The Performance of a Loop Seal in a CFB Boiler

2006 ◽  
Vol 128 (2) ◽  
pp. 135-142 ◽  
Author(s):  
Andreas Johansson ◽  
Filip Johnsson ◽  
Bengt-Åke Andersson
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Fluidized Bed ◽  
Scaling Laws ◽  
Circulating Fluidized Bed ◽  
Vertical Direction ◽  
Scale Model ◽  
Corrosive Environment ◽  
Cfb Boiler ◽  
Load Conditions

High in-bed heat transfer and low corrosive environment imply that the loop seal of a circulating fluidized bed (CFB) boiler is an advantageous location for superheaters. In order to increase the knowledge on the flow pattern and the heat transfer distribution to the tubes within a loop seal, measurements were performed in the loop seal of a 30MW CFB boiler as well as in a 1∕3 scaled-down seal operated according to simplified scaling laws. The scale model measurements show that the solids recirculation flux can be maintained with a substantial decrease of the fluidization flow in the seal compared to that currently used at full load conditions. It was also possible to significantly decrease the fraction of the bottom of the seal that was fluidized without affecting the solids flux through the seal. A gradient in the solids flow were detected in the vertical direction.

scholarly journals Heat transfer characteristics of an external tube heat exchanger in a 1296t/h circulating fluidized bed boiler

2019 ◽  
Vol 137 ◽  
pp. 01014 ◽  
Author(s):  
Artur Blaszczuk ◽  
Szymon Jagodzik
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Tube Bundle ◽  
Horizontal Tube ◽  
Transfer Model ◽  
Heat Transfer Characteristics ◽  
Cfb Boiler ◽  
Transfer Data ◽  
Transfer Characteristics

In this research article, experimental study was carried out to obtain the heat transfer characteristics between a submerged horizontal tube bundle and a fluidized bed in a large-scale circulating fluidized bed (CFB) boiler with an external heat exchanger (EHE). The operational parameters in the tube EHE were measured during performance tests at variable load conditions. The average heat transfer coefficient (HTC) was calculated using a mechanistic heat transfer model based on packed renewal theory. The heat transfer characteristics are considered in terms of heat transfer mechanisms such as emulsion phase convection, gas convection and also thermal radiation. The obtained heat transfer data exhibit a maximum value with variation mean bed particle size irrespective of pressure. The results showed that the average HTC increases with a decrease of the Sauter mean particle diameter and with the increase of the fluidizing number as a result of good mixing dynamics in emulsion phase (i.e. emulsion wall contact time, bubble fraction in the bed). Based on the heat transfer data, empirical correlations are proposed for predicting a heat transfer coefficient from fluidized bed to horizontal tube bundle. The mechanistic heat transfer model predicted the average HTC in sufficiently good agreement with CFB boiler data accessible in the literature.

Design Theory of Circulating Fluidized Bed Boilers

2005 ◽  
Author(s):  
Guangxi Yue ◽  
Junfu Lu ◽  
Hai Zhang ◽  
Hairui Yang ◽  
Jiansheng Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Design Theory ◽  
Circulating Fluidized Bed ◽  
Material Balance ◽  
The State ◽  
Transfer Model ◽  
Volatile Content ◽  
Cfb Boiler ◽  
Bubbling Bed

Studies on circulating fluidized bed (CFB) boilers have being conducted at the Tsinghua University (TH) for about two decades and much of works are done to link the fundamentals with practical application. A full set of design theory was developed and some key elements of this theory are presented in this paper. First, a classification of state of the solid-gas two-phase flow in CFB boiler is given. TH’s studies validated that a CFB boiler can be generally described as the superposition of a fast bed in the upper part with a bubbling bed or turbulent bed in the bottom part. A concept model of material balance for the open system of CFB boiler was developed and later improved as a more comprehensive 1-D model taking ash formation, particle attrition and segregation in bed into account. Some results of the models are discussed. Then the concept of State Specification of a CFB boiler is defined and discussed. The State Specification is regarded as the first step to design a CFB and a base to classify different style of CFB boiler technologies for various CFB boiler manufacturers. The State Specification adopted by major CFB boiler makers is summarized and associated importance issues are addressed. The heat transfer model originally developed by Leckner and his coworkers is adopted and improved. It is further calibrated with experimental data obtained on the commercial CFB boiler measurements. The principle, improvements and application of the model are introduced. Some special tools developed for heat transfer field test are also given. Also, combustion behaviors of char and volatile content are studied, and the combustion difference between a CFB boiler and a bubbling bed is analyzed. The influence of volatile content and size distribution is discussed. The concept of vertical distribution of combustion and heat in CFB boiler furnace is introduced and discussed as well. In the last, the suggested design theory of CFB boiler is summarized.

