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.     

Development of a proton exchange membrane fuel cell cogeneration system

A proton exchange membrane fuel cell (PEMFC) cogeneration system that provides high-quality electricity and hot water has been developed. A specially designed thermal management system together with a microcontroller embedded with appropriate control algorithm is integrated into a PEM fuel cell system. The thermal management system does not only control the fuel cell operation temperature but also recover the heat dissipated by FC stack. The dynamic behaviors of thermal and electrical characteristics are presented to verify the stability of the fuel cell cogeneration system. In addition, the reliability of the fuel cell cogeneration system is proved by one-day demonstration that deals with the daily power demand in a typical family. Finally, the effects of external loads on the efficiencies of the fuel cell cogeneration system are examined. Results reveal that the maximum system efficiency was as high as 81% when combining heat and power.     

Energy and exergy performance assessments of a high temperature-proton exchange membrane fuel cell based integrated cogeneration system

High-temperature proton exchange membrane fuel cell (HT-PEMFC), which operates between 160 °C and 200 °C, is considered to be a promising technology, especially for cogeneration applications. In this study, a mathematical model of a natural gas fed integrated energy system based on HT-PEMFC is first developed using the principles of electrochemistry and thermodynamics (including energy and exergy analyses). The effects of some key operating parameters (e.g., steam-to-carbon ratio, HT-PEMFC operating temperature, and anode stoichiometric ratio) on the system performance (electrical, cogeneration, and exergetic efficiencies) are examined. The exergy destruction rates of each component in the integrated system are found for different values of these parameters. The results show that the most influential parameter which affects the performance of the integrated system is the anode stoichiometric ratio. For the baseline conditions, when the anode stoichiometric ratio increases from 1.2 to 2, the electrical, cogeneration, and exergetic efficiencies decrease by 42.04%, 33.15%, and 37.39%, respectively. The highest electrical power output of the system is obtained when the SCR, operating temperature, and anode stoichiometric ratio are taken as 2, 160 °C, and 1.2, respectively. For this case, the electrical, cogeneration, and exergetic efficiencies are found as 26.20%, 70.34%, and 26.74%, respectively.     

Improved modelling of the fuel cell power module within a system-level model for solid-oxide fuel cell cogeneration systems

A generic system-level model for SOFC cogeneration devices has been developed under the umbrella of an International Energy Agency/Energy Conservation in Buildings and Community Systems project known as Annex 42. This paper addresses a limitation of the Annex 42 model by developing a more refined semi-mechanistic treatment for the fuel cell power module (FCPM). The electrochemical, thermal, and reformation modelling methods as well as techniques for treating the FCPM's balance of plant are first described. The methods used to calibrate and validate the enhanced model using previously collected data from a 2.8 kW_AC prototype SOFC cogeneration device are then discussed. Excellent agreement was found between model predictions and the measurements. The new modelling capabilities are then demonstrated through a parametric study that examines the influences of fuel utilization, excess air ratio and stack temperature.     

Thermal economic analysis of hybrid open-cathode hydrogen fuel cell and heat pump cogeneration

Proton exchange membrane fuel cell (PEMFC) receives increasing attention as an alternative in small-scale residential distributed generation (DG) application, especially for remote cold region where the utility electricity is not accessible. The open-cathode PEMFC is featured with the integrated fabrication of air supply and coolant flow cathode. Although simple, the waste heat of the exhaust air is difficult to reuse by heat exchangers, because of the low exhaust temperature. To this end, this paper investigates a hybrid structure consisting of open-cathode PEMFC and heat pump. It is revealed in this paper that the oxygen excess ratio of open-cathode PEMFC is usually as big as 100, which makes it doable and safe to directly exporting the exhaust air into the indoor environment. The temperature of the mixed air is thereby lifted. The thermal load of the heat pump is consequently alleviated and the power consumption is reduced. A comprehensive quantitative model is developed by considering the fuel cell electrochemical characteristic, cathode thermodynamics and heat pump coefficient. A case study is carried out by comparing the coefficient of performance (COP) of the system with and without the cogeneration design, showing a 7.6% improvement of the proposed hybrid structure. The results of the paper depict a promising prospect in accelerating the commercialization of open-cathode PEMFC in the field of domestic cogeneration filed.     

