145 research outputs found
Life cycle assessment of ocean liming for carbon dioxide removal from the atmosphere
No full textThe world's oceans are an important part of the global carbon cycle, having already absorbed one-quarter of the anthropogenic carbon emissions, however, at the expense of surface ocean acidity, which has increased around 30% since the Industrial Revolution, affecting marine ecosystems. Ocean liming, whereby particulate calcium oxide or, more likely, hydroxide is spread to surface ocean waters can address, at least partly, both the need for carbon dioxide removal (CDR) and ocean acidification. While the idea was proposed almost three decades ago, previous studies have focused on techno-economic feasibility but not on environmental sustainability. Life cycle assessment revealed that limestone calcination is the main environmental hotspot followed by the capture and storage of the calcination CO2 emissions. Mining, comminution, and hydration had a small impact, while results were sensitive to the kiln technology, fuel type, electricity mix, and transportation. Differences between the carbon and environmental footprint highlight that multi-issue life cycle impact assessment methods may be more appropriate when assessing CDR rather than only using carbon balances. Clean and energy efficient kilns (e.g., solar calciners) and the use of renewable energy optimize the system's environmental performance (total carbon and environmental footprint −1031 kgCO2eq and −15.1 Pt per ton of lime spread in the ocean, respectively). The valorisation of the CO2 emissions from limestone calcination, e.g., for fuels, chemicals, or plastics production, could potentially further improve ocean liming's environmental profile, through avoided emissions, however net removal would depend on the longevity of the use. Results imply that CO2 removal at the Gt yr.−1 scale can be achieved, however more research is required on the biological and ecological implications of this CDR approach.</p
Buffered accelerated weathering of limestone for storing CO2: Chemical background
No full textWe present an evolution of the Accelerated Weathering of Limestone (AWL) method to store CO2 in seawater in the form of bicarbonates. Buffered Accelerated Weathering of Limestone (BAWL) is designed to produce a buffered ionic solution, at seawater pH, which derives from the reaction between a CO2 stream and a powder of micron-sized calcium carbonate particles in a long tubular reactor. Addition of calcium hydroxide to buffer the unreacted CO2 before the discharge in seawater is also provided. BAWL aims to overcome the main limitations of AWL, such as the high amount of water needed, the large size of the reactor, the risk of CO2 degassing back into the atmosphere, if the ionic solution is released into shallow waters, as well as the induced seawater acidification. This paper presents the chemical background of the technology and evaluates its feasibility by considering the chemical equilibria in the different phases of the process. The CO2 emitted for limestone calcination leads to a 24% CO2 penalty; a preliminary cost analysis assesses a storage cost of 100 € per tonne of CO2 from an external source. It finally discusses the main features to be considered for the design at the industrial scale
Potential of Maritime Transport for Ocean Liming and Atmospheric CO2 Removal
No full textProposals to increase ocean alkalinity may make an important contribution to meeting climate change net emission targets, while also helping to ameliorate the effects of ocean acidification. However, the practical feasibility of spreading large amounts of alkaline materials in the seawater is poorly understood. In this study, the potential of discharging calcium hydroxide (slaked lime, SL) using existing maritime transport is evaluated, at the global scale and for the Mediterranean Sea. The potential discharge of SL from existing vessels depends on many factors, mainly their number and load capacity, the distance traveled along the route, the frequency of reloading, and the discharge rate. The latter may be constrained by the localized pH increase in the wake of the ship, which could be detrimental for marine ecosystems. Based on maritime traffic data from the International Maritime Organization for bulk carriers and container ships, and assuming low discharge rates and 15% of the deadweight capacity dedicated for SL transport, the maximum SL potential discharge from all active vessels worldwide is estimated to be between 1.7 and 4.0 Gt/year. For the Mediterranean Sea, based on detailed maritime traffic data, a potential discharge of about 186 Mt/year is estimated. The discharge using a fleet of 1,000 new dedicated ships has also been discussed, with a potential distribution of 1.3 Gt/year. Using average literature values of CO2 removal per unit of SL added to the sea, the global potential of CO2 removal from SL discharge by existing or new ships is estimated at several Gt/year, depending on the discharge rate. Since the potential impacts of SL discharge on the marine environment in the ships' wake limits the rate at which SL can be applied, an overview of methodologies for the assessment of SL concentration in the wake of the ships is presented. A first assessment performed with a three-dimensional non-reactive and a one-dimensional reactive fluid dynamic model simulating the shrinking of particle radii, shows that low discharge rates of a SL slurry lead to pH variations of about 1 unit for a duration of just a few minutes
