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We intensively investigated the kinetic enhancement of dielectric-barrier-discharge (DBD) plasma on the pyrolysis and ignition of n-heptane, iso-octane, and n-decane fuels in a counterflow diffusion burner. The DBD plasma generated upstream from the fuel nozzle can contribute to low-temperature pyrolysis and high-temperature oxidation of pre-vaporized liquid fuels. Stable and short-lived intermediate species generated by plasma were measured by e x situ gas chromatography (GC) and in situ planar laser induced fluorescence (PLIF), respectively. GC results indicate that with plasma assistance approximately 2–3% of large hydrocarbons decompose at temperatures as low as 370 K and within 1 s. High-temperature oxidation experiments demonstrate that DBD can lower the ignition temperature of all three fuels with various global flow stretch rates. Experiments were compared with numerical analysis performed using the OPPDIF code that is formulated for the counterflow geometry. Finally, the discrete chemical explosive mode analysis (CEMA) elucidates the promotion of plasma-induced species, such as H 2 , C 2 H 4 , and OH radicals. [ABSTRACT FROM AUTHOR]

With the increasing use of low-grade lignite for energy production, ash related problems have received renewed attention due to their detrimental effects on power plant equipment. This study investigates the fuel effect on the ash deposition in a 25 kW self-sustained down-fired furnace, with practical implications to the efficient utilization of a sodium-rich Zhundong (ZD) lignite. The active fouling control methods include co-firing with Si/Al-dominated HAF-2 bituminous coal and pretreatment using water leaching. Both manipulation methods reduce the propensity to form ultrafine PM 0.2 particles and ash deposition for simulated furnace exit conditions compared with combustion of only ZD lignite. While the deposits formed by HAF-2 bituminous are prone to shed, blending with ZD lignite increases the ash collection efficiency and prevents massive deposit collapse. The morphology of the ZD ash deposits is characterized by a smooth shape with wide spreading angle, whereas those formed by the blended samples with ≥33 wt% bituminous coal have sharp and pointed shapes with smaller spreading angles. Deposits by samples with ≥67 wt% ZD lignite have an inner layer of micro-size particles. The local basic to acid ratio of the deposits gradually decreases from the inner to the outer layers. The apparent particle sticking probability due to the fuel effect derived from the experimental and theoretical results positively correlates with the yield of ultrafine PM 0.2 particles for the various coal samples. [ABSTRACT FROM AUTHOR]

The migration of K and Cl during biomass thermal utilization can cause serious ash-related problems. Pyrolysis experiments with KCl-loaded cellulose were conducted in a fixed-bed reactor to investigate the reaction of KCl with organic functional groups. The migration pathways of K and Cl were obtained based on the analysis of char samples after pyrolysis. Results showed that the amounts of generated K 2 CO 3 were negligible after pyrolysis at both temperature levels. After pyrolysis at 500 °C, char-Cl and char-K were generated, and the unreacted KCl existed in char as crystal particles. The released Cl amount increased first and then remained stable, whereas the Cl release ratio decreased monotonously with KCl content. Meanwhile, a small fraction of organic K was released. At 900 °C, almost all of the Cl (including KCl and char-Cl) was released, whereas a significant amount of char-K remained in char. Similar to the trend of O content, the amount of char-K increased first and then reached near-saturation with the increase in KCl content, indicating that char-K is associated with the char matrix via O. At 500 °C, during pyrolysis of cellulose with low KCl content, the formation of char-K and the release of Cl are the dominant migration pathways of K and Cl, respectively. With the increase in KCl content, unreacted KCl became the main existing form of K and Cl. The amounts of formed char-K and released Cl, as well as the formation ratio of char-Cl increased first and then reached saturation gradually. [ABSTRACT FROM AUTHOR]

With the increasing use of low-rank coal, the upgraded semi-char produced through low-temperature pyrolysis of lignite is one of promising alternatives towards the clean and high efficient utilization. The co-firing of these pyrolytic semi-chars with parent coals has received more attention. In this paper, a kind of semi-char, produced from Hulunbuir (HB) lignite under a pyrolysis temperature of 504 °C, was burned in a 25 kW self-sustained pulverized coal combustor. Different mass blending ratios of semi-char (0%, 40%, 60% and 100%) were used. The results indicate that the PM 0.1 yield from pure combustion of HB lignite is ∼1.6 times of that from semi-char. The PM 0.1 yields of the coal/char blends are much less than the linear summation of yields of two blending fuels without considering their interactions. As for coarser PM mode, the reductions still exist for both PM 0.1–1 and PM 1–10 particles. The different PM yields of pure combustion cases are attributed to less volatile mineral species and also less fragmentation degree of semi-chars during combustion. A mechanism is postulated for PM reduction during the combustion of coal blends. PM 0.1 amounts are decreased since the volatilized mineral species is considerably scavenged by the previously formed semi-char surfaces, as partly evidenced from a time scale analysis. The scavenged compounds then serve as “glue” to convert ash particles to larger agglomerates, which may result in the reduction of PM 0.1–10 yields. [ABSTRACT FROM AUTHOR]