Performance simulation of solar-boosted ocean thermal energy conversion plant

Ocean thermal energy conversion (OTEC) is a power generation method that utilizes small temperature difference between the warm surface water and cold deep water of the ocean. This paper describes the performance simulation results of an OTEC plant that utilizes not only ocean thermal energy but also solar thermal energy as a heat source. This power generation system was termed SOTEC (solar-boosted ocean thermal energy conversion). In SOTEC, the temperature of warm sea water was boosted by using a typical low-cost solar thermal collector. In order to estimate the potential thermal efficiency and required effective area of a solar collector for a 100-kWe SOTEC plant, first-order modeling and simulation were carried out under the ambient conditions at Kumejima Island in southern part of Japan. The results show that the proposed SOTEC plant can potentially enhance the annual mean net thermal efficiency up to a value that is approximately 1.5 times higher than that of the conventional OTEC plant if a single-glazed flat-plate solar collector of 5000-m² effective area is installed to boost the temperature of warm sea water by 20 K.     

Energy and exergy analyses of hydrogen production via solar-boosted ocean thermal energy conversion and PEM electrolysis

Energy and exergy analyses are reported of hydrogen production via an ocean thermal energy conversion (OTEC) system coupled with a solar-enhanced proton exchange membrane (PEM) electrolyzer. This system is composed of a turbine, an evaporator, a condenser, a pump, a solar collector and a PEM electrolyzer. Electricity is generated in the turbine, which is used by the PEM electrolyzer to produce hydrogen. A simulation program using Matlab software is developed to model the PEM electrolyzer and OTEC system. The simulation model for the PEM electrolyzer used in this study is validated with experimental data from the literature. The amount of hydrogen produced, the exergy destruction of each component and the overall system, and the exergy efficiency of the system are calculated. To better understand the effect of various parameters on system performance, a parametric analysis is carried out. The energy and exergy efficiencies of the integrated OTEC system are 3.6% and 22.7% respectively, and the exergy efficiency of the PEM electrolyzer is about 56.5% while the amount of hydrogen produced by it is 1.2 kg/h.     

Design and modeling of an integrated combined plant with SOFC for hydrogen and ammonia generation

Because of the requirement of the utilization of energy resources in a way that is both effective and efficient, solid oxide fuel cells have become a notable preference due to their advantages such as high efficiency and use with different fuels. In addition, the integration of these systems in the production of alternative fuels such as hydrogen and ammonia are important for a sustainable future to combat environmental problems. For this reason, the main intention of this paper is to introduce a new plant combining the different systems that use the solid oxide fuel cell for a cleaner and sustainable future. In the modeled work, a solid oxide fuel cell, a gas turbine, an organic Rankine cycle, a Kalina cycle with ejector, a hydrogen generation and storage process, a wood steaming plant, and an ammonia production system is integrated, to generate useful products. Detailed thermodynamic modeling is performed through energy and exergy methods, to determine the performance of the advised system and subsystem. Moreover, energy efficiency, exergy efficiency, and exergy destruction analyses methods are applied to each sub-plant and the whole system separately. In addition, parametric research is carried out to examine the effects of modifying key parameters on the plant's and subsystems' performance. Looking at the analysis results, the amount of the hydrogen and ammonia generation capacities of this work are 0.0085 kgs^?1and 0.2023 kgs^?1, respectively. In addition, the modeled power plant produces a power rate of about 20,180 kW. As a result, this proposed study is calculated to have 61.04% energy efficiency, and 57.13% exergy efficiency.     

Design of a sea thermal energy power plant

A unique 8000-kw gross power and sea water conversion plant is described which uses the temperature difference of the ocean to produce usable energy and fresh water. This plant has been designed by the research and development department, Clearing Division of U.S. Industries, Inc., for installation along coastlines in a semitropical area. Estimated cost for the sea thermal energy plant is 2.5 to 3 million dollars, including building and erection costs. This is equal to $310 to $375 per kw, amounts which are competitive with fossil-fuel burning plants in remote areas.     

