Biomass Ash – Bed Material Interactions Leading to Agglomeration in FBC

2003 ◽  
Author(s):  
H. J. M. Visser ◽  
S. C. van Lith ◽  
J. H. A. Kiel
Keyword(s):  
Coating Thickness ◽  
Problem Area ◽  
Critical Conditions ◽  
Fluidized Bed Combustion ◽  
Biomass Ash ◽  
Fundamental Study ◽  
Fluidization Velocity ◽  
Bubbling Fluidized Bed ◽  
Bed Agglomeration ◽  
Bed Material

In (bubbling) fluidized-bed combustion and gasification of biomass, several potential problems are associated with the inorganic components of the fuel. A major problem area is de-fluidization due to bed agglomeration. The most common found process leading to de-fluidization in commercial-scale installations is “coating-induced” agglomeration. During reactor operation, a coating is formed on the surface of bed material grains and at certain critical conditions (e.g., coating thickness or temperature) sintering of the coatings initiates the agglomeration. In an experimental approach, this work describes a fundamental study on the mechanisms of de-fluidization. For the studied process of bed de-fluidization due to sintering of grain-coating layers, it was found that the onset of the process depends on: a) a critical coating thickness, b) on the fluidization velocity when it is below approx. four times the minimum fluidization velocity and c) on the viscosity (stickiness) of the outside of the grains (coating).

Biomass Ash-Bed Material Interactions Leading to Agglomeration in FBC

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
H. J. M. Visser ◽  
S. C. van Lith ◽  
J. H. A. Kiel
Keyword(s):  
Coating Thickness ◽  
Problem Area ◽  
Critical Conditions ◽  
Fluidized Bed Combustion ◽  
Biomass Ash ◽  
Fundamental Study ◽  
Fluidization Velocity ◽  
Bubbling Fluidized Bed ◽  
Bed Agglomeration ◽  
Bed Material

In (bubbling) fluidized-bed combustion and gasification of biomass, several potential problems are associated with the inorganic components of the fuel. A major problem area is defluidization due to bed agglomeration. The most common found process leading to defluidization in commercial-scale installations is “coating-induced” agglomeration. During reactor operation, a coating is formed on the surface of bed material grains and at certain critical conditions (e.g., coating thickness or temperature) sintering of the coatings initiates the agglomeration. In an experimental approach, this work describes a fundamental study on the mechanisms of defluidization. For the studied process of bed defluidization due to sintering of grain-coating layers, it was found that the onset of the process depends on (a) a critical coating thickness, (b) on the fluidization velocity when it is below approximately four times the minimum fluidization velocity, and (c) on the viscosity (stickiness) of the outside of the grains (coating).

The Phase Transformations during Fluidized-Bed Combustion of Biomass

2013 ◽  
Vol 419 ◽  
pp. 366-369 ◽  
Author(s):  
Hai Peng Teng ◽  
Bin Yang ◽  
Bin Liang
Keyword(s):  
Gas Phase ◽  
Fluidized Bed ◽  
Solid Phase ◽  
Fluidized Bed Reactor ◽  
Biomass Combustion ◽  
Material Surface ◽  
Fluidized Bed Combustion ◽  
Biomass Ash ◽  
Equilibrium Modeling ◽  
Bed Material

FactSage6.1 was used to study the phase transformation at high temperature when biomass combustion in a fluidized bed reactor. The results show that eutectic was formed during the reaction process, the eutectics are formed mainly by the reaction between the silica in bed particles and the alkali species in biomass ash. The solid phase transformed to melt layer on the surface of sands particle mainly contains potassium, some calcium and magnesium, and also a few phosphorus and chlorine are found in the melt layer. The result utilizing FactSage equilibrium modeling shown that the distribution ratio of potassium in the gas phase increased with the increase of temperature, moreover, the melt of bed material surface increased when defluidized occurred.

