Effect of temperature fluctuation on hydrate-based CO_2 separation from fuel gas

A new method of temperature fluctuation is proposed to promote the process of hydrate-based CO2 separation from fuel gas in this work according to the dual nature of CO2 solubility in hydrate forming and non-hydrate forming regions [1].The temperature fluctuation operated in the process of hydrate formation improves the formation of gas hydrate observably.The amount of the gas consumed with temperature fluctuation is approximately 35% more than that without temperature fluctuation.It is found that only the temperature fluctuation operated in the period of forming hydrate leads to a good effect on CO2 separation.Meanwhile,with the proceeding of hydrate formation,the effect of temperature fluctuation on the gas hydrate gradually reduces,and little effect is left in the completion term.The CO2 separation efficiencies in the separation processes with the effective temperature fluctuations are improved remarkably.

Experiments on Ni/γ-Al_2O_3 catalyst for improving lower heating value of biomass gasification fuel gas via methanation

Ni-based catalysts supported by γ-Al_2O_3 were prepared for improving the lower heating value( LHV) of biomass gasification fuel gas through methanation. Prior to the performance tests, the physico-chemical properties of the catalyst samples were characterized by N_2 isothermal adsorption/desorption, X-ray diffraction( XRD) and a scanning electron microscope( SEM). Afterwards, a series of experiments were carried out to investigate the catalytic performance and the results showthat catalysts with 15% and20% Ni loadings have better methanation catalytic effect than those with 5% and 10% Ni loadings in terms of elevating the LHV of biomass gasification fuel gas. M oreover, controllable influential factors such as the reaction temperature, the H_2/CO ratio and the water content occupy an important position in the methanation of biomass gasification fuel gas. 15 Ni/γ-Al_2O_3 and 20 Ni/γ-Al_2O_3 catalysts have a higher CO conversion and CH_4 selectivity at 350 ℃ and the LHV of biomass gasification fuel gas can be largely increased by 34. 3 % at 350 ℃. Higher H_2/CO ratio and a lower water content are more beneficial for improving the LHV of biomass gasification fuel gas when considering the combination of both CO conversion and CH_4 selectivity. This is due to the fact that a higher H_2/CO ratio and lower water content can increase the extent of the methanation reaction.

Characteristics of a coherent jet enshrouded in a supersonic fuel gas

Based on a current coherent jet,this study proposes a supersonic combustion(SC)coherent jet in which the main oxygen jet is surrounded by a supersonic fuel gas.The characteristics of the proposed coherent jet are analyzed using experimental methods and numerical simulations in the high-temperature environment of electric arc furnace(EAF)steelmaking.The SC coherent jet achieved stable combustion in the EAF steelmaking environment.The simulated combustion temperature of the supersonic shrouding methane gas was 2930 K,slightly below the theoretical combustion temperature of methane–oxygen gas.The high speed and temperature of the supersonic flame effectively weakened the interaction between the main oxygen jet and the external ambient gas,inhibiting the radial expansion of the main oxygen jet and maintaining its high speed and low turbulence over a long distance.These features improved the impact capacity of the coherent jet and strengthened the stirring intensity in the EAF bath.

FSRU燃料消耗比率计算分析

随着全球碳中和碳达峰排放政策的宣布,清洁能源尤其是液化天然气(LNG)在这一过程中起着重要的作用。FSRU装置是LNG再气化的关键装备,其运营的经济性是浮式储存与再气化装置(FSRU)设计关键因素之一。文章深入研究各种工况在不同外输能力下浮式储存与再气化装置(FSRU)设备的运行情况,分析不同工况下浮式储存与再气化装置(FSRU)燃料消耗比率,以指导浮式储存与再气化装置(FSRU)再气化能力的设计,为运营方提供技术支撑。

蒸汽透平推进式LNG船改造为FSRU的发电方案研究

目前很多船龄较大的汽轮机推进式LNG运输船,由于与新型内燃机LNG运输船竞争处于劣势,被改造成FSRU(Floating Storage and Regasification Unit)运营。针对此类方案的电力改造,如果采用增加双燃料发电机及其附属设施,需要耗资约2亿元人民币。为了降低投入和运营费用,根据运营数据,通过论证和对比,设计采用主透平改造的发电方案,深入分析结果表明,采用主透平改造的发电方案优于新增双燃料发电机发电方案。

