Investigation of oxy-fuel combustion for methane and acid gas in a diffusion flame

Co-combustion of methane(CH4)and acid gas(AG)is required to sustain the temperature in Claus reaction furnace.In this study,oxy-fuel combustion of methane and acid gas has been experimentally studied in a diffusion flame.Three equivalence ratios(ER=1.0,1.5,2.0)and CH_(4)-addition ratios(CH_(4)/AG=0.3,0.5,0.7)were examined and the flame was interpreted by analyzing the distributions of the temperature and species concentration along central axial.CH_(4)-AG diffusion flame could be classified into three sections namely initial reaction,oxidation and complex reaction sections.Competitive oxidation of CH_(4)and H_(2)S was noted in the first section wherein H_(2)S was preferred and both were mainly proceeding decomposition and partial oxidation.SO_(2)was formed at oxidation section together with obvious presence of H2 and CO.However,H2 and CO were inclined to be sustained under fuel rich condition in the complex reaction section.Reducing ER and increasing CH4/AG contributed to higher temperature,H_(2)S and CH_(4)oxidation and CO_(2)reactivity.Hence a growing trend for CH_(4)and AG to convert into H_(2),CO and SO_(2)could be witnessed.And this factor enhanced the generation of CS2 and COS in the flame inner core by interactions of CH4 and CO_(2)with sulfur species.COS was formed through the interactions of CO and CO_(2)with sulfur species.The CS_(2)production directly relied on reaction of CH_(4)with sulfur species.The concentration of COS was greater than CS_(2)since CS_(2)was probably inhibited due to the presence of H_(2).COS and CS_(2)could be consumed by further oxidation or other complex reactions.

The regulation of ferrocene-based catalysts on heat transfer in highpressure combustion of ammonium perchlorate/hydroxyl-terminated polybutadiene/aluminum composite propellants

The regulation of the burning rate pressure exponent for the ammonium perchlorate/hydroxylterminated polybutadiene/aluminum(AP/HTPB/Al)composite propellants under high pressures is a crucial step for its application in high-pressure solid rocket motors.In this work,the combustion characteristics of AP/HTPB/Al composite propellants containing ferrocene-based catalysts were investigated,including the burning rate,thermal behavior,the local heat transfer,and temperature profile in the range of 7-28 MPa.The results showed that the exponent breaks were still observed in the propellants after the addition of positive catalysts(Ce-Fc-MOF),the burning rate inhibitor((Ferrocenylmethyl)trimethylammonium bromide,Fc Br)and the mixture of Fc Br/catocene(GFP).However,the characteristic pressure has increased,and the exponent decreased from 1.14 to 0.66,0.55,and 0.48 when the addition of Ce-FcMOF,Fc Br and Fc Br/GFP in the propellants.In addition,the temperature in the first decomposition stage was increased by 7.50℃ and 11.40℃ for the AP/Fc Br mixture and the AP/Fc Br/GFP mixture,respectively,compared to the pure AP.On the other hand,the temperature in the second decomposition stage decreased by 48.30℃ and 81.70℃ for AP/Fc Br and AP/Fc Br/GFP mixtures,respectively.It was also found that Fc Br might generate ammonia to cover the AP surface.In this case,a reaction between the methyl in Fc Br and perchloric acid caused more ammonia to appear at the AP surface,resulting in the suppression of ammonia desorption.In addition,the coarse AP particles on the quenched surface were of a concave shape relative to the binder matrix under low and high pressures when the catalysts were added.In the process,the decline at the AP/HTPB interface was only exhibited in the propellant with the addition of Ce-Fc-MOF.The ratio of the gas-phase temperature gradient of the propellants containing catalysts was reduced significantly below and above the characteristic pressure,rather than 3.6 times of the difference in the blank propellant.Overall,the obtained results demonstrated that the pressure exponent could be effectively regulated and controlled by adjusting the propellant local heat and mass transfer under high and low pressures.

