Combustion Of Residual Char Research Articles

Analysis of landfill leachate promoting efficient application of weathered coal anaerobic fermentation

This research aimed to develop a new method for clean utilization and treatment of landfill leachate and solid waste weathered coal. Landfill leachate and weathered coal were adopted for combined anaerobic fermentation for methane production. The characteristics of microbial community, mechanism of biological methane production, and utilization characteristics of fermentation broth and solid residue for co-fermentation were analyzed through metagenomics, soluble organic matter detection and thermogravimetric (TG) analysis. The obtained results revealed that combined anaerobic fermentation increased methane production by 80.1%. Syntrophomonas, Salipiger, Methanosaeta and Methanothrix were highly correlated. Gene abundances of 2-oxoacid ferredoxin oxidoreductase and enolase were increased in methane conversion pathway mainly by acetic acid. Pyruvate-ferroredoxin oxidoreductase, 2-oxoglutarate synthase and succinate dehydrogenase acetate synthase intensified electron transfer pathways among microorganisms. Fulvic acid, tyrosine and tryptophan contents were high in fermentation broth. Volatile decomposition temperature, ignition point and residual char combustion temperature of residual coal were decreased and combustion was more stable. The obtained results showed that the co-fermentation of landfill leachate and weathered coal improved biological methane gas production, degraded weathered coal and improved combustion performance, which provided a new idea for weathered coal clean utilization.

Mineral carbonation of thermally treated and weathered biomass ashes with respect to their CO2 capture and storage

Five long-term stored biomass ashes (BAs) from beech wood chips, corn cobs, sunflower shells, plum pits, and walnut shells produced at 500 °C were thermally treated at 900 °C and subsequently weathered to evaluate their CO2 capture and storage (CCS) potential by mineral carbonation. A combination of different mineralogical, chemical and thermal analyses was used for that purpose. The BAs studied are highly enriched in alkaline-earth and alkaline oxides (52–91%) and they belong to diverse chemical ash types. The minerals responsible for CCS of these BAs include Ca, K, K-Ca and Ca-Mg carbonates and bicarbonates such as calcite, fairchildite, kalicinite, dolomite, and butschliite. The formation of these minerals is a result of interactions between alkaline-earth and alkaline oxyhydroxides in BA and flue CO2 gas during residual char combustion and especially atmospheric CO2 during BA storage and weathering. It was found that the BAs studied show significant CCS capacity, namely about 19–33% (mean 27%). It was emphasized that the renewable and carbon-neutral biomass also has some extra CCS potential due to the sequestration of atmospheric CO2 during BA storage and weathering. Therefore, the future large-scale bioenergy production in a sustainable way can contribute greatly for decreasing CO2 emissions in the atmosphere and can reduce the use of costly CCS technologies.

Enhancement of dynamic mechanical properties and flame resistance of nanocomposites based on epoxy and nanosilica modified with KR‐12 coupling agent

AbstractThe epoxy/silica nanocomposites containing a wide range of isopropyltri[di(octyl) phosphate] titanate coupling agent (KR‐12) modified nanosilica (m‐nanosilica) loading (0–7 wt%) cured with tetrabutyl titanate hardener were prepared. Their morphology, thermal stability, thermal expansion, and mechanical properties including hardness, abrasion resistance were investigated. The wetting ability of epoxy‐nanosilica systems on glass surface was assessed based on static contact angle. The obtained results showed that the contact angle of the nanocomposites containing m‐nanosilica is slightly changed as compared to the contact angle of pure epoxy resin and lower than that of the nanocomposite containing unmodified nanosilica. The data of dynamic mechanical analysis of the nanocomposites using different nanosilica content indicated that the presence of m‐nanosilica lowered the recovery energy of the nanocomposites to 41.62% as compared to neat epoxy. The limiting oxygen index (LOI) of the nanocomposites confirmed that the m‐nanosilica increased the flame retardance of epoxy matrix. When using 7 wt% of m‐nanosilca, the LOI value of the nanocomposite was 27.4 while this index of neat epoxy was 21.6. The scanning electron microscopic images of residual char combustion of the nanocompsites indicated a formation of nanosilica layer contributed to restrain combustion of the material.

