Process modelling and techno-economic analysis of natural gas combined cycle integrated with calcium looping

Calcium looping (CaL) is promising for large-scale CO2 capture in the power generation and industrial sectors due to the cheap sorbent used and the relatively low energy penalties achieved with this process. Because of the high operating temperatures the heat utilisation is a major advantage of the process, since a significant amount of power can be generated from it. However, this increases its complexity and capital costs. Therefore, not only the energy efficiency performance is important for these cycles, but also the capital costs must be taken into account, i.e. techno-economic analyses are required in order to determine which parameters and configurations are optimal to enhance technology viability in different integration scenarios. In this study the integration scenarios of CaL cycles and natural gas combined cycles (NGCC) are explored. The process models of the NGCC and CaL capture plant are developed to explore the most promising scenarios for NGCC-CaL integration with regards to efficiency penalties. Two scenarios are analysed in detail, and show that the system with heat recovery steam generator (HRSG) before and after the capture plant exhibited better performance of 49.1% efficiency compared with that of 45.7% when only one HRSG is located after the capture plant. However, the techno-economic analyses showed that the more energy efficient case, with two HRSGs, implies relatively higher cost of electricity (COE), 44.1€/MWh, when compared to that of the reference plant system (33.1€/MWh). The predicted cost of CO2 avoided for the case with two HRSGS is 29.3 €/ton CO2

Highly efficient CO2 capture with simultaneous iron and CaO recycling for the iron and steel industry

An efficient CO2 capture process has been developed by integrating calcium looping (CaL) and waste recycling technologies into iron and steel production. A key advantage of such a process is that CO2 capture is accompanied by simultaneous iron and CaO recycling from waste steel slag. High-purity CaO-based CO2 sorbents, with CaO content as high as 90 wt%, were prepared easily via acid extraction of steel slag using acetic acid. The steel slag-derived CO2 sorbents exhibited better CO2 reactivity and slower (linear) deactivation than commercial CaO during calcium looping cycles. Importantly, the recycling efficiency of iron from steel slag with an acid extraction is improved significantly due to a simultaneous increase in the recovery of iron-rich materials and the iron content of the materials recovered. High-quality iron ore with iron content of 55.1–70.6% has been recovered from waste slag in this study. Although costing nearly six times as much as naturally derived CaO in the purchase of feedstock, the final cost of the steel slag-derived, CaO-based sorbent developed is compensated by the byproducts recovered, i.e., high-purity CaO, high-quality iron ore, and acetone. This could reduce the cost of the steel slag-derived CO2 sorbent to 57.7 € t−1, appreciably lower than that of the naturally derived CaO. The proposed integrated CO2 capture process using steel slag-derived, CaO-based CO2 sorbents developed appears to be cost-effective and promising for CO2 abatement from the iron and steel industry

Lime-Based Sorbents for High-Temperature CO2 Capture—A Review of Sorbent Modification Methods

This paper presents a review of the research on CO2 capture by lime-based looping cycles undertaken at CanmetENERGY’s (Ottawa, Canada) research laboratories. This is a new and very promising technology that may help in mitigation of global warming and climate change caused primarily by the use of fossil fuels. The intensity of the anticipated changes urgently requires solutions such as more cost-effective technologies for CO2 capture. This new technology is based on the use of lime-based sorbents in a dual fluidized bed combustion (FBC) reactor which contains a carbonator—a unit for CO2 capture, and a calciner—a unit for CaO regeneration. However, even though natural materials are cheap and abundant and very good candidates as solid CO2 carriers, their performance in a practical system still shows significant limitations. These limitations include rapid loss of activity during the capture cycles, which is a result of sintering, attrition, and consequent elutriation from FBC reactors. Therefore, research on sorbent performance is critical and this paper reviews some of the promising ways to overcome these shortcomings. It is shown that reactivation by steam/water, thermal pre-treatment, and doping simultaneously with sorbent reforming and pelletization are promising potential solutions to reduce the loss of activity of these sorbents over multiple cycles of use