Design Considerations of Oxy-Fuel Fired Supercritical Pressure Circulating Fluidized Bed Boilers

2006 ◽  
Author(s):  
Prabir K. Halder
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Flue Gas ◽  
Circulating Fluidized Bed ◽  
Fuel Combustion ◽  
Cfb Boiler ◽  
Design Considerations ◽  
Effective Manner ◽  
The Impact ◽  
Fluidized Bed Boilers

Researchers around the globe are focussing on the capture and storage of carbon dioxide generated from the combustion of coal in boilers for power generation. Oxygen fired boilers have the advantage of creating CO2 rich flue gas which enables the CO2 to be captured in a more cost effective manner compared to post combustion capture of CO2 from an air fired boiler. This paper discusses design considerations for oxy-fuel fired supercritical circulating fluidized bed boilers. A 420 MWe supercritical CFB boiler firing coal with oxygen has been considered for the study. An analytical/semi-empirical model has been developed to model fuel combustion and heat transfer in the furnace and convection pass. The fuel burns with oxygen supplied at the bottom of the bed and the fluidization velocity and bed temperature is controlled by flue gas recirculation. The model is used to design the boiler and determine its performance characteristics. The heating surfaces, recirculation ratios and other parameters have been designed to achieve the required boiler capacity. The impact of the CO2 rich flue gas on CFB boiler design is compared with conventional air blown CFB boilers. The study reveals that oxy-fuel combustion in a CFB combustor does not alter the heat transfer characteristics when compared with combustion with air. In the convection bank, oxyfuel combustion increases both convective and radiative components of heat transfer, thereby reducing the size of the heat transfer banks required.

An Investigation Into the Operation of the Twin-Exit Loop-Seal of a Circulating Fluidized Bed Boiler in a Thermal Power Plant and Its Design Implication

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Prabir Basu ◽  
Munish Chandel ◽  
James Butler ◽  
Animesh Dutta
Keyword(s):  
Power Plant ◽  
Fluidized Bed ◽  
Thermal Power Plant ◽  
Circulating Fluidized Bed ◽  
Thermal Power ◽  
Scale Model ◽  
Circulation Rate ◽  
Cfb Boiler ◽  
Solids Circulation Rate ◽  
New Findings

Loop-seal is a critical component of a circulating fluidized bed (CFB) boiler, and yet very little information on its working or design is available in published literature. Among the limited available information, none is on twin-exit loop-seal though it is one of the most commonly used loop-seal in large commercial CFB boilers. To circulate larger amounts of solids, a twin-exit loop-seal provides larger solids flow sections. It receives solids from one standpipe but delivers it through two recycle chambers and two delivery pipes. The present research was conducted in a twin-exit loop-seal of a 3.2 MWth CFB boiler operating in a thermal power plant for cofiring purpose. Data obtained in this industrial unit were supplemented with those collected in a single-exit bench-scale loop-seal in the authors’ laboratory from the single-exit loop-seal in a 65 t/h CFB boiler and a scale model of a 30 MW CFB boiler. The effect of recycle chamber’s aeration on the solids circulation rate was studied for several particle sizes. Results suggest that the total solids circulation rate does not increase proportionately with the increase in loop-seal discharge area provided by the twin-exit loop-seals. The linear horizontal velocities of solids and the minimum aeration in the recycle chambers are comparable to those measured in a single-exit loop-seal. The implication of these new findings on the design procedure of loop-seals is discussed.

