Cryogenic Air Separation Unit Research Articles

Techno-economic analysis of blue ammonia synthesis using cryogenic CO2 capture Process-A Danish case investigation

Ammonia is a vital chemical with numerous applications. Currently, the primary methods for generating the necessary reactants for ammonia production involve steam methane reforming (SMR) and cryogenic air separation unit (CASU), while the Haber-Bosch process converts these reactants into ammonia. However, the SMR process releases substantial amounts of CO2, making it imperative to employ an efficient and cost-effective CO2 capture technology to mitigate emissions. This investigation focuses on evaluating the cryogenic CO2 capture (CCC) process for blue ammonia production and provides a thorough economic analysis, estimating both the initial investment costs and operational expenses involved in producing blue ammonia. The results indicated that the CCC process can capture 90% of the CO2 content in the flue gas emitted by the SMR, incurring an energy penalty of 0.724 MJe/kgCO2 while capturing CO2 in the liquid phase with purities exceeding 99.9%. In this case, the estimated CO2 capture costs would be 18.05, 45.1, and 16.65 USD/ton in 2021, 2022, and 2023, respectively. This represents a 40% reduction compared to the CO2 capture costs associated with conventional amine-based technology. The results of this study indicate that the annual electricity costs for ammonia production increase by 38.5% and 64.2% when employing the CCC and amine-based processes, respectively. This investigation employed an isothermal reactor for ammonia synthesis, using the heat from the exothermic reaction in a water ammonia absorption refrigeration cycle (ARC) to condense and purify ammonia. The results show that the ARC system can effectively condense ammonia at −6 °C, producing a liquid ammonia stream with 99.3% purity. This leads to a 95% reduction in power consumption compared to a vapor compression refrigeration cycle (VCRC). Consequently, this method has the potential to decrease the annual operational costs for ammonia production by 2.92%, 2.69%, and 3.13% in 2021, 2022, and 2023, respectively. This study indicated that the hydrogen production unit incurs the highest initial investment costs, as well as operating costs, in the blue ammonia production process, followed by CASU and the Haber-Bosch process.

Analysis and optimization of a sustainable hybrid solar-biomass polygeneration system for production of power, heating, drying, oxygen and ammonia

In this study, we introduce an innovative polygeneration system that combines solar and biomass energies to generate power, heating, hot air for the drying process, oxygen, and ammonia. The proposed polygeneration system comprises a solar tower subsystem (STS) integrated with two energy storage tanks (cold and hot), a gas turbine cycle (GTC), an organic Rankine cycle (ORC), a proton exchange membrane (PEM) electrolyzer, a thermoelectric generator (TEG), a cryogenic air separation unit (CASU), and an ammonia synthesis reactor (ASR). The GTC and the ORC equipped with the TEG are utilized for power production. The steam for the gasification process, hot air for the drying process and heating are produced by three regenerators. The PEM electrolyzer is used for the decomposition of water into hydrogen and oxygen, while the air separator (cryogenic method) is employed for the separation of air into nitrogen and oxygen. The separated oxygen is stored in an oxygen tank, while nitrogen and hydrogen are utilized for the ammonia generation. The system is evaluated from energy, exergy, economic and, environmental standpoints. Based on the findings, the proposed system is capable of generating approximately 163 MW of net power, 150 MW of heating, 100 MW of drying, 21.7 kmol/hr of oxygen and 23.24 kg/hr of ammonia. The total energy and exergy efficiencies, as well as the life cycle cost (LCC) and CO2 emissions are determined to be 70.68 %, 48.71 %, 1.175 × 109 $ and 381.3 kg/MWh, respectively. Additionally, a multi-objective Grey Wolf optimization algorithm is utilized to optimize the exergy efficiency, LCC, and CO2 emissions. The optimized results yield an exergy efficiency of 51.02 %, an LCC of 1.16 × 109 $, and a CO2 emissions of 359.73 kg/MWh. The proposed system demonstrates encouraging thermodynamic and economic performances, providing an appealing solution for efficient utilization of abundant solar and biomass resources.

