Maximizing the Mitigation Potential of Curtailed Wind: A Comparison Between Carbon Capture and Utilization, and Direct Air Capture Processes for the UK

Carbon capture and storage (CCS) with fossil fuel or biomass plants (BECCS) is considered a critical technology to meet mitigation targets set by the Paris Agreement1. However, several drawbacks including high upfront investment costs, significant energy penalty and long-term permanent storage challenges have limited the uptake of CCS on the required scale. Carbon capture and utilisation (CCU) provides an alternative route to recycle CO2 into chemical feedstock and/or synthetic transport fuels (e.g. methanol, DME) that can displace fossil-derived fuels. As the carbon is only transformed, CCU must be integrated with capture/storage to actually offset subsequent emissions from the vehicles consuming them. The mitigation of decentralised emissions poses significant challenges and necessitates the use of carbon dioxide removal technologies (CDR), one of which is direct capture of CO2 from the atmosphere (DAC). The last decade has seen increasing penetration of wind power in the UK electricity system to meet mitigation targets. Because of this, periods of surplus wind generation and low demand or limited/full storage capacity arise. Constraint payments then have to be made to wind farms to curtail generation. This work investigates two possible options to achieve mitigation with this curtailed electricity. In Process A, curtailed electricity is used to produce electrolytic hydrogen and operate methanol synthesis plants. It is then integrated with a direct air capture (DAC) plant to recapture and recycle emissions from the vehicles. Process B assumes curtailed electricity is used to run a DAC plant directly in order to capture decentralised carbon emissions and provide CO2 feedstock for CCU processes. The UK was used as a case study and the methanol synthesis process described by Rihko-Struckmann et al.2 was used as the reference. A range of energy requirements for DAC are cited in literature; the lower and upper bounds of 6.7 GJ/tCO2 and 12.6 GJ/tCO23, respectively, were used. This work has taken a base case curtailment level of 2.5% of the UK total electricity demand, which is equivalent to 390 GWh/y4. Both processes have been compared on the basis of mitigation potential, defined by the proportion of CO2 emissions from gasoline vehicles that are avoided, and mitigation costs per tonne of CO2 captured. Process A resulted in avoiding 0.12% of gasoline emissions (~0.05 MtCO2/y). Surplus energy (~64% of the curtailed electricity) was required to run the DAC plant and an associated air separation unit. The mitigation of potential of Process B was 0.10% or 0.18%, depending on energy requirement used. Therefore, the process that maximises mitigation potential depends on the DAC process considered; using the lower-bound energy requirement, surplus electricity for DAC only is preferable. Neither process is economically viable. CCU costs ($905/tCO2) were found to be double the DAC-only costs ($449/tCO2), mainly due to high H2 costs. It will remain financially-unattractive unless the methanol production becomes profitable. This is unlikely as it requires methanol price to almost double, a carbon price of $313/t to be in effect, or H2 price to reduce to a third of today’s price to$1800/t. References 1. IPCC. Climate Change 2014: Mitigation of Climate Change. Working Group III Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (2014). doi:10.1017/CBO9781107415416 2. Rihko-Struckmann, L. K., Peschel, A., Hanke-Rauschenbach, R. & Sundmacher, K. Assessment of methanol synthesis utilizing exhaust CO2 for chemical storage of electrical energy. Ind. Eng. Chem. Res. 49, 11073–11078 (2010). 3. Socolow, R. et al. Direct Air Capture of CO 2 with Chemicals Panel on Public Affairs. Am. Phys. Soc. - Panel Public Aff. 100 (2011). 4. Messiou, A. Centre for Environmental Policy Investigating the role of power storage in accommodating the future wind. (2012)