Measurement of Heat Transfer in a 465t/h Circulating Fluidized Bed Boiler

2005 ◽  
Author(s):  
Yu Wang ◽  
Junfu Lu ◽  
Hairui Yang ◽  
Xinmu Zhao ◽  
Guangxi Yue
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Bulk Density ◽  
Fluidized Bed ◽  
Thermal Boundary Layer ◽  
Circulating Fluidized Bed ◽  
Transfer Coefficients ◽  
Cfb Boiler ◽  
Heat Transfer Coefficients ◽  
Solid Bulk

The study of heat transfer and thermal boundary layer in the combustor of a circulating fluidized bed (CFB) is important to the boiler design and operation. Both heat transfer coefficient between the solid-gas flow and the water-wall and the thickness of thermal boundary layer are key data to determine the amount and layout of the tube walls in a CFB furnace. A series of experiments was conducted on a 465t/h commercial CFB boiler, which operated at bed temperature between 850 and 900°C, and at superficial gas velocity between 5.2 to 5.9m/s. Local bed to water wall heat transfer coefficients and temperature profiles near the wall were measured at a set of test ports at different heights of the sidewall. In the same time, the local solid bulk density near the wall was also measured. Special tools such as heat flux probe, solid bulk density sampling probe and temperature probe were developed for the experiments and their structures were introduced. The experimental results were compared with the data from previous studies. Theoretical analysis of the factors that play important role in heat transfer in a CFB boiler was also performed. The relationship between heat transfer and thermal boundary layer was also discussed. Furthermore, a simple model correlating the local heat transfer coefficients with bulk density was developed.

Investigation on Heat Transfer Performance of External Heat Exchanger for Circulating Fluidized Bed Boiler

2013 ◽  
Vol 732-733 ◽  
pp. 11-17
Author(s):  
Da Long Zhang ◽  
Ding Hua Yang ◽  
Gen Sheng Yang ◽  
Zhong Li ◽  
Jun Fu Lv
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Fluidized Bed ◽  
Large Scale ◽  
Heat Transfer Performance ◽  
Circulating Fluidized Bed ◽  
External Heat ◽  
Transfer Performance ◽  
Cfb Boiler ◽  
External Heat Exchanger

A heat transfer model of external heat exchanger (EHE) in large-scale circulating fluidized bed (CFB) boiler was suggested based on experiment data and theoretical analysis. And the model parameters were also provided. With this model, the heat transfer performance of the EHE in an actual operating 300MW CFB boiler was predicted. The comparison between the model predictive results and the actual results showed that the relative error is less than 7%. This indicated that the model established in this paper is reliable and can provide a significant reference in EHE of large-scale CFB boiler design.

Effect of particle collision behavior on heat transfer performance in a down-flow circulating fluidized bed evaporator

2021 ◽  
Vol 381 ◽  
pp. 55-67
Author(s):  
Feng Jiang ◽  
Hongyu Wang ◽  
Yi Liu ◽  
Guopeng Qi ◽  
Ahmed Esmail Al-Rawni ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Heat Transfer Performance ◽  
Circulating Fluidized Bed ◽  
Particle Collision ◽  
Transfer Performance

Performance evaluation of a supercritical circulating fluidized bed boiler for power generation under flexible operation

2021 ◽  
pp. 095765092199396
Author(s):  
Matteo Bruzzone ◽  
Silvia Ravelli
Keyword(s):  
Power Generation ◽  
Fluidized Bed ◽  
High Performance ◽  
Circulating Fluidized Bed ◽  
Thermal Power ◽  
Rankine Cycle ◽  
Hard Coal ◽  
Cfb Boiler ◽  
Power Cycles ◽  
Commercial Code

It is well known that the Łagisza power plant in Poland is the world’s first supercritical circulating fluidized bed (CFB) boiler, whose commercial operation started on June 2009. It has attracted a great deal of interest and operational data are publicly available, therefore it has been chosen as the object of the present study aimed at assessing load and fuel flexibility of supercritical CFB plants. First, the thermal cycle was modelled, by means of the commercial code Thermoflex®, at nominal and part load conditions for validation purposes. After having verified the validity of the applied modelling and simulation tool, the advantage of having supercritical steam combined with CFB boiler over subcritical steam and pulverized coal (PC) boiler, respectively, was quantified in terms of electric efficiency. As a next step, the designed fuel, i.e. locally mined hard coal, was replaced with biomass: 100% biomass firing was taken into account in the case of subcritical CFB boiler whereas the maximum share of biomass with coal was set at 50% with supercritical CFB boiler, consistently with the guidelines provided by the world leading manufacturers of CFB units. A broad range of biomass types was tested to conceive mixtures of fuel capable of preserving quite high performance, despite the energy consumption in pretreatment. However, the overall efficiency penalty, due to biomass co-firing, was found to potentially undermine the benefit of supercritical steam conditions compared to conventional subcritical power cycles. Indeed, the use of low-quality biomass in thermal power generation based on steam Rankine cycle may frustrate efforts to push the steam cycle boundaries.

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