Methane and Ethane Combustion in an Inert Fluidized Bed

2005 ◽  
Author(s):  
Witold Z˙ukowski
Keyword(s):  
Fluidized Bed ◽  
Flue Gases ◽  
Temperature Profiles ◽  
Unsteady Combustion ◽  
Vertical Temperature ◽  
Obvious Effect ◽  
Bubbling Bed ◽  
Bed Temperature ◽  
Bubbling Fluidized Bed ◽  
Bed Material

Burning premixed fuel-air mixtures in a bubbling fluidized bed is accompanied by some characteristic phenomena. The most striking one is the production of acoustic effects, indicating that combustion is not really continuous. A second, less obvious effect, is the NOx concentration in the flue gases falling with increasing bed temperature, observed above a certain critical mean bed temperature. To investigate the periodic burning of portions of methane-air mixture, photometric and acoustic signals were recorded simultaneously. Using a laboratory quartz reactor, explosions could be optically recorded in the bed, millimeters above distributor. With ethane fuel, the effective “combustion zone” in the reactor was also located by determining vertical temperature profiles, using eight thermocouples. When the bed temperature rises, maxima in the vertical temperature profiles associated with the “reaction zone” move from above the bubbling bed to the distributor. A mathematical model of unsteady combustion in a single bubble surrounded by bed material was used to simulate the process. Computed temperature maxima were compared with the experimental profiles. This meant finding the region where bubbles of premixed gases exploded, experimentally and from the model. A correlation between the NOx concentration and the location of the explosions (and diameter of the exploding bubbles) has also been found.

Prediction of Temperature Profiles in Fluid Bed Boilers

1978 ◽  
Vol 100 (3) ◽  
pp. 508-513 ◽  
Author(s):  
J. L. Hodges ◽  
R. C. Hoke ◽  
R. Bertrand
Keyword(s):  
Large Scale ◽  
Solid Material ◽  
Temperature Gradients ◽  
Temperature Profiles ◽  
Mixing Height ◽  
Vertical Temperature ◽  
Bed Temperature ◽  
Fluid Bed ◽  
Solids Mixing ◽  
Vertical Tubes

Data acquired in the Exxon Research and Engineering Company’s fluid bed boiler program indicate that the arrangement and orientation of internal boiler tubes has a strong effect on the measured bed temperature profile. Horizontally oriented tubes yield much steeper temperature gradients than do vertical tubes. Excessive vertical temperature gradients in coal fired fluid bed boilers can either limit coal feed rates or result in the formation of agglomerates of solid material which are destructive of bed internals. This study represents an attempt to understand the influence of orientation on vertical temperature profiles in fluid bed boilers. A back-mixing model for solids recirculation was developed and applied to the prediction of bed temperatures. Bubbling bed theory is not suitable for estimating solids circulation rates in pressurized beds of large particles with immersed tubes. However, by introducing the concept of a solids mixing height it was possible to estimate solid movement. The solids mixing height and vertical boiler tube dimensions were correlated in a manner which resulted in good agreement between theoretical and experimental bed temperature profiles. It is felt that this simple model may prove quite useful in the design of large scale commercial fluid bed boilers.

scholarly journals Experimental Investigation of Radial Gas Dispersion Coefficients in a Fluidized Bed

10.14311/1568 ◽  
2012 ◽  
Vol 52 (3) ◽  
Author(s):  
Jiří Štefanica ◽  
Jan Hrdlička
Keyword(s):  
Fluidized Bed ◽  
Formation Rate ◽  
Combustion Efficiency ◽  
Tracer Gas ◽  
Cold Model ◽  
Nox Formation ◽  
Gas Dispersion ◽  
Bed Height ◽  
Bubbling Fluidized Bed ◽  
Bed Material

In a fluidized bed boiler, the combustion efficiency, the NOX formation rate, flue gas desulphurization and fluidized bed heat transfer are all ruled by the gas distribution. In this investigation, the tracer gas method is used for evaluating the radial gas dispersion coefficient. CO2 is used as a tracer gas, and the experiment is carried out in a bubbling fluidized bed cold model. Ceramic balls are used as the bed material. The effect of gas velocity, radial position and bed height is investigated.

