Vapor Recompression System Research Articles

Sensitivity analysis on heat pump - mechanical vapor recompression desalination system by recovering waste heat of offshore power converter station

Abstract Offshore wind power converter stations produce massive low-temperature waste heat, which can hardly be used constrained by their offshore location. Therefore, the recovery of the waste heat has been raising widespread concern. Meanwhile, a large amount of fresh water is needed for its cooling system. So, a novel system combining high temperature heat pump and a mechanical vapor recompression system (HP-MVR) was proposed, and sensitivity analysis was performed to optimize it. The heat pump was used to absorb the waste heat and to produce high temperature water. The mechanical vapor recompression system was adopted to produce fresh water and to recover the condensation heat from the steam. In order to determine the impact parameters on the two crucial performance indicators of freshwater production and unit energy consumption, this article introduces a sensitivity analysis method, focusing on analyzing the sensitivity of the three operating parameters of heat pump condensation temperature, saturated water vapor inlet temperature entering the compressor, and freshwater condensation temperature to these two performance indicators. The results show that the sensitivity coefficients of heat pump condensation temperature, saturated water vapor inlet temperature entering the compressor, and freshwater condensation temperature are 1.13, -0.26, and 1.56. So, the freshwater condensation temperature has the most significant effect on freshwater output. Their sensitivity coefficients to unit energy consumption are 1.02, 1.41, and -0.64. The saturated water vapor inlet temperature entering the compressor has the most significant impact on the required power consumption per unit of freshwater. It will give some guidance for the application of low-temperature waste heat in seawater desalination and the reduction of operating costs.

Loss model of low pressure compressor for mechanical vapor recompression system

Abstract Low pressure compressor (LPC) serves the role of enhancing pressure levels of secondary steam at nominal pressure ratios (1.5), procured from the evaporator as a primary thermal energy source. A loss model has been proficiently proposed to rapidly predict the performance of the LPC. Instead of conventional lump sum loss equations, the model adopts well-established one-dimensional (1D) loss formulations scattered across scholarly publications. Given an explicit configuration of the LPC, the environmental conditions, rotational velocity, and capacity, static and total temperatures, static and total pressures, pressure reductions, polytropic head, and efficiencies of each individual segment of the compressor can be calculated. Validation of this model was done using computational fluid dynamics (CFD) analysis. This model renders it feasible to conduct a parametric examination of the impact of each loss apparatus on the LPC’s capability, thereby aiding designers in substantiating design choices that minimize these losses and consequently positively influencing the comprehensive efficiency.

A novel heat integrated double extractive divided-wall column avoiding vapor recompression system in water purification from petrochemical

The chemical plant produces wastewater with tetrahydrofuran (THF), methanol, and water, which form two energy-intensive binary azeotropes. With this aim, this research introduces a novel extractive divided-wall column (DWC) to efficiently separate water from the THF-methanol mixture. The study utilizes a combination of a solvent and steam, leading to the creation of a double extractive DWC (DEDWC) as the foundational model. A key innovation of this study is the recovery and reuse of waste heat from the column's top vapor through vapor recompression, which is used for further separation. While this method requires a significant initial compression ratio and, by extension, a considerable capital investment, the study introduces a heat integration system to mitigate these costs. This system raises the vapor temperature by combining it with the heated solvent (bottom product) and strategically employing intermediate steam-driven reboilers. This inventive method, known as the heat-integrated DEDWC (HiDEDWC), notably increases the vapor temperature by 15 K beyond the reboiler liquid. Impressively, HiDEDWC demonstrates a remarkable improvement in energy and cost efficiency over the standard DEDWC and the version with vapor recompression. Specifically, HiDEDWC achieves an impressive energy saving of 52.81% and reduces the total annual cost by 52.11% compared to DEDWC.

Joint Modeling and Operational Optimization of a Reverse Osmosis-Mechanical Vapor Recompression System for Coal-Fired Power Plant Wastewater.