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (<2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution(external) (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6∙H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications

Economic feasibility of calcium looping under uncertainty

An emerging calcium looping process has been shown to be a promising alternative to solvent scrubbing, which is regarded as the most mature CO2 capture technology. Its retrofits to coal-fired power plants have the potential to reduce both energy and economic penalties associated with the mature CO2 capture technologies. However, these conclusions have been made based on the deterministic outputs of the economic models that have not considered uncertainties in the model inputs. Therefore, this study incorporates a stochastic approach into the economic analysis of the retrofit of such emerging CO2 capture technology to the coal-fired power plant. The stochastic analysis revealed that levelised cost of electricity (LCOE) and specific total capital requirement were highly affected by the uncertainty in the input variables to the process and economic models. The most probable values for these key economic performance indicators were shown to fall between 75 and 115 €/MWelh, and 2100 and 2300 €/kWel,gross, respectively. Interestingly, the most probable LCOE values for the coal-fired power plant will fall between 50 and 150 €/MWelh. This indicated that the calcium looping retrofit scenario can become economically favoured, mainly due to the high economic penalties incurred by unabated coal-fired power plant associated with carbon tax. Importantly, the outputs of the stochastic economic assessment aligned well with the deterministic results reported in the literature. As the latter were generated using different sets of assumptions regarding the process and economic models, the stochastic approach to the economic assessment can minimise the impact of the model assumptions on estimates of the key economic parameters. Moreover, by indicating the probability of particular outputs, as well as ranking the model input variables according to their influence on the key economic performance, such analysis would allow making more insightful decisions regarding further funding and development of the calcium looping process. Finally, use of the stochastic approach in the economic feasibility assessment enables a more profound and reliable comparison of the different calcium looping retrofit configurations, as well as benchmarking different CO2 capture technologies

Techno-economic feasibility assessment of CO2 capture from coal-fired power plants using molecularly imprinted polymer

Mature CO2 capture technologies would reduce the net thermal efficiency of the coal-fired power plant by 7–13% points, leading to an electricity cost increase of at least 60%. To minimise the energy-intensity of CO2 capture, novel technologies and CO2 capture materials are being developed. This study assessed the techno-economic feasibility of the CO2 capture system using acrylamide-based molecularly imprinted polymer (MIP) sorbent in a 580 MWel coal-fired power plant retrofit scenario. Under the initial design basis, the net efficiency penalty and the energy penalty of the MIP retrofit scenario were estimated to be 5.3%HHV points and 14.1%, respectively. Furthermore, the cost of CO2 avoided was estimated to be 29.3 £/tCO2. Such techno-economic performance was found to be superior to the CO2 capture system using chemical solvents. The parametric study revealed that the thermodynamic performance of the MIP retrofit scenario is mainly affected by the sorbent capacity, as the net efficiency penalty was found to increase from 4.4 to 8.9%HHV points on reduction of the sorbent capacity from 1 to 0.2 mmol CO2/g. Moreover, the economic performance was not only found to be affected by sorbent capacity, but primarily on the cyclic performance of the MIP sorbent. It was shown that the cost of CO2 avoided would increase linearly with increase of the MIP sorbent make-up at a rate of 6.8 £/tCO2 per 0.1% of sorbent make-up

Combined heat and power generation with lime production for direct air capture

Carbon capture and storage (CCS) has been shown to be the least cost-intensive option for decarbonisation of the power, heat, and industrial sectors. Importantly, negative-emission technologies, including direct air capture (DAC), may still be required after near-complete decarbonisation of the stationary emission sources. This study evaluates the feasibility of a novel polygeneration process for combined heat and power using a solid-oxide fuel cell, and lime production for DAC (CHP-DAC) that could contribute towards decarbonisation of the power, heat, and industrial sectors. Evaluation of the thermodynamic performance indicated that such process can achieve the total efficiency and effective electric efficiency of 65%LHV and 60%LHV, respectively, while removing CO2 from the air at a rate of 88.6 gCO2/kWchh. With the total expenditure spread over a number of revenue streams, the product prices required for the CHP-DAC process to break even were found to be competitive compared to figures for the existing standalone technologies, even if there was no revenue from CO2 capture from the air. Moreover, the considered process was shown to be economically feasible, even under uncertainty. Hence, it can be considered as the carbon–neutral polygeneration process for sustainable and affordable production of heat, power, and lime that is negative-emission ready

