Pilot-scale Experimental Work on the Production of Precipitated Calcium Carbonate (PCC) from Steel Slag for CO2 Fixation

The production of steel is a very energy intensive process and the industry contributes a significant amount to global carbon dioxide (CO2) emissions. Steel production also generates steel slag, a calcium-rich waste which has few useful applications and is partly landfilled. Producing precipitated calcium carbonate (PCC) from steelmaking slag (Slag2PCC) is a way to reduce CO2 emissions while at the same time turning slag waste into a valuable product. In the Slag2PCC process, a solution of ammonium chloride (NH4Cl) is used to extract calcium from steelmaking slag which is then bubbled with a CO2-containing gas in a process called carbonation to form PCC. This thesis has focussed on how the process conditions during carbonation affect the carbonation process as well as the quality parameters of the PCC produced. Carbonation tests were performed at laboratory scale (5L) and at a recently constructed pilot-scale Slag2PCC plant (200L). From the laboratory tests it was found that temperature, calcium concentration [Ca2+], NH4Cl solvent concentration [NH4Cl], CO2 flow and agitation speed have important effects on the carbonation process and the quality of the PCC produced. PCC particle size can be reduced by lower temperature, lower [Ca2+], lower [NH4Cl], lower CO2 flow and higher agitation speed. It was also found that increasing [NH4Cl] and CO2 flow is likely to increase particle agglomeration. Temperature, [Ca2+], [NH4Cl], and calcium to carbonate ratio [Ca2+]/[CO32-] appear to be the most significant factors determining the crystal morphology. Work with the pilot plant showed that the equipment should be modified to improve mixing and solid suspension performance. While the production of rhombohedral calcite and aragonite polymorphs was successfully demonstrated, attempts to make scalenohedral PCC in the pilot plant based on conventional Ca(OH)2 slurry carbonation conditions were not successful, believed to be due to the NH4Cl, [Ca2+], pH, or the difference in supersaturation conditions compared with conventional Ca(OH)2 slurry carbonation. The cost of PCC production from the Slag2PCC process was also estimated as 65 €/t based on the results of the pilot scale work. The CO2 emissions of the Slag2PCC process were estimated as -0.229 tCO2/tPCC, giving a CO2 capture cost of 284 €/t. However, if the PCC can be produced at high quality and sold at market price (120 €/t), the process delivers a profit of 55 €/tPCC and CO2 capture becomes profitable at 239 €/tCO2

Can liberalised electricity markets support decarbonised portfolios in line with the Paris Agreement?:A case study of Central Western Europe

We model the evolution of the Central Western Europe power system until 2040 with an increasing carbon price and strong growth of variable renewable energy sources (vRES) for four electricity market designs: the current energy-only market, a reformed energy-only market, both also with the addition of a capacity market. Each design is modelled for two decarbonisation pathways: one targeting net-zero emissions by 2040 for a 2 degrees C warming limit, and the other targeting -850 Mt CO2 y(-) for a 1.5 degrees C warming limit. We compare these scenarios against the high-level objectives of delivering low-carbon electricity reliably to consumers at the lowest possible cost. Our results suggest that both 2 degrees C and 1.5 degrees C compliant systems could be achieved and deliver electricity reliably. In terms of cost, we find the 1.5 degrees C warming scenarios lead to system costs which are twice as high as the 2 degrees C scenarios due to the high cost of negative emission technologies - in particular direct air carbon capture (DAC). To make a 1.5 degrees C target more affordable, policymakers should investigate lower cost alternatives in other sectors, and increase research and development in DAC to reduce its cost

GRAthena++: puncture evolutions on vertex-centered oct-tree AMR

Numerical relativity is central to the investigation of astrophysical sources in the dynamical and strong-field gravity regime, such as binary black hole and neutron star coalescences. Current challenges set by gravitational-wave and multi-messenger astronomy call for highly performant and scalable codes on modern massively-parallel architectures. We present GR-Athena++, a general-relativistic, high-order, vertex-centered solver that extends the oct-tree, adaptive mesh refinement capabilities of the astrophysical (radiation) magnetohydrodynamics code Athena++. To simulate dynamical space-times GR-Athena++ uses the Z4c evolution scheme of numerical relativity coupled to the moving puncture gauge. We demonstrate stable and accurate binary black hole merger evolutions via extensive convergence testing, cross-code validation, and verification against state-of-the-art effective-one-body waveforms. GR-Athena++ leverages the task-based parallelism paradigm of Athena++ to achieve excellent scalability. We measure strong scaling efficiencies above $95\%$ for up to $\sim 1.2\times10^4$ CPUs and excellent weak scaling is shown up to $\sim 10^5$ CPUs in a production binary black hole setup with adaptive mesh refinement. GR-Athena++ thus allows for the robust simulation of compact binary coalescences and offers a viable path towards numerical relativity at exascale

