Co-combustion Of Lignite Research Articles

Experimental study on enrichment of heavy metals by modified mullite during co-combustion of lignite with eucalyptus wood

ABSTRACT Modifying the content of oxygen vacancies (OVs) has emerged as a crucial approach to tailoring silicate's adsorption properties, microstructure, conductivity, and catalytic performance. Some studies have reported the formation of OVs during ammonia treatment. However, there are limited studies on the production of OV-enriched mullite by treating it with N-containing compounds at low temperatures. In this work, formamide, urea, and ammonium acetate were used as ammonia-assisted reduction modifiers to induce oxygen vacancies in mullite at 30 ℃, 60 ℃, and 90 °C. The aim was to enhance the enrichment effect of heavy metals (Cr, Cu, Mn, Ni, Pb, Zn) during the co-combustion of coal and biomass. The modified mullite was analyzed by using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results indicated that the particle size of mullite decreased, and the concentration of internal Al3+ ions and oxygen vacancies was enhanced. Coal-biomass-mullite combustion experiments were conducted in a tubular furnace at 900 °C, revealing a significant enhancement in the enrichment of heavy metals during the combustion process, particularly when the modification temperature was 60 °C using ammonium acetate as the modifier. This work holds significant importance for developing novel heavy metal adsorbents and the reduction of pollutant emissions from coal-biomass co-combustion in industrial applications.

Reduction of CO2 emissions through the co-combustion of lignite with biomass residues: Renewable and non-renewable CO2 per produced megajoule and fuel characterization

Accumulation of unmanaged agricultural wastes is related to increased environmental concern, as they usually are left unexploited and/or burned uncontrolled in the fields. The reduction/utilization of these wastes by turning them into solid biofuels for energy production is a viable solution for addressing the related environmental issues. In this study, twelve alternative solid biofuels of biomass residues and lignite (sunflower husk - BSH, stem, disk florets and seeds biodiesel sunflower wastes -BSW, corn husk -HKC, corn stalk and husk -SHC) were mixed with lignite in several proportions and assessed by using energy content analysis, proximate analysis, and ultimate analysis. Empirical chemical formulas were also determined. Furthermore, it introduces a novel concept to separate and quantify the renewable CO2 emissions, from the non-renewable emissions resulting from biomass co-combustion with lignite (alternative solid composite biofuels). The renewable and non-renewable CO2 emissions were expressed per produced megajoule (MJ) and per kilogram (Kg). The non-renewable CO2 emissions per produced MJ of the blends were compared to lignite emissions. The results showed that blends with 70 wt%, 50 wt% and 30 wt% biomass in blend could reduce about 75 %, 57 % and 34 % the non-renewable CO2 emissions per produced MJ, respectively. The present work suggests that blends of agricultural residues with lignite not only could be used as alternative solid biofuels (with better combustion characteristics than lignite sample, e.g. better energy content, less ash content, less Sulphur content, and similar Nitrogen content), but also could help to reduce carbon emissions via the co-combustion process.

PCDD/Fs, PAHs and HCl emissions from co-combustion of lignite and chicken manure in a circulating fluidized bed boiler with compact refractory casting

Chicken manure (CM) should be used in energy production due to its high production potential for the waste-to-energy approach. Co-combustion of CM with lignites may be a good practice in terms of reducing its environmental impact and the need for fossil fuels. However, the level of organic pollutants originated from CM combustion is not clear. This study investigated the potential of CM to be combusted in a circulating fluidized bed boiler (CFBB) with a local lignite. Combustion and co-combustion tests of CM and Kale Lignite (L) were performed in the CFBB to measure PCDD/Fs, PAHs and HCl emissions. CM burned in the upper parts of the boiler due to its high volatile matter content and low density compared to coal. This caused the bed temperature to decrease with the increase in the amount of CM in the fuel mixture. It was also observed that the combustion efficiency increased as the share of CM in the fuel mixture increased. Total PCDD/F emissions increased with CM share in the fuel mixture. However, all are less than emission limit value (100 pg I-TEQ/m3). Co-combustion of CM with lignite at different ratios did not have a significant effect on HCl emissions. PAH emissions were found to increase with the increase of the CM share when the CM share was more than 50% by weight.

