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It is critical for flotation to accomplish the bubble-mineral particle attachment as well as mineralization process. The surface free energy of mineral particle and liquid is a key parameter which affects the wettability and wetting process of mineral in mineralization. In this paper, the surface free energy components of coal sample were calculated by Washburn equation and Oss Chaudhury-Good-Van theory. Additionally, the wetting ability of modified diesel oil for coal sample was studied by Washburn dynamic capillary method while Lipophilic Hydrophilic Ratio and relative contact angle were calculated. Furthermore, the effect of both surfactants, 2-ethylhexanol and didodecyldimethylammonium bromide (DDAB), on the induction time between oily bubbles and coal particles was investigated. Results indicated that wetting ability of modified diesel oil for coal sample did not entirely increase with the decrease of surface tension, and liquid viscosity was also a relevant factor. The adhesion strength enhanced whereas the detachment probability reduced with the increase of collector viscosity. But too large viscosity was bad for fluidity of liquid, which therefore decreased its wettability for coal sample. The induction time between coal particles and reactive oily bubbles modified by 2-ethylhexanol and DDAB decreased by 74.35% and 86.45% respectively. As a result, the maximum combustible matter recovery of 72.20% (increasing by 22.23%) and highest flotation efficiency index of 56.50% were obtained when the weight ratio of 2-ethylhexanol to diesel oil was 0.04, while that of using reactive oily bubbles modified by DDAB showed an apparent decrease. It indicated that it was crucial to the flotation of low rank coal that proper surfactant was used to generate reactive oily bubbles. [ABSTRACT FROM AUTHOR]

[Display omitted] • The change laws of flammability limits with ignition energy for flammable working fluids are studied. • The influence laws of ignition energy on flame propagation are acquired. • The burning velocity in stable propagation stage is independent of ignition energy. • The influence mechanism of ignition energy on combustion characteristics is obtained. Working fluids with low global warming potential (GWP) will play an important role in the research and development of alternative working fluids for organic Rankine cycles and refrigeration cycles. However, the flammability of low GWP working fluid limits their development, and the energy of typical fire sources has a significant impact on their safe application. At present, there is a lack of relevant research on the effect of ignition energy on their flammability. In this paper, the effect of ignition energy on the combustion characteristics for propane (R290), fluoroethane (R161), 1,1-Difluoroethane (R152a), and 3,3,3-Trifluoropropene (R1243zf) was studied using a variable ignition energy system. The initial flame propagation process, flammability limit, and burning velocity were tested and analyzed in the range of 50 mJ to 20 J. The results showed that with the increase of ignition energy, the lower flammability limit (LFL) decreased and the upper flammability limit (UFL) increased, but their rate of change decreased with the increasing ignition energy. The effect of ignition energy on the flammability limit of R1243zf was significantly greater than that of the other three working fluids. In addition, the effect of ignition energy on flame propagation was mainly limited to the initial stage, and the burning velocity was independent of ignition energy. The mechanism of ignition energy on combustion characteristics was obtained. The research results have guiding significance for the safe application of flammable working fluids. [ABSTRACT FROM AUTHOR]

• Flammability characteristics of R1216 mixed with R32 and R152a were investigated. • The suppression effect of R1216, R134a, R1233zd(E), and R13I1 was compared. • The flame inhibition mechanism of R1216 was analyzed. R1216 (1,1,2,3,3,3-hexafluoro-1-propene), which has a low global warming potential, is regarded as the new generation of environmentally friendly working fluid in ORCs (organic Rankine cycle) and refrigeration systems. Besides, it also has the advantage of nonflammable property. Thus, R1216 can be mixed with some flammable working fluids to develop new mixed alternatives, which can possess a combination of chemical, environmental, thermodynamic, and safety properties. In this work, the flammability limits of R1216/R32 and R1216/R152a were measured in a 12L spherical glass vessel according to the method of ASTM E681. And the critical flammable volumetric ratios of R1216 on R32 and R152a were about 0.15 and 1.1, respectively. This study also found that the ratio of F atoms to H atoms for the two mixtures had a close relationship with the flammability limit ranges. Finally, the flame inhibition performances of R1216 were compared with other commonly used flame retardants, such as R134a, R13I1 (trifluoroiodomethane), and R1233zd(E) (trans -1-Chloro-3,3,3-trifluoro-propene). It can be concluded that the rank of the inhibition effects was R1216 > R13I1 > R134a > R1233zd(E). And a flame retardant, which contained a higher F/H ratio and much more Cl, I, and CF 3 radicals, can possess a higher flammability inhibition efficiency. [ABSTRACT FROM AUTHOR]

