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.     

Thermodynamic performance analysis of the coal‐fired power plant with solar thermal utilizations

A new way of energy saving for existing coal‐fired power plant that uses low‐or medium‐temperature solar energy as assistant heat source was proposed to generate ‘green’ electricity. This paper has built the mathematical models of the solar‐aided power generation system focusing on the NZK600‐16.7/538/538 units. Based on the combination of the first and second law of thermodynamics, the thermodynamic performance of different components of the integrated system was evaluated under the changing operating condition aiming at different substitution options for turbine bleed streams. It has been found that the efficiency of the solar heat to electricity enhances with the increase of the load and the replaced extraction level. Additionally, when the second extraction is replaced, the effect is the best, which makes the power output increase around 6.13% or the coal consumption rate decrease 13.14 g/(kW · h) under 100%THA load and CO₂ emission reduce about 32.76 g/(kW · h), while the energy and exergy efficiencies of the integrated system are 39.35% and 39.12%, respectively. The results provide not only theory basis and scientific support for the design of solar‐aided coal‐fired power plants, but also a new way of energy saving and optimization for the units. Copyright © 2014 John Wiley & Sons, Ltd.     

Grid to wheel energy efficiency analysis of battery‐ and fuel cell–powered vehicles

Sustainable energy consumption is an important part of the renewable energy economy as renewable energy generation and storage. Almost one‐third of the global energy consumption can be credited to the transportation of goods and people around the globe. To move towards a renewable energy–based economy, we must adopt to a more sustainable energy consumption pattern worldwide especially in the transportation sector. In this article, a comparison is being made between the energy efficiency of a fuel cell vehicle and a battery electric vehicle. A very simple yet logical approach has been followed to determine the overall energy required by each vehicle. Other factors that hinder the progress of fuel cell vehicle in market are also discussed. Additionally, the prospects of a hydrogen economy are also discussed in detail. The arguments raised in this article are based on physics, economic analyses, and laws of thermodynamics. It clearly shows that an “electric economy” makes far greater sense than a “hydrogen economy.” The main objective of this analysis is to determine the energy efficacy of battery‐powered vehicles as compared to fuel cell–powered vehicles.     

2~#PX装置加热炉炉群热效率下降原因分析及对策

分析某石化公司2#PX装置加热炉系统热效率下降的原因,介绍提高热效率的具体措施,通过更换余热系统失效热管,并建议增加加热炉对流室换热面积及改造空气预热器的方法,提高系统整体热效率,保证装置高负荷长周期经济运行。     

Energy and exergy system analysis of thermal improvements of blast‐furnace plants

The blast‐furnace process dominating in the production of steel all over the world is still continuously improved due to its effectiveness (exergy efficiency is about 70%). The thermal improvement consist in an increase of the temperature of the blast and its oxygen enrichment, as well as the injection of cheaper auxiliary fuels. The main aim is to save coke because its consumption is the predominating item of the input energy both in the blast‐furnace plant and in ironworks. Besides coke also other energy carriers undergo changes, like the consumption of blast, production of the chemical energy of blast‐furnace gas, its consumption in Cowper‐stoves and by other consumers, as well as the production of electricity in the recovery turbine. These changes affect the whole energy management of ironworks due to the close connections between energy and technological processes. That means the production of steam, electricity, compressed air, tonnage oxygen, industrial water, feed water undergo changes as well. In order to determine the system changes inside the ironworks a mathematical model of the energy management of the industrial plant was applied. The results of calculations of the supply of energy carriers to ironworks can then be used to determine the cumulative energy and exergy consumption basing on average values of cumulative energy and exergy indices concerning the whole country. Such a model was also used in the system analysis of exergy losses. Copyright © 2005 John Wiley & Sons, Ltd.     

Prediction of thermal buffer zone effectiveness in real‐size buildings—An experimental and analytical study

Global warming is caused by greenhouse gas (GHG) emissions produced from the use of fossil fuel–based energy sources. Buildings consume about 30% to 35% of the global energy use, which makes buildings a major contributor to the global warming problem. A long‐term plan has been established at the Thermal Processing Laboratory (TPL) at McMaster University to investigate the use of various renewable energy–based technologies to achieve net‐zero energy buildings (NZEB) in Canada. This paper presents results of an investigation of the effectiveness of using a thermal buffer zone (TBZ) in real‐size buildings. A TBZ is a closed passage built around the building that allows air to passively redistribute heat energy from solar radiation received on the south side throughout the building. A TBZ offers an effective solution of the overheating problem usually experienced on the south side of the building, and at the same time, it helps in reducing the heating load of the north side of the building. An experimental setup employing TBZ in a lab‐scale model of a typical building floor has been built. An analytical model of the TBZ has been developed. The experimental data has been used to validate the developed analytical model, which then was used to predict the performance of the TBZ implemented in a real‐size building floor, considering four cases. Results of the first three case studies considering the use of TBZ in cold and hot climates, with and without thermal insulation, show that the predicted effectiveness of TBZ could reach 117% and 72.5% in the winter and summer, respectively. Results of the fourth case study considering the effect of integrating a fan with the TBZ show that a fan is beneficial up to a certain fan power, beyond which the use of the fan would not be feasible. Results presented herein confirm that the TBZ is an effective means of integrating solar energy into buildings, thereby reducing buildings' fossil fuel–based energy consumption.     

