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When realizing CSS steam power plants based on oxy-combustion, the energy demand for oxygen production is one of the main causes for efficiency losses. This comparative study focuses on the impact of the air separation technology - cryogenic as well as high temperature membrane based - on the efficiency of a coal-fired oxyfuel steam power plant. As...
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... basic idea of the HTM-ASU, as illustrated schematically in figure 1, is the elevation of the oxygen partial pressure on the air side with an air compressor. The partial pressure difference across the membrane can be further enhanced by lowering the oxygen partial pressure on the oxygen receiving side of the membrane by sweeping with flue gas 3 , which contains only a small amount of oxygen. ...
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Semi-closed oxyfuel-combustion combined cycle plants are one possibility to realise CCS technologies with natural gas-fired power plants. Due to the recirculation of exhaust gas the working fluid in the gas turbine consists mainly of CO2. This leads to the necessity for an increased pressure ratio to achieve the efficiency and the exhaust gas tempe...
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... At present, oxygen is mainly produced via cryogenic distillation on a large scale. However, the efficiencies of liquefaction and distillation steps are limited by the thermodynamics second law, resulting in a large energy consumption [1,2]. The air separation technology based on pressure swing adsorption (PSA) with porous adsorbents, such as zeolites, has been widely studied and developed in recent years. ...
... The location and number of these oxygen vacancies vary with ambient temperature and oxygen partial pressure. When oxygen is absorbed at the sites of oxygen vacancies, oxygen is stored in the oxide lattice, as shown in equation (1). During desorption, oxygen is released from the oxide lattices and oxygen vacancies are produced, as shown in equation (2) [20]. ...
... The greater CO 2 concentration (80-98% based on fuel used) present in the remaining gases can be stored after compression and transportation. It is technically viable [60], though large quantities of oxygen are consumed [61]. In comparison to a plant without CCS, this system not only involves higher costs but also has an energy penalty of over 7% [57,62]. ...
Bioenergy with carbon capture and storage (BECCS) is gaining attention as an energy source and the most effective path to achieve negative CO 2 emissions by photosynthesis and capturing CO 2. However, BECCS has certain challenges and limitation which needs to be addressed to make the technology feasible. Concerns about food security, land, water use, and the possibility of large-scale implementation are critical in commercialization. As an emerging field, BECCS will need dynamic research and development over the next few decades, as well as strong policy backing, to clinch that it can be implemented on time for fulfilling the Paris agreement targets. The goal of this critical review is to find the impending obstacles that BECCS is facing, as well as the approaches to overcome them, while also emphasizing the advances in the field over the last decade. Detailed technology assessment is provided for a better understanding.
... However, it requires a large amount of high-purity oxygen, necessitating an energy-intensive Air Separation Unit (ASU) for oxygen production. Membrane-based technology for air separation may offer competition to cryogenic ASU through greater integration into the power cycle [133]. The ASU and CO2 compression units used in this process significantly decrease net power output. ...
... After nearly 100 years of development, the performance of the components in the cryogenic ASUs have basically reached the limit. However, the energy consumption of compression module still accounts for about 80% of the total energy consumption of the cryogenic ASUs [6], of which more than 60% is discharged in the form of compression heat and has not been used [7]. Therefore, it is necessary recover and utilize this part of compression heat efficiently for energy saving and environment protection. ...
... u (6) change interval more than 8 min/1% to ensure that each varying-duty operation runs after the system reaching a stable state. Fig. 15 shows the change of system energy saving during varyingduty conditions. ...
... 1,2 The predominant method for industrial air separation is cryogenic distillation, which has a relatively high capital cost and energy requirements of around 200−240 kWh/t Od 2 . 3,4 Hence, the high resulting cost of producing refined gases cryogenically limits the cost-effectiveness of technologies that utilize pure O 2 . ...