Optimization of a dual cycle cogeneration system based on a new exergetic performance criterion

An ecological performance analysis for an irreversible dual-cycle cogeneration system has been performed. The objective function is called as the exergetic-performance coefficient (EPC) and defined as the ratio of total exergy output to the loss rate of availability. The general and optimal performances of the irreversible dual-cycle cogeneration system, having a finite-rate of heat transfer, heat leak and internal irreversibilities based on the EPC objective function have been investigated. Comparisons with respect to the optimal total-exergy output are also provided in order to establish the utility of the new exergetic-performance coefficient. The analyzed results of the dual-cycle cogeneration system considered, working at maximum EPC conditions, have a significant advantage in terms of entropy-generation rate and can be used for the selection of optimal design parameters.     

Development of efficiency-enhanced cogeneration system utilizing high-temperature exhaust-gas from a regenerative thermal oxidizer for waste volatile-organic-compound gases

We have developed a gas-turbine cogeneration system that makes effective use of the calorific value of the volatile organic compound (VOC) gases exhausted during production processes at a manufacturing plant. The system utilizes the high-temperature exhaust-gas from the regenerative thermal oxidizer (RTO) which is used for incinerating VOC gases. The high-temperature exhaust gas is employed to resuperheat the steam injected into the gasturbine. The steam-injection temperature raised in this way increases the heat input, resulting in the improved efficiency of the gas-turbine. Based on the actual operation of the system, we obtained the following results:     

Utilizing coke oven gases as a fuel for a cogeneration system based on high temperature proton exchange membrane fuel cell; energy,exergy and economic assessment

Based on a high temperature proton exchange membrane fuel cell (HT-PEMFC), a cogeneration system is proposed to produce heat and power. The system includes a coke oven gas steam reformer, a water gas shift reactor, and an afterburner. The system is analyzed in detail considering the energy, exergy and economic viewpoints. The analyses reveal the importance of HT-PEMFC in the system and according to the results, 9.03 kW power is generated with energy and exergy efficiencies of 88.2% and 26.2%, respectively and the total product unit cost is calculated as 91.8 $/GJ. Through a parametric study the effects on system performance are studied of such variables as the current density, fuel cell and reformer operating temperatures, and cathode stoichiometric ratio. It is found that an increase in the fuel cell temperature and/or a decrease in the reformer temperature enhance the exergy efficiency. The exergy efficiency is also maximized at the cathode stoichiometric ratio of 2.4. By performing a two-objective optimization using genetic algorithm, the best operating point is determined at which the exergy efficiency is (32.86%) and the total product unit cost is (78.68 $/GJ).     

Modeling electrochemical partial oxidation of methane for cogeneration of electricity and syngas in solid-oxide fuel cells

This paper uses computational models to evaluate strategies for scaling electrochemical partial oxidation (EPOX) processes from the laboratory scale to practical application. In addition to producing electrical energy alone, solid-oxide fuel cells (SOFC) can be operated with hydrocarbon fuel streams to produce synthesis gas (H₂ and CO) as well. SOFC systems are usually operated to consume most of the fuel and produce electricity. However, by operating with a hydrocarbon fuel at relatively high flow rates, the exhaust-gas composition can be predominantly syngas. In this case the steam (and CO₂), produced from electrochemical and thermal reactions, reacts to reform the hydrocarbon fuel within the catalytic anode support structure. A practical limitation of electrochemical partial oxidation operation is the fact that carbon tends to deposit on Ni-based anode catalysts. The present paper explores the use of barrier layers to prevent carbon deposits. The results show that a tubular cell can be designed to deliver syngas and electricity using methane as the primary fuel.     

Development of a case-based reasoning prototype for cogeneration plant design

This paper deals with the design problem associated with natural gas cogeneration systems. Despite the task complexity, this design process is strongly based on knowledge that experts formally apply in their activities. Through an appropriate knowledge representation scheme this study demonstrates that the knowledge-based system (KBS) is an approach well-suited to cogeneration plant design. The research involves the use of rule-based expert systems (RBES) and case-based reasoning (CBR). In this paper, the basic concepts of the CBR technique and a CBR prototype for assistance in cogeneration plant design are presented. An RBES prototype for natural gas cogeneration system design previously developed by the authors is used to generate cases for the CBR prototype. A solution generated by the CBR prototype for a plant design requiring 4 MW of power and 0.7 kg/s of saturated steam at 0.9 MPa is presented. The application of CBR in cogeneration plant design represents an original and important contribution of this work.     

