weighted-sum-of-gray-gases model was developed. The modified model shows high accuracy in validation. In computational fluid dynamics simulation, the calculated steam production is only 0.63% in error with the industrial data. Compared with Smith’s model, the temperature decay along the axial direction calculated by the modified model is faster. Syngas components are of great significance to heat recovery capacity, especially when the absorbing gas fraction is less than 10%. After considering the influence of particles, the outlet temperature and the proportion of radiative heat transfer are less affected, but the difference in steam output reaches 2.7 t·h–1. The particle deposition on the wall greatly reduces the heat recovery performance of an RSC.

Crystallization-controlled fusion mechanism of the amorphous fly ash from the Shell coal gasifier by particle sieving

The mineral in coal is transformed to the fly ash of different particle sizes during the entrained flow coal gasification, causing the ash deposition problem on the radiant syngas cooler. In this study, the fusion behavior of fly ash collected from a Shell coal gasifier was analyzed by particle sieving. Results indicated that the fusibility of amorphous fly ash was influenced by the anorthite crystallization at high temperature. The fusion process of fly ash particle was divided into the sintering stage, plateau stage, and melting stage, which were caused by the flow of the amorphous fly ash, anorthite crystallization, and anorthite melting, respectively. The high theoretical anorthite content and the low fly ash viscosity improved the anorthite crystallization reaction in the fly ash particles <45 μm, resulting in a wide plateau stage, narrow melting stage, and high ash fusion temperatures (AFTs). Therefore, the fusion behavior of fly ash particles <45 μm followed “melting-dissolution” mechanism. In contrast, the fusion of fly ash particles >45 μm belonged to the “softening-melting” mechanism for the weak anorthite crystallization behavior. The fly ash particles <45 μm may cause the serious ash deposition problems for its low viscosity.

Deposition characteristics of particles in backward-facing step flow and a radiant syngas cooler

Investigation of the mechanism of particle transport and deposition in backward-facing step (BFS) flow is conducive to enhancing the understanding of the deposition characteristics of fly ash in the radiant syngas cooler (RSC). In this study, the regional characteristics of particle deposition in BFS and RSC are deeply studied by numerical simulation. The results show that the deposition of small particles in the recirculation (RC) zone and most particles in the reattachment and redevelopment (RR) zone is promoted while that of large particles in the RC zone is inhibited by the main flow. The variation curves of dimensionless deposition velocity gradually approach to that in straight channel with the increase in deposition length, but they are little affected by the step height and inlet velocity. The differences in particle deposition rates and size distributions between the two zones in RSC are analyzed. The average deposition rate in the RC zone is 21% lower than that in the RR zone, and the proportion of particles smaller than 45.03 μm in the RC zone is higher than that in the RR zone by 24%. This study can provide a basis for the establishment of ash deposition control strategies.

Simulation analysis of instantaneous impact on the radiant syngas cooler by rapping vibrators

AbstractSlag or ash removal from water wall tubes in a radiant syngas cooler (RSC) is a routine task in operation, which can effectively increase the overall thermal efficiency. Rapping ash removal is one of the valid methods for shedding off the ash deposits in the high‐pressure surroundings of the RSC. In this study, the model of a real RSC was established by a numerical simulation based on the finite element software ABAQUS, and modal analysis and instantaneous response analysis (IRA) were researched to reveal the natural vibration characteristics of the RSC and aid the design of rapping ash removal. On the basis of the results of natural vibration characteristics and a subsequent harmony response, 16 Hz was set as the impact frequency, balancing off the vibrator number and the water‐tube displacement effect. It was indicated that ash deposit in the area around 1/2 longitudinal position was easy to remove due to great response to rapping action. Moreover, rapping at ½ position generally obtained greater displacement response in the whole RSC. A rapping design was proposed with six vibrators at the ½ longitudinal position and 16 Hz frequency, and then two rapping intervals were investigated comparatively. The case with a half‐cycle interval had a slightly larger response than the one‐cycle case, with a larger displacement in more circumferential tubes as well as with a greater sound pressure response in the RSC.