The redox behavior of the nonstoichiometric perovskite oxide SrFeO3−δ modified with Ag, CeO2, and Ce was assessed for chemical looping air separation (CLAS) via thermogravimetric analysis and by cyclic release and uptake of O2 in a packed bed reactor. The results demonstrated that the addition of ∼15 wt % Ag at the surface of SrFeO3−δ lowers the temperature of oxygen release in N2 by ∼60 °C (i.e., from 370 °C for bare SrFeO3−δ to 310 °C) and more than triples the amount of oxygen released per CLAS cycle at 500 °C. Impregnation of SrFeO3−δ with Ag increased the concentration of oxygen vacancies at equilibrium, lowering (3 – δ) under all investigated oxygen partial pressures. The addition of CeO2 at the surface or into the bulk of SrFeO3−δ resulted in more modest changes, with a decrease in temperature for O2 release of 20–25 °C as compared to SrFeO3−δ and a moderate increase in oxygen yield per reduction cycle. The apparent kinetic parameters for reduction of SrFeO3−δ, with Ag and CeO2 additives, were determined from the CLAS experiments in a packed bed reactor, giving activation energies and pre-exponential factors of Ea,reduction = 66.3 kJ mol–1 and Areduction = 152 mol s–1 m–3 Pa–1 for SrFeO3−δ impregnated with 10.7 wt % CeO2, 75.7 kJ mol–1 and 623 molO2 s–1 m –3 Pa–1 for SrFeO3−δ mixed with 2.5 wt % CeO2 in the bulk, 29.9 kJ mol–1 and 0.88 molO2 s–1 m–3 Pa–1 for Sr0.95Ce0.05FeO3−δ, and 69.0 kJ mol–1 and 278 molO2 s–1 m–3 Pa–1 for SrFeO3−δ impregnated with 12.7 wt % Ag, respectively. Kinetics for reoxidation were much faster and were assessed for two materials with the slowest oxygen uptake, SrFeO3−δ, giving the activation energy Ea,oxidation = 177.1 kJ mol–1 and pre-exponential factor Aoxidation = 3.40 × 1010 molO2 s–1 m–3 Pa–1, and Sr0.95Ce0.05FeO3−δ, giving the activation energy Ea,oxidation = 64.0 kJ mol–1, and pre-exponential factor Aoxidation = 584 molO2 s–1 m–3 Pa–1.
... However, attempts have been made in recent years to enhance the performance of cryogenic ASU and reduce energy consumption to 139.0 kWh/t O 2 (Brigagão, de Medeiros, & Ofélia de Queiroz, 2019) by using novel methods like liquefied natural gas processes (Mehrpooya, Sharifzadeh, & Rosen, 2015) or newly invented processes. Technologies using ceramic and polymeric membranes reduce the capital cost and energy (Pfaff & Kather, 2009) to roughly 145.0 kWh/t O 2 . However, there are challenges such as oxygen flux and purity when using ceramic and polymeric membranes, respectively (Nemitallah et al., 2017). ...
... As the largest energy consumption unit of the cryogenic ASU, the energy consumption of the air compression module accounts for about 80% of the total system [5]. Although a large number of studies have been made on the air compressor optimization in the past decades [6][7][8][9][10][11][12][13][14][15], more than 60% of the compression work is still dissipated as waste heat [16,17]. ...
Off-design performance of the ORC-based compression heat recovery system in cryogenic air separation units (ASU) with various operation methods is conducted in this paper, in order to explore the energy-saving potential during annual off-design operation. An operation method considering the temperature matching between the heat source and working fluid is proposed and compared with the other four operation methods (i.e., constant superheat operation method, constant pressure operation method, sliding pressure operation method and free operation method). With a 60,000-Nm³/h scale cryogenic ASU taken as the study case, the proposed operation method has the best energy-saving effect in all cases with a maximum annual energy saving reaching 13.83 GWh, corresponding to an energy-saving ratio of 9.6%, which produces a maximum energy-saving difference of 1.47 GWh with the other operation methods. At the same time, the system with the proposed operation method can realize normal operation under all annual working conditions. This study may provide guidelines for the design and operation of the compression heat recovery system in cryogenic ASU along with other waste heat recovery systems.