An ocean thermal energy conversion based system for district cooling,ammonia and power production

In this study, a novel Ocean Thermal Energy Conversion (OTEC) based tri-generation system that produces ammonia, cooling and power is developed and analysed. This OTEC plant operates on the naturally existing temperature difference that exists in various depths of the ocean. The OTEC plant used in this study is operated using a single-stage ammonia Rankine cycle. The discharge seawater from the condenser in the organic Rankine cycle is used to provide district cooling. Two different operation cases of the analysed system are considered, where for the first case 50% of the power produced is stored in the form of ammonia during the off-peak hours. The second case is for complete power production proposed for peak hours. For the case where 50% of the power produced (case 1) is used to produce ammonia the highest energy and exergy efficiency is found to be 1.37% and 56.17% respectively. As for the case where, only power is produced (case 2) the maximum energy and exergy efficiency of the OTEC plant is found to be 1.83% and 78.02% respectively. The corresponding maximum power production was 6612 kW and 13,224 kW for cases 1 and 2. The maximum hydrogen and ammonia production rate is found to be 94.35 kg/h and 534.7 kg/h at peak efficiency values. The cooling duty at the peak energy and exergy efficiency is found to be 64.4 MW where the condenser temperature is 11.38 °C.     

Thermodynamic performance assessment of ocean thermal energy conversion based hydrogen production and liquefaction process

In the proposed study, the thermodynamic performance assessment of ocean thermal energy conversion (OTEC) based hydrogen generation and liquefaction system are evaluated. In this context, the energetic and exergetic analyses of integrated system are conducted for multigeneration. This integrated process is consisted of the heat exchangers, turbine, condenser, pumps, solar collector system, hot storage tank, cold storage tank and proton exchange membrane (PEM) electrolyzer. In addition to that, the impacts of different design indicators and reference ambient parameters on the exergetic performance and exergy destruction rate of OTEC based hydrogen production system are analyzed. The energetic and exergetic efficiencies of integrated system are founded as 43.49% and 36.49%, respectively.     

Development of a novel combined energy plant for multigeneration with hydrogen and ammonia production

In order to meet the energy and fuel needs of societies in a sustainable way and hence preserve the environment, there is a strong need for clean, efficient and low-emission energy systems. In this regard, it is aimed to generate cleaner energy outputs, such as electricity, hydrogen and ammonia as well as some additional useful commodities by utilizing both methane gas and the waste heat of an integrated unit to the whole system. In this paper, a novel multi-generation plant is proposed to generate power, hydrogen and ammonia as a chemical fuel, drying, freshwater, heating, and cooling. For this reason, the Brayton cycle as prime unit using methane gas is integrated into the s-CO₂ power cycle, organic Rankine cycle, PEM electrolyzer, freshwater production unit, cooling cycle and dryer unit. In order then to evaluate the designed integrated multigeneration system, thermodynamic analyses and parametric studies are performed, revealing that the energy and exergy efficiencies of the whole plant are found to be 69.08% and 65.42%. In addition, ammonia and hydrogen production rates have been found to be 0.2462 kg/s and 0.0631 kg/s for the methane fuel mass flow rate of 1.51 kg/s. Also, the effects of the reference temperature, pinch point temperature of superheater, combustion chamber temperature, gas turbine input pressure, and mass flow rate of fuel on numerous parameters and performance of the plant are investigated.     