Combustion characteristics and synergistic effects during co-combustion of lignite and lignocellulosic components under oxy-fuel condition

Co-combustion of lignocellulosic biomass and coal has been recognized as a promising route to deliver carbon neutrality. In this study, the combustion characteristics of lignocellulosic biomass main components (cellulose, hemicellulose, and lignin), one kind of lignite, and their mixtures were investigated under air and oxy-fuel conditions, respectively. The combustion reactivity of cellulose and hemicellulose was better than that of lignite, while that of lignin was worse. Under the oxy-fuel condition with the same oxygen mole fraction as air, the combustion of cellulose and hemicellulose was slightly delayed, while a distinct combustion delay was observed for lignin similar to lignite. For the co-combustion, compared to lignite, the combustion reactivity could be improved by blending cellulose and hemicellulose, while it got worse by mixing lignin. Cellulose and hemicellulose had a positive synergistic effect on the release of lignite volatiles, while lignin showed a negative synergy on it. All the lignocellulosic components showed positive synergies with lignite on the char oxidation due to the high structural porosity of lignite char and the advanced oxidation of lignocellulosic char.

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

The integration of intermittent renewable energy sources into the electricity market requires flexible and efficient technologies that compensate for the fluctuating electricity demand. A circulating fluidized bed (CFB) boiler is a suitable solution due to its fuel flexibility, but the thermal inertia of the fluidized bed can have negative effects on the load following capabilities. This study investigates the influence of the operating parameters of the fire side on the speed of load changes on the waterside. Co-combustion of lignite, straw, and refuse derived fuel (RDF) was carried out. In a 1 MWth pilot CFB combustor fifteen load changes were performed with a varying step input of the primary air, the secondary air, and the fuel mass flow. The step input of the primary air had a large influence on the load ramps, as it strongly affects the solids concentration in the upper furnace. The step size of the fuel mass flow had a positive effect on the load change rate. Based on the results, concepts were developed to accelerate load ramping by controlling the hydrodynamic conditions and the temperature on the fireside.

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

The integration of intermittent renewable energy sources into the electricity market requires flexible and efficient technologies that compensate for the fluctuating electricity demand. A circulating fluidized bed (CFB) boiler is a suitable solution due to its fuel flexibility, but the thermal inertia of the fluidized bed can have negative effects on the load following capabilities. This study investigates the influence of the operating parameters of the fire side on the speed of load changes on the waterside. Co-combustion of lignite, straw, and refuse derived fuel (RDF) was carried out. In a 1 MWth pilot CFB combustor fifteen load changes were performed with a varying step input of the primary air, the secondary air, and the fuel mass flow. The step input of the primary air had a large influence on the load ramps, as it strongly affects the solids concentration in the upper furnace. The step size of the fuel mass flow had a positive effect on the load change rate. Based on the results, concepts were developed to accelerate load ramping by controlling the hydrodynamic conditions and the temperature on the fireside.

Compost of Biodegradable Municipal Solid Waste as a Fuel in Lignite Co-combustion

In Greece, 5.8 million tons of municipal solid wastes (MSW) are produced annually, of which 2.47 million tons are bio-wastes. Composting is an alternative treatment of bio-wastes instead of landfill. Τwo composting plants operate in Greece, one in Ano Liossia (capacity 1,200 tons/day, producing 120 tpd compost) and another in Chania (capacity 70,000 tons/year, producing 20,000 tpa compost). In addition, since 2018, the first integrated waste management plant was set off in the region of Kozani (capacity 120,000 tons/year). An alternative utilization of the compost, produced in the latter plant, was investigated in this study. In particular, instead of using compost as fertilizer, the energy recovery from this bio-waste was attested. Utilization of compost of MSW for energy production purposes has rarely been studied in the literature. Several blends of compost with lignite were prepared and their energetic potential was determined. Proximate analyses and gross calorific value (GCV) determination were conducted. Wastes and biomass-based fuels differ in many ways from fossil fuels. The CLOF sample revealed the highest GCV and the lowest ash content than all analyzed samples. Based on all analytical determinations, compost and its mixtures with lignite could be regarded suitable for energy recovery by thermal processes, such us combustion. Further studies should be done including emission analysis, ash deposition during combustion (corrosion, slagging and fouling).

