Surface-response analysis for the optimization of a carbon dioxide absorption process using [hmim][Tf2N]

The [hmim][Tf2N] ionic liquid is considered in this work to develop a model in Aspen Plus® capturing carbon dioxide from shifted flue gas through physical absorption. Ionic liquids are innovative and promising green solvents for the capture of carbon dioxide. As an important aspect of this research, optimization is carried out for the carbon capture system through a central composite design: simulation and statistical analysis are combined together. This leads to important results such as the identification of significant factors and their combinations. Surface plots and mathematical models are developed for capital costs, operating costs and removal of carbon dioxide. These models can be used to find optimal operating conditions maximizing the amount of captured carbon dioxide and minimizing total costs: the percentage of carbon dioxide removal is 93.7%, operating costs are 0.66 million ¿/tonCO2 captured (due to the high costs of ionic liquid), and capital costs are 52.2 ¿/tonCO2 captured

Innovative Process Integrating Air Source Heat Pumps and Direct Air Capture Processes

Most integrated assessment models indicate a need for technological carbon dioxide removal from the atmosphere to achieve climate mitigation targets. Currently, direct air capture (DAC) appears to be one the “backstop” technologies suitable to provide this service. These technologies usually require low-carbon heat as part of their operation cycle. Here, we consider a way of providing this heat when no local heat source is available. Air source heat pump (ASHP) water heaters are a well-known technology that takes heat from the air to supply hot water. Variations on their operating conditions could provide water at 100 °C, when a trans-critical cycle is used. This level of temperature is required by several DAC adsorption processes as the thermal energy for the regeneration stage. For this reason, an innovative process integrating an ASHP and a DAC adsorption system is proposed here. The heat pump provides not only heating but also cooling, while three separate stages (adsorption, cooling, and regeneration) are considered for the DAC. In the integrated process, the air is sent to the adsorbent bed at first and after that to the evaporator of the heat pump and then used for the cooling stage. The hot water supplied by the heat pump is used for the desorption. Different working fluids (CO2, CO2-ethane, CO2-R41), with low ozone depletion and global warming potentials, are investigated. The results show that a high level of efficiency is possible for heat pumps supplying hot water at 100 °C. Moreover, energetic advantages are present with reference to the base case, where heat is provided by a municipal water incinerator and cooling by a cooling tower. Savings in the energy consumption of 55, 60, and 53% for the integrated process using CO2, CO2/R41, and CO2/ethane, respectively, are possible. Economic benefits are present when economic incentives are provided, ensuring lower costs up to 39 $/tonCO2, and the technology benefits from location flexibility as only a power supply (and not a heat source) is required

Modelling and analysis of direct air capture systems in different locations

Direct air capture is an important negative emission technology with the aim to reduce carbon dioxide emissions in the atmosphere and to face the current environmental problems such as global warming and climate change. This emerging technology can be based on an adsorption system affected by the used sorbent (physisorbents or chemisorbents). Efficiencies can be measured through the use of key performance indicators that allow a comparison among different processes. An independent analysis was conducted in our previous research to evaluate key performance indicators (total cost, energy consumption, environmental impact and capture capacity) for a direct air capture system based on adsorption using different sorbents (three metal organic frameworks and two amine functionalized sorbents). In this research, the same analysis was extended to several Countries around the world, changing the ambient air temperature according to the yearly average value of the location. Results show that by increasing the air temperature, the adsorption capacity decreases, in a more significant way for metal organic frameworks compared to amine functionalized sorbents. An opposite effect is for energy consumption. Moreover, by increasing the ambient air temperature, a higher environmental impact (in terms of climate change) is present. A trend with the air temperature was not found for total costs. Overall, locations with lower ambient air temperatures are preferred due to a lower environmental impact and energy consumption

A Comparative Study of Different Sorbents in the Context of Direct Air Capture (DAC): Evaluation of Key Performance Indicators and Comparisons

Direct air capture can be based on an adsorption system, and the used sorbent (chemisorbents or physisorbents) influences process. In this work, two amine-functionalized sorbents, as chemisorbents, and three different metal organic frameworks, as physisorbents, are considered and compared in terms of some key performance indicators. This was carried out by developing a mathematical model describing the adsorption and desorption stages. An independent analysis was carried out in order to verify data reported in the literature. Results show that the equilibrium loading is a critical parameter for adsorption capacity, energy consumption, and cost. The considered metal organic frameworks are characterized by a lower equilibrium loading (10−4 mol/kg) compared to chemisorbents (10−1 mol/kg). For this reason, physisorbents have higher overall energy consumptions and costs, while capturing a lower amount of carbon dioxide. A reasonable agreement is found on the basis of the operating conditions of the Climeworks company, modelling the use of the same amine cellulose-based sorbent. The same order of magnitude is found for total costs (751 USD/tonneCO2 for our analysis, compared to the value of 600 USD/tonneCO2 proposed by this company)

Optimization of CCUS supply chains in the UK: A strategic role for emissions reduction