Maximum efficiency point tracking for an ocean thermal energy harvesting system

Limited energy is the most critical factor that restricts the persistent presence of underwater vehicles in the oceans; thus, harvesting the ocean's thermal energy that is stored in the water column between the sea surface and deep water is a particularly promising solution for the current power shortage. This paper has designed a new ocean thermal energy conversion system which using phase change material as energy storage medium, and proposed a novel maximum efficiency point tracking (MEPT) method for energy conversion. This new method, which is integrated with a radial basis function neural network (RBFNN), particle swarm optimization (PSO) and the proportion integration differentiation (PID) control method, could effectively improve the efficiency of energy conversion. Compared with the power generation system that does not use the MEPT method, experimental results show that the proposed method can improve the efficiency of the power generation from less than 19.05% to more than 34.3% and has higher stability (using this method: the efficiency changes from 34.3%-34.7%; without using this method: the efficiency changes from 13.56% -19.05%) when the load changes. This novel method can be used in many conditions, especially when the mathematical model of the generation system is unknown or researchers want to use fewer sensors for maximum efficiency point tracking.     

On the ocean heat budget and ocean thermal energy conversion

Ocean water covers a vast portion of the Earth's surface and is also the world's largest solar energy collector. It plays an important role in maintaining the global energy balance as well as in preventing the Earth's surface from continually heating up because of solar radiation. The ocean also plays an important role in driving the atmospheric processes. The heat exchange processes across the ocean surface are represented in an ocean thermal energy budget, which is important because the ocean stores and releases thermal energy. The solar energy absorbed by the ocean heats up the surface water, despite the loss of heat energy from the surface due to back‐radiation, evaporation, conduction, and convection, and the seasonal change in the surface water temperature is less in the tropics. The cold water from the higher latitudes is carried by ocean currents along the ocean bottom from the poles towards the equator, displacing the lower‐density water above and creating a thermal structure with a large reservoir of warm water at the ocean surface and a large reservoir of cold water at the bottom, with a temperature difference of 22°C to 25°C between them. The available thermal energy, which is the almost constant temperature water at the beginning and end of the thermocline, in some areas of the oceans, is suitable to drive ocean thermal energy conversion (OTEC) plants. These plants are basically heat engines that use the temperature difference between the surface and deep ocean water to drive turbines to generate electricity. A detailed heat energy budget of the ocean is presented in the paper taking into consideration all the major heat inputs and outputs. The basic OTEC systems are also presented and analyzed in this paper. Copyright © 2011 John Wiley & Sons, Ltd.     

A micro reforming system integrated with a heat-recirculating micro-combustor to produce hydrogen from ammonia

In order to evaluate the potential of reforming ammonia as a carbon-free fuel in production of hydrogen, a new configuration of a micro reforming system integrated with a micro-combustor is studied experimentally. The micro-combustor as a heat source is a simple cylinder with an annular-type shield that applies a heat-recirculation concept. A micro-reformer to convert ammonia to hydrogen is an annulus, which is effective to transfer heat from the micro-combustor. The annulus-type micro reforming system is designed to produce 1-10 W (based on lower heating value, LHV) of hydrogen using various catalysts. The feed rate of ammonia, the micro-combustor inlet velocity of fuel-air mixtures and the catalyst materials substantially affect the performance of the designed micro reforming system. Under optimized design and operating conditions, the micro reforming system using ruthenium as a catalyst produces 5.4 W (based on LHV) of hydrogen with a conversion rate of 98.0% and an overall system efficiency of 13.7%. Thus, the present configuration can be applied to practical micro reforming systems, supporting the potential of using ammonia as a clean fuel.     

An ammonia energy vector for the hydrogen economy

This paper proposes the use of ammonia as a multipurpose energy vector. Synthesized from hydrogen produced in a large, centralized facility using nuclear process heat from a high-temperature, gas-cooled reactor (HTGR), the ammonia serves as a low-cost vehicle for energy storage and transmission, via pipeline, to remote demand centers where some of it serves as a clean-burning fuel for local cogeneration and process heat applications, and some of it is used for direct agricultural application or as feedstock for production of nitrogen-based fertilizers or other chemical processes.     

