Numerically Study on Combustion and NOx Emission Characteristics in Tangentially Fired Boiler Co-Firing Semi-Coke

Semi-coke is a specific solid fuel, which is mainly produced by upgrading low-rank coal. The poor reactivity of semi-coke makes a difficulty to its practical utilization in utility boilers. Previous research was mainly focused on the combustion behavior of semi-coke, while the industrial application has to be understood. In this paper, the effect of co-firing semi-coke and bituminous coal on the operation performance of pulverized boiler was numerically studied. The work was conducted on a 300 MW tangentially fired boiler, and the temperature distribution, the char burnout and NOx production were mainly examined. The results indicate that the incomplete combustion heat loss drops with the increase in semi-coke blending ratio. The NOx concentration increases from 186 mg/Nm3 for only firing the bituminous coal to 200, 214, and 255 mg/Nm3, when the blending ratio was 17%, 33% and 50%, respectively. With enhancing excess air coefficient for the co-firing condition, the combustion efficiency got improved, while NOx production increased very slightly. In general, the boiler is well adapted to co-firing semi-coke, and the semi-coke blending ratio of 1/3 with an excess air coefficient of 1.235 is recommended.

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Modeling and Experiment on Combustion Characteristics for Biomass Rotary Burner

Current Alternative Energy ◽

10.2174/2405463104666200120113721 ◽

2020 ◽

Vol 04 ◽

Author(s):

Guohai Jia ◽

Lijun Li ◽

Li Dai ◽

Zicheng Gao ◽

Jiping Li

Keyword(s):

Combustion Chamber ◽

Combustion Temperature ◽

Combustion Efficiency ◽

Middle Part ◽

Combustion Characteristics ◽

Maximum Temperature ◽

Excess Air ◽

Element Simulation ◽

Excess Air Coefficient ◽

Secondary Air

Background: A biomass pellet rotary burner was chosen as the research object in order to study the influence of excess air coefficient on the combustion efficiency. The finite element simulation model of biomass rotary burner was established. Methods: The computational fluid dynamics software was applied to simulate the combustion characteristics of biomass rotary burner in steady condition and the effects of excess air ratio on pressure field, velocity field and temperature field was analyzed. Results: The results show that the flow velocity inside the burner gradually increases with the increase of inlet velocity and the maximum combustion temperature is also appeared in the middle part of the combustion chamber. Conclusion: When the excess air coefficient is 1.0 with the secondary air outlet velocity of 4.16 m/s, the maximum temperature of the rotary combustion chamber is 2730K with the secondary air outlet velocity of 6.66 m/s. When the excess air ratio is 1.6, the maximum temperature of the rotary combustion chamber is 2410K. When the air ratio is 2.4, the maximum temperature of the rotary combustion chamber is 2340K with the secondary air outlet velocity of 9.99 m/s. The best excess air coefficient is 1.0. The experimental value of combustion temperature of biomass rotary burner is in good agreement with the simulation results.

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Effects of Air Flowrate on the Combustion and Emissions of Blended Corn Straw and Pinewood Wastes

Journal of Energy Resources Technology ◽

10.1115/1.4042005 ◽

2018 ◽

Vol 141 (4) ◽

Cited By ~ 5

Author(s):

Xiaoxiao Meng ◽

Wei Zhou ◽

Emad Rokni ◽

Honghua Zhao ◽

Rui Sun ◽

...

Keyword(s):

Gas Phase ◽

Ignition Delay Time ◽

Fixed Bed ◽

Combustion Efficiency ◽

Fixed Bed Reactor ◽

Corn Straw ◽

Excess Air ◽

Burning Rates ◽

Excess Air Coefficient ◽

Hazardous Pollutants

This research investigated the effects of the specific primary (under-fire) air flowrate (m˙air) on the combustion behavior of a 50–50 wt % blend of raw corn straw (CS) and raw pinewood wastes in a fixed-bed reactor. This parameter was varied in the range of 0.079–0.226 kg m−2 s−1, which changed the overall combustion stoichiometry from air-lean (excess air coefficient λ = 0.73) to air-rich (excess air coefficient λ = 1.25) and affected the combustion efficiency and stability as well as the emissions of hazardous pollutants. It was observed that by increasing m˙air, the ignition delay time first increased and then decreased, the average bed temperatures increased, both the average flame propagation rates and the fuel burning rates increased, and the combustion efficiencies also increased. The emissions of CO as well as those of cumulative gas phase nitrogen compounds increased, the latter mostly because of increasing HCN, while those of NO were rather constant. The emissions of HCl decreased but those of other chlorine-containing species increased. The effect of m˙air on the conversion of sulfur to SO2 was minor. By considering all of the aforesaid factors, a mildly overall air-rich (fuel-lean) (λ = 1.04) operating condition can be suggested for corn-straw/pinewood burning fixed-bed grate-fired reactors.

