不同煤燃烧方式降低NOx排放比较及解耦燃烧应用

采用两段反应器研究了三种煤在不同燃烧方式下抑制NO_x生成的效果。结果表明,煤的热解气和部分气化生成气再燃均能较好的抑制NO_x生成,抑制效果优于空气分级燃烧,解耦燃烧方式抑制NO_x生成的效果最显著,相对于传统燃烧其NO_x排放降低了32%以上。煤种对各种燃烧方式降低NO_x的程度有明显影响,煤中单位氮含量的燃料比(固定碳/挥发分)越小,煤的热解气和部分气化生成气再燃以及解耦燃烧方式下NO_x的排放量越低。在煤部分气化生成气再燃烧方式中,部分氧化气化段通氧量不同,降低NO_x排放的效果也不同,在氧气体积分数为8%~10%时的NO_x生成量最低。基于解耦燃烧技术原理,研制了1.4 MW解耦燃烧工业锅炉,在燃烧同一煤种时,解耦燃烧锅炉和传统立式锅炉相比,烟气中NO_x排放量降低了32.9%。     

Gasification of Powdered Solid Fuel in the Filtration Combustion Mode

A new procedure for gasification of powdered solid fuel in a flow of a gaseous oxidant in the course of filtration of the mixture through an inert packing was suggested and tested. This procedure allows the productive capacity of a single reactor to be increased owing to acceleration of the reactions, i.e., to an increase in the reaction surface area with a decrease in the fuel particle size. As shown in cold (without ignition) experiments, the powdered fuel was partially accumulated in the inert porous packing, which led to the pressure buildup in the reactor. In gasification experiments with ignition, the powdered fuel was not accumulated in the reactor if the temperature in the fuel feeding zone was no less than 500°С. In this case, the linear velocity of the gas increased owing to thermal expansion, and this velocity was sufficient for the coal particles fed to the reactor to be entrained by the flow.     

基于镍基修饰的铁矿石载氧体煤化学链燃烧实验

使用1 kW_th串行流化床反应器,研究了以铁矿石为载氧体以及对铁矿石进行镍基修饰情况下煤化学链燃烧特性,对两种修饰方法(机械混合和浸渍)进行了对比评价。结果表明,铁矿石载氧体具有良好的反应性能和稳定性,是实现煤化学链燃烧的一种比较理想的载氧体。向矿石中机械添加少量NiO/Al₂O₃载氧体,能够有效改善其反应活性,提高系统CO₂捕集率;采用浸渍法修饰的铁矿石载氧体煅烧后,总体微观孔隙结构变差,导致煤气化产物与载氧体间的反应无法充分进行,系统CO₂捕集率显著下降。浸渍修饰的方法和过程需要进一步的研究和改善。     

Gasification of Municipal Solid Wastes in Plasma Arc Medium

Many thermal processes have been developed in order to eliminate the municipal solid wastes or produce energy from them. These processes include a wide range of applications from the simplest burning system to plasma gasification. Plasma gasification is based on re-forming of molecules after all molecules convert to smaller molecules or atoms at high temperatures. In this work, the production of fuel gas is aimed by plasma gasification of municipal solid wastes in high temperatures. Because of this, a plasma reactor of the capacity of 10 kg h^?1 was designed which can gasify municipal solid wastes. Plasma gasification with and without steam and oxygen was performed in temperatures of 600, 800, 1000, 1200, 1400 and 1600 °C in the reactor. A gas mixture containing methane, ethane, hydrogen, carbon dioxide and monoxide, whose content varies with temperature, was obtained. It was found that plasma gasification (or plasma pyrolysis, PG), plasma gasification with oxygen (PGO) and plasma gasification with steam (PGS) were more prone to CO formation. A gas product which was consisted of 95% CO between 1200 and 1400 °C was produced. It was observed that a gas with high energy capacity may be produced by feeding oxygen and steam into the entrance of the high temperature region of the reactor.

