Cryogenic Air Separation Process Research Articles

Cryogenic Air Separation Process Integrated with Cold Utilization of Liquefied Natural Gas: Design, Simulation and Performance Analysis

Cryogenic Air Separation Process Integrated with Cold Utilization of Liquefied Natural Gas: Design, Simulation and Performance Analysis

Conceptual assessment of sustainable methane production from oxycombustion CO2 capture in waste-to-energy power plants

The worldwide deployment of renewable energy is growing exponentially. However, its intermittency limits its impact on the yearly energy contribution to the grid. Thus, coal remains the largest source of electricity generation in the world. Developing negative emissions technologies, such as Bioenergy with Carbon Capture and Utilization (BECCU), is a promising pathway. This study focuses on integrating waste biomass oxycombustion and a power-to-methane system. A proton exchange membrane electrolysis driven by photovoltaic solar energy is considered to produce hydrogen and oxygen, which is used for oxy-waste combustion in a sub-critical steam power cycle. Depending on the operation strategy, a certain amount of additional O2 would be required, produced by a cryogenic distillation air separation process. At the exit of the boiler, the almost pure CO2 stream is further purified, compressed, and sent to the methanation reactor. A quasi-stationary model of the entire plant is developed to simulate different operation conditions and assess the integration efficiency. The results show an excellent integration of the whole plant, with a yearly average efficiency penalty associated with the CO2 avoided of 6 % points. Since waste biomass is used as fuel, the system provides −610 kg CO2/MWh emissions compared to biomass plants without CO2 capture. Results from a yearly detailed techno-economic analysis show an average levelized cost of electricity of 199.56 €/MWh and an average green methane production cost of around 110.12 €/MWh. These yearly results involve a CO2 capture cost of about 65.66 €/ton CO2, which justify the potential interest in the proposed system for new and retrofitted biomass power plants.

Optimization of Energy Consumption of a Synthetic Ammonia Process

Ammonia can be produced from a wide range of raw materials such as coal, natural gas, coke and oil. Coal gasification is a process that converts biomass or fossil fuel-based carbonaceous materials into CO, H2 and CO2. A cryogenic air separation process was used to obtain oxygen from air because of high purity and high amount of oxygen, which will be used for coal gasification. For an ammonia synthesis process using pure oxygen gasification, the energy consumption of cryogenic air separation occupies a large proportion. The aim is to reduce energy consumed in the ammonia plant. The models of the process were developed with the aid of Aspen Plus. The energy consumption of the different processes was obtained through energy analysis, economic analysis and sensitivity analysis. From the three simulations, it can be seen that Simulation 3 produced oxygen with the highest purity of 0.979. From the energy analysis, the energy consumed on the total utilities in Simulation 1 was 5.626×1010 BTU/h with an energy savings of 1.55%, the energy consumed in Simulation 2 was 5.286×1010 BTU/h with an energy savings of 1.53% while the energy consumed on the total utilities in Simulation 3 was 1.425×109 BTU/h with an energy savings of 74.90%. Simulation 3 consumed the least energy. The economic analysis showed the total cost of each plant for a 10-year duration. Simulation 1 had a total operating cost of 42.083 billion USD/year, Simulation 2 had a total operating cost of 41.9615 billion USD/year and Simulation 3 had a total operating cost of 918.841 million USD/year. Therefore, Simulation 3 consumed the least cost of total operation. It can also be seen that the higher the energy consumption in a plant, the higher the total cost of the plant as Simulation 3 consumed the least energy, which justified that. Simulation 3 is the air separation plant that optimises the energy consumption, thereby reducing the energy consumed in the whole ammonia plant.

Energy analysis and optimization of heat integrated air separation column based on non-equilibrium stage model

A large scale of nitrogen and oxygen production has been through a cryogenic air separation process. This process takes place in a distillation column at excessive energy consumption. The heat-integrated air separation column (HIASC) can save energy when utilizing minimum pressure while ensuring adequate heat distribution along the portion of the column. However, accurate prediction of thermodynamic and fluid properties requirement is critical for process optimization and potential energy saving. The nonequilibrium stage model is employed to gain insight into the thermodynamic properties. While examining the influence of these properties, essential process operating variables are optimized to save energy. The research result shows that more than 17% of energy is preservable in the HIASC.

