Thermal Vapor Compression Research Articles

Industrial optimization of multi-effect desalination equipment for olefin complex

This research consists of a brief overview of some methods used to produce freshwater and how they work, the obvious points of performance, and the advantages and disadvantages of each of these methods. The effects of change in operation parameters on the performance as well as thermal energy consumption of sample MED–TVC (MED with thermal vapor compression) are investigated. This article represents the result of experimental and actual changes provided by process engineering department in Kavian Petrochemical Company (11th Olefin) to find best operating conditions for system stability. The most significant reason to opt these MED units is the internal steam source (5 * 140 ton h−1 boilers) which is located inside the complex’s battery limit making the control of operational variables more accessible. Also, the performance of the system and thermodynamic and thermo-hydraulic equations have been studied carefully. By writing a solving algorithm for the governing equations and implementing it in the MATLAB software, a conceptual design of the system has been considered. By using the written program, the effect of change in parameters such as inlet steam pressure, seawater temperature, feed water temperature, inlet seawater flow, the performance ratio on the steam consumption has been reviewed. Although most of the above-mentioned changes cannot be implemented after the system designing, changes in the steam consumption that is generated inside the complex have been investigated and the results have been communicated to the operation department through the process engineering department to modify the system.

Mathematical modeling and performance analysis for multi-effect evaporation/multi-effect evaporation with thermal vapor compression desalination system

Multi-effect evaporation/multi-effect evaporation with thermal vapor compression processes have shown more remarkable advantages than the other thermal desalination technologies, especially applicable to large scale and utilization of the industrial waste heat. A precise model is essential for development and improvement of the desalination system. In this paper, a detailed mathematical model of multi-effect evaporation/multi-effect evaporation with thermal vapor compression desalination system is developed based on the first law and second law of thermodynamics, of which the key parameters derive from the database established by targeted experimental studies. Verification of the model is conducted by comparison with various commercial plants. Results indicate that the simulation results agree well with the available data of actual plants. In addition, advantages and limitations of the present model are discussed by comparing with three models from the literature. Based on the mathematical model, the effects of pressures of motive steam and suction steam are deeply investigated. Performance comparison between multi-effect evaporation and that with thermal vapor compression was accomplished from the perspective of exergy destruction as well. Results show that higher gained output ratio and lower specific cooling water can be acquired when the compression ratio of thermal vapor compressor is 2.1–2.6.

Various Approaches to Thermodynamic Optimization of a Hybrid Multi-effect Evaporation with Thermal Vapour Compression and Reverse Osmosis Desalination System Integrated to a Gas Turbine Power Plant

This paper investigates the simulation of a hybrid desalination system composed of multi-effect evaporation with thermal vapour compression desalination (METVC) and reverse osmosis (RO) plant. The hybrid desalination system is also integrated with a gas turbine power plant through a heat recovery steam generator (HRSG). First, a comprehensive Thermodynamic model for HRSG, METVC, and RO are developed for predicting thermal behaviour of hybrid desalination system. Depending on the interconnection between input and output streams of METVC and RO, six configurations are proposed, and their results are compared in two different scenarios. In the first scenario, METVC desalination production is fixed at its maximum capacity of 70000 m3/day. The heat potential of power plants is fully extracted at maximum capacity of production of METVC. In the second scenario, METVC desalination production is not fixed. The limitation on the total production of the desalination plant (METVC+RO) is imposed as a constraint to the optimization problem. The results show that, regardless of the scenario under consideration, cconfiguration 1(the outlet water of the cooling system in METVC has been used for the feed water of the RO system) has the minimum energy consumption as well as maximum exergy efficiency.

Performance investigation of an auto-tuning area ratio ejector for MED-TVC desalination system

In Multi-Effect Distillation with Thermal Vapor Compression (MED-TVC) desalination system driven by low-grade thermal energy, it is arduous for conventional fixed geometry ejectors to operate efficiently with unstable feeding motive steam. In this paper, a variable geometry ejector named auto-tuning Area Ratio (AR) ejector equipped with a bellows-driven spindle is proposed to enhance the performance of MED-TVC desalination system under varying operating conditions. A Computational Fluid Dynamics (CFD) model has been built and validated to investigate the influence of AR on the system performance. A correlation to calculate the optimal opening degree under varying primary pressure with different critical back pressures is established and identified by data regression method. Moreover, with this correlation, an optimization strategy for auto-tuning AR ejector in MED-TVC desalination system is presented. Simulation results show that by using the auto-tuning AR ejector, relatively higher entrainment ratios (Er) can be achieved under varying motive steam. When the pressure of motive steam fluctuates from 800 kPa to 2000 kPa, the average Er of auto-tuning AR ejector is 1.39, higher than fixed geometry ejector of 0.69 with a critical back pressure of 20 kPa. The proposed auto-tuning AR ejector would have wide applications in MED-TVC desalination systems and other systems driven by low-grade energy.

