Fuel Processing Technology (v.157, #C)

This study investigates the ignition characteristics of pulverised coal, biomass and co-firing by use of a visual drop tube furnace (VDTF) and a high speed imaging technique. Three coals (anthracite, a bituminous coal and a lignite), four biomasses (Pine, Eucalyptus, Olive Residue and Miscanthus) and various biomass-coal mixtures were tested. With each coal, biomass or their mixture, a distinct flame was established within the VDTF through the continuous feeding of the fuel under the environment of air and at a furnace temperature of 800 °C. To observe the ignition point, a Phantom v12.1 high-speed camera was used to capture the videos of fuel combustion at 500 frames per second (FPS). A technique was developed using MATLAB's image analysis tool to automate the ignition point detection. The results of the image processing were used to statistically analyse and determine the changes to the ignition behaviour with different fuels and co-firing ratios.The results obtained with the tested coals have shown that the distance to ignition increases as the coal volatile matter content decreases, whereas the opposite trend was found for the biomass fuels. Further, the addition of biomass to the anthracite significantly reduces the distance to ignition but a much less pronounced effect on the ignition was found when biomass was co-fired with the bituminous coal or lignite. The synergistic effect on the ignition of biomass-anthracite mixture is mainly attributed to the high volatile content and the potential effects of catalysis from the alkali metals present in the biomass. The results of this study have shown that the VDTF testing coupled with the image analysis technique allows for an effective and simple method of characterising ignition behaviours of pulverised coal, biomass and their mixtures.
Keywords: Pulverised fuel particle; Ignition distance; Combustion image analysis; Visual drop tube furnace; Biomass co-firing with coal;

High volatile coal fines do not meet the requirements of various industrial production processes and cause large resource losses. Recycling coal fines by the production of formed coal briquettes has a great realistic significance in saving coal resources and protecting the environment. In order to utilize high volatile coal fines to produce coal briquettes as a substitute for COREX ironmaking process, thermal behaviors of coal, coal tar pitch and briquettes were analyzed. A blended binder composed of pitch and molasses was obtained and ventilation drying was applied to strengthen their bonding strength. Microstructure and composition of briquettes were tested by SEM and EDS. Results showed that both volatilization and carbonization of briquette should be processed in protecting atmosphere because of coal's low combustion temperature at 351 °C. The strengths of cured and carbonized briquettes are weaker than dried briquettes because of coal's violent volatilization which causes vast pores and loose structure in briquettes. Molasses can significantly improve the strength of dried briquettes. Ventilation drying with short time provides briquettes with higher strength than static drying. By adding 15% blended binders (pitch: molasses = 13:2), drop resistance of green briquettes reaches 19.4 times/2 m. After drying at 130 °C for 1 h with a gentle air flow of 1.2 m/s, drop resistance and compressive strength of dried briquettes are up to 56.6 times/2 m and 13.06 MPa, respectively. The briquettes consist of primarily C, a small amount of O and very small amounts of Al, Si, Ca, S and Fe. The strength and composition of briquettes favorably meet the requirement of COREX ironmaking process.
Keywords: Coal tar pitch; Molasses; High volatile coal; Formed coal; Ventilation drying; Thermal behavior;

This paper reports the use of piperazine promoted 2-amino-2-methyl-1-propanol (PZ + AMP) blended solution for the removal of high concentration CO2 in natural gas (NG). The process behaviour was investigated by conducting the experiments in a bench-scale packed absorption column at high pressure conditions. The CO2 concentration and temperature profiles along the column were presented in order to study the process behaviour in the column at various operating pressures, CO2 concentration in NG, total gas flow rates, liquid flow rates, amine concentration and inlet liquid temperature. The temperature bulge was observed in the column and further discussed in this paper.
Keywords: CO2 capture; High CO2 partial pressure; Amine solvent; Packed absorption column; Temperature bulge;

Air staging strategies in biomass combustion-gaseous and particulate emission reduction potentials by Hassan Khodaei; Ferdinando Guzzomi; David Patiño; Babak Rashidian; Guan H. Yeoh (29-41).
Gaseous and particulate emissions have been investigated with different air staging strategies over a wide range of secondary air flow rates. Laboratory scale wood pellet combustor, supplied by an underfeed fuel bed input, is used. The air staging strategies have been employed to study burning rate, temperature in primary and post combustion zones, and NO, CO and PM emissions, taking into account the air to fuel stoichiometric ratio. 50% CO reduction and 9 times less particle mass concentration than non-staged combustion are achieved by deploying a uniform secondary air module in a higher position from the bed. The minimum NO (37% reduction than non-staged) measured in the non-uniform air distribution module at the higher flow rate with lower distance from the fuel bed. The results demonstrate a trade-off between NO and CO, PM emissions but also significant potential for reducing particulate and gaseous emissions by deploying air staging in the pellet combustor.Display Omitted
Keywords: Air staging; NO; CO; PM; Temperature;