... Taking the energy consumption per unit production of oxygen of about 0.6 kWh/Nm 3 into consideration, the annual energy consumption of cryogenic ASUs reaches 205 TWh. In order to reduce carbon-dioxide emissions under the Paris Agreement [6], it is imperative to improve the energy efficiency of cryogenic ASUs, of which air compression processes are one of the key sectors, with a fraction of over 80% in the total energy consumption [7][8][9]. ...
The annual energy consumption of the cryogenic air separation units (ASUs) reaches 205 TWh in China, over 80% of which is consumed in the compression processes while over 60% of the compression work is dissipated as waste heat. Efficient recovery and utilization of this amount of heat is expected to bring significant economic and environmental benefits. Organic Rankine cycle (ORC) based waste heat recovery systems for generating extra electricity or/and cooling the inlet air of the air compressors are proposed to achieve power saving and evaluated in terms of thermodynamic, economic and environmental metrics. These include an ORC-based electric generator (ORC-e) for extra electricity, an electrically coupled ORC and vapor compression refrigerator (ORC-e-VCR) and a mechanically coupled ORC and VCR (ORC-m-VCR) for extra electricity and compression power saving. A 60,000-Nm³/h scale cryogenic ASUs is selected for case studies and influence of the feed-air temperature and humidity is focused in the analyses. The results show that among these three systems, the ORC-m-VCR and ORC-e-VCR systems have similar performance when the expansion work-electricity conversion efficiency (ηe) is 90%, reaching the highest energy saving ratio of 11.7% and economic benefits with net present value achieving 154 million CNY. The ORC-m-VCR system outperforms the other two systems with ηe of 60% and 30%. This work presents comprehensive comparison of various heat recovery systems and provides practical guidance for configuration selection and design to achieve effective energy saving in air compression processes.
... Integration of ASU with oxy-fuel steam power plant and its impact on the net efficiency of the plant was investigated by Pfaff and Kather [14]. For this purpose, a cryogenic ASU and a high-temperature membrane ASU were compared and it was found that a higher degree of integration into the power cycle for the later ASU was needed to compete with efficiencies obtained by utilizing a cryogenic ASU into the plant. ...
Cryogenic air separation is an efficient method to produce oxygen and nitrogen that has been investigated extensively. However, the production of rare gas components of air such as neon through air separation has not been explored enough. In this paper, a cryogenic process to produce neon in a recovery column along with nitrogen and liquid oxygen from a two-column air separation unit is proposed. Besides, energy, exergy, and sensitivity analyses of the process are performed. Neon, nitrogen, and oxygen mole fractions obtained were 0.206%, 98.75%, and 74.47% respectively. Results showed that increasing the temperature of the feed streams and the reflux ratio of the columns have a negative effect on the recovery of neon while increasing feed’s pressure up to a point improves the recovery.
... One promising alternative to state-of-the-art oxygen production methods such as cryogenic distillation of air [15][16][17] or pressure swing absorption (PSA) [18,19] are oxygen transport membranes (OTMs). They are particularly promising for decreasing the mentioned energy demand for O 2 production, especially to decrease the demand for expensive electricity. ...
Oxygen transport membranes are a possible low-cost alternative to cryogenic air separation units or pressure swing adsorption for oxygen production, and could facilitate carbon capture by oxy-fuel combustion processes. In this work, a proof-of-concept module with 7 ceramic tubular membranes was designed and tested in a high pressure test stand. To ensure high oxygen production rates, asymmetric membranes with a length of 70 cm consisting of a porous Ba0.5Sr0.5(Co0.8Fe0.2)0.97Zr0.03O3-δ support and a dense Ba0.5Sr0.5(Co0.8Fe0.2)0.97Zr0.03O3-δ thin separation layer were used. The module was successfully operated at up to 5.4 bar for 280 h in a temperature range from 650 °C to 850 °C. Oxygen purities up to 96.5% and flow rates up to 6.2 ml/cm²/min were measured, and a total maximum oxygen production of 227 NLPH was demonstrated.