Influence of blast‐furnace process thermal parameters on energy and exergy characteristics and exergy losses

The technology ‘blast furnace—converter’ dominates at present in the production of steel all over the world. Therefore, the blast‐furnace process is continuously being improved, among others, by raising the thermal parameters, such as temperature and oxygen‐enrichment of the blast, as well as the addition of auxiliary fuels. The changes in the consumption of coke go together with changes in the consumption of blast, the production of top‐gas and its consumption in Cowper stoves, as well as the production of electricity in the recovery turbogenerator utilizing the waste exergy of the top‐gas due to raised pressure. Related to a unit of pig iron production, these values are called energy (exergy) characteristics of the blast‐furnace plant. They serve as a quantity measure of the thermal improvement of the blast‐furnace process. This paper presents an algorithm of the process exergy analysis of simulative investigations of the influence of increased thermal parameters on the thermodynamic perfection of the process and the blast‐furnace plant. This algorithm bases on the theoretical empirical balance method of the ‘input–output’ type. By means of this algorithm the influence of increased thermal parameters of the process not only on the saving of coke but also of the blast can be determined, as well as of the production and composition of top‐gas, the consumption of top‐gas in the Cowper stoves and the production of electric energy in the recovery turbine. The blast‐furnace process displays a high exergy efficiency, whereas the process of compressing and preheating the blast is characterized by rather high exergy losses due to the application of the combustion process. It has been shown that the internal exergy losses in the blast furnace are comparable with the exergy losses in the processes of compressing and preheating of the blast. Calculations were carried out for a modern Polish blast furnace with a volume of 3200 m³. Copyright © 2005 John Wiley & Sons, Ltd.     

Cost‐effectiveness analysis of energy efficiency measures in the Swiss chemical and pharmaceutical industry

Energy efficiency improvement is an effective way of reducing energy demand and CO₂ emissions. Although the overall final energy savings potential in chemical industry has been estimated in a few countries, energy efficiency potentials by concrete measures applicable in the sector have been scarcely explored and their associated costs are hardly analyzed. In Switzerland, the production of chemicals and pharmaceuticals exceeds all other industrial sectors in terms of energy use and CO₂ emissions, and it accounted for 22% of the total industry's overall final energy demand and 25% of the CO₂ emissions related to non‐renewable energy sources in 2016. In this study, the economic potentials for energy efficiency improvement and CO₂ emissions reduction in the Swiss chemical and pharmaceutical industry are investigated in the form of energy efficiency cost curves. The economic potential for final energy savings and CO₂ abatement based on energy‐relevant investments is estimated at 15% and 22% of the sector's final energy use and fossil fuel‐related CO₂ emissions in 2016, respectively. Measures related to process heat integration are expected to play a key role for final energy savings. The economic electricity savings potential by improving motor systems is estimated at 15% of the electricity demand by these systems in 2016. The size of economic potential of energy efficiency improvement across the sector decreases from 15% to 11% for 0.5 times lower final energy prices while the size increases insignificantly for 1.5 times higher final energy prices. The additional power generation potential based on Combined Heat and Power plants is estimated at 14 MW for 2016. This study is a contribution to the so far limited international literature on economic energy efficiency measures applicable in this heterogeneous sector and can support policy development. The results for specific costs of energy efficiency measures can also be adapted to other parts of the world by making suitable adjustments which in return may provide useful insights for decision makers to invest in economically viable clean energy solutions.     

Enhancement of energy efficiency and economics of process designs for catalytic co‐production of bioenergy and bio‐based products from lignocellulosic biomass

This study presents an integrated strategy for the co‐production of bioenergy (biofuels: butene oligomers) and bio‐based products (biomaterials: cyclopentanone (CPON) and alkylphenols) from hemicellulose (C₅), cellulose (C₆), and lignin fractions of lignocellulosic biomass based on experimental catalysis studies. To evaluate techno‐economic feasibility of the strategy, we performed a system‐level design study with three steps: process synthesis, energy analysis, and economic analysis. The results of process synthesis show that all biomass fractions are effectively converted with high numerical carbon yields (C₆‐to‐butene oligomers: 52.5%, C₅‐to‐CPON: 68.2%, and lignin‐to‐alkylphenols: 13.3%) but an efficient separation system for high recovery of bioenergy and bio‐based products is crucial. Moreover, an efficient design of a heat exchanger network leads that the total energy requirements of the process are satisfied by the combustion of biomass degradation products (humins). Finally, an economic analysis is performed to estimate the minimum selling price of CPON as the highest energy material (201 Mt/day of CPON production using 2000 Mt/day of corn stover feedstock processing). This result shows that the process ($1.79/kg CPON) can be cost competitive with current petro‐based production approaches. Copyright © 2017 John Wiley & Sons, Ltd.     