A novel cryogenic air separation unit with energy storage: Recovering waste heat and reusing storage media

The combination of the air separation unit and cryogenic energy storage enhances system efficiency; however, there are still significant irreversible losses in the energy conversion process and high investment costs. This paper explored the potential for deep integration of these two process and proposed a novel air separation with liquid nitrogen energy storage process recovering waste heat and reusing storage media process. The proposed process improved the liquefaction and power generation processes and recovered the compression heat for air purification processes. Taking an actual plant as a research case, the integrated system was simulated using Aspen Plus software. The round-trip efficiency, exergy efficiency, and power generation of the proposed process are 0.537, 0.722, and 10.52 MWh respectively, which are 6.2 %, 20.9 %, and 68.3 % higher than those of conventional process. By reusing storage nitrogen and recovering compression heat, the proposed process reduces the initial investment cost by half while achieving a dynamic payback period of 6 years with a levelized cost of electricity at $82.8/MWh. Furthermore, it is worth noting that media reuse operations have a greater impact on economy when off-peak electricity cost is low; whereas utilization of compression heat has a greater impact when off-peak electricity cost is high.

Novel ASU–LAES system with flexible energy release: Analysis of cycle performance, economics, and peak shaving advantages

This study uses a cryogenic distillation method air separation unit (ASU) coupled with liquid air energy storage (LAES) to improve the round-trip efficiency and reduce the initial investment of LAES. We propose an integrated system (ASU–LAES–DER) with different ways of energy release. In the novel system, the liquid air can be reheated and expanded to produce additional power, or the liquid air energy stream and part of the material stream can be used for ASU distillation to produce power saving effects. This novel integration allows the ASU to have load regulation capability and facilitates the implementation of demand-side power management. Furthermore, the flexible and efficient energy release methods improve the energy efficiency and economic value of LAES. The comprehensive round-trip efficiency of the system can reach 52.1%–69.2 % with a payback period of 3.25–6.72 years. The peaking index is used to analyze the peak-to-valley load transfer capability of the novel system. Results show that the peaking index ranges from 25.5 MW to 50.1 MW at different scales, indicating that the system can be used as an important grid peaking unit when applied on a large scale.

Ion transport membrane heat engine integration with autothermal reforming-based methanol production

This study focused on improving the energy demand of conventional large-scale natural gas to methanol flow sheet where even a small efficiency improvement has significant economics and carbon emissions benefits. A conventional flow sheet, case A, was based on best available literature information. A case B where the conventional cryogenic air separation unit (ASU) is replaced with the novel ion transport membrane (ITM) oxygen unit was developed. The ITM oxygen is also heat integrated into the autothermal reformer (ATR) process. A case C where the methanol synthesis process is configured into a gas turbine cycle was developed from further modifying case B. The flow sheets were constructed and modelled in Aspen Plus V10 and, heat and material balance results are reported. To our knowledge, the integration of ITM oxygen membranes into the ATR-based methanol process has not been assessed previously.Energy and exergy results are generated and analysed. It was found that is it possible to replace the cryogenic ASU with the ITM oxygen for oxygen production in the ATR process. There is enough process syngas heat available to provide the ITM oxygen unit heating requirement and to generate process steam feed to the ATR. Case A was found to consume only 12 % natural gas as utility fuel which is lower than typical SMR-based methanol processes. This reduced to about 5 % in case B and C. Power production improved by 47 % in case B and 68 % in case C compared to case A.A thermal efficiency definition suitable for combined process steam, power and oxygen production was proposed. This showed that integration of a high temperature gas power cycle enables combined steam (heat) and power configuration which has a higher efficiency compared to single cycles, such as the steam cycles. The overall plant exergy losses decreased by up to 21 %.

Optimization of the air separation process in single stage cryogenic units

The industrial use of cryogenic air separation units started more than 130 years ago. Cryogenic air separation units produce oxygen, pure nitrogen and argon in liquid and/or gaseous state. Different configurations of these cryogenic plants lead to different quantities of gas and liquid products. In addition, product purity is also affected by the proposed scheme. As a result, the paper analyzes different variants of installations for the separation of binary gas mixtures based on the Linde process. By comparing energy indices and constructive considerations, the separation plant with external air pre-cooling and the use of a single-stage separation column is chosen. Finally, a study is carried out on the processes in the separation column and a calculation of the minimum mechanical work of separation. The real air consumption curve will also be built, with the help of which we shall determine what quantities of O2 and N2 are obtained by air separation at a specific consumption.