     

不同反应气氛下准东高钠煤中钠的迁移转化与积灰特性

为了获得循环流化床工艺下不同反应气氛对准东高钠煤中钠的迁移转化与积灰特性的影响,在0.4t/d循环流化床实验装置上开展了相同床温(950℃)下的新疆沙尔湖高钠煤的气化(还原性气氛)与燃烧(氧化性气氛)实验研究。结果表明,气化和燃烧气氛下飞灰与积灰中Na主要以NaCl的形式存在;气化比燃烧更容易将Na、Cl固留在底渣和飞灰中,相应的进入气相中的Na、Cl更少;燃烧气氛下,部分NaCl会被烟气中的SO_2硫化,生成稳定性更高的Na_2SO_4并冷凝在飞灰和积灰棒表面,燃烧过程中产生的飞灰粒径更细,积灰更严重;沙尔湖煤燃烧与气化过程中存在HCl对金属壁面的腐蚀。     

Natural iron ore as an oxygen carrier for biomass chemical looping gasification in a fluidized bed reactor

Chemical looping gasification (CLG) of biomass was performed in a thermogravimetric analyzer (TG) reactor together with a fluidized reactor with natural iron ore oxygen carrier under inert atmosphere. TG experiments indicated that iron ore can provide oxygen source for biomass conversion in the form of lattice oxygen. In the fluidized bed experiments, the influences of reduction temperature on CLG of biomass were emphatically investigated in terms of gas distribution and solid characters. The gas yield and carbon conversion increased, but the tar content decreased in the temperature range of 1,013–1,213 K. In this temperature range, the conversion of oxygen carrier increased from 24.11 to 53.59 %. X-ray diffraction analysis shows that more FeO was generated with temperature increasing. Scanning electron microscope analysis indicates that sintering was observed at elevated temperature. An optimum mass ratio of biomass/oxygen carrier (B/O) of 0.67 was obtained with aim of achieving maximum gasification efficiency of 76.93 %.     

循环流化床(CFB)煤/焦气化反应的研究Ⅱ.温度、氧含量及煤种对CFB气化反应的影响

报道了两种煤／焦（西山焦煤飞灰、神木煤），在小型循环流化床（ＣＦＢ）气化反应装置上，以二氧化碳及氧气混合物为气化介质，在不同条件（９００～９７０°Ｃ，０～３０％氧含量）下的气化反应的研究。结果表明，提高气化温度，气化反应速度提高，尾气中可燃气体浓度（ＣＯ，Ｈ２，ＣＨ４）、碳转化率及气化效率明显提高。气化介质中的氧含量增加，ＣＯ浓度、碳转化率及气化强度明显增加。反应性高、挥发分多的煤种更适合在ＣＦＢ气化反应装置上进行气化反应。     

Plasma-Assisted Treatment of Municipal Solid Waste: A Scenario Analysis

Small-scale thermal treatment of municipal solid waste (MSW) was investigated using mass and energy balances based on the assumption of thermodynamic equilibrium. A typical average MSW composition from the literature was used as basis for modelling of a one ton per day waste gasification facility (plant). Syngas production by pyrolysis, stoichiometric O₂ addition and auto-thermal (gasification with oxygen and/or air where no external heat input is required) combustion were considered. These cases were evaluated for production of electricity only, and steam. From purely thermodynamic considerations, it was observed that auto-thermal oxygen gasification produces the most electricity (47.00 kWe) and oxygen plasma gasification produces a positive net amount (4.07 kWe) on a 1 ton per day scale. Although auto-thermal air gasification also produces a net positive amount, the calorific value of the syngas is too low to fuel an internal combustion engine. As expected, the amount of steam generated by the different scenarios is high due to higher process efficiencies. The close-coupled auto-thermal oxygen process proved to be the most efficient. The cost of additional oxygen generation was however not taken into account, and may change the picture significantly.     

Chemical-looping gasification of biomass in a 10 kW_(th) interconnected fluidized bed reactor using Fe_2O_3/Al_2O_3 oxygen carrier

Abstract:The aim of this research is to design and operate a 10 kW hot chemical-looping gasification(CLG)unit using Fe2O3/Al2O3as an oxygen carrier and saw dust as a fuel.The effect of the operation temperature on gas composition in the air reactor and the fuel reactor,and the carbon conversion of biomass to CO2and CO in the fuel reactor have been experimentally studied.A total60 h run has been obtained with the same batch of oxygen carrier of iron oxide supported with alumina.The results show that CO and H2concentrations are increased with increasing temperature in the fuel reactor.It is also found that with increasing fuel reactor temperature,both the amount of residual char in the fuel reactor and CO2concentration of the exit gas from the air reactor are degreased.Carbon conversion rate and gasification efficiency are increased by increasing temperature and H2production at 870℃reaches the highest rate.Scanning electron microscopy(SEM),X-ray diffraction(XRD)and BET-surface area tests have been used to characterize fresh and reacted oxygen carrier particles.The results display that the oxygen carrier activity is not declined and the specific surface area of the oxygen carrier particles is not decreased significantly.     

