| 1. |
- Gong, Mei, 1967-
(författare)
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Using exergy and optimization models to improve industrial energy systems towards sustainability
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With finite natural resources and large energy demands in the world, a sustainable development approach becomes increasingly important in the improvement of energy systems. The concept of sustainability is examined with relation to exergy flows on the earth. The present industrial society is obviously not sustainable. The main aim of this study is to analyze and improve industrial energy systems towards an increased sustainability.Exergy analysis is used for evaluating energy systems and for guiding efficiency-improvement efforts. An existing optimization method is improved and applied to an energy system in order to maximize its economic feasibility and profitability. Life cycle analysis based on exergy is applied in order to further guide towards sustainable development. This thesis offers tools to better evaluate energy systems with regard to physical resource use, economy and environment. These tools are particularly useful for decision-making in long-term plarming.The concepts and methods presented are useful in the design and optimization of more sustainable energy systems, particularly in industrial processes. A typical Swedish industry, a pulp and board mill, is examined using an improved optimization method together with the exergy method. The main cause of the low exergy efficiency in the mill is irreversibility of combustion and of heat transfer in the steam generator. The change in the price of electricity has a greater effect on the energy cost than the change in the price of fuel, which means a unified European electricity market has large impact on the Swedish industry. Increasing efficiency of processes usually minimizes environmental damage and maximizes economic benefits. In spite of increasing the exergy loss switching from fossil fuel to bio-fuels can decrease the net CO2 emission as well as the energy cost, and is a step towards increased sustainability. The investments in an oil-bark boiler, evaporation plant and recovery boiler give a good supply of sustainable resources, a reduction of environmental impact, and both energy and economical saving. In addition, with replacing the present evaporation plant with the non-conventional one, even more benefits could be achieved. Still, there are more potential for further improvement in the mill.
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| 2. |
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| 3. |
- Ji, Xiaoyan, et al.
(författare)
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Phase equilibria for the oxygen-water system up to elevated temperatures and pressures
- 2004
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Ingår i: Fluid Phase Equilibria. - : Elsevier BV. - 0378-3812 .- 1879-0224. ; 222-223, s. 39-47
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Tidskriftsartikel (refereegranskat)abstract
- A new thermodynamic model was presented to calculate the phase equilibria for the oxygen-water system. The modified Redlich-Kwong equation of state with a new correlated cross-interaction parameter was used to calculate fugacity coefficients for the vapor phase. The dissolved oxygen followed Henry's law. A new expression was correlated from the experimental data to calculate Henry's constant of oxygen. The calculated results of equilibrium composition were compared with the available experimental data and those calculated by other models with different parameters. The comparison revealed that the new model is suitable for calculating both liquid and vapor compositions while the empirical method is only suitable for estimating the liquid composition. Furthermore, compared to the model proposed by Rebenovich and Beketov, the calculated results of the vapor composition with the new model are better.
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| 4. |
- Ji, Xiaoyan, et al.
(författare)
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Saturated thermodynamic properties for the air-water system at elevated temperature and pressure
- 2003
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 58, s. 5069-5077
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Tidskriftsartikel (refereegranskat)abstract
- A new thermodynamic model is proposed to calculate the thermodynamic properties for the air-water system in which the dry air was assumed to be a mixture of nitrogen and oxygen with the mole fractions of 0.7812 and 0.2188, respectively. For the vapor phase, fugacity coefficients were calculated with the modified Redlich-Kwong equation of state in which a new interaction parameter of oxygen and water was correlated from the experimental data of oxygen-water system. The dissolved gas followed Henry's law. Henry's constant of nitrogen was calculated with the Helgeson equation of state and that for oxygen was correlated from the experimental data of oxygen-water system. The proposed model was verified by comparing the calculated results with the available experimental data. It is shown that the proposed model is suitable for predicting saturated thermodynamic properties for the air-water system up to 300°C and 200 atm. Furthermore, the prediction results of the proposed model are better than those calculated with the model of Rabinovich and Beketov (Moist Gases, Thermodynamic Properties. Begell: House, 1995), and the application range is wider than that of the model of Hyland and Wexler (ASHRAE Trans. 89(2A) (1983a, b) 500-519, 520-535) which are among the best of today's models
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| 5. |
- Ji, Xiaoyan, et al.
