Condenser Duty Research Articles

Circulation of self-supplied water for significant energy recovery through heat integration

This study introduces an overhead heat-integrated distillation column (OHIDiC), a novel approach that maximizes heat recovery by multiple heat exchanges and product circulation. By utilizing the overhead vapor as a direct heat source, low-temperature feed and product water were used as cooling agents, thereby significantly reducing the condenser duty and reliance on cooling utilities. Additionally, the heated feed transfers heat to the column, leading to a substantial reduction of reboiler heat duty. Some of the heated product water is recycled back to the decanter for product cycling, while the rest is released as the final product. This circulation process ensures a continuous coolant supply, which contributes the reduction of condenser duty. Two processes were considered in this study, utilizing the water product from a non-reactive, and from a reactive separation within the system. When applied to the separation of a water-dodecanol mixture, OHIDiC reduced the condenser duty by 69.21% compared to a traditional distillation column, with a 31.46% reduction in the total utility consumption. When reactive distillation was incorporated into the OHIDiC, the higher overhead vapor temperature facilitated high heat transfer in the multiple heat exchange sections, thereby significantly reducing the total thermal load. This resulted in a reduction of up to 46.96% in total heat duty and a 36.06% decrease in CO2 emissions. These findings confirm that the OHIDiC achieves significant energy savings through the utilization of process-derived substances, with pronounced benefits when the temperature of the overhead vapor becomes higher.

Reactive distillation with inter-integrated vapor permeation for 1,3-Dioxolane production: Experiments, modeling, process analysis and design

To overcome the problem of difficult separation of the 1,3-dioxane (DOL)-H2O azeotrope in the production of DOL, a new high-integrated technology via reactive distillation (RD) with inter-integrated vapor permeation (VP) (abbreived as R-VP-D) was established. A series of R-VP-D experiments were conducted to find the effect of dedydration on reactant conversion and DOL content in the distillate. A two-dimensional VP module modeled by Aspen Custom Modeler (ACM) was combined with two RD modules in Aspen Plus to simulate the entire R-VP-D process, and the R-VP-D model was verified by experimental results. Then, by this model, systematic research on VP inserting position and membrane area on the reaction performance, reboiler and condenser duty, catalyst load, and TAC of the R-VP-D column was performed. The mechanism of how dehydration promotes reaction was explored. Finally, a new RD-VP-D technology for producing 99.9wt% DOL was designed and optimized. Two goals were achieved by inserting VP: obtaining a DOL-H2O mixture that crosses the azeotropic point in the distillate and improving reaction performance by removing by-product H2O. Under the optimal parameter, the energy consumption per unit product was reduced by 3.9% with less equipment, a simpler process, and less required land area compared with the RD with pressure swing distillation technology reported in the literature, and CO2 emissions were reduced by 4.0%. The reason why promotion effect is insignificant was explored, which is related to which of separation or reaction is the control step in RD process.

Pilot-scale CO2 capture demonstration of heat integration through split flow configuration using 30 wt[formula omitted] MEA at a Waste-to-Energy facility

Post-combustion carbon capture is a well-established technology to limit CO2 from industrial emissions. However, challenges such as high energy requirements for solvent regeneration persist. Research is still being conducted to improve the energy efficiency of the process. This study aims to present the results of process intensification in a pilot-scale CO2 capture plant. The pilot-scale investigations were carried out at Amager Bakke, a Waste-to-Energy facility in Copenhagen, Denmark. The tests were conducted by implementing the split flow configuration as a method of process intensification. The CO2 rich stream was split before flowing through the rich/lean heat exchanger. One of the split streams was fed to the stripper top, and the other was sent through the heat exchanger and then fed to the stripper. The cold split stream at the stripper top is heated by the overhead vapours which would otherwise escape the stripper. The current work discusses the split flow configuration results of the pilot plant by employing 30wt% MEA as the solvent and compares it to the base-case performance of the pilot. Experiments were conducted by splitting 22% of the rich solvent and feeding it to the stripper top. The performance of the split flow configuration was analysed at different reboiler duties. A minimum specific reboiler duty of 3.45 GJ/tonne CO2 is obtained for the split flow configuration, which is less than the base case by 7.8%. Additionally, a reduction in the condenser duty by at least 68% was achieved by the implementation of the split flow configuration.