The operation of coal-fired power plants generates a large amount of wastewater. With the issuance of increasingly strict drainage standards, the cost of wastewater treatment is increasing, and the need to reduce the cost of wastewater treatment is becoming increasingly urgent. Thus, based on the principles of reverse osmosis (RO) and mechanical vapor recompression (MVR) in wastewater treatment, the operational optimization of an RO-MVR joint system was studied in this work with the consideration of reducing the operating costs of wastewater treatment under given operational conditions. Firstly, based on the basic principles of RO and MVR, corresponding mechanism models were established and their accuracy was verified. Then, an economic model of the RO-MVR joint system was established, with the goal of minimizing the water production unit price and daily operating costs of the joint system for optimization analysis. Finally, we analyzed the cost and water production performance of the RO-MVR joint system before and after optimization under different operating conditions. The results show that this optimization based on the RO-MVR joint system will reduce the unit price of water production to 3.16 CNY/m3, with the daily operating costs being decreased by 22% compared to before optimization. This result helps to reduce the cost of zero-discharge wastewater treatment in coal-fired power plants.

Techno-economic and environmental analysis of high temperature heat pumps integration into industrial processes: the ammonia plant and pulp mill cases

Heat pumps will play an important role in improving the performance of the industrial processes aiming to decarbonize their heating requirements. Yet, defining the best operating conditions of those devices may be a challenging task, as they are embedded in larger energy conversion systems and in direct competition with fired and electric heaters and other waste heat recovery systems. The costs of the energy inputs also influence the selection of either a heat pump or a gas boiler, which affects the overall efficiency and the incremental cost of the final solution. Thus, a systematic analysis must be applied in order to determine the best option to supply the heating requirement, without considerably impacting the operational feasibility of the overall plant. In this work, the base-case performance of two industrial applications with intensive heating demand, namely, the solvent regeneration process of a carbon capture unit and the black liquor concentration process of a kraft pulp mill, are compared to that of the scenarios in which a high temperature heat pump or a mechanical vapor recompression unit are integrated, aiming to reduce the energy consumption and the environmental impact. The benefits of the integration of a heat pump or a mechanical vapor recompression unit over a conventional reboiler and a multiple effect evaporation system are discussed in the light of thermodynamic, economic and environmental indicators. As a result, the alternative approaches remain competitive vis-à-vis the conventional solutions in terms of energy consumption and operating costs. In addition, the emissions associated to the heating applications could be reduced by 45% if a high temperature heat pump is integrated. The optimized solution using a heat pump has an overall exergy efficiency 9% higher compared to the typical configuration of the ammonia plant. In pulp mills, the integration of mechanical vapor recompression systems slightly affects the performance compared to the conventional scenario with a multiple effect evaporation system.

Performance comparison of vertical and horizontal vacuum membrane distillation module coupled with mechanical vapor recompression

This paper focuses on the comparative study of vertical and horizontal vacuum membrane distillation (VMD) modules coupled with mechanical vapor recompression (MVR) system to obtain the optimal system layout structure and further improve operation stability and energy efficiency in the wastewater treatment. Firstly, freshwater accumulation characteristic in the vertical VMD module was explored under different working conditions. Then, comparative experiments of vertical and horizontal VMD-MVR systems were conducted. Finally, comprehensive performance of horizontal VMD-MVR system were evaluated. The obtained results showed that freshwater production in the distilling tank and freshwater accumulation in the VMD module were affected by operation time, feed temperature, feed flow rate, feed concentration and vacuum side pressure. Furthermore, the horizontal VMD-MVR system was proved to be a better choice due to lower freshwater accumulation in the VMD module and energy consumption in comparison to the vertical VMD-MVR system. Finally, long term operation experiment of 240 h indicated evaporation rate dropped to 55 kg/h as operation time reached to 180 h owing to membrane fouling. After membrane cleaning, evaporation rate recovered from 55 to 62 kg/h with a higher recovery efficiency of 95.1 %. Compared to conventional wastewater treatment systems, the horizontal VMD-MVR system exhibited excellent comprehensive performance.