Reaction Characteristics and MILD Combustion of Residual Char in a Pilot-Scale Furnace

Residual char is an important product of the coal chemical industry, and the reasonable utilization of residual char is of great significance. This work systematically investigates the combustion characteristics of residual char by thermogravimetric analysis (TGA), fixed-bed reactor (FBR) basic experiments, and 300 kW pilot-scale experiments. The pilot-scale experiments cover the conventional swirl flame combustion and moderate or intense low-oxygen dilution (MILD) combustion. The TGA and FBR basic experiments show that, in comparison to the pulverized coal, the residual char has a higher ignition temperature and lower reaction rate, resulting in lower reactivity. The pilot-scale experiments display that the MILD combustion of residual char can be established even without preheating the secondary air. For the same combustion condition (swirl flame or MILD combustion), the NO emissions from burning residual char are lower than those of firing pulverized coal by approximately 50%, mainly as a result of the much lower amount of fuel N in the residual char. Moreover, the MILD combustion can further reduce the NO emissions of residual char by approximately 30% compared to the swirl combustion, and the burnout rate of the MILD combustion of residual char is about 93%. Increasing residence time, reducing particle size, or preheating secondary air appropriately can further improve the burnout rate. Considering the relatively low pollutant emissions and high burnout rate, the MILD combustion is the promising approach for the large-scale direct utilization of residual char.

Time-resolved chemical composition of small-scale batch combustion emissions from various wood species

Small-scale batch combustion of wood is a major source of fine particles, black carbon emission and polycyclic aromatic hydrocarbons in Finland. The mass and chemical compositions of batch combustion emissions are known to be highly time-dependent. In this study, the gaseous and particulate batch combustion emissions of three European wood species (beech, birch and spruce) were quantified in detail with an extensive set of online analysers, including a soot particle aerosol mass spectrometer (SP-AMS) for real-time detection of particulate chemical composition. Ignition and a new batch addition on top of glowing embers were identified as the primary low temperature events during which both particulate and gaseous organic emissions peaked. The flaming combustion created high temperature conditions and produced increased emissions of refractory black carbon (rBC) and PAHs. The residual char combustion phase was characterized by low particulate mass emission consisting mainly of alkali salts and elevated concentrations of gaseous organic emissions and CO. Overall, hardwood species (beech and birch) had the highest PM1 emissions, and the difference between the lowest average emission (spruce) and the highest (birch) was more than 3-fold. The increasing combustion chamber temperature during sequential combustion of wood batches was found to decrease the carbonaceous fraction of the PM as well as OC/EC ratio, as the result of more efficient secondary combustion.

Gasification of low-rank coal for hydrogen-rich gas production in a dual loop gasification system

A dual loop gasification (DLG) system consisting of three separated reactors and two bed material circulation loops has been proposed for steam gasification of low-rank coal to obtain hydrogen-rich gas with low tar content. The system decouples the gasification process into fuel gasification, tar destruction and residual char combustion, which occur in three independent reactors correspondingly, i.e. a gasifier, a reformer and a combustor. Both the gasifier and the reformer are separately interconnected with the single combustor, forming two bed material circulation loops in parallel. In this way, both the gasifier and the reformer could be operated individually under optimized conditions. With Shenmu bituminous coal as feedstock and calcined olivine as both solid heat carrier and in-situ tar destruction catalyst, the performance of the system for the steam gasification of the coal has been investigated. It has been found that the tar was effectively removed under higher reformer temperature and in the presence of the olivine catalyst, and the coal gasification was promoted at higher gasifier temperature, S/C and ER.