Exploring Exergy Performance in Tetrahydrofuran/Water and Acetone/Chloroform Separations

Distillation is significantly influenced by energy costs, prompting a need to explore effective strategies for reducing energy consumption. Among these, heat integration is a key approach, but evaluating its efficiency is paramount. Therefore, this study presents exergy as an energy quality indicator, analyzing irreversibility and efficiencies in tetrahydrofuran/water and acetone/chloroform distillations. Both systems have equimolar feed streams, yielding products with 99.99 mol% purity. The simulations are performed using Aspen Plus™, enabling evaluation at the column level, as a standalone process, or from a lean perspective that considers integration opportunities with other plants. The results show that, despite anticipated energy savings from heat integration, economic viability depends on pressure sensitivity. The results demonstrate that heat-integrated extractive distillation for acetone/chloroform raises utility energy consumption. Exergy calculations comparing standalone and total site integration reveal the variation in distillation efficiency with operation mode. Global exergy efficiency in both extractive and pressure-swing distillation depends on the fate of condenser duty. In heat-integrated extractive distillation, global exergy efficiency drops from 8.7% to 5.7% for tetrahydrofuran/water and 11.5% to 8.3% for acetone/chloroform. Similarly, heat-integrated pressure-swing distillation sees global exergy efficiency decrease from 34.2% to 23.7% for tetrahydrofuran/water and 9.5% to 3.6% for acetone/chloroform, underscoring the nuanced impact of heat integration, urging careful process design consideration.

Comparative analysis of isopropyl alcohol dehydration using ionic liquids and deep eutectic solvent

The current article deals with the separation of the azeotropic mixture of isopropyl alcohol (IPA) and water using an ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and Deep Eutectic Solvents (DESs), Choline Chloride/glycerol (Glyceline) and Choline Chloride/Ethylene Glycol (Ethaline). Conventional dimethyl sulfoxide (DMSO) solvents are used to compare the results for IPA dehydration. Process modelling and simulation were carried out in the Aspen Plus simulator (v.8.6). The NRTL model was used to calculate the thermodynamic properties as well as the vapour-liquid equilibria of the ternary systems. The process parameters such as entrainer flow rate, binary feed stage, entrainer feed stage, column stages, reflux ratio, reboiler and condenser duties were evaluated using sensitivity analysis and design spec tools of the simulator. The industrial process for both systems, containing a separation column and a recovery column, was simulated at a steady state. Both processes were optimised using the optimisation tool of the simulator and compared based on the energy requirement. Further, based on the simulation results, we proposed an alternate process design for solvent recovery using a flash drum. The results show that more than 99.9 mol% IPA purity can be achieved using both ILs as well as DESs. The overall energy requirement for the separation of IPA-water mixture using [EMIM][BF4] entrainer in a conventional process was found to be lower than DMSO. The proposed alternate process further reduces the energy requirement compared to the conventional process for both IL and DESs systems.

A strategy for CO2 capture and utilization towards methanol production at industrial scale: An integrated highly efficient process based on multi-criteria assessment

CO2 capture and utilization are an effective solution to the problem of CO2 emissions, and a combination of ammonia-based CO2 capture and its use for methanol production is a highly feasible strategy. However, the uses of conventional technologies have resulted in a high demand for energy, with limited use of hydrogen. To address these problems, an innovative strategy is proposed and demonstrated in this study that enhances the conventional design, i.e., to use ammonia-based CO2 capture with double tower absorption and solvent split, along with wet hydrogen for methanol production at industrial scale. The process is further improved through a multi-criteria assessment that considered the CO2 capture rate, NH3 loss rate, CO2 conversion rate, and energy saving factors, in which the latter is based on two components, namely the reboiler duty and the condenser duty. Moreover, an exergy analysis method is used to optimize the improved process, and a highly efficient integrated process is finally established. It has been found that the use of a double-tower absorption process ensures high rates of CO2 capture and low rates of NH3 loss. Additionally, adjusting the molar ratio of H2 to CO2 leads to an impressive 8% increase in the CO2 conversion rate, reaching 25%. In terms of energy savings, the average reboiler duty was reduced from 13.39 to 11.85 MJ/kgCO2, i.e., by 11.50%; while the condenser duty was reduced by 11.36%; both contributed to the overall energy savings. In the I-ACCMP process, the total exergy loss is 437.24 kW, of which the exergy loss of the heat exchangers accounts for 16%, and the desorption tower (DES) accounts for 48%. After optimization, the exergy loss of the heat exchangers decreases from 70.02 kW to 40.45 kW, the exergy loss of the DES decreases from 209.29 kW to 180.91 kW, and the reboiler duty is reduced from 10.60 MJ/kgCO2 to 7.71 MJ/kgCO2. The total exergy loss decreases from 437.24 kW to 372.68 kW, which is a reduction by 14.8%.

