Impact of boiler load and limestone addition on SO3 and corrosive cold-end deposits in a coal-fired CFB boiler

When the load of Circulating Fluidized Bed (CFB) boiler changes dynamically, the accumulation and consumption of residual char causes a large inertia and hysteresis in the boiler combustion system. Therefore, accurate estimation of the residual char in the boiler is of great significance to the control system and improve the combustion efficiency. Based on the Computational Particles Fluid Dynamics (CPFD) method, a numerical simulation of the variable load process of CFB boiler was carried out, and the dynamic changes of the residual char inventory were analyzed by combining the coal feed, ash discharge, and furnace calorific value. The results showed that after CFB boiler reached stable operation, the residual char fluctuated from 11,000 kg to 16,000 kg, accounting for about 3.7% of the total bed material, and the residual char was in a dynamic balance. During the load-up phase, the average residual char was 17,500 kg, and during the load-down phase, the average residual char was 15,000 kg. In the process of load dynamic change, reasonable residual char stock can ensure the boiler load from one steady state to another steady state rapid transition.

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Process Simulation of Oil Shale Circulating Fluidized Bed Boiler Based on Aspen Plus

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.614-615.49 ◽

2012 ◽

Vol 614-615 ◽

pp. 49-52

Author(s):

Qing Wang ◽

Hai Bo Long ◽

Hong Peng Liu ◽

Zhi Feng Wang

Keyword(s):

Fluidized Bed ◽

Flue Gas ◽

Oil Shale ◽

Circulating Fluidized Bed ◽

Circulation System ◽

Performance Parameters ◽

Gas Emission ◽

Boiler Load ◽

Cfb Boiler ◽

Experimental Values

A model for the combustion of oil shale in the 65t/h circulating fluidized bed (CFB) boiler was developed, consisting of oil shale combustion, steam-water and ash circulation system, calculating the O2 and RO2 content of flue gas emission under three kinds of oil shale combustion in 65t/h CFB boiler. The calculated results indicate that the simulation values are consistent with the experimental values. Effect of boiler load on the temperature of furnace, flue gas emission, inlet and outlet flue gas of economizer was discussed based on the model. Boiler load on the increase results in a increase in temperature of furnace, flue gas emission, inlet and outlet flue gas of economizer. The main performance parameters of 65t/h oil shale CFB boiler system were discussed and preliminarily predicted by the model.

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

Energies ◽

10.3390/en14185679 ◽

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.

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Pilot-scale combustion studies with kraft lignin in a powder burner and a CFB boiler

TAPPI Journal ◽

10.32964/tj9.6.24 ◽

2010 ◽

Vol 9 (6) ◽

pp. 24-30 ◽

Cited By ~ 2

Author(s):

NIKLAS BERGLIN ◽

PER TOMANI ◽

HASSAN SALMAN ◽

SOLVIE HERSTAD SVÄRD ◽

LARS-ERIK ÅMAND

Keyword(s):

Circulating Fluidized Bed ◽

Black Liquor ◽

Chloride Content ◽

Pilot Scale ◽

High Energy ◽

Kraft Lignin ◽

High Energy Density ◽

Alkali Chloride ◽

Cfb Boiler ◽

Solid Biofuel

Processes have been developed to produce a solid biofuel with high energy density and low ash content from kraft lignin precipitated from black liquor. Pilot-scale tests of the lignin biofuel were carried out with a 150 kW powder burner and a 12 MW circulating fluidized bed (CFB) boiler. Lignin powder could be fired in a powder burner with good combustion performance after some trimming of the air flows to reduce swirl. Lignin dried to 10% moisture content was easy to feed smoothly and had less bridging tendencies in the feeding system than did wood/bark powder. In the CFB boiler, lignin was easily handled and cofired together with bark. Although the filter cake was broken into smaller pieces and fines, the combustion was not disturbed. When cofiring lignin with bark, the sulfur emission increased compared with bark firing only, but most of the sulfur was captured by calcium in the bark ash. Conventional sulfur capture also occurred with addition of limestone to the bed. The sulfur content in the lignin had a significantly positive effect on reducing the alkali chloride content in the deposits, thus reducing the high temperature corrosion risk.

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Investigation of Ash Deposition Dynamic Process in an Industrial Biomass CFB Boiler Burning High-Alkali and Low-Chlorine Fuel

Energies ◽

10.3390/en13051092 ◽

2020 ◽

Vol 13 (5) ◽

pp. 1092

Author(s):

Hengli Zhang ◽

Chunjiang Yu ◽

Zhongyang Luo ◽

Yu’an Li

Keyword(s):

Gas Flow ◽

Circulating Fluidized Bed ◽

Deposition Process ◽

Biomass Combustion ◽

Ash Deposition ◽

Biomass Ash ◽

Cfb Boiler ◽

Third Stage ◽

Ash Deposit ◽

High Alkali

The circulating fluidized bed (CFB) boiler is a mainstream technology of biomass combustion generation in China. The high flue gas flow rate and relatively low combustion temperature of CFB make the deposition process different from that of a grate furnace. The dynamic deposition process of biomass ash needs further research, especially in industrial CFB boilers. In this study, a temperature-controlled ash deposit probe was used to sample the deposits in a 12 MW CFB boiler. Through the analysis of multiple deposit samples with different deposition times, the changes in micromorphology and chemical composition of the deposits in each deposition stage can be observed more distinctively. The initial deposits mainly consist of particles smaller than 2 μm, caused by thermophoretic deposition. The second stage is the condensation of alkali metal. Different from the condensation of KCl reported by most previous literatures, KOH is found in deposits in place of KCl. Then, it reacts with SO2, O2 and H2O to form K2SO4. In the third stage, the higher outer layer temperature of deposits reduces the condensation rate of KOH significantly. Meanwhile, the rougher surface of deposits allowed more calcium salts in fly ash to deposit through inertial impact. Thus, the elemental composition of deposits surface shows an overall trend of K decreasing and Ca increasing.

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

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650921993964 ◽

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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