Effect of charcoal addition on the properties of a coke subjected to simulated blast furnace conditions by Xing Xing; Harold Rogers; Guangqing Zhang; Kim Hockings; Paul Zulli; Alex Deev; John Mathieson; Oleg Ostrovski (42-51).
A pilot oven produced coke with the addition of 7.5 wt% charcoal (bio-coke) and the similarly produced base blend coke were subjected to gasification and annealing under the simulated blast furnace conditions. The effect of charcoal addition on the coke properties after gasification and annealing was characterised using Raman spectroscopy, ultra-micro indentation and tensile testing. The addition of charcoal significantly increased the coke reactivity with CO2 as a result of its increased surface area by charcoal. The addition of charcoal made no further contribution to the devolatilisation or mineral reactions of coke during annealing. The charcoal particles were well preserved after annealing at 2273 K, but preferentially consumed in the gasification. Annealing temperature had less effect on the graphitisation of the charcoal component compared to the coexisting inert maceral derived component (IMDC) and reactive maceral derived component (RMDC). The charcoal addition had no effect on the microstructure and microstrength of coexisting microtextural types during annealing and gasification. The charcoal presented a higher resistance to fracture than IMDC and RMDC under annealing conditions. The addition of charcoal did not deteriorate the coke resistance to strength degradation under the thermal load of blast furnace. However, charcoal addition caused more severe degradation by gasification as demonstrated by more reduction in the tensile strength of the bio-coke. This was attributed to the preferential solution loss reaction of the charcoal particles leaving voids which coalesced the pores in coke, thereby increasing the defects that cause stress concentration under loading.
Keywords: Charcoal; Coke properties; Blast furnace conditions;

HCCI engine operated with unscrubbed biomass syngas by Subir Bhaduri; Benjamin Berger; Maxime Pochet; Hervé Jeanmart; Francesco Contino (52-58).
Power generation from biomass gasification through the use of spark ignition engines requires the cooling of the biomass syngas to avoid knock. This cooling leads to the condensation of tar impurities, which foul and clog up critical process components leading to significant maintenance issues and costs. Conventionally, tar related problems are addressed by optimizing the gasification process along with developing tar purification systems, both of which result in increased investment and maintenance costs. A novel method is being developed at the Université catholique de Louvain, where the entire process, from the exit of the biomass gasifier to the combustion of tar loaded impure syngas in an internal combustion engine, is carried out at a temperature of 250 ° C, thereby avoiding tar condensation and its consequent problems. A Homogeneous Charge Compression Ignition (HCCI) engine is utilized for such a high intake temperature operation. This paper describes the first experiments with an impure and hot biomass syngas, produced from a two-stage gasifier, which is burned in a HCCI engine without the intermediate cooling and tar purification steps. The objective of the experiment was to test the stability of the engine in response to the naturally occurring random variations in the syngas composition. The experiments were carried out over a continuous period of 24  h. Indicated efficiencies of 33%–39% and IMEP around 2.5 bar were observed while the emissions of NOx were relatively high, probably due to the presence of ammonia in the syngas. The implementation of a closed control loop, with the combustion phasing as the feedback parameter and the fueling rate as the controlled parameter, ensured a stable operation over the experimental duration.
Keywords: Homogeneous Charge Compression Ignition; Biomass syngas; Tars;

Storage of woodchips in pressed bales by Marco Manzone (59-64).
Transportation and storage are two mainly critical operations of biomass supply chain because the transport must be performed using specific trucks, while in storage large areas are required. The goal of this work is to evaluate if the woodchip stored in pressed bales wrapped with waterproof sheets, as well as being a viable solution to reduce the storage area, is also a valid storage technique.The study was carried out in northwest Italy whereby pressed bales made of woodchip produced by two different tree species (poplar and black locust) were stored by two different methods (covered and uncovered).During the whole storage period the internal temperature values of bales were similar to air temperature values in all storage systems. Furthermore, no significant variations were obtained from two tree species tested between initial and final values of moisture contents (55% for poplar and 44% for black locust) and LHV (7.92 MJ kg− 1 for black locust and 7.04 MJ kg− 1 for poplar).This storage method, although it does not allow an adequate woodchip drying, could be considered an acceptable alternative to other storage techniques because it does not show losses in terms of energy and dry matter for a period of two years.
Keywords: Woodchip; Poplar; Black locust; Pressed bales; Storage;