Oxygen production routes assessment for oxy-fuel combustion

Oxyfuel combustion is a promising alternative to decarbonize the power sector. However, the main barrier to commercial deployment of the technology is the high energy consumption associated with oxygen production (∼200–300 kWh per ton of O2), which penalizes the thermal-to-electric efficiency of 8.5–12% compared to traditional air combustion plants. Typically, oxygen is obtained from a cryogenic air separation process. However, other technologies have been gaining momentum in recent years, such as membrane technologies, chemical looping air separation, and renewable-driven electrolysis. The present work evaluates all these options for O2 production to retrofit a 550 MWe coal-fired power plant with oxyfuel combustion. A techno-economic assessment is carried out to estimate the energy penalty, the O2 production cost (€/ton) and the Levelized Cost of Electricity. The best results are obtained by combining oxygen transport membranes and electrolysis since the energy consumption has been reduced to 98.56 kWh/ton of O2, decreasing by 59.31% the cryogenic distillation energy consumption (242.24 kWh/ton O2), reducing the overall energy penalty compared to cryogenic air separation from 8.88% points to 7.56%points. The oxygen transport membrane presents the lowest cost of electricity in retrofitting cases, 51.48 $/MWh, while cryogenic distillation estimated cost is 52.7 $/MWh. Their costs of avoided CO2 are 31.79 $/ton CO2 and 34.15 $/ton CO2 respectively.

Design and System Evaluation of Mixed Waste Plastic Gasification Process Based on Integrated Gasification Combined Cycle System

Plastic products are widely used due to their superior performance, but there are still limitations in the current methods and technologies for recycling and processing of waste plastics, resulting in a huge wasting of resources and environmental pollution. The element composition of waste plastics determines its great gasification potential. In this paper, three different waste plastic gasification processes are designed in a process simulator based on the conventional Integrated Gasification Combined Cycle (IGCC) system to achieve waste conversion and utilization as well as carbon capture. Design 1 is based on the cryogenic air separation (CAS) process to obtain oxygen, which is sent to the gasifier together with steam and pretreated waste plastics. The synthesis gas is purified and synthesized into methanol, and the residual gas is passed to the gas turbine and steam turbine to achieve multiple production of heat, electricity, and methanol. Design 2 uses a Vacuum Pressure Swing Adsorption (VPSA) process to produce oxygen, which reduces the energy consumption by 56.3% compared to Design 1. Design 3 adds a calcium-looping (CaL) reaction coupled with a steam conversion reaction to produce high-purity hydrogen as a product, while capturing the generated CO2 to improve the conversion rate of the reaction.

Conventional and Advanced Exergy Analyses of an Integrated LNG Regasification–Air Separation Process

Liquefied natural gas (LNG) is being imported in Pakistan to bridge the gap between the indigenous production and demand for natural gas. The calorific value of imported LNG must be lowered to meet the design requirements of the existing gas-fired power plants. This reduction in calorific value requires mixing with high-purity nitrogen, which can be obtained from the cryogenic distillation of air. Because imported LNG has a significant amount of cold energy and must be regasified/vaporized before injecting into the gas pipeline network, there is potential for recovering this cold energy by integrating the LNG regasification process with the cryogenic air separation process. To achieve these objectives, we developed an integrated LNG regasification–air separation process and compared it with the standalone air separation process. Conventional exergy analysis shows that the integrated process is better than the standalone air separation process both in terms of total power consumption and total exergy destruction ratio. The integrated process was further analyzed using advanced exergy analysis to identify the origin and nature of exergy destruction in the process. The results show that 44.3% of total exergy destruction in the process can be classified as avoidable. Moreover, 91.7% of the avoidable exergy destruction is of endogenous nature, showing that improving the efficiency of individual pieces of equipment should be the topmost priority for process improvement.