Effect of utilization of hydrogen-rich reformed biogas on the performance and emission characteristics of common rail diesel engine

The utilization of renewable gaseous fuels in the diesel engine has gained significant interest in recent years due to its clean-burning nature and higher availability. In this study, hydrogen-rich reformed biogas was used as a gaseous fuel in a common rail diesel engine with diesel as pilot fuel. The hydrogen-rich reformed gas was synthesized through dry-oxidative reforming. The experimentations were performed in the load range from 6 to 24 N m with two different flow rates of gaseous fuel (0.5 and 1.5 kg/h) at a constant speed of 1800 RPM. The effects on engine performance parameters (brake thermal efficiency, brake specific energy consumption, and brake specific diesel consumption), combustion parameters (rate of pressure rise and maximum heat release rate) and emission parameters (Unburnt hydrocarbons, nitrogen oxides, carbon monoxide, and carbon dioxide) were assessed. The induction of gaseous fuel led to an increase in brake thermal efficiency by 10.5%, reduction in brake specific energy consumption by 13.6%, and a reduction of 26.4% in brake specific diesel consumption with a flow rate of 0.5 kg/h when compared to diesel-only mode at 24 N m load. The HC, NO_X and CO₂ emissions were reduced by 18.2%, 7.4% and 1.4% with a flow rate of 0.5 kg/h when compared to diesel-only mode at 24 N m load due to lower availability of carbon content in the combustible mixture. The utilization of renewable fuel like hydrogen-rich reformed biogas has great potential for overcoming the issue related to both biogas and hydrogen in diesel engines. Moreover, the higher diesel substitution also demonstrates the potential for cost-saving and fossil fuel conservation.     

Performance study of a microturbine system for cogeneration application

A microturbine cogeneration system providing electrical power and space cooling to a laboratory space is presented. The system comprises a microturbine, a lithium bromide absorption chiller, heat exchangers and a propane fuel supply system. Results from the performance tests conducted on the cogeneration system showed that the microturbine electrical efficiency was 21% at near full load of 24 kW whilst the chiller operated with COP ranging from 0.5 to 0.58, depending on the electrical output. The overall system efficiency ranged from 40% to 49%. In addition, the performance of the cogeneration system under varying heat load in the cooling space and longer microturbine operating period were also studied.     

Evaluating the role of cogeneration for carbon management in Alberta

Developing long-term carbon control strategies is important in energy intensive industries such as the oil sands operations in Alberta. We examine the use of cogeneration to satisfy the energy demands of oil sands operations in Alberta in the context of carbon management. This paper evaluates the role of cogeneration in meeting Provincial carbon management goals and discusses the arbitrary characteristics of facility- and product-based carbon emissions control regulations. We model an oil sands operation that operates with and without incorporated cogeneration. We compare CO₂ emissions and associated costs under different carbon emissions control regulations, including the present carbon emissions control regulation of Alberta. The results suggest that incorporating cogeneration into the growing oil sands industry could contribute in the near-term to reducing CO₂ emissions in Alberta. This analysis also shows that the different accounting methods and calculations of electricity offsets could lead to very different levels of incentives for cogeneration. Regulations that attempt to manage emissions on a product and facility basis may become arbitrary and complex as regulators attempt to approximate the effect of an economy-wide carbon price.     

Performance assessment and optimization of an integrated solid oxide fuel cell-gas turbine cogeneration system

The combined solid oxide fuel cells and gas turbine (SOFC/GT) system is known to be a potential alternative for distributed power generation. In this paper, a novel SOFC/GT based cogeneration system, which integrated a transcritical carbon dioxide cycle (TRCC) with a LNG cold energy utilization system is proposed. A mathematical (zero-dimensional) model is developed to analyze the co-generation system performance from the perspective of thermodynamic (energy and exergy) and economic costs. The main parameters of the system are chosen to analyze their effects on thermodynamic performance. The results show that the current system can achieve 64.40% thermal efficiency and 62.13% exergy efficiency under given conditions, and can further improve efficiency through parameter optimization. Finally, the multi-objective optimization program using NSGA-II (Non-dominated Sorting Genetic Algorithm II) is used to obtain the optimal value of the system design parameters. In the multi-objective analysis, the thermodynamic efficiency and economic cost of the system are considered as objective functions. The optimization results show that the final optimized design selected from the Pareto front can achieve 63.08% thermal efficiency and 61.10% exergy efficiency, respectively.     

Research of boiler combustion regulation for reducing NOx emission and its effect on boiler efficiency

The effect of boiler combustion regulation on NO_x emission of two 1025t/h boilers has been studied.The re-searches show that NOx emission is influenced by coal species,operation conditions,etc,and can be reduced byregulating the combustion conditions.The effect of combustion regulation on boiler efficiency has also beenchecked.     

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.     