Pyrolysis of used automobile tires and residual char utilization

In the present study the rubber portion of used car tires was transformed by atmospheric pyrolysis into oil, gas and char. The experiments have been performed in a captive sample reactor at atmospheric pressure, under helium atmosphere. The effect of temperature on the products yield was investigated. In a second step, alternative uses of pyrolysis char such as combustion, gasification and active carbons preparation were examined, in order to produce fuels and high added value materials. First, pyrolysis char was burned and its reactivity was measured in function with pyrolysis temperature. Second, char was gasified with Steam and CO₂ to produce fuel gases, in a tubular stainless steel reactor. It was also activated to produce high added value materials. It was shown that tire chars present higher reactivity with steam than with CO₂ and also active carbons produced from tire chars possess surface areas, comparable with those of commercially available active carbons.     

生物质在流化床中的空气-水蒸气气化研究

以流化床为反应器，对生物质的空气-水蒸气气化特性进行了研究。考察了一些主要参变量，如温度 (700 ℃～900 ℃)、水蒸气/生物质比(0～4.04)、空气当量比(0.19～0.27)以及生物质粒度(0.2 mm～0.9 mm)等对气化结果的影响。在实验研究的条件范围内，生物质产气率在1.43 m3/kg～2.57 m3/kg范围内变化，产气的低热值在6 741 kJ/m3～9 143 kJ/m3范围内变化。实验结果表明：较高的气化温度有利于氢的产生；但气化温度过高会使气体热值下降；与常规的空气气化相比，水蒸气的加入使生物质气化产气率显著提高，但水蒸气加入量过多使气化温度下降，产气率和产气热值降低；生物质颗粒粒度的大小对产气组分的分布和产气率均有影响，较小颗粒的生物质会产生较多的CH4、CO和较少的CO2。     

Development of two-dimensional gas chromatography/isotope ratio mass spectrometry for the stable carbon isotopic analysis of C(2)-C(5) non-methane hydrocarbons emitted from biomass burning

A two-dimensional gas chromatography/combustion/isotope ratio mass spectrometry (2D-GC/C/IRMS) system was developed for stable carbon isotopic measurements of C(2)-C(5) non-methane hydrocarbons (NMHCs) in biomass burning smoke. The 2D-GC/C/IRMS system successfully improved the accuracy and precision for the measurements of C(4) and C(5) saturated compounds in a smoke sample by selective injection of target compounds into a combustion furnace and consequently allowed us to provide complete baseline separation for all individual NMHCs. The analytical precision of the delta(13)C of each compound was better than 0.5 per thousand for more than 500 pmolC injections and 2.1 per thousand for 30 pmolC injections, which was estimated from replicate analysis of standard gases. This system was applied to the analysis of NMHCs in smoke samples collected from laboratory biomass burning experiments. From the combustion of three fuel materials (rice straw, pine wood, and maize), we found that the isotopic fractionation between fuel material and individual NMHCs is almost independent of the fuel material and thus the delta(13)C values of the fuel materials are reflected in delta(13)C values of most of NMHCs. However, only i-butane emitted from maize combustion showed anomalous (13)C-depletion of -11.6 per thousand relative to the delta(13)C value of maize. Such a large (13)C depletion suggests the specific isotopic fractionation process which is attributed to the maize combustion itself or the chemical properties of i-butane during production from a radical recombination reaction.     

氯对苯氧化过程影响机制的实验研究

针对高含氯垃圾气化-燃烧工艺中焦油的氧化裂解过程,利用均相管流反应器配合傅里叶红外光谱仪,以C_6H_6为焦油模型化合物,对比研究了氯参与前后,裂解产物组成和氧化完全程度随温度和当量比的变化,探索了氯对C_6H_6氧化裂解过程的影响机制。结果表明,低温下氯对C_6H_6的氧化有明显的激发作用,但由于氯对OH的消耗,对裂解产物进一步转化为完全氧化产物CO_2又存在抑制作用。此外,在高温低当量比条件下氯对聚合反应也有促进作用。因此,在工程应用中,高含氯垃圾气化产物的燃烧可适应更低的温度,但应避免高温低当量比反应环境的形成以避免聚合产物。此外,还应控制垃圾原料中的氯元素比例,以保障氧化反应的充分进行。     

Experimental and kinetic investigation of the pyrolysis,combustion, and gasification of deoiled asphalt