FSRU双燃料主机燃料气系统设计

本文以EXMAR FSRU项目为例,介绍了FSRU燃料气系统设计要点,主要包括:流程图、燃料气组份模拟、燃料气耗量计算、管径选择、燃料气管及通风管水力计算、GVU排风机风量及压头计算、自动化要求、双层管制作工艺等。

Pd/activated carbon sorbents for mid-temperature capture of mercury from coal-derived fuel gas

Higher concentrations of Hg can be emitted from coal pyrolysis or gasification than from coal combustion, especially elemental Hg. Highly efficient Hg removal technology from coal-derived fuel gas is thus of great importance. Based on the very excellent Hg removal ability of Pd and the high adsorption abilities of activated carbon（AC） for H2 S and Hg, a series of Pd/AC sorbents was prepared by using pore volume impregnation, and their performance in capturing Hg and H2 S from coal-derived fuel gas was investigated using a laboratory-scale fixed-bed reactor. The effects of loading amount, reaction temperature and reaction atmosphere on Hg removal from coal-derived fuel gas were studied. The sorbents were characterized by N2 adsorption, X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS）. The results indicated that the efficiency of Hg removal increased with the increasing of Pd loading amount, but the effective utilization rate of the active component Pd decreased significantly at the same time. High temperature had a negative influence on the Hg removal. The efficiency of Hg removal in the N2-H2S-H2-CO-Hg atmosphere（simulated coal gas） was higher than that in N2-H2S-Hg and N2-Hg atmospheres, which showed that H2 and CO, with their reducing capacity, could benefit promote the removal of Hg. The XPS results suggested that there were two different ways of capturing Hg over sorbents in N2-H2S-Hg and N2-Hg atmospheres.

Numerical simulation and experimental measurement of transport phenomena for coherent jet with CH4 ＋ N2 mixed fuel gas

Coherent jet technology has been widely used in EAF steelmaking process because of the longer potential core length and stronger impacting power of the supersonic oxygen jet. However, more oxygen and fuel gas are consumed to achieve excel- lent characteristics of coherent jets, which causes the increase in steelmaking cost. Computational fluid dynamics simulation and experimental measurement of the coherent jets with CH4 ＋ N2 mixed fuel gas were carried out aiming at reducing the consumption of fuel gas. The numerical simulation results showed good agreement with the experimental data. As a result, high proportion of N2 negatively affects the combustion of CH4, which is not good for the protection of oxygen jets. While the gas composition is 75% CH4 ＋ 25% N2, the N2 addition to the CH4 leads to an expanding of CH4 combustion zone, and the energy generated by the combustion reaction could be delivered to the molten bath more efficiently, which is one control scheme with high performance-price ratio.

Enhanced application for FSRU recondensing equipment during periods of low or no gas send out to minimize LNG cargo losses

Most modern floating storage and regasification units(FSRU)are fitted with recondensing equipment that feed condensed boil-off gas(BOG)to the regasification unit in addition to a stream of liquefied natural gas(LNG)extracted from the cargo tanks.Use of the recondenser during regasification operations reduces gas losses on FSRU.It does so by avoiding consumption of excess BOG,with no associated commercial benefit,in gas combustion units(GCU),steam dumps,flares etc.Here we consider the benefits of also using the recondenser in recirculation mode,returning condensed BOG to the cargo tanks in the form of slightly warmed LNG.Such recirculation can be beneficial during periods of low or no gas send out from the FSRU,often achieving significant reductions in gas losses,although it is not standard practice in the industry to do so.Once regasification is halted not much BOG is required by the FSRU engine room,so the vessel must handle this excess.By condensing the BOG to LNG and returning it to the cargo tanks,the significant volume reduction involved has the beneficial impact of slowing down tank pressure increase.The saturated vapor pressure(SVP)of the LNG,linked to its composition and temperature,plays a key role in the boil-off rate and resulting cargo tank pressure changes.Detailed analysis is provided to explain how using the FSRU recondenser in recirculation mode can be best exploited by considering the prevailing fill levels,temperatures and pressures in each of the cargo tanks,and returning the condensed LNG preferentially to certain tanks.FSRU efficiency can be improved,gas losses and emissions can be reduced,and more cargo sold by exploiting the capabilities of the FSRU recondenser in recirculation mode.Running the FSRU in recirculation mode requires no equipment modifications to standard recondensers,neither does it increase FSRU operating costs.