Synergistic Interactions During Cocombustion of Lignite, Biomass, and Their Chars

Woody biomasses such as ash tree (AT), hybrid poplar (HP), and rhododendron (RD) were subjected to torrefaction and carbonization at temperatures of 200 °C and 400 °C. Likewise, several lignite samples were carbonized at 750 °C. Various binary fuel blends such as raw lignite/raw biomass, raw lignite/biochar, lignitic char/raw biomass, and lignitic char/biochar were prepared where the fraction of biomass or biochar was 10 wt% in the blends. The cocombustion characteristics of these blends were investigated through a thermal analysis method from the synergetic point of view considering the fuel properties and the combustion performance. Some parameters relevant to the combustion reactivity such as ignition point, maximum rate, peak temperature, and burnout temperature were commented to figure out whether synergistic interaction or additive behavior governs the combustion characteristics of the blends. Also, the combustion performance indices such as ignition index (Ci), burnout index (Cb), comprehensive combustibility index (S), and the burning stability index (DW) were estimated. It was concluded that the combinations of the additive behavior and the synergistic interactions governs the cocombustion process, and the kind of the fuels and their thermal history determine the reactivity and the interactions during cocombustion.

Synergetic effect on the combustion of lignite blended with humus: Thermochemical characterization and kinetics

The co-combustion of lignite with humus was investigated as an effective way to mitigate carbon emission. The thermal characteristics of the co-combustion were successfully evaluated, which was the prerequisite for predicting synergy and blending optimization of this process. A novel synergy index (SI) was proposed to quantify the synergetic effect and differentiate the effect of minerals and organics in humus during co-combustion. The non-catalytic synergy of organics (SI = 1.76) was stronger than the catalytic synergy of minerals (SI = 1.55) for the 20 wt% humus blend. However, catalytic synergy was more dominant at high humus blending ratios. The kinetic parameters were estimated through two model-free methods. The activation energy of the blend by Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods was 104.99 and 110.71 kJ/mol, respectively. The more precise kinetic model of the blend was determined by master-plots method. This study also demonstrated that humus could be used as a potential fuel in co-combustion system.

Thermogravimetric investigation of the co-combustion between the pyrolysis oil distillation residue and lignite

Co-combustion of lignite with distillation residue derived from rice straw pyrolysis oil was investigated by non-isothermal thermogravimetric analysis (TGA). The addition of distillation residue improved the reactivity and combustion efficiency of lignite, such as increasing the weight loss rate at peak temperature and decreasing the burnout temperature and the total burnout. With increasing distillation residue content in the blended fuels, the synergistic interactions between distillation residue and lignite firstly increased and then decreased during co-combustion stage. Results of XRF, FTIR, 13C NMR and SEM analysis indicated that chemical structure, mineral components and morphology of samples have great influence on the synergistic interactions. The combustion mechanisms and kinetic parameters were calculated by the Coats Redfern model, suggesting that the lowest apparent activation energy (120.19kJ/mol) for the blended fuels was obtained by blending 60wt.% distillation residue during main co-combustion stage.

