Carbonation of Industrial Residues for CCUS: Fundamentals, Energy Requirements and Scale-up Opportunities

Injection in deep geological formations is considered as the most promising option for CO2 storage. Limitation of the available storage capacity with acceptable leaking rates may limit its application, at least in some geographical locations, thus prompting the need for developing alternative storage options. Among these, accelerated carbonation has been proposed as an effective way for carbon dioxide sequestration. This process mimics natural weathering, where CO2 reacts exothermically with alkaline elements present in natural metal-oxide bearing material, forming thermodynamically stable and benign carbonates. A valuable source of alkalinity for the carbonation process is represented by alkaline industrial residues produced by different industrial activities such as steelmaking, cement production, waste incineration and coal combustion. These residues are typically more reactive than minerals and are often available at CO2 point source emissions. This presentation will give an overview on the research activities carried out by our group in this field, which was mostly performed on the so called “wet” or “thin-film” route, operated adopting a liquid to solid ratio below 1 l/kg. The results obtained through lab-scale tests performed on different types of industrial residues will be first presented, making reference specifically to EAF, AOD and BOF steel slags. Based on these results, the energy requirements of the wet route carbonation will be presented, discussed and compared with those of the more traditional slurry-phase route, allowing to identify the critical steps of the overall process route. Finally, scale-up opportunities of the wet-route carbonation, based on a combined carbonation-granulation process, will be discussed. The aim of this combined process is to obtain artificial aggregates suitable for use in civil engineering applications, thus potentially reducing the consumption of abiotic natural resources and reducing the need for disposal of the residues. The results obtained in a lab-scale granulator and more recently in a pilot-scale rotary reactor, in terms of CO2 uptake, environmental and mechanical properties of the obtained granules, will be presented

Biological treatment of PAH-contaminated sediments in a sequencing batch reactor

The technical feasibility of a sequential batch process for the biological treatment of sediments contaminated by polycyclic aromatic hydrocarbons (PAHs) was evaluated through an experimental study. A bench-scale Sediment Slurry Sequencing Batch Reactor (SS-SBR) was fed with river sediments contaminated by a PAH mixture made by fluorene, anthracene, pyrene and crysene. The process performance was evaluated under different operating conditions, obtained by modifying the influent organic load, the feed composition and the hydraulic residence time. Measurements of the Oxygen Uptake Rates (OURs) provided useful insights on the biological kinetics occurring in the SS-SBR, suggesting the minimum applied cycle time-length of 7 days could be eventually halved, as also confirmed by the trend observed in the volatile solid and total organic carbon data. The removal efficiencies gradually improved during the SS-SBR operation, achieving at the end of the study rather constant removal rates above 80% for both 3-rings PAHs (fluorene and anthracene) and 4-ring PAHs (pyrene and crysene) for an inlet total PAH concentration of 70 mg/kg as dry weight (dw)

Assessment of the Energy Requirements for CO2 Storage by Carbonation of Industrial Residues. Part 1: Definition of the Process Layout

Abstract Mineral carbonation is an ex situ CO 2 storage option that could allow to fix large amounts of CO 2 in a solid and thermodynamically stable form. Its feasibility has been proven at lab-scale both employing natural minerals or alkaline industrial residues. However the energy requirements of this process can be quite significant depending on the type of material and operating conditions adopted and thus represent a crucial factor for its full scale applicability. The focus of this paper is the assessment of the energy requirements of CO 2 storage by accelerated carbonation of alkaline materials applying the direct aqueous route. From the analysis of the main studies on energy penalties associated to the carbonation process large differences were observed on the assumptions made, the selected layout and operating conditions, in particular for alkaline residues. In addition most of the evaluations were carried out considering only experimental tests performed with high liquid to solid ratios (slurry phase route) while specific evaluations for tests with liquid to solid ratios lower than 1 (wet route) were not carried out. The overall aim of this study is to estimate the energy duties required to store the CO 2 emissions of a small-medium size power plant (20 MW) by carbonation of different types of residues (steel slags and waste incineration residues) applying either the slurry phase or wet routes. In this paper the layouts of the proposed carbonation processes are presented and discussed