Effect of Static Bed Height on the Combustion of Rice Husk in a Fluidized Bed Combustor

2005 ◽  
Author(s):  
M. Rozainee ◽  
S. P. Ngo
Keyword(s):  
Fluidized Bed ◽  
Residence Time ◽  
Rice Husk ◽  
Bubble Formation ◽  
Combustion Process ◽  
High Heat ◽  
Transfer Rates ◽  
Bed Height ◽  
Bed Temperature ◽  
Bed Material

The combustion process is largely controlled by temperature, turbulence and residence time. When the temperature is sufficiently high so that the reaction is no longer kinetically-controlled, turbulence and residence time play a significant role. The reaction is thus diffusion-controlled. During the combustion of rice husk in a fluidized bed, the turbulence is largely governed by the mixing behavior in the inert sand bed, which in turn is governed by the bubble formation characteristics. Further, the residence time among the reactants (air and rice husk) and the heat source is also dependent on the turbulence in the bed. When all other parameters are held constant, the bubble phenomena vary according to the expanded bed height corresponding to a given static bed height. For high heat and mass transfer rates, small slowly rising bubbles are desired. Thus, the purpose of this study is to investigate the effect of static bed height on the quality of ash during the combustion of rice husk. The degree of rice husk burning in the bed could be deduced from the bed temperature as a higher bed temperature indicated that a higher portion of the rice husk feed is being burnt in the bed. Moreover, the particle size of the resulting ash is also able to give indication of the degree of rice husk burning in the bed as the turbulence arising from the bubbling action of the bed material is known to break down the char skeleton of the rice husk, thereby, resulting in ash with finer size. From this study, the static bed height of 0.5 DC was found to give the lowest residual carbon content in the ash (1.9 wt%) and the highest bed temperature (670°C) among the other range of static bed heights investigated.

An Experimental Study of the Gaseous Pollution Emissions in Petroleum-Coke-Fired Fluidized Beds

2003 ◽  
Author(s):  
Chun-Lin Zhang ◽  
Gui-Cheng Yuan ◽  
De-Chang Liu ◽  
Han-Ping Chen ◽  
Ding-Yu Liu ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Petroleum Coke ◽  
Calorific Value ◽  
Excess Oxygen ◽  
N2o Emissions ◽  
Bed Temperature ◽  
High Sulfur Content ◽  
Bubbling Fluidized Bed ◽  
Pollution Emissions ◽  
Gaseous Pollution

Petroleum cokes have high calorific value (about 37 MJkg−1), high sulfur content (2–7% wt.), and high nitrogen content (1∼3% wt.), introducing serious environmental problems when using as fuel. In this paper the effects of operating parameters (bed temperature, Ca/S mole ratio, and excess oxygen) on gaseous pollutant (SO2, NO, and N2O) emissions in a well-controlled bench scale fluidized bed reactor and an 1t/h bubbling fluidized bed for different type of petroleum cokes. Finally, the pollution emission differences between petroleum coke and coal were compared and the reasons were analyzed.

scholarly journals NOx EMISSIONS FROM BUBBLING FLUIDIZED BED COMBUSTION OF LIGNITE COAL

2015 ◽  
Vol 55 (4) ◽  
pp. 275 ◽  
Author(s):  
Pavel Skopec ◽  
Jan Hrdlička ◽  
Jan Opatřil ◽  
Jiří Štefanica
Keyword(s):  
Nitrogen Content ◽  
Fluidized Bed ◽  
Oxygen Concentration ◽  
Brown Coal ◽  
Conversion Factor ◽  
Nox Emissions ◽  
Fluidization Velocity ◽  
Bed Temperature ◽  
Bubbling Fluidized Bed ◽  
Air Staging