Comparative study of waste heat recovery systems based on thermally driven refrigeration cycles in cryogenic air separation units

Recovering compression heat generated in the air compression process is expected for energy saving of cryogenic air separation units. However, the effective utilization of compression heat remains a challenge due to the low-grade feature of the available heat source. Therefore, the selection of the waste heat recovery system configuration is critical to the optimum utilization of the compression heat. In this study, two waste heat recovery systems based on different thermally driven refrigeration cycles for compression heat recovery are proposed, including an organic Rankine vapor compression-based air compression system (ORVC-ACS) and an absorption refrigeration-based air compression system (ARS-ACS). A 60,000-Nm3/h scale cryogenic air separation unit is considered as a case study for assessing and comparing the energetic, exergy and economic potential of the two proposed systems. The results reveal that the ORVC-ACS is preferable to the ARS-ACS in terms of energy-saving and economic performance. Operation optimization is conducted to identify the maximum energy saving of the preferred system. The optimization results show that the ORVC-ACS is capable of saving a total electricity of 8.52 GWh/year, corresponding to 4.53% of the annual electricity consumption for air compressors, while the values are 6.43 GWh/year and 3.37% for the ARS-ACS. This work may provide guidelines for configuration selection and optimum design of waste heat recovery systems in cryogenic air separation units.

Dynamic modeling of a mechanically coupled organic Rankine-vapor compression system for compression heat recovery based on an improved lumped parameter model

Compression heat recovery is getting attention in cryogenic air separation units for its high energy saving potential, while the organic Rankine-vapor compression system (ORVC) is considered as an attractive technology for both compression heat recovery and air pretreatment. As the states of the compression heat inevitably change with the ambient environment, dynamic simulation of the ORVC-air compression heat recovery system (ORVC-ACS) is carried out in this paper. An improved lumped parameter model that enables to solve the dynamic model with complex structure and on large-time scale is proposed and validated. The working fluid density in the heat exchanger is treated as phase-based average in this improved model. The average relative deviations between the simulation results and experimental data are less than 6.8%. The annual dynamic characteristics and varying-duty operation performance of the ORVC-ACS are further studied. The results show that the ORVC-ACS could basically work under the design condition, with the maximum temperature fluctuation amplitude of about 6.9 °C, response time of about 4–6 min without varying-duty conditions and 8 min with duty changing. Besides, for a 60,000 Nm3/h scale ORVC-ACS, the annual energy saving reaches about 13.75 GWh, equivalent to CO2 emission reduction of about 9.9 Mt, and heat recovery ratio of about 76.4%, illustrating great energy saving and environmental protection performance. This research may benefit subsequent control scheme design and actual operation.

Coupling chemical looping air separation with the Allam cycle – A thermodynamic analysis

The Allam cycle is a class of oxy-fuel combustion power cycles using supercritical CO2 (s-CO2) as the thermal fluid to achieve power generation with inherent capture of CO2. Compared to other conventional CO2 capture techniques, the Allam cycle stands out owing to its high fuel-to-electricity conversion efficiency (55–59%), the elimination of the Rankine cycle and reduced physical footprint. A key source of energy penalty of Allam cycle comes from the air separation unit (ASU), which supplies pure oxygen via an energy intensive cryogenic process. This paper presents a thermodynamic analysis of a novel supercritical CO2-based power generation scheme, in which a natural gas fuelled Allam cycle is integrated with a chemical looping air separation (CLAS) system, which supplies oxygen to the combustor. The modelling results show that the Allam-chemical looping air separation (Allam-CLAS) process can achieve 56.04% net electrical efficiency with a 100% CO2 capture rate, when a Co3O4-based oxygen carrier is used. This is 6% higher than the Allam cycle coupled to a cryogenic ASU. The exergetic efficiency of the Allam-CLAS system driven by the Co3O4-CoO redox cycle is 57.13%, also more favourable than a conventional Allam-ASU system (with reported exergetic efficiency of 53.4%). This newly proposed Allam-CLAS power cycle presents a highly efficient, and simple solution to generate zero-carbon electricity from natural gas.