GAS FUEL-POWERED HOPPER

Based on the hopping principle, a miniature gas fuel-powered hopper is designed and manufactured. According to thermodynamic analysis, the pressure-displacement curve in the combustion chamber after ignition is obtained through iterative calculation, then the work on the cylinder done by high-pressure gas is calculated and the initial hopping velocity of the hopper is obtained. The wireless control system is developed to realize the tele-control of the hopper, including fuel injection and ignition. Experimental results agree well with analytical results. The hopper has a jumping ability of height 2.2 m and distance 3.5 m, and it is more than 14 times its dimension.

Effects of Freeze/Thaw Cycles and Gas Purging Method on Polymer Electrolyte Membrane Fuel Cells

At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components of PEMFC-membrane-electrode assembly (MEA) and seek feasible measures to avoid degradation. The effect of freeze/thaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freeze/thaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable performance under subzero temperature and gas purging is proved to be the effective operation.

Effect of exhaust gas recirculation and intake pre-heating on performance and emission characteristics of dual fuel engines at part loads

Achieving simultaneous reduction of NOx,CO and unburned hydrocarbon(UHC) emissions without compromising engine performance at part loads is the current focus of dual fuel engine research.The present work focuses on an experimental investigation conducted on a dual fuel(diesel-natural gas) engine to examine the simultaneous effect of inlet air pre-heating and exhaust gas recirculation(EGR) ratio on performance and emission characteristics at part loads.The use of EGR at high levels seems to be unable to improve the engine performance at part loads.However,it is shown that EGR combined with pre-heating of inlet air can slightly increase thermal efficiency,resulting in reduced levels of both unburned hydrocarbon and NOx emissions.CO and UHC emissions are reduced by 24% and 31%,respectively,The NOx emissions decrease by 21% because of the lower combustion temperature due to the much inert gas brought by EGR and decreased oxygen concentration in the cylinder.

Key CO_(2)capture technology of pure oxygen exhaust gas combustion for syngas-fueled high-temperature fuel cells

Integrated gasification fuel cells(IGFCs)integrating high-temperature solid oxide fuel cell technology with CO_(2)capture processes represents highly-efficient power systems with negligible CO_(2)emissions.Flame burning with pure oxygen is an ideal method for fuel cell exhaust gas treatment,and this report describes experimental and numerical studies regarding an oxy-combustor for treating the exhaust gas of a 10 kW IGFC system anode.The applied simulation method was verified based on experiments,and the key performance indices of the combustor were studied under various conditions.It was determined that 315 K was the ideal condensation temperature to obtain flame stability.Under these pure oxygen flame burning conditions,CO was almost completely converted,and the dry mole fraction of CO_(2)after burning was C 0.958 when there was up to 5%excess O_(2).Overall,5%excess O_(2)was recommended to maximize CO_(2)capture and promote other environmental considerations.Additionally,the optimal tangential fuel jet angle to control the liner temperature was approximately 25°.The total fuel utilization had to be high enough to maintain the oxygen flame temperature of the anode exhaust gas below 1800 K to ensure that the system was environmentally friendly.The results presented herein have great value for designing IGFCs coupled with CO_(2)capture systems.

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NOx) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NOx and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.

Electromotive Force for Solid Oxide Fuel Cells Using Biomass Produced Gas as Fuel

The electromotive force （e.m.f.） of solid oxide fuel cells using biomass produced gas （BPG） as the fuels is calculated at 700-1,200 K using an in-house computer program, based on thermodynamic equilibrium analysis. Tour program also predicts the concentration of oxygen in the fuel chamber as well as the concentration of equilibrium species such as H2, CO, CO2 and CH4. Compared with using hydrogen as a fuel, the e.m.f. for cells using BPG as the fuels is relative low and strongly influenced by carbon deposition. To remove carbon deposition, the optimum amount of H2O to add is determined at various operating temperatures. Further the e.m.f, for cells based on yttria stabilized zirconia and doped ceria as electrolytes are compared. The study reveals that when using BPG as fuel, the depression of e.m.f, for a SOFC using doped ceria as electrolyte is relatively small when compared with that using Yttria stabilized zirconia.