Minimum Air Fluidization Velocity Study of Specific 2-D Bubbling Fluidized Bed Reactor

2014 ◽  
Vol 699 ◽  
pp. 660-665
Author(s):  
M. Fadhil ◽  
M.S. Aris ◽  
A.H. Abbas ◽  
A.B.A. Ibrahim ◽  
N. Aniza
Keyword(s):  
Fluidized Bed ◽  
Particle Density ◽  
Flow Behavior ◽  
Numerical Approach ◽  
Combustion Efficiency ◽  
Fluidized Bed Combustion ◽  
Fluidization Velocity ◽  
Bubbling Fluidized Bed ◽  
Flow Through ◽  
Bed Expansion

Research on the thermodynamic behavior of sand beds was carried out using a commercial computational dynamic package. The work involved simulating, with the use of the Ergun equation, the air flow through a two-dimensional bubbling bed reactor to predict the bed character whilst considering the major effective function (particle size, particle density, bed height and reactor width). The Minimum Fluidization Velocity (Umf) values were then calculated before the optimum value of Umfneeded to ensure a workable Bubbling Fluidize Bed Combustor (BFBC) system. The effects of using different Umfvalues on the flow behavior were also investigated using the numerical approach at different times. The results from these investigations indicate that the bubbling region in the fluidized bed combustion can be correlated to the sand bed expansion with minimum errors and assist in enhancing the combustion efficiency by supplying the required volume of oxygen into the system.

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.

Model of combustion and dispersion of carbon deposited on porous bed material during bubbling fluidized bed combustion

Fuel ◽  
2008 ◽  
Vol 87 (10-11) ◽  
pp. 1974-1981 ◽  
Author(s):  
I Nyoman Suprapta Winaya ◽  
Tadaaki Shimizu ◽  
Yousuke Nonaka ◽  
Kazuaki Yamagiwa
Keyword(s):  
Fluidized Bed ◽  
Fluidized Bed Combustion ◽  
Porous Bed ◽  
Bubbling Fluidized Bed ◽  
Bed Material

scholarly journals Investigating Agglomeration Tendency of Co-Gasification between High Alkali Biomass and Woody Biomass in a Bubbling Fluidized Bed System

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 56 ◽  
Author(s):  
Tanakorn Kittivech ◽  
Suneerat Fukuda
Keyword(s):  
Chemical Properties ◽  
Silica Sand ◽  
Empty Fruit Bunches ◽  
Wood Sawdust ◽  
Inorganic Matter ◽  
Bubbling Fluidized Bed ◽  
Blended Fuel ◽  
Bed Agglomeration ◽  
High Alkali ◽  
Bed Material

Palm empty fruit bunches (EFB) is known as problematic biomass due to its high alkali content, i.e., more than half of inorganic matter is potassium (K). EFB when used as a fuel in fluidized beds with silica sand as bed material could form the sticky compound K2O·nSiO2 starting at around 750 °C and adhere bed particles together, resulting in bed agglomeration. Blending EFB with rubber wood sawdust (RWS) could improve the chemical properties and consequent ash composition of the blended fuel. In this study, RWS was blended with EFB at three ratios: RWS:EFB = 25:75, RWS:EFB = 50:50, and RWS:EFB = 75:25. Adding RWS to the fuel prolonged de-fluidization time. The high content of CaO in the RWS ash acted as an inhibitor to prevent the formation of K2O·nSiO2 and, instead, enhanced the formation of K2CO3, a higher melting point compound, which reduced bed agglomeration. During the experiment using RWS:EFB = 75:25, no bed agglomeration was found.

Bubbling Fluidized Bed Co-Combustion of Different Sustainable Fuels: Trace Element Behaviour

2003 ◽  
Author(s):  
N. Wolski ◽  
R. Berger ◽  
J. Maier ◽  
K. R. G. Hein
Keyword(s):  
Fluidized Bed ◽  
Large Scale ◽  
Fuel Mixture ◽  
Paper Sludge ◽  
Fluidized Bed Combustion ◽  
Input Concentration ◽  
Industrial Plants ◽  
Bubbling Fluidized Bed ◽  
Bed Capacity ◽  
Bed Material