Dynamic characteristics of a mechanically coupled organic Rankine-vapor compression system for heat-driven cooling

There are large quantities of compression heat wasted and cooling capacity required in cryogenic air separation units (ASUs). Mechanically coupled organic Rankine-vapor compression (ORVC) system is an attractive technology to realize heat-driven refrigeration for compression heat recovery and compression power saving in cryogenic ASUs. As the states of the compression heat inevitably change with the ambient environment, off-design operation of the ORVC system is worth investigating. A mechanically coupled ORVC test bench is designed and built in this paper. Off-design experiments are carried out to figure out the dynamic response characteristics and system performance variations. Results show that, the ORC working fluid flowrate and the opening of the throttle valve are the key operation parameters affecting the system dynamic response. The experimental system responds quickly with delay time less than 10 s and response time less than 1 min. The opening of the throttle valve has the greatest impact on the cooling capacity and system COP which reaches up to 0.61. This research may provide reference for control scheme design and actual operation for the compression heat recovery system in cryogenic ASUs.

A deep reinforcement learning based multi-objective optimization for the scheduling of oxygen production system in integrated iron and steel plants

The oxygen production system in integrated iron and steel plants is a highly energy-intensive sector producing gaseous oxygen for the manufacturing processes. This study investigates an oxygen production system with cryogenic air separation units (ASU), vaporizers, and liquefiers under frequent demand-changing scenarios and various electricity price contracts. A multi-objective optimization model is established to minimize the total operating cost to reduce energy consumption and simultaneously minimize switching times of operating modes to pursue operational stability. The proposed model not only schedules operation modes of ASUs and on/off modes of vaporizers and liquefiers but also determines the production level of these units. To solve the problem, a multi-objective evolutionary algorithm (MOEA) is proposed, in which the proximal policy optimization, one of deep reinforcement learning (DRL) methods, is incorporated to adaptively select the mating individuals and determine the crossover ratio at each evolutionary iteration. Besides, a surrogate model for optimizing the total operating cost is presented to accelerate the training process of the proposed deep reinforcement learning based multi-objective evolutionary algorithm (DRL-MOEA). The performance of the proposed algorithms is demonstrated using practical instances, and experiment results show that it saves the total operating cost up to 0.86% and decreases the operating modes switches as much as 14.41%, compared to MOEA. The model offers the on-site manager solutions to coordinate the supply and demand with a good trade-off between reducing overall energy consumption and pursuing streamlined operating conditions.

New technology to produce raw neon-helium mixture

Until 2022, Ukraine was a major producer of pure neon gas. The crude neon product is obtained as a byproduct at large cryogenic air separation units (ASUs) that supply oxygen and nitrogen to steelmakers. After the stop of such industries in Ukraine, a global shortage of neon, which is necessary for the production of semiconductor microchips, appeared. The conceptually new technology for obtaining the crude neon product at ASUs, which is not adapted for the selection of a raw neon-helium mixture, is proposed. The enrichment of the neon-helium mixture taken from the ASU condenser-evaporator is carried out by the pressure swing adsorption method. Calculations of the adsorption enrichment processes of the neon-helium mixture were carried out using the wave method. The wave method is based on the physically accurate concept that the nonstationary flow of components occurs as a result of propagation concentration waves in the entire adsorption layer and inside the adsorbent grains. It is shown that the proposed technology makes it possible to obtain a crude neon-helium mixture with a total concentration of neon and helium of more than 90% at an extraction ratio of 40–50%.

