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• 1-dimensional simulation for radial geometry shell and tube heat exchanger. • Annual simulation for optimal design of phase change material storage. • Solar collector cost should be less than 103 $/m2 for economic feasibility. • Approximate method for calculating the mass of fin required. A direct steam generation (DSG) solar collector can be an efficient process-heat application compared to electricity generation, and it can significantly reduce dependence on non-renewable energy sources for steam generation. Due to intermittency of the sun, thermal energy storage is required to increase the capacity factor or the yearly utilization of the system. For this study, phase change material (PCM) is used to store the heat from the steam produced in the solar collector. Sodium formate is selected as the PCM material on a cost basis. A detailed off-design analysis is carried to predict the annual performance of the system. Fins are used to enhance the thermal performance of the PCM, and an simplified method is derived to predict the required fin mass. With an increase in the number of fins, the thermal performance of the system increases significantly at design point. But the fins are expensive, so an annual simulation and techno-economic analysis is carried to calculate the optimal number of fins and other operating parameters. For the case study of Imperial, California (USA), the minimum value of the levelized cost of heat (LCOH) for steam generation is 4.2 cents/kWh th , and the optimal value for the equivalent PCM thermal conductivity is 1.5 W/mK with 4 h of storage and a solar multiple of 2.1. A sensitivity of LCOH with the solar installation cost shows that the collector cost should be less than 220 $/m2 for California and 103 $/m2 for the rest of the United States, for the steam generated from DSG collector and PCM storage to be competitive with the traditionally produced steam from natural gas. Where natural gas prices are higher, steam produced from a DSG collector and PCM storage can be an economical option. For example, in Kahului, Hawaii (USA), the LCOH for steam generation from a DSG collector and PCM storage is 43% cheaper compared to natural gas steam generation, even at a current solar installation price of 300 $/m2. The breakeven price of natural gas is 8.7 $/MMBTU for the current solar installation price; in other words, steam produced from DSG collector and PCM storage can be an economical option for locations having good solar radiation and a natural gas price greater than 8.7 $/MMBTU. [ABSTRACT FROM AUTHOR]

Multi-effect distillation is often integrated with a Rankine power cycle for cogeneration (simultaneous production of power and desalinated water). Such integration increases the condenser operating pressure for the Rankine cycle (and increases the heat-rejection temperature) to produce desalinated water, resulting in decreased power-plant efficiency. The supercritical carbon dioxide Brayton cycle has a higher efficiency compared to the Rankine cycle. The waste heat rejected from supercritical carbon dioxide Brayton cycle is at sufficiently hot temperature to have feasible energy integration with multi-effect distillation system. The paper introduces the novel concept of cogeneration without being a parasitic load to the power cycle. For the illustrative example considered, integrating 4-effect distillation system with a 115 MW e power plant can produce 3041 m 3 of distillate per day at 1.06 $/m 3 , at a constant power plant efficiency of 49.2%. The pattern in which feed enters the desalination system often dictates its energy consumption. The two most commonly used feed configurations for multi-effect distillation system are parallel/cross feed and forward feed. With steam as a heat source (i.e., a latent heat source), parallel/cross feed is the most energy-efficient feed configuration. The other objective of this paper is to identify the optimal feed flow configuration for multi-effect distillation system integrated with a supercritical carbon dioxide power cycle (i.e., a sensible heat source). For the simplified network, forward feed is the best feed configuration, which yields a 7.5% increase in distillate production at 2.6% reduced distillate cost. Additionally, different methods for reducing the brine discharge are studied, which can help to achieve zero liquid discharge. Result show increasing the maximum brine concentration gives superior results compared to brine recycling. The system modelling is done using the principle of process integration, and an analytical methodology for cogeneration is derived. [ABSTRACT FROM AUTHOR]

Multiple-effect evaporators are commonly used in various industries such as food process, desalination, pulp and paper, etc. for increasing the liquor concentration. Multiple-effect evaporator is an energy intensive equipment. It is often integrated with various energy saving techniques for minimizing the energy consumption. A common technique is integration of multiple-effect evaporator with thermo-vapor compressor. In thermo-vapor compressor the low-pressure vapor produced in multiple-effect evaporator is compressed with the help of the high-pressure motive steam to produce an intermediate-pressure vapor, which in turn acts as a heat source for the multiple-effect evaporator. The optimal location of vapor suction position for thermo-vapor compressor can significantly affect the energy consumption of integrated multiple-effect evaporator and thermo-vapor compressor system. The other way of reducing the energy consumption is by integrating multiple-effect evaporator with the background process. The present work focuses on the development of a methodology to minimize the overall energy consumption by thermally integrating multiple-effect evaporator, thermo-vapor compressor, and the background process. A theorem for optimal location of vapor suction position for thermo-vapor compressor is proposed. Two examples are considered in this study for demonstrating the proposed methodology. An economic analysis is also carried out for calculating the cost benefit for the overall integration. Overall integration leads to 28% of energy saving and 22% reduction in annual cost for corn glucose example compared to standalone system. Similarly, for desalination example, 44% energy and 20% annual cost savings are observed. [ABSTRACT FROM AUTHOR]

