Application of the exergy method to the environmental impact estimation: The nitric acid production as a case study

In this work the exergy method is used to compare various methods for removal of NO_x from waste (tail) gas released into the atmosphere from nitric acid production plants with respect to their overall environmental impact. Three basic methods for NO_x abatement are analysed: selective catalytic reduction (SCR), non-selective catalytic reduction (NSCR) and extended absorption. The positive and negative effects and the net effect from the NO_x abatement are calculated. The following exergy-based indicators are used for comparing the energy efficiency and the environmental impact of different treatment processes as a result from pollutants removal: reduction of the exergy of the emissions from the whole process route (ammonia and nitric acid production units); exergy of the additional emissions, arising as a result of the treatment process; total net reduction of the exergy consumption, Cumulative Energy Consumption (CEnC) and Cumulative Exergy Consumption (CExC) of natural resources as a result of the waste flows treatment.     

Cumulative exergy losses associated with the production of lead metal

Cumulative exergy losses result from the irreversibility of the links of a technological network leading from raw materials and fuels extracted from nature to the product under consideration. The sum of these losses can be apportioned into partial exergy losses (associated with particular links of the technological network) or into constituent exergy losses (associated with constituent subprocesses of the network). The methods of calculation of the partial and constituent exergy losses are presented, taking into account the useful byproducts substituting the major products of other processes. Analyses of partial and constituent exergy losses are made for the technological network of lead metal production.     

Natural resource demand of global biofuels in the Anthropocene: A review

The Anthropocene is the later part of the Holocene where human activity has become a major driver for global ecosystem development. The demand of natural resources, renewable and non-renewable, is a crucial aspect of environmental (un-) sustainability. When considering a societal transition scheme towards sustainability, bio-based options come to the fore. The article develops a global framework for the analysis of natural resource demand of global biofuels. The framework defines the biofuel system in terms of exergy at four levels, i.e., the foreground system, the supply chain, the anthroposphere, and the ecosphere. Various measures of resource demand, such as cumulative exergy demand, global and anthropogenic exergy budgets are incorporated into the framework. Based on reviews of global biofuel production and natural resource demand of the anthroposphere, the study finds that the production of conventional biofuels, i.e., first generation of biodiesel and bioethanol by key producer countries in 2008 consumed 9.32 E+11 MJ of exergy from non-renewable resources and accounted for 0.23% of the total anthropogenic non-renewable resource demand. In addition, it shows that the contribution to climate change due to the heat emission of the global biofuel production was 5.79 E−05 W/m², which would reach up to 0.002% of global greenhouse warming if anthropogenic heat flux is treated as a climate forcing.     

Aggregate industrial energy consumer response to wholesale prices in the restructured Texas electricity market

The aggregate response of consumers to wholesale price signals is very limited in the restructured Electric Reliability Council of Texas (ERCOT) market. An overall average own-price elasticity of demand of − 0.000008 for industrial energy consumers served at transmission voltage is estimated using a Symmetric Generalized McFadden cost function model. To date, ERCOT has sought to promote demand response to price signals without reliance on “stand alone” demand response programs, but with a market structure that is designed to facilitate economic demand response. This very limited responsiveness to wholesale price signals may prove problematic in light of policy decisions to pursue an “energy only” resource adequacy mechanism for ERCOT.     

Impact of wind farm integration on electricity market prices

Wind generation is considered one of the most rapidly increasing resources among other distributed generation technologies. Recently, wind farms with considerable output power rating are installed. The variability of the wind output power, and the forecast inaccuracy could have an impact on electricity market prices. These issues have been addressed by developing a single auction market model to determine the close to real-time electricity market prices. The market-clearing price was determined by formulating an optimal power flow problem while considering different operational strategies. Inaccurate power prediction can result in either underestimated or overestimated market prices, which would lead to either savings to customers or additional revenue for generator suppliers.     

