Investigation of gasification reactivity and properties of biocarbon at high temperature in a mixture of CO/CO2

Understanding the conversion behaviors of biocarbon under conditions relevant to industrial conditions is important to ensure proper and efficient utilization of the biocarbon for a dedicated metallurgical process. The present work studied the reactivity of biocarbon by using a Macro-TGA at 1100 °C in a gas mixture of CO2 and CO to simulate the conditions in an industrial closed submerged arc manganese alloy furnace. The conversion residues from the Macro-TGA tests were collected for detailed characterization through a combination of different analytical techniques. Results showed that biocarbons produced under various conditions have different reactivities under the studied conditions. The biocarbon produced in an atmospheric fixed bed reactor with continuous purging of N2 has the highest reactivity. Its fixed carbon loss started as the gas atmosphere shifted from the inert Ar to a mixture of CO and CO2 at 1100 °C. And only 450 s was needed to reach a desired fixed-carbon loss of 20%. The high reactivity of the biocarbon is mainly related to its porous structure and high content of catalytic inorganic elements, which favor gasification reactions of the carbon matrix towards the surrounding gas atmosphere and consumption of carbon consequently. In contrast, biocarbon produced under constrained conditions and from wood pellets and steam exploded pellets have more compact appearance and dense structures. Significant fixed carbon loss for these biocarbons started 80–200 s later than that of the biocarbon produced at atmospheric conditions with purging of N2. Additionally, it took longer time, 557–1167 s, for these biocarbons to realize the desired fixed-carbon loss. SEM-EDX analyses results revealed clear accumulation and aggregation of inorganic elements, mainly Ca, on the external surface of the residues from gasification of biocarbon produced in the fixed bed reactor with purging of N2. It indicates more intensive migration and transformation of inorganic elements during gasification at this condition. This resulted in formation of a carbon matrix with more porous structure and active sites on the carbon surface, promoting the Boudouard reaction and conversion of carbon.publishedVersio

HIGH TEMPERATURE STEAM GASIFICATION OF SOLID WASTES: CHARACTERISTICS AND KINETICS

Greater use of renewable energy sources is of pinnacle importance especially with the limited reserves of fossil fuels. It is expected that future energy use will have increased utilization of different energy sources, including biomass, municipal solid wastes, industrial wastes, agricultural wastes and other low grade fuels. Gasification is a good practical solution to solve the growing problem of landfills, with simultaneous energy extraction and nonleachable minimum residue. Gasification also provides good solution to the problem of plastics and rubber in to useful fuel. The characteristics and kinetics of syngas evolution from the gasification of different samples is examined here. The characteristics of syngas based on its quality, distribution of chemical species, carbon conversion efficiency, thermal efficiency and hydrogen concentration has been examined. Modeling the kinetics of syngas evolution from the process is also examined. Models are compared with the experimental results. Experimental results on the gasification and pyrolysis of several solid wastes, such as, biomass, plastics and mixture of char based and plastic fuels have been provided. Differences and similarities in the behavior of char based fuel and a plastic sample has been discussed. Global reaction mechanisms of char based fuel as well polystyrene gasification are presented based on the characteristic of syngas evolution. The mixture of polyethylene and woodchips gasification provided superior results in terms of syngas yield, hydrogen yield, total hydrocarbons yield, energy yield and apparent thermal efficiency from polyethylene-woodchips blends as compared to expected weighed average yields from gasification of the individual components. A possible interaction mechanism has been established to explain the synergetic effect of co-gasification of woodchips and polyethylene. Kinetics of char gasification is presented with special consideration of sample temperature, catalytic effect of ash, geometric changes of pores inside char and diffusion limitations inside and outside the char particle

Characterization And Catalytic Cracking Of Tar Obtained In Coal / Biomass / Municipal Solid Waste Gasification: The Use Of Basic Mineral Catalysts And Miscibility, Properties, And Corrosivity Of Petroleum-Biofuel Oils And Blends For Application In Oil-Fired Power Stations

To meet the metrics set forth by the Clean Power Plan, industry can use gasification or replacement of petroleum with biofuels. However, tars formed in gasification are difficult to remove, and biofuel-petroleum blends may have issues with fuel stability, corrosion, and miscibility. Tar cracking was studied in both a laboratory-scale updraft gasifier, with a municipal solid waste feedstock, and tar cracking reactor system and in a bench-scale tar cracking reactor. The laboratory-scale system demonstrated that the optimal temperature was at least 800°C, that thermal cracking accounted for 85% of tar destruction, and that metal-based catalysts were the most promising. The bench-scale system, which used naphthalene as a model tar compound, demonstrated that a powder dolomite catalyst was most effective, that trona compared similarly to Plum Run dolomite, and that nahcolite was ineffective. Hi-pour fuel oil, lo-pour fuel oil, crude jatropha oil, biocrude derived from animal renderings, biodiesel (refined biocrude), crude palm oil, and ultra-low sulfur diesel were blended at 75°F, 170°F, and 220°F. Flash points, pour points, and cloud points were determined for select oils and blends. 304 stainless steel, 316 stainless steel, brass, mild steel, and 410 stainless steel coupons were immersed in samples of each oil type and heated to 175°F to test for corrosive activity; these samples were examined every two weeks for fourteen weeks. Overall, blends containing biocrude and palm oil were marginal to unacceptable due to the large proportion of waxes at ambient temperatures; all other fuel blends were acceptable for use in industry. Significant corrosion was observed on the brass in biocrude, brass in jatropha, brass in biodiesel, brass in palm, and brass in lo-pour fuel oil; the most significant corrosion was observed on the mild steel in biocrude. All samples had corrosion rates of \u3c 1 mpy. Overall, the oils had the most effect on the brass samples