Retrofit of ammonia plant for improving energy efficiency

The aim of this work is to perform a retrofit study of an ammonia plant, in purpose of improving energy efficiency. As a common practice, one can divide an ammonia plant into two parts: the hot-end and the cold-end. In the hot section, two different options are investigated that both lead to a threshold condition and achieve maximum energy saving. The first option covers only process-to-process energy integration, while the second option considers some modification in the convection section of the primary reformer through a new arrangement of the heating coils. Thus, a considerable reduction in cooling water, HP steam and fuel gas consumption is achieved. In the cold section, retrofit study is dominated by reducing the amount of shaft work or power consumption in the refrigeration system. Application of the Combined Pinch & Exergy Analysis revealed that part of the shaft work, which was originally being used, was inefficient and could have been avoided in a well-integrated design. Therefore, by proposing optimum refrigeration levels, reasonable saving (15%) in power consumption was observed without the need for new investment.     

Hydrogen production through an ocean thermal energy conversion system operating at an optimum temperature drop

Storage of electrical energy produced from an ocean thermal energy conversion (OTEC) system is considered to be extremely essential, since the conversion process could take place in a remote offshore area and distant from the actual utilization sites. Energy conversion from an OTEC system into hydrogen energy, which is used for power generation through fuel cells, is an important approach of storing such energy for further utilizations. In this paper, a technical analysis of hydrogen production through an OTEC system coupled with a polymer electrolyte membrane electrolyser (PEM), which is developed by the Japanese international clean energy network using hydrogen conversion (WE-NET), is performed. The analysis is conducted at an optimum temperature drop between the working fluid and seawater, δT_op. Furthermore, the analysis is carried out at various temperature differences between the surface and deep sea water, ΔT. The calculated results demonstrated the significance of temperature drop and temperature difference on the electrical power output and conversion efficiency. Moreover, the actual rate of hydrogen production varied from 2.5 N m³/h to 60 N m³/h as ΔT raised from 5 °C to 25 °C, respectively.     

A thermal performance evaluation of a new integrated gas turbine-based multigeneration plant with hydrogen and ammonia production

In this study, a new combined system driving a gas turbine cycle has been proposed for seven useful outputs of power, hydrogen, ammonia, heating-cooling, drying and hot water. The proposed integrated plant mainly consists of the gas turbine cycle, Rankine cycle, two organic Rankine cycles, ejector-based cooling, hydrogen production and liquefaction, ammonia production and storage, drying and hot water generation sub-systems. In order to demonstrate that the designed system is an efficient and environmentally plant, the performance analysis was performed by using a software package. Before performing the performance assessment of the plant, the mathematical model of the integrated plant is prepared in accordance with thermodynamic equations. Basic equilibrium equations are used for the thermodynamic equations used. Obtaining multiple useful outputs from the system also have the positive effect on the system effectiveness. The energetic effectiveness of integrated plant for multigeneration with hydrogen and ammonia production is computed to be 62.18% and exergetic efficiency is 58.37%. In addition, the energetic and exergetic effectiveness of hydrogen production and liquefaction process are 57.92% and 54.23%, respectively.     

Prioritization of potential locations for harnessing wind energy to produce hydrogen in Afghanistan