美国加州电力市场电价的分形特征

以美国加州电力市场长期电价序列为研究对象，并由此引入了分数布朗运动模型和R／S分析法，计算出了不同时间区间内电价的赫斯特指数，发现加州电力市场符合分形市场假设，电价遵循有偏的随机游走．具有长期相关性和统计自相关性等性质。这些发现为描述市场环境下的电价分布提供了一种新模式。     

Advanced exergetic analysis of a novel system for generating electricity and vaporizing liquefied natural gas

LNG technology has been in use since the 1960s. During the last 20 years the total cost of LNG technology has decreased by 30% due mainly to improvements of the liquefaction process and shipping. However, the regasification system has not been significantly improved. The paper presents a detailed advanced exergetic analysis of a novel co-generation concept that combines LNG regasification with the generation of electricity. The analysis includes splitting the exergy destruction within each component into its unavoidable, avoidable, endogenous and exogenous parts as well as a detailed splitting of the avoidable exogenous exergy destruction. The results of the advanced exergetic analysis are confirmed through a sensitivity analysis. Finally, some suggestions for improving the overall system efficiency are developed.     

Evolution of the decrease in mineral exergy throughout the 20th century. The case of copper in the US

A mineral deposit is a natural resource whose exergy can be calculated from a defined reference environment (RE). This RE can be compared to a thermodynamically dead planet, where all materials have reacted, dispersed and mixed. Like any substance, a mine is characterized by its quantity, chemical composition and concentration (ore grade). The mine’s exergy measures the minimum (reversible) energy to extract and concentrate the materials from the RE to the conditions in the mine. And the mine’s exergy replacement cost accounts for the actual exergy required to accomplish this, with available technologies. The exergy assessment of the natural resource wealth of the Earth defined from a RE is named as exergoecology. The aim of this paper is to prove the usefulness of these two indicators for assessing the degradation of mineral deposits over history. As an example, the exergy decrease of US copper mines due to copper extraction throughout the 20th century has been determined. The results indicate that the exergy decrease was 65.4 Mtoe, while the exergy replacement cost 889.9 Mtoe. During the past century, the US extracted the equivalent of 2.5 and 1.2 times of its current national exergy reserves and base reserve of copper, respectively.     

The impact of wind power on electricity prices

This paper investigates the impact of wind power on electricity prices using a production cost model of the Independent System Operator – New England power system. Different scenarios in terms of wind penetration, wind forecasts, and wind curtailment are modeled in order to analyze the impact of wind power on electricity prices for different wind penetration levels and for different levels of wind power visibility and controllability. The analysis concludes that electricity price volatility increases even as electricity prices decrease with increasing wind penetration levels. The impact of wind power on price volatility is larger in the shorter term (5-min compared to hour-to-hour). The results presented show that over-forecasting wind power increases electricity prices while under-forecasting wind power reduces them. The modeling results also show that controlling wind power by allowing curtailment increases electricity prices, and for higher wind penetrations it also reduces their volatility.     

Advanced exergetic analysis: Approaches for splitting the exergy destruction into endogenous and exogenous parts

The irreversibilities (exergy destruction) within a component of an energy conversion system can be represented by two parts. The first part depends on the inefficiencies of the considered component while the second part depends on the system structure and the inefficiencies of the other components of the overall system. Thus, the exergy destruction occurring within a component can be split into two parts: (a) endogenous exergy destruction due exclusively to the performance of the component being considered and (b) exogenous exergy destruction caused also by the inefficiencies within the remaining components of the overall system. The paper discusses four different approaches developed by the authors for calculating the endogenous part of exergy destruction as well as the approach based on the structural theory. The advantages, disadvantages and restrictions for applications associated with each approach are presented. It is concluded that all approaches developed by the authors lead to comparable and acceptable results, whereas the structural theory approach should not be used for calculating the endogenous part of exergy destruction because it delivers unacceptable results. Splitting the exergy destruction into endogenous and exogenous parts improves our understanding of the interactions among system components and provides very useful information for improving an exergy conversion system, particularly when this concept is combined with the concept of avoidable and unavoidable exergy destruction.     

