Effect of co-combustion on the burnout of lignite/biomass blends: a Turkish case study

A Comparison of Combustion Properties in Biomass-Coal Blends Using Characteristic and Kinetic Analyses

This paper presents comparative research on the combustion of coal, wheat, corn straw (CS), beet residues after extracting sugar (BR), and their blends, coal–corn straw blends (CCSBs), coal–wheat blends (CWBs), and coal–beet residue blends (CBRBs), using thermogravimetric (TG) analysis under 10, 20, 30, 40 and 50 °C/min. The test results indicate that CS and wheat show better combustion properties than BR, which are recommended to be used in biomass combustion. Under the heating rate of 20 °C/min, the coal has the longest thermal reaction time when compared with 10 and 30 °C/min. Adding coal to the biomass can improve the burnout level of biomass materials (BM), reduce the burning speed, and make the reaction more thorough. The authors employed the Flynn–Wall–Ozawa (FWO) method and the Kissinger–Akahira–Sunose (KAS) method to calculate kinetics parameters. It was proven that overall, the FWO method is better than the KAS method for coal, BM, and coal–biomass blends (CBBs), as it provides higher correlations in this study. It is shown that adding coal to wheat and BR decreases the activation energy and makes conversion more stable under particular α. The authors selected a wider range of biomass raw materials, made more kinds of CBB, and conducted more studies on different heating rates. This research can provide useful insights into how to choose agricultural residuals and how to use them.

Investigation on thermal degradation kinetics and mechanisms of chicken manure, lignite, and their blends by TGA

In this study, thermogravimetric analysis (TGA) was performed under the air environment for four different heating rates (10, 20, 30, and 40 °C min^-1) in order to find out thermal degradation and mechanisms of the chicken manure, a Turkish lignite, and their blends (25 lignite + 75 manure, 50 lignite + 50 manure, and 75 lignite + 25 manure). To calculate thermal kinetics and responsible solid-state mechanisms of the samples, the Flynn-Wall-Ozawa and Coats-Redfern methods were applied. Significant differences between Turkish lignite and chicken manure samples were observed in terms of thermal kinetics and mechanisms. D1 and D4 mechanisms were found to be the responsible mechanisms for the main oxidation region of the lignite and chicken manure/blends, respectively. A similar decreasing trend for the calculated activation energies and pre-exponential constants was observed with increasing biomass content in the manure blends from 25 to 75% by both Flynn-Wall-Ozawa and Coats-Redfern methods. Furthermore, biomass content has an effect on the mechanisms of chicken manure blends during the combustion. D3 was found to be the responsible solid-state mechanism for the third regions (pre-combustion of the manure) of the chicken manure samples. However, D1 and D2 mechanisms were found to be responsible mechanisms for the blends.

Briquettes Production from Olive Mill Waste under Optimal Temperature and Pressure Conditions: Physico-Chemical and Mechanical Characterizations

This paper aims at investigating the production of high quality briquettes from olive mill solid waste (OMSW) mixed with corn starch as a binder for energy production. For this purpose, different mass percentages of OMSW and binder were considered; 100%-0%, 90%-10%, 85%-15%, and 70%-30%, respectively. The briquetting process of the raw mixtures was carried out based on high pressures. Physico-chemical and mechanical characterizations were performed in order to select the best conditions for the briquettes production. It was observed that during the densification process, the optimal applied pressure increases notably the unit density, the bulk density, and the compressive strength. Mechanical characterization shows that the prepared sample with 15% of corn starch shows the best mechanical properties. Moreover, the corn starch binder affects quietly the high heating value (HHV) which increases from 16.36 MJ/Kg for the 100%-0% sample to 16.92 MJ/Kg for the 85%-15% sample. In addition, the kinetic study shows that the binder agent does not affect negatively the thermal degradation of the briquettes. Finally, the briquettes characterization shows that the studied samples with particles size less than 100 μm and blended with 15% of corn starch binder are promising biofuels either for household or industrial plants use.

