The Local Heat Balance in a Stationary Fluidized-Bed Furnace Burning Biomass Fuels

2003 ◽  
Author(s):  
Fredrik Niklasson ◽  
Filip Johnsson
Keyword(s):  
Fluidized Bed ◽  
Combustion Rate ◽  
Heat Balance ◽  
Circulating Fluidized Bed ◽  
Local Heat ◽  
Splash Zone ◽  
Two Phase ◽  
Bed Temperature ◽  
Temperature Constant ◽  
The Vertical Distribution

This work investigates the influence of biomass fuel properties on the local heat balance in a commercial-scale fluidized bed furnace. Experiments with different wood based fuels were performed in the Chalmers 12 MWth circulating fluidized bed boiler, temporarily modified to run under stationary conditions. A two-phase flow model of the bed and splash zone is applied, where the combustion rate in the bed is estimated by global kinetic expressions, limited by gas exchange between oxygen-rich bubbles and a fuel-rich emulsion phase. The outflow of bubbles from the bed is treated as “ghost bubbles” in the splash zone, where the combustion rate is determined from turbulent properties. It is found that a large amount of heat is required for the fuel and air to reach the temperature of the bed, in which the heat from combustion is limited by a low char content of the fuel. This implies that a substantial fraction of the heat from combustion of volatiles in the splash zone has to be transferred back to the bed to keep the bed temperature constant. It is concluded that the moisture content of the fuel does not considerably alter the vertical distribution of heat emitted, as long as the bed temperature is kept constant by means of flue gas recycling.

Identification of Circulating Fluidized Bed Boiler Bed Temperature Based on Hyper-Plane-Shaped Fuzzy C-Regression Model

2020 ◽  
Vol 19 (04) ◽  
pp. 2050029
Author(s):  
Jianzhong Shi
Keyword(s):  
Regression Model ◽  
Fluidized Bed ◽  
Membership Function ◽  
Clustering Algorithm ◽  
Circulating Fluidized Bed ◽  
Fuzzy Model ◽  
Identification Algorithm ◽  
Identification Process ◽  
Bed Temperature ◽  
Hyper Plane

Bed temperature in dense-phase zone is the key parameter of circulating fluidized bed (CFB) boiler for stable combustion and economic operation. It is difficult to establish an accurate bed temperature model as the complexity of circulating fluidized bed combustion system. T-S fuzzy model was widely applied in the system identification for it can approximate complex nonlinear system with high accuracy. Fuzzy c-regression model (FCRM) clustering based on hyper-plane-shaped distance has the advantages in describing T-S fuzzy model, and Gaussian function was adapted in antecedent membership function of T-S fuzzy model. However, Gaussian fuzzy membership function was more suitable for clustering algorithm using point to point distance, such as fuzzy c-means (FCM). In this paper, a hyper-plane-shaped FCRM clustering algorithm for T-S fuzzy model identification algorithm is proposed. The antecedent membership function of proposed identification algorithm is defined by a hyper-plane-shaped membership function and an improved fuzzy partition method is applied. To illustrate the efficiency of the proposed identification algorithm, the algorithm is applied in four nonlinear systems which shows higher identification accuracy and simplified identification process. At last, the algorithm is used in a circulating fluidized bed boiler bed temperature identification process, and gets better identification result.

Combustion Behavior and SO2, NOx Emissions of an Anthracite Coal in a Circulating Fluidized Bed

2005 ◽  
Author(s):  
Leming Cheng ◽  
Zhongyang Luo ◽  
Zhenglun Shi ◽  
Haixiao Zheng ◽  
Qinghui Wang ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Cross Section ◽  
Circulating Fluidized Bed ◽  
Nox Emissions ◽  
So2 Emission ◽  
Combustion Behavior ◽  
Excess Air ◽  
Anthracite Coal ◽  
Bed Temperature ◽  
Experimental Researches

Combustion behavior and SO2, NOx emissions of anthracite coal in a circulating fluidized bed are reported in this paper. Experimental researches were done on a 1 MWt circulating fluidized bed facility with a 0.31 m × 0.31 m cross section and 11.2 m height combustor. The anthracite coal with 6.28% volatile and 3.76% sulfur content burns steadily during the test. The bed was operated under different temperature, Ca/S ratio and excess air. A limestone containing 75% CaCO3 and 15% MgCO3 was used as the sulfur sorbent. Results show that the SO2 emission varies with operating bed temperature and more than 90% sulfur capture efficiency can be reached while Ca/S is about 3. With Rosemount Analytical NGA2000, N2O, NO and NO2 were also measured in the test. It was found the majority content of NOx was NO and the least was NO2. Those NOx emissions change highly with the excess air number.