Chemical looping pyrolysis-gasification of biomass for high H2/CO syngas production

Chemical Looping Pyrolysis-Gasification (CLPG) of biomass is established as a novel concept for high quality syngas production. The process divides the main chemical reactions in different zones for biomass pyrolysis and gasification, then achieves residual char combustion and Oxygen Carrier (OC) regeneration consistently. The understanding of the process is first determined by calculation of possible chemical reactions using Gibbs Free Energy (ΔG). Experimental work for different effects of the fuel reactor (FR) temperature and the Steam-to-Biomass Mass Ratio (S/B) are then investigated in terms of syngas components, Hydrogen to Carbon Monoxide Molar Ratio (H2/CO), and Cold Gas Efficiency (CGE). Results show that at the FR temperature of 820°C and S/B of 1.00kgkg−1, the optimized condition of H2/CO and CGE are obtained at 2.45molmol−1 and 61.87%, respectively. With S/B increasing from 1.25kgkg−1 to 2.00kgkg−1, the H2/CO increases to 2.99kgkg−1, while the CGE decreases to 51.64%. The water-gas shift (WGS) reaction and the steam-iron reaction are approaching 0kJmol−1 over the FR temperature of 820°C in calculation, which confirms the contribution of these two reactions comparing with experimental tests. The research proposes an approach for efficient gasification of high volatile-content solid fuel using the advanced chemical looping technology.

The generation of carbon monoxide and carbonyl compounds in reconstituted tobacco sheet

In recent years, reconstituted tobacco sheet (RTs) has played an increasingly significant role in tobacco industry. The yields of CO and carbonyl compounds (formaldehyde, acetaldehyde, acetone, acrolein, propanal, butenal, 2-butanone, and butyraldehyde) in cigarette mainstream smoke of RTs and their formation mechanisms were investigated in this paper. Self-made RTs (SRTs) was studied and compared with foreign Mauduit RTs (MRTs) and three commercial tobacco leaves on routine chemical constituents, thermal behavior, and subsequent gaseous products evolution. The cigarette smoking results illustrated that the yields of CO (2.9 mg per puff) and carbonyl compounds (about 208 μg per puff) in mainstream smoke of SRTs and MRTs were at the same level, and obviously higher than those of three commercial tobacco leaves. The routine chemical constituent results demonstrated that bright tobacco and oriental tobacco contained particularly higher contents of reducing sugar and total sugar than RTs, while burley tobacco had a high content of nitrogen compounds. The thermal behavior results showed that SRTs (11.6 % min−1) and MRTs (14.5 % min−1) presented higher maximum mass-loss rate than bright tobacco (7.8 % min−1), burley tobacco (7.1 % min−1), and oriental tobacco (6.8 % min−1). The thermal decomposition of saccharides and combustion of residual char played the most important roles in mass-loss and gaseous products formation. The decomposition of saccharides and incomplete combustion of carbonized residual char primarily contributed to the formation of CO, while carbonyl compounds evolution was mainly attributed to the decomposition of saccharides alone.

Study of Oil Palm Biomass Resources (Part 1) - Characteristics of Thermal Decomposition of Oil Palm Biomass -

In this study, oil palm biomass such as empty fruit bunch (EFP) and palm kernel shell (PKS) was used as raw materials for making pellets. EFB and PKS are valuable lignocellulosic biomass that can be used for various purposes. If EFB and PKS are used as alternative raw materials for making pellets instead of wood, wood could be saved for making pulps or other value-added products. In order to explore their combustion characteristics, EFB and PKS were analyzed using thermal gravimetric analyzer (TGA) with ultimate and proximate analyses. From the TGA results, thermal decomposition of EFB and PKS occurred in the range of 280 to through devolatilization and combustion of fixed carbon. After , their combustion were stabilized with combustion of residual lignin and char. PKS contained more fixed carbons and less ash contents than EFB, which indicated that PKS could be more active in combustion than EFB.