Approximate Relations for Optimum Turbine Operating Parameters in Allam Cycle

Abstract This article explores the relations between the cycle performance and the main operating parameters of the Allam cycle with uncooled turbine through a simplified thermodynamic analysis. The cycle efficiency is maximized with respect to turbine parameters. Expressions are derived for the estimation of optimum turbine inlet temperature (TIT) and pressure as well as optimum turbine exhaust pressure. The cryogenic air separation process developed by Allam is employed, which produces supercritical oxygen at combustion pressure. Typical numerical results are presented using the new expressions for optimum turbine parameters. The highest cycle efficiency is found to be 66.4% at a TIT/inlet pressure/exhaust pressure of 1306 K/300 bar/39.4 bar and a CO2 compressor exit pressure of 60 bar. The newly derived relationships for the key process parameters allow a better understanding of the operation of the Allam cycle.

Integration of Supply and Demand Side Management Using Renewable Power Sources: Application on an Air Separation Plant

Exploitation and implementation of renewable energy can substantially advance development, improve energy security, and alleviate the climate change problem. Integrating multiple renewable energy sources with grid power could potentially reduce the dependency on nonrenewable energy sources. However, because of the intermittent nature of the former, a tight integration between the supply and demand side management is necessary to facilitate uninterrupted power distribution and efficient energy consumption. This paper discusses an optimization framework that integrates supply and demand side management with application toward an energy-intensive cryogenic air separation process that is equipped with an in-house power generation system comprising multiple renewable and deterministic power sources as well as an energy storage system. The proposed framework integrates the power generation and purchase decisions along with the production complexities of the air separation plant (ASP). The optimal power generation schedule and the optimal production schedule provided by the proposed integration framework have been shown to minimize the total energy cost required to operate and meet the production requirement of the cryogenic ASP. An economic analysis is also performed to study the economic viability of including an in-house renewable source-based power generation and storage system with the ASP.

Performance modeling of Allam cycle integrated with a cryogenic air separation process

The performance of an integrated Allam cycle and a cryogenic air separation process is numerically simulated. In contrast to previous research which has primarily focused on the design of the cycle alone, this work accounts for the operational co-dependence of the cycle and a co-located air separation unit (ASU). Heat integration between the cycle and ASU includes adiabatic heat of the main air compressor (MAC), and booster compressor of the ASU overlooked in past studies. The discharge pressure of the recycled CO2 compressor is determined based on its saturation pressure at cycle minimum temperature. The cycle efficiency exhibits a maximum at a MAC discharge pressure of 4.2 bar whereas it consistently decreases with discharge pressure of the booster. A genetic algorithm optimization is applied to estimate an optimum operational point. A maximum efficiency of 59.7% is obtained at turbine inlet temperature, inlet pressure, and outlet pressure of 1500 K, 305.5 bar, and 28.1 bar, respectively.

Evaluation of Two-Column Air Separation Processes Based on Exergy Analysis

Cryogenic air separation processes are widely used for the large-scale production of nitrogen and oxygen. The most widely used design for this process involves two distillation columns operating at different pressures. This work focuses on the selection of suitable cryogenic air separation process by evaluating seven alternative designs of the two-column air separation process based on detailed exergy analysis. The feed conditions (500 tons/h, and 50% relative humidity of air), product purities (99 mole% for both nitrogen and oxygen), and operational conditions (pressures of both distillation columns) are kept same in all designs. The two cryogenic distillation columns in each configuration are heat-integrated to eliminate the need for external utilities. Steady-state simulation results are used to calculate the exergy efficiency (%) of each equipment as well as its contribution toward the overall exergy destruction rate (kW) of the process. The results show that the compression section is a major source of exergy destruction, followed by the low-pressure column, and the multi-stream heat exchanger. A Petlyuk-like configuration, labeled as C1, provides the lowest exergy destruction rate.