Numerical study on dynamic ash deposition and heat transfer characteristics of radiant syngas cooler

Ash deposition greatly influences the performance of Radiant Syngas Cooler (RSC) which plays a pivotal role in the heat recovering process in coal gasification technology. Therefore, a numerical model of ash deposition coupled with heat transfer is established in present study to predict the ash deposition of RSC, and the effects of inlet temperature and division wall structure on deposition characteristics are further discussed. The simulation results indicate that the particle impact mainly occurs in the transition region of the jet flow to plug flow, while the particle deposit mainly occurs in the recirculation region. The deposition of inner wall and division wall shows a malignant growth pattern successively with the width increase of division wall. The division wall of 400 mm width is more conducive to the safe and stable operation of the RSC than those of 250 mm and 650 mm. The deposition becomes heavy with the increase of inlet temperature, and the deposition of division wall belongs to the slow growth, the large-scale detaching and the malignant growth pattern at the inlet temperature of 1573 K, 1673 K and 1773 K, respectively. Present result may provide a reference for the structural design and operational adjustment of RSC.

Chemistry variation of slag and the layered characteristics of deposits in an industrialized entrained-flow gasifier system with radiant syngas cooler

Slag particles experience a series continuous transformation during the industrial gasification system and slag behavior is critical for stable operation. A proper slag layer needs to be formed in the gasifier to protect the reactor wall and the fluidity of liquid should be maintained for smooth tapping. When slag particles enter the syngas cooler, deposition is one of the obstacles restricting stable operation. This study took slag samples from a stable operational gasifier, syngas cooler and slag pool respectively, which can reveal slag chemistry transformation from the input ash to the output slag. The deposits taken from gasifier and syngas cooler are in layers. The chemical comparison result shows that the deposition in syngas cooler is more sensitive to slag composition than that in gasifier and the elements Fe, Na and K are abundant in the first deposition layer. The in-situ observation by a confocal scanning laser microscope shows that crystallization of this slag can last as low as 1000 °C. Thus, the solid-liquid mixture leads to sticky particles due to low liquid viscosity, increasing the deposition tendency.

CFD modeling of ash deposition distribution in an industrial radiant syngas cooler to enhance the operation performance

Radiant syngas cooler (RSC) is a crucial heat recovery equipment for entrained-flow coal gasification. Ash depositions in the industrial RSC endanger its operation efficiency and operation safety. In this work, the critical viscosity model and the ash shedding model are coupled to explore the ash deposition behavior in the industrial RSC for a 2000 t/d entrained-flow coal gasifier. Simulation results are in good agreement with the industrial conditions. The results show that ash depositions in RSC are mainly distributed in the upper part and the bottom cone, and the maximum ash thickness are 9.67 mm and 36.71 mm respectively. Due to ash depositions, the outlet temperature of RSC increases by 19.76%, the total heat transfer rate decreases by 21.88%, and the steam yield decreases by 22.41%. Employing low-ash coal as gasification raw coal is a good suggestion to enhance the operation performance of the industrial RSC. Moreover, when the industrial RSC is fully loaded, an appropriate increase in syngas mass flow rate can also contribute to a better operation performance.

Numerical study on the effects of homogeneous reactions on the composition distributions of syngas in radiant syngas cooler

The radiant syngas cooler (RSC) is a crucial equipment for recovering the sensible heat of high-temperature syngas produced by coal gasification. Most of the previous studies on RSC focused on the flow field and heat transfer, ignoring the chemical reactions in RSC. In this work, a three-dimensional RSC model is established to investigate the effects of homogeneous reactions on the composition distributions of syngas in RSC. The simulation results show that the composition distributions of syngas are similar to the temperature distribution of RSC. From the inlet to the outlet of RSC, the mole fraction of CO decreases by 2.81%, and the mole fraction of H2, CO2 and CH4 increases by 3.44%, 8.08% and 182.09%, respectively. The relationship between temperature and the mole fraction of CH4 is concluded, which can be used as an indirect method to predict the temperature of RSC. The homogeneous reaction in RSC is dominated by water–gas shift reaction (WGSR). There are backward WGSR and forward methane-steam reforming reaction (MSR) in the inlet area, which is contrary to the situation in the outlet area. Moreover, the composition distributions of syngas present a polarized distribution under the influence of operating pressure or operating load, because the homogeneous reactions in the inlet and outlet area of RSC are affected by syngas velocity and temperature, respectively.