Linking renewables and fossil fuels with carbon capture via energy storage for a sustainable energy future

Renewable energy sources and low-carbon power generation systems with carbon capture and storage (CCS) are expected to be key contributors towards the decarbonisation of the energy sector and to ensure sustainable energy supply in the future. However, the variable nature of wind and solar power generation systems may affect the operation of the electricity system grid. Deployment of energy storage is expected to increase grid stability and renewable energy utilisation. The power sector of the future, therefore, needs to seek a synergy between renewable energy sources and low-carbon fossil fuel power generation. This can be achieved via wide deployment of CCS linked with energy storage. Interestingly, recent progress in both the CCS and energy storage fields reveals that technologies such as calcium looping are technically viable and promising options in both cases. Novel integrated systems can be achieved by integrating these applications into CCS with inherent energy storage capacity, as well as linking other CCS technologies with renewable energy sources via energy storage technologies, which will maximise the profit from electricity production, mitigate efficiency and economic penalties related to CCS, and improve renewable energy utilisation

Techno-economic feasibility assessment of calcium looping combustion using commercial technology appraisal tools

Calcium looping combustion (CaLC) is a new class of lowCO2emission technologies for thermochemical conversion of carbonaceous fuels that can help achieve the emissions reduction targets set out in the Paris Agreement. Compared to mature CO2 capture technologies, which cause net efficiency penalties higher than 7% points, CaLC results in a net efficiency penalty of 2.9% points. However, a thorough economic assessment of CaLC needs to be undertaken to evaluate its economic viability. The levelised cost of electricity is commonly used to assess the economic performance of clean energy systems. However, this method does not account for commercially important parameters, such as tax, interest, and depreciation charges. This study aimed to improve the reliability and accuracy of economic assessments of clean energy systems by implementing the net present value (NPV) approach. This approach was applied to assess the economic performance of two concepts of the CaLC-based power plant with either the conventional steam cycle (SC) or the supercritical CO2 cycle (s-CO2) for heat utilisation along with the bottom-up approach to total capital cost estimation. A parametric study for both concepts was also conducted to assess the impact of the key thermodynamic parameters on the economic performance. Although the s-CO2 case with revised assumptions was shown to result in a 1%-point lower net efficiency compared to the SC case, its break-even cost of electricity was lower by 0.81 €/MWh. Further improvements of the techno-economic performance can be sought by optimisation of the s-CO2 cycle structure

Pilot-scale calcination of limestone in steam-rich gas for direct air capture

A novel polygeneration concept, which has been proposed recently, comprises a fuel-cell calciner integrated system in order to produce electricity and lime which can be used for direct air capture (DAC) to remove CO2 from the atmosphere. However, the scalability of the integrated system needs to be further studied. In this work, calcination of limestone under steam-rich conditions simulating flue gas from a solid oxide fuel cell (SOFC), and subsequent ambient carbonation has been explored. Limestone was calcined under two steam concentration (21% and 35% vol) conditions in a 25 kWth pilot-scale bubbling fluidised bed (BFB), and then exposed to ambient air to evaluate DAC performance. Samples were characterised in order to quantify the hydration and carbonation conversions over time and, therefore, their DAC capacity. It was observed that steam reduces calcination time, confirming its catalytic effect, while the calcination temperature remained the same regardless of the steam composition at the same CO2 partial pressure. Moreover, increasing steam concentration during calcination affected the material performance and DAC capacity at ambient conditions positively. Therefore, these findings demonstrate that limestone calcined under typical SOFC afterburner exhaust conditions is suitable as a DAC sorbent