Detailed kinetic and control of alkali metal compounds during coal combustion

Takuwa, Tsuyoshi; Naruse, Ichiro

doi:10.1016/j.fuproc.2007.06.010

Cited by 37 publications

(25 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The behavior of sodium species during coal combustion has been studied using both offline and online measurements. Offline analysis of fuel and ash compositions continues to be used for supporting and complementing online data [11][12][13][14][15]. These results reveal physical and chemical characteristics of sodium in the ash residues, which aids in understanding the transformations of sodium.…”

Section: Introductionmentioning

confidence: 94%

Measurement of atomic sodium release during pyrolysis and combustion of sodium-enriched Zhundong coal pellet

Wang

Liu

Whiddon

et al. 2017

Combustion and Flame

View full text Add to dashboard Cite

Temporally resolved measurements of surface temperature, pellet diameter and proximal sodium concentration field are presented for the combustion of a high sodium coal (Zhundong) pellet. Non-resonant Planar laser-induced fluorescence (PLIF) was used to image the atomic sodium distribution around the coal pellet. The release profile of atomic sodium demonstrates three phases of combustion: (I) the devolatilization stage, (II) the char burnout stage, and (III) the ash reaction stage. Highest peak sodium concentration occurred in the char burnout stage, while the ash stage had the longest duration. The radial and axial sodium concentration decay during different phases of combustion was analyzed. During char burnout and ash stages, the maximum concentration of atomic sodium was near the pellet. In the devolatilization stage, burning of volatile-gases creates a high temperature region away from the surface of the coal pellet, which enhances the decomposition of sodium compounds in this region. Axial decay of atomic sodium concentration was governed by chemical reactions during all combustion stages. Calculation of atomic sodium flux (Na * flux) indicate that the smaller pellet releases atomic sodium more strongly in the devolatilization and char burnout stages than larger pellet. The mechanism of sodium release was inferred from the time derivatives of Na * flux , pellet-surface temperature (T) and pellet diameter (d). During the devolatilization stage, only Na * flux and T show variations, indicating that atomic sodium release is due to pyrolysis of the coal pellet. In the char burnout stage, time derivatives of the three parameters obey a common trend, indicating that the sodium release is associated with the burning of organic components in the pellet. In the ash reaction stage, T and d remain constant, indicating that the release of atomic sodium may be attributed to slow processes in the ash, likely vaporization of sodium from crystalline solids. A two-steps sodium release kinetics has been developed in this study and the simulation results agree well with measurements at three burning stages of coal pellet.

show abstract

Section: Introductionmentioning

confidence: 94%

Measurement of atomic sodium release during pyrolysis and combustion of sodium-enriched Zhundong coal pellet

Wang

Liu

Whiddon

et al. 2017

Combustion and Flame

View full text Add to dashboard Cite

show abstract

“…However, sodium was hardly to be released into the flue gas in the form of Na2O or NaOH, because even if NaOH was produced by Na 2 O and H 2 O at high temperatures, it would also equilibrate to produce atomic Na [22]. The results of chemical equilibrium calculation for sodium compounds by Takuwa and Naruse [23] also indicated that there was no gaseous NaOH at the temperature below 1100 o C. However, another work on particulate matter emission from brown coal combustion found NaCl mainly contributed to the emission of particles with aerodynamic diameter less than 0.1μm [24]. Li [3] reviewed the existing forms of sodium in Victorian brown coal with high content of AAEMs, which is very similar to Zhundong coal.…”

Section: Figure 6 Residual Ash Morphologies At (A)-600 O C (B)-815 mentioning

confidence: 99%

The ash deposition mechanism in boilers burning Zhundong coal with high contents of sodium and calcium: A study from ash evaporating to condensing

Wang

Wei

et al. 2015

Applied Thermal Engineering

264

138

View full text Add to dashboard Cite

ABSTRACT:The high contents of sodium and calcium in Zhundong coal induce severe slagging and ash deposition in boilers. In this study, the ash deposition mechanism was investigated based on the results obtained from a full-scale boiler (350 MW) burning Zhundong coal, anda fixed bed reactor used for ash evaporating-condensing. In the full-scale boiler, the condensing and depositing of sodium and calcium sulfates play an important role on ash depositing on convection heating surfaces. Sulfates start to significantly condense and deposit at the flue gas temperature of about 850 o C (at Medium and High Temperature Reheater). Ash evaporating tests proved that, with the increasing in temperature from 400 o C to 1200 o C, the ash evaporating process is divided into three stages: 1) 400-800 o C, 80% of sodium, and 100% of chlorine are released; 2) 800-1000 o C, all the left sodium evaporates and sulfur starts to be released with the formation of partial aluminosilicates; 3) 1000-1200 o C, all the left sulfur is released through the decomposition of calcium sulfates and then calcium starts to evaporate, while silicon oxides disappears due to the formation of new complex silicates. Ash condensing tests further proved that, the sodium in Zhundong coal was released mainly in the forms of atom, oxide, and chloride, in which sodium chloride account for about 50%. When the evaporating temperature increased higher than 1000 o C, partial alkali and alkaline earth metals were released as gaseous sulfates, and afterwards condense and deposit on the heating surfaces. At last, a temperature-dependent ash deposition mechanism in Zhundong coal combustion was proposed.

show abstract

“…Several authors found aluminosilicates such as bauxite and kaolinite to be suitable alkali sorbents. These same materials were shown to be effective in combustion atmospheres, removing alkalis to as little as 50 ppbv through formation of stable alkali silicate compounds. Alumina can also act as a physical sorbent: activated alumina was found to adsorb NaCl vapour with 98% efficiency to a loading of 6.20 mg/g .…”

Section: Emissions and Abatementmentioning

confidence: 99%

Alkali, boron and phosphorous removal from coal‐derived syngas: review and thermodynamic considerations

Dolan

Ilyushechkin

McLennan

et al. 2011

Asia-Pacific J Chem Eng

View full text Add to dashboard Cite

Alkalis are highly corrosive towards materials associated with syngas processing and utilisation, including ceramic particulate filters and metallic components. The removal of alkali species, consequently, is an important step in the cleaning of coal and biomass-derived syngas. The origins of the alkali contaminant govern the ability of specific sorbents to remove these species via chemical means. Alkali salt removal is dependent on the formation of an acid halide species, a reaction, which in the absence of H 2 O, involves hydrogen and carbon dioxide. This reaction becomes increasingly unfavourable above 1000 C, but below this temperature, equilibrium conversion approaches 100%. The fluxing of a gasifier slag, which is often necessary to reduce viscosity to a level that allows tapping, reduces its ability to absorb alkali halides. This effect however was not observed with oxide-based alkalis, which shows strong affinity for gasifier slag regardless of fluxing, up to 1600 C. Furthermore, there is a potential for removal of boron and phosphorous contaminants using these same sorbents. In a complete high-temperature, dry gas cleaning sequence, alkali removal would ideally be undertaken prior (or simultaneously to) halide removal and prior to sulfur removal.

show abstract

Detailed kinetic and control of alkali metal compounds during coal combustion

Cited by 37 publications

References 44 publications

Measurement of atomic sodium release during pyrolysis and combustion of sodium-enriched Zhundong coal pellet

Measurement of atomic sodium release during pyrolysis and combustion of sodium-enriched Zhundong coal pellet

The ash deposition mechanism in boilers burning Zhundong coal with high contents of sodium and calcium: A study from ash evaporating to condensing

Alkali, boron and phosphorous removal from coal‐derived syngas: review and thermodynamic considerations

Contact Info

Product

Resources

About