In this paper, a novel type of composite inhibitor (PAA/SA-CC) was developed and characterized with the aim of achieving sustained and highly effective inhibition on spontaneous combustion of low-rank coal. A concept of realizing the caged-wrapping and sustained-releasing function of polymer as regard to high-activity chemical inhibitor was proposed, basing on which the composite inhibitor was prepared with poly(acrylic acid)/sodium alginate super absorbent and (+)-catechin. Subsequently, synchronous thermal analysis was carried out to investigate the influence of inhibitors on the tendency of coal to spontaneous combustion, which was characterized by four characteristic temperatures and three other characteristic parameters marked. Furthermore, hot-surface ignition tests were conducted to validate the inhibition on coal ignition behavior. Finally, non-isothermal isoconversional methods were performed by Starink model and Friedman-Reich-Levi model, respectively. The results demonstrate that PAA/SA-CC synergizes the inhibiting characteristics of the two distinctive inhibitors, especially exerts a continuously high-efficiency inhibition on the coal-oxygen chemisorption, which performs better than the case of mechanically blending. Besides, both the two kinetic analysis approaches agree on the results that the incorporation of 3 wt.% PAA/SA-CC shifts the apparent activation energy-temperature evolution to higher levels.
Keywords: Coal spontaneous combustion; Inhibition; Catechin; Thermal analysis; Ignition behavior; Kinetic analysis;

Quantification of the influence of parameters determining radiative heat transfer in an oxy-fuel operated boiler by Tim Gronarz; Jan Schulze; Mischka Laemmerhold; Philipp Graeser; Jeanette Gorewoda; Vitali Kez; Martin Habermehl; Martin Schiemann; Jochen Ströhle; Bernd Epple; Viktor Scherer; Reinhold Kneer (76-89).
Radiative heat transfer is a very important heat transfer mechanism in pulverized coal combustion. To identify the influence of parameters determining radiatve heat transfer and to give recommendations on the required accuracy of corresponding submodels, a 3D-periodic oxy-fuel pulverized coal combustion test case is investigated. Measurement values determined by the authors or elaborate submodels are applied for each parameter and compared to simplified models or empirical constants. To investigate the interaction between particle radiation and the strong spectral dependence of gas radiation in oxy-fuel scenarios, a comparison between spectrally averaged and spectrally resolved calculations performed. To the best knowledge of the authors, for the first time the contribution of the parameters determining radiative heat transfer are quantified and compared in one comprehensive study.The results indicate a strong influence of coal particle emissivity and scattering phase function as well as the projected particle surface on the radiative source term. For the wall heat flux, the largest influences were found for ash and coal particle emissivity, projected particle surface and the scattering phase function. Additionally, the difference between coal particle and gas temperature was found to have a significant influence on wall heat flux. A comparison of spectrally averaged to spectrally resolved results and the corresponding models for gas radiation (WSGGM and SNBM) yielded similar trends for the influence of each parameter. Thus, based on the models and parameters involved in this study, a spectrally averaged approach seems to be of sufficient accuracy to describe radiative heat transfer in oxy-fuel combustion systems.
Keywords: Sensitivity analysis; Radiative transfer; Coal combustion; Absorption; Emissivity; Scattering phase function; Particle radiation;

Improvement on oxidation and storage stability of biodiesel derived from an emerging feedstock camelina by Jie Yang; Quan Sophia He; Kenneth Corscadden; Claude Caldwell (90-98).
Camelina is recognized as a promising feedstock for biodiesel production. Similarly to biodiesel derived from other vegetable oils, the oxidative stability is not satisfactory. This issue can be addressed by treating biodiesel with synthetic antioxidants to increase its resistance to oxidation. This study examined the effectiveness of four commonly used antioxidants, butylated hydroxytoluene (BHT), butylated hydroxyanisol (BHA), tert-butylhydrooquinone (TBHQ) and propyl gallate (PrG) on both oxidation stability and storage stability of camelina biodiesel. The antioxidative activity of four antioxidants was found to be in the order of BHA < BHT < PrG < TBHQ; The oil stability index (OSI) of camelina biodiesel was increased (≥ 8 h), meeting the stability requirement regulated in EN 14214:2014, through adding either 2000 ppm BHT, 1000 ppm PrG or 1000 ppm TBHQ. Regarding the long term storage, it was predicted that treating camelina biodiesel with 3000 ppm TBHQ was enable satisfactory oxidation stability to be maintained for one year.
Keywords: Camelina sativa; Biodiesel; Antioxidant; Oil stability index; Peroxide value; Storage stability;