Multi-Level Process Integration of Heat Pumps in Meat Processing

Many countries across the globe are facing the challenge of replacing coal and natural gas-derived process heat with low-emission alternatives. In countries such as New Zealand, which have access to renewably generated electricity, industrial heat pumps offer great potential to reduce sitewide industrial carbon emissions. In this paper, a new Pinch-based Total Site Heat Integration (TSHI) method is proposed and used to explore and identify multi-level heat pump integration options at a meat processing site in New Zealand. This novel method improves upon standard methods that are currently used in industry and successfully identifies heat pump opportunities that might otherwise be missed by said standard methods. The results of the novel method application suggest that a Mechanical Vapour Recompression (MVR) system in the Rendering plant and a centralized air-source heat pump around the hot water ring main could reduce site emissions by over 50%. Future research will develop these preliminary results into a dynamic emissions reduction plan for the site, the novel methods for which will be transferrable to similar industrial sites.

Vapor recompression: An interesting option for vacuum columns?

The need to reduce greenhouse gas emissions and decrease the use of fossil fuels will greatly change the design of process plants. Besides improved heat-integration, an obvious option to achieve more sustainable operations is to make use of highly efficient and therefore smart methods of electrification. Hence, heat pumps and vapor recompression systems effectively recirculating “waste” energy to the process may become economical in applications where experience had quickly eliminated them in the past. In this changing socio-economic context, process engineers will have to re-think, challenge and even un-learn many accepted design practices. One example is the use of vapor recompression in distillation. While applications in close-boiling high pressure systems have been reported in literature, the number of actual realizations is comparatively small. In vacuum systems, the practical hurdles are even higher, since large volumetric flowrates result in high compressor investment. In this paper, alternative designs are presented opening the way to electrification of a well-known vacuum system. Furthermore, the advantageous application to wide-boiling systems is demonstrated in two examples.

Study on multi-effect mechanical vapor recompression systems used for the concentration of industrial high salt wastewater

Study on multi-effect mechanical vapor recompression systems used for the concentration of industrial high salt wastewater

Mechanical vapor recompression coupling organic rankine cycle process for purification of crude biodiesel obtained by solid base-catalyzed transesterification

In this study, an effective method of mechanical vapor recompression coupling Organic Rankine Cycle process is introduced to purify crude biodiesel obtained by solid base-catalyzed transesterification. Mechanical vapor recompression is used for recovering the waste heat of the methanol, while the Organic Rankine Cycle is applied for converting the waste heat of biodiesel into electric energy. Pinch technology is proposed to guide the coupling of mechanical vapor recompression and Organic Rankine Cycle process, the electric energy and waste heat generated by Organic Rankine Cycle are supplied to the mechanical vapor recompression system. Compared with conventional purification process, the total annual cost of proposed process decreases by 55.40% and the greenhouse gas emissions decrease by 76.31% for CO2, 76.41% for SO2, and 76.42% for NOx, respectively. In addition, the parameters of the proposed process are optimized to achieve a coefficient of performance of 16.03 for mechanical vapor recompression and 14.06% thermal efficiency for Organic Rankine Cycle.

Multi-Objective Optimization of Parallel-Connected Double-Effect Mechanical Vapor Recompression System Based on Genetic Algorithm

Abstract To realize multi-objective optimization of the parallel-connected double-effect mechanical vapor recompression (MVR) system, this article established an optimization model based on the Strength Pareto Evolution Algorithm 2 (SPEA2), where the total power consumption and the heat exchange area were taken as the optimization objectives. The optimal combination of evaporation temperature, compression temperature rise, and emission concentration was obtained by employing the SPEA2-based multi-objective evolutionary algorithm together with the fuzzy set theory. The emission concentration was added as a variable on the basis of the original optimization, and the optimization results were compared with the original operation conditions. The results showed that the total power consumption of the system lowered by 22.9 kW, and the heat exchange area was reduced by 110.5m2; the coefficient of performance (COP) and exergy efficiency heightened by 8.4% and 24.0%, respectively, and the exergy destruction decreased by 84.6 kW. These results indicate that the established model for system optimization can make up for the deficiency of evaluating and optimizing system performance by manipulating a single-decision variable and improve the energy utilization and thermodynamic perfection of the target system.