Study of Oil Palm Biomass Resources (Part 2) - Manufacturing Characteristics of Pellets Using Oil Palm Biomass-

In this study, oil palm biomass such as empty fruit bunch (EFB) and palm kernel shell (PKS) was used as raw materials for making pellets. Hardwood sawdusts were also mixed with EFB and PKS for making pellets. For improving a bad forming behavior in a pelletizer, 1 to 3 per cent of corn starch based on oven-dried weight biomass was added. The starch contributed to the decrease of dust generation in addition to the improvement of forming capability during pellet forming. Heating values of every pellets made of EFB and PKS were higher than 4,300 kcal/kg for the first grade pellet, irrespective of addition of sawdusts. However, the pellets made of EFB and PKS had ash contents over 3 per cent, which made it impossible to be applied for home use. Instead, they could be applied for industrial use. For studying their combustion characteristics, the pellets from the mixtures of EFB, PKS and sawdusts were analyzed using thermal gravimetric analyzer (TGA). From the TGA results, thermal decomposition of EFB and PKS occurred following three including endothermic reaction and dehydration, devolatilization of the major chemical components, and finally combustion of residual lignin and char.

Heat transfer in the rotary ash cooler with residual char combustion considered

In circulating fluidized-bed (CFB) boilers, some residual char is left in the ash when the ash is drained into the rotary ash cooler (RAC). The residue char will combust in the RAC given oxygen is present. It is important to understand and predict the influence of residual char combustion on the heat transfer process in the RAC in order to avoid slagging and fouling inside the RAC. In this paper, an improved heat transfer model of the RAC was developed in which the residual char combustion process was considered. Based on the analysis, the shrinking sphere model was selected to describe the residual char combustion. The improved model was validated by the final ash temperature and cooling water temperature data measured from a few RACs equipped with the coal fired CFB boilers with different steam output. The predictions of the improved model agree well with the field measurement data, within an error range of ± 10%. The simulation results also show that the heat released from residual char combustion counts for about 60–80% of the total heat released by ash in the inlet section of the RAC, and the influence of residual char combustion decreases rapidly along the ash flow. The final ash temperature increases accordingly with the increase of inlet carbon content, and decreases with the increases of residual char size. As particle size is larger than 3 mm, the final ash temperature changes little at a given carbon content due to a low mass burning rate. It is suggested that combustion of residual char should be considered when the inlet carbon content is over 2.5%; otherwise, the combustion of residual char in the RAC could be neglected.

Modeling and experimental studies on single particle coal devolatilization and residual char combustion in fluidized bed

Single particle devolatilization followed by combustion of the residual coal char particle has been analyzed in a batch-fluidized bed. The kinetic scheme with distributed activation energy is used for coal devolatilization while multiple chemical reactions with volume reaction mechanism are considered for residual char combustion. Both the models couple kinetics with heat transfer. Finite Volume Method (FVM) is employed to solve fully transient partial differential equations coupled with reaction kinetics. The devolatilization model is used to predict the devolatilization time along with residual mass and particle temperature, while the combined devolatilization and char combustion model is used to predict the overall mass loss and temperature profile of coal. The computed results are compared with the experimental results of the present authors for combustion of Indian sub-bituminous coal (15% ash) in a fluidized bed combustor as well as with published experimental results for coal with low ash high volatile matter. The effects of various operating parameters like bed temperature, oxygen mole fraction in bulk phase on devolatilization time and burn-out time of coal particle in bubbling fluidized bed have been examined through simulation.

Comparison of dual fluidized bed steam gasification of biomass with and without selective transport of CO2

Abstract A comparison of dual fluidized bed gasification of biomass with and without selective transport of CO 2 from the gasification to the combustion reactor is presented. The dual fluidized bed technology provides the necessary heat for steam gasification by circulating hot bed material that is heated in a separate fluidized bed reactor by combustion of residual biomass char. The hydrogen content in producer gas of gasifiers based on this concept is about 40 vol% (dry basis). Addition of carbonates to the bed material and adequate adjustment of operation temperatures in the reactors allow selective transport of CO 2 (absorption enhanced reforming—AER concept). Thus, hydrogen contents of up to 75 vol% (dry basis) can be achieved. Experimental data from a 120 kW Fuel input pilot plant as well as thermodynamic data are used to determine the mass- and energy-balances. Carbon, hydrogen, oxygen, and energy balances for both concepts are presented and discussed.