Parametric assessment of stochastic variability in co-combustion of textile dyeing sludge and shaddock peel

This study aimed at quantification of co-combustion behaviors and kinetic parameters of textile dyeing sludge (TDS) and shaddock peel (SP) in response to blend ratio, heating rate, and temperature. The experimental responses of mass loss (ML) and mass loss rate (MLR) measured using a thermogravimetric analyzer were also estimated using the best-fit multiple non-linear regression (MNLR) models. The independent validations of the models led to high coefficients of determination of 99.8% for ML and 83.8% for MLR. Stochastic uncertainty associated with the model predictors was assessed using Monte Carlo simulations. Our results indicated that the overall cumulative uncertainty was greater in the model predictions of MLR than ML.

Biodrying performance and combustion characteristics related to bulking agent amendments during kitchen waste biodrying

Biodrying of kitchen waste amended with different bulking agents was carried out to evaluate performance, heat values and combustion characteristics. Results showed that adding bulking agents produced higher water removal rates of 55.6%-65.4%. Addition of bulking agents also yielded higher volatile solid contents related to slower degradation. Lower heat values of bulking agent treatments increased from 2000-3218 kJ·kg^-1 to 8544-9849 kJ·kg^-1. Organic degradation did not influence ignition or combustion temperatures during the second combustion stage, but did influence combustion rate. Maximum combustion rate and temperature of the third combustion stage remained stable. Bulking agents produced higher apparent activation energies compared with the control, although biodrying made combustion of kitchen waste easier, because of an overall decrease in apparent activation energy.

Energy Properties of Sunflower Seed Husk as Industrial Extrusion Residue

The paper presents possibilities of using by ‒ products of the agri-food sector, in the form of sunflower husks, for energy purposes. Physical and chemical properties in the form of heat of combustion, calorific value for three moisture levels and ash content for two temperatures of combustion were determined and the carbon content (C), hydrogen content (H) and nitrogen content (N) were calculated pursuant to the PN-EN 15104 standard. Analysis of the heat of combustion and calorific value proved good energy properties of the investigated biomass. For the moisture level of 9%, 16%, 32% the heat of combustion was respectively 19.44 MJ∙kg-1, 17.94 MJ∙kg-1, 15.03 MJ∙kg-1, and the calorific value 18.09 MJ∙kg-1, 16.28 MJ∙kg-1, 13.16 MJ∙kg-1. The average ash content of the investigated biomass for the combustion temperature of 600°C and 815°C was respectively 2.12% and 2.04. In the analyzed biomass the nitrogen content was determined at the level of 1.57%, carbon of 43.87% and hydrogen of 6.29%.

Evaluation of co-pyrolysis petrochemical wastewater sludge with lignite in a thermogravimetric analyzer and a packed-bed reactor: Pyrolysis characteristics, kinetics, and products analysis

Co-pyrolysis characteristics of petrochemical wastewater sludge and Huolinhe lignite were investigated using thermogravimetric analyzer and packed-bed reactor coupled with Fourier transform infrared spectrometer and gas chromatography. The pyrolysis characteristics of the blends at various sludge blending ratios were compared with those of the individual materials. Thermogravimetric experiments showed that the interactions between the blends were beneficial to generate more residues. In packed-bed reactor, synergetic effects promoted the release of gas products and left less liquid and solid products than those calculated by additive manner. Fourier transform infrared spectrometer analysis showed that main functional groups in chars gradually disappeared with pyrolysis temperatures increasing, and H₂O, CH₄, CO, and CO₂ appeared in volatiles during pyrolysis. Gas compositions analysis indicated that, the yields of H₂ and CO clearly increased as the pyrolysis temperature and sludge blending ratio increasing, while the changes of CH₄ and CO₂ yields were relatively complex.