Numerical simulation of radiant syngas cooler with different connection to entrained-flow gasifier

The throat region of radiant syngas cooler (RSC) is a key part for connecting the entrained-flow gasifier with RSC, and an annular step is employed in the throat region of the connection to separate the molten slag from the high-temperature gasification products discharged from the gasifier. Multiphase flow and heat transfer in four types of connection designs (i.e., straight cylindrical connection (SCC), straight cylindrical connection with annular-step (SCCA), tapered connection with annular-step (TCA), and divergent connection with annular-step (DCA)) have been studied in this work. The radiation heat transfer is simulated by the discrete ordinates model (DOM). Comparing simulated values with industrial measured values, the reliability and accuracy of the mathematic models are validated with the maximum relative error of 3.7%. Simulation results show that a torch shape inject flow is formed at the top of the RSC, and the temperature of inject region is higher than that of nearby zone. Flow field distribution is changed by the annular step and tapered region, and thus results in twice dissipation of the central jet flow. The annular step can accelerate the dissipation of the turbulent flow, and the geometry of the throat region has a great influence on the size and intensity of the recirculation bubble. The tapered region of TCA makes the first recirculation more obvious than that of the DCA and SCCA, which causes that the recirculation regions have a tendency to coalescence. The jet dissipation position moves upwards due to the changes of connection structure, which is beneficial to enhance the heat exchange performance between the syngas and membrane wall. The changes of connection structure make the particle dispersion position move upward, but can alleviate the particle dispersion.

Experimental and numerical modal analysis of wall tubes in the coal‐fired boiler or radiant syngas cooler

AbstractThe slag deposited on the wall tubes in the coal‐fired boiler or radiant syngas cooler (RSC) of the entrained flow gasifier could reduce the heat transfer efficiency and degrade the tubes by corrosion. During the operation of the boiler or RSC, the rapping‐off‐ash method is an effective method to remove slag deposits, especially in a high‐pressure environment. The operating parameters of the rapping‐off‐ash method are related to the modal parameters of wall tubes, including the natural frequency, damping ratio, and mode shapes. In this study, modal parameters of wall tubes composed of three single tubes and fins were experimentally determined through the modal test analysis under both empty and water‐filled conditions. The dynamic characteristics of wall tubes were extracted by using the roving hammer‐impact test and the frequency response function (FRF). A numerical simulation based on the finite element method in ABAQUS was conducted to compare with the experimental modal analysis. The first five natural modes ranged from 14 to 154 Hz, and the maximum vibration or torsion locations of wall tubes under the corresponding mode frequencies were investigated. The water inside the wall tubes could reduce the stiffness of the structure and decrease the values of natural frequency.

Opposed multi-burner gasification technology: Recent process of fundamental research and industrial application

Opposed multi-burner (OMB) gasification technology is the first large-scale gasification technology developed in China with completely independent intellectual property rights. It has been widely used around the world, involving synthetic ammonia, methanol, ethylene glycol, coal liquefaction, hydrogen production and other fields. This paper summarizes the research and development process of OMB gasification technology from the perspective of the cold model experiment and process simulation, pilot-scale study and industrial demonstration. The latest progress of fundamental research in nozzle atomization and dispersion, mixing enhancement of impinging flow, multiscale reaction of different carbonaceous feedstocks, spectral characteristic of impinging flame and particle characteristics inside gasifier, and comprehensive gasification model are reviewed. The latest industrial application progress of ultra-large-scale OMB gasifier and radiant syngas cooler (RSC) combined with quenching chamber OMB gasifier are introduced, and the prospects for the future technical development are proposed as well.

Average Wall Radiative Heat Transfer Characteristic of Isothermal Radiative Medium in Inner Straight Fin Tubes