Distribution of Polycyclic Aromatic Hydrocarbons in Fly Ash during Coal and Residual Char Combustion in a Pressurized Fluidized Bed

To investigate the distribution of polycyclic aromatic hydrocarbons (PAHs) in fly ash, the combustion of coal and residual char was performed in a pressurized spouted fluidized bed. After Soxhlet extraction and Kuderna-Danish (K-D) concentration, the contents of 16 PAHs recommended by the United States Environmental Protection Agency (U.S. EPA) in coal, residual char, and fly ash were analyzed by a high-performance liquid chromatography (HPLC) coupled with fluorescence and diode array detection. The experimental results show that the combustion efficiency is lower and the carbon content in fly ash is higher during coal pressurized combustion, compared to the residual char pressurized combustion at the pressure of 0.3 MPa. Under the same pressure, the PAH amounts in fly ash produced from residual char combustion are lower than that in fly ash produced from coal combustion. The total PAHs in fly ash produced from coal and residual char combustion are dominated by three- and four-ring PAHs. The amounts of PAHs in fly ash produced from residual char combustion increase and then decrease with the increase of pressure in a fluidized bed. 21 refs., 1 fig., 4 tabs.

In-Situ CO2-Absorption in a Dual Fluidized Bed Biomass Steam Gasifier to Produce a Hydrogen Rich Syngas

Within the last years renewable energy sources came more and more into the public focus. Steam gasification of solid biomass yields high quality producer gases that can be used for efficient combined heat and power production (CHP) and as a renewable resource for chemical syntheses. The dual fluidized bed steam gasification technology provides the necessary heat for steam gasification by circulating hot bed material that is heated in a second fluidized bed reactor by combustion of residual biomass char. The hydrogen content in producer gas of such gasifiers is about 40vol% (dry basis). Addition of carbonates to the bed material and adequate adjustment of operation conditions in the reactors allow selective transport of CO2 from gasification to combustion zone (Absorption Enhanced Reforming – AER concept). An 8MW (fuel power) CHP plant successfully demonstrates gasification in Guessing, Austria since 2002. A process development unit (100 kW fuel power) has been recently operated to investigate the potential of the selective CO2 transport achieving a H2 content of up to 75vol% (dry basis) in the producer gas. No significant increase in tar formation occurs despite the low gasification temperatures (600-700°C). It can be shown, that the selective transport of CO2 yields high hydrogen contents in the producer gas and the possibility of operating at lower temperatures increases the efficiency of energy conversion.

Gasification of Kentucky bluegrass (Poa pratensis l.) straw in a farm-scale reactor☆

A novel gasification reactor was designed for conversion of grass straw to synthesis gas. Our design goal was to improve synthetic gas yield and thermal stability at a scale suitable for on-farm use at a cost similar to that of a combine harvester. The reactor that was constructed and tested in this study follows the newly emerging design technique whereby the endothermic pyrolysis or gasification and exothermic char combustion co-exist in the same reactor. It operates in a dual mode where straw gasification occurs in the annulus of an outer tube and an inner (draft) tube. Our trials established that the dual-mode operation could be performed without material flow problems. Sustained tests demonstrated reactor stability at gasification temperatures up to 650 °C and successful gasification of Kentucky bluegrass straw utilizing combustion heat from the inner tube. Calculated equivalence ratios of combustion in the inner tube ranged from 0.3 to 0.78 indicating fuel lean combustion of residual char without slagging. Carbon conversion ranged between 35.4 and 44.8%. Energy recovery, estimated as the ratio of the heat of combustion of the gas to that of the dry-ash-free feedstock, ranged from 14.7% to 30.92%. The estimated heating value for the synthesis gas ranged from 1.27 to 2.85 MJ m−3. Although these conversion parameters are low, a proof of the design concept was established. They can be improved with little modification by increasing the residence time in the draft tube and complete isolation of the gaseous products of combustion and the gasification. More tests are required to evaluate the economic feasibility of the farm-scale unit.

