Reduction of greenhouse gas emission on a medium-pressure boiler using hydrogen-rich fuel control

The increasing emission of greenhouse gases from the combustion of fossil fuel is believed to be responsible for global warming. A study was carried out to probe the influence of replacing fuel gas with hydrogen-rich refinery gas (R.G.) on the reduction of gas emission (CO₂ and NO_x) and energy saving. Test results show that the emission of CO₂ can be reduced by 16.4% annually (or 21,500 tons per year). The NO_x emission can be 8.2% lower, or 75 tons less per year. Furthermore, the use of refinery gas leads to a saving of NT$57 million (approximately US$1.73 million) on fuel costs each year. There are no CO₂, CO, SO_x, unburned hydrocarbon, or particles generated from the combustion of added hydrogen. The hydrogen content in R.G. employed in this study was between 50 and 80 mol%, so the C/H ratio of the feeding fuel was reduced. Therefore, the use of hydrogen-rich fuel has practical benefits for both energy saving and the reduction of greenhouse gas emission.     

Bounding the climate viability of natural gas as a bridge fuel to displace coal

Natural gas has significant potential carbon benefits over coal when used for electricity generation, but these benefits can be offset by emissions of fugitive methane or delays in the adoption of near-zero carbon technologies. We analyze the time-evolution of radiative forcing from both natural gas and coal-based electricity generation by calculating average radiative forcing over an interval of time from greenhouse gas emissions under a range of assumptions for fugitive methane leakage, electricity generation efficiency, and delays in the adoption of near-zero carbon technologies. We find that leakage rates of between 5.2% and 9.9% are required for natural gas to result in greater mean forcing than coal over the next 100 years. We show that natural gas infrastructure with modest leakage could remain in place for 1.5–2.4 times the time interval that coal generation would have persisted prior to replacement with near-zero carbon technologies before the climate benefits of replacing coal with natural gas are negated. Natural gas can serve a viable bridge away from coal-based generation if avoiding longer-term climate impacts is prioritized, fugitive methane emissions are minimized, and the large-scale transition to near-zero carbon alternatives is unlikely to happen in the near-term.     

Reduction of energy cost and CO2 emission for the furnace using energy recovered from waste tail-gas

In this research, the waste tail gas emitted from petrochemical processes, e.g. catalytic reforming unit, catalytic cracking unit and residue desulfurization unit, was recovered and reused as a replacement of natural gas (NG). On-site experimental results show that both the flame length and orange-yellowish brightness decrease with more proportion of waste gas fuel added to the natural gas, and that the adiabatic temperature of the mixed fuel is greater than 1800 °C. A complete replacement of natural gas by the recovered waste gas fuel will save 5.8 × 10⁶ m³ of natural gas consumption, and 3.5 × 10⁴ tons of CO₂ emission annually. In addition, the reduction of residual O₂ concentration in flue gases from 4% to 3% will save 1.1 × 10⁶ m³ of natural gas consumption, reduce 43.0% of NO_x emission, and 1.3 × 10³ tons of CO₂ emission annually. Thus, from the viewpoint of the overall economics and sustainable energy policy, recovering the waste tail gas energy as an independent fuel source to replace natural gas is of great importance for saving energy, reducing CO₂ emission reduction, and lowering environmental impact.     

A novel design for a flow field configuration, of a direct methanol fuel cell

We proposed and tested a new and novel arrangement for a direct methanol fuel cell consisting of one inlet for a methanol solution and four outlets for oxidant gas (air), in both the anode and cathode flow fields. It utilizes different operating temperatures of 40 °C and 60 °C, and different methanol solution flow rates of 5 ml min⁻¹, 10 ml min⁻¹, and 20 ml min⁻¹. Test results indicate a significant reduction in produced CO₂ gas in the anode flow channels and product water in the cathode flow channels; consequently, cell performance can be greatly improved. Furthermore, methanol crossover can also be avoided and reduced.     

Steam catalytic gasification of municipal solid waste for producing tar-free fuel gas

In the paper, a two-region municipal solid waste (MSW) steam catalytic gasification process was proposed. The gasifier was composed of two individual reactors: one is the gasification reactors and the other is the catalytic reactor. The MSW was initially gasified and the produced tar was gasified in the gasification reactor, and further, the tar not gasified entered the catalytic reactor together with the fuel gas and was catalytically decomposed to fuel gas. The influences of the catalysts, steam and temperature on the content of tar, dry gas yield and composition, and carbon conversion efficiency were studied. The results indicated that under the optimum operating conditions, the dry gas yield can be up to 1.97 Nm³/kg MSW and the tar in the product can be completely eliminated. The concentration of hydrogen, carbon monoxide and methane in the fuel gas produced was 50.8%, 9.32% and 13.3%, respectively.     

