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•Hydrothermal carbonization of food waste and its digestate were comparatively investigated.•Investigation the possibilities for integration of thermal processes with biochemical ...process.•A new concept to enhance the hydrogen production from food wastes.•No significant difference between fuel properties of hydrochars derived from FW and FD.•The combustion reactivity of hydrochars was higher compared to lignite.
The aim of this study was to comparatively evaluate the effect of hydrothermal carbonization (HTC) conditions on the yield and the fuel properties of hydrochar obtained from food waste (FW) and its digestate (FD). The mass yield of hydrochars from FW and FD were found between 47.0 and 69.8%, 43.0 and 58.2%, respectively, under tested conditions. Based on both mass and energy yields, optimum temperature and duration were selected as 200 °C and 60 min for FW and 200 °C and 30 min for FD. FW and FD hydrochars produced optimum conditions had similar properties to lignite. The selected hydrochars were also subjected to steam gasification and combustion experiments. The combustion reactivity of hydrochars was found to be higher than that of lignite. Steam gasification produced 57–59 mol H2/kg hydrochar. The overall results emphasize the potential of H2 production by integrated systems of dark fermentation, HTC and steam gasification, besides production of solid fuel.
•Co-pyrolysis of cornstalk with lignite and bituminous coal was studied.•Characteristic values and stages of all single and blended samples were identified.•Slight synergistic effects were evidenced ...by both TG/DTG and FTIR profiles.•0.3–7.4 % higher final residual yields than expected were confirmed in co-pyrolysis.•Thermal behavior of biomass was influenced by the presence of coal at 286–306 °C.
Co-pyrolysis characteristics of cornstalk with two types of coal (lignite, bituminous coal) were investigated using thermogravimetry coupled with Fourier transform infrared spectrometry (TG-FTIR). Pyrolysis thermal behaviors of biomass and coal samples and their blends in different blending ratios were revealed by TG and DTG profiles, and an online monitoring of gas products evolved was realized by FTIR measurement. In order to explore potential synergistic effect, characteristic values of TG and DTG curves were identified for all blended and parent samples. In the meantime, evolution characteristics of CO2, CO, CH4, H2O and formic acid were identified by FTIR profiles against temperature. Slight synergistic effects were approved by both TG and FTIR analysis, which resulted in higher char yields and influences on volatile evolution during co-pyrolysis. 0.3∼7.4 % higher final residual yields than expected were confirmed in co-pyrolysis. TG results showed that thermal behavior of biomass was remarkably influenced with the presence of coal in blended samples at 286–306 °C. FTIR profiles also indicated that the evolution of formic acid was affected according to the releasing characteristics of CO and C–O groups at the same temperature region. SEM images and BET analysis of residual char provided further information about synergy. Disparity of thermal behaviors and void spaces between parent biomass and coal brought favorable conditions for adsorption and coking of both biomass and coal volatiles, which led to different gas-solid interactions and significantly changed the surface morphology and porous structure of co-pyrolyzed char particles.
The first coalification jump (FCJ) has a significant impact on low-rank coal reservoir heterogeneity, and is of great importance for coalbed methane (CBM) development. Here, a series of experiments ...were performed for 10 coal samples collected from eastern Junggar Basin, to compare the material composition, pore structure and adsorption capacity of lignite and candle coal. Contrast with the candle coal, the lignite has a higher inertinite content, larger pore volume, better connectivity, and greater specific surface area (SSA). During the process of FCJ, the polycondensation of coal molecules and the compaction of coal matrix occur, leading to a rapid decline of moisture, porosity and permeability, and the cell wall in the candle coal is badly crushed with clay minerals filled from optical microscopy. In general, the larger total pore volume (1.7–300 nm, measured by N2 adsorption) contributes to the larger SSA. The SSA of candle coal mainly comes from the contribution of micropore (<10 nm), especially the 2–3 nm pores, while the micropore and transition pore (10–100 nm) contribute to most of SSA of lignite. However, though the SSA of the candle coal is largely lower than that of the lignite, the CH4 adsorption capacity tends to decrease from the lignite to the candle coal due to material composition difference. Low-field NMR was used to determine the pore and fracture system by analyzing the transverse relaxation time, which showed that only two obvious peaks could be identified in lignite and three peaks at about 0.25 ms, 30 ms and 200 ms are present in the candle coal. The fractal results indicate that the pore surface and complexity inside the coal increase gradually from lignite to candle coal. These observations could deepen awareness and understanding of low-rank coal reservoir heterogeneity and the influence of FCJ on reservoir property.
•High content of AAEM species Zhundong lignite was combusted.•The formation of eutectic mixtures contributes to the severe slagging near burner.•Zhundong lignite presents higher deposition propensity ...than other contrast fuels.•Zhundong lignite produces more fine particles than other contrast fuels.•Sticky surfaces enhance deposition tendency of Zhundong lignite.
The high-reserve Zhundong lignite, rich in Alkali and Alkaline Earth Metal (AAEM) elements, causes severe fouling and slagging problems in stationary combustion systems. In this paper, the ash deposition propensity as well as its relation to AAEM-rich fine particulates was investigated in a 25kW down-fired furnace possessing similar conditions to practical combustors. The high content AAEM (mainly calcium) species in Zhundong lignite results in the molten slag at the vicinity of the burner inlet, differing from other case burning high-ash-fusion (HAF) bituminous coal. The ash deposits were collected at a position with gas temperature of 800°C, whereas the fine particulates were sampled at the same position by a two-stage nitrogen-dilution isokinetic probe. The deposition tendency of ash particles from Zhundong lignite is apparently higher than those from contrast fuels and even herbaceous biomass. It is then related to the sticky surfaces of both bare deposition tube and bulk fly ash particles, forming from large amounts of AAEM species, which enhances the deposition propensity.