Effect of carbon dioxide on oxy-fuel combustion of hydrogen sulfide:An experimental and kinetic modeling

CO_(2) is an important component in the acid gas and it is necessary to study the effect of CO_(2) presence on the oxy-fuel combustion of H_(2)S with particular focus on the formation of carbonyl sulfide(COS).The oxyfuel combustion of acid gas was conducted in a coaxial jet double channel burner.The distribution of flame temperature and products under stoichiometric condition along axial(R=0.0)and radial at about 3.0 mm(R=0.75)were analyzed,respectively.The Chemkin-Pro software was used to analyze the rate of production(ROP)for gas products and the reaction pathway of acid gas combustion.Both experimental and simulation results showed that acid gas combustion experienced the H2S chemical decomposition,H_(2)S oxidation and accompanied by H_(2) oxidation.The CO_(2) presence reduced the peak flame temperature and triggered the formation of COS in the flame area.COS formation at R=0.0 was mainly through the reaction of CO_(2) and CO with sulfur species,whereas at R=0.75 it was through the reaction of CO with sulfur species.The ROP results indicated that H_(2) was mainly from H_(2)O decomposition in the H_(2)S oxidation stage,and COS was formed by the reaction of CO_(2) with H_(2)S.ROP and other detailed analysis further revealed the role of H,OH and SH radicals in each stage of H_(2)S conversion.This study revealed the COS formation mechanisms with CO_(2) presence in the oxy-fuel combustion of H_(2)S and could offer important insights for pollutant control.

Gas-phase oxidation of NO at high pressure relevant to sour gas compression purification process for oxy-fuel combustion flue gas

The removal of NO from oxy-fuel combustion is typically incorporated in sour gas compression purification process. This process involves the oxidation of NO to NO2 at a high pressure of 1–3 MPa, followed by absorption of NO2 by water. In this pressure range, the NO conversion rates calculated using the existing kinetic constants are often higher than those obtained experimentally. This study aimed to achieve the regression of kinetic parameters of NO oxidation based on the existing experimental results and theoretical models.Based on three existing NO oxidation mechanisms, first, the expressions for NO conversion against residence time were derived. By minimizing the mean-square errors of NO conversion ratio, the optimum kinetic rate constants were obtained. Without considering the reverse reaction for NO oxidation, similar mean-square errors for NO conversion ratio were calculated. Considering the reverse reaction for NO oxidation based on the termolecular reaction mechanism, the minimum mean-square error for NO conversion ratio was obtained. Thus, the optimum NO oxidation rate in the pressure range 0.1–3 MPa can be expressed as follows:-d[NO]/dt=d[NO2]/dt=0.0026[NO]2[O2]-0.0034[NO2]2 Detailed elementary reactions for N2/NO/NO2/O2 system were established to simulate the NO oxidation rate. A sensitivity analysis showed that the critical elementary reaction is 2 NO + O2? 2 NO2. However, the simulated NO conversions at a high pressure of 10–30 bar are still higher than the experimental values and similar to those obtained from the models without considering the reverse reaction for NO oxidation.

Study on the emission characteristics of nitrogen oxides with coal combustion in pressurized fluidized bed

Nitrogen oxides are one of the most significant pollution sources during coal combustion. This experimental study was conducted in a 15 kWth lab-scale pressurized fluidized bed (inner diameter = 81-100 mm, H = 2100 mm) firing with bituminous coals. The effects of operating parameters, including bed temperature (800℃-900℃), operating pressure (0.1-0.4 MPa), excess air level (16%-30%) and flow pattern on NOX and N2O emissions were systematically studied during the tests. During each test the interaction effects of all the operating parameters were properly controlled. The results show that most operating parameters have an opposite effect on NOX and N2O emissions, and the N2O emissions mainly depend on the bed temperature. Increasing the operating pressure can significantly suppress the fuel-N conversion to NOX but enhance its conversion to N2O. With the rise of the excess air level and fluidization number, NOX emissions grow distinctly while N2O emissions remain almost unchanged. Total nitrogen oxide emissions increase with the bed temperature while decrease with the operating pressure.

