| 11. |
- Beiron, Johanna, 1992, et al.
(författare)
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An assessment of the flexibility of combined heat and power plants in power systems with high shares of intermittent power sources
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There is an urgent need to reduce anthropogenic CO2 emissions from the power sector as a climate change mitigating strategy. Thus, the share of renewable energy sources in power systems, for example wind power, is increasing. However, the variability in wind power generation poses a challenge to conventional thermal power plants, as well as yielding volatile electricity prices. Once in place, wind power with low operating cost will replace higher-cost electricity generation units in the merit order, while during low-wind periods the need for thermal plants remains. Traditionally designed for stable base load, thermal power plants might thus face a future with new demands for flexible operation to stay competitive. Combined heat and power (CHP) plants are thermal power plants that produce electricity and district heating simultaneously and, depending on plant type and fuel, they have different possibilities to vary the ratio between power and heat production. However, technical constraints place limitations on flexibility, including ramp rates and efficiency. The interconnection between the power and heat markets provides additional opportunities for load variation management. With the comparably slower dynamics of the heat market, and the possibility to store thermal energy, prospects of adapting to new and profitable operating strategies that can aid the balancing of the power system arise. This study focuses on how CHP plants can provide flexibility in a scenario with fluctuating power demand and associated volatility in electricity prices. Plant and market dynamics are analyzed to estimate the need for flexibility, and what is required of CHP units in terms of operation to meet these requirements. A CHP plant is modelled in detail with a boiler, steam cycle and its link to the district heating system, both under steady state and transient conditions, using the softwares Ebsilon and Dymola, respectively. The models are validated against operational data from a Swedish CHP plant. Transient responses to load ramps are characterized, as well as the flexibility in power-to-heat ratio, and their effects on efficiency.
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| 12. |
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| 13. |
- Berntsson, Thore, 1947, et al.
(författare)
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Towards Sustainabel Oil Refinery - Pre-study for larger co-operation project
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report, the Chalmers EnergiCentrum (CEC) presents the results of a pre-study commissioned by Preem relating to the effective production of future vehicle fuels.This pre-study was made up of three studies focusing on energy streamlining, the utilisation of waste heat and carbon-dioxide separation and biorefinement relating to the gasification and hydration of vegetable oils. One of the common starting points for these studies was the current situation at the Preem refineries in Göteborg and Lysekil from where the measurement data were obtained and analysed. The report summarises the knowledge situation based on current research in the individual technical fields. The results present some interesting future opportunities for developing the sustainable production of future vehicle fuels. The sections vary, as the areas that have been examined differ and the sections have been written by different people. The reports ends with some joint conclusions and a number of questions which could be included and answered in a more extensive future main study, as part of a developed research partnership between Preem and the Chalmers University of Technology. The preliminary results of this work were analysed with the client at workshops on 1 October and 29 November 2007. The report is written in English combined with an extensive summary in Swedish including a proposal on a future main study. The study was conducted by the Chalmers EnergiCentrum (CEC), in collaboration with a number of researchers in the CEC’s network. They included Thore Berntsson, Jessica Algehed, Erik Hektor and Lennart Persson Elmeroth, all from Heat and Power Technology, Börje Gevert, Chemical and Biological Engineering, Tobias Richards, Forest Products and Chemical Engineering, Filip Johnsson and Anders Lyngfelt, Energy Technology, and Per-Åke Franck and Anders Åsblad, CIT Industriell Energianalys AB. The client, Preem, was represented by Bengt Ahlén, Sören Eriksson, Johan Jervehed, Bertil Karlsson, Gunnar Olsson, Ulf Kuylenstierna, Stefan Nyström, Martin Sjöberg and Thomas Ögren. Tobias Richards was responsible for compiling the report and Bertil Pettersson was the project manager.
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| 14. |
- Biermann, Max, 1989, et al.