• The flammability limits and burning velocities of R1234yf mixtures were measured. • The relationship between flammability limit ranges and the n F /n H was analyzed. • The factors affecting the burning velocity were explored in the molecular structure. In response to the pressure of environmental protection, a series of environment-hazardous refrigerants will be phased out. And the selection of the substitutions for the future will need to balance thermodynamic property, safety and sustainability. Thus, the mixed refrigerants are receiving increasing attentions for their special performances. In this paper, the flammability characteristics of the commonly used mixtures R32/R1234yf and R152a/R1234yf were experimentally researched. The flammability limits of the two binary mixtures at different proportions of R1234yf were measured in a 12L spherical glass vessel. And the burning velocities of the two mixtures at different equivalence ratios were measured in a cylindrical quartz vertical tube. It can be found that the flammability limit curves of R32/R1234yf were different from that of R152a/R1234yf. The ratio of F atoms to H atoms (n F /n H) for the two mixtures had a close relationship with the flammability limit ranges. The maximum burning velocity for R32/R1234yf and R152a/R1234yf tended to decrease with the increase of the R1234yf proportion, and also decreased with the increasing of the n F /n H. But the n F /n H was not the only impact on the burning velocity. The number of C–H bonds and the molecular structure reflected in the heat of combustion would be correlated with the burning velocities of the mixtures. The results will provide a guidance for the development and safe application of R1234yf mixtures. [ABSTRACT FROM AUTHOR]

• The flammability limits of R290 and R600a were measured and analyzed in different temperature and humidity range. • The flammability limits of R290 and R600a showed linear temperature dependences. • A special case for the influence of humidity on the flammability limits of hydrocarbons was found, especially for UFLs. • Two effects with maximum and minimum were found for the UFLs of R290 and R600a. In this study, the flammability limits of R290 and R600a were measured in different environmental conditions. All the experiments were performed on a self-made experimental rig at temperature ranging from 5 to 55 °C and relative humidity of air ranging from 0 to 100%. The results showed that the temperature dependences for the flammability limits of both R290 and R600a can be predicted by linear model precisely. The humidity dependences for the flammability limits of R290 and R600a were distinctive, which was increased slowly for lower flammability limits (LFLs) but changeable for the upper flammability limits (UFLs). Meanwhile, it was found that the flammability limits of both R290 and R600a became sensitive with the relative humidity changing. A special case for the water vapor influencing on the flammability limits of hydrocarbons was found, especially for UFLs. It has maximum and minimum values in the experimental curve of UFLs when the relative humidity increased from 0 to 100%, which revealed that water vapor does not inhibit the combustion of hydrocarbons simply. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flammability limits of the new binary mixture R1234ze(E)/R32 was measured. • Oxidative decomposition and interaction mechanisms of R234ze(E)/R32 were studied. • R32 decomposes preferentially and R1234ze(E) is more likely to react with radicals. • CF 3 plays an important role in R1234ze(E) inhibiting flammability of R32. At present, mixed working fluids have received increasing attention due to their excellent comprehensive performance. Among them, R1234ze(E) (trans -1,3,3,3-tetrafluoropropene) and the R32 (difluoromethane) with excellent thermal properties can form a safe and environmentally friendly new mixture through advantageous complementarity. In this paper, the flammability of the binary mixture R1234ze(E)/R32 mentioned above was studied. Firstly, the flammability limits and critical concentration inhibition ratio of R1234ze(E)/R32 were tested at different ratios. Then, based on density functional theory (DFT), the interaction mechanism between the two components in the mixture was analyzed. The results show that with the increase of R1234ze(E), the flammable limit range becomes narrower. In the early stage of the reaction between R1234ze(E)/R32, R32 preferentially breaks the bond to generate H and F radicals, but the reactions between R1234ze(E) and free radicals are dominant. CF 3 radical is an important free radical for R1234ze(E) to inhibit the flammability of R32. The research results will have guiding significance for the internal interaction mechanism of the flammability of new binary mixtures and their safe applications. [ABSTRACT FROM AUTHOR]