Power-to-transport: Using curtailed wind to run CCU processes

The Paris Agreement signaled global commitment to limit average global temperature rise to 2˚C and to make efforts to achieve 1.5˚C increase (UNFCCC, 2015). The IPCC AR5 cites carbon capture and storage (CCS) as a necessary technology to achieve this (IPCC, 2014). However, several drawbacks including high upfront investment costs, significant energy penalty and long-term permanent storage challenges have limited the uptake of CCS on the required scale (Styring, et al., 2011). Carbon capture and utilisation (CCU) provides an alternative route to recycle CO2 into chemical feedstock and/or synthetic transport fuels (e.g. methanol, DME) that can displace fossil-derived fuels. As the carbon is only transformed, CCU must be integrated with capture/storage to actually offset subsequent emissions from the vehicles consuming them. The mitigation of decentralised emissions poses significant challenges and necessitates the use of carbon dioxide removal technologies (CDR), one of which is direct capture of CO2 from the atmosphere (DAC). This work investigates two possible options for CCU integrated with DAC: Option A is the storage of curtailed wind as methanol which can be used in road vehicles to displace gasoline emissions (power-to-transport), and Option B is the use curtailed wind directly to run a DAC plant in order to capture decentralised carbon emissions and provide CO2 feedstock for CCU processes. A high-level analysis has been carried out to determine the gasoline substitution and emissions offset potential of both options, the overall conversion efficiency of the power-to-transport process, and the economics of each option. The UK was used as a case study and the methanol synthesis process described by (Rihko-Struckmann, et al., 2010) was used as the reference. Work by (Messiou, 2012) investigated the curtailment levels for the UK electricity system with increased wind generation; the ‘medium integration’ scenario assumed the UK had 5 times the current wind generation capacity. A corresponding curtailment level of 2.5% (of total electricity dispatched) was determined, this has been used as the base case in our analysis. The gasoline substitution potential of methanol produced via option A was ~0.12% (equivalent to ~0.05 MtCO2/y) with the overall power-to-transport efficiency being ~11%. Surplus energy (~64% of the curtailed electricity) was required to run the DAC plant and an associated air separation unit. The methanol production plant was found to be economically infeasible unless current methanol price increased by a factor of 1.8 to $988/t, the cost of hydrogen fell by a factor of 2.3 to$1811/t or a carbon price of $313/t was in effect. For option B, the emissions offset potential of the DAC process was ~0.18% for the same curtailment, capturing ~0.07 MtCO2/y. Therefore, the utilisation of curtailed electricity for direct capture of CO2 from the atmosphere results in greater avoided emissions than if it was stored as methanol. References IPCC, 2014. Climate Change 2014: Mitigation of Climate Change. Working Group III Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, s.l.: Cambridge University Press. Messiou, A., 2012. Investigating the role of power storage in accommodating the future wind integration into UK’s power system. London: Imperial College London. Rihko-Struckmann, L. K., Peschel, A., Hanke-Rauschenbach, R. & Sundmacher, K., 2010. Assessment of Methanol Synthesis Utilizing Exhaust CO2 for Chemical Storage of Electrical Energy. Industrial and Engineering Chemistry Research, Issue 49, pp. 11073-11078. Styring, P., Jansen, D., de Coninck, H. & Reith, H., 2011. Carbon Capture and Utilisation in the green economy: Using CO2 to manufacture fuel, chemicals and materials, s.l.: The Centre for Low Carbon Futures

Fractional differentiability of nowhere differentiable functions and dimensions

Weierstrass's everywhere continuous but nowhere differentiable function is shown to be locally continuously fractionally differentiable everywhere for all orders below the `critical order' 2-s and not so for orders between 2-s and 1, where s, 1<s<2 is the box dimension of the graph of the function. This observation is consolidated in the general result showing a direct connection between local fractional differentiability and the box dimension/ local Holder exponent. Levy index for one dimensional Levy flights is shown to be the critical order of its characteristic function. Local fractional derivatives of multifractal signals (non-random functions) are shown to provide the local Holder exponent. It is argued that Local fractional derivatives provide a powerful tool to analyze pointwise behavior of irregular signals.Comment: minor changes, 19 pages, Late

Holder exponents of irregular signals and local fractional derivatives

It has been recognized recently that fractional calculus is useful for handling scaling structures and processes. We begin this survey by pointing out the relevance of the subject to physical situations. Then the essential definitions and formulae from fractional calculus are summarized and their immediate use in the study of scaling in physical systems is given. This is followed by a brief summary of classical results. The main theme of the review rests on the notion of local fractional derivatives. There is a direct connection between local fractional differentiability properties and the dimensions/ local Holder exponents of nowhere differentiable functions. It is argued that local fractional derivatives provide a powerful tool to analyse the pointwise behaviour of irregular signals and functions.Comment: 20 pages, Late

The pharmacokinetics of penicillamine in a female mongrel dog

The pharmacokinetic parameters of D-penicillamine were investigated by administering four intravenous bolus doses, four oral doses, and six constant rate intravenous infusions to a female mongrel dog at dosages comparable to 250, 500, 750, and 1000 mg in man. The pharmacokinetics of D-penicillamine demonstrated nonlinearity in the dog. There was more than proportional increase in the area under the whole blood concentration curve for an increase in the bolus intravenous dose. The steady state whole blood, plasma, and packed cell levels of penicillamine were increased more than proportionately for an increase in the intravenous infusion rate. Total body clearance of penicillamine was decreased by increasing the dose or the infusion rate of penicillamine. Correspondingly, the estimated half-life of unchanged penicillamine in the whole blood was decreased for increased intravenous bolus doses. The renal clearance of penicillamine was nonlinear, decreasing with time during the bolus experiments and increasing at higher infusion rates. The nonrenal clearance was decreased at higher infusion rates, suggesting that a saturable nonrenal elimination process exists for penicillamine in the dog. The nonlinearities that were observed in the dog, if also present in man, may be responsible in part for the dose related side effects reported clinically for penicillamine .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45080/1/10928_2005_Article_BF01061028.pd