(författare)
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Survey of experimental data and assessment of calculation methods of properties for the air–water mixture
- 2003
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Ingår i: Applied Thermal Engineering. - 1359-4311 .- 1873-5606. ; 23:17, s. 2213-2228
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic properties of the air-water mixture at elevated temperatures and pressures are of importance in the design and simulation of the advanced gas turbine systems with water addition. In this paper, comprehensive available experimental data and calculation methods for the air-water mixture were reviewed. It is found that the available experimental data are limited, and the determined temperature is within 75 °C. New experimental data are needed to supply in order to verify the model further. Three kinds of models (ideal model, ideal mixing model and real model) were used to calculate saturated vapor composition and enthalpy for the air-water mixture, and the calculated results of these models were compared with experimental data and each other. The comparison shows that for the calculation of saturated vapor composition, the reliable range of the ideal model and ideal mixing model is up to 10 bar. The real model is reliable over a wide temperature and pressure range, and the model proposed by Hyland and Wexler is the best one of today. However, the reliability of the Hyland and Wexler model approved by experimental data is only up to 75 °C and 50 bar, and it is necessary to propose a new predictive model based on the available experimental data to be used up to elevated temperatures and pressures. In the calculation of enthalpy, compared to the ideal model, the calculated results of the ideal mixing model are closer to those of real model.
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| 6. |
- Jonsson, M., et al.
(författare)
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Ammonia-water bottoming cycles : a comparison between gas engines and gas diesel engines as prime movers
- 2001
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Ingår i: Energy. - 0360-5442 .- 1873-6785. ; 26:1, s. 31-44
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Tidskriftsartikel (refereegranskat)abstract
- Ammonia-water cycles can produce more power than steam Rankine cycles in several applications. One of these applications is as a bottoming cycle to internal combustion engines. In the present study, ammonia-water bottoming cycle configurations for spark-ignition gas engines and compression-ignition gas diesel engines have been compared, Single-pressure Rankine cycles have been used as a basis for the comparison. Low heat source temperatures should increase the difference in power output between the ammonia-water cycle and the Rankine cycle. However, in this study, the results of the simulations show different trends. In most cases, the ammonia-water bottoming cycles with gas engines as prime movers generate more power compared to a Rankine cycle than when gas diesel engines are the prime movers. The temperature of the most important waste heat source, the exhaust gas, is approximately 100 degreesC higher for the gas engines than for the gas diesel engines. Therefore, for the gas engines, most of the waste heat available to a bottoming cycle is in the form of relatively high-temperature exhaust gas, while for the gas diesel engines more of the waste heat is in the form of relatively low-temperature heat sources.
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| 7. |
- Maunsbach, K., et al.
(författare)
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Integration of advanced gas turbines in pulp and paper mills for increased power generation
- 2001
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Ingår i: Journal of engineering for gas turbines and power. - : ASME International. - 0742-4795 .- 1528-8919. ; 123:4, s. 734-740
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Tidskriftsartikel (refereegranskat)abstract
- The pulp and paper industry handles large amounts of energy and today produces the steam needed for the process and some of the required electricity. Several studies have shown that black liquor gasification and combined cycles increase the power production significantly compared to the traditional processes used today. It is of interest to investigate the performance when advanced gas turbines are integrated with next-generation pulp and paper mills. The present study focused on comparing the combined cycle with the integration of advanced gas turbines such as steam injected gas turbine (STIG) and evaporative gas turbine (EvGT) in pulp and paper mills. Two categories of simulations have been performed: (1) comparison of gasification of both black liquor and biomass connected to either a combined cycle or steam injected gas turbine with a heat recovery steam generator: (2) externally fired gas turbine in combination with the traditional recovery boiler The energy demand of the pulp and paper mills is satisfied in all cases and the possibility to deliver a power surplus for external use is verified. The study investigates new system combinations of applications for advanced gas turbines.