页岩油剩余瓦斯发电后尾气的合理利用

页岩油剩余瓦斯通过燃气机发电后 ,排放的尾气中含有大量的热量 ,这些热量通过针形换热器进行热交换 ,从而实现汽暖改水暖的目的。     

The usage of waste hydrogen from outlet gas as a fuel in different fuel cells

This paper aims at selecting different types of fuel cells using an MINLP (mixed-integer nonlinear programming) model, whilst considering the usage of waste hydrogen from the outlet gas. Hydrogen separation from the outlet gas is a good alternative from the economical and environmental perspectives.     

Production of electricity from the treatment of urban waste water using a microbial fuel cell

In this work, is studied the oxidation of the pollutants contained in an actual urban wastewater using a two-chamber microbial fuel cell (MFC). By using an anaerobic pre-treatment of the activated sludge of an urban wastewater treatment plant, the electricity generation in a MFC was obtained after a short acclimatization period of less than 10 days. The power density generated was found to depend mainly on the organic matter contain (COD) but not on the wastewater flow-rate. Maximum power densities of 25 mW m⁻² (at a cell potential of 0.23 V) were obtained. The rate of consumption of oxygen in the cathodic chamber was very low. As the oxygen reduction is coupled with the COD oxidation in the anodic chamber, the COD removed by the electricity-generating process is very small. Thus, taking into account the oxygen consumption, it was concluded that only 0.25% of the removed COD was used for the electricity-generation processes. The remaining COD should be removed by anaerobic processes. The presence of oxygen in the anodic chamber leads to a deterioration of the MFC performance. This deterioration of the MFC process occurs rapidly after the appearance of non-negligible concentrations of oxygen. Hence, to assure a good performance of this type of MFC, the growth of algae should be avoided.     

Technical,economic, and environmental analyses of the modernization of a chamber furnace operating on natural gas or hydrogen

The paper presents a technical, economic and environmental analyses of a chamber furnace used to heat the charge before forging. The energy efficiency of the furnace before the modernization was 18%, after the modernization it was 31% (partial modernization due to large financial outlays). Other variants were also analysed: complete modernization, the variant of furnace modernization with 30% hydrogen content in the gas and the variant with 100% hydrogen as fuel. The analyses showed that with the current gas price (0.025 EUR/kWh) and the price of emission allowances (nearly 60 EUR/MgCO₂) and 100 cycles/year, the difference in Net Present Value (NPV) before base variant and partial modernization is around 900,000 EUR and before base variant and full modernization is 1,200,000 EUR. The introduction of the gas and 30% of hydrogen co-combustion option versus the base scenario option for 150 cycles per year results in a NPV difference of at least 2 million EUR. The option of 100% hydrogen as a fuel is the most advantageous from the point of view of reducing CO₂ emissions - it is largely influenced by the rising prices of CO₂ emission allowances.     

Effects of future fossil fuel use on CO2 levels in the atmosphere

A model based on fossil fuel use per capita and United Nations population predictions has been developed to predict global fossil fuel use and the resulting levels of CO₂ in the atmosphere. The results suggest levels of CO₂ will increase to between 415 and 421 ppm by 2025. Countries with energy-intensive economies will be responsible for the majority of CO₂ emissions, while nations with large populations but low energy consumption per capita will have less of an effect. A major increase in nuclear power generation will not have a significant impact on CO₂ levels over this time scale.     

Utilization of waste heat from cement plant to generate hydrogen and blend it with natural gas