Thermo-economic optimization of a novel hybrid structure for power generation and portable hydrogen and ammonia storage based on magnesium–chloride thermochemical process and liquefied natural gas cryogenic energy

Storage and transfer of hydrogen (H2) from production sites/plants to large-scale demanding industries are one of the most challenging obstacles to hydrogen adoption. Hydrogen liquefaction and its chemical storage in the form of ammonia (NH3) can be used for safe and economic transportation. High energy consumption and carbon dioxide (CO2) emissions to supply the utility of these systems can limit the production of liquid H2 and liquid NH3. Therefore, efficient design and practical strategies to store hydrogen at a large scale with minimal energy consumption and CO2 emissions are necessary. In this research, an innovative hybrid system for portable hydrogen storage and power generation with zero CO2 emission through liquefied natural gas (LNG) regasification is developed. The proposed structure includes a cryogenic air separation unit, magnesium–chloride hydrogen production process, ammonia production system, hydrogen liquefaction cycle, and Rankine/oxy-fuel power plants. The heat loss of the proposed structure is utilized to supply the required heat load for the thermo-electrochemical unit. The LNG regasification operation is utilized for pre-cooling the hydrogen liquefaction system and the necessary refrigeration of the air separation process and the final products. The developed structure is fed by 1883 kmol/h LNG, which is converted to 120 kmol/h liquid NH3, 180 kmol/h liquid H2, 924.5 liquid CO2, and 16.09 MW power. The thermal and exergy efficiencies for the designed system are 20.33% and 22.76%, respectively. The results of the exergy investigation reveal that the largest contribution of exergy destruction occurs in heat exchangers (31.27%), combustion chamber (34.65%), and turbines (8.12%). The economic evaluation indicates that the net annual profit, added value, and payback period are 15.93 US$/yr, 0.0779 US$/kWh, and 5.646 yr, respectively, based on the energy potential of Newfoundland and Labrador in Canada. Three-objective optimization approach using the combination of genetic algorithm and neural network exhibits that the energy efficiency and net annual profit based on the Bellman-Zadeh approach increase up to 27.04% and 45.20 US$/MMBTU, respectively, and the irreversibility reduces to 99.4 MW.

Techno-economic analysis of plastic wastes-based polygeneration processes

To address the plastic waste reduction and reutilization, three designs of mixed plastic wastes-based polygeneration processes are named Designs 1–3. Designs 1 and 2 produce MeOH and electricity simultaneously by using the cryogenic air separation unit (CASU) and the vacuum pressure swing adsorption unit (VPSA), respectively. To increase the capacity of capturing CO2, the calcium looping process (CaLP) is involved in Design 3 to produce the products of H2 and CO2 and recover waste heat for power generation. The complicated CaLP dramatically increases the total costs of Design 3, although the carbon capture ratio of Design 3 is superior to other designs. If the cumulative carbon revenue is counted into the total annual income according to the emission trading scheme, the economic evaluation shows that Design 3 has a higher net present value (NPV), or a higher internal rate of return (IRR), or a shorter dynamic payback period (DPP) than other designs.

Energy, exergy and economic analyses of an optimal use of cryogenic liquid turbine expander in air separation units

Cryogenic liquid turbine expanders have emerged quite recently as a replacement for traditional Joule-Thomson valves in cryogenic processes for energy saving purpose. However, introducing a liquid turbine expander into the cryogenic air separation unit (ASU) can influence the operating points of ASU components, and the maximum benefits arising from the liquid turbine expander have not yet been reported. To fill such a gap, thermodynamic models are first established for ASU components, including the main air compressor, booster air compressor, cryogenic gas and liquid turbine expanders, main heat exchanger, cryogenic pump, and distillation column. To achieve the best possible use of the liquid turbine expander, an optimization method is developed by incorporating the thermodynamic models with the particle swarm optimization algorithm, in which the total minimization power consumption of ASU is the optimization goal while the flow rates and pressures of the high pressure air stream and the air stream drawn from the booster air compressor middle section together with the temperature of the medium pressure air stream exiting the main heat exchanger midway act as the optimization variables. Then, energy, exergy and economic analyses are conducted and the corresponding indexes are chosen to quantitatively evaluate the influence of the liquid turbine expander on the air separation process. For the case study, ASUs of 35000 Nm3/h oxygen production capacity with and without a cryogenic liquid turbine expander are optimized, respectively. The results show that the ASU total power saving through the use of liquid turbine expander is 4.2-fold its output shaft power; thus, the energy consumption of unit oxygen decreases by 2.12% and the overall exergy efficiency increases by 1%. In addition, the economic analysis shows that the period of return of the liquid turbine expander in the ASU is estimated to be 1.75 years.

