Technological aspects of sunflower biomass and brown coal co-firing

The technological problems occurring in the co-firing of biomass and brown coal (lignite) prompted this research project. During the fuel preparation, accidental self-ignition and explosions were several times reported by power plants operators. The aim of this study was to evaluate brown coal, sunflower husks and sunflower husk pellets as fuels for co-firing in energetic boilers. Sunflower husk had a lower ash content and calorific value than the pellets. The range of the combustion temperatures of the biomass (200–300 °C) was narrower than that of brown coal (200–800 °C). The formation of highly alkaline ash from the biomass resulted in the formation in boiler of agglomerates of ash. The elemental composition, thermogravimetric and biological analyses suggested that the pellets contained synthetic additives difficult to identify. The biological method was proposed for evaluating biomass additives. The use of additional agents in the pelletizing process may influence on the combustion parameters. Mixing biomass with brown coal may occasionally result in self-ignition in the logistic chain. Plastic additives and biological activity may contribute to self-ignition.     

Partial slagging coal gasifier operational performance and product characteristics for energy sustainability in an integrated gasification combined cycle system

Operational performance of two ton/day coal partial slagging entrained-bed gasifier has been investigated. Coal to syngas conversion under operating temperature (1100–1300 °C), pressure (19.7–20.4 bar) and oxygen to coal ratio of 0.70 produced syngas at a flow rate of 177.5 Nm³/h. Composition of produced syngas was; CO 38–40 vol%, H₂ 22–23 vol%, CO₂ 7–8 vol%, and CH₄ 1.0–1.5 vol%. Carbon conversion and cold gas efficiency after one pass through operation were found to be 92.81% and 73.83% respectively. Fly ash fines produced were high in carbon content and acidic oxides than the bottom slag. Non-metal leaching nature of bottom slag was confirmed with ICP analysis. Based on the results, an industrial symbiosis can be established by recycling and reusing high carbon content fly ash fines in the gasifier. The same can be sold to other industries as a quality energy fuel. Slag produced can be used for the construction of roads and pavements.     

Ash deposition behavior under coal and wood co-firing conditions in a 300 kW downfired furnace

Growth of ash deposits when wood was co-fired with coal was visually investigated in a 300 kW pilot-scale furnace. For comparison, combustion of pure coal was also conducted. A total of 10% and 20% wood were mixed with coal. The thickness and heat flux were obtained. The collected ash deposits and fly ash were characterized by a series of analysis methods to determine the physical and mineral properties. Their relationships were also revealed. Results showed that co-firing of coal with wood dramatically increased the ash deposition propensity. During the coal combustion, shedding of ash deposit occurred and the maximum deposit thickness was 15.33 mm. A deposit thickness of up to 27.02 mm was achieved for 10% wood, and the thickness increased to 34.20 mm for 20% wood. The variation in heat flux with deposit thickness substantially changed when wood was co-fired. A significant change was also observed in the mineral composition of ash deposit with the increase in wood ratio. The proportion of anorthite increased because that of lime in fly ash increased with wood ratio. In addition, the mean diameter of fly ash particles increased as wood ratio increased.     

生物质与煤混烧灰的熔融性实验研究

为解决生物质与煤混燃存在的结渣积灰问题.以稻秸秆、白杨木屑、稻壳和煤在不同配比下混合燃烧的灰分作为研究对象,利用HR-3C灰熔融性测定仪研究了生物质与煤混合燃烧的熔融特性.研究表明:生物质燃料中碱金属含量比煤中的含量要高,提高生物质的掺入比总体上会使灰熔融温度降低;此外,对于二氧化硅含量不同的生物质燃料其灰熔融性有所差...     