• The mono-combustion of coal slime was achieved on a 75 t/h CFB boiler. • Temperatures in middle of the furnace were the lowest in this coal slime CFB boiler. • Post-combustion air was an effective means to adjust the main steam parameters. • NO x emissions were decreased below 50 mg/m3 by post-combustion technology. Coal slime was a kind of industrial solid waste and it was hard to utilize. To realize the resource utilization of coal slime, a 75 t/h circulating fluidized bed (CFB) boiler with post-combustion technology was built. The operating and emission characteristics during mono-combustion of coal slime were investigated in detail. The fuel characteristics of coal slime and feeding from the top of the furnace resulted in the temperatures at the top and the bottom were higher than the middle of the furnace. When the furnace differential pressure increased, the furnace temperature and the main steam temperature both decreased, but the main steam flow increased. The main steam temperature could significantly increase after the soot blowing. The post-combustion air (PCA) was an effective means to adjust the main steam parameters. The main steam temperature increased as PCA increasing. The average SO 2 emissions were only 8.4 mg·m−3 benefited from the excellent desulfurization effect of the combination of dry and semi-dry desulfurization. Nevertheless, due to the fluctuations of coal slime characteristics, the standard deviation of SO 2 emission reached 8.6 mg·m−3. Under the conditions without desulphurization and SNCR, the NO x emissions of coal slime could be decreased to 38 mg·m−3 and reach the ultra-low NO x emission when post-combustion technology was used. [ABSTRACT FROM AUTHOR]

Zhundong (ZD) coal gasification/combustion fly ash is a high Na content residual product and contains a large quantity of harmful elements, including as Cl, S, and Na that must be removed and recovered. Water-soluble Na is the predominant Na form in ZD coal fly ash, accounting for 34.7–92.8% of the total Na. The main minerals of Na identified were NaCl and Na 2 SO 4 . Most of the water-soluble Na in the ZD coal fly ash can be effectively removed by water washing, the removal yields have been found to be 31–93%. Increasing the washing time, water temperature, liquid–solid ratio and acid concentration can increase the Na removal yield. For the ZD coal combustion fly ash (SEHcf) and gasification fly ash (SEHf), NaCl particles are present on the fly ash surface, most water-soluble Na was washed by water in 5 min at 30 °C. However, the removal of Na by water washing was inhibited by the water insoluble calcium oxides and sulfides that covered the surface of the ZD coal gasification fly ashes (TCf and SHf), Na removal required higher wash water temperatures and longer washing times. It is feasible to recover Na from ZD coal fly ash by water washing, and the recovered Na products are primarily NaCl and Na 2 SO 4 . The recovery yields of Na in the SEHcf, SEHf and TCf were 49.4%, 81.2%, and 65.4%. But the recovery yield of Na in SHf was 16.6%. SEHcf, SEHf and TCf were more suitable for recovering Na. the recovery of Na from ZD coal fly ash is economically feasible. [ABSTRACT FROM AUTHOR]

An effective bed material is crucial to remit slagging/agglomeration for high-sodium lignite during circulating fluidized bed (CFB) gasification. In this study, the exploration of effective bed material for use as slagging/agglomeration preventatives of high-sodium lignite mined from Zhundong district was conducted in a 0.4 T/D CFB test system. Three mineral materials, SiO 2 -based quartz sand, Al 2 O 3 -based corundum and CaO/Fe 2 O 3 -rich boiler ash collected from bottom ash of a CFB industrial boiler, were selected as the potential bed material. Their impacts on the de-fluidization tendency, transformation and migration of alkali metals, priority of reactions involving sodium-based species, formation of liquid slags and ash fusibility were investigated through the characterization of ash samples and thermodynamic equilibrium calculation by Factsage 6.1. The particle-size analysis results presented the improvement of three bed materials in the growth of ash particles followed the order of quartz sand > corundum > boiler ash. This order was ascribed to their reaction priority with sodium-based compounds in coal and the chemical property (mainly referring to ash fusibility) of corresponding products. Generally, reactions between sodium-based species and minerals (Al 2 O 3 and SiO 2 ) were the main way of sodium retention within the ash in gasifier. As boiler ash was used, however, Al 2 O 3 and SiO 2 preferentially reacted with the CaO enriched in boiler ash rather than sodium-based species in coal, resulting in very low sodium retention. Under such circumstances, computing results suggested the ash in gasifier could withstand higher gasification temperature, consistent with the measured results of ash fusibility. Additionally, the gasification temperature operating range could be largely widened by simply increasing CaO/Fe 2 O 3 content in gasified ash. Therefore, boiler ash is an effective and low-cost bed material for use as the slagging/agglomeration preventative of high-sodium lignite during CFB gasification. [ABSTRACT FROM AUTHOR]