Direct air capture of CO2 with chemicals: optimization of a two-loop hydroxide carbonate system using a countercurrent air-liquid contactor

Direct Air Capture (DAC) of CO2 with chemicals, recently assessed in a dedicated study by the American Physical Society (APS), is further investigated with the aim of optimizing the design of the front-end section of its benchmark two-loop hydroxide-carbonate system. Two new correlations are developed that relate mass transfer and pressure drop to the air and liquid flow velocities in the countercurrent packed absorption column. These relationships enable an optimization to be performed over the parameters of the air contactor, specifically the velocities of air and liquid sorbent and the fraction of CO2 captured. Three structured Sulzer packings are considered: Mellapak-250Y, Mellapak-500Y, and Mellapak-CC. These differ in cost and pressure drop per unit length; Mellapak-CC is new and specifically designed for CO2 capture. Scaling laws are developed to estimate the costs of the alternative DAC systems relative to the APS benchmark, for plants capturing 1Mt of CO2 per year from ambient air at 500ppm CO2 concentration. The optimized avoided cost hardly differs across the three packing materials, ranging from $518/tCO2 for M-CC to$568/tCO2 for M-250Y. The $610/tCO2 avoided cost for the APS-DAC design used M-250 Y but was not optimized; thus, optimization with the same packing lowered the avoided cost of the APS system by 7% and improved packing lowered the avoided cost by a further 9% The overall optimization exercise confirms that capture from air with the APS benchmark system or systems with comparable avoided costs is not a competitive mitigation strategy as long as the energy system contains high-carbon power, since implementation of Carbon Capture and Storage, substitution with low-carbon power and end-use efficiency will offer lower avoided-cost strategie

Influence of particle size on the carbonation of stainless steel slag for CO2 storage

Abstract The main aims of this work were to assess the CO2 storage capacity of different particle size fractions of stainless steel slag subjected to accelerated carbonation under mild operating conditions, to study the influence on reaction kinetics of some of the main operating parameters (temperature, pressure and liquid to solid ratio) and to determine the effects of the process on slag mineralogy and leaching behavior. Maximum CO2 uptakes of 130 g CO2/kg residues were measured for the finest grain size and decreased with particle size owing to differences in reacting species availability and specific surface. Process kinetics proved relatively fast, achieving completion in around 2 hours with a CO2 pressure of 3 bar and an optimal liquid to solid ratio of 0.4; temperature was the parameter that most influenced CO2 uptake, due to its enhancement effect on silicates dissolution

Comparison of different reaction routes for carbonation of APC residues

Abstract This paper analyses and compares the results of accelerated carbonation experiments for CO2 storage carried out on the air pollution control (APC) residues of a waste incineration plant, via both the dry and the wet route. The two routes achieved a similar maximum calcium conversion to carbonates (around 65%) corresponding to a potential CO2 storage capacity of 250 g/kg residues. For the dry route, maximum conversion was achieved in a few minutes at 400 ∘C under a 10% CO2 atmosphere, whereas for the wet route it was obtained in about 10 minutes under a 100% CO2 atmosphere, with a liquid to solid ratio of 0.2, at 30 ∘C and 3 bar, or without water addition at 50 ∘C. These results suggest that carbonation of APC residues, and possibly of other combustion residues, through either the dry or wet route, may be effectively applied for CO2 storage, at least in the niche market of waste incineration