Pitfalls of Power Systems Modelling Metrics

In power system modelling the unit commitment problem is used to simulate the wholesale electricity market. A solution to the unit commitment problem is a least-cost schedule that contains information regarding the capacity factors of each generator, the total CO2 emissions, and unserved energy per hour. However, since there might be a large variety of (sub)-optimal solutions, these characteristics might be arbitrary and conclusions about them may be presumptuous.In this article, we illustrate this by running multiple experiments on a future European power system. Each scenario was run multiple times by adding additional terms to the objective function such as the minimization and maximization of generator capacity factors, carbon emissions, and loss of load hours. The results showed that schedules can be equivalent in terms of cost, but that relative capacity factors, emissions, and loss of load hours could differ by large factors.</p

Statistics of surface divergence and their relation to air-water gas transfer velocity

Air-sea gas fluxes are generally defined in terms of the air/water concentration difference of the gas and the gas transfer velocity,kL. Because it is difficult to measure kLin the ocean, it is often parameterized using more easily measured physical properties. Surface divergence theory suggests that infrared (IR) images of the water surface, which contain information concerning the movement of water very near the air-water interface, might be used to estimatekL. Therefore, a series of experiments testing whether IR imagery could provide a convenient means for estimating the surface divergence applicable to air-sea exchange were conducted in a synthetic jet array tank embedded in a wind tunnel. Gas transfer velocities were measured as a function of wind stress and mechanically generated turbulence; laser-induced fluorescence was used to measure the concentration of carbon dioxide in the top 300 μm of the water surface; IR imagery was used to measure the spatial and temporal distribution of the aqueous skin temperature; and particle image velocimetry was used to measure turbulence at a depth of 1 cm below the air-water interface. It is shown that an estimate of the surface divergence for both wind-shear driven turbulence and mechanically generated turbulence can be derived from the surface skin temperature. The estimates derived from the IR images are compared to velocity field divergences measured by the PIV and to independent estimates of the divergence made using the laser-induced fluorescence data. Divergence is shown to scale withkLvalues measured using gaseous tracers as predicted by conceptual models for both wind-driven and mechanically generated turbulence

Scaling the gas transfer velocity and hydraulic geometry in streams and small rivers

Scaling is an integral component of ecology and earth science. To date, the ability to determine the importance of air–water gas exchange across large spatial scales is hampered partly by our ability to scale the gas transfer velocity and stream hydraulics. Here we report on a metadata analysis of 563 direct gas tracer release experiments that examines scaling laws for the gas transfer velocity. We found that the gas transfer velocity scales with the product of stream slope and velocity, which is in alignment with theory on stream energy dissipation. In addition to providing equations that predict the gas transfer velocity based on stream hydraulics, we used our hydraulic data set to report a new set of hydraulic exponents and coefficients that allow the prediction of stream width, depth, and velocity based on discharge. Finally, we report a new table of gas Schmidt number dependencies to allow researchers to estimate a gas transfer velocity using our equation for many gasses of interest

Stratus 10 tenth setting of the Stratus Ocean Reference Station : cruise RB-10-01, January 2 - January 30, 2010 Charleston, South Carolina - Valparaiso, Chile

The Ocean Reference Station at 20°S, 85°W under the stratus clouds west of northern Chile is being maintained to provide ongoing climate-quality records of surface meteorology, air-sea fluxes of heat, freshwater, and momentum, and of upper ocean temperature, salinity, and velocity variability. The Stratus Ocean Reference Station (ORS Stratus) is supported by the National Oceanic and Atmospheric Administration’s (NOAA) Climate Observation Program. It is recovered and redeployed annually, with past cruises that have come between October and December. Due to necessary repairs on the electric motors of the ship’s propulsion system, this year the cruise was delayed until January. During the 2009/2010 cruise on the NOAA ship Ronald H. Brown to the ORS Stratus site, the primary activities were the recovery of the Stratus 9 WHOI surface mooring that had been deployed in October 2008, deployment of a new (Stratus 10) WHOI surface mooring at that site, in-situ calibration of the buoy meteorological sensors by comparison with instrumentation installed on the ship by staff of the NOAA Earth System Research Laboratory (ESRL), and collection of underway and on station oceanographic data to continue to characterize the upper ocean in the stratus region. Both underway CTD (UCTD) profiles and Vertical Microstructure Profiles (VMP) were collected along the track and during surveys dedicated to investigating eddy variability in the region. Surface drifters were also launched along the track. The intent was also to visit a buoy for the Pacific tsunami warning system maintained by the Hydrographic and Oceanographic Service of the Chilean Navy (SHOA). This DART (Deep- Ocean Assessment and Reporting of Tsunami) buoy had been equipped with IMET sensors and subsurface oceanographic instruments, and a recovery and replacement of the IMET sensors was planned. However, the DART buoy broke free from its mooring on January 3rd and was recovered by the Chilean navy; the work done at that site during this cruise was the recovery of the bottom pressure unit.Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA17RJ1223 for the Cooperative Institute for Climate and Ocean Research (CICOR)

