Engineering, environmental and economic performance evaluation of high-gravity carbonation process for carbon capture and utilization
Graphical abstract
A 3E triangle model was used to evaluate tradeoffs in CO2 capture performance by the developed HiGCarb process while considering the larger life-cycle environmental impacts due to energy use and material consumption as well as the economic implications of the revenue gained and the operating costs.
Introduction
Accelerated mineralization, so-called accelerated carbonation, refers to the reaction of CO2 with alkaline divalent cations from natural ores [1] or alkaline solid wastes, such as steel slag [2] and fly ash [3], to produce carbonate minerals. The process chemistry of accelerated mineralization, in the presence of water, can be briefly expressed as Eq. (1):where M is a divalent cation (e.g., Ca2+ or Mg2+), and MCO3 is a carbonate product (e.g., CaCO3 or MgCO3). Since the carbonate product is stable at atmospheric conditions, accelerated mineralization has been considered as one of the permanent CO2 sequestration technologies in a scalable manner, especially when alkaline solid wastes are used as the feedstock of the mineralization process [4], [5], [6]. Kirchofer et al. [7], [8] estimated a direct mitigation potential of 1.8–23.7% of the total CO2 emissions in the U.S., depending on the availability of alkalinity sources and the performance of the mineral carbonation. In addition, indirect CO2 emissions from the cement industry can be avoided since the reacted product (e.g., carbonated solid wastes) can be used as supplementary cementitious materials in cement and concrete [7], [9]. Compared to the total global CO2 emissions, although the CO2 sequestration potential by accelerated mineralization using the solid wastes is low, it offers unique application for hazardous waste remediation and provides a means for industries to produce valuable by-products from the waste while reducing the CO2 emissions [10].
For mineralization using solid wastes, extensive efforts have been underway to evaluate the effect of various key operating factors on carbonation conversion and to characterize the carbonate product for potential utilization [11], [12], [13]. The carbonation performance, i.e., rates of metal ion leaching and CO2 dissolution, can also be promoted by introducing wastewater from the steelmaking industries [14], [15], [16]. Since accelerated mineralization has been shown to be a diffusion-controlled reaction [9], [17], [18], [19], the mass transfer rate of the CO2 dissolution and metal ion diffusion has increased using enhanced leaching [20], autoclave [21], rotating packed bed (RPB) [14], [15], [22], and ultrasound [23], [24].
Among the aforementioned methods, accelerated mineralization using the RPB, also referred to as the high-gravity carbonation (HiGCarb) process, is an attractive approach. The HiGCarb process achieves a high CO2 capture efficiency (i.e., >98%) with a relatively short reaction time at ambient temperature and pressure [22]. Using the centrifugal force provided by the RPB reactor, the mass transfer rate of carbonation in the HiGCarb process was significantly greater than that using a fix packed bed. The height of a transfer unit in a liquid-film limited system (i.e., carbonation) can be reduced to 4–66 cm using the HiGCarb process [25]. In addition, the environmental impacts of the HiGCarb process were lower compared to using conventional processes, such as autoclave reactor [26].
The life-cycle assessment (LCA) approach has been used as the most suitable tool for environmental assessment of CO2 utilization technologies and processes along their entire life cycles [27], [28], [29], [30]. Several studies on the LCA of mineral carbonation using different processes have been published [26], [31], [32], [33], [34]. These studies employed inventory data from lab-scale experiments in contrast to our work which is based on a real industry installation. For this reason, stages of the life-cycle such as raw material production and end-product utilization were not included in the literature. Furthermore, several critical issues for the HiGCarb process such as energy consumption, net CO2 emission reduction, indirect CO2 emission avoidance, and cost-benefit analysis of the HiGCarb process have not been comprehensively addressed yet.
For these reasons, in this study, the HiGCarb process is systematically assessed from the perspectives of engineering, environment and economy (referred to as 3E in this paper) using a triangle model. Since the complex relationships among 3E aspects can be easily visualized on a ternary plot among different scenarios, the triangle graphical presentation can be used for evaluating key factors that are related but also complementary [35], [36]. The energy consumption, net CO2 capture amount, and environmental impacts by the HiGCarb process were evaluated by means of LCA. In addition, the revenue gained of HiGCarb was estimated by considering operating cost and process profits (such as carbon credits and product sales). Furthermore, according to the results of the comprehensive performance evaluation through the 3E triangle model, operating guidelines for the HiGCarb process were proposed.
Section snippets
Scopes and definitions of business-as-usual and HiGCarb process
To critically evaluate the benefits of integrating the HiGCarb process in the steelmaking industry, the performance before (i.e., business-as-usual case) and after integration of HiGCarb process was evaluated. Table S1 (see Appendix A) presents a comparison of business-as-usual and integration of the HiGCarb process in the steelmaking industry from the 3E aspects. In the business-as-usual case, the alkaline cold-rolling mill wastewater is neutralized and adjusted by chemical agents at a
Analysis of energy uses for HiGCarb process
Fig. 3 shows the energy consumption of the main unit processes in the nine HiGCarb scenarios. It should be noted that the results, herein, are referred to a different functional unit, i.e., per t-CO2, since energy consumption is one of the major concerns to the cost effectiveness of a CO2 capture process. The total energy consumption of the HiGCarb process was estimated to range from 205 to 440 kW h/t-CO2, with a capture scale of 75–170 kg CO2 per day. The pre-processing of material, i.e., BOFS
Conclusions
To develop and implement the waste-to-resource supply chain between the steelmaking and cement industries, a comprehensive performance evaluation on the high-gravity carbonation (HiGCarb) process was carried out by the 3E triangle model, i.e., from the engineering, environmental and economic point of view. The capture capacity of the HiGCarb process was 75–170 kg CO2 per day, associated with an energy consumption ranging from 205 to 440 kW h/t-CO2. Compared to the business-as usual case, the
Acknowledgements
High appreciation goes to the Green Talents Program granted by BMBF through the Project Management Agency c/o German Aerospace Center (PT-DLR) in Germany. The authors also acknowledge the support of Ministry of Science and Technology (MOST) of Taiwan (R.O.C.) under Grant Number MOST 105-3113-E-007-001. In addition, Prof. André Bardow from Institute of Technical Thermodynamics at RWTH Aachen University, Germany, is greatly appreciated for his suggestions to this work.
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