No abstract

Mercury emission is an important issue during in-situ gasification chemical-looping combustion (iG-CLC) of coal. This work focused on experimentally “isolating” two elementary subprocesses (coal pyrolysis and char gasification) during iG-CLC of coal, identifying mercury distribution within the two subprocesses, and examining the effects of a hematite oxygen carrier (OC) on the mercury fate. The mercury measurement accuracy was carefully ensured by comparing online measurements (by a VM 3000 instrument) and benchmark measurements (by the standard Ontario Hydro Method, ASTM D6784) as well as repeated tests (10 times for each case). The mercury mass balance was 115% for the entire iG-CLC. A total of 44.7% of the mercury was released as the gas phase form within the coal pyrolysis process at a typical CLC operation temperature (950 °C), whereas 13.4% was released during the char gasification process. The release rate and amount of mercury were minimally affected by the presence of OC; however, the OC promoted the conversion of Hg0(g) to Hg2+(g). Only a small amount of mercury was absorbed by the OC and transported into the air reactor along with carbon residue, released as Hg0(g) and Hg2+(g) or remained in the OC and coal ash as particulate mercury.

Chemical-looping combustion (CLC) is a novel technology with the feature of CO 2 inherent separation in which the fuel is converted via lattice oxygen (instead of gaseous oxygen) provided by the oxygen carrier that circulates between two structurally interconnected but atmosphere-isolated reactors, i.e., fuel reactor and air reactor. In the fuel reactor of in situ gasification CLC (iG-CLC), the pyrolysis and gasification products of coal are oxidized by lattice oxygen in the O 2 -free environment. Therefore, the characteristics of sulfur species evolution and distribution in the coal pyrolysis products are significantly different from those in the conventional combustion, gasification, and pyrolysis processes. In this study, a two-stage fluidized bed reactor was utilized to investigate the reaction between the oxygen carrier and in situ coal pyrolysis products, in which the coal and oxygen carrier particles are separately loaded in two reactors. In this way, the influence of oxygen carrier on the coal pyrolysis process could be eliminated. As obtained from the experiment, the distribution of sulfur species in coal pyrolysis products changed significantly after being oxidized by the oxygen carrier. To be more specific, the sulfur species were 70.1% H 2 S, 0.2% SO 2 , 0.8% COS, and 13.1% CS 2 , respectively, during the coal pyrolysis process in the blank experiment loaded with silica sand, whereas the concentrations of the sulfur species (in the same order) changed to 26.0%, 68.2%, 0%, and 0%, respectively, once the pyrolysis products went through the Fe 2 O 3 /Al 2 O 3 oxygen carrier. The result indicates that most of the H 2 S, COS, and CS 2 contents could be oxidized by the oxygen carrier to generate SO 2 in the CLC environment. The sulfurous gas conversion rate at the CLC experiment was higher than that at blank experiment due to the fast evolution of sulfur in tar, which was also converted by oxygen carrier to enhance the sulfur conversion at the CLC experiment. Most of the H 2 S could be oxidized by the oxygen carrier to generate SO 2 via the reaction H 2 S(g) + 9Fe 2 O 3 = 6Fe 3 O 4 + H 2 O(g) + SO 2 (g), and this has been confirmed by both experiment and HSC simulation. Moreover, scanning electron microscopy and energy-dispersive X-ray spectroscopy results indicated that no metallic sulfide was formed on the surface of reduced oxygen carrier.

Summary In most legumes, two typical features found in leaves are diverse compound forms and the pulvinus‐driven nyctinastic movement. Many genes have been identified for leaf‐shape determination, but the underlying nature of leaf movement as well as its association with the compound form remains largely unknown. Using forward‐genetic screening and whole‐genome resequencing, we found that two allelic mutants of Medicago truncatula with unclosed leaflets at night were impaired in MtDWARF4A (MtDWF4A), a gene encoding a cytochrome P450 protein orthologous to Arabidopsis DWARF4. The mtdwf4a mutant also had a mild brassinosteroid (BR)‐deficient phenotype bearing pulvini without significant deficiency in organ identity. Both mtdwf4a and dwf4 could be fully rescued by MtDWF4A, and mtdwf4a could close their leaflets at night after the application of exogenous 24‐epi‐BL. Surgical experiments and genetic analysis of double mutants revealed that the failure to exhibit leaf movement in mtdwf4a is a consequence of the physical obstruction of the overlapping leaflet laminae, suggesting a proper geometry of leaflets is important for their movement in M. truncatula. These observations provide a novel insight into the nyctinastic movement of compound leaves, shedding light on the importance of open space for organ movements in plants.