Combustion of Wood Processing Residues in a Circulating Fluidized Bed

2003 ◽  
Author(s):  
Fernando Preto
Keyword(s):  
Fluidized Bed ◽  
Pilot Plant ◽  
Circulating Fluidized Bed ◽  
Combustion Efficiency ◽  
Tree Bark ◽  
Feed System ◽  
Wood Processing ◽  
System A ◽  
Bed Temperature ◽  
High Moisture Level

The combustion of wood processing residues was tested in the 0.8 MWth CANMET Circulating Fluidized Bed Combustor (CFBC) pilot plant. The specific residues tested were three different types of coniferous tree bark (i.e. from different locations to represent a range of possible fuels and fuel properties). Combustion conditions may be summarized as follows: fuel moisture levels 42–60%, fluidizing velocity 2.1–2.4 m/s; bed temperature 785–910 °C; maximum freeboard temperature 980–1070 °C and excess air levels 20–75%. The CFBC unit was able to burn the high moisture level fuels with no detrimental effect. In all trials the residues burned very well, with combustion efficiency greater than 99% based on overhead carbon loss. Emissions measurements were made of the following pollutant species CO, NOx, N2O, SO2, and dioxins and furans. The emissions levels were: 100–130 ppm NOx; <1 ppm N2O; 5–20 ppm SO2 and 400–1800 ppm CO. These emission levels are well below pollution guidelines for all major pollutants except CO. This however can be traced to the non-homogeneous nature of the coarse feed in the pilot plant. The problem can reasonably be addressed in a full-scale unit by a more stable feed system. A preliminary economic analysis of a new 25 MW FBC power plant firing these fuels was performed. Conservative inputs give a cost of 6 cents/kWh for the electricity produced and a economic wood haulage radius of 70 km.

Internally Circulating Fluidized Bed Reactor Using m-ZrO2 Supported NiFe2O4 Particles for Thermochemical Two-Step Water Splitting

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Nobuyuki Gokon ◽  
Hiroki Yamamoto ◽  
Nobuyuki Kondo ◽  
Tatsuya Kodama
Keyword(s):  
Fluidized Bed ◽  
Water Splitting ◽  
Gas Flow ◽  
Circulating Fluidized Bed ◽  
Fluidized Bed Reactor ◽  
Thermal Reduction ◽  
Input Power ◽  
Light Irradiation ◽  
Bed Temperature ◽  
N2 Flow Rate

A windowed internally circulating fluidized bed reactor was tested using m-ZrO2-supported NiFe2O4(NiFe2O4/m-ZrO2) particles as redox material for thermochemical two-step water splitting to produce hydrogen from water. The internally circulating fluidized bed of NiFe2O4/m-ZrO2 particles is directly heated by solar-simulated Xe light irradiation through a transparent quartz window mounted on top of the reactor. A sun simulator with three Xe lamps at laboratory scale has been newly installed in our laboratory for testing the fluidized bed reactor. The input power of incident Xe light can be scaled up to 2.6 kWth. Temperature distributions within the fluidized bed are measured under concentrated Xe light irradiation with an input power of 2.6 kWth. Hydrogen productivity and reactivity for the fluidized bed of NiFe2O4/m-ZrO2 particles are examined using two different reactors under the N2 flow rate and flow ratio, which yield a higher bed temperature. The feasibility of successive two-step water splitting using the fluidized bed reactor is examined by switching from N2 gas flow in the thermal reduction step to a steam/N2 gas mixture in the water decomposition step. It is confirmed that hydrogen production takes place in the single fluidized bed reactor by successive two-step water splitting.

Characteristics of Circulating Fluidized Bed Evaporator with Vapor-Liquid-Solid Three-Phase Flow

2012 ◽  
Vol 455-456 ◽  
pp. 1618-1626 ◽  
Author(s):  
Ji Tian Song ◽  
Jun Chi ◽  
Han Fei Zhang ◽  
Zhen Ying Liu
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Research Work ◽  
Correlation Equation ◽  
Evaporation Process ◽  
Two Phase ◽  
Heat Transfer Efficiency ◽  
Three Phase ◽  
Three Phase Flow

In this paper, pumpkin juice concentrations were carried out using a three-phase circulating fluidized bed evaporator. The flow and heat transfer characteristics of this evaporation process were investigated and parametric studies were conducted to identify the governing parameters in the process. It was found that compared with two-phase evaporation process, addition of inert particles improved the heat transfer efficiency by 35% and also inhibit forming and clean fouls during the pumpkin juice concentration. A correlation equation of boiling heat transfer coefficient was established for the three-phase circulating fluidized bed evaporator. This research work improves the understanding of the three-phase circulating fluidized bed evaporator and benefit to its wider application in foodstuff field.

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