A simulation and thermodynamic improvement of the methanol production process with economic analysis: natural gas vapor reforming and utilization of carbon capture

Abstract The current investigation proposes an efficient process to produce methanol through the natural gas vapor reforming and direct hydrogenating of CO2 that reduces CO2 emission. The proposed process includes methanol synthesis in the catalytic reactor with an injection of carbon dioxide recovered from the plant’s flue and separation of methanol by distillation. An Aspen HYSYS code analyzes the proposed plant to assess the energy, exergy, economic, and environmental performances. Also, the effect of captured CO2 flow on the methanol production, carbon efficiency, stoichiometric number of synthesized gas, and reboiler and condenser duties are investigated as a sensitivity analysis. The results indicate that the methanol production rate of 82,040 kg/h provides carbon, energy and exergy efficiencies of 85 %, 77.26 % and 77.32 %, which are higher than the similar proposed plants. Regarding exergy analysis, the total exergy destruction rate is about 238,468.21 kW, in which the reforming and burner sections contribute to the highest portions of about 47 % and 30 %. The global warming potential of the process is obtained at about 0.26 k g C O 2 , e q / k g M e O H ${\mathrm{k}\mathrm{g}}_{{\mathrm{C}\mathrm{O}}_{2,\mathrm{e}\mathrm{q}}}/{\mathrm{k}\mathrm{g}}_{\mathrm{M}\mathrm{e}\mathrm{O}\mathrm{H}}$ , which is reduced by captured CO2. The annual costs of investment and income are about 416,772,399 $ and 236,292,429 $, yielding 1.72 years payback period.

Design and analysis of reactive distillation for the production of isopropyl myristate

This work explains the production of isopropyl myristate (IPM), an ester formed from the esterification reaction of myristic acid and isopropyl alcohol in a reactive-distillation column. The design of the column has been done to achieve a dual process objective of achieving product purity of 99% and reactant conversion (99%) to produce 1000 kg/hr IPM at 30°C and about 1 bar pressure conditions existing within the column. The reboiler duty comes to be 190 kW against the condenser duty of 160 kW when an entrainer, cyclohexane at 1975 kg/hr is used, which can be reduced by employing two columns. The nonlinear quaternary system is solved using NRTL thermodynamic package, and the reactive distillation column is designed. The IMC-PID-based temperature controller has been designed for a closed-loop structure to achieve safe operation and desired dynamic control behavior and simulated by using MATLAB. The column has been stable under both steady-state and dynamic conditions by stabilizing the non-linear performance of the column by the controllers. The process integration of the reactor and separator into one column has minimized a process plant's operating and investment cost.

Biogas to advanced biofuels: Techno-economic analysis of one-step dimethyl ether synthesis

Bio-dimethyl ether (bio-DME) is a promising advanced biofuel for the disposal of conventional diesel fuel, which is one of the most relevant sources of particulate matter and nitrogen oxides in urban centres and is completely banned from some European cities. DME is produced in two ways: dehydration of methanol produced from syngas (indirect or two-step process) and direct synthesis from syngas (direct or one-step process). This work aims at studying, optimizing and economically and environmentally assessing a novel conceptual design to convert biogas into bio-DME. Contrarily to traditional DME processes, the synthesis from biogas strongly benefits from milder conditions due to the smaller plant size, rural context, and biological feedstock fluctuations, motivating an ex-novo techno-economic feasibility study and sensitivity analysis performed in Aspen HYSYS V11 suite. The proposed process layout allows converting 1045 kg/h of silomais-based biogas (67%v/v CH4 content) into 516 kg/h of bio-DME at ASTM D7901-14 standard specification for fuel purposes. Sensitivity analysis identifies reactor temperatures as important process variables and defines three key performance indicators as: (i) global yield of the process; (ii) DME versus methanol selectivity; (iii) and the thermal load for the downstream section. The last one is computed as the sum of reboiler and condenser duties normalized with respect to the DME massive flowrate, and the study provides 1.05 kWh/kgDME as downstream section global specific duty. The process provides an innovative way to face the EU RED II challenge due to a 49.4 wt.% bio-DME yield and also thanks to a competitive 9.5 yr of payback period.

