scholarly journals Numerical Study of the Influence of Secondary Air Uniformity on Jet Penetration and Gas-Solid Diffusion Characteristics in a Large-Scale CFB Boiler

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5679
Author(s):  
Xiong Zheng ◽  
Jin Yan ◽  
Jinping Wang ◽  
Xiaofeng Lu
Keyword(s):  
Penetration Depth ◽  
Large Scale ◽  
Numerical Study ◽  
Diffusion Distance ◽  
Boiler Load ◽  
Cfb Boiler ◽  
Diffusion Characteristics ◽  
Jet Penetration ◽  
Secondary Air ◽  
And Diffusion

The uniformity of secondary air (SA) in large-scale CFB boilers has an important influence on gas-solid flow and combustion, but was seldom considered in previous studies. Numerical simulation based on the Eulerian–Eulerian and RNG k-ε turbulence models was conducted to explore the influence of SA uniformity and load variation on jet penetration, diffusion characteristics and gas-solid mixing in the first 600 MW supercritical CFB boiler. The results showed that better SA uniformity was conductive to the uniformity of SA penetration and gas-solid mixing along the furnace height, although the penetration depth and diffusion distance showed an opposite trend. In addition, the penetration depth and diffusion distance got enhanced with higher boiler load. The inner and outer SA jets could not cover the furnace width, and the uneven SA uniformity led to a huge deviation of the solid concentration within 10 m of the air distributor. Eventually, a calculation model was successfully established for predicting the penetration depth of inclined thermal SA jets during boiler operation.

Model-Based Analysis of Transient Behavior of Large Scale CFB Boilers

2003 ◽  
Author(s):  
Ari Kettunen ◽  
Timo Hyppa¨nen ◽  
Ari-Pekka Kirkinen ◽  
Esa Maikkola
Keyword(s):  
Flow Rate ◽  
Large Scale ◽  
Air Flow ◽  
Model Parameters ◽  
Air Flow Rate ◽  
Process Data ◽  
Cfb Boiler ◽  
Flow Rates ◽  
Load Change ◽  
Secondary Air

The main objective of this study was to investigate the load change capability and effect of the individual control variables, such as fuel, primary air and secondary air flow rates, on the dynamics of large-scale CFB boilers. The dynamics of the CFB process were examined by dynamic process tests and by simulation studies. A multi-faceted set of transient process tests were performed at a commercial 235 MWe CFB unit. Fuel reactivity and interaction between gas flow rates, solid concentration profiles and heat transfer were studied by step changes of the following controllable variables: fuel feed rate, primary air flow rate, secondary air flow rate and primary to secondary air flow ratio. Load change performance was tested using two different types of tests: open and closed loop load changes. A tailored dynamic simulator for the CFB boiler was built and fine-tuned by determining the model parameters and by validating the models of each process component against measured process data of the transient test program. The know-how about the boiler dynamics obtained from the model analysis and the developed CFB simulator were utilized in designing the control systems of three new 262 MWe CFB units, which are now under construction. Further, the simulator was applied for the control system development and transient analysis of the supercritical OTU CFB boiler.

scholarly journals Study of the Penetration and Diffusion Characteristics of Inorganic Solidified Foam in Rock Fractures

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Yi Lu ◽  
Tao Wang ◽  
Qing Ye
Keyword(s):  
Effective Diffusion ◽  
Rock Fractures ◽  
Prediction Formula ◽  
Diffusion Distance ◽  
Coal Fire ◽  
Diffusion Characteristics ◽  
Diffusion Pattern ◽  
The Right ◽  
Fluid Penetration ◽  
And Diffusion

To explore the penetration and diffusion law in coal and rock fractures when inorganic solidified foam (ISF) is used to prevent coal fire, the penetration experiment was conducted; the results showed that the penetration pressure fluctuates within a certain range and decreases with the diffusion distance. In theXYplane, the diffusion pattern presents an ellipsoid shape, and the diffusion area becomes increasingly large over time; in theXZplane, the foam fluid penetration changes from dense to loose in theXdirection and it does not undergo downward penetration and diffuses via its own weight in theZdirection; in theYZplane, it is loose on the left and dense on the right. The viscosity of ISF was tested and then the time-varying formula was fitted. The formula of the effective diffusion radius for foam fluid diffusing in the fracture channel was determined theoretically. The permeability coefficient and other related parameters were calculated in terms of the penetration pressure and diffusion time of two monitoring points. At last, the prediction formula of effective diffusion distance of foam fluid was verified with the remaining seven monitoring points and all the relative error of monitoring is within 10%.

Numerical study of the stand-off distance and liner thickness effect on the penetration depth efficiency of shaped charge process

2018 ◽  
Vol 233 (3) ◽  
pp. 977-986 ◽  
Author(s):  
P Dehestani ◽  
AR Fathi ◽  
HR Mohammadi Daniali
Keyword(s):  
Finite Element ◽  
Penetration Depth ◽  
Numerical Study ◽  
Experimental Tests ◽  
Shaped Charge ◽  
Thickness Effect ◽  
Geometrical Parameters ◽  
Element Analysis ◽  
Finite Element Software ◽  
Jet Penetration

The aim of this paper is to investigate the effect of geometrical parameters on the performance of jet penetration in the process of shaped charge. To this end, the finite element analysis was used to simulate the process. The simulated process was validated by experimental tests and the effect of some parameters including stand-off distance and the liner thickness on the jet penetration depth was studied. The results indicated that choosing the optimal distance between the liner and the target (stand-off distance) can significantly affect the performance of jet penetration in the target. In addition, examining the effect of liner thickness on the penetration depth efficiency revealed that by decreasing the liner thickness, the jet penetration depth on the target increases. It should be noted that ABAQUS finite element software was used in this simulation to analyze the process of shaped charge.