Carbon Dioxide Removal and Capture for Landfill Gas Up-grading

Abstract Within the frame of an EC financially supported project - LIFE05 ENV/IT/000874 GHERL (Greenhouse Effect Reduction from Landfill)–a pilot plant was set up in order to demonstrate the feasibility of applying chemical absorption to remove carbon dioxide from landfill gas. After proper upgrading - basically removal of carbon dioxide, hydrogen sulphide, ammonia and other trace gas compound–the gas might be fed into the distribution grid for natural gas or used as vehicle fuel, replacing a fossil fuel thus saving natural resources and carbon dioxide emissions. Several experiences in Europe have been carried out concerning the landfill gas - and biogas from anaerobic digestion - quality up-grading through CO 2 removal, but in all of them carbon dioxide was vented to the atmosphere after separation, without any direct benefit in terms of greenhouse gases reduction. With respect to those previous experiences, in this work the attention was focused on CO 2 removal from landfill gas with an effective capture process, capable of removing carbon dioxide from atmosphere, through a globally carbon negative process. In particular, processes capable of producing final solid products were investigated, with the aim of obtaining as output solid compounds which can be either used in the chemical industry or disposed off. The adopted absorption process is based on using aqueous solutions of potassium hydroxide, with the final aim of producing potassium carbonate. Potassium carbonate is a product which has several applications in the chemical industry if obtained with adequate quality. It can be sold as a pulverised solid, or in aqueous solution. Several tests were carried out at the pilot plant, which was located at a landfill site, in order to feed it with a fraction of the on-site collected landfill gas. The results of the experimental campaign are reported, explained and commented in the paper. Also a discussion on economic issues is presented

comparative life cycle assessment of slurry and wet accelerated carbonation of bof slag

This work reports the results of the life cycle assessment (LCA) of two carbonation processes aimed at permanent CO2 storage, employing Basic Oxygen Furnace (BOF) slag from steel manufacturing as a ..

Accelerated carbonation of steel slags using CO2 diluted sources: CO2 uptakes and energy requirements

This work presents the results of carbonation experiments performed on Basic Oxygen Furnace (BOF) steel slag samples employing gas mixtures containing 40 and 10% CO2 vol. simulating the gaseous effluents of gasification and combustion processes respectively, as well as 100% CO2 for comparison purposes. Two routes were tested, the slurry-phase (L/S = 5 l/kg, T = 100°C and Ptot = 10 bar) and the thin-film (L/S = 0.3–0.4 l kg, T = 50°C and Ptot = 7–10 bar) routes. For each one, the CO2 uptake achieved as a function of the reaction time was analyzed and on this basis, the energy requirements associated with each carbonation route and gas mixture composition were estimated considering to store the CO2 emissions of a medium size natural gas fired power plant (20 MW). For the slurry-phase route, maximum CO2 uptakes ranged from around 8% at 10% CO2, to 21.1% (BOF-a) and 29.2% (BOF-b) at 40% CO2 and 32.5% (BOF-a) and 40.3% (BOF-b) at 100% CO2. For the thin-film route, maximum uptakes of 13% (BOF-c) and 19.5% (BOF-d) at 40% CO2, and 17.8% (BOF-c) and 20.2% (BOF-d) at 100% were attained. The energy requirements of the two analyzed process routes appeared to depend chiefly on the CO2 uptake of the slag. For both process route, the minimum overall energy requirements were found for the tests with 40% CO2 flows (i.e., 1400−1600 MJ/tCO2 for the slurry-phase and 2220 – 2550 MJ/tCO2 for the thin-film route)

Storage of carbon dioxide captured in a pilot-scale biogas upgrading plant by accelerated carbonation of industrial residues

AbstractThis work reports the preliminary evaluations obtained within the UPGAS-LOW CO2 project (LIFE08 ENV/IT/000429) concerning innovative methods for biogas upgrading through CO2 capture and storage. One of the methods studied in this project is chemical absorption of the CO2 contained in landfill gas with a KOH solution followed by carbonation of the spent solution with selected industrial residues to regenerate the alkaline solution and store CO2 in a solid phase (calcite). This paper presents the main results of the lab scale experiments carried out to evaluate the effects o f the main operating parameters on the carbonation reaction so to identify the conditions that allow to maximize the CO2 uptake of the solid residues and the percentage of KOH that can be regenerated for the absorption process. These results provide the dataset for the design of a pilot plant unit to be built and operated in the follow-up of the project