Combined ammonia recovery and solid oxide fuel cell use at wastewater treatment plants for energy and greenhouse gas emission improvements

Current standard practice at wastewater treatment plants (WWTPs) involves the recycling of digestate liquor, produced from the anaerobic digestion of sludge, back into the treatment process. However, a significant amount of energy is required to enable biological breakdown of ammonia present in the liquor. This biological processing also results in the emission of damaging quantities of greenhouse gases, making diversion of liquor and recovery of ammonia a noteworthy option for improving the sustainability of wastewater treatment. This study presents a novel process which combines ammonia recovery from diverted digestate liquor for use (alongside biomethane) in a solid oxide fuel cell (SOFC) system for implementation at WWTPs. Aspen Plus V.8.8 and numerical steady state models have been developed, using data from a WWTP in West Yorkshire (UK) as a reference facility (750,000 p.e.). Aspen Plus simulations demonstrate an ability to recover 82% of ammoniacal nitrogen present in digestate liquor produced at the WWTP. The recovery process uses a series of stripping, absorption and flash separation units where water is recovered alongside ammonia. This facilitates effective internal steam methane reforming in the fuel cell with a molar steam:CH4 ratio of 2.5. The installation of the process at the WWTP used as a case of study has the potential to make significant impacts energetically and environmentally; findings suggest the treatment facility could transform from a net consumer of electricity to a net producer. The SOFC has been demonstrated to run at an electrical efficiency of 48%, with NH3 contributing 4.6% of its power output. It has also been demonstrated that 3.5 kg CO2e per person served by the WWTP could be mitigated a year due to a combination of emissions savings by diversion of ammonia from biological processing and lifecycle emissions associated with the lack of reliance on grid electricity

Sorption enhanced catalytic reforming of methane for pure hydrogen production : experimental and modeling

H2 is well perceived as a pollution-free energy carrier for future transportation as well as electricity generation. This thesis presents an experimental and modeling study for an improved process of sorption enhanced catalytic reforming of methane using novel catalyst/sorbent materials for low temperature high purity H2 with in situ CO2 capture. A highly active Rh/CeaZr1-aO2 catalyst and K2CO3–promoted hydrotalcite and lithium zirconate are utilized as newly developed catalyst/sorbent materials for an efficient H2 production at low temperature (400–500oC) and pressure (1.5–4.5 bar) in a fixed bed reactor. Experimental results showed that direct production of high H2 purity and fuel conversion (>99%) is achieved with low level of carbon oxides impurities

Mg-Al Layered Double Hydroxide: A Potential Nanofiller and Flame-Retardant for Polyethylene

The presented research report deals with the investigation of magnesium aluminum based layered double hydroxide (LDH) as a potential nanofiller and flame-retardant for polymers with special reference to polyethylene. LDH is a mixed hydroxide of di- and trivalent metal ions that crystallizes in the form of mineral brucite. The basic reason for selecting LDH or more specifically magnesium-aluminum based LDH (Mg-Al LDH) is their typical metal hydroxide-like chemistry and conventional clay-like layered crystalline structure. The former is helpful in the direct participation in flame inhibition through endothermic decomposition and stable char formation. On the other hand, the later makes LDH suitable for polymer nanocomposite preparation, which can address the poor dispersibility problem associated with conventional metal hydroxide type fillers in polyolefin matrix. Besides, unlike layered silicate type clays (often reported for their capability to improve flame retardancy of polymers), LDH being reactive during combustion has higher efficiency to reduce the heat released during combustion of the composites. LDH clay with fixed Al:Mg ratio was synthesized using urea hydrolysis method and characterized. The organic modification of Mg-Al LDH using anionic surfactants has been studied in details. The main purpose of such modification is to enlarge the interlayer distance and to render it more organophilic. The surfactants were selected based on their functionality, chain length, etc and the modification was carried out by regeneration method. In the modified LDHs, the surfactants anions are arranged as a monolayer in the interlayer region and expand the interlayer distance according to their tail size. PE/LDH nanocomposites were prepared by melt-compounding method using a co-rotating tightly intermeshed twin-screw extruder and the morphological, mechanical and flammability properties of the nanocomposites were investigated in details. The X-ray diffraction analysis and electron microscopic analysis show a complex LDH particle morphology with hierarchy of particle size and shape starting from exfoliated particles fragments to particle aggregates over few hundred nm size. The exfoliated LDH platelets are distributed both in the vicinity of large particles and also in the bulk matrix. The melt rheological characterization of the nanocomposites also reflects the similar complex particle morphology. The dynamic oscillatory shear experiments showed that with increasing LDH concentration, the rheological behavior of the nanocomposite melts deviates strongly from that of the unfilled polyethylene. Thermogravimetric analysis (TGA) shows that LDH significantly improves the thermal stability of the polymer matrix in comparison to the unfilled polymer. The flammability studies of the PE/LDH nanocomposites have been reported in terms of various standard methods, like limited oxygen index (LOI), cone-calorimetry and UL-94 vertical and horizontal burn tests. The cone-calorimetric investigation shows that the nanocomposites have significantly lower burning rate and heat released during combustion. With increasing concentration of LDH though the LOI value of the nanocomposite increases marginally, the burning behavior, like dripping, rate of burning, etc are significantly improved. The flammability performance of LDH in combination with other commonly used flame-retardant (magnesium hydroxide) was also investigated. It has been observed that in polyethylene, a 50 wt% combination filler (4:1 weight ratio of magnesium hydroxide and LDH) can provide similar flammability ratings (like V0 rating in UL94 test, no dripping, etc) as that observed with 60 wt% magnesium hydroxide alone