The interaction between long-flame coal particles and oily bubbles controls the crucial processes of attachment and mineralization in oily-bubble flotation thus dominates the recovery of coal. In this study, the interaction energy between long-flame coal particles and diesel oily bubbles was estimated by both DLVO and EDLVO theories, while the attachment of coal particles to oily bubbles was evaluated by induction time measurements and oily-bubble flotation tests. The results indicated that the isoelectric points of oily bubbles and coal particles were observed at about pH 3.5 and 2.3, respectively. Over the entire range of pH 2–11, the attachment between coal particles and oily bubbles was confirmed by the results of the induction time and oily-bubbles flotation tests. Additionally, it was found that the flotation recovery of coals was inversely related to the induction time. The attachment could be accurately predicted by the EDLVO theory over the tested pH range. On the contrary, it showed a great deviation for the DLVO theory to predict the attachment over the tested pH range except at pH 3. The reason for the deviation in prediction may be that the hydrophobic force on the interface of coal particles and oily bubbles is too great to be ignored. [ABSTRACT FROM AUTHOR]

A high-sodium, high-chlorine Xinjiang lignite was used as fuel in a 0.4 t/d circulating fluidized bed (CFB) test system to investigate ash deposition and corrosion characteristics using an air-cooled stainless steel probe. Different wall temperatures of the probe, exposed to the similar flue gas environment for 8 h, were achieved by adjusting cooling air flow separately at 1.0 m 3 /h, 3.0 m 3 /h and 5.0 m 3 /h. The probe wall temperature variation was analyzed, and deposited ash was characterized via a series of analytical techniques. Experimental results confirmed the disturbance of ash deposition to the heat flux through the probe, and this disturbance was enhanced due to the faster ash deposition rate at lower wall temperature. The selective deposition of mineral species including Na-, Cl-, K- and Mg-species occurred, resulting in a larger ash deposition amount on the lower-temperature probe. The corrosion caused by NaCl-rich deposited ash was accompanied with the oxidation of metallic matrix. It is found that the antioxidation of metals was in the order of Ni > Cr > Fe. During corrosion, metal chlorides with strong volatility were the main corrosion products, resulting in the presence of voids in deposited ash because of their release. This corrosion was accelerated at high temperatures and had repeatability. [ABSTRACT FROM AUTHOR]

The surface properties of coal play a crucial role in its flotation, therefore it is of great significance to investigate the changes in both chemical structure and surface morphology in oxidation process of low rank coal. In this paper, the mechanism of difficult floatation of oxidized coal was highlighted. The surface hydrophobicity and floatability of Meizhiyou long-flame coal before and after oxidation processing with H 2 O 2 solution at different concentration were evaluated by induction time and contact angle analyses as well as flotation tests, while the changes in its surface properties in the oxidation process were analyzed by XPS, FTIR, BET and SEM measurements. The maximum increase extent of induction time between bubbles and oxidized coal particles reached to 13217% while the maximum reduction extent of combustible matter recovery reached to 95.28%, which indicated the floatability of oxidized coal particles almost decreased exponentially along with the increase of concentration of H 2 O 2 solution. Additionally, the results suggested the active chemical functional groups of >CH 2 peak at 1437 cm −1 , CH 3 peak at 1373 cm −1 and C O C peak at 1215 cm −1 were susceptible to oxidation. After oxidation processing, on the one hand, the content of hydrophobic groups on coal surface showed an obvious decrease while that of hydrophilic groups showed a significant increase. What’s more, the content of carbonyl group had a close correlation with the extent of oxidation of the coal sample. On the other hand, it was found that the surface morphology of coals was significantly changed after oxidation process, and there were more pores and cracks on the coal surface. As a result, the contact angle of coals showed a significant decline after oxidation processing and it declined more quickly with the increase of contact time. Consequently, the poor flotation performance of oxidized coals may be attributed to the dramatic changes in both surface chemical structure and surface morphology in oxidation process. [ABSTRACT FROM AUTHOR]