Study on the distribution of PAHs in fly ash from coal and residual char combustion in a pressurized fluidized bed

sieved by a nylon sieve and fine portions of each soil samples (<m) were analyzed for heavy metals (Sc, Cr, Co, Ni, Cu, Zn, Cd and Pb) and arsenic using a Thermo Finnigan Element 2 High Resolution Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Ten sequential extraction samples from different localities were also fractionated using previously published methods (Tessier et al., 1979), and analyzed for four heavy metals (Co, Ni, Cu and Pb) using a Varian Zeeman Graphite Furnace Atomic Absorption Spectrometer (GFAAS). This study indicates that in the downwind direction, the concentrations of some heavy metals (such as Co, Ni and Pb) may increase from 3xl06to 6 3x10 "6 even at a distance of up to 10 km. Polluting heavy metals mostly remain at the top of the soil profile, but polluting Co and Ni exist in all speciations, and polluting Cu mainly exists in the residues of the sequential extraction, whereas the polluting Pb is identified in the extractable speciations.

Mathematical modeling of fluidized bed combustion 3. Simultaneous combustion of char and combustible gases

The difficulties involved in developing system models for fluidized bed combustion which include details of the release of volatiles from coal and the subsequent simultaneous combustion of volatiles and residual char are well recognized. In previous papers, the heterogeneous combustion of char in air–fluidized beds, and the homogeneous combustion of combustible gases injected or pre–mixed with the fluidizing air were considered individually as parts of the more complex problem. The simultaneous combustion of char and propane (premixed with air used to fluidize the bed) is considered in this paper. The hydrodynamic description of the bubbling fluidized bed, as in our previous work, is based on the three–phase model. The non–isothermality of the bed resulting from the gas–phase combustion reactions is taken into account through inclusion of an energy balance for the bubble phase. The effect of the variation in superficial gas velocity — on bubble properties and cross–flow — is included through an overall mass balance. Calculations are compared with experimental data on the combustion of: (a) char; (b) propane; and (c) simultaneous combustion of char and propane. The agreement, in all cases, is very good. Particularly encouraging is the agreement with data on the variation of CO, CO 2 and O 2 concentrations in the freeboard with time resulting from the batch combustion of char in sand fluidized by air/2.5 vol.% propane. This agreement suggests that the model provides a good representation of the dynamics of the combustion of char as well as combustible gases. The model is then used to investigate the interaction of heterogeneous and homogeneous combustion reactions within the bed.

Pollutant formation during coal combustion in a CFB test furnace

Experiments were carried out in a CFB test unit to investigate how fuel conversion and pollutant formation during coal combustion is affected by air staging. Staging of combustion air, in particular the variation of its most important parameters, the primary stoichiometric ratio and the residence time in the zone before secondary air addition were of prime importance. An anthracite, a bitunninous coal, and a lignite were used in the experiments. The exhaust concentrations and axial concentration profiles of flue gas constituents were measured. The fuel conversion and pollutant formation occur primarily in the oxygen-rich zone directly above the bottom nozzle plate. If the residence time in the air-lean operated primary zone is sufficiently long, the main combustion phase will be followed, after the consumption of oxygen, by a phase dominated by further devolatilization of the still nonconverted fuel proportion, which strongly affects formation and decomposition of pollutants in both the primary and secondary zones. In the stoichiometric ratio range between 0.7 and 0.9, the efficiency of desulphurization is reduced because of the thermodynamic instability of the sulphur capture phases CaS and CaSO 4 . In CFB combustion, primary stoichiometric ratio and primary residence time can be varied within a large range, in contrast to pulverized coal combustion, without significant change in the exhaust NO concentration. The reason for this is seen especially in the retardation of the H 2 /O 2 mechanism and the residual char combustion, due to the low combustion temperature. The exhaust N 2 O concentration is largely determined by the homogeneous N 2 O reduction through H radicals and the heterogeneous N 2 O formation from NO reduction on the surface of residual char. The suppression of the heterogeneous N 2 O formation in the secondary zone is an important key to the reduction of the exhaust N 2 O concentration.

DSC determination of coal specific energy

The specific energy of several types of Australian coal was determined directly by DSC, using a standard coal as calibrant. By subdivision of the combustion profile into separate peaks representing combustion of volatile matter and residual char, the specific energies of these components were also determined.