(författare)
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Efficient utilization of industrial excess heat for carbon capture and district heating
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Carbon capture and storage (CCS) from fossil and biogenic (BECCS) emission sources is necessary to limit global warming to well below 2°C. The EU as well as Swedish national agencies emphasize the importance of CCS for emission intensive industries. However, the cost of implementing CCS is currently still higher than the cost of emitting CO2 via the EU ETS, for example. To incentivize rapid deployment of CCS, the concept of partial capture has been suggested, i.e. capturing only a fraction of the site emissions to reduce capture cost. Several studies have found that the utilization of excess heat from industrial processes could significantly reduce the capture cost as the heat required (~120°C) may be available in significant quantities. However, available excess heat will not be sufficient to power full capture at most industrial sites. In Sweden, many industries utilize all or part of their excess heat in heat recovery units or in combined heat and power (CHP) plants to produce electricity and deliver heat to municipal district heating (MDH) systems. A broad implementation of CCS will, thus, effect the availability of excess heat for industrial heat and power generation. The future product portfolio of industrial processes with excess heat export and CHP plants can therefore be expected to include not only heat and power production, but also climate services (CCS/BECCS) and grid services (frequency regulation due to intermittent renewables). The aim of this work is to assess partial capture at sites that have access to low-value excess heat to power the capture process, whilst considering competition from using the excess heat for MDH delivery. The work is based on process modelling and cost estimation of CO2 capture processes using amine absorption for two illustrative case studies, a refinery and a steel mill, which both currently use excess heat for MDH. The main focus is on investigating how seasonal variations in the availability of excess heat as well as the demand of district heating impact cost-efficient design and operation of partial capture at industrial sites. A challenge when utilizing excess heat in connection to a process connected to a district heating system is that the heat source which can be used to power part of the capture process will exhibit seasonal availability, and thus may inflict extra cost for the CCS plant not running at full load, and therefore may counteract the economic motivation for partial capture. To prevent this, heat integration between CCS and municipal district heating is investigated, for example by utilizing heat from the CO2 compression so that low-pressure steam is released from MDH to provide heat to capture CO2 whilst maintaining MDH supply. The design of the amine absorption capture process will have to handle significant load changes and still maintain high separation efficiency within hydrodynamic boundaries of the absorber and stripper columns. The cost of such operation will depend on the solvent circulation flows, the number of absorber columns (including packing and liquid collectors/distributors) and capacity of solvent buffer tanks for storing unused solvent during the winter season. Assuming that a constant amount of CO2 is avoided, the avoidance cost of CCS based on excess heat with seasonal heat load variations is compared to the avoidance cost of CCS based on the use of external fuel to achieve a constant heat load to the reboiler.
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| 15. |
- Biermann, Max, 1989, et al.
(författare)
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Evaluation of Steel Mills as Carbon Sinks
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The iron and steel industry is one of the industries with the largest global contribution to CO2 emissions. Possible mitigation options include use of biomass and carbon capture and storage. Combining these two mitigation options, this study evaluates the potential for BECCS at an integrated steel mill in Sweden. The injection of pulverized biocoal from torrefaction or pyrolysis into a blast furnace and CO2 capture by amine absorption of the blast furnace gas leaving at the top of the furnace can reduce CO2 site emissions by up to 61 %, when accounting for negative emissions (biogenic CO2 being captured). The mitigation cost are estimated to 43 – 100 € per tonne CO2 avoided, depending primarily on biomass prices and the share of biomass used in the process (the study assumes a cost effective capture rate of 84%). Besides a reduction in CO2 emissions, the study highlights the potential for green by-products from injecting biogenic carbon into the blast furnace in the form of renewable electricity and CO2 neutral steel. The study concludes that it is theoretically possible to reach carbon neutrality or even net-negative emissions in an integrated steel mill, but this would require considerable process changes and high demand of biomass. Nonetheless, the implementation of BECCS based on feasible biomass injection volumes in integrated steel mills is interesting as a near-term and possibly cost-effective option for CO2 mitigation.
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| 16. |
- Biermann, Max, 1989, et al.