With this paper the author will show interesting results of the co-combustion of coal in combination with bark and paper sludge in fluidized bed combustion. The results presented were collected during two measurement campaigns at a 30 kW electrically stabilized bubbling fluidized bed. The fluidized bed combustor was compared to large scale combustors in different campaigns before and thus gives an idea of the output of industrial plants. The main focus of the measurements was the behavior of trace elements of Ni Pb, Zn, Cr and Cu with a changing bed material. One bed material was pre-used under the exposure of combustion of a ternary fuel mixture of coal, bark and paper sludge over a long period of time resulting in a bed composition of 2/3 SiO2 and 1/3 Al2O3. The second bed material utilized, which was a sand (primarily SiO2) not used before thus not enriched in any compounds. When comparing the results of all trials three different trace metal partitioning effects were monitored. First an increase in the elemental concentration in the bed material which was primarily due to the higher input concentration with the pre-used bed material which was found for all three alternatives plus a decrease in filter and cyclone concentrations (Ni, Pb). Secondly an increase in all three ash fractions was detected for Cu. The third was a mixture of both with increasing filter concentrations but decreasing cyclone concentrations (Zn, Cr). An attempt was made to link the before primarily to the enrichment in Al-compounds and to a bed capacity of retention. The results presented indicate the need for longer periods of testing even at small scaled facilities if the comparison to large scale facilities is attempted.

Bed Agglomeration Characteristics in Fluidized-Bed Combustion of Biomass Fuels Using Olivine as Bed Material

2012 ◽  
Vol 26 (7) ◽  
pp. 4550-4559 ◽  
Author(s):  
Alejandro Grimm ◽  
Marcus Öhman ◽  
Therése Lindberg ◽  
Andreas Fredriksson ◽  
Dan Boström
Keyword(s):  
Fluidized Bed ◽  
Fluidized Bed Combustion ◽  
Biomass Fuels ◽  
Bed Agglomeration ◽  
Bed Material

A New Method to Inhibit Bed Agglomeration Problems in Fluidized Bed Boilers

2003 ◽  
Author(s):  
Jaani Silvennoinen
Keyword(s):  
Fluidized Bed ◽  
Industrial Scale ◽  
Fluidized Bed Combustion ◽  
Natural Sand ◽  
Worst Case ◽  
Free Quartz ◽  
Bed Materials ◽  
Bed Agglomeration ◽  
High Alkali ◽  
Bed Material

Fluidized bed combustion (FBC) technology was commercialized in the 70s. Both bubbling fluidized bed (BFB) and circulating fluidized bed (CFB) technology are capable of handling a wide variety of solid fuels. Natural sand is typically used as the fluidizing material. However, the properties and behavior of some solid fuel ash may limit the use of these fuels due to bed agglomeration problems. Natural sand contains several minerals, typically mainly consisting of 20–50 wt.-% of plagioclase (NaAlSi3O8 + CaAlSi3O8), 10–30 wt.-% of potash feldspar (KAlSi3O8), and 25–100 wt.-% of quartz (SiO2). Biomass based fuels contain high amounts of alkali. Ash high in alkali may react with the free quartz of the natural sand, producing an alkali silicate mixture with low melting point. This mixture may act as an adhesive between fluidized bed particles and may, in the worst-case, result in serious fluidization problems. This problem can be avoided by using AGGLOSTOP™ quartz-free bed material. Four different bed materials were tested in a 15 kW laboratory-scale FBC test rig with plywood residue, which is known to cause severe fluidization problems in FB boilers. Two of the tested bed materials were quartz-free. When quartz-free bed materials were used, no signs of bed agglomeration were observed. The other two bed materials containing free quartz caused total defluidization at a temperature of around 750°C after about half an hour of operation. The concept of using AGGLOSTOP™ quartz-free bed material with high alkali fuels has been successfully applied in two industrial scale BFB boilers (15 and 74 MWth). The use of AGGLOSTOP™ fluidized bed material enables energy production in FB boilers based on high alkali fuels, which were earlier impossible to utilize due severe bed agglomeration problems. This paper focuses on the bed agglomeration phenomenon by discussing the results from laboratory and industrial-scale boilers and presents a new solution to extend the use of high alkali fuels in FB boilers.

Sign in / Sign up

Export Citation Format

Share Document