Gleichgewichtsprüfung bei Kindern mit sensorineuraler Hörstörung

Hintergrund: Bei Kindern mit einer Innenohrschwerhörigkeit finden sich häufig Beeinträchtigungen der Vestibularorganfunktion. Die Literatur zu diesem Thema ist sehr rar, so dass keine standardisierte, altersabhängige Testbatterie für realisierbare Gleichgewichtsuntersuchungen existiert.Material und Methoden: In einer klinischen Querschnittsstudie wurden 100 Kinder (51 Jungen, 49 Mädchen) im Alter von 2-10 Jahren (Median 5 Jahre) anhand der audiologischen Diagnostik (Art der Hörstörung, Hörschwellenbestimmung) ausgewählt und untersucht. Es erfolgten: Leuchtbrillentestung (Spontan- und Kopfschüttelnystagmus), okulomotorische Prüfung, Koordinationsprüfungen, vestibulospinale Tests (Gangbild, Romberg und Tandem-Romberg - jeweils auf fester und weicher Unterlage), Ableitung der cVEMP und Bestimmung der subjektiven visuellen Vertikalen (SVV mittels Eimervertikalentest) zur Otolithenfunktionsprüfung. Die Daten wurden in eine Datenmaske eingegeben und mit SPSS ausgewertet.Ergebnisse: Exemplarisch wird die alters- und hörschwellenabhängige Durchführbarkeit dargestellt: 75 Kinder (mittleres Alter 5,57 Jahre, medianer Hörverlust 57,5 dB) absolvierten die cVEMP-Ableitung. Das Alter der Kinder die nicht untersucht werden konnten, lag im Mittel bei 3,72 Jahren (medianer Hörverlust 86,88 dB). Bei 68 Kindern (mittleres Alter 6,15 Jahre, medianer Hörverlust 55,63 dB) war der Eimervertikalentest durchführbar. Das Alter der Kinder die nicht untersucht werden konnten, lag im Mittel bei 3,11 Jahren (medianer Hörverlust 76,88 dB).Diskussion: Die Beurteilung der altersabhängigen Durchführbarkeit von Gleichgewichtsuntersuchungen bei Kindern mittels logistischer Regression ermöglicht erstmals die Abschätzung des wahrscheinlichen Untersuchungserfolgs. Während Untersuchungen zur Bestimmung der cVEMP bei Kindern vorliegen, überraschen die Ergebnisse zur Einschätzung der SVV aufgrund der hohen Genauigkeit und Reproduzierbarkeit.Fazit: Die Durchführbarkeit der Tests wird neben dem Alter anscheinend auch durch die Schwere der Hörstörung beeinflusst

Closing the carbon cycle to maximise climate change mitigation: power-to-methanol vs. power-to-direct air capture

It is broadly recognised that CO2 capture and storage (CCS) and associated negative emissions technologies (NETs) are vital to meeting the Paris agreement target. The hitherto failure to deploy CCS on the required scale has led to the search for options to improve its economic return. CO2 capture and utilisation (CCU) has been proposed as an opportunity to generate value from waste CO2 emissions and improve the economic viability of CCS, with the suggestion of using curtailed renewable energy as a core component of this strategy. This study sets out to quantify (a) the amount of curtailed renewable energy that is likely to be available in the coming decades, (b) the amount of fossil CO2 emissions which can be avoided by using this curtailed energy to convert CO2 to methanol for use as a transport fuel – power-to-fuel, with the counterfactual of using that curtailed energy to directly remove CO2 from the atmosphere via direct air capture (DAC) and subsequent underground storage, power-to-DAC. In 2015, the UK curtailed 1277 GWh of renewable power, or 1.5% of total renewable power generated. Our analysis shows that the level of curtailed energy is unlikely to increase beyond 2.5% until renewable power accounts for more than 50% of total installed capacity. This is unlikely to be the case in the UK before 2035. It was found that: (1) power-to-DAC could achieve 0.23–0.67 tCO2 avoided MWh−1 of curtailed power, and (2) power-to-Fuel could achieve 0.13 tCO2 avoided MWh−1. The power-to-fuel concept was estimated to cost $209 tCO2 avoided−1 in addition to requiring an additional$430–660 tCO2 avoided−1 to finally close the carbon cycle by air capture. The power-to-DAC concept was found to cost only the $430–660 tCO2 avoided−1 for air capture. For power-to-fuel to become profitable, hydrogen prices would need to be less than or equal to$1635 tH2−1 or methanol prices must increase to $960 tMeOH−1. Absent this change in H2 price or methanol value, a subsidy of approximately$283 tCO2−1 would be required. A core conclusion of this study is that using (surplus) renewable energy for direct air capture and CO2 storage is a less costly and more effective option to mitigate climate change than using this energy to produce methanol to substitute gasoline