Enhancement of Proton Exchange Membrane Fuel Cell Performance Using a Novel Tapered Gas Channel

Based on use of multi-dimensional models,this investigation simulates the performance of a proton exchange membrane fuel cell by varying the channel pattern.In the one-dimensional model,the porosity of the gas diffusion layer is 0.3.The model reveals the water vapor distribution of the fuel cell and demonstrates that the amount of water vapor increases linearly with the reduction reaction adjacent to the gas channel and the gas diffusion layer.Secondly,four novel tapered gas channels are simulated by a two-dimensional model.The model considers the distributions of oxygen,the pressure drop,the amount of water vapor distribution and the polarization curves.The results indicate that as the channel depth decreases,the oxygen in the tapered gas channel can be accel-erated and forced into the gas diffusion layer to improve the cell performance.The three-dimensional model is employed to simulate the phenomenon associated with four novel tapered gas channels.The results also show that the best performance is realized in the least tapered gas channel.Finally,an experimentally determined mechanism is found to be consistent with the results of the simulation.

Fundamental study on iron ore sintering new process of flue gas recirculation together with using biochar as fuel

It is of great significance for cleaner production to substitute bio-energy for fossil fuels in iron ore sintering. However, with the replacement ratio increasing, the consistency of heat front and flame front is broken, and the thermal utilizing efficiency of fuel is reduced, which results in the decrease of yield and tumble index of sinter. Circulating flue gas to sintering bed as biochar replacing 40% coke, CO in flue gas can be reused so as to increase the thermal utilizing efficiency of fuels, and the consistency of two fronts is recovered for the circulating flue gas containing certain CO2, H2 O and lower O2, which contributes to increasing the maximum temperature, extending the high temperature duration time of sintering bed, and results in improving the output and quality of sinter. In the condition of circulating 40% flue gas, the sintering with biomass fuels is strengthened, and the sintering indexes with biomass fuel replacing 40% coke breeze are comparative to those of using coke breeze completely.

Fault Tree Analysis of Fire and Explosion Accidents for Dual Fuel （Diesel/Natural Gas） Ship Engine Rooms

In recent years, China's increased interest in environmental protection has led to a promotion of energy-efficient dual fuel(diesel/natural gas) ships in Chinese inland rivers. A natural gas as ship fuel may pose dangers of fire and explosion if a gas leak occurs. If explosions or fires occur in the engine rooms of a ship, heavy damage and losses will be incurred. In this paper, a fault tree model is presented that considers both fires and explosions in a dual fuel ship; in this model, dual fuel engine rooms are the top events. All the basic events along with the minimum cut sets are obtained through the analysis.The primary factors that affect accidents involving fires and explosions are determined by calculating the degree of structure importance of the basic events.According to these results, corresponding measures are proposed to ensure and improve the safety and reliability of Chinese inland dual fuel ships.

Recovery of greenhouse gas as cleaner fossil fuel contributes to carbon neutrality

Under the context of carbon neutrality of China,it is urgent to shift our energy supply towards cleaner fuels as well as to reduce the greenhouse gas emission.Currently,coal is the main fossil fuel energy source of China.The country is striving hard to replace it with methane,a cleaner fossil fuel.Although China has rich geological resources of methane as coal bed methane(CBM)reserves,it is quite challenging to utilize them due to low concentration.The CBM is however mainly emitted directly to atmosphere during coal mining,causing waste of the resource and huge contribution to greenhouse effect.The recent work by Yang et al.demonstrated a potential solution to extract low concentration methane selectively from CBM through using MOF materials as sorbents.Such kind of materials and associated separation technology are promising to reduce greenhouse gas emission and promote the methane production capability,which would contribute to carbon neutrality in dual pathways.

A 10kW-scale Distributed Power Plant of Natural Gas-Proton Exchange Membrane Fuel Cell

A 10 kW-scale natural gas fueled proton exchange membrane fuel cell(PEMFC) distributed power plant is presented in this paper,which is designed for cogeneration of power and heat. With homemade catalysts for CO removal in a two-stage methanation process and integrated reactor in the fuel processing system,the reformed fuel with CO molar fraction less than 10-5 is obtained for the fuel cell stack. Based on Matlab/Simulink/Stateflow and xPC Target platform,a rapid control prototype(RCP) is developed for real-time condition management,signal tracking and parameter tuning,data storing,and man-machine interaction. In a typical running with 4.3 kW stack power,the hydrogen production efficiency,gross power generation efficiency and heat recovery efficiency approach to 76%,41% and 50%,respectively. The peak stack power reaches 7.3 kW. Though there is still considerable dis-tance to long-term operation at 10 kW-scale net power generation,it is a milestone for the PEMFC-based stationary application in China.