Due to the devastating ecological effects and constrained reserves of fossil fuels, renewable energies are now globally accepted as viable alternative sources of energy. Among renewable energy sources, wind energy has become globally popular, primarily because wind farms can be rapidly built and easily maintained at a relatively low cost. Wind-powered hydrogen production is an effective solution for storing the excess energy output of wind farms. The hydrogen produced in this way can be used not only in fuel cells but also in cooling, oil, gas, and petrochemical fields. As a country devastated by war and instability, Afghanistan has major energy generation challenges and a substantially large power supply deficiency. However, there are good wind energy potentials in several parts of this country. There are also several hydrogen-consuming fields in Afghanistan that can benefit from hydrogen production from wind energy. This paper endeavored to distinguish the appropriate areas in Afghanistan for harvesting wind energy for hydrogen production using multi-criteria decision-making techniques. Eleven criteria were utilized to prioritize 20 Afghan provinces with wind energy potential. The Step-wise Weight Assessment Ratio Analysis (SWARA) was utilized to weight the criteria and Evaluation based on Distance from Average Solution (EDAS) were utilized to prioritize the provinces. Then, ARAS, TOPSIS, and VIKOR methods were used to validate the resultants. For criteria weighting with SWARA, “wind speed”, “wind power density” and “area of windy regions” with weights of 0.1423, 0.1356, and 0.1221 were introduced as the most significant criteria for this ranking. In all the rankings, Herat, Farah, and Jowzjan were identified as the top three most suitable provinces for wind power generation. The power output and hydrogen output to be achieved in Herat province using a 900-kW turbine were estimated to 2558.4 MW per year and 41.4 tons per year, respectively.     

发电厂中央空调系统的节能设计

分析了电厂空调系统存在的问题，在介绍变频控制节能原理的基础上，对某电厂主厂房空调系统改造一期工程中的节能设计进行了分析。实践证明，该设计能够以最小的成本实现节能降耗的目的，对同类空调系统的设计具有借鉴作用。     

Energy retrofit study of an ammonia plant

Detailed energy integration study of the front-end of an existing ammonia plant has been performed, using recent advances in Pinch technology. Utility loads demanded by the existing process were found to be very close to the calculated minimum targets. This indicated that the selected ammonia plant is well integrated, and not much saving is expected through process-to-process energy integration. Alternatively, the retrofit study concentrated on better placement of available utilities. Two promising options have been investigated. The first one studied the flue gas temperature in the convection section of the primary reformer, and proposed new arrangements of the heating coils. Boiler feed water heating for high-pressure steam generation has been also considered as a possible source for reduction in energy consumption. Total benefit claimed amounted to 17.6% reduction in combustion fuel consumption. The overall results of this case study are promising. However, economical evaluation of the proposed modifications is essential. Additional possible reduction in energy consumption is also possible in energy and power integration of the back-end section.     

The exergy of the ocean thermal resource and analysis of second-law efficiencies of idealized ocean thermal energy conversion power cycles

We develop a fomula here to compute the maximum amount of work which can be extracted from a given combined mass of warm and cold ocean water (a quantity called the exergy of the ocean thermal resource). We then compare the second-law efficiencies of various proposed ocean thermal energy conversion power cycles to determine which best utilizes the exergy of the ocean thermal resource. The second-law efficiencies of the multicomponent working fluid cycle, the Beck cycle, and the open and closed single- and multiple-stage Rankine cycles are compared. These types of OTEC power plants are analyzed in a consistent manner, which assumes that all deviations from a plant making use of all the exergy (one with a second-law efficiency of 100%) occur because of irreversible transfer of heat across a finite temperature difference. Conversion of thermal energy to other forms is assumed to occur reversibly. The comparison of second-law efficiencies of various OTEC power cycles shows that the multistage Rankine open cycle with just three stages has the potential of best using the exergy of the ocean thermal resource.     

Electrolysis of waste water containing aniline to produce polyaniline and hydrogen with low energy consumption

Hydrogen generation from water electrolysis is attempted to be one of the replacement of sources as a clean fuel with high energy density. However, its application is limited by the high overpotential of oxygen evolution reaction (OER). Herein, hydrogen fuel is obtained from waste water by replacing OER with aniline electrochemical polymerization. Compared to the OER, the potential of aniline electro-polymerization greatly decreases 1240 mV at the current density of 30 mA cm⁻² even using carbon paper electrode. Moreover, the Faradaic efficiency of hydrogen production is close to 100%. The as-prepared polyaniline demonstrates good performance as electrochemical capitative materials. This work provides efficient and lower energy consumed access to co-generate hydrogen and polyaniline in a convenient step by starting from the toxic and environmental-unfriendly wastewater.