Optimization of a novel cryogenic air separation process based on cold energy recovery of LNG with exergoeconomic analysis

Oxyfuel combustion is deemed as one of the most potential technology to reduce CO2 emission from power plant. Exploring the technology of low-cost high-purity oxygen is a key issue to the implement of oxyfuel combustion. Cryogenic air separation is routinely used in large-scale production of high-purity oxygen. However, the relatively high power consumption of traditional cryogenic air separation no longer satisfies the requirement for cost-effective high-purity oxygen generation in the industrial field. A novel three-column cryogenic air separation process integrated with liquefied natural gas (LNG) regasification is introduced and evaluated in this paper. Waste nitrogen full utilization, cascade heat transfer and multi-column air distillation strategies are employed. To confirm the rationality and validity of the process, pinch point, energetic, exergetic and exergoeconomic analyses are performed. The obtained results indicate that the specific power consumption of liquid oxygen and liquid nitrogen are 0.252 kWh·kg-1 and 0.258 kWh·kg-1 in the proposed integrated system. The overall exergy efficiency and the LNG cold exergy utilization efficiency reach 0.7165 and 0.5318, respectively. Furthermore, sensitivity analysis is employed to investigate the effects of the outlet temperature of sub-coolers and stage number of low pressure column on total power consumption and equipment investment of the proposed process.

Heat-transfer distribution optimization for the heat-integrated air separation column

The heat-integrated air separation column (HIASC) is an advanced energy-saving technology for the cryogenic air separation process, although a large capital investment is required for installed heat exchangers. These heat exchangers have a location-dependent effect upon the separation which leaves room for optimization. This paper, therefore, aims to optimize the heat-transfer distribution of HIASC regarding minimum heat exchanger costs while maintaining the low energy consumption level. Results indicate that the heat-transfer tends to concentrate at both ends of the column. The influence of operational parameters is further studied by the idea based on the liquid-vapor ratio. Finally, an optimal HIASC with respect to the minimal heat exchanger investment is obtained, and the heat exchanger costs are reduced by 44.4% compared with the uniform distribution with a similar energy-saving level.

Exergy Analysis of Liquid Nitrogen Power Cycles

Nitrogen is by-product from cryogenic air separation processes used for oxygen production for metallurgy and oxygen-enriched combustion purposes. If the gases are delivered from air separation unit (ASU) in liquid phase, liquid nitrogen (LN2) can be used as energy accumulator for stabilization of electrical grid system with large share of renewable energy sources. When the energy demand is high and not enough electricity is generated in power plants, energy accumulated inLN2may be recovered in a cryogenic power cycle. In this research complete exergy analysis of liquid nitrogen direct expansion cycle and combined direct expansion/Brayton cycle was performed.

Feasibility analysis and simulation of argon recovery in low oxygen-purity cryogenic air separation process with low energy consumption

This paper has discussed and simulated different low oxygen-purity air separation processes with or without argon recovery to find out efficient air separation process using HYSYS platform, and proposed a novel mixing-column process that provides high argon recovery rate based on energy saving effect. For comparison, all the proposed cases are simulated under the same process conditions of 50,000 Nm3/h feed air, 95% gaseous oxygen purity, 0.03 MPa gauge pressure, and 300 Nm3/h liquid oxygen output. Three main performance parameters including oxygen recovery rate, energy consumption and argon recovery rate are compared, and the simulation results show that among five types of processes without argon recovery, the triple-column process, whose energy requirement decreases by 14.9% compared with conventional dual-column process, achieves the lowest energy consumption. Argon production is required in many aspects during air separation process. The feasibility of argon recovery in low oxygen-purity air separation process is studied. The process with argon recovery named mixing-column process is proposed, whose argon recovery rate can reach up to 60.88%, which further increases up to 62.23% with the optimized raw argon flow rate and mixing-ingredient. The energy consumption of the proposed mixing-column process is decreased by 3.5% compared with conventional dual-column process, while the argon recovery rate of the triple-column process can only reach to 4.55% in despite of energy saving by 12%. In addition, more stable argon recovery performance as well as higher argon recovery rate is realized by this novel process when using varied oxygen purity in low oxygen-purity (≤99%) process.