scholarly journals A Comprehensive, Three-Dimensional Analysis of a Large-Scale, Multi-Fuel, CFB Boiler Burning Coal and Syngas. Part 2. Numerical Simulations of Coal and Syngas Co-Combustion

Entropy ◽  
2020 ◽  
Vol 22 (8) ◽  
pp. 856 ◽  
Author(s):  
Jaroslaw Krzywanski ◽  
Karol Sztekler ◽  
Mateusz Szubel ◽  
Tomasz Siwek ◽  
Wojciech Nowak ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Large Scale ◽  
Bituminous Coal ◽  
Circulating Fluidized Bed ◽  
Three Dimensional ◽  
Cfb Boiler ◽  
Start Up ◽  
Carbon Dioxide Concentrations ◽  
Secondary Air ◽  
Burning Coal

This paper presents the results of numerical computations for a large-scale OFz-425 CFB (circulating fluidized bed) boiler utilizing coal and syngas. Four different operating scenarios are considered, including the reference variant, corresponding to the conventional, mono-combustion of bituminous coal, and three tests involving replacement of secondary air and part of the coal stream with syngas fed by start-up burners. Pressure, gas velocity, temperature, and carbon dioxide distribution in the combustion chamber are discussed in the paper. The results indicate that the syngas supply leads to an increase in local temperature and carbon dioxide concentrations. The proposed concept is not advisable as it may lead to frequent emergency stops of the CFB boiler.

Accidental Sustainability

2017 ◽  
Author(s):  
Geoffrey Jones
Keyword(s):  
Large Scale ◽  
Negative Impact ◽  
Positive Impact ◽  
Organic Food ◽  
The United States ◽  
Air Travel ◽  
Business Leaders ◽  
Natural Beauty ◽  
And Diffusion ◽  
Whole Foods

This chapter examines the scaling and diffusion of green entrepreneurship between 1980 and the present. It explores how entrepreneurs and business leaders promoted the idea that business and sustainability were compatible. It then examines the rapid growth of organic foods, natural beauty, ecological architecture, and eco-tourism. Green firms sometimes grew to a large scale, such as the retailer Whole Foods Market in the United States. The chapter explores how greater mainstreaming of these businesses resulted in a new set of challenges arising from scaling. Organic food was now transported across large distances causing a negative impact on carbon emissions. More eco-tourism resulted in more air travel and bigger airports. In other industries scaling had a more positive impact. Towns were major polluters, so more ecological buildings had a positive impact.

scholarly journals Interaction of Very Large Scale Motion of Coherent Structures with Sediment Particle Exposure

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 248
Author(s):  
Sencer Yücesan ◽  
Daniel Wildt ◽  
Philipp Gmeiner ◽  
Johannes Schobesberger ◽  
Christoph Hauer ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Numerical Study ◽  
Local Maximum ◽  
Wave Number ◽  
Exposure Level ◽  
Sediment Particle ◽  
High Wave Number ◽  
Large Scale Motion ◽  
Scale Motion

A systematic variation of the exposure level of a spherical particle in an array of multiple spheres in a high Reynolds number turbulent open-channel flow regime was investigated while using the Large Eddy Simulation method. Our numerical study analysed hydrodynamic conditions of a sediment particle based on three different channel configurations, from full exposure to zero exposure level. Premultiplied spectrum analysis revealed that the effect of very-large-scale motion of coherent structures on the lift force on a fully exposed particle resulted in a bi-modal distribution with a weak low wave number and a local maximum of a high wave number. Lower exposure levels were found to exhibit a uni-modal distribution.

A numerical study of the transition of jet diffusion flames

1990 ◽  
Vol 431 (1882) ◽  
pp. 301-314 ◽  
Keyword(s):  
Reynolds Number ◽  
Diffusion Coefficient ◽  
Large Scale ◽  
Numerical Study ◽  
Small Scale ◽  
Surface Model ◽  
Flame Surface ◽  
Transition Mechanism ◽  
Air Stream ◽  
Scale Fluctuation

A numerical study on the transition from laminar to turbulent of two-dimensional fuel jet flames developed in a co-flowing air stream was made by adopting the flame surface model of infinite chemical reaction rate and unit Lewis number. The time dependent compressible Navier–Stokes equation was solved numerically with the equation for coupling function by using a finite difference method. The temperature-dependence of viscosity and diffusion coefficient were taken into account so as to study effects of increases of these coefficients on the transition. The numerical calculation was done for the case when methane is injected into a co-flowing air stream with variable injection Reynolds number up to 2500. When the Reynolds number was smaller than 1000 the flame, as well as the flow, remained laminar in the calculated domain. As the Reynolds number was increased above this value, a transition point appeared along the flame, downstream of which the flame and flow began to fluctuate. Two kinds of fluctuations were observed, a small scale fluctuation near the jet axis and a large scale fluctuation outside the flame surface, both of the same origin, due to the Kelvin–Helmholtz instability. The radial distributions of density and transport coefficients were found to play dominant roles in this instability, and hence in the transition mechanism. The decreased density in the flame accelerated the instability, while the increase in viscosity had a stabilizing effect. However, the most important effect was the increase in diffusion coefficient. The increase shifted the flame surface, where the large density decrease occurs, outside the shear layer of the jet and produced a thick viscous layer surrounding the jet which effectively suppressed the instability.

Sign in / Sign up

Export Citation Format

Share Document