A Comparison of the Exergy Efficiencies of Various Heat-Integrated Distillation Columns

Distillation has relatively low thermodynamic efficiency, so it is a prime target for process intensification studies. The current research aims to study exergy losses in various heat-integrated distillation columns. A conventional industrial-scale i-butane/n-butane fractionator has been selected as a case study for the comparison of the performances of various heat-integrated designs. The Aspen Plus® process simulator is used to perform steady-state simulations and exergy analyses of the conventional distillation column (CDC), internally heat-integrated distillation column (iHIDiC), externally heat-integrated double distillation columns (EHIDDiC), and vapor recompression (VRC) systems. The results of these exergy analyses show that a modified VRC system (ηE = 10.69%) is the most efficient design for this separation. The exergy efficiency of the conventional VRC system is the same as that of the CDC (ηE = 9.27%). The EHIDDiC system (ηE = 9.77%) is somewhat better than the CDC, whereas iHIDiC shows poor exergy efficiency (ηE = 8.09%), even lower than the CDC.

Analysis of a novel double-effect split mechanical vapor recompression systems for wastewater concentration

A novel double-effect split mechanical vapor recompression (MVR) system is proposed in this paper to reduce the system operation cost together with the technical requirements for the steam compressor. Theoretical models of the novel double-effect split MVR system together with the double-stage MVR system and double-effect downstream MVR system are established by the simulation software of Aspen Plus. Performances of the three systems for the concentration of calcium chloride solution with a mass flow rate of 1000 kg/h are simulated. For a better evaluation, analysis of the energy consumption, operation cost, compressor operating parameters and gained output ratio are carried out with the simulation results. It is concluded that an optimal steam ratio exists for the smallest compressor power consumption of the double-effect split MVR system which is 0.3 for the simulated conditions. The operation cost beneficial of the novel system increases with the rise of electricity price and final mass fraction of the solute. The maximal suction volume flow and pressure ratio of the steam compressor in the novel system are both the smallest among the three MVR systems. The pressure ratio ranges from 1.2 to 1.7 which can be easily realized by mature roots compressor or centrifugal compressor. Exergy efficiency of the novel system is also the highest. Development and application of heat pump or solar energy fresh steam generator can further enhance advantages of the novel system.

Study on the operation characteristic and transfer resistance of mechanical vapor recompression and vacuum membrane distillation system under multiple working conditions

In order to alleviate the freshwater resource shortage worldwide, the multiple vacuum membrane distillation (VMD) modules were drawn into a mechanical vapor recompression (MVR) system to recover industrial wasterwater in this paper. An experimental platform was constructed and several experiments were conducted under multiple working conditions. The operation characteristic by varying membrane area was investigated to achieve stable freshwater production, and the influences of operation parameters on the energy efficiency were analyzed, the distribution characteristic of transfer resistance was also revealed. The experimental results showed that an excellent freshwater production performance with a separation efficiency of 99.9% was achieved, and increasing membrane area was effective to elevate the evaporation rate. Furthermore, lower feed concentration or higher feed temperature, feed flow rate and vacuum side pressure were helpful for reducing the specific heating energy consumption (SHEC) and improving the energy efficiency. The proposed system was superior to VMD in energy efficiency, and was superior to MVR in separation performance, but still exhibited a lower energy efficiency than that of MVR due to the transfer resistance. Accordingly, the involved transfer resistances including boundary layer resistance, fouling layer resistance and membrane resistance were obtained by the iterative calculation. Increasing the number of experiment from 1 to 10 increased the transfer resistance from 14.219 Pa·m2·h·kg−1 to 18.082 Pa·m2·h·kg−1, resulting in a rise of SHEC from 70.63 kWh·t−1 to 82.77 kWh·t−1. Finally, the methods to reduce transfer resistance and improve energy efficiency were suggested. The obtained results provides the basis for such system industrial application.