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| 8. |
- Mollersten, K., et al.
(författare)
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Potential and cost-effectiveness of CO2 reductions through energy measures in Swedish pulp and paper mills
- 2003
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 28:7, s. 691-710
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Tidskriftsartikel (refereegranskat)abstract
- Using the two criteria of potential CO2 reduction and Cost Of CO2 reduction, technical energy measures in Swedish pulp. and paper mills are investigated. Principal CO2-reducing measures analysed are: decreased specific energy utilisation, fuel switch, and CO2 capture and sequestration. Among the investigated measures, conventional technologies for electricity conservation and improved electrical conversion efficiency in existing systems for cogeneration of heat and power are identified as the most cost-effective alternatives that also have large CO2 reduction potentials. For commercially available technologies, the results indicate an accumulated reduction potential of up to 8 MtCO(2)/y (14% of the Swedish net emissions). If emerging technologies for black liquor gasification (BLG) with pre-combustion CO2 capture and sequestration are considered, the CO2 reduction potential increases by up to 6 MtCO(2)/y (10% of the Swedish net emissions). Commercialised BLG, CO2 capture and reliable CO2 sequestration technologies are identified as important potential contributors to Swedish compliance with Kyoto Protocol targets, especially in a scenario of nuclear power closure.
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| 9. |
- Möllersten, Kenneth, 1966-, et al.
(författare)
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Bioenergy with CO2 Removal and Disposal : An Approach to Negative CO2 Emissions in Energy Systems
- 2001
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we present results from studies on bioenergy systems with CO2 removal and disposal (BCRD). CO2 removal and disposal that could prevent CO2 from fuel combustion entering the atmosphere is usually discussed in connection to fossil fuels. Even with very efficient CO2 removal in fossil fuel-based systems, there will always be positive net CO2 emissions. We show, on the other hand, that BCRD enables energy utilisation with a clearly negative CO2 balance. We present the first preliminary results from an economic assessment of BCRD, and review studies on the economics of CO2 removal in fossil-based systems for further guidance in estimating BCRD costs. We conclude that co-firing biomass and coal with end-of-pipe scrubbing technology promises to be one cost-effective BCRD option in the short term. In the long-term, systems with integrated biomass gasification promise lower additional CO2 removal costs, and black liquor gasification in chemical pulp mills is a particularly promising niche. Swedish and global CO2 reductions potential of this technology are estimated. Finally, some important policy-relevant questions related to the potential of BCRD are raised.
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| 10. |
- Möllersten, Kenneth, 1966-, et al.
(författare)
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CO2 balances and mitigation costs of advanced CHP systems with CO2 capture in pulp and paper mills
- 2003
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the energy efficiency, CO2 mitigation potential and CO2 mitigation cost of biomass-based combined heat and power production (CHP) with a CO2 capture option in Kraft pulp and paper mills. CHP systems based on black liquor and biomass gasifier with combined cycle technology and biomass boiler with steam turbine technology are considered. The study shows that steep CO2 reductions can be achieved through CO2 capture and storage regardless of CHP technology used although alternatives based on black liquor and biomass gasification provide the most efficient systems from a resource and energy point of view. Moreover, using black liquor and biomass gasification technology both pulp mills and integrated pulp and paper mills can potentially become net electricity exporters while at the same time removing CO2 from the atmosphere on a net basis. Furthermore, cost curves are constructed, which show how the cost of CO2 capture and storage in pulp and paper mills depends on system configuration and the distance that the CO2 must be transported to injection sites. The assessment shows that systems based on black liquor and biomass gasification with CO2 capture in integrated pulp and paper mills remove CO2 most cost-effectively.
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