Determination of the Criteria for Comparative Analysis of Desalination Plant

The problem of fresh water lack can be solved my desalination of the seawater. Desalination of the seawater can be accomplished by several methods. Distillation of the seawater is one of the most promising among them. Comparative analysis of distillation desalination plant requires certain criteria. This criterion must take into account both energy consumption and seawater salinity. Relation of the minimal work required for seawater desalination to energy consumption was selected as such criterion. Four types of the distillation plants were considered: Multi-effect distillation plants (MED), multi-effect distillation plants with mechanical vapor compression (MVC) plants, MVC desalination plants have the best multi-effect distillation plant with thermal vapor compression (TVC) plants and Multistage flash distillation plants (MSF). MSF plants gave dependency that their efficiency rise along the gain ratio. That may be explained by the fact that its steam consumption does not depend on seawater consumption. TVC plants have slightly higher efficiency than MED plants. Thus, MVC plants can be recommended to use if there is no heat source, MSF plants - if there is heat source and plant must have a high gain ratio and TVC plant in the rest cases.

Techno-Economics of Cogeneration Approaches for Combined Power and Desalination From Concentrated Solar Power

For many decades, integration of concentrated solar power (CSP) and desalination relied solely on the use of conventional steam Rankine cycles with thermally based desalination technologies. However, CSP research focus is shifting toward the use of supercritical CO2 Brayton cycles due to the significant improvement in thermal efficiencies. Here, we present a techno-economic study that compares the generated power and freshwater produced from a CSP system operated with a Rankine and Brayton cycle. Such a study facilitates co-analysis of the costs of producing both electricity and water among the other trade-off assessments. To minimize the levelized cost of water (LCOW), a desalination facility utilizing multi-effect distillation with thermal vapor compression (MED/TVC) instead of multistage flash distillation (MSF) is most suitable. The techno-economic analysis reveals that in areas where water production is crucial to be optimized, although levelized cost of electricity (LCOE) values are lowest for wet-cooled recompression closed Brayton cycle (RCBR) with MSF (12.1 cents/kWhe) and MED/TVC (12.4 cents/kWhe), there is only a 0.35 cents/kWhe increase for dry-cooled RCBR with MED/TVC to a cost of 12.8 cents/kWhe. This suggests that the best candidate for optimizing water production while minimizing both LCOW and LCOE is dry-cooled RCBR with MED/TVC desalination.

A Demonstration of High Temperature MED-TVC Desalination Technology in the Gulf Area

This work focuses on a multiple effect desalination system with thermal vapor compressor (MED-TVC) operating at a top brine temperature (TBT) of 85°C which is significantly above the common operation temperatures of conventional MED-TVC systems, limited to a range below 70°C mainly due to scale risk. Such increase in TBT would enhance the production and system economics. A pilot plant installed at the Desalination Technologies Research Institute (DTRI) of the Saline Water Conversion Corporation (SWCC) in Jubail, Saudi Arabia was operated at the TBT of 85°C over a 5-month test period. Visual inspection of tube bundles after the test, in conjunction with chemical scale analysis showed that scaling was limited to a soft thin film scale, which was easily removed by flushing with water, which confirmed a low fouling potential analyzed from operation data. Techno-economic analysis of the MED-TVC system operating at a TBT of 85°C, indicated up to 34% reduction in steam consumption and up to 16% reduction in the levelized cost of water (LCOW), when compared with a MED-TVC unit operating at a conventional TBT of 65°C. Accordingly, the high temperature MED-TVC systems operating at a TBT of 85°C can be considered as a financially competitive and technologically reliable desalination option for the Gulf area which has challenging seawater characteristics.

An evaluation of multi-effect desalination with a thermal vapour compression system in terms of thermo-economics

An evaluation of multi-effect desalination with a thermal vapour compression system in terms of thermo-economics

An evaluation of multi-effect desalination with a thermal vapour compression system in terms of thermo-economics

In this study, a multi-effect distillation system (MED-TVC) that is presently in use in a thermal power plant was analysed. The operating data of an existing MED-TVC (2,000 m3/day) desalination process were used for thepresent analysis. The analysis of the considered system was performed based on the energy, exergy and thermoeconomic approach. Also, the effect of operating plant load, seawater temperatures and upper brine temperatures on the performance of the desalination plant was investigated. The gain output ratio and exergy efficiency increased with increasing production load and seawater temperature. When the production load and seawater temperatures were 100% and 33°C, respectively, the gain output ratio and exergy efficiency obtained was 7.73 and 2% respectively. The results showed that the steam ejector was responsible for about 45% of the total exergy destruction. The unit product cost of the distilled water at the full load was calculated by 1.7 $/m3.