In this paper, a waste heat recovery system for a cement plant is developed and analyzed with the softwares of Engineering Equation Solver (EES) and Aspen Plus. This system is novel in a way that hydrogen is uniquely produced from waste heat obtained from the cement slag and blended with natural gas for domestic use. The presented system has a steam Rankine cycle combined with an organic Rankine cycle, an alkaline electrolyzer unit, oxygen and hydrogen storage tanks, a blending unit, and a combustor. Moreover, multiple useful outputs are obtained, such as power, hydrogen, and natural gas, as well as hydrogen blend. The power obtained from the organic Rankine cycle becomes the highest when the organic fluid R600a is used as a working fluid. The power generated from turbines is fed to the grid externally and the cement plant for internal use. Also, some power is utilized to produce hydrogen via an alkaline electrolyzer which has an efficiency of 62.94%. With the change of the percentage of hydrogen in the blend from 0% to 50%, the annual consumption of natural gas reduces from 48.261 billion m³ to 37.086 billion m³. Furthermore, the overall exergy and energy efficiencies for the plant are found at 55% and 22%, respectively. The carbon dioxide emissions in the released exhaust gas reduce from 34% to 28% when the same volumetric flow rates of the blend and oxygen gas are fed to the reactor. NO and NO₂ emissions increase from 4.06 g/day to 7.45 g/day, and from 0.02 g/day to 0.09 g/day when the hydrogen content is increased from 5% to 20%. Moreover, carbon monoxide emissions decrease from 0.05 g/day to 0.02 g/day, accordingly. As a result, both combustion energy and exergy efficiencies increase with the addition of hydrogen. Furthermore, CO and CO₂ emissions decrease with the hydrogen content increases.     

Techno-economic assessment on the fuel flexibility of a commercial scale combined cycle gas turbine integrated with a CO2 capture plant

Post-combustion carbon capture is a valuable technology, capable of being deployed to meet global CO₂ emissions targets. The technology is mature and can be retrofitted easily with existing carbon emitting energy generation sources, such as natural gas combined cycles. This study investigates the effect of operating a natural gas combined cycle plant coupled with carbon capture and storage while using varying fuel compositions, with a strong focus on the influence of the CO₂ concentration in the fuel. The novelty of this study lies in exploring the technical and economic performance of the integrated system, whilst operating with different fuel compositions. The study reports the design of a natural gas combined cycle gas turbine and CO₂ capture plant (with 30 wt% monoethanolamine), which were modelled using the gCCS process modelling application. The fuel compositions analysed were varied, with focus on the CO₂ content increasing from 1% to 5%, 7.5% and 10%. The operation of the CO₂ capture plant is also investigated with focus on the CO₂ capture efficiency, specific reboiler duty and the flooding point. The economic analysis highlights the effect of the varying fuel compositions on the cost of electricity as well as the cost of CO₂ avoided. The study revealed that increased CO₂ concentrations in the fuel cause a decrease in the efficiency of the natural gas combined cycle gas turbine; however, rising the CO₂ concentration and flowrate of the flue gas improves the operation of the capture plant at the risk of an increase in the flooding velocity in the column. The economic analysis shows a slight increase in cost of electricity for fuels with higher CO₂ contents; however, the results also show a reduction in the cost of CO₂ avoided by larger margins.     

阳极焙烧炉燃烧煤气和天然气的数值比较

针对燃烧低热值煤气的阳极焙烧炉炉内情况，采用数值模拟的方法和CFD软件进行了计算和分析，并探讨了将燃料改为高热值天然气的可行性．通过比较煤气和天然气的燃烧计算结果，指出燃烧煤气的阳极焙烧炉改为燃烧天然气，可以解决煤气燃烧速度过快导致的炉内温度分布不均匀的问题．     

Utilization of combustible waste gas as a supplementary fuel in coal‐fired boilers

A system is proposed to use the combustible waste gas as a supplementary fuel in coal‐fired boilers. The combustion air can be partially or fully substituted by ventilation air methane or diluted combustible waste gases. The recommended volume fraction of combustible waste gas in combustion air is no more than 1.0%. The effect of waste gas introduction on thermodynamic parameters of boiler is evaluated through thermal calculation based on material balance, heat balance, and heat transfer principles. A case study is conducted by referring to a 600 MW supercritical pressure boiler. The results show that no retrofit of boiler is required. The operation of boiler is scarcely influenced, and the original forced and induced draft fans can meet the requirement. With increasing volume fraction of combustible waste gas, the flue gas temperature at the furnace exit decreases monotonically, resulting in an increment of heat absorption in furnace and a decrement of heat transferred in convective heating surfaces. When 1.0% volume fraction of hydrocarbon gas is introduced, the thermal efficiency of boiler is increased by 0.5%, and the coal consumption rate is reduced by 25.4%. The cost analysis of the proposed system is conducted, and break‐even curves are given as references for the utilization of waste gas as a supplementary fuel. The economic velocity of the combustion air is suggested to be 18.2 m s^?1.     