Green on-site power generation : environmental considerations on small-scale biomass gasifier fuel-cell CHP systems for the residential sector

Contemporary combined heat and power (CHP) systems are often based on fossil fuels, such as natural gas or heating oil. Thereby, small-scale cogeneration systems are intended to replace or complement traditional heating equipment in residential buildings. In addition to space heating or domestic hot water supply, electricity is generated for the own consumption of the building or to be sold to the electric power grid. The adaptation of CHP-systems to renewable energy sources, such as solid biomass applications is challenging, because of feedstock composition and heat integration. Nevertheless, in particular smallscale CHP technologies based on biomass gasification and solid oxide fuel cells (SOFCs) offer significant potentials, also regarding important co-benefits, such as security of energy supply as well as emission reductions in terms of greenhouse gases or air pollutants. Besides emission or air quality regulations, the development of CHP technologies for clean on-site small-scale power generation is also strongly incentivised by energy efficiency policies for residential appliances, such as e.g. Ecodesign and Energy Labelling in the European Union (EU). Furthermore, solid residual biomass as renewable local energy source is best suited for decentralised operations such as micro-grids, also to reduce long-haul fuel transports. By this means such distributed energy resource technology can become an essential part of a forward-looking strategy for net zero energy or even smart plus energy buildings. In this context, this paper presents preliminary impact assessment results and most recent environmental considerations from the EU Horizon 2020 project "FlexiFuel-SOFC" (Grant Agreement no. 641229), which aims at the development of a novel CHP system, consisting of a fuel flexible smallscale fixed-bed updraft gasifier technology, a compact gas cleaning concept and an SOFC for electricity generation. Besides sole system efficiencies, in particular resource and emission aspects of solid fuel combustion and net electricity effects need to be considered. The latter means that vastly less emission intensive gasifier-fuel cell CHP technologies cause significant less fuel related emissions than traditional heating systems, an effect which is further strengthened by avoided emissions from more emission intensive traditional grid electricity generation. As promising result, operation "net" emissions of such on-site generation installations may be virtually zero or even negative. Additionally, this paper scopes central regulatory instruments for small-scale CHP systems in the EU to discuss ways to improve the framework for system deployment

Linking Unserved Energy to Weather Regimes

The integration of renewable energy sources into power systems is expected to increase significantly in the coming decades. This can result in critical situations related to the strong variability in space and time of weather patterns. During these critical situations the power system experiences a structural shortage of energy across multiple time steps and regions, leading to Energy Not Served (ENS) events. Our research explores the relationship between six weather regimes that describe the large scale atmospheric flow and ENS events in Europe by simulating future power systems. Our results indicate that most regions have a specific weather regime that leads to the highest number of ENS events. However, ENS events can still occur during any weather regime, but with a lower probability. In particular, our findings show that ENS events in western and central European countries often coincide with either the positive Scandinavian Blocking (SB+), characterised by cold air penetrating Europe under calm weather conditions from north-eastern regions, or North Atlantic Oscillation (NAO+) weather regime, characterised by westerly flow and cold air in the southern half of Europe. Additionally, we found that the relative impact of one of these regimes reaches a peak 10 days before ENS events in these countries. In Scandinavian and Baltic countries, on the other hand, our results indicate that the relative prevalence of the negative Atlantic Ridge (AR-) weather regime is higher during and leading up to the ENS event.Comment: Rogier H. Wuijts and Laurens P. Stoop contributed equally to this wor

Towards a future-proof climate database for European energy system studies

In 2013, the European Network of Transmission System Operators (TSOs) for electricity (ENTSO-E) created the Pan-European Climate Database (PECD), a tool that has underpinned most studies conducted by TSOs ever since. So far, the different versions of the PECD have used so-called modern-era ‘reanalysis’ products that represent a gridded amalgamation of historical conditions from observations. However, scientific evidence suggests, and recent European regulation requires, that power system adequacy studies should take climate change into account when estimating the future potential of variable renewable resources, such as wind, solar and hydro, and the impact of temperature on electricity demand. This paper explains the need for future climate data in energy systems studies and provides high-level recommendations for building a future-proof reference climate dataset for TSOs, not just in Europe, but also globally