Integration of a cryogenic ASU within an IGCC process with simultaneous optimization and energy targeting

The effect of oxygen purity on the thermal efficiency of an enriched-oxygen-fed integrated gasification carbon cycle (IGCC) was studied. A simultaneous process optimization with heat integration framework is proposed and used for the study. Rigorous models were used to represent the cryogenic air separation unit (ASU), gasifier and combined cycle. It was found that the thermal efficiency was highest (41.3–42.3%) within a range of 35–85 mol% O2, with the optimum at 45.5 mol% O2. Furthermore, injection of the nitrogen-rich vapor distillate from the high-pressure column of the ASU to the gas turbine was found to be the optimal nitrogen integration scheme compared to no nitrogen integration or using vapor distillate from the low-pressure column. In the optimized solution, heat integration results showed that pre-heating of the gasifier's oxygen feed occurs at the pinch and steam turbine inlet pressure values were 165, 28.6 and 4.9 bar.

Off-design performance analysis with various operation methods for ORC-based compression heat recovery system in cryogenic air separation units

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.

Flexible cryogenic air separation unit—An application for low-carbon fossil-fuel plants

The rapid integration of intermittent renewable sources into the electricity grid is driving the need for a flexible cryogenic air separation unit (ASU) coupled with a low-carbon fossil-fuel plant. However, the state-of-the-art ASU process is highly integrated and nonlinear, which can significantly restrict its ramping rate. In this work, we study the fundamental dynamics of a state-of-the-art double-column ASU, focusing on the dynamic characteristics of the highly integrated and nonlinear heat and mass transfers, and we propose basic control methods for achieving high process ramping rates. We found that the vapor–liquid countercurrent flows in the low-pressure column are critical to the cryogenic rectification of air, which governs the ramp rate of the ASU. This countercurrent flow structure is created through a complex heat integration process in the ASU. Here, this process is simplified as a countercurrent heat transfer to reduce the complexity of studying the ASU dynamics. To preserve this flow structure, the heat integration is maintained so that its heat duty follows the ASU load, using several basic controllers on the critical stream flowrates. A flow-driven dynamic ASU model is built in Aspen Plus Dynamics to capture the basic ramping dynamics. This model revealed a fundamental mismatch in the dynamics in the ASU column that causes a significant loss of O2 product purity when ramping down the ASU and slightly increases the purity when ramping up. Based on these findings, we propose a basic control method for rapidly ramping down/up the ASU while maintaining O2 product purity. Simulation results show the ASU basic dynamic process successfully ramps at a rate up to 10 %/min (40–100 % load) while maintaining the O2 product purity at 95.2–95.6 mol%.

Potential for Energy Utilization of Air Compression Section Using an Open Absorption Refrigeration System

In this paper, an open absorption refrigeration system is proposed to recover part of the waste compression heat while producing cooling capacity to further cool the compressed air itself. The self-utilization of the compression waste heat can significantly reduce the energy consumption of air compression, and hence increase the energy efficiency of the cryogenic air separation unit. To illuminate the energy distribution and energy conversion principle of the open absorption refrigerator-assisted air compression section, a thermodynamic model is built and the simulation work conducted based on a practical triple-stage air compression section of a middle-scale cryogenic air separation unit. Our results indicate that the energy saving ratio is mainly constrained by the distribution of the cooling load of compressed air, which corresponds to the heat load of the generator and cooling capacity of the evaporator in the open absorption refrigerator. The energy saving ratio ranges from 0.52–8.05%, corresponding to the temperature range of 5–30 °C and humidity range of 0.002–0.010 kg/kg. It is also estimated, based on the economic analysis, that the payback period of the open absorption refrigeration system is less than one year, and the net project revenue during its life cycle reaches USD 5.7 M, thus showing an attractive economic potential.

Comparative study for air compression heat recovery based on organic Rankine cycle (ORC) in cryogenic air separation units

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.