The UK is the second largest emitter of carbon dioxide in Europe. It aims to take urgent actions to achieve the 2030 target for CO_{2} emissions reduction imposed by EU environmental policies. Three different carbon capture utilization and storage (CCUS) supply chains are developed giving economic indicators for CO_{2} utilization routes not implying carbon dioxide hydrogenation (i.e. with high TRL). The study presents an innovative proposal to reduce CO_{2} impact in the UK, a country rich in coal, which requires reduction of carbon dioxide emissions from flue gases as the easiest and best performing solution. Bunter Sandstone, Scottish offshore and Ormskirk Sandstone are the storage sites considered, while several attractive potential utilization options are considered. Through minimization of total costs, the CCUS supply chain with Bunter Sandstone as storage site results in the most economically profitable solution due to the highest value of net present value (€ 0.554 trillion) and lowest value of pay back period (2.85 years). Only carbon tax is considered. The total cost is € 1.04 billion/year. Across the supply chain, 6.4 Mton/year of carbon dioxide emissions are avoided, to be either stored or used for calcium carbonate production. Future work should consider uncertainty, dynamics of market demand and social aspects

Environmental performance of different sorbents used for direct air capture

Currently, conventional carbon dioxide (CO2) mitigation solutions may be insufficient to achieve the stringent environmental targets set for the coming decades. CO2 removal (CDR) technologies, such as direct air capture (DAC), capturing CO2 from the ambient air, are required. In this research, an independent life cycle assessment (LCA) of DAC adsorption systems based on three physisorbents (metal organic frameworks) and two chemisorbents (amine functionalized sorbents) is presented. These capture processes have been optimised by us in previous work. Results show that for the overall capture process, negative CO2 emissions are ensured by using a cellulose-based amine sorbent (cradle-to-gate) ensuring even the net removal of CO2 from the atmosphere (cradle-to-grave). Processes using physisorbents have poorer performances. Chemisorbents yield operating conditions allowing lower impacts on the environment. In 2050, these processes could reduce climate change but can generate other environmental impacts. With the aim to have better environmental performances of DAC systems, future research should be focused on improving the physical properties of sorbents such as the silica gel based amine sorbent to increase their capture capacities. If metal organic frameworks are to be used, it is necessary to drop their energy consumption (by increasing the loading) and the required mass of sorbent

Analysis of technologies for carbon dioxide capture from the air

The increase in CO2 concentration in the atmosphere has prompted the research community to find solutions for this environmental problem, which causes climate change and global warming. CO2 removal through the use of negative emissions technologies could lead to global emission levels becoming net negative towards the end of this century. Among these negative emissions technologies, direct air capture (DAC), in which CO2 is captured directly from the atmosphere, could play an important role. The captured CO2 can be removed in the long term and through its storage can be used for chemical processes, allowing closed carbon cycles in the short term. For DAC, different technologies have been suggested in the literature, and an overview of these is proposed in this work. Absorption and adsorption are the most studied and mature technologies, but others are also under investigation. An analysis of the main key performance indicators is also presented here and it is suggested that more efforts should be made to develop DAC at a large scale by reducing costs and improving efficiency. An additional discussion, addressing the social concern, is indicated as well

Environmental performance of different sorbents used for direct air capture

Currently, conventional carbon dioxide (CO2) mitigation solutions may be insufficient to achieve the stringent environmental targets set for the coming decades. CO2 removal (CDR) technologies, such as direct air capture (DAC), capturing CO2 from the ambient air, are required. In this research, an independent life cycle assessment (LCA) of DAC adsorption systems based on three physisorbents (metal organic frameworks) and two chemisorbents (amine functionalized sorbents) is presented. These capture processes have been optimised by us in previous work. Results show that for the overall capture process, negative CO2 emissions are ensured by using a cellulose-based amine sorbent (cradle-to-gate) ensuring even the net removal of CO2 from the atmosphere (cradle-to-grave). Processes using physisorbents have poorer performances. Chemisorbents yield operating conditions allowing lower impacts on the environment. In 2050, these processes could reduce climate change but can generate other environmental impacts. With the aim to have better environmental performances of DAC systems, future research should be focused on improving the physical properties of sorbents such as the silica gel based amine sorbent to increase their capture capacities. If metal organic frameworks are to be used, it is necessary to drop their energy consumption (by increasing the loading) and the required mass of sorbent

Forest ecosystem monitoring in Tuscany (Italy): past activities, present status and future perspectives

Since 1987 the Region of Tuscany has been actively monitoring crown status in its forests, in order to protect them from atmospheric pollution, biotic factors and environmental change. Over this period the Region has performed periodical inventories on crown condition in publicly-owned forests (Level I network) and established a network of permanent plots (MON.I.TO., Level II – III) to study long-term changes occurring in forest ecosystems. Some of these permanent plots were later included in the national programme CONECOFOR, managed by the Ministry for Policy in Agriculture and Forest. Currently a further development of MON.I.TO. is being implemented, called MONITO III – TOpModel, the aim of which is to broaden the information potential of the monitoring system to include carbon stocks and biodiversity evaluation. This paper provides an up-to-date report on the status of the various surveys and recommends a closer connection between MON.I.TO. and the other regional information systems, especially the Regional Forest Inventory, in order to produce information that may be useful in forest planning and in Sustainable Forest Management