Design optimization and control of dividing wall column for purification of trichlorosilane

• TA C appr . is proposed as a novel objective function for DWC parameter optimization. • Optimal energy control structure can be achieved by manipulating liquid split ratio. • MPC-PI hybrid structure balances both control performance and safety performance. • Simulated annealing algorithm is employed to optimize the weights of MPC controller. Polysilicon quality and energy consumption are directly affected by the purification process of trichlorosilane. In this work, the dividing wall column (DWC) as a promising energy-saving technology is utilized for trichlorosilane purification, with the design optimization carried out using steady-state simulation. Compared with conventional distillation process, DWC can reduce total annual cost (TAC), CO 2 emissions and exergy loss ( El ) by 35.81%, 53.56% and 54.10% on average, respectively. Established on the characteristics of superfractionator, four control structures are proposed in this work, two of which are multi-loop proportional-integral (PI) control schemes including condenser duty ( C ), distillate flow rate ( D ), bottom flow rate ( B )/reflux flow rate ( R ), side flow rate ( S ), reboiler duty ( V ) control structure and optimal energy control structure. The other two are model predictive control (MPC) schemes including standard MPC structure and MPC-PI hybrid structure. The weights of MPC controller are optimized using the simulated annealing (SA) algorithm. Dynamic simulation results demonstrate that MPC schemes achieve improved closed-loop performance in terms of minor overshoot, shorter transition time and reduced oscillation than PI control schemes. The integral absolute error (IAE) is introduced to further quantitatively evaluate MPC schemes. The simulation results demonstrate that the standard MPC structure achieves the best control performance and the MPC-PI hybrid structure enhances process safety while maintaining the desired control performance.

Insights into Dynamic Process Intensification for Reactive Distillation Columns

In Dynamic Process Intensification (DPI) a more economic operation compared to a steady state is achieved by blending the product of multiple operating states. In our study we present a systematic approach for the determination of these operating states for reactive distillation processes. Furthermore a closed loop control scheme is presented and validated with a dynamic simulation. As DPI has already been shown to be feasible for the reactive distillation of dimethyl ether from methanol, it was used as the first case study. The combined reboiler and condenser duty is reduced by 4.2% compared to the optimal operating point without DPI. The time average methanol conversion and the product purity remain unchanged compared to the optimal steady state. It is demonstrated that the proposed closed loop control scheme ensures stable operation in the event of disturbances up to 10% to the column feed flow, while maintaining the characteristics of DPI. The reactive distillation of methyl acetate from methanol and acetic acid is used as a second case study, since extensive literature data are available for such an analysis. It is demonstrated that DPI is infeasible for this process and the column should be operated in the optimal steady state.

Sensitivity Analysis of Bioethanol Simulation from Microalgae with Pressure Swing Distillation Process

Energy is an important parameter in the social and economic development of a country. Thus, it is necessary to seek renewable energy to supply energy needs in Indonesia. The production of bioethanol from microalgae as a biofuel is one way to reduce the use of fossil fuels. Microalgae has an advantage over other types of biomass sources due to its high biomass productivity and do not compete with agricultural crops for land and water resources. In the bioethanol production process, the ethanol and water form an azeotrope mixture of 95.6% of ethanol at 1 atm and 78.15°C. The objective of this research was to analyse and determine the operating conditions and the optimum distillation column configuration which results in high ethanol purity according to fuel specifications (fuel grade ethanol). The method of pressure-swing distillation was applied to separate the azeotrope of ethanol-water and obtain high purity ethanol. A simulation model of bioethanol production with pressure-swing distillation system was conducted by using Aspen Plus V10. In this research, the influence of process parameters such as distillation column pressure, reflux ratio, feed stage location, and the number of theoretical stages was analysed by using model analysis tools. The results showed that the obtained bioethanol purity of 99.9% with the condenser and reboiler duty of the LP column -79.931 kW and 667.651 kW, respectively; while the HP column is -47.627 kW and 57.698 kW.

Process intensification for energy efficient reactive distillation of trioxane production from aqueous formaldehyde

Trioxane is an essential platform chemical for producing polyoxymethylene dimethyl ethers and polyformaldehyde. However, the traditional manufacturing process requires high energy consumption because of the conversion limited by the chemical equilibrium (6%) and azeotrope of formaldehyde, water, and trioxane. Therefore, this study proposes the novel reactive distillation followed by the pressure-swing distillation process as an attractive energy-saving candidate. The kinetic was performed by D006-BD cationic-exchange resin catalyst and fitted by pseudo-homogeneous model. The rigorous model of reactive distillation process was established, and the experiments of reactive distillation were carried out to verify the accuracy of modeling. Based on the rigorous model, the effect of operating parameters on reactive distillation column was analyzed. The result showed that formaldehyde conversion could be improved to 79.55% in the reactive distillation column, and the whole process condenser duty reduced by 6.33%, reboiler duty reduced by 18.35% compared with the conventional process involving reactor.