Heat Transfer Characteristics of Boiler Convective Heating Surface Under Pressurized Oxygen-fuel Combustion Conditions

增压富氧燃烧是一项极具前景的减排CO2新技术。对增压富氧燃烧条件下,对流受热面换热特性进行研究具有重要的意义。该文以一台实际300MW等级机组煤粉锅炉为计算对象,采用维里方程及Chun等的计算方法计算确定增压富氧燃烧烟气物性,采用宽带关联k模型计算富氧燃烧烟气辐射特性。进行了常规空气燃烧以及φ（O2）：φ（CO2）=21：79、φ（O2）：φ（CO2）=30：70两种比例的0.1、0.5、1.0、1.5、6 MPa五种压力下增压富氧燃烧各对流受热面的热力计算,分析了增压富氧燃烧条件烟气压力变化对各受热面换热特性的影响。研究结果表明：随烟气压力的升高,烟气流速下降,但烟气的Re却基本保持不变,对流换热系数有所增加。增压富氧燃烧烟气的辐射换热系数比空气燃烧烟气辐射换热系数大。实现同样的换热量,增压富氧燃烧条件下（φ（O2）：φ（CO2）=21：79、φ（O2）：φ（CO2）=30：70）对流受热面所需换热面积比常规空气燃烧条件下少。

EXPERIMENTAL INVESTIGATIONS ON PRESSURIZED FLUIDIZED BED COMBUSTION(PFBC)FOR HIGH ASH COAL

The first phase of the experimental investigation in our institute on pressur-ized fluidized bed combustion(PFBC)technology is introduced,and the results of fivetests are presented.The combustion efficiencies were as high as 97% 98% when high ashcontent coal was burnt in PFBC,and the sulphur retention efficiencics were 80%-85%with the Ca/S mole ratios between 1.5-1.8.The particulate content in flue gas at the out-let of high temperature gas clean-up system was 189mg/m^3(normalized).The average di-ameter of particles was 2.5-3μm and the weight fraction of particles with diameter largerthan 10μm was not greater than 3%.

Transformation of alkali and alkaline-earth metals during coal oxy-fuel combustion in the presence of SO_2 and H_2O

The occurrence modes of alkali and alkaline-earth metals（AAEMs） in coal relate to their release behavior and ash formation during combustion. To better understand the transformation of AAEMs,the release behavior of water-soluble,HCl-soluble,HCl-insoluble AAEMs during Shenmu coal（SM coal） oxy-fuel combustion in the presence of SO2 and H2O in a drop-tube reactor was investigated through serial dissolution using H2O and HCl solutions. The results show that the release rates of AAEMs increase with an increase in temperature under the three atmospheres studied. The high release rates of Mg and Ca from SM coal are dependent on the high content of soluble Mg and Ca in SM coal. SO2 inhibits the release rates of AAEMs,while H2O promotes them. The effects of SO2 and H2O on the Na and K species are more evident than those on Mg and Ca species. All three types of AAEMs in coal can volatilize in the gas phase during coal combustion. The W-type AAEMs release excessively,whereas the release rates of I-type AAEMs are relatively lower. Different types of AAEM may interconvert through different pathways under certain conditions. Both SO2 and H2O promote the transformation reactions. The effect of SO2 was related to sulfate formation and the promotion by H2O occurs because of a decrease in the melting point of the solid as well as the reaction of H2O.

Riemann problem of a Chapman-Jouguet combustion model for pressure-gradient system

In this paper,the Riemann problem of a Chapman-Jouguet combustion model for the pressure-gradient equations is considered.By analyzing in phase space,existence and uniqueness of the solution to the Riemann problem are obtained constructively under the global entropy conditions.

Microstructure and Performances of Glasses Melt under Oxy-fuel Combustion

We prepared a series of glass samples under the different simulated atmosphere.Systematic evaluation about the performances of the glasses fabricated under the different simulated atmosphere indicates that the increase of the H2O：CO2 ratio under the simulated atmosphere will decrease the softening point temperature,microhardness,viscosity,and chemical resistance,while increase the thermal expansion coefficient.Through the analysis of the hydroxyl content and network structure according to the IR transmitting spectra and NMR spectra,the structural origin of the evolution of the performances for the samples fabricated under different simulated atmosphere was elucidated.According to the feedback information from the customers,despite the decrease of some performances,the glass produced under oxy-fuel combustion can also fulfill the requirements of the engineering applications.Therefore,the technique of oxy-fuel combustion is worthy to be promoted in glass industry.