Grindability and combustion behavior of coal and torrefied biomass blends

Biomass samples (pine, black poplar and chestnut woodchips) were torrefied to improve their grindability before being combusted in blends with coal. Torrefaction temperatures between 240 and 300 °C and residence times between 11 and 43 min were studied. The grindability of the torrefied biomass, evaluated from the particle size distribution of the ground sample, significantly improved compared to raw biomass. Higher temperatures increased the proportion of smaller-sized particles after grinding. Torrefied chestnut woodchips (280 °C, 22 min) showed the best grinding properties. This sample was blended with coal (5-55 wt.% biomass). The addition of torrefied biomass to coal up to 15 wt.% did not significantly increase the proportion of large-sized particles after grinding. No relevant differences in the burnout value were detected between the coal and coal/torrefied biomass blends due to the high reactivity of the coal. NO and SO2 emissions decreased as the percentage of torrefied biomass in the blend with coal increased.

Thermogravimetric analysis of the behavior of sub-bituminous coal and cellulosic ethanol residue during co-combustion

The influence of the addition of cellulosic ethanol residue (CER) on the combustion of Indonesian sub-bituminous coal was analyzed by non isothermal thermo-gravimetric analysis (TGA). The effect of blends ratio (5%, 10%, 15% and 20%), interaction mechanism, and heating rate (5°C/min, 10°C/min, 15°C/min, 20°C/min) on the combustion process was studied. The results show that the increase of the blending ratio allows to achieve the increase of the combustibility index from 7.49E-08 to 5.26E-07 at the blending ratio of 20%. Two types of non-isothermal kinetic analysis methods (Ozawa-Flynn-Wall and Vyazovkin) were also applied. Results indicate that the activation energy of the blends decreases with increasing the conversion rate. In particular, the blending ratio of 20% confirms to have the better combustion performance, with the average value of the activation energy equal to 41.10 kJ/mol obtained by Ozawa-Flynn-Wall model and 31.17 kJ/mol obtained by Vyazovkin model.

Impact of blend ratio on the co-firing of a commercial torrefied biomass and coal via analysis of oxidation kinetics

Incorporation of torrefied biomass into coal-fired power plants could potentially lower the SOx and net CO2 emissions resulting from electricity generation. However, concerns over lower heating values and slightly higher ash content of torrefied biomass suggest that blending it with coal in industrial boilers may be preferable to complete fuel transition. By studying the oxidation kinetics of coal-torrefied biomass blends in a thermogravimetric analyzer at a heating rate of 100°C/min, we find an additive nature among the fuels for peak mass loss rates and enthalpies of combustion. The activation energy required to initiate decomposition decreases from 132.6 to 77.6 kJ/mol as the torrefied biomass increases from 0 to 100 wt%, with a sharp decrease between 0 and 40 wt%. Data suggest that incorporation of torrefied biomass into coal-fired boilers is dependent on the ability to sacrifice heating value for the lower emissions of SOx and net CO2 garnered using bio-coal.

A comparison of thermal behaviors of raw biomass, pyrolytic biochar and their blends with lignite

In this study, thermal characteristics of raw biomass, corresponding pyrolytic biochars and their blends with lignite were investigated. The results showed that pyrolytic biochars had better fuel qualities than their parent biomass. In comparison to raw biomass, the combustion of the biochars shifted towards higher temperature and occurred at continuous temperature zones. The biochar addition in lignite increased the reactivities of the blends. Obvious interactions were observed between biomass/biochar and lignite and resulted in increased total burnout, shortened combustion time and increased maximum weight loss rate, indicating increased combustion efficiencies than that of lignite combustion alone. Regarding ash-related problems, the tendency to form slagging and fouling increased, when pyrolytic biochars were co-combusted with coal. This present study demonstrated that the pyrolytic biochars were more suitable than raw biomass to be co-combusted with lignite for energy generation in existing coal-fired power plants.