The pyrolysis, combustion, and gasification behaviors of deoiled asphalt were studied by a thermogravimetric analyzer and the kinetics were also analyzed using a multi-stage first-order integral model. All the experiments were conducted at non-isothermal conditions with heating rates range of 10–40 K min^?1 under N₂ (pyrolysis), air (combustion), or CO₂ (gasification) atmosphere, respectively. The results showed that, for pyrolysis, the reaction mainly occurred between 498 and 798 K and could be divided into two stages: the first was caused by the volatilization of small molecules and the second probably due to the cracking reactions. For combustion, the mass loss process could be divided into three stages: the devolatilization and oxidation first, the ignition and combustion of the volatiles second, and finally the combustion of the formed char. Under CO₂ atmosphere, the mass loss behavior was similar with that of the N₂ atmosphere at lower temperatures, but when the temperature was higher than 1,233 K, the gasification reaction obviously happened. The results of kinetic investigation showed that the multi-stage first-order integral method agreed well with the above experiments.     

污泥水分含量对其空气气化特性的影响(英文)

利用外热式下吸固定床气化实验装置,研究了在一定的空气流量(0.05 m3/h)、气化温度(800℃)下污泥水分含量对3种不同性质污泥空气气化特性的影响。结果表明,气化气中CO2、CH4和H2含量、气化气热值以及水相生成量均随污泥水分含量的增加而增加,而CO含量和焦油生成量呈降低趋势。污泥厌氧消化使气化气中CO、CH4、H2、CmHn含量以及气化气品质降低;而污水处理工艺中的厌氧过程可改善气化气品质,其中来自A2/O工艺消化污泥的气化气品质高于普通活性污泥法消化污泥的气化气品质。随着污泥水分含量的增加,2种不同污水处理工艺产生的消化污泥气化气中CO、CO2和H2含量的差距逐渐加大,来自于同一A2/O工艺的消化与未消化污泥气化气中H2和CO2含量的差距亦逐渐加大,而消化与未消化污泥气化气中CO含量的差距则逐渐接近。     

Integration of biomass drying with combustion/gasification technologies and minimization of emissions of organic compounds

Moisture content (MC) of green biomass or raw biomass materials (wood, bark, plants, etc.) commonly exceeds 50 mass % (wet basis). The maximum possible MC of biomass fuel for big scale combustion (e.g. fluidized bed combustion with low external heat losses) is approximately 60–65 mass %. Higher biomass MC generally causes operational problems of biomass combustors, lower stability of burning and higher CO and VOC emissions. Gasification of biomass with higher MC produces fuel gas of lower effective heating values and higher tar concentrations. In this review, various technological schemes for wood drying in combination with combustion/gasification with the assessment of factors for possible minimization of emissions of organics from the drying processes are compared. The simple direct flue gas biomass drying technologies lead to exhaust drying gases containing high VOC emissions (terpenes, alcohols, organic acids, etc.). VOC emissions depend on the drying temperature, residence time and final MC of the dried biomass. Indirect biomass drying has an advantage in the possibility of reaching very low emissions of organic compounds from the drying process. Exhaust drying gases can be simply destroyed as a part of the total combustion air (gas) in a combustion chamber or a gasifier. Liquid, condensed effluents have to be treated properly because they have relatively high content of organic compounds, some of them accompanied by odor. Drying of biomass with superheated steam offers more uniform drying of both small and bigger particles and shorter periods of higher temperatures of the dried biomass, particularly if drying to the final MC below 15 mass % is required. In practical modern drying technologies, biomass (mainly wood) is dried in recirculated gas of relatively high humidity (approaching saturation) and the period of constant rate drying is longer. Drying of moist wood material (saw dust, chips, etc.) is required in wood pellet production. Emissions of organics in drying depend on biomass properties, content of resins, storing time and on operational aspects of the drying process: drying temperature, drying medium, final MC, residence time, and particle size distribution of the dried biomass (wood). Integration of biomass drying with combustion/gasification processes includes the choice of the drying medium (flue gas, air, superheated steam). Properties of the drying media and operational parameters are strongly dependent on local conditions, fuel input of the combustion/gasification unit, cleaning of the exhaust drying media (gas, steam, wastewater), and on environmental factors and requirements.     