Effect of Atmosphere on Volatile Emission Characteristic in Oxy-Fuel Combustion

A new type of power supply which was called oxy-fuel combustion power plant was introduced to reduce greenhouse gasses emission. In this paper the volatile emission characteristic of pulverized coal is studied under air atmosphere and oxy-fuel atmosphere. Combustion experiments of Datong bituminous coal were carried out in a wire mesh reactor at heating rates of 1 K/s, 10 K/s and 1000 K/s respectively under air and O2/CO2 atmosphere conditions in order to investigate the volatile emission characteristic. The concentrations of volatile (mainly CO and CH4) emission were on-line measured by infrared gas analyzer. It was indicated that the concentrations of CO and CH4 in O2/CO2 atmosphere were higher than those in air. The direct oxidation of carbon and gasification reaction between carbon and CO2 are the main causes of the increased amount of CO. The higher concentration of CO2 also results in the increased amount of CH4 in O2/CO2 conditions.

COMPUTER SIMULATION OF VENTILATION PRESSURE BALANCING FOR THE PREVENTION OF SPONTANEOUS COMBUSTION IN MINES

Qualitative analysis plus trial and error method are still the routine to achieve ventilation pressure balancing. These methods may cause large errors in pressure balancing so that sometimes the spontaneous combustion can not be extinguished effectively. This paper introduces a quantitative analysis of pressure balancing for different causes of ventilation networks and develops a computer program (SPFPB) specifically written for pressure balancing between faces and connected gobs. It allows a user to choose different metheds to meet his various needs and the underground conditions. The different balancing results are compared, and the proper locations and sizes of the control devices are recommended.

Experimental and Modelling Study on Emission of Volatile Nitrogen Derived NO during Pressured Oxy-fuel Combustion under Wet Flue Gas Environment

Pressurised oxy-fuel combustion(POFC)is a clean and efficient combustion technology with great potential.Due to the recycling of flue gas,the concentration of steam in the flue gas is higher than that of conventional combustion,which enriches the free radical pool in the flue gas and thus affects the emission of gaseous pollutants.Therefore,further research into the effect of high steam concentrations on NO_(x)emission mechanisms in POFC is necessary.In this work,a fixed-bed reactor was used to conduct combustion experiments of volatiles and combined with chemical kinetic models to study the NO release characteristics for different pressures and steam concentrations in an O_(2)/CO_(2)atmosphere at 800℃/900℃temperature.The results of the study indicated that the volatile nitrogen comes from the pyrolysis of part of pyrrole,pyridine,and all quaternary nitrogen in coal.The increase in temperature promoted the formation of NO during combustion.Higher pressure affects the main reaction pathway for NO formation,promoting NO consumption by HCCO and C_(2)O groups while enhancing the overall NO reduction.Steam promoted NO consumption by NCO.In addition,steam increased the amount of H/OH groups during the reaction,which affected both NO formation and consumption.However,from the overall effect,the steam still inhibits the emission of NO.

Method for prevention and control of spontaneous combustion of coal seam and its application in mining field

Spontaneous combustion of coal seam has been and continues to be a big problem in coal mines. It could pose great threat to the safety of the whole mine and all miners, especially when it occurs in or nearby coal mines. Besides, environment of area surrounded mines during combustion can be threatened where large amount of toxic gases including CO_2, CO, SO_2 and H_2S can be leased by fire in mine. Hence, it is important and significant for scholars to study the controlling and preventing of the coal seam fire. In this paper, the complicated reasons for the occurrence and development of spontaneous combustion in coal seam are analysed and different models under various air leakage situations are built as well. Based on the model and approximately calculation, the difficulty of fire extinguishment in coal seam is pointed out as the difficulty and poor effect to remove the large amount of heat released. Detailed measurements about backfilling and case analyses are also provided on the basis of the recent ten years' practice of controlling spontaneous combustion in coal seams in China. A technical fire prevention and control method has been concluded as five steps including detection, prevention, sealing, injection and pressure adjustment. However, various backfill materials require different application and environmental factors, so in this paper, analyses and discussion about the effect and engineering application of prevention of spontaneous combustion are provided according to different backfilling technologies and methods. Once the aforementioned fire prevention can be widely applied and regulated in mines, green mining will be achievable concerning mine fire prevention and control.