Abstract Wall radiative heat transfer in inner straight fin tubes is very complex considering the coupling of heat conduction in fins and radiative heat transfer of medium with solid surfaces, influenced by a number of factors such as fin parameters, radiative properties and run conditions. The method of simulation is very inconvenient to design the heat exchanger involving the enhancement of inner straight fins on wall radiative heat transfer in tube, such as ascension pipe heat exchanger and radiant syngas cooler. In this study, a simplified method is used. The average radiative heat transfer between radiative medium and solid surfaces is first studied by simulation with fins supposed have a constant temperature. Then an approximate correlation of this radiative heat transfer coefficient is proposed using the traditional radiative heat transfer calculation method with a view coefficient, which has a little error within 15%. A calculation method of average wall radiative heat transfer coefficient is further derived based on fin theory with an average temperature of fin surface used to consider the varying of the temperature along the fin when the conductivity of fins is finite. Using the predicting method proposed, a method for design calculation of fins in tubes to optimize wall radiative heat transfer is also given with three dimensionless numbers of π/n, 2H/D, and nt/πD representing the structural properties of fins defined. Three cases of (ks = 43 W/(m•K), ɛw = 0.7, Tg = 1073.15 K, Tw = 573.15 K, D = 0.66 m, κD = 1.32), (ks = 162 W/(m•K), ɛw = 0.7, Tg = 1073.15 K, Tw = 573.15 K, D = 0.66 m, κD = 1.32) and (ks = 43 W/(m•K), ɛw = 0.3, Tg = 973.15 K, Tw = 673.15 K, D = 0.66 m, κD = 0.66) are analyzed in detail based on the design calculation method. It is verified that the radiative heat transfer could be enhanced twice by introducing fins. Under the same h0, conductivity and emissivity are two important factors that should be considered to choose the material for fins. The microfins or the special treatments on the tube wall are a best choice for the fin material having a relatively small conductivity.

Dynamic characteristics of deposit fracture and impacts of operating pressure during sootblowing in the radiant syngas cooler

AbstractDuring the operation of entrained‐flow gasifiers, the ash deposits located on the wall tubes in the radiant syngas coolers (RSC) reduce the heat transfer efficiency. Syngas sootblowing is an effective method to remove the slag deposits in the RSC. In this study, a 3D numerical model was developed by combining the cohesive zone method (CZM) and the coupled Eulerian–Lagrangian analysis to investigate the deposit fracture process in RSC during sootblowing. The quasi‐static analysis using ABAQUS obtained the stress–strain curve of the slag sample, which agreed well with the experimental tests and provided the detailed mechanical parameters to the CZM model. The dynamic characteristics of deposit fracture were discovered. The main fracture occurred between 1.0 and 1.5 ms, and the shape of the fracture area was not round but elliptical. The RSC operating pressure (P) was also investigated. The study found that higher pressure led to lower fracture speed, longer sootblowing time, and more syngas consumption. Based on the same extent of deposit fracture, syngas consumption increased when P &lt; 3.5 MPa, and the density of syngas (ρsyngas) has a more significant influence on the syngas consumption than the velocity of sootblowing syngas flow (vavg), especially when the sootblowing time is small.

Numerical Simulation of Heat Transfer and a Forging Plate Structure in a Radiant Syngas Cooler with Radiation Screens

High-temperature syngas is produced by entrained-flow coal gasification. A traditional quenching process has the drawback of low heat recovery efficiency, and the cleaning of convective syngas cool...

Investigation on the ash deposition of a radiant syngas cooler using critical velocity model

Coal gasification technology is a very important industrial technology, in which the Radiant Syngas Cooler (RSC) plays a pivotal role in the heat storage and heat recovering process. Ash deposit in RSC is a critical factor which may seriously affect the performance of RSC or even result in a shutdown. Therefore, conducting research on the deposit process of RSC is extremely worthwhile. In this study, we create an RSC model with the application of an optimized Critical Velocity Model (CVM) and perform simulations using the CFD method. With the simulating method, we conduct a series of analysis to obtain a more detailed description of the ash distribution and heat transfer in the RSC. Research shows that the CVM proposed in this paper can be precisely applied to the heat transfer process in a RSC, and not only can this method obtain the distribution of ash deposit similar to other methods but also determine the conversion of the ash deposit thickness to heat resistance, which makes the forecast of the overall heat exchange more accurate. According to the study, the ash thickness changes with the vertical height of RSC. For the division wall and panels, the ash thickness increased from the bottom, and then reached a maximum value at about 2/3 of total height. Under the influence of ash deposition, the total heat transfer rate of RSC decreased by 10.4%, and the outlet temperature of syngas increased by 5.7%. This result can provide a reference for the predictive analysis of RSC.