New considerations for modelling a MED-TVC plant under dynamic conditions

The multiple-effect distillation (MED) technology is nowadays the most promising desalination process to be coupled with variable heat sources, thus leading to a more sustainable way to produce water. In order to prove the potential of this, it is of major interest to develop powerful modelling tools to predict the performance of this coupling. Only a few models have been presented so far. They show promising results but were based on some simplifying assumptions and non-physical constraints that could limit the analysis of the dynamic behaviour of a MED plant. This paper presents new considerations for the dynamic modelling of a MED plant associated with a thermal vapour compression unit, starting from a previous work “A dynamic model for MED-TVC transient operation”. After several improvements, this model is now more representative of the real operating modes of a MED-TVC plant by considering real process inputs. This paper also highlights the importance of accurately modelling the interconnection between effects, the evaporation and condensation processes and the other components, such as the pre-heaters. Here is also presented a control strategy for operating a MED plant under dynamic conditions. Indeed, when a perturbation occurs in the motive steam pressure, it is possible to stabilize the whole plant by a simultaneous variation in the intake seawater mass flow rate at the final condenser. The model has been validated in steady-state conditions with experimental data from a MED-TVC plant operated in Trapani (Sicily) and was used to perform dynamic simulation to prove the feasibility of operating a MED-TVC plant under dynamic conditions, which is a major step toward proving the possibility of a coupling with renewable energies.

Transient and thermo-economic analysis of MED-MVC desalination system

An exergo-economic model is used to assess the performance of a multi-effect desalination plant integrated to a mechanical vapor compressor unit (MED-MVC) with a water production capacity of 1500 m3/day. The results show that the second law efficiency (ηII) is 2.8%. The MVC and evaporator units are responsible for about 39 and 52% of the total exergy destruction, respectively. The total water price (TWP) is 1.70 $/m3 when calculated using a simple conventional economic model and 1.63 $/m3 when calculated using an exergy-based cost model. Increasing the number of effects from 1 to 6 results in a 39% reduction in the specific power consumption (SPC), a 70% increase in ηII and a 24% decrease in TWP. A dynamic model is developed to investigate the effect of fluctuations of compressor work (W˙c) and inlet seawater temperature (Tsw) on the plant behavior and performance. The dynamic model results show that the disturbance in W˙c has a significant effect on the plant transient behavior and may cause the plant to cease operation while a disturbance in Tsw has only a moderate impact. Increasing Tsw above a certain value of the steady-state condition without proper control on the plant response could lead to evaporator dry out. In term of performance, a reduction in W˙c causes a decrease in the plant production capacity and SPC, while it increases the plant performance ratio (PR). On the other hand, a reduction in the inlet Tsw causes a reduction in the plant production capacity and PR and an increase in SPC for the same compressor work. Furthermore, a comparison between a MED-MVC system and a MED integrated to a thermal vapor compressor system (MED-TVC) reveals that the latter system is rather sensitive to the reduction in Tsw due to the presence of the condenser unit in the MED-TVC. The response of the MED-MVC system is slower than the MED-TVC which is due to the high thermal capacity of the preheaters for the feed in the MED-MVC.

Energy, exergy and economic analysis of a hybrid spray-assisted low-temperature desalination/thermal vapor compression system

Integrating thermal desalination systems with vapor compression is an effective way to improve the energy efficiency. This paper investigates a spray-assisted low-temperature desalination system that is integrated with a thermal vapor compression system (SLTD-TVC). A detailed thermodynamic model is judiciously developed based on the principles of heat and mass transfer, heat balance, mass balance, and exergy balance. Applying the model, the energy efficiency of the combined SLTD-TVC process is first evaluated. The production ratio of the combined system is found to be 10–35% higher than that of the conventional SLTD process. Accordingly, an exergy analysis is conducted to quantify the sources of irreversibility within the system. The steam jet ejector is found to be the major source of thermodynamic irreversibility, accounting for more than 40% of the exergy destruction. The overall system efficiency is improved at a lower motive steam pressure, a higher number of operating stages and a medium cooling water flowrate. Finally an economic analysis is carried out, which reveals that the changes of both initial plant cost and operation cost are marginal after the integration of the thermal vapor compression system.