3D electro‐thermal modelling and experimental validation of lithium polymer‐based batteries for automotive applications

This article presents an electro‐thermal model of a stack of three lithium ion batteries for automotive applications. This tool can help to predict thermal behaviour of battery cells inside a stack. The open source software OpenFOAM provides the possibility to add heat generation because of Joule losses in a CFD model. Heat sources are introduced at the connectors and are calculated as a function of battery discharge current and internal resistance. The internal resistance is described in function of temperature. Simulation results are validated against experimental results with regard to cooling air flow field characteristic and thermal behaviour of the cell surface. The validation shows that the simulation is capable to anticipate air flow field characteristics inside the battery box. It also predicts correctly the thermal behaviour of the battery cells for various discharge rates and different cooling system conditions. The simulation supports the observation that batteries have a higher temperature close to the connectors and that the temperature increase depends highly on discharge rate and cooling system conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Optimization of Output Power and Thermal Efficiency of Solar‐Dish Stirling Engine Using Finite Time Thermodynamic Analysis

This paper presents an investigation on finite time thermodynamic (FTT) evaluation of a solar‐dish Stirling heat engine. FTTs has been applied to determine the output power and the corresponding thermal efficiency, exergetic efficiency, and the rate of entropy generation of a solar Stirling system with a finite rate of heat transfer, regenerative heat loss, conductive thermal bridging loss, and finite regeneration process time. Further imperfect performance of the dish collector and convective/radiative heat transfer mechanisms in the hot end as well as the convective heat transfer in the heat sink of the engine are considered in the developed model. The output power of the engine is maximized while the highest temperature of the engine is considered as a design parameter. In addition, thermal efficiency, exergetic efficiency, and the rate of entropy generation corresponding to the optimum value of the output power is evaluated. Results imply that the optimized absorber temperature is some where between 850 K and 1000 K. Sensitivity of results against variations of the system parameters are studied in detail. The present analysis provides a good theoretical guidance for the designing of dish collectors and operating the Stirling heat engine system.     

Efficiency and effectiveness enhancement of an intercooler of two‐stage air compressor by low‐cost Al2O3/water nanofluids

The present study was aimed to utilize low‐cost alumina (Al₂O₃) nanoparticles for improving the heat transfer behavior in an intercooler of two‐stage air compressor. Experimental investigation was carried out with three different volume concentrations of 0.5%, 0.75%, and 1.0% Al₂O₃/water nanofluids to assess the performance of the intercooler, that is, counterflow heat exchanger at different loads. Thermal properties such as thermal conductivity and overall heat transfer coefficient of nanofluid increased substantially with increasing concentration of Al₂O₃ nanoparticles. Specific heat capacity of nanofluids were lower than base water. The intercooler performance parameters such as effectiveness and efficiency improved appreciably with the employment of nanofluid. The efficiency increased by about 6.1% with maximum concentration of nanofluid, that is, 1% at 3‐bar compressor load. It is concluded from the study that high concentration of Al₂O₃ nanoparticles dispersion in water would offer better heat transfer performance of the intercooler.     

NOx emission and thermal efficiency of a 300 MWe utility boiler retrofitted by air staging

Full-scale experiments were performed on a 300 MWe utility boiler retrofitted with air staging. In order to improve boiler thermal efficiency and to reduce NO_x emission, the influencing factors including the overall excessive air ratio, the secondary air distribution pattern, the damper openings of CCOFA and SOFA, and pulverized coal fineness were investigated. Through comprehensive combustion adjustment, NO_x emission decreased 182 ppm (NO_x reduction efficiency was 44%), and boiler heat efficiency merely decreased 0.21%. After combustion improvement, high efficiency and low NO_x emission was achieved in the utility coal-fired boiler retrofitted with air staging, and the unburned carbon in ash can maintain at a desired level where the utilization of fly-ash as byproducts was not influenced.     

Thermal performance of an MHD radiative Oldroyd‐B nanofluid by utilizing generalized models for heat and mass fluxes in the presence of bioconvective gyrotactic microorganisms and variable thermal conductivity

The current paper analyzes the thermal and concentration attributes with the temperature‐dependent mass diffusion coefficient and thermal conductivity for the flow of an Oldroyd‐B nanoliquid over a stretchable configuration using the Buongiorno model under the application of boundary layers. The mechanisms of heat and mass transport are modeled by using the revised definitions of heat and mass fluxes. Mathematical expressions for the conservation laws are transformed into ordinary differential expressions by making the appropriate changes. The resulting complexly structured expressions are handled via an optimal homotopy procedure. The impact of influential variables on the desired solutions is plotted, tabulated, and discussed in detail. Comparative analysis of the thermal wall flux coefficient, concentration flux coefficient, density magnitude of the motile microorganisms, and reduced dimensionless stresses with already published research as a limiting case of this exploration is presented for the validity of the proposed scheme, and an excellent agreement is observed, which confirms the reliability of the homotopic solution.