Comparison of Limestone Adsorption Reactivity During Desulfurisation of Flue Gas From Co-Combustion of Lignite and Woodchips in Fluidised-Bed Boilers

Comparison of Limestone Adsorption Reactivity During Desulfurisation of Flue Gas From Co-Combustion of Lignite and Woodchips in Fluidised-Bed Boilers

Emission characteristics of co-combustion of a low calorie and high-sulfur-lignite coal and woodchips in a circulating fluidized bed combustor: Part 2. Effect of secondary air and its location

In this study, co-combustion of woodchips and Bursa–Orhaneli lignite was carried out in a circulating fluidized bed combustor, 6m long and 108mm inside diameter. Co-combustion of lignite and woodchips was performed in order to investigate the effect of secondary air ratio (SAR) on the flue gas emissions. The woodchips content of the fuel mixture was 30% and 50% by wt. Secondary air (SA) was supplied to the combustor from five different locations along the combustor and at several SARs. During the combustion experiments, CO2, CO, O2, NO, and SO2 emissions in the flue gas were continuously measured and recorded by ABB-AO 2000 flue gas analyzer.Increasing SAR lowered the recirculation rate which was followed by an increase in temperature of the dense phase and a decrease in the temperature of the dilute phase in the combustor. CO emissions were increased for the co-combustion of 30% by wt. woodchips and lignite, and for SAR greater than 15%. Increasing SAR caused cyclone outlet temperature to decrease and this indirectly increased the CO emissions. NO emission decreased with increasing SAR. It was observed that the location of SA given into the combustor had a distinctive effect on NO emission especially for SA higher than 15% for the co-combustion of 30% by wt. woodchips with lignite coal. NO emissions increased with the increase in woodchips share in fuel mixture. While SO2 emissions increased with SAR in all cases for the co-combustion of 30% by wt. woodchips, they did not change too much with SAR up to 20% for the co-combustion of 50% by wt. woodchips with coal.

Ash and chlorine deposition during co-combustion of lignite and a chlorine-rich Canadian peat in a fluidized bed – Effects of blending ratio, moisture content and sulfur addition

A Canadian chlorine-rich peat was co-fired with lignite in a bubbling fluidized bed combustor (FBC) in this study. With an air-cooled probe installed in the freeboard of the riser, effects of portion of peat, moisture content and addition of sulfur on ash and chlorine deposition during combustion/co-combustion of lignite–peat blends were investigated. The results indicated that the contents of chlorine element, alkali/alkaline earth metals and SiO2 and Al2O3 of the feed played a key role in the ash deposition in all tests. A higher chlorine concentration in the feed would generally result in a higher tendency of ash deposition. For instance, combustion of 100% peat pellet showed a much higher tendency of ash deposition than combustion of the lignite alone. Nevertheless, co-firing of the lignite–peat blends with 20% or 50% peat resulted in lower relative ash deposition rates (RDA). Combustion of relatively wet solid fuels produced a decreased RDA value and reduced chlorine deposition. Adding sulfur into the fuel of coal or peat could effectively decrease the chloride deposition in the ash deposits via sulfation. The sulfur addition could also reduce the ash deposition rate for the combustion of lignite, while it slightly increased the ash deposition rate for the peat fuel. The deposited Ca, Mg, Al and Si elements were present mostly in the forms of calcium and magnesium sulfates, aluminates and silicates that have relatively lower melting points.

Investigation of Lignite and Firewood Co-combustion in a Furnace for Tobacco Curing Application

Co-combustion of lignite and firewood was investigated for an application in tobacco curing industry in Northern Thailand. Extensive experiments have been carried out in a newly developed furnace suitable for small curing unit, in place of locally made furnace. The aim of this investigation is to evaluate the performance of the combustion chamber in the required thermal output range for tobacco curing and to examine the influence of fuel feed rate, fuel mixture ratio and air staging on the combustion and emission characteristics of the furnace during steady state operation. Their effects are characterized in terms of the observed variations of temperature distributions, emissions of CO, SO2, CO2, O2 and combustion efficiency. Co-firing of firewood and lignite has been found to exhibit acceptable temperature distribution, high combustion efficiency and low emissions over a wide thermal output span. Stable operation at low (50 kW) and high (150 kW) thermal output was achieved with average CO and SO2 content in flue gas typically below 1400 and 100 ppm, respectively. Under the conditions considered, it was showed that the fuel feed rate had greater influence on combustion and emissions than firewood and lignite mixture ratio and air staging.