Condition and development of the cogeneration facilities based on autoproduction investment model in Turkey

Turkey, with its young population and growing energy demand per person, its fast growing urbanization, and its economic development, has been one of the fast growing power markets of the world for the last 20 years. It is expected that the demand for electric energy in Turkey will be 294 billion kWh by the year 2010 and 556 billion kWh by the year 2020. Turkey’s electric energy demand is growing 7% yearly. Because a substantial amount of Turkey’s energy need has been met by cogeneration facilities in recent years. Cogeneration facilities have an important role in Turkey’s energy strategy. While there were only four cogeneration facilities and the total capacity of them was 30 MW_e in 1994, in 1999, 10.6% of total electric production was produced by these facilities. In accordance with the governmental decree numbered 85/9799, cogeneration is the technology which produces electricity and heat synchronously and autoproduction is the name of the firm which was founded for the purpose of producing electricity and heat. In this study, the development of autoproduction facilities in Turkey, which are the most convenient legal investment model for cogeneration investors, has been investigated.     

Direct production of hydrogen-rich gas and/or pure-hydrogen with high-pressure from alcohol/water/metal-powder mixture at low processing temperature

High-pressure hydrogen-rich gas producing experiments from various alcohol/water/metal-powder mixtures at low processing temperatures from 473 to 723 K are carried out in a prototype airtight apparatus possessing a withstand pressure of 15 MPa in the aim of technologizing an incidentally emerged high-pressure hydrogen-rich gas production from a methanol/water/aluminum-powder mixture at 723 K. Methanol/water due to a proven track record and ethanol/water in order to make an allowance for replacing the reagent to commercially-available potable alcohols are selected as main hydrogen sources. As tested metal-powders, aluminum, cobalt, iron, magnesium and nickel are chosen, taking their ready-availabilities and costs into consideration.Among tested metal-powders, aluminum and cobalt are found optimal adding metals for the high-pressure hydrogen-rich gas productions from 60.0 wt% methanol/water and ethanol/water solutions, respectively. From 60.0 wt% methanol/water and Al-powder mixture at 723 K, pure-hydrogen with 10.0 MPa is produced at a great hydrogen producing rate of 24.9 L_N/(dm²min). All carbons discharged from methanol are fixed as a wide variety of solid higher hydrocarbons and organic liquid residues of benzyl alcohol and toluene. Almost all oxygens from methanol/water solution are fixed as aluminum-compounds of aluminum oxide hydroxide and aluminum hydroxide. From 60.0 wt% ethanol/water and Co-powder mixture, pure-hydrogen with pretty high pressure over 15 MPa can be produced at 723 K with simultaneous fixations of all the carbons and oxygens from the main hydrogen source as solid/liquid residues of wide variety of solid higher hydrocarbons, benzyl alcohol, toluene, cobalt oxide, cobalt hydroxide, tricobalt tetroxide and cobalt carbonate. Responding to the outcome from 60.0 wt% ethanol/water and Co-powder mixture, a certain rice-wine having an alcohol degree 60 with Co-powder at 723 K is experimented, and provides high-pressure hydrogen-rich gas with hydrogen concentration of 80 % and hydrogen partial pressure of around 8 MPa.All the produced hydrogen-rich gases are confirmed to keep a full declared potential in polymer electrolyte fuel cell for over 24 h without any exceptions. These findings speak by themselves that this developing high-pressure hydrogen-rich gas (pure-hydrogen) direct producing method is surely approaching a self-operating dispersed hydrogen producing appliance (i.e. a part of a dispersion type power source) anywhere whole the world. And, this method still leaves unlimited room for far higher pure-hydrogen pressures and hydrogen producing rates by slight changing the operating conditions, and its applicable fields are broadening for eternity. Finally, some recommended future strategies to improve this method so as to supply complete solutions to any global-scale issues are also proposed in every part through this paper.     

Power and cogeneration technology environomic performance typification in the context of CO2 abatement part II: Combined heat and power cogeneration

This is the second of a series of two articles, dealing with a new approach of environomic (thermodynamic, economic and environmental) performance ‘Typification’ and optimization of power generation technologies. This part treats specifically of combined heat and power (CHP) cogeneration technologies in the context of CO₂ abatement and provides a methodology for a flexible and fast project based CHP system design evaluation. One of the aspect of the approach is the post-optimization integration of the operating and capital costs, in order to effectively deal with the uncertainty of the project specific design and operation conditions (fuel, electricity and heat selling prices, project financial conditions such as investment amortization periods, annual operating hours, etc). In addition the approach also allows to efficiently evaluate the influence of the external cost such as the CO₂ tax level under a tax scheme or the CO₂ permit price in the emission trading market.     

利用锅炉烟道气处理工业废水

介绍了当前国内利用燃煤锅炉类道气处理工业废水的研究及应用，并对其工业应用进行了分析。