Exergy analysis in the assessment of hydrogen production from UCG

The demand for H₂ increases rapidly with the gradual recognition of the potential of H₂ as an important secondary energy. At present, coal gasification is the main way to obtain hydrogen on a large scale and at a low cost in China. The underground coal gasification (UCG), as a kind of in-situ utilization technology that can exploit the unreachable deep coal resources, could become an alternative H₂ production pathway. This paper presents comparative study of energy utilization and resource consumption in H₂ production by UCG and typical surface coal gasification (SCG) technology, namely Lurgi fixed bed gasification, with 1.2 billion Nm³/a throughput of H₂ as example, to offer corresponding data support. The efficiency and the amount of resources consumed in constructing and operating each coal-to-hydrogen system under different conditions have been researched from exergetic point of view, which is not reported in existing literatures. In this paper, the exergy efficiency is calculated to be 40.48% and 40.98% for hydrogen production using UCG and SCG. The result indicates the competitiveness of UCG in the field of hydrogen production comparing with widely used coal gasification technology. The resource consumption is measured by cumulative exergy consumption (CExC), which is 8.17E+10 MJ and 6.57E+10 MJ for H₂ production from UCG and SCG. The result shows that although the H₂ production from UCG has higher CExC, it can significantly reduce the resource consumption of equipment comparing with H₂ production from SCG, indicating its advantage in total investment. It is found that the exergy efficiency increases with the rise in H₂O-to-O₂ and O₂-to-CO₂ ratio, while the value of CExC decreases with the appreciation of H₂O-to-O₂ ratio yet increases as the O₂-to-CO₂ ratio rises. In addition, the sensitivity analysis of production capacity reveals that the exergy efficiency gap and CExC gap between hydrogen production by UCG and SCG diminishes at smaller scale production capacities, showing that UCG is more suitable for small-scale hydrogen production.     

RES support in Russia: Impact on capacity and electricity market prices

Russian renewable energy policy has undergone changes following an establishment of targets for installed capacity and power production using renewable energy sources and the introduction of new capacity based support scheme for renewable energy. The forecasted amount of future renewable power will not provide enough power production to meet growing demand for renewable energy; although, it will help with modernization of the energy sector and development of renewable technology and innovation. At the same time, the capacity support scheme for renewable energy may adversely affect capacity prices and become an additional burden for industrial consumers, who are already paying the cost of capacity support for conventional power plants, so-called Capacity Delivery Agreements (CDAs). This work assesses the impact of the new capacity based support scheme on capacity and electricity price formation. Modeling results show that the impact of capacity support for renewable energy is small compared to that of capacity support for conventional energy, suggesting that the Russian energy production mix will continue to be dominated by fossil fuel based generation.     

Electricity prices in the Finnish retail market

This study focuses, firstly, on the pricing of electricity in the Finnish retail market. In particular, the impact of the ownership structure on prices is tested empirically. Secondly, the influence of low-cost electricity sources on retail prices is considered. The question about whether the average fuel costs rather than the wholesale price determine the retail prices is thus addressed. The supply side behaviour characterised may explain the passivity of client activity in the seemingly competitive Finnish market.     

Comparative analysis of features of Polish and Lithuanian Day-ahead electricity market prices

The goal of this article is to better understand the processes of electricity market price formation in Poland and Lithuania through an analysis of the features (volatility and spikes) of Lithuanian and Polish day-ahead electricity market prices and to assess how acquired electricity price features could affect the achievement of the main goals of the national energy policy. The following indicators have been calculated to determine electricity market price volatility: the oscillation coefficient, the coefficient of variation, an adjusted coefficient of variation, the standard deviation indicator, the daily velocity indicator (based on the overall average price) and the daily velocity indicator (based on the daily average price). Critical values for electricity market price have been calculated to evaluate price spikes. This analysis reveals that electricity market-price volatility is moderate in Poland and high in Lithuania. Electricity price spikes have been an observable phenomenon both in Lithuanian and in Polish day-ahead electricity markets, but they are more common in Lithuania, encompassing 3.15% of the time period analysed in Poland and 4.68% of the time period analysed in Lithuania. Volatile, spiking and increasing electricity prices in day-ahead electricity markets in Lithuania and Poland create preconditions and substantiate the relevance of implementation of the national energy policies and measures.     