不同采矿深度准东煤物化特性和燃烧性能研究

选取天池能源浅层和深层煤样进行研究,以大同烟煤作为对比,了解采矿深度对煤质及燃烧特性的影响,为准东煤的勘探和燃烧提供必要的理论依据。研究发现,随着采矿深度的增加,煤中水分减少、灰分降低、发热量增加、含硫量减少,煤质更加接近烟煤;煤灰中Fe2O3明显减少,煤的结渣趋势减轻;煤的着火温度略有降低,燃烧速率提高,燃烧特性变好。与大同烟煤相比,准东煤高水分、低发热量、低氮含量,燃烧时着火温度显著降低且燃烧速率低。     

Movable injection point–based syngas production in the context of underground coal gasification

Underground coal gasification (UCG) has been proven as a viable technology for the generation of high calorific value syngas using deep mine coal seams. The use of multiple injection points/movable injection point method could be an alternate technique for efficient gasification of high ash Indian coals. In this context, the present study is focused on evaluating the heating value of syngas using a variety of gasifying agents such as pure O₂, air, humidified O₂, and CO₂-O₂ dual-stage gasification under movable injection method for high ash coals. It is found that the use of movable injection point method had significantly increased the heating value of the product gas, compared with the fixed point injection method. For high and low ash coal under pure O₂ gasification, the calorific value of syngas obtained using movable injection point is 123.2 and 153.9 kJ/mol, which are 33.5% and 24.3% higher than the syngas calorific value obtained using fixed injection point, respectively. Further, the air as a gasification agent for high ash coals had increased the gross calorific value of the syngas by 24%, using this technology. The results of high ash coal gasification using humidified oxygen at optimum conditions (0.027-kg moisture/kg dry O₂) and CO₂-O₂ gas had enhanced the syngas calorific value by 12.6% and 5%, respectively. Humidified O₂ and CO₂-O₂ gasifying agents produced a high-quality syngas with the calorific value of 190 kJ/mol, among the gasifying agents used. The experimental results had shown that the movable injection point method is found to be a better alternative for the generation of calorific value-enriched syngas using high ash-based Indian coals.     

Refuse-derived fuels as a renewable energy source in comparison to coal,rice husk,and sugarcane bagasse

The calorific potential of refuse-derived fuels (RDFs) was investigated with different coals, rice husk, and sugarcane bagasse. Carbon-sulfur analysis, gross calorific value (kJ/kg), and proximate analysis (%) were carried out. Total carbon of coal samples was found to be in the range from 62.65 to 79.19%, while RDF samples were ranged from 40.21 to 57.34% which were almost similar to rice husk (49.13%) and sugarcane bagasse (46.13%). Comparison of the total sulfur content of the coal (Duki) (10.52%) was very high as compared to RDF samples ranged from 0.17 to 0.46% and almost similar to rice husk (0.34%) and sugarcane bagasse (0.187%), while other coal samples ranged from 2.1 to 4.5%. The gross calorific value of the coal (Duki) (6,163 kJ/kg) was higher to other coal samples ranged from 4,935 to 4,972 kJ/kg, while found to be almost double to rise husk (3,518 kJ/kg), sugarcane bagasse (3,285 kJ/kg), and RDF samples (3,125–4,689 kJ/kg). The moisture content, volatile matter, and ash content were found higher in RDF 1 (42.14%), RFD 2 (66.55%), and coal (stone) (33.14%), respectively. Appropriate gross calorific value and very low sulfur content of the RDFs, especially RDF 2, appeared adequate to be used as a fuel with a lesser pollution potential and as an alternative fuel in mega cement industry of Pakistan.     

Investigation on ash deposition characteristics during Zhundong coal combustion

The reserves of Zhundong (ZD) coal in China are huge. However, the high content of Na and Ca induces serious slagging and fouling problems. In this study, the ZD coal was burned in a DTF (drop tube furnace), and the ashes collected at different gas temperature with non-cooling probe were analyzed to obtain the ash particle properties and their combination mode. The results showed that Na, Ca and Fe are the main elements leading to slagging when the gas temperature is about 1000 °C during ZD coal combustion, but their mechanisms are quite different. Some sodium silicates and aluminosilicates and calcium sulfate keep molten state in the ashes collected at 1000 °C. These molten ash particles may impact and adhere on the bare tube surface, and then solidified quickly. With the growth of slag thickness, the depositing surface temperature is increased. The molten ash particles might form a layer of molten film, which could capture the other high fusion temperature particles. The Fe₂O₃ sphere were captured by the formed molten slag and then they blended together to form a new molten slag with lower melting temperature.     