Energy efficient distillation column configuration: an exergy analysis

The column targeting tools and exergy analysis are used to set energy targets and improve energy efficiency in the distillation column. The combination of process options like feed stage location, reflux ratio, feed conditioning, side-reboiler and side-condenser greatly improves thermodynamic efficiency and reduces exergy loss throughout the column. The converged base-case simulation for propane-propylene binary mixture obtained from Aspen Plus was evaluated with both column targeting tools and exergy loss analysis. The study reveals significant decrease in reboiler (∼29%) and condenser (∼15%) duties, and increase in thermodynamic efficiency by ∼33% as compared to base-case design by reduction in total exergy losses.

Composition-temperature cascade control of vapor recompression assisted dividing wall column with side heat exchanger

The vapor recompression assisted dividing wall column with side heat exchanger configurations have high energy efficiency but low controllability. In this paper, the control strategies of these configurations are studied, and two composition-temperature cascade control structures of these configurations are proposed for the first time. For the vapor recompression assisted dividing wall column with side condenser configuration, the side condenser duty is chosen to control the bottom purity instead of the bottom reboiler duty. For the vapor recompression assisted dividing wall column with side reboiler configuration, both of bottom and side reboilers duties are chosen to control the bottom purity and the sensitive stage temperature respectively. The control results of two separation cases shown that the proposed control structures are effective for these two kinds of configurations. This work makes a contribution for the industrialization of the vapor recompression assisted dividing wall column with side heat exchanger processes.

CFD-aided design of internally heat-integrated pressure-swing distillation for ternary azeotropic separation constrained by pinch pressure

• Novel HIPSD for separating an azeotropic ternary mixture is proposed. • An extended pinch-based method to determine the pressure of HIPSD is introduced. • HIPSD alternatives are generated for the given initial feed composition. • Practical heat transfer rates in HIPSD are determined by the CFD method. • Significant energy savings in HIPSD are achieved for ternary azeotropic separation. This study addresses computational fluid dynamics (CFD) for designing internally heat-integrated pressure-swing distillation (HIPSD) with improved energy efficiency in azeotropic distillation. An extended concept of pinch pressure is applied to determine the operating pressure of the HIPSD in a double annular column configuration for the circumvention of a distillation boundary and adequate heat transfer. For the separation of a highly azeotropic ternary mixture of butyl acetate, butanol, and water, the combination of a single unit of HIPSD and a decanter is employed. This azeotropic mixture is separated in different design alternatives for the given initial feed compositions. In each sequence, the heat transfer rate inside the HIPSD was calculated by the CFD method, and the total utility consumption accordingly decreased by 9.72% and 15.44%. The reboiler and condenser duty in the HIPSD were reduced by up to 48.65%. The separation efficiency in the condenser of the high-pressure column was improved enough to reach a zero reflux by the internal heat integration.

English

This paper presents the effect of feed composition, xF, and feed thermal conditions on benzene-toluene distillation plant performance. An interactive computer model was developed to simulate the process using vapor-liquid equilibrium (VLE) data, mass and energy balances and McCabe-Thiele method. The feed thermal conditions studied were vaporized feed (VF), feed at its boiling point (FBP) and subcooled liquid (SCL) feed. The feed composition was varied between 0.20 and 0.45 kmol/kmol. The process was simulated at fixed feed flow rate (1000 kmol/h), reflux ratio (R = 4.0) and distillate and bottoms compositions (95 and 5%, respectively). The minimum reflux ratio, theoretical and actual number of stages, reboiler duty and steam mass flow rate, and boil-up ratio changed with increasing xF according to fourth-order polynomial functions. The condenser duty and cooling water flow rate increased linearly with xF. The effect of increasing xF on the stripping section operating line (SOL) is reported separately for different feed thermal conditions. While all q-lines for VF passed at (xB, xD) with decreasing slope; the q-lines for FBP were vertical and those for SCL feed were parallel. Graphical presentations of q-lines and SOLs for increasing xF were developed in this study. Key words: Distillation plant performance, feed composition, feed thermal conditions, number of stages, reboiler duty, condenser duty, boil-up ratio, mass and energy balances, vapor liquid equilibrium.