Manufacturing cement-based materials and building products via extrusion: From laboratory to factory
No full textManufacturing is critical to the economies of the UK and many other countries in the rest of the world. However, manufacturing of cement-based materials and building products predominantly remains based on old batch processing such as casting and pressing technologies and this may limit the applications and performance of the materials and products formed. In this paper, research is reported on transforming manufacturing of precast cement-based materials and building products from in batches to continuous processes via extrusion. Techniques used for producing plastic products are transferred into manufacturing cement-based building products like flat and corrugated sheet tiles, down pipes, door/window frames, door panels, solid wall/facade panels, honeycomb wall/facade panels etc. at laboratory and factory scales. In combination with sustainable cementitious materials with low carbon and low energy as matrix, this enables sustainable building products with key characteristics required by the 21st century can be manufactured via extrusion. The cement-based building products extrusion technique has been successfully transferred to industry. For instance, fibre reinforced cement-based partition wall panels, with a honeycomb cross section as large as 600 mm wide and 90 mm high, have been produced by a continuous extrusion process in a precast concrete products factory in Hangzhou, China.European Commission Seventh Framework Programme, (grant agreement no. 262954) and from the Hong Kong Research Grants Council through grants 6091/00E, 6226/01E, 6273/03E and 6167/06
The potential of enhanced weathering in the UK
No full textEnhanced weathering is the process by which carbon dioxide is sequestered from the atmosphere through the dissolution of silicate minerals on the land surface. The carbon capture potential of enhanced weathering is large, yet there are few data on the effectiveness or engineering feasibility of such a scheme. Here, an energy/carbon balance is presented together with the associated operational costs for the United Kingdom as a case study. The silicate resources are large and could theoretically capture 430 billion tonnes (Gt) of CO2. The majority of this resource is contained in basic rocks (with a carbon capture potential of ∼0.3 tCO2 t−1 rock). There are a limited number of ultrabasic formations (0.8 tCO2 t−1 rock) with a total carbon capture potential of 25.4 GtCO2. It is shown that the energy costs of enhanced weathering may be 656–3501 kWh tCO2−1(net CO2 draw-down, which accounts for emissions during production) for basic rocks and 224–748 kWh tCO2−1 for ultrabasic rocks. Comminution and material transport are the most energy intensive processes accounting for 77–94% of the energy requirements collectively. The operational costs of enhanced weathering could be £44–361 tCO2−1 (24–123 tCO2−1) for basic and ultrabasic rocks respectively. Providing sufficient weathering rates full exploitation of this resource is not possible given the environmental and amenity value of some of the rock formations. Furthermore, the weathering rate and environmental impact of silicate mineral application to the land surface is not fully understood, and further investigation in this area is required to reduce the uncertainty in the estimated costs presented here
Coupling mineral carbonation and ocean liming
No full textThe process by which basic/ultrabasic silicate minerals (e.g., olivine) are reacted with CO2 to produce solid carbonate minerals ("mineral carbonation") has been suggested as a method to sequester carbon dioxide from point sources into stable carbonate minerals. Alternatively, the addition of lime (produced from calcining carbonate minerals) to the surface ocean ("ocean liming"), which results in an increase in ocean pH and a draw-down of atmospheric CO2 has been proposed as a "geoengineering" technology, which stores carbon as dissolved alkalinity in the surface ocean. Combining these approaches, in which the magnesium carbonate minerals produced from mineral carbonation are used as a feedstock for ocean liming (mineral carbonation-ocean liming; MC-OL), may reduce the limitations of individual technologies while maximizing the benefits. Approximately 1.9 metric tons of magnesium silicate (producing 0.7 ton of magnesium oxide) are required for every net ton of CO2 sequestered. A total of 0.7 ton of CO2 is produced from this activity, 70% of which is high-purity (>98%) from calcining and potentially amenable for geological storage. The technology can be conceptually viewed as an alternative to direct air capture and swaps ambient CO2 for high-purity point source CO2. MC-OL requires approximately 4.9 and 2.2 GJ of thermal and electrical energy ton-1 of CO2 sequestered. MC-OL has less demand for geological storage; only 0.5 ton of CO2 needs to be injected for every ton of CO2 removed from the atmosphere. However, manipulation of ocean chemistry in this way potentially creates an additional environmental impact (localized elevated pH or co-dissolution of trace metals) and requires additional attention.</p
Relational subcontracting: the case of contractual joint ventures in China