Application of ventilation simulation to spontaneous combustion control in underground coal mine:A case study from Bulianta colliery

Spontaneous combustion of residual coal in longwall goaf is a long standing hazard. Airflow leakage into goaf is a major driver to the hazard and this issue deteriorates where longwalls are operating in multiple seams and shallow covers because mining-induced cracks are very likely to draw fresh airflow into goaf due to presence of pressure differential between longwall face and surface. To study the problem more critically, a ventilation simulation package ‘‘Ventsim" is used to conduct a case study from Bulianta colliery. It was found that isolating and pressurizing active longwall panel can mitigate the problem and the pressure differential can be adjusted by varying performance of auxiliary fan and resistance of ventilation regulator. A booster ventilation system can also mitigate the problem by adjusting fan duties. Ventilation simulation is a powerful tool to study spontaneous combustion control in underground coal mine.

On the Use of Accurate Ignition and Combustion Models in Internal Ballistics Gun Codes

The desire for increased performance from guns is driving the charge designer towards charges that present challenges to numerical modelling.There is a pressing need for accurate,validated ignition and combustion models that can be used to predict the performance of advanced charges and ensure pressure waves are not developed or,if they are,then they can be managed.This paper describes efforts to model complex charge designs using a two-dimensional axi-symmetric multi-phase flow internal ballistics model.

The surface activation of boron to improve ignition and combustion characteristic

Boron is a very promising and highly attractive fuel because of high calorific value. However, the practical applications in explosives and propellants of boron have been limited by long ignition delay time and low combustion efficiency. Herein, nano-Al and graphene fluoride(GF) as surface activated materials are employed to coat boron(B) particles to improve ignition and combustion performance. The reaction heat of nano-Al coated B/KNO_(3)and GF coated B/KNO_(3)are 1116.83 J/g and 862.69 J/g, respectively, which are higher than that of pure B/KNO_(3)(823.39 J/g). The ignition delay time of B/KNO_(3)could be reduced through nano-Al coating. The shortest ignition delay time is only 75 ms for B coated with nano-Al of 8 wt%, which is much shorter than that of pure B/KNO_(3)(109 ms). However, the ignition delay time of B/KNOcoated with GF has been increased from 109 to 187 ms. B coated with GF and nano-Al shown significantly influence on the pressure output and flame structure of B/KNO_(3). Furthermore, the effects of B/O ratios on the pressure output and ignition delay time have been further fully studied. For B/KNO_(3)coated with nano-Al and GF, the highest pressures are 88 KPa and 59 KPa for B/O ratio of 4:6, and the minimum ignition delay time are 94 ms and 148 ms for B/O ratio of 7:3. Based on the above results, the reaction process of boron coated with GF and nano-Al has been proposed to understand combustion mechanism.

Thermal Aspects in Lubrication System Design for Internal Combustion Engines

The mechanical losses in an internal combustion engine cause a significant decrease in the engine’s overall efficiency. Wherever friction work is dissipated a heat load will inevitably appear. This heat load has to be taken care of in some way, usually with both the water-cooling and the lubrication system. Despite its name, one of the major tasks of the latter one is, to draw out heat from between lubricated surfaces. In contrast to the water cooling system, which is primarily designed for cooling the cylinder block, the lubrication system is mainly required for cooling the crankshaft and piston rod bearings. A lubrication system for today’s automotive engines consists of several components, i.e. an oil pump, a pressure relief valve and an oil filter. This study focuses on the dynamic characteristics of a pressure relief valve and how the system temperature is affected by the critical design parameters of the valve. Using a thermodynamic simulation model together with an optimisation strategy makes it possible to express the desired system characteristics. Then, the optimisation strategy seeks for a similar system configuration with help of the model.