Plasma Assisted Low Temperature Combustion

This paper presents recent kinetic and flame studies in plasma assisted low temperature combustion. First, the kinetic pathways of plasma chemistry to enhance low temperature fuel oxidation are discussed. The impacts of plasma chemistry on fuel oxidation pathways at low temperature conditions, substantially enhancing ignition and flame stabilization, are analyzed base on the ignition and extinction S-curve. Secondly, plasma assisted low temperature ignition, direct ignition to flame transition, diffusion cool flames, and premixed cool flames are demonstrated experimentally by using dimethyl ether and n-heptane as fuels. The results show that non-equilibrium plasma is an effective way to accelerate low temperature ignition and fuel oxidation, thus enabling the establishment of stable cool flames at atmospheric pressure. Finally, the experiments from both a non-equilibrium plasma reactor and a photolysis reactor are discussed, in which the direct measurements of intermediate species during the low temperature oxidations of methane/methanol and ethylene are performed, allowing the investigation of modified kinetic pathways by plasma-combustion chemistry interactions. Finally, the validity of kinetic mechanisms for plasma assisted low temperature combustion is investigated. Technical challenges for future research in plasma assisted low temperature combustion are then summarized.     

Sewage sludge ash as an alternative low-cost oxygen carrier for chemical looping combustion

In this paper, novel low-cost oxygen carriers containing Fe₂O₃ are evaluated for use in chemical looping combustion. Sewage sludge ashes and reference samples were prepared and used in cyclic reduction and oxidation experiments in a thermogravimetric analyzer (TG). A gaseous (3 % H₂) fuel and a solid fuel (hard coal) were tested. Three-cycle CLC tests were carried out in the 600–800 °C temperature range and long-term testing was performed at 950 °C. A reactivity study showed that the natural sewage sludge ash sample was stable during the cycling TG tests when hydrogen was used as a fuel at all of the temperatures investigated. Strong temperature effects on the oxygen transport capacity were observed. An one-cycle test at 900 °C showed also that the sewage sludge ash successfully reacted with coal. The oxygen released was fully used for coal combustion, with appreciable reaction rate at temperature of ~750–800 °C, that is significantly lower than that obtained for pure Fe₂O₃-based oxygen carrier. The oxidation reaction was much faster than the reduction reaction. Moreover, the sewage sludge ash showed a low tendency toward agglomeration in the cyclic test, which was superior to the behavior of synthetic materials. The sewage sludge ash exhibited also high mechanical strength, an attrition index of 1 % and a high-temperature resistance of 1,170 °C in a reducing atmosphere. We conclude that sewage sludge ash can be effectively used as a low-cost, valuable oxygen carrier in practical application in chemical looping combustion technology for power generation.     

Numerical Modelling of Wood Gasification in Thermal Plasma Reactor

Biomass gasification for synthesis gas production represents a promising source of energy based on plasma treatment of renewable fuel resources. Gasification/pyrolysis of crushed wood as a model substance of biomass has been experimentally carried out in the plasma-chemical reactor equipped with gas–water stabilized torch which offer advantage of low plasma mass-flow, high enthalpy and temperature making it possible to attain an optimal conversion ratio with respect to synthesis gas production in comparison with other types of plasma torches. To investigate this process of gasification in detail with possible impact on performance, a numerical model has been created using ANSYS FLUENT program package. The aim of the work presented is to create a parametric study of biomass gasification based on various diameters of wooden particles. Results for molar fractions of CO for three different particles diameters obtained by the modeling (0.55, 0.52 and 0.48) at the exit are relatively good approximation to the corresponding experimental value (0.60). The numerical results reveal that the efficiency of gasification and syngas production slightly decreases with increasing diameter of the particles. Computed temperature inhomogeneities in the volume of the reactor are strongest for the largest particle diameter and decrease with decreasing size of the particles.     

Pulsed Corona Discharges for Tar Removal from Biomass Derived Fuel Gas

To supply combustion engines or gasturbines with fuel gas obtained from biomass gasification, it is necessary to clean the fuel gas. Also the production of chemicals by processes such as Fisher-Tropsch requires a high gas quality. Especially heavy aromatic hydrocarbons (tars) must be removed. In this work, we give an overview of our investigations on tar removal by pulsed corona discharges as an alternative approach to catalytic or thermal tar cracking. Experimental results (at a gas temperature of 200°C) are reported for the removal of various model tar components in synthetic fuel gas. In order to identify the major reaction pathways, experiments were also done on tars in individual fuel gas components. The results show that tar removal by pulsed corona processing is possible. The process for tar removal is mainly via oxidation. Also termination reactions by CO play an important role.