(författare)
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Scenario for near-term implementation of partial capture from blast furnace gases in Swedish steel industry
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Iron-and-steel making is a carbon-intensive industry and responsible for about 8% of global CO2 emissions. Meeting CO2 reduction targets is challenging, since carbon is inherent in the dominating production route in blast furnaces. Long-term plans to phase out carbon and change production technique are under way, such as iron ore reduction with hydrogen[1][2] won from renewable energies or electro winning[3], however unlikely to be implemented at scale before 2040 [4]. Until a transition to such technologies is completed, carbon leakage will remain to be a threat to steel industry inside EU ETS system. CCS remains an option for steel industry to comply with reduction targets and meet rising allowance (EUA) prices, currently above 20 €/t. Most studies on CCS propose a capture rate of ≥ 90 %[5–7], however, CCS could be considered as a part of a series of measures (e.g. fuel change, energy efficiency measures) that together achieve a significant reduction in CO2 emissions until a carbon-neutral production is in place. This line of thought motivates the concept of partial capture, where only the most cost effective part of the CO2 emissions are separated for storage [8]. In steel industry, high CO2 concentrations at large flows and the availability of excess heat make partial capture attractive. Previous work on the steel mill in Luleå, Sweden, emits around 3.1 Mt CO2 per year, has found that 40-45 % of site emissions can be captured fueled by excess heat alone[9]. Therein, five heat recovery technologies were assessed, ranging from back pressure operation of CHP turbine to dry slag granulation. Promising CO2 sources on site include flue gases from hot stoves and the combined-heat and power plant, and the process gas originating from the blast furnace – blast furnace gas (BFG). BFG is a pressurized, low value fuel used for heating on site. CO2 separation from BFG requires less reboiler heat for MEA regeneration, and the enhanced heating value of the CO2 lean BFG increases energy efficiency of the steel mill [9]. This work discusses the near-term (the 2020s) implementation of partial capture at a Swedish steel mill and the economic viability of such implementation dependent on the energy price, carbon price, and required reductions in CO2 emissions. Based on previous work [9][10,11] on partial capture in steel industry a cost estimation of a capture system for the BFG is conducted including CAPEX and OPEX of the MEA capture unit, gas piping, and recovering heat from the steel mill. The costs are summarized as equivalent annualized capture cost (EAC) and set into relation to transport and storage costs as well as carbon emission costs to form the net abatement cost (NAC) according to Eq. (1) ???=???+ ?????????&??????? ???? −?????? ????? [€/???2] (1) Figure 1 shows how EAC for BFG varies with the capture rate and the cost of steam for different heat recovery technologies represented by the steps in the curve ( see explanation in [9]). Note that partial capture from BFG is more economical than the full capture benchmark. The most cost-efficient case of 28 €/t CO2 captured is achieved for BFG capture fueled by steam from back-pressure operation (at the expense of electricity production), flue gas heat recovery and flare gas combustion. The transport and storage cost applied in Eq (1) represent ship transport from the Bothnian Bay to a storage site in the Baltic Sea , according to Kjärstad et el.[12]. Transport and storage cost range within 17 – 27 €/t CO2 depending on scale. These installation and operation cost for capture, transport and storage are set into relation with various scenarios on future carbon and energy (electricity) prices in Europe and Sweden. For example, Figure 2 illustrates a scenario in line with IEA’s sustainable development scenario to restrict global warming to 2°C. The carbon prices are adapted from WEO 2018 [13] and increase from 20 € to 120 € per tonne CO2 by 2040 and the electricity prices of 42-52 €/MWh (increasing with time) are based on latest results from the NEPP project [14]. In this scenario, partial capture from BFG could become economic viable in 2029, construction in 2020 with operation from 2022/23 onwards is likely to pay off within a lifetime of 20 years only. This work demonstrates the viability of partial capture as cost-efficient mitigation measure for the steel industry and illustrates conditions for an early implementation in the 2020s. This work is part of the CO2stCap project (Cutting Cost of CO2 Capture in Process Industry) and funded by Gassnova (CLIMIT programme), the Swedish Energy Agency, and industry partners.
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| 17. |
- Bäckström, Daniel, 1985, et al.
(författare)
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Gas temperature and radiative heat transfer in oxy-fuel flames
- 2012
-
Ingår i: The 37th International Technical Conference on Clean Coal & Fuel Systems, Clearwater USA, 3-7/6-2012. - 9780932066374
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work presents measurements of the gas temperature, including fluctuations, and its influence on the radiative heat transfer in oxy-fuel flames. The measurements were carried out in the Chalmers 100 kW oxy-fuel test unit. The in-furnace gas temperature was measured by a suction pyrometer and by an optical system based on FTIR-spectroscopy. The radiation intensity was measured by a Narrow Angle Radiometer and the gas radiation was calculated with a Statistical Narrow Band model. The overall agreement between the two temperature measurement techniques was good. The optical system showed a lower temperature than the suction pyrometer in the low velocity regions of the furnace, a difference which is likely to be an effect of the purge gas added in the optical probe. The measured temperature fluctuations were evaluated by modeling of the gas radiation. The influence from the measured fluctuations on the radiative heat transfer shows no effect of turbulence-radiation interaction. However, by comparing with temperature fluctuations in other flames it can be seen that the fluctuations measured here are relatively small. Further research is needed to clarify to which extent the applied methods can account for the turbulence-radiation interaction in the investigated flame.
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| 18. |
- Djerf, Tove, 1989, et al.