Manganese dioxide-coated carbon nanotubes as an improved cathodic catalyst for oxygen reduction in a microbial fuel cell

To develop an efficient and cost-effective cathodic electrocatalyst for microbial fuel cells (MFCs), carbon nanotubes (CNTs) coated with manganese dioxide using an in situ hydrothermal method (in situ MnO₂/CNTs) have been investigated for electrochemical oxygen reduction reaction (ORR). Examination by transmission electron microscopy shows that MnO₂ is sufficiently and uniformly dispersed over the surfaces of the CNTs. Using linear sweep voltammetry, we determine that the in situ MnO₂/CNTs are a better catalyst for the ORR than CNTs that are simply mechanically mixed with MnO₂ powder, suggesting that the surface coating of MnO₂ onto CNTs enhances their catalytic activity. Additionally, a maximum power density of 210 mW m⁻² produced from the MFC with in situ MnO₂/CNTs cathode is 2.3 times of that produced from the MFC using mechanically mixed MnO₂/CNTs (93 mW m⁻²), and comparable to that of the MFC with a conventional Pt/C cathode (229 mW m⁻²). Electrochemical impedance spectroscopy analysis indicates that the uniform surface dispersion of MnO₂ on the CNTs enhanced electron transfer of the ORR, resulting in higher MFC power output. The results of this study demonstrate that CNTs are an ideal catalyst support for MnO₂ and that in situ MnO₂/CNTs offer a good alternative to Pt/C for practical MFC applications.     

The production of hydrogen-rich gas by wet sludge gasification using waste heat of blast-furnace slag: Mass and energy balance analysis

Sludge gasification for the production of hydrogen-rich gas is a promising technology. In this paper, a pilot study on the hydrogen-rich gas production by sludge gasification using waste heat of blast furnace slag was carried out, and the mass and energy balance of gasification process using waste heat from blast furnace slag were evaluated. The results show that the higher the gasification temperature, the higher the hydrogen content in the gas. When the gasification temperature reaches 880 °C, the hydrogen content in the gas reaches the maximum,35.3%. The technology of sludge gasification combined with waste heat recovery of high furnace slag is feasible. Its efficiency of heat recovery can reach up to 64.35%, and the gasification efficiency and energy consumption ratio can reach to 42.30% and 3.67, respectively.     

机车尾气余热加热燃油系统的定量分析优化

对利用机车尾气进行燃油系统加热进行定量分析,提出加热系统不影响增压器工作的一个保守判据,并对加热系统进行效能优化。结果表明：加热系统具有广泛的实用性,通过增加用能终端,适当扩展系统的用途以及优化设计参数,可显著提高加热系统性能。     

Direct oxidation of waste vegetable oil in solid-oxide fuel cells

Solid-oxide fuel cells with ceria, ceria-Cu, and ceria-Rh anode were demonstrated to generate stable electric power with waste vegetable oil through direct oxidation of the fuel. The only pre-treatment to the fuel was a filtration to remove particulates. The performance of the fuel cell was stable over 100 h for the waste vegetable oil without dilution. The generated power was up to 0.25 W cm⁻² for ceria-Rh fuel cell. This compares favorably with previously studied hydrocarbon fuels including jet fuels and Pennsylvania crude oil.     

高炉煤气锅炉燃烧中氮氧化物污染物的控制

文章介绍了氮氧化物生成机理及高炉煤气锅炉燃烧中氮氧化物污染物的控制.通过对NOx生成机理的讨论,高炉煤气燃烧时主要产生的NOX为热力型NOX,采用多层燃烧器的布置,把燃烧器组设计成浓淡燃烧器, 从而降低NOX的生成,使锅炉NOX排放达标,使之成为一种环保型污染气体治理设备.     

Hydrogen-rich gas as a product of two-stage co-gasification of lignite/waste plastics mixtures

Under atmospheric pressure, mixtures of lignite with waste plastics were gasified on a laboratory scale. The resulting tar was cracked in a thermal cracking reactor. For experiments, low-ash and low-sulfur lignite was used; the percentage of waste plastics in the mixtures was 10 and 20 wt.%. The main product of co-gasification was hydrogen-rich gas, as by-products, soot and non-gasified solid residue were obtained. It was found that the higher heating value of obtained gas is fully comparable with that of industrial gas from lignite gasification. Probably, at least 20 wt.% of lignite can be replaced with mixed waste plastics in this process. The effect of waste plastics addition on properties of the obtained gas and of the non-gasified solid residue was evaluated and discussed.