Mechanical durability and combustion characteristics of pellets from biomass blends

Biofuel pellets were prepared from biomass (pine, chestnut and eucalyptus sawdust, cellulose residue, coffee husks and grape waste) and from blends of biomass with two coals (bituminous and semianthracite). Their mechanical properties and combustion behaviour were studied by means of an abrasion index and thermogravimetric analysis (TGA), respectively, in order to select the best raw materials available in the area of study for pellet production. Chestnut and pine sawdust pellets exhibited the highest durability, whereas grape waste and coffee husks pellets were the least durable. Blends of pine sawdust with 10-30% chestnut sawdust were the best for pellet production. Blends of cellulose residue and coals (<20%) with chestnut and pine sawdusts did not decrease pellet durability. The biomass/biomass blends presented combustion profiles similar to those of the individual raw materials. The addition of coal to the biomass in low amounts did not affect the thermal characteristics of the blends.

Combustion characteristics of coal and refuse from passenger trains

Refuse from passenger trains is becoming a significant issue with the development of the Chinese railway. Co-firing is regarded as a promising thermal technology, both environmentally and economically, in reducing the quantity of refuse. The co-firing property of passenger train refuse with coal, however, may differ due to the differences in the composition of the refuse. In the present study, combustion properties of refuse from passenger train samples and the mixture of refuse with coal were studied in a tube furnace. Thermo analysis methods, such as thermogravimetry (TG), differential scanning calorimetry (DSC), differential thermal analysis (DTA) and derivative thermogravimetry (DTG) analyses were employed to evaluate combustion performance. We found that the mixture of passenger train refuse and coal at a ratio of 1:1 has a lower ignition and burnout temperature than the coal-only sample. Moreover, refuse from railway passenger trains has more reactive combustion properties than the coal-only sample, and the addition of railway passenger train refuse to coal can promote the reactivity of coal.

Sorting efficiency and combustion properties of municipal solid waste during bio-drying

One aerobic and two combined bio-drying processes were set up to investigate the quantitative relationships of sorting efficiency and combustion properties with organics degradation and water removal during bio-drying. Results showed that the bio-drying could enhance the sorting efficiency of municipal solid waste (MSW) up to 71% from the initial of 34%. The sorting efficiency was correlated with water content negatively (correlation coefficient, r=-0.89) and organics degradation rate positively (r=0.92). The higher heating values (HHVs) were correlated with organics degradation negatively for FP (i.e. the sum of only food and paper) (r=-0.93) but positively for the mixing waste (MW) (r=0.90), whereas the lower heating values (LHVs) were negatively correlated with water content for both FP (r=-0.71) and MW (r=-0.96). Other combustion properties depended on organics degradation performance, except for ignition performance and combustion rate. The LHVs could be greatly enhanced by the combined process with insufficient aeration during the hydrolytic stage. Compared with FP, MW had higher LHVs and ratios of volatile matter to fixed carbon. Nevertheless, FP had higher final burnout values than MW.

Quantitative evaluation of minerals in fly ashes of biomass, coal and biomass-coal mixture derived from circulating fluidised bed combustion technology

The chemical and mineralogical composition of fly ash samples collected from laboratory scale circulating fluidised bed (CFB) combustion facility have been investigated. Three fly ashes were collected from the second cyclone in a 50 kW laboratory scale boiler, after the combustion of different solid fuels. Characterisation of the fly ash samples was conducted by means of X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Quantitative analysis of the crystalline (mineral) and amorphous phases in each ash sample was carried out using the Rietveld-based Siroquant system, with an added spike of ZnO to evaluate the amorphous content. SiO(2) is the dominant oxide in the fly ashes, with CaO, Al(2)O(3) and Fe(2)O(3) also present in significant proportions. XRD results show that all three fly ashes contain quartz, anhydrite, hematite, illite and amorphous phases. The minerals calcite, feldspar, lime and periclase are present in ashes derived from Polish coal and/or woodchips. Ash from FBC combustion of a Greek lignite contains abundant illite, whereas illite is present only in minor proportions in the other ash samples.