Evaluating the EU ETS impacts on profits,investments and prices of the Italian electricity market

Climate change is a global issue, but actions to mitigate its development are regional. Europe has taken the leadership in the carbon emission policy by introducing the Emissions Trading Scheme (EU ETS), formerly regulated by Directive 2003/87/EC and since 2013 by Directive 2009/29/EC. This new Directive imposes a full auctioning system for allocating CO₂ allowances to the power sector and encourages the use of renewable energy sources.We investigate the economic impacts of the EU ETS on the Italian electricity market using a power generation expansion model. We adopt a technological representation of the energy market that also accounts for power exchanges with foreign countries and we assume that generators operate in different zones connected by interconnections with limited capacity. We study both an oligopolistic and a perfectly competitive behavior of Italian generators and we compare the corresponding outcomes under different EU ETS scenarios. Our analysis shows that, in perfect competition, generators generally invest more than in an oligopolistic framework, but in both market configurations, investments in Italy are mainly concentrated in fossil-fired plants, especially in 2020. This happens also when incentives are given to renewables.The developed models are implemented as complementarity problems and solved in GAMS using the PATH solver.     

Industrial customer response to wholesale prices in the restructured Texas electricity market

This paper estimates the demand responsiveness of the 20 largest industrial energy consumers in the Houston area to wholesale price signals in the restructured Electric Reliability Council of Texas (ERCOT) market. Statistical analysis of their load patterns employing a Symmetric Generalized McFadden cost function model suggests that ERCOT achieved limited success in establishing a market that facilitates demand response from the largest industrial energy consumers in the Houston area to wholesale price signals in its second year of retail competition. The muted price response is at least partially because energy consumers who opt to offer their “interruptibility” to the market as an ancillary service are constrained in their ability to respond to wholesale energy prices.     

A new approach to the exergy analysis of absorption refrigeration machines

Splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts represents a new development in the exergy analysis of energy conversion systems. This splitting improves the accuracy of exergy analysis, improves our understanding of the thermodynamic inefficiencies and facilitates the improvement of a system.

An absorption refrigeration machine is used here as an application example. This refrigeration machine represents the most complex type of a refrigeration machine, in which the sum of physical and chemical exergy is used for each material stream.     

High penetration wind generation impacts on spot prices in the Australian national electricity market

This paper explores wind power integration issues for the South Australian (SA) region of the Australian National Electricity Market (NEM) by assessing the interaction of regional wind generation, electricity demand and spot prices over 2 recent years of market operation. SA's wind energy penetration has recently surpassed 20% and it has only a limited interconnection with other regions of the NEM. As such, it represents an interesting example of high wind penetration in a gross wholesale pool market electricity industry. Our findings suggest that while electricity demand continues to have the greatest influence on spot prices in SA, wind generation levels have become a significant secondary influence, and there is an inverse relationship between wind generation and price. No clear relationship between wind generation and demand has been identified although some periods of extremely high demand may coincide with lower wind generation. Periods of high wind output are associated with generally lower market prices, and also appear to contribute to extreme negative price events. The results highlight the importance of electricity market and renewable policy design in facilitating economically efficient high wind penetrations.     

Fattening up for the market? Higher electricity prices and the value of the CEGB

A mathematical model of the evolution of the electricity supply industry to beyond the end of the century is used to forecast the cost and revenues of electricity generation after privatization. Subracting the costs from the revenues gives a time profile of profits that is discounted back to the date privatization to give a valuation of the Central Electricity Generating Board (CEGB). The model shows that every 1% rise in the price of electricity before privatization adds between 2.2% and 3.3% to the value of the CEGB. The exact increase depends mainly on whether the price rises are permanent, or are clawed back after privatization by price cuts until turn of the century. The tougher financial targets for the industry announced by the Department of Energy in 1987 are expected to add about 7% in real terms to the price of electricity before privatization. The government's proceeds from the sale of the CEGB should receive a 15–20% boost as a result.