Transactions of the Canadian Society for Mechanical Engineering

Volume 33 (2009), Issue 1

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Nuclear plants emit virtually no greenhouse gases over their full life-cycle. Consequently, continued operation of existing nuclear plants is recognized as essential to meeting even the modest greenhouse gas reduction targets of the Kyoto Accord. However, much expanded nuclear deployment will be needed as developing economies aggressively grow GDP with its associated growth in electrical power. Projecting to 2040 and based on the scenarios of the United Nations Intergovernmental Panel on Climate Change's (IPCC), we have examined deploying increased non-carbon energy sources for electricity production, including further conversion of electricity to hydrogen using conventional low-temperature water electrolysis. Our NuWind© model has been used to calculate the production costs for hydrogen in typical potential markets, using the actual prices of electricity paid by the Alberta Power Pool and by the Ontario Grid. The analysis shows clearly that by optimizing the co-production of hydrogen and electricity (referred to as the H2/e process) the cost for hydrogen produced can comfortably meet the US Department of Energy's target for realistic nuclear investment costs, hydrogen generation systems, and wind capacity factors. The synergy of nuclear plus wind power for hydrogen generation plus co-production of electricity improves the economics of harnessing wind energy to produce hydrogen.

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Distributed or decentralised generation (DG) using advanced fossil fuel and renewable energy technologies is an attractive alternative to traditional electricity generation. Over 75% of new generating capacity installed in the Australian state of Victoria between 2000 and 2010 will be DG from gas turbines and wind farms. However, it is uncertain if this new capacity will be sufficient to maintain historic levels of electricity supply reliability. The contribution of DG to Victoria's electricity supply in 2010 has been assessed, through analysis of modelled supply and demand data and comparisons with data from 2000. While it was assumed that new gas turbines will provide peak load and emergency generation, the role of wind farms was evaluated by considering their equivalent firm capacity estimated using statistical and probabilistic methods. Results show that all DG from gas turbines will contribute to Victoria's electricity supply in 2010, but only 4-30% of installed wind farm capacity can be considered firm or reliable. Technical performance indicators suggest that the new generating capacity will be unable to satisfy increased demand with adequate reliability. Additional base load capacity and demand reduction measures are required to ensure Victoria's electricity supply reliability is maintained in the future.

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A design study was conducted to evaluate the cost-effectiveness of solar thermal power generation in a 50 kWe power plant that could be used in a remote location. The system combines a solar collector-thermal storage system utilizing a heat transfer Huid and a simple Rankine cycle power generator utilizing R123 refrigerant. Evacuated tube solar collectors heat mineral oil and supply it to a thermal storage tank. A mineral oil to refrigerant heat exchanger generates superheated refrigerant vapor, which drives a radial turbogenerator. Supplemental natural gas firing maintains a constant thermal storage temperature irregardless of solar conditions enabling the system to produce a constant 50 kWe output. A simulation was carried out to predict the performance of the system in the hottest summer day and the coldest winter day for southern California solar conditions. A rigorous economic analysis was conducted. The system offers advantages over advanced solar thermal power plants by implementing simple fixed evacuated tube collectors, which are less prone to damage in harsh desert environment. Also, backed up by fossil fuel power generation, it is possible to obtain continued operation even during low insolation sky conditions and at night, a feature that stand-alone PV systems do not offer.

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As one of the most developed and energy intensive cities in China, the Shanghai's municipal government tries to make Shanghai one of the leading cities of energy conservation in China. Expanding the use of combined heat and power (CHP) system is the one of the main ways to optimize Shanghai's energy structure and to protect its environment. This paper aims to analyze the feasibility of introducing CHP in the central business district, in Shanghai, to determine the energy savings, environmental impact and economic efficiency. Three types of energy supply systems are considered: electricity-only system, 2 CHP systems with electric tracking and thermal tracking. Relative to the conventional electricity-only system, the CHP systems are capable of reducing the primary energy consumption by approximately 24% and 4%, CO₂ emission by 38% and 11%, respectively. For CHP, although the initial costs are often substantially higher than a conventional system, it is expected to dramatically reduce the cost of running. The result shows if introducing CHP, it only takes approximately 5 years can return the initial investment, in each case. This implies that the introduction of CHP can achieve high profitability.

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There are several benefits to district heating systems. The system design requires knowledge of community peak heating load and annual heating energy requirements. For this purpose, a residential energy model was developed using several energy usage databases. Hourly, peak, and annual heating demands were estimated by simulating 15 archetype houses using an hour-byhour building simulation program, ENERPASS. Estimated heating profiles from model houses were used to design a district heating system for a hypothetical rural community in Nova Scotia. The findings show that building simulation is a very flexible and valuable tool in identifying the required peak and hourly energy demand of a community for the design of district energy

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Combined cycle power plants with a gas turbine topping cycle and a steam turbine bottoming cycle are widely used due to their high efficiencies. Combined cycle cogeneration has the possibility to produce power and process heat more efficiently, leading to higher performance and reduced green house gas emissions. The objective of the present work is to analyze and simulate a natural gas fired combined cycle cogeneration unit with multiple process heaters and to investigate the effect of operating variables on the performance. The operating conditions investigated include, gas turbine pressure ratio, process heat loads and process steam extraction pressure. The gas turbine pressure ratio significantly influences the performance of the combined cycle cogeneration system. It is also identified that extracting process steam at lower pressures improves the power generation and cogeneration efficiencies. The process heat load influences combined cycle efficiency and combined cycle cogeneration efficiency in opposite ways. It is also observed that using multiple process heaters with different process steam pressures, rather than a single process heater, improves the combined cycle cogeneration plant efficiency.