Experimental measurements for torrefied biomass Co-combustion in a 1 MWth pulverized coal-fired furnace

Biogenic residues upgraded by torrefaction are well suited for co-firing in existing thermal power plants due to their increased net calorific value, their improved grindability and their good characteristics regarding storage and transport. In this work, torrefied and pelletized biomass (coniferous wood sawdust) and hard coal (Columbian Calenturitas) were co-combusted in a 1 MW_th pulverized coal-fired furnace. The mixture of both fuels (torrefied biomass and hard coal) was co-grinded at two ratios with a thermal share of biomass of 3.8% and 7.3% using the same coal mill. For comparison purpose, experiments on pure hard coal combustion (only coal) were carried out, too. Despite torrefaction, the throughput of the mill was sharply reduced at higher biomass shares and the average grain size of pulverized fuel was increased. However, both fuel blends were co-combusted without any difficulty. Compared to mono-combustion of the hard coal, no significant differences were detected, neither in the flue gas emissions nor in the char burnout. Gas measurements in the flame profile show higher levels of released volatile matter close to the burner, resulting in a higher oxygen demand.     

准东煤掺烧煤矸石安全性与经济性分析

高岭土与低钠煤可以有效抑制燃用准东煤时炉内的沾污结渣问题,但由于其价格升高,为降低电厂燃煤成本,因此提出将煤灰成分相似的煤矸石作为准东煤防结渣添加剂.分析煤矸石作为添加剂抑制炉内沾污结渣的可行性,根据入炉煤灰中折算Na2O含量低于3.0％,确定掺烧比例,并在某150 MW机组上进行实炉掺烧试验.通过掺烧试验分析可见,煤...     

Synergy effects of co-firing wooden biomass with Bosnian coal

The paper presents synergy effects found during the co-firing of wooden biomass with Bosnian coal types in an experimental reactor. The co-firing tests used spruce sawdust in combination with Kakanj brown coal and a lignite blend of Dubrave lignite and Sikulje lignite. Coal/biomass mixtures at 93:7 and 80:20 wt% were fired in a 20 kW pulverized fuel (PF) entrained flow reactor. Over 20 test trials were performed to investigate ash deposition behavior and emissions under different conditions, varying the process temperature, excess air ratio, and air distribution. During the tests, the temperature in the experimental facility varied between 880 and 1550 °C, while the excess air ratio varied between 0.95 and 1.4. There was sufficient combustion efficiency under all co-firing regimes, with burning out at 96.5–99.5% for brown coal–sawdust co-firing. Synergy effects were detected for all co-firing regimes with regard to SO₂ emission, as well for slagging at the process temperature suitable for the slag tap furnace. CO₂ emissions were also calculated for the blends tested and significant reductions of CO₂ found, due to the very low ranking of Bosnian coals.     

Influence of coal co-firing on the particulate matter formation during pulverized biomass combustion

Biomass is regarded as CO₂-neutral, while the high contents of potassium and chlorine in biomass induce severe particulate matter emission, ash deposition, and corrosion in combustion facilities. Co-firing biomass with coal in pulverized-combustion (PC) furnaces is able to solve these problems, as well as achieve a much higher generating efficiency than grate furnaces. In this work, the particulate matter (PM) emission from biomass co-firing with coal was studied in an entrained flow reactor at a temperature of 1623 K simulating PC furnace condition. PMs were sampled through a 13-stage impactor, and their morphology and elemental composition were characterized by scanning electron microscopy and electron dispersive X-ray spectroscopy. SO₂ emissions were measured to interpret the possibility of potassium sulfation during co-firing. Results show that PMs from the separated combustion of both biomass and coal present a bimodal particle size distribution (PSD). The concentration and size of fine-mode submicron particles (PM_1.0) from biomass combustion are much higher than those from coal combustion because of the high potassium content in biomass. For the co-firing cases, with the coal ratio increasing from 0% to 50%, the PM_1.0 yield is reduced by more than half and the PM_1.0 size becomes smaller, in contrast, the concentration of coarse-mode particles with the size of 1.0–10 μm (PM_1.0-10) increases. The measured PM_1.0 yields of co-firing are lower than the theoretically weight-averaged ones, which proves that during the biomass and coal co-firing in PC furnaces, the vaporized potassium from biomass can be efficiently captured by these silicon-aluminate oxides in coal ash. In the studied range of coal co-firing ratio (≤50 wt.%), the chlorides and sulfates of alkali metals from biomass burning are the dominating components in PM_1.0, and a certain amount of silicon is observed in PM_0.1-1. The analysis of chemical composition in PM_1.0, together with that of SO₂ emission, indicates a marginal sulfation of alkali metal chloride occurring at high temperatures in PC furnaces.     