Comprehensive environmental impact assessment of a combined petroleum coke and natural gas to Fischer-Tropsch diesel process

In this study, a well-to-wheels life cycle assessment was conducted to determine the environmental impacts from disposing of petroleum coke by converting it into liquid fuel. Specifically, this work is an extension of the life cycle assessment of the petcoke standalone gasification to diesel study which also includes two new pathways for converting petroleum coke and natural gas to Fischer Tropsch diesel operated with and without carbon capture and sequestration (CCS). Impact categories were calculated using the EPA’s TRACI 2.1 US-Canada 2008 midpoint method in SimaPro software. In addition, the impact of grid emissions on the overall process was assessed using two representative Canadian locations with high (Alberta) and low (Ontario) grid emissions. The results of each impact category were compared among the designs and against conventional petroleum and oil sands derived diesel. Key findings showed that the proposed designs when operated with CCS in the low-emissions-grid location had life cycle GHG emissions between 281–291 gCO2-eq/km compared to the conventional petroleum and oil sands derived diesel with GHG emissions of 305 and 348 gCO2-eq/km respectively. Nevertheless, the various tradeoffs between processes indicated that there was no clearly superior design among the candidates. However, the design which uses a natural gas reformer that is integrated directly into the radiant syngas cooler of a petcoke gasification unit has the lowest cost of CO2 avoided ($144/tCO2-eq), and so is likely the best choice for reducing environmental impacts.

Numerical study on heat transfer and thermal stress of the upper cone membrane wall in radiant syngas cooler

The high temperature syngas induced from the entrained-flow gasifier contains a large amount of sensible heat, which can be efficiently recovered by radiant syngas cooler (RSC). In this work, the membrane wall models of the upper cone section in the RSC are established. The heat transfer characteristics between membrane wall and syngas are explored by numerical simulation under different operating conditions, and the thermal stress distribution on the membrane wall surface is calculated by the fluid-structure coupling method. The results show that the inner surface of the fin is partially overheated and the maximum stress exceeds the allowable stress of the material when there is no protection for the membrane wall. The increase of inlet syngas temperature and flow rate will enhance heat transfer of the upper cone membrane wall, and the effect of the inlet syngas temperature is more obvious. After the application of the silicon carbide refractory, the surface temperature of the membrane wall, especially the temperature of the wide fin parts, is greatly reduced. Moreover, the membrane wall is slightly deformed and warped due to the temperature difference between the two sides of the membrane wall.

Experimental Study on the Radiative Properties of Fly Ash in the Radiant Syngas Cooler of Gasifier

Radiant syngas cooler (RSC) is the key heat recovery equipment in coal gasification system. The syngas from gasifier carries large amount of slags in which the mass fraction of fly ash less than 100 μm is about 20%. Studying the optical properties of fly ash has high significance for the optimization of heat transfer calculation in RSC. A new experimental method was proposed to inversely calculate the radiative parameters of particles—“KBr transmittance-reflectance method”. By measuring the “directional-hemispherical” reflectance and transmittance of fly ash particles by FTIR under the wavelength range of 0.55 - 1.65 μm, using the four-flux model to solve the radiative transfer equation and combing with Mie theory, the absorption and scattering efficiency of 22.7 μm fly ash and optical constant (also known as complex refractive index, m = n + ik) of fly ash were inversely calculated. The results indicated that for fly ash with large size parameter, there was no obvious change of the absorption and scattering efficiency when the mass fraction of Fe2O3 was between 5.65% and 16.53%, which was well explained by Mie theory; The obtained optical constant was close to the results of KBr trans-mittance method.

Dynamic analysis and open‐loop start‐up of an integrated radiant syngas cooler and steam methane reformer

The transient performance of an integrated radiant syngas cooler (RSC) of an entrained‐bed gasifier and steam methane reformer (SMR) is investigated. Base‐case designs using either co‐current or counter‐current configurations are subjected to operating transients to evaluate the feasibility to transition to new steady states. Each system, under open loop, is subjected to changes in key variables of the SMR feed on the tube side and disturbances to variables of the coal‐derived syngas on the RSC side to determine the dynamics and stability of the integrated system. The results indicate that the co‐current configuration is flexible to move to new operating steady states and more safe than the counter‐current configuration, although it provides less cooling and has poorer methane conversion. The variables likely to violate the design limit in the event of a disturbance are identified. A start‐up procedure is also established based on industrial practices employed for entrained‐bed gasifiers and methane reformers. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1602–1619, 2017