(författare)
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Solids circulation in circulating fluidized beds with low riser aspect ratio and varying total solids inventory
- 2016
-
Ingår i: Fluidization XV (2016), Quebec, Canada.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents an experimental study with the aim tounderstand the relation between the flow conditions - the riser pressure drop and fluidization velocity - in a CFB riser and the net (external)solids flux (Gs [kg/m2s]), applying a riser geometry and overall flow conditions similar to CFB boilers.The experiments are carried out in a CFB unit operated under ambient conditions. The riser has a cross section of 0.7 m x 0.12 m and a height of 8.5 m, yielding a riser height-to-width aspect ratio of 10.6 (in the wide dimension), similar to that of CFB boilers. The unit is equipped with densely spaced pressure taps providing a fine resolution of the measured vertical pressure profile along the riser and an automatic system to accurately measure Gs. The experiments cover fluidization velocities of 0.3-7 m/s, riser pressure drops of 1.7-10.5 kPa and loopseal fluidization velocities of 0.12-0.54 m/s (secondary air flows are not considered). These ranges correspond to conditions both with and without a dense bottom region.The results show that Gs is determined by the solids concentration at the riser top, which depends riser pressure drop and fluidization velocity, and the backflow effect, which depends on the configuration and flow conditions of the loop seal and the exit region. For operating conditions with a dense bottom bed present, Gs is independent of riser pressure drop, whereas when operating without a dense bed an increase in riser pressure drop yields an increase in Gs.
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| 19. |
- Ekvall, Thomas, 1986, et al.
(författare)
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CO-KCl-SO2 interactions in an 80 kW propane-fired flame
- 2014
-
Ingår i: the proceedings of the Impacts of Fuel Quality on Power production conference, 2014. ; , s. 13-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It is well known that combustion of biomass derived fuels may lead to problems with high-temperature corrosion (HTC). The HTC process is largely based on the release and transformation of chlorine, sulphur and alkali components during the combustion process. However, these components may also interact with other critical parts of the combustion chemistry and the present work focuses on how potassium chloride and sulphur dioxide influence the oxidation of carbon monoxide. This is investigated during combustion of propane (80 kW) applying both air and oxy-fuel combustion conditions. The experiments were carried out in Chalmers 100 kW oxy-fuel test facility in which sulphur dioxide and potassium chloride was added to the flame. The experimental results are also supported by modelling work including a detailed reaction mechanism of the related alkali-S-Cl chemistry. The results show that KCl promotes CO-oxidation in oxy-fuel combustion. However, for the experimental conditions tested in the present work, no significant effect was detected in air combustion. In addition, when adding water as well as SO2 to the flames, there were no significant effects on the measured CO concentrations in the respective flames.
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| 20. |
- Ekvall, Thomas, 1986, et al.
(författare)
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Sulphation of potassium chloride in air and oxy-fuel combustion
- 2013
-
Ingår i: The Proceedings of the 38th International Technical Conference on Clean Coal & Fuel Systems, June 2-6 2013, Clearwater, Florida, USA.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During combustion of biomass, alkali and chlorine species are released to the gas phase, species which can react to form corrosive salts that potentially may cause severe corrosion problems on heat transfer surfaces upon condensation. This corrosion process is referred to as high-temperature corrosion (HTC) and it limits steam data in biomass combustion, with corresponding limitation in thermal efficiency. The flue gas composition and also the HTC conditions can be altered by introducing a second fuel, e.g. coal for co-combustion. The flue gas composition can be altered even more drastically when applying oxy-fuel combustion where the concentration of combustion products are higher than in air firing due to the use of pure oxygen and flue gas recycling. In this work, the alkali sulphation process in different oxy-fuel and air-fuel atmospheres has been investigated by modelling the gas phase chemistry. The overall purpose is to examine the combined effects of oxy-combustion and co-combustion on the HTC process and to make a comparison with air-fired conditions. The flue gas composition in oxy-fuel combustion depends on the recirculation strategy used which in turn also influences the sulphation. According to the modelling results the degree of sulphation of gas-phase alkali metals is in general higher for oxy-fuel combustion compared to air-fuel combustion. It is concluded from the modelling results that an increased amount of sulphur and water contribute to a substantial effect on the degree of sulphation of alkali species. On the other hand, the modelling also shows that an increased content of HCl, which is present during wet recirculation, has a negative effect on the sulphation; the degree of sulphation is therefore lower in wet compared to dry recirculation. The effects of other important parameters such as sulphur-to-potassium and air-to-fuel ratios, temperature and residence time are also discussed further in the paper.
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