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The Influence of Excess Air Coefficient of Boiler Efficiency

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.409-410.548 ◽

2013 ◽

Vol 409-410 ◽

pp. 548-552

Author(s):

Jiu Sheng Shi ◽

Fei Peng ◽

Bing Wen Zhang

Keyword(s):

Thermal Efficiency ◽

Linear Relation ◽

Combustion Efficiency ◽

Efficiency Analysis ◽

Furnace Temperature ◽

Excess Air ◽

Important Impact ◽

Boiler Efficiency ◽

Excess Air Coefficient ◽

One To One

Excess air coefficient has an important impact on the combustion conditions of boiler and thermal efficiency, analysis shows that the furnace temperature and the combustion efficiency is the linear relation of one to one correspondence. Any combustion conditions, there is an optimum excess air coefficient makes the top of furnace temperature, thus it can establish a control relationship, furnace temperature is optimization index, excess air coefficient is disturbance.It can achieve the purpose of improving the efficiency of boiler combustion.

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Optimized Operation of Boiler

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.960-961.399 ◽

2014 ◽

Vol 960-961 ◽

pp. 399-404

Author(s):

Chang Liu

Keyword(s):

Heat Loss ◽

Power Plants ◽

Thermal Power ◽

Optimal Operation ◽

Operating Efficiency ◽

Combustion Heat ◽

Correlative Analysis ◽

Excess Air ◽

Boiler Efficiency ◽

Excess Air Coefficient

This paper studies the problem of optimal operation of 300MW boiler. We combine the actual situation of the device and the theory of heat together, and improve the operating efficiency of the boiler through adjustment of device parameters, thus improving the economic benefit of thermal power plants. Firstly, according to coal characteristics and the theory of heat, we establish an improved utility model to calculate the heat loss of exhaust - gas, chemical incomplete combustion heat loss and heat loss of mechanical incomplete combusting. Then, we use fitting and interpolation, which is always applied to problems of Discrete Mathematical Statistics, to analyze discrete form of experiment data record, and give the relationship between 300MW boiler efficiency and excess air coefficient, which leads us to a new way to ascertain optimal excess air coefficient. And then, we use Principal Components Analysis (PCA) and Correlative Analysis (CA) to study the affection of operation parameters on boiler efficiency. Finally, we combine local optimization with global optimization, and establish an optimal operational model.

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The Optimal Operation Problem of Boilers

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.953-954.1454 ◽

2014 ◽

Vol 953-954 ◽

pp. 1454-1458

Author(s):

Cong Sun

Keyword(s):

Heat Loss ◽

Optimal Operation ◽

Combustion Heat ◽

Incomplete Combustion ◽

Excess Air ◽

Exhaust Heat ◽

Excess Air Coefficient ◽

Main Factors ◽

The Relationship

Boiler optimum efficiency problem can be solved by optimum excess air coefficient model. It is the key to find the relationship between main factors and the excess air coefficient. These main factors are smoke exhaust heat losschemistry incomplete combustion heat loss and mechanical incomplete combustion heat loss.In this paper, we projected the relationship between the factors and the excess air coefficient by using the computational formulas of principles of boiler. Then we synthesized the three formulas to establish the excess air coefficient model. Finally, this paper geted the optimum excess air coefficient using extremum method.That is αp=1.152596.

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98/01501 Monitoring of the combustion heat of fuel gas and excess air coefficient by flame electroconductivity

Fuel and Energy Abstracts ◽

10.1016/s0140-6701(98)97643-3 ◽

1998 ◽

Vol 39 (2) ◽

pp. 132

Keyword(s):

Combustion Heat ◽

Fuel Gas ◽

Excess Air ◽

Excess Air Coefficient

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Computational fluid dynamics investigation on the effect of co-firing semi-coke and bituminous coal in a 300 MW tangentially fired boiler

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

10.1177/0957650918783923 ◽

2018 ◽

Vol 233 (2) ◽

pp. 221-231 ◽

Cited By ~ 5

Author(s):

Yongbo Du ◽

Chang’an Wang ◽

Pengqian Wang ◽

Yi Meng ◽

Zhichao Wang ◽

...

Keyword(s):

Bituminous Coal ◽

Bottom Layer ◽

Combustion Efficiency ◽

Unburned Carbon ◽

Stoichiometric Ratio ◽

High Carbon ◽

Coke Particle ◽

Carbon Loss ◽

High Carbon Content ◽

Combustion Heat

In this paper, the effect of co-firing semi-coke in a 300 MW tangentially fired boiler was numerically investigated. The results indicate that the incomplete combustion heat loss and NO x emission both increase with semi-coke co-fired ratio. Semi-coke may be injected into the furnace at a different height, which can lead to different thermal efficiency and NO x emission. It is suggested that semi-coke should not be fed from the top or bottom layer burners, since this could give rise to high carbon content respectively in fly ash and bottom slag. In addition, injecting semi-coke from the top burners could significantly increase the NO x emission. Under 1/2 co-firing ratio, the optimal fuel allocation is that feeding semi-coke from the B, D, and E layer burners. The growth in semi-coke particle size could increase the unburned carbon loss and NO x emission. It is highly recommended to reduce the unburned carbon loss under semi-coke co-fired condition by increasing the stoichiometric ratio of primary air for semi-coke. As it is increased from 0.25 to 0.3, the combustion efficiency of the co-fired condition is 99.47%, the same as when only firing bituminous coal, and the NO x emission is about 30% higher.

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