This paper presents experimental results of NO<sub>x</sub> emission measurements for combustion of two kinds of coal in a bubbling fluidized bed combustor. The tested fuels were Czech brown coal (CBC) and German young brown coal (GYC). These fuels have different nitrogen contents. The experiments were performed in the pilot scale BFB experimental unit with power output of 500 kW. The influence of several parameters on NO<sub>x</sub> formation are investigated in this paper. The parameters studied here include the effect of the nitrogen content in the fuel, the effect of the oxygen concentration in the bed, the effect of bed temperature, the effect of air staging, and the effect of fluidization velocity. Significantly different behaviour of the fuels was found. Although GYC has a lower nitrogen content than CBC, it is more reactive and produces higher NO<sub>x</sub> emissions. The biggest dependence of NO<sub>x</sub> production for CBC was found for the effects of air staging and fluidization velocity. As the fluidization velocity increases and the amount of secondary air decreases, there is an increase in NOx emissions. The oxygen concentration in the bed has the strongest effect on the NO<sub>x</sub> production of GYCs. With increasing oxygen concentration, the production of NO<sub>x</sub> also increases. On the basis of the NO<sub>x</sub> measurements, the N-NO conversion factor was calculated and the effect of the operating parameters on this conversion factor was investigated.

Bed Material Agglomeration Behavior in a Bubbling Fluidized Bed (BFB) at High Temperatures using KCl and K2SO4 as Simulated Molten Ash

2017 ◽  
Vol 16 (4) ◽  
Author(s):  
Ehsan Ghiasi ◽  
Alejandro Montes ◽  
Fatemeh Ferdosian ◽  
Honghi Tran ◽  
Chunbao (Charles) Xu
Keyword(s):  
Melting Point ◽  
Fluidized Bed ◽  
Sharp Decrease ◽  
Differential Pressure ◽  
Silica Sand ◽  
Molar Ratio ◽  
Biomass Ash ◽  
Bubbling Fluidized Bed ◽  
Sand Particles ◽  
Bed Material

Abstract The agglomeration of bed material is one of the most serious problems in combustion of biomass in fluidized-bed boilers, due to the presence of some inorganic alkali elements such as K and Na in the biomass ash, which form low-melting-point alkali compounds during the process. In this study, agglomeration behaviors of bed materials (silica sand particles) were investigated in a bench-scale bubbling fluidized-bed reactor operating at 800 °C using simulated biomass ash components: KCl, K2SO4, and a mixture of KCl and K2SO4 at eutectic composition (molar ratio K2SO4/(KCl+ K2SO4)=0.26). The signals of temperature and differential pressure across the bed were monitored while heating up the fluidized bed of silica sand particles premixed with various amounts of KCl, and the KCl-K2SO4 mixture in bubbling bed regime. A sharp decrease in temperature and differential pressure was observed around 750 °C and 690 °C for 0.4–0.6 wt% loading of the low melting-point KCl and KCl-K2SO4 mixture, respectively, suggesting the formation of bed material agglomeration and even de-fluidization of the bed. Moreover, this work demonstrated the effectiveness of kaolin and aluminum sulfate to minimize agglomeration. The results indicated that these additives could successfully prevent the formation of agglomerates by forming compounds with high melting points.

A Study of Operation Performance of Circulating Fluidized Bed Combustion Boiler

2003 ◽  
Author(s):  
Zhengshun Wu ◽  
Hanping Chen ◽  
Dechang Liu ◽  
Jie Wang ◽  
Chuangzhi Wu ◽  
...  
Keyword(s):  
Regression Analysis ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Fluidized Bed Combustion ◽  
Operation Performance ◽  
Cfb Boiler ◽  
Bed Temperature ◽  
Suitable Temperature ◽  
Bed Material ◽  
Circulating Fluidized Bed Combustion

The operation performance of circulating fluidized bed combustion (CFBC) boiler was studied in this paper. The experimental results indicate that the load of CFB boiler has linear relation with bed temperature and bed material height of operation. By multiple regression analysis, the relation of the load of CFB boiler with bed temperature and bed material height of operation can be expressed as a formula. The suitable temperature and the bed material height corresponding to the load of CFB boiler can be found using the formula; the problem of the boiler to be blindly operated can be reduced in practice.

Sign in / Sign up

Export Citation Format

Share Document