Design study of a cryogenic distillation column for hydrogen isotope separation system

This paper presents a design study of a cryogenic distillation column for hydrogen isotope separation. The column was modeled as a theoretical equilibrium-based stage column. Thermodynamic properties were evaluated with the Peng–Robinson Twu equation of state model. The liquid holdup and pressure drop of each theoretical stage were modeled with a general packed column model. The models were implemented in an equation-oriented optimization framework. The effects of parameters such as the number of theoretical stages, feed location, diameter, flow rate of the distillate, and condenser duty on the tritium inventory, total pressure drop, and product quality were investigated. An optimal design that minimizes the total amount of tritium in the liquid holdup under a tritium product quality constraint and non-flooding constraints is presented.

Design and optimization of an integrated process for the purification of propylene oxide and the separation of propylene glycol by-product

It is difficult to separate the methanol and hydrocarbons in the propylene oxide (PO) purification process due to their forming azeotrope. As for this, a novel PO separation process, in that the deionized water is employed as extractant and 1,2-propylene glycol (MPG) that is formed from the PO hydrolysis reaction is recovered, is presented in this work. The salient feature of this process is that both the non-catalyzed reactions of PO hydrolysis to form MPG and dipropylene glycol (DPG) are simultaneously considered and MPG by-product with high purity is obtained in virtue of the deionized water as reflux liquid and side take-off in MPG column. In addition, the ionic liquid (IL) extractant is screened through the conductor-like screening model for segment activity coefficient (COSMO-SAC) and the comparisons of separation efficiency between the IL and normal octane (nC8) extractant for the separation of PO and 2-methylpentane are made. With the non-random two-liquid (NRTL) thermodynamic model, the simulation and optimization design for the full flow sheet are performed and the effects of the key operation parameters such as solvent ratio, theoretical stages, feeding stage etc. on separation efficiency are detailedly discussed. The results show that the mass purity and the mass yield of PO can be up to 99.99% and 99.0%, and the condenser duty, reboiler duty and PO loss in the process with IL extractant can be decreased by 69.66%, 30.21% and 78.86% compared to ones with nC8. The total annual cost (TAC) calculation also suggests that the TAC would be significantly reduced if using IL in replace of nC8 for the investigated process. The presented results would provide a useful guide for improving the quality of PO product and the economic efficiency of industrial plant.

CO2-Tolerant Cryogenic Nitrogen Rejection Schemes: Analysis of Their Performances

In the transition to a sustainable energy future, natural gas is a key player supporting a shift away from coal, where renewables and other nonfossil fuels may not be able to grow sufficiently on their own. The growing importance of natural gas has led to a re-evaluation of the potential of unconventional, stranded, and contaminated gas reserves that were previously considered economically unviable. Among them, nitrogen-rich natural gas feedstocks, which in the past were thought to be a not-so-interesting methane source, are now becoming a considerable fraction of the total treated gas. For this kind of low-quality gases, nitrogen removal is necessary to lower the inert content and to produce a pipeline-quality gas or liquefied natural gas (LNG). Considering the available nitrogen removal technologies, cryogenic nitrogen rejection is nowadays the leading one for large-scale applications, with capacities exceeding 0.5 million standard cubic meters per day (MSCMD), being very flexible regarding the inlet N2 content. Depending on the feed composition, different nitrogen rejection units (NRUs—i.e., the single-, the double-, and the three-column systems) are available for treating inlet gas mixtures. The aim of the present work is to evaluate the performances of different cryogenic nitrogen rejection schemes through energy and exergy analysis. Specifically, single-column and three-column nitrogen rejection schemes have been considered with various natural gas feed compositions, focusing on the range where different nitrogen removal schemes are applicable. The net-equivalent methane analysis accounts for the amount of methane required to supply the overall process energy demands through specific processes assumed as reference. On the other hand, exergy analysis evaluates the exergy efficiency of each process scheme through a thermodynamically rigorous approach, converting energy and material flows into their exergy equivalents. Results prove that the three-column process scheme reaches the highest thermodynamic performances, resulting in the best values of exergy efficiency and equivalent methane requirements with respect to the other configurations. This is mainly due to the lower prefractionation column condenser duty, resulting in a less irreversible heat exchanging process.