Simulation and heat exchanger network designs for a novel single-column cryogenic air separation process

Abstract To realize the industrialization of the novel single-column air separation process proposed in previous work, steady-state simulation for four different configurations of the single-column process with ternary (nitrogen, oxygen and argon) is developed. Then, exergy analysis of the single-column processes is also carried out and compared with the conventional double-column air separation process at the same capacity. Furthermore, based on the steady-state simulation of single-column processes, the different heat exchanger networks (HENs) for the main heat exchanger and subcooler in each process are designed. To obtain better performance for this novel process, optimization of process configuration and operation is investigated. The optimal condition and configuration for this process is consisted as: feedstock is divided into two streams and the reflux nitrogen is compressed at the approximate temperature of 301 K. In addition, HEN is optimized to minimize the utilities. HENs without utilities are obtained for the four different configurations of single-column process. Furthermore, capital costs of the HEN for different cases are estimated and compared.

Enclave Optimization: A Novel Multiplant Production Scheduling Approach for Cryogenic Air Separation Plants

The cryogenic air separation process is among the most energy-intensive operations and requires intelligent approaches to minimize its operational cost, the main constituent of which is the power cost. Some of the air separation plants operate in a co-operative manner with each other, and to capture the intricacies of these arrangements, a novel multisite framework is needed. In this paper, a novel approach called enclave optimization, which incorporates a small product exchange network among plants in the enclave, along with the multiplant production network, is introduced. The merits of enclave level framework lie in its ability to address the major challenges that originate from multiplant arrangements such as shared inventory, common customer and global liquid demands, etc. Motivated by the time scales of (i) gas and liquid demands and (ii) other operational factors, we adopt a nonuniform time discretization framework, which helps to define constraints regarding different products in various time scal...

Multiperiod model for the optimal production planning in the industrial gases sector

Cryogenic air separation to produce nitrogen, oxygen and argon with high quality requirements is an energy-intensive industrial process that requires large quantities of electricity. The complexity in operating these networks stems from the volatile conditions, namely electricity prices and products demands, which vary every hour, creating a clear need for computer-aided tools to attain economic and energy savings. In this article, we present a multiperiod mixed-integer linear programming (MILP) model to determine the optimal production schedule of an industrial cryogenic air separation process so as to maximize the net profit by minimizing energy consumption (which is the main contributor to the operating costs). The capabilities of the model are demonstrated by means of its application to an existing industrial process, where significant improvements are attained through the implementation of the MILP.

6-3-4 冷熱循環による省エネルギーな深冷空気分離プロセスの設計(6-3 設計による省エネルギー,Session 6 省エネルギー,研究発表)

6-3-4 冷熱循環による省エネルギーな深冷空気分離プロセスの設計(6-3 設計による省エネルギー,Session 6 省エネルギー,研究発表)

A novel optimization framework for designing multi-stream compact heat exchangers and associated network

Despite the performance gains of heat exchangers by thermal-hydraulic optimization, many design approaches suffer from a long process of trial-and-error, limited practical problem formulation and poor robustness. This paper addresses those challenges and develops an optimization framework for designing multi-stream compact heat exchangers. The optimization framework consists of a multi-stream matching organization design with Pinch analysis principles on the heat exchanger network, fin selection and relevant layer pattern using multi-objective algorithm for the thermal-hydraulic modeling, and a field synergy optimization analysis for the temperature field of exchanger. There are compatible with each other by the mutual restriction of design parameters and the process requirements. Finally, by means of a segmented differential calculation, the designed temperature field of all the streams and layers can be obtained. Design capabilities of this optimization framework are investigated on two multi-stream heat exchangers for cryogenic air separation processes. The optimization results are compared with traditional design methods, proving that this framework not only satisfies the specific energy requirement, but also to some extent improves the heat transfer efficiency and reduces the fluid resistance. The developed optimization framework provides a flexible and robust method for numerical simulation and optimization design of multi-stream heat exchangers.