Influence of crystal size on the catalytic performance of H-ZSM-5 and Zn/H-ZSM-5 in the conversion of methanol to aromatics by Xianjun Niu; Jie Gao; Kai Wang; Qing Miao; Mei Dong; Guofu Wang; Weibin Fan; Zhangfeng Qin; Jianguo Wang (99-107).
H-ZSM-5 zeolites with a uniform crystal size from 0.25 to 2 μm were obtained by adding colloidal silicalite-1 seed in the synthesis gel; with H-ZSM-5 as the support, Zn/H-ZSM-5 was prepared by incipient wet impregnation. The influence of crystal size on the state of Zn species and its relation to the catalytic performance of Zn/H-ZSM-5 in the conversion of methanol to aromatics (MTA) was then investigated. The results illustrated that the state of Zn species and catalytic performance of Zn/H-ZSM-5 are closely related to the crystal size, though the crystal size has little influence on the overall acidity. There exist mainly two types of zinc species, viz., ZnO and ZnOH+; Zn/H-ZSM-5 with smaller crystal size is provided with more ZnOH+ species. The selectivity to aromatics and catalyst stability can be improved greatly by using small crystal Zn/H-ZSM-5. A good linear correlation is observed between the amount of ZnOH+ species and the selectivity to aromatics, suggesting that ZnOH+ species plays an important role in enhancing the dehydrogenation of alkanes and aromatization of alkenes to aromatics. As a result, small crystal Zn/H-ZSM-5 with large portion of ZnOH+ species exhibits high selectivity to aromatics and long lifetime in MTA.The state of Zn species and catalytic performance of Zn/H-ZSM-5 are closely related to the crystal size; small crystal Zn/H-ZSM-5 with large portion of ZnOH+ species exhibits high selectivity to aromatics in MTA.Display Omitted
Keywords: Methanol to aromatics; H-ZSM-5; Zn/H-ZSM-5; Crystal size; Zinc species;

Plastic waste is an ideal source of energy due to its high heating value and abundance. It can be converted into oil through the pyrolysis process and utilised in internal combustion engines to produce power and heat. In the present work, plastic pyrolysis oil is manufactured via a fast pyrolysis process using a feedstock consisting of different types of plastic. The oil was analysed and it was found that its properties are similar to diesel fuel. The plastic pyrolysis oil was tested on a four-cylinder direct injection diesel engine running at various blends of plastic pyrolysis oil and diesel fuel from 0% to 100% at different engine loads from 25% to 100%. The engine combustion characteristics, performance and exhaust emissions were analysed and compared with diesel fuel operation. The results showed that the engine is able to run on plastic pyrolysis oil at high loads presenting similar performance to diesel while at lower loads the longer ignition delay period causes stability issues. The brake thermal efficiency for plastic pyrolysis oil at full load was slightly lower than diesel, but NOX emissions were considerably higher. The results suggested that the plastic pyrolysis oil is a promising alternative fuel for certain engine application at certain operation conditions.
Keywords: Plastic pyrolysis oil; Diesel engine; Combustion; Performance; Emissions;

Role of surface phosphorus complexes on the oxidation of porous carbons by M.J. Valero-Romero; F.J. García-Mateos; J. Rodríguez-Mirasol; T. Cordero (116-126).
Chemical activation of olive stone with phosphoric acid produces activated carbons with relatively high content of P surface groups that remain very stable on the carbon surface at relatively high temperatures. Changes in the surface chemistry of a phosphoric acid activated carbon after subjecting it to thermal treatments in oxidizing and inert conditions are studied by temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and adsorption/desorption of NH3. TPD and XPS results point out that P surface groups preferentially reacts with molecular oxygen, prior to carbon gasification, through the oxidation of C-P bond to form C-O-P ones, which are thermally stable at temperatures lower than 700 °C. At higher temperatures, these C-O-P type surface groups decompose to less oxygenated P groups on the carbon surface (of C-P type) generating CO (and CO2) in the gas phase. These C-P type surface groups seem to be very reactive and are (re)oxidized upon contact with air, even at room temperature, forming again C-O-P type groups. Thus, the presence of these oxygen-containing P surface groups with an interesting redox functionality of high chemical and thermal stability seems to be responsible of the high oxidation resistance and high oxygen content (once exposed to ambient air) of this type of porous carbons.Display Omitted
Keywords: Phosphorus surface groups; Carbon inhibition oxidation; Surface redox functionality; Activated carbon; Temperature-programmed desorption; Carbon reduction;