No full textContractual joint ventures (CJVs) are a major form of investment in China, especially for Hong Kong firms in South China province of Guangdong. Despite its i111 portance, the complex character of the CJV form has remained understudied. This paper reveals the nature of CJV s as a relational subcontracting arrangement between Hong Kong ru1d Chinese firms, possessing aspects of both long-term subcontracting and an equity-based hierarchy. Drawing on data from structured interviews with 65 CJVs in Guangdong during 2000, we found that the CN had contracting advantages that reduced the costs of contracting compared to equity joint ventures (EJVs) and processing and assembling (P&A) arrangements, including flexibility, quick return on investments and low adjustment costs to market changes or technical upgrading. Over time, CJV s remain an efficient governance structure in line with the moderate changes of transaction-specific features of the CJV subcontracting activities. These findings hold when CJV size, age and industry are considered
Assessing ocean alkalinity for carbon sequestration
No full textOver the coming century humanity may need to find reservoirs to store several trillions of tons of carbon dioxide (CO2) emitted from fossil fuel combustion, which would otherwise cause dangerous climate change if it were left in the atmosphere. Carbon storage in the ocean as bicarbonate ions (by increasing ocean alkalinity) has received very little attention. Yet recent work suggests sufficient capacity to sequester copious quantities of CO2. It may be possible to sequester hundreds of billions to trillions of tons of C without surpassing postindustrial average carbonate saturation states in the surface ocean. When globally distributed, the impact of elevated alkalinity is potentially small and may help ameliorate the effects of ocean acidification. However, the local impact around addition sites may be more acute but is specific to the mineral and technology. The alkalinity of the ocean increases naturally because of rock weathering in which >1.5 mol of carbon are removed from the atmosphere for every mole of magnesium or calcium dissolved from silicate minerals (e.g., wollastonite, olivine, and anorthite) and 0.5 mol for carbonate minerals (e.g., calcite and dolomite). These processes are responsible for naturally sequestering 0.5 billion tons of CO2 per year. Alkalinity is reduced in the ocean through carbonate mineral precipitation, which is almost exclusively formed from biological activity. Most of the previous work on the biological response to changes in carbonate chemistry have focused on acidifying conditions. More research is required to understand carbonate precipitation at elevated alkalinity to constrain the longevity of carbon storage. A range of technologies have been proposed to increase ocean alkalinity (accelerated weathering of limestone, enhanced weathering, electrochemical promoted weathering, and ocean liming), the cost of which may be comparable to alternative carbon sequestration proposals (e.g., $20–100 tCO2 −1). There are still many unanswered technical, environmental, social, and ethical questions, but the scale of the carbon sequestration challenge warrants research to address these.</p
Potential of Maritime Transport for Ocean Liming and Atmospheric CO<sub>2</sub> Removal
No full textProposals to increase ocean alkalinity may make an important contribution to meeting climate change net emission targets, while also helping to ameliorate the effects of ocean acidification. However, the practical feasibility of spreading large amounts of alkaline materials in the seawater is poorly understood. In this study, the potential of discharging calcium hydroxide (slaked lime, SL) using existing maritime transport is evaluated, at the global scale and for the Mediterranean Sea. The potential discharge of SL from existing vessels depends on many factors, mainly their number and load capacity, the distance traveled along the route, the frequency of reloading, and the discharge rate. The latter may be constrained by the localized pH increase in the wake of the ship, which could be detrimental for marine ecosystems. Based on maritime traffic data from the International Maritime Organization for bulk carriers and container ships, and assuming low discharge rates and 15% of the deadweight capacity dedicated for SL transport, the maximum SL potential discharge from all active vessels worldwide is estimated to be between 1.7 and 4.0 Gt/year. For the Mediterranean Sea, based on detailed maritime traffic data, a potential discharge of about 186 Mt/year is estimated. The discharge using a fleet of 1,000 new dedicated ships has also been discussed, with a potential distribution of 1.3 Gt/year. Using average literature values of CO2 removal per unit of SL added to the sea, the global potential of CO2 removal from SL discharge by existing or new ships is estimated at several Gt/year, depending on the discharge rate. Since the potential impacts of SL discharge on the marine environment in the ships' wake limits the rate at which SL can be applied, an overview of methodologies for the assessment of SL concentration in the wake of the ships is presented. A first assessment performed with a three-dimensional non-reactive and a one-dimensional reactive fluid dynamic model simulating the shrinking of particle radii, shows that low discharge rates of a SL slurry lead to pH variations of about 1 unit for a duration of just a few minutes.</p
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