Evaluation of the influence of biomass co-combustion on boiler furnace slagging by means of fusibility correlations

In order to show the influence of co-firing biomass with bituminous coal on ash properties, calculations of fusibility correlations have been carried out. Two Upper Silesian coals (with lower—LS and higher—HS slagging inclination) were chosen for emphasizing the influence of basic fuel. Four kinds of biomass were considered: straw, wood, dried sewage sludge and bone meal. Chemical constitutions of the mineral matter as well as the results of calculations are presented in Tables 2–5. The general conclusion is that co-firing biomass increases the fireside slagging hazard. The most difficult additional fuels are sludge and bone meal.     

生物质与煤混合燃烧成灰特性研究进展

基于能源与环境的双重压力以及生物质与煤单独燃用存在的问题,生物质与煤混燃已成为一种发展趋势.生物质与煤混燃存在的结渣积灰等问题制约着混燃技术的推广利用,因此研究生物质与煤混合燃烧的成灰特性具有现实意义.文章详细介绍了生物质与煤混合燃烧成灰特性的影响因素和分析方法,认为温度是影响生物质与煤混合燃烧成灰特性的主要因素;生物质与煤的混合比例对灰渣成分有一定影响,但二者间不存在明显的线性关系.燃料中的碱金属、氯、硫是引起结渣积灰的主要物质.由于生物质与煤的成灰特性相近,只是灰渣成分的含量差异较大,因此可以利用已有的煤结渣特性研究成果,分析混燃的成灰特性,但须要考虑生物质灰分的特征.     

掺烧稻壳对煤粉炉飞灰特性的影响

在某300MW机组煤粉锅炉上进行稻壳掺烧试验,掺烧后飞灰的性质发生变化。对掺烧后锅炉飞灰的微观形貌、化学性质和稻壳灰的孔隙结构等性质进行试验分析。发现:掺烧稻壳后飞灰的物相中出现鳞石英和方石英晶形,飞灰中稻壳灰呈现熔融后块状的不规则颗粒物和黑色的大粒径的不规则片状灰粒,SiO2的含量从掺烧前的55.93%增加到75.05%。利用压汞仪对稻壳灰的孔隙特性进行分析。稻壳和煤共燃的飞灰的利用方式需要重新评估,而分离的稻壳灰可用作多孔材料。     

基于煤质变化的燃料运行分析

煤质变化会对电厂的燃料运行造成严重的影响,进行了基于煤质变化的电厂燃料运行分析.从发热量的变化、煤中灰分的变化和煤中水分的变化等方面分析了煤质变化对燃料运行的影响,并提出了相应的应对措施.     

Jet flames of a refuse derived fuel

This paper is concerned with combustion of a refuse derived fuel in a small-scale flame. The objective is to provide a direct comparison of the RDF flame properties with properties of pulverized coal flames fired under similar boundary conditions. Measurements of temperature, gas composition (O₂, CO₂, CO, NO) and burnout have demonstrated fundamental differences between the coal flames and the RDF flames. The pulverized coals ignite in the close vicinity of the burner and most of the combustion is completed within the first 300 ms. Despite the high volatile content of the RDF, its combustion extends far into the furnace and after 1.8 s residence time only a 94% burnout has been achieved. This effect has been attributed not only to the larger particle size of fluffy RDF particles but also to differences in RDF volatiles if compared to coal volatiles. Substantial amounts of oily tars have been observed in the RDF flames even though the flame temperatures exceeded 1300 °C. The presence of these tars has enhanced the slagging propensity of RDF flames and rapidly growing deposits of high carbon content have been observed.     