Multiple-effect evaporator (MEE) is used for concentrating the liquor. A substantial energy saving can be achieved by integrating MEE with a thermo-vapor compressor (TVC). TVC is a device in which the low-pressure vapor produced from MEE is compressed with the help of the high-pressure motive steam supplied externally, to produce a medium pressure vapor. This medium pressure vapor acts as a heat source for MEE. The high-pressure motive steam can be produced from concentrating solar thermal system, which is a renewable and non-polluting source of energy. The present study deals with the integration of linear Fresnel reflector (LFR) with MEE-TVC system. The objective of the present work is to minimize the total annual cost for the integrated MEE-TVC and LFR system. The important parameters affecting the annual cost for the integrated system are solar design radiation and temperature of the motive steam. A methodology is developed to determine the optimal solar radiation and steam temperature. The proposed methodology is demonstrated through a case study for manufacturing of corn glucose. The annual cost for the system is 87,106 $/y, with optimal steam temperature 250 °C and optimal design radiation 600 W/m 2 . Sensitivity analysis is also carried out for the selection of the optimal operating parameters. The cost of the auxiliary heating source plays a dominating factor on the economic feasibility of the integrated system. [ABSTRACT FROM AUTHOR]

Thermo-vapor compressor (TVC) is used for compressing the low-pressure vapor with the help of the high-pressure motive steam, to produce the medium pressure vapor. A substantial portion of energy may be conserved by integrating TVC with the multiple-effect evaporator (MEE). The common practice in desalination industry is to compress the vapor produced in the last effect of a MEE using TVC to reduce the overall motive steam requirement. Such integration does not necessarily guarantee energy optimality. The objective of the present work is to optimally integrate TVC with a MEE system to maximize the gain output ratio (GOR). GOR is defined as the ratio of the mass flow rate of vapor produced in MEE to the mass flow rate of the motive steam supplied to TVC. GOR is the measure of the energy efficiency of MEE system. Using the principles of Pinch Analysis and techniques of mathematical optimization, a new methodology for integration of TVC with MEE is proposed in this paper. This is the first analytical methodology to optimally integrate TVC with MEE, avoiding multiple simulations of the overall system. A Theorem is proposed to directly calculate the optimal location of TVC suction position. The proposed methodology gives the designer the freedom to design an MEE-TVC with minimum energy consumption and without carrying out the detailed simulation of the entire system. The methodology is demonstrated through the illustrative case studies for concentrating corn glucose, and freshwater production through thermal desalination. In the case of corn glucose, the optimal integration of TVC with 2-effect MEE resulted in the increase in GOR by 10.1% with a decrease in the specific area requirement by 4.1%. For a desalination system with 11-effect MEE, the optimal integration of TVC improves the GOR by 1.5% and reduces the specific area by 4.3%. Furthermore, sensitivity analysis is carried out to determine the optimal operating parameters for both case studies. [ABSTRACT FROM AUTHOR]

Desalination of sea water involving multiple-effect evaporator (MEE) is commonly used in industry, especially with the introduction of the low temperature MEE. Parallel/cross feed flow sequence is one of the most commonly used configurations on account of its high gain output ratio (GOR). GOR is defined as the ratio of the distillate produced to the mass of the steam supplied and it measures the energy intensity of a desalination process. Generally, for parallel/cross flow MEE the feed flow rate is same for all the effects. However, the equal feed flow rate may not guarantee an energy optimal solution. A new methodology, based on the principle of process integration combined with mathematical optimization, is developed in this paper to determine the optimal feed flow rate to each effect. MEE is represented as a Grand Composite Curve (GCC) for understanding energy integration and providing better insight of the overall problem. Through an illustrative example, it is shown that the GOR for 12-effect MEE can be increased by 11% with optimized feed flow rate. Sensitivity analysis is carried out for calculating the optimal operating parameters. Finally, it is proposed to design MEE with high temperature driving force for reduction in capital cost as well as specific energy consumption. [ABSTRACT FROM AUTHOR]

This paper proposes a novel concept for the optimal design of multi-stage vacuum membrane distillation (VMD). Generally, a multi-stage VMD is designed with an equal temperature difference between each stage. However, such a design is energy inefficient and increases VMD area. An analytical methodology for calculating the optimal stage temperature is proposed. By selecting the optimal stage temperature, the energy efficiency and required membrane area can be potentially improved by 16% and 30%, respectively. The proposed concept applies to all heat sources, including latent, sensible, and waste heat. To illustrate the method, multi-stage VMD is integrated with the waste heat from a supercritical water desalination (SCWD) system to achieve zero liquid discharge. SCWD is an energy-intensive process, requires high-quality thermal heat (>450 °C), and exhibits high waste heat rejection. The integrated VMD-SCWD approach is approximately 50% more energy-efficient and 35% more cost-efficient than the standalone SCWD system. Compared to the commercially used brine concentrator and crystallizer, the multi-stage VMD-SCWD system is more energy efficient for feed concentrations >5%. VMD-SCWD system is 30% cheaper, due to less expensive membrane distillation modules compared to a brine concentrator. The proposed design concept can replace the brine concentrator and crystallizer as an improved alternative for a zero-liquid discharge desalination system. [Display omitted] [ABSTRACT FROM AUTHOR]