Performance analysis of hybrid system of multi effect distillation and reverse osmosis for seawater desalination via modelling and simulation

The coupling of thermal (multi stage flash, MSF) and membrane processes (reverse osmosis, RO) in desalination systems has been widely presented in the literature to achieve an improvement of performance compared to an individual process. However, very little study has been made to the combined multi effect distillation (MED) and reverse osmosis (RO) processes. Therefore, this research investigates several design options of MED with thermal vapor compression (MED_TVC) coupled with RO system. To achieve this aim, detailed mathematical models for the two processes are developed, which are independently validated against the literature. Then, the integrated model is used to investigate the performance of several configurations of the MED_TVC and RO processes in the hybrid system. The performance indicators include the fresh water productivity, energy consumption, fresh water purity, and recovery ratio. Basically, the sensitivity analysis for each configuration is conducted with respect to seawater conditions and steam supply variation. Most importantly, placing the RO membrane process upstream in the hybrid system generates the overall best configuration in terms of the quantity and quality of fresh water produced. This is attributed to acquiring the best recovery ratio and lower energy consumption over a wide range of seawater salinity.

Exergy and thermo-economic analysis for MED-TVC desalination systems

An exergo-economic model is used to simulate four different feed configurations of multi-effect desalination with thermal vapor compressor (MED-TVC) system. The feed configurations considered are backward feed (BF), forward feed (FF), parallel feed (PF) and parallel cross feed (PCF). The model results indicate that the PCF configuration has better performance characteristics than the other feed configurations regarding gain output ratio (GOR) and specific heat consumption (SHC), but it has the highest specific cooling seawater flow rate (sMcw). On the other hand, the BF configuration has the lowest sMcw. The highest exergy destruction (58%) occurs within the TVC unit and this can be reduced by lowering the supplied motive steam pressure. The exergy destructions in the condenser and pumps account for 4 to 6.7% of the total exergy destruction for all feed configurations. The MED-TVC under consideration has a second law efficiency between 3.9 and 4.6%. Lowering the motive steam pressure for the PCF from 2300 to 300 kPa results in a 7.5% reduction in GOR and a 25.4% increase in the second law efficiency. Reducing the exergy destruction in the TVC unit is cost-effective for the entire system even with the increase in capital investment costs. The specific exergy cost flow method is used to estimate the total water price for BF, FF, PF and PCF as 2.12, 2.30, 2.16 and 2.09 $/m3, respectively.

Reducing electric energy consumption in linear Fresnel collector solar fields coupled to thermal desalination plants by optimal mirror defocusing

In many parts of the world, desalination is the only viable and economic solution to the problem of fresh water shortage. The current commercial desalination technologies rely on fossil fuels and are thus associated with high greenhouse gas emissions that are a major cause of climatic changes. Solar thermal-driven multi-effect distillation with thermal vapor compression is a clean alternative to conventional desalination technologies. To comprehend this process, as well as its features and limitations, extensive modeling is required. In this work, we proposed a plant design based on a solar field with a linear Fresnel collector that supplies heat to a multi-effect distillation plant with thermal vapor compression. The solar desalination plant model is implemented in the Engineering Equation Solver (EES). The system performance is investigated and a control strategy for reducing electric pumping is proposed. Results showed that 1 m2 of the solar field produces 8.5 m3 of distillate per year. The proposed control strategy resulted in a 40% reduction in electric pumping energy. Our results highlight the versatility of the linear Fresnel collector when coupled with thermal desalination.

Experimental Investigation of the Steam Ejector in a Single-Effect Thermal Vapor Compression Desalination System Driven by a Low-Temperature Heat Source

The paper presents an experimental investigation of a steam ejector in a single-effect thermal vapor compression (S-TVC) desalination system driven by a low-temperature (below 100 °C) heat source. To investigate the performance of the steam ejector in the S-TVC desalination system, an experimental steam ejector system was designed and built. The influences of the nozzle exit position (NXP), operating temperatures, and the area ratio of the ejector (AR) on the steam ejector performance were investigated at primary steam temperatures ranging from 40 °C to 70 °C, and at secondary steam temperatures ranging from 10 °C to 25 °C. The experimental results showed that the steam ejector can work well in the S-TVC desalination system driven by a low-temperature heat source below 100 °C. The steam ejector could achieve a higher coefficient of performance (COP) by decreasing the primary steam temperature, increasing the secondary steam temperature, and increasing the AR. The steam ejector could also be operated at a higher critical condensation temperature by increasing the primary steam temperature and secondary steam temperature, and decreasing the AR. This study will allow S-TVC desalination to compete with adsorption desalination (AD).