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Wet ammonia-water compression-resorption heat pumps constitute an attractive alternative to the commonly known heat pumps based on Osenbriick cycle because they eliminate the necessity of oil-liquid refrigerant separation. In this respect, a special designed oil-free compressor operating under wet (two-phase) conditions equips the heat pump. The compressor is lubricated by the liquid refrigerant which is carried-out while compressing the vapor. The thermodynamic cycle is located completely inside the two-phase region. In this paper are demonstrated two procedures to optimize the design for COP maximization. It is shown that there is: (i) an optimal choice of the vapor quality at suction, and (ii) an optimal distribution of heat transfer surface between the resorber and the desorber (the total amount of heat transfer surface, being an expression of investment cost, is fixed). The circulating concentration of ammonia has to be chosen such that the minimum pressure in the system is over one bar (to avoid air penetration from the atmosphere) and the maximum pressure is bounded by a technical-economical maximal limit. A general procedure for calculation of the optimal cycle parameters is presented and exemplified for a case with practical relevance. The paper presents only the trends and rough quantitative estimations because the analyzed case is restricted to the ideal isentropic compression. Further research is needed to quantify in detail the effect of compression irreversibility.

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Historic trends and future projections of energy use and carbon dioxide emissions associated with the United Kingdom building stock are analysed for the period 1970-2050. Energy use in housing is found to rise at a slightly slower rate than the increase in household numbers, which totalled some 25.5 million in 2000. It appears feasible to reduce carbon dioxide (C02) emissions in the UK domestic building stock by more than 65% by 2050. But this would require a significant take-up of energy saving measures and the adoption of various low or zero carbon (LZC) energy technologies. Non-domestic buildings consisted of some 1.98 million premises in 2000. Anticipated changes in the UK Building Regulations will lead to reductions in energy use and carbon emissions of up to 17% and 12% respectively for 2010 standard buildings. Improvements in the non-domestic building stock and industrial processing could lead to a reduction of nearly 59% in C02 emissions, via the adoption of LZC energy technologies. Thus, the potential for 'greening' the UK building stock - making it environmentally benign - is large, but the measures needed to achieve this would present a significant challenge to the UK government, domestic householders, and industry in the broadest sense.

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In this research, seasonal greenhouse gas (GHG) errusslOn factors were developed to realize the true CO2 reduction potential of a small scale renewable energy technology. From this data Time Dependent Valuation (TDV) emission factors and hourly emission factors were developed which provided upper and lower limits, respectively. The use of regionally specific climate-modeled factors, such as those identified, allowed for a better representation of the benefits associated with GHG reducing technologies, such as photovoltaic (PV).

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The effect of varying environment temperature on the efficiency of glycol cold thermal energy storage (CTES) is investigated. Several thermodynamic system parameters are analyzed, such as change in storage temperature, storage heat load, energy and exergy efficiencies and exergy destruction. Glycol CTES is treated as a potential application of sensible heat storage systems. A storage tank with a capacity of 150,000 kg is considered with an ethylene glycolbased water solution storage medium. Exergy analysis is used, which provides more useful information than energy analysis about energy quality, efficiency, losses and irreversibilities. Modelling results indicate that the system exergy efficiency is 46% less than energy efficiency. The system exergy efficiencies are 40% and 20% at 50°C and WoC ambient temperatures, respectively. The results imply that cold energy is more efficient at higher ambient temperatures, storage heat loss depends weakly on ambient temperature, and the reference-environment temperature affects significantly exergy destruction and efficiency.

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The use of electrical-utility cogeneration from nuclear energy and coal is examined for improving regional efficiency regarding energy-resource utilization and environmental stewardship. A case study is presented for a large and diverse hypothetical region which has nuclear and fossil facilities in its electrical utility sector. Utility-based cogeneration is determined to reduce significantly annual use of uranium and coal, as well as other fossil fuels, and related emissions for the region and its electrical-utility sector. The reduced emissions of greenhouse gases are significant, and indicate that electrical utility-based cogeneration has a key role to play in combating climate change.

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Exergy is compared with other indicators for the environmental impact of waste emissions in an effort to better understand its potential as, or as the basis for, an effective indicator of the potential of an emitted substance to impact the environment. Relations between environmental impact and exergy in general and chemical exergy of waste emissions in particular are observed to support the use of exergy as such an indicator. The measure of disequilibrium with respect to a reference environment provided by exergy is considered, along with the consequence that the exergy of unrestricted waste emissions has the potential to impact the environment. Exergy is observed to exhibit many characteristics of other indicators of environmental impact, which are mainly empirical in nature. An exergy-based indicator could contribute to the development of rational and objective procedures for assessing the harmful effects on the environment of a substance and predicting its potential for environmental impact. The potential usefulness of exergy in addressing environmental problems is concluded to be significant, but further research is needed to develop objective exergy-based indicators that are practical for the potential of a substance to impact on the environment.