Slagging behavior and mechanism of high-sodium–chlorine coal combustion in a full-scale circulating fluidized bed boiler

The contents of chlorine and sodium in Xinjiang Shaerhu (SEH) coal are extremely high, leading to severe slagging. In this paper, the slag was sampled from a circulating fluidized bed (CFB) boiler purely burning SEH coal, to analyze the slagging mechanism based on the characterization of morphology and composition. The results show a three-layer structure for the slag sampled from the buried heat-exchanger in the dense-phase zone of the CFB boiler. The inner layer close to the heat-exchanger is NaCl, which enhances the adhesion of ash particles, while the middle layer and the outer layer are mainly composed of Ca₂Al₂SiO₇ and other Si–Al materials. In comparison, the slag sampled from the refractory wall shows a molten state without a layered structure and mainly composed of NaCl, NaAlSiO₄, Ca₂Al₂SiO₇, and CaSiO₃. The effect of mixing bed material, on the ash melting and release of chlorine and sodium was further conducted, which indicates that the mixing of bed material has no significant effect on the release of chlorine(Cl) and sodium(Na) but highly affects the melting temperature and compositions. The ash fusion temperature reaches the lowest with a 50% mixing ratio of bed material, which is 120 °C lower than that of SEH coal ash. This study can provide better guidance for controlling severe slagging, from the combustion of high Na and Cl coal in industrial furnaces.     

Oxy-fuel combustion of coal and biomass, the effect on radiative and convective heat transfer and burnout

This paper focuses on results of co-firing coal and biomass under oxy-fuel combustion conditions on the RWEn 0.5 MWt Combustion Test Facility (CTF). Results are presented of radiative and convective heat transfer and burnout measurements. Two coals were fired: a South African coal and a Russian Coal under air and oxy-fuel firing conditions. The two coals were also co-fired with Shea Meal at a co-firing mass fraction of 20%. Shea Meal was also co-fired at a mass fraction of 40% and sawdust at 20% with the Russian Coal. An IFRF Aerodynamically Air Staged Burner (AASB) was used. The thermal input was maintained at 0.5 MWt for all conditions studied. The test matrix comprised of varying the Recycle Ratio (RR) between 65% and 75% and furnace exit O₂ was maintained at 3%. Carbon-in-ash samples for burnout determination were also taken.Results show that the highest peak radiative heat flux and highest flame luminosity corresponded to the lowest recycle ratio. The effect of co-firing of biomass resulted in lower radiative heat fluxes for corresponding recycle ratios. Furthermore, the highest levels of radiative heat flux corresponded to the lowest convective heat flux. Results are compared to air firing and the air equivalent radiative and convective heat fluxes are fuel type dependent. Reasons for these differences are discussed in the main text. Burnout improves with biomass co-firing under both air and oxy-fuel firing conditions and burnout is also seen to improve under oxy-fuel firing conditions compared to air.     

Co-firing potential of raw and thermally treated Phyllostachys aurea bamboo with coal

Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were used to assess the thermal behavior of raw bamboo Phyllostachys aurea (PA) and thermally treated PA under the conditions equating to torrefaction and low-temperature carbonization. The thermally treated products were blended with coal A and subjected to thermal analyses at temperatures ranging from 25 to 900°C. All samples were characterized in terms of their elemental composition (CHON and S), calorific value, and chemical structure using Fourier transform infrared spectroscopy (FTIR). The results revealed that the ignition temperature and devolatilization of the raw PA occurred earlier than coal A and the thermally treated bamboo, thus indicating higher fuel reactivity in the raw form. Raw PA was found to have a calorific value of 18.01 MJ/kg, whereas torrefied and low-temperature carbonized PA produced fuels with 20.60 and 27 MJ/kg, respectively. The thermal profiles of the thermally treated samples, when blended with coal, provided an insight into the co-firing compatibility of the fuels.