Thermo-economic performance enhancement in batch evaporation process via mechanical vapor recompression system coupled with steam accumulator

Energy consumption in batch evaporation process has aroused widespread concern around the world. In this investigation, a mechanical vapor recompression system coupled with steam accumulator (MVR-SA) was proposed to reduce the start-up time and enhance energy efficiency during the batch evaporation process. Mathematical models were established considering the first and second laws of thermodynamics and relevant economic theory. Performance analysis was carried out from energy, exergy and economic viewpoints. Experimental results showed that the MVR-SA system could achieve distinctly faster intermittent start-up than conventional MVR. Energy efficiency ratio was experimentally obtained as 6.25, the input exergy, output exergy, exergy destruction and exergy efficiency were 21.7 kW, 2.04 kW, 19.66 kW and 9.4%, respectively. Simulated results indicated that increasing the heat transfer temperature difference of heat exchanger and liquid level height of steam accumulator, or decreasing evaporation pressure, could increase the system input exergy and exergy destruction, which reduced the system exergy efficiency. The optimum compression ratio and heat transfer temperature difference were obtained to achieve the minimum total cost considering annual investment, operation and environmental costs. Finally, an economic performance comparison confirmed greater superiority for the novel MVR-SA compared to conventional single effect system in the batch evaporation fields.

Experimental performance evaluation and model-based optimal design of a mechanical vapour recompression system for radioactive wastewater treatment

High-security and cost-effective disposal of radioactive wastewater plays a significant role in the wide deployment of nuclear energy. This paper presents an experimental study to investigate the feasibility of using mechanical vapour recompression systems for radioactive wastewater treatment, and a model-based design optimisation to maximise its economic benefits. A lab-scale mechanical vapour recompression system was established to experimentally assess its performance in terms of decontamination effect, energy efficiency, and exergy destruction. Based on the understanding of system performance, a numerical model for the proposed mechanical vapour recompression system was developed and validated, which was then utilised as a platform for optimal system design. A bi-objective design optimisation was formulated with the targets to minimise the payback period of the additional cost referencing to a traditional three-effect-evaporation system while maximising the system primary energy efficiency. Two intermediate variables, including the evaporation temperature and the heat transfer temperature difference, were selected as the optimisation variables. The experimental results verified the feasibility of using mechanical vapour recompression technology for radioactive wastewater treatment, demonstrating an excellent decontamination capability. It was found that an optimal evaporation temperature of 90 °C existed for maximising the decontamination factors for ions of strontium, cobalt, and cesium to 5.90 × 103, 1.45 × 104, and 1.74 × 104, respectively, while a higher system efficiency (coefficient of performance ranging from 7.33 to 8.21) has resulted when increasing the evaporation temperature (from 70 to 100 °C, correspondingly). The design optimisation resulted in an optimal Pareto front presenting the trade-off between the two optimisation objectives. By adopting the design corresponding to the optimal solutions identified, the mechanical vapour recompression system was found to feature a relative payback period of 0.69–2.32 years and a primary energy efficiency of 3.94–13.46, which outperformed a comparison case without optimisation (with that of 2.79 years and 3.03, respectively). The outcomes of study will provide guidance for the optimal application of mechanical vapour recompression evaporation system in nuclear wastewater treatment.

Experimental research on falling film flow and heat transfer characteristics outside the vertical tube

• Flow and heat transfer characteristics of falling film are studied experimentally. • The experimental data show large differences with values of existing correlations. • Correlations of heat transfer coefficient and dry burning condition are developed. • The study provides a reference for the research on evaporator of MVR. The falling film flow has attracted much attention recently due to its advantages of low temperature difference, low flow rate, high heat transfer coefficient and high heat flux density. In this paper, a series of experiments were carried out to investigate the falling film flow and heat transfer characteristics outside the vertical tube based on the established experimental system. Flow patterns, the trend of heat transfer coefficients along the tube as well as the falling film breakdown phenomenon were described. Two new correlations were obtained to predict the heat transfer coefficient and falling film dry burning based on experimental data, and the maximum deviation between the experimental data and predicted values were −13.36% and 16.81%, respectively. The new correlations can provide a reference for the design of the heater in the Mechanical vapor recompression systems.