Energy efficient multi-effect distillation powered by a solar linear Fresnel collector

Solar-driven desalination is a potential solution to the problem of freshwater scarcity in many parts of the world. However, this technology requires considerable efforts to overcome a number of technical challenges such as high-energy consumption, intermittency of solar radiation, and high-water consumption. This paper proposes an optimized multi-effect distillation (MED) process driven by steam at 70 °C and 0.3 bar, which is provided by a linear Fresnel collector. The aim of the proposed integrated system is to reduce the equivalent mechanical energy of the MED process, and utilize the most cost-effective storage system. Moreover, we incorporated an air-cooled condenser instead of a water-cooled condenser, to reduce the water cooling facilities. A computer model was developed using the Engineering Equation Solver tool, to solve the mass and energy balance equations of the integrated system (under different operating conditions). Under the operating conditions of Qatar, the simulation results showed that 1 m2 of solar linear Fresnel collector produces 8.6 m3 of freshwater per year. The equivalent mechanical energy of the optimized MED desalination plant is 8 kWh/m3, which is 59% lower than that of existing commercial MED facilities with thermal vapor compression (19 kWh/m3). This significant reduction in equivalent energy consumption would reduce the required solar field size by 25%. This study also showed that using a water storage system (instead of thermal energy storage) results in a lower total system capital cost. Furthermore, by integrating an air-cooled condenser, the overall plant water consumption reduced by 2 m3 of sea water per m3 of feed water. The performance of the air-cooled condenser can vary by as much as 300% due to fluctuations in dry-bulb temperature and relative humidity.

Methods for compressible multiphase flows and their applications

This paper presents an efficient and robust numerical framework to deal with multiphase real-fluid flows and their broad spectrum of engineering applications. A homogeneous mixture model incorporated with a real-fluid equation of state and a phase change model is considered to calculate complex multiphase problems. As robust and accurate numerical methods to handle multiphase shocks and phase interfaces over a wide range of flow speeds, the AUSMPW+_N and RoeM_N schemes with a system preconditioning method are presented. These methods are assessed by extensive validation problems with various types of equation of state and phase change models. Representative realistic multiphase phenomena, including the flow inside a thermal vapor compressor, pressurization in a cryogenic tank, and unsteady cavitating flow around a wedge, are then investigated as application problems. With appropriate physical modeling followed by robust and accurate numerical treatments, compressible multiphase flow physics such as phase changes, shock discontinuities, and their interactions are well captured, confirming the suitability of the proposed numerical framework to wide engineering applications.

Energy and exergy investigation of a combined cooling, heating, power generation, and seawater desalination system

In the present paper, a combined cooling, heating and power and a multi effect desalination with thermal vapor compression system was used to simultaneously produce electricity, fresh water, refrigeration, and hot water for domestic use. In order to link the Brayton cycle to the water desalination and ejector refrigeration systems, a dual-pressure heat recovery steam generator unit was utilized. In this research, the considered system was analyzed in terms of exergy and energy under various operational conditions and also pollution generated by combustion process is determined. To consider the effects of design parameters on the efficiency of the system, a parametric analysis was further conducted to examine influences of such factors as compressor compression ratio, inlet temperature of turbine, vapor pressure entering into the desalination unit, and the number of desalination units on exergy and energy efficiencies of the cycle. The results indicated the capability of the proposed system for providing fresh water, power, cooling and heating loads of 85.57 kg/s, 30 MW, 2.03 MW and 1.11 MW, respectively. Finally, total exergy destruction and exergy and energy efficiencies of the cycle were obtained to be 55.82 MW, 36.03%, and 39.22%, respectively.

Exergoeconomic optimization of a double effect desalination unit used in an industrial steam power plant

An exergoeconomic optimization of a double effect thermal vapor compression desalination system is performed. This unit is integrated in the thermal power plant of Phosphoric Acid factory owned by The Tunisian Chemical Group. The daily production of this unit is about 528 m3 of fresh water. A mathematical model based on energy, exergy and economic balances is established using EES software. Multi-objective optimization is carried out in the purpose to obtain the maximum exergy efficiency with minimum production cost. The effects of the main operating parameters on the desalination unit performances are analyzed.Obtained results show that, the maximum exergy efficiency is obtained for the evaporator II followed by the distillate and brine pumps. The condenser has the lowest exergy efficiency.The thermocompressor is the major contributor in exergy destruction. The mass flow rate and the pressure of the motive steam affect positively the GOR. The SPECO method is used to perform the economic optimization. The maximum exergoeconomic factor f is obtained for the evaporator II followed by the evaporator I, the thermocompressor, the distillate pump and the condenser. The optimum operating conditions leading to suitable overall exergy efficiency with low production cost of distillate water are determined.