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Toluene as a model tar compound was used to study the effect of atmosphere on carbon deposition during biomass tar reforming. A novel Ni-loaded on lignite char (Ni/LC) and commercial ...Ni/Al2O3 was employed for stability evaluation in a thermogravimetric analyzer. The mechanism of coke formation under N2, H2 and steam with different steam/carbon (S/C) ratio were investigated during 5 h test. Nickel particle growth is the main reasons responsible for the deactivation of Ni-based catalysts for tar reforming. Steam remarkably suppressed the carbon deposition on Ni/Al2O3, especially in a high S/C ratio. Ni/Al2O3 exhibited high activity and stability for 5 h operation in S/C ratio of 2. H2 significantly promoted the carbon deposition on Ni/Al2O3 and caused the catalyst deactivation within 0.5 h. Ni/LC exhibited great resistance to coke deposition under inert and H2 reforming of toluene. The catalysts before and after catalytic cracking were characterized by X-ray diffraction and transmission electron microscopy to investigate the behavior of carbon deposition. Except for H2 reforming, an obvious change of the Ni crystallite size (NCS) can be found after reforming for 5 h under all conditions used in this study. The NCS in Ni/LC was significantly increased with increasing time and S/C ratio, which should be partly responsible for the deactivation of the Ni/LC.
HZSM-5 was modified via alkaline treatment and wet impregnation method which loading transition metals (Co, Mo–Co and Ni–Co). The performance of catalysts for the catalytic fast pyrolysis of lignite ...was tested in a drop tube reactor at 600 °C. In comparison to non-catalytic experiment, the chemical composition of upgrading tar was obviously simplified, which mainly contains light aromatics such as benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN). The yield of BTEXN was significantly increased from 12.9 to 26.4 mg/g when Ni/Co-H-5 was used. Meanwhile, the Ni/Co-H-5 treated by NaOH solution achieved considerable deoxygenation performance (86.6%) than other ones. The addition of bimetallic Mo–Co or Ni–Co significantly enhanced the BTEXN selectivity of HZSM-5. Ni promoted H2 formation in gaseous product and caused the decrease of naphthalenes yield. Whereas the yields of toluene and o-xylene increased after the pyrolysis vapors pass through Mo/Co-H-5. The zeolite treated by NaOH solution (AT-HZSM-5) favors the generation of aromatics and phenolics, conversely naphthalene derivatives. Moreover, AT-Mo/Co-H-5 and AT-Ni/Co-H-5 inhibited the coke formation. A catalytic pathway was also proposed to describe the diffusion process of pyrolysis vapors on the active site of catalyst.
Using lignite as an adsorbent and subsequently as a material for coal water slurry (CWS) preparation represents an alternative method for coal chemical wastewater treatment. However, the components ...in these wastewaters could affect the CWS performance, especially ammonia nitrogen (NH4+-N). The influencing mechanism of NH4+-N was studied through adsorption method. Associated with adsorption reaction model, Fourier transform infrared spectrum and zeta potential detection, it was found that the adsorption reaction of NH4+-N, driven by ion-exchange interactions with H+ of –OH and –COOH on the lignite surface, displayed a typical monolayer mode and was much faster than that of NSF which displayed a double-layer mode and was adsorbed preferentially at hydrophobic sites. In binary adsorption, the adsorption amount of NSF was increased remarkably by adding NH4+-N. This was attributed to the modified lignite surface and hydrophilic group by NH4+-N that decreased the surface electronegativity as well as the electrostatic repulsion among –SO3− in NSF molecules. The enhanced adsorption of NSF resulted in capturing more water molecules in hydration film surrounding the particles in CWS. The hydration film was then thickened and stabilized, thus leading to a decrease in free water for CWS flowing. As a result, the apparent viscosity was increased, and CWS tended to be dilatant. In addition, the thickened and stabilized hydration film also increased the yield stress of CWS prepared with NH4+-N, resulting in improved stability.
•The hydrothermal upgrading of biowastes is developed at 120–300 °C and 30–120 min.•The fuel properties, aromatic degree and coal maturity were improved after HTC.•The conversion routes of carbon ...chemical bonds during carbonization are clarified.•Changes from –C–H/C–O to aromatic –C–C/CC facilitated combustion behaviors.•Kinetic analysis and combustibility index of upgraded hydrochars were calculated.
The aim of this work was to study the correlation between dynamic mechanisms of carbon structure associated with their upgrading effects with the help of XPS, 13C NMR and 2D-PCIS methods. Results showed the fuel qualifies of biowastes were improved and became comparable to lignite or even bitumite after HTC. The carbon chemical bonds of –C–H and –C–O in biowaste components (mainly protein and polysaccharide) were thermally cracked and enriched in liquid phase in the form of soluble intermediates, which subsequently generated coal-like structures via cyclization as well as polymerization at higher temperatures. The further investigation on thermogravimetric analysis found that the conversion of “–C–H/C–O to aromatic –C–C/CC” was beneficial for stabilizing their combustion behavior by integrating two stages of biowastes (devolatilization stage and combustion stage) into one stage of hydrochars (combustion stage).
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