Experimental investigation on the mechanical vapor recompression evaporation system coupled with multiple vacuum membrane distillation modules to treat industrial wastewater

• A multiple vacuum membrane distillation modules system (MVMD) was constructed. • A mechanical vapor recompression system coupled with MVMD was constructed. • An experimental study of the MVMD and MVR-MVMD systems was conducted. • Economic assessment of the MVMD and MVR-MVMD systems was made. • The MVR-MVMD system can save 79.24% energy than that of the MVMD system. Excessive population growth has increased the importances of industrial wastewater treatment as well as energy conservation. This paper presented an experimental study of a mechanical vapor recompression evaporation system coupled with multiple vacuum membrane distillation modules (MVR-MVMD) for energy saving in the wastewater treatment process. For this aim, the MVMD system was constructed to investigate the water production performance in the VMD process, and then the MVR was joined to the MVMD system to examine the energy-saving performance. The experiment results showed that: In the experiment of the MVMD system, an excellent water production performance was observed with the sodium chloride solution as evaporation object, and the parameters that significantly affected the water production performance were obtained as follows: feed temperature was the highest effect, and then permeate side pressure, feed flow rate, and feed concentration had the lowest effect through an orthogonal multi-factor experiment. In the experiment of the MVR-MVMD system, the specific heating energy consumption was 81.95 kWh t −1 , which could save 79.24% energy than that of the conventional MVMD system, at conditions of feed concentration of 5%, feed flow rate of 25 m 3 /h and membrane area of 200 m 2 . Finally, a detailed economic assessment had been made concerning the capital investment, operation, and environment costs compared to the MVMD system. From a long-term perspective, the MVR-MVMD system showed excellent economic performance comparable to the MVMD system.

Energy saving alternatives for renewable ethanol production with the focus on separation/purification units: A techno-economic analysis

The bioethanol production process includes energy-demanding units with high operating costs, i.e., separation, dehydration, and stillage evaporation units. The present study attempts to reduce energy consumption and, ultimately, ethanol price through industrially feasible methods. These methods include adopting thermally-coupled columns, dividing-wall columns, single/multi-stage pervaporation process, and evaporators. Nine scenarios were studied and compared with an industrial process case using heat-integration and thermal vapor recompression system. Each scenario was simulated with Aspen Plus® and analyzed with Aspen Process Economic Analyzer. The pervaporation process with a hydrophilic polymer membrane was modeled with MATLAB using sorption-diffusion theory and three-conservation law. Then, the required membrane area and the temperature drop during the pervaporation process were estimated. The dividing-wall column reduced the separation unit's energy consumption by 67% and the capital costs by 19%. The energy consumption decreased by 49% by adopting thermally-coupled and heat-integrated columns, and capital costs were reduced by 17%. Moreover, the four-stage pervaporation process for ethanol dehydration proved to be more profitable than the pressure swing adsorption. The proposed and investigated methods reduce the cost associated with the processes' energy consumption and decrease bioethanol's overall production cost.

Evaluation of mechanical vapor recompression in the reactive distillation of the N-butanol esterification process

The process of producing esters is usually performed through esterification in a reactor followed by a distillation column to separate the products. However, this design limits the reagent conversion. Reactive distillation is an alternative to get around this issue as it allows greater reagent conversions in reactions limited by chemical equilibrium. It is one of the most famous process intensification techniques. On the other hand, mechanical vapor recompression has been used to recycle waste heat to improve efficiency of conventional distillation columns. In this context, this work evaluated the inclusion of a mechanical vapor recompression system in a reactive distillation process to obtain n-butyl acetate via n-butanol esterification with acetic acid. Systems with and without recompression were simulated in an Aspen Plus™ environment. The addition of recompression resulted in a reduction of 33.65% in the annual cost of the process, while not significantly affecting the purity of the desired product and the reagents’ conversion. From an environmental point of view, the mechanical vapor recompression system adoption resulted in a 12.69% reduction in CO2 emissions, contributing positively to meeting the requirements of the environmental regulations.