Turbomachinery for small solar power plants

Conversion of solar energy into mechanical or electrical energy in small solar power plants (10–500 kW) requires new design criteria, especially with regard to turbomachinary. The cycles suitable for solar power production are affected by many variable such as kinds of working fluid, range of power and maximum cycle temperature determined by the type of collector. Also, the size of the plant will influence the selection of the various components of the plant, especially that of the turbomachinery. A study of a suitable thermodynamic cycle and working fluid is done for diffèrent ranges of power and temperature. The working fluids considered are steam, toluene, and refrigerant 113 for the Rankine cycle systems and air for gas turbine systems. For Rankine cycles, turbine selection is a problem in the small power range. This is mainly due to the fact, that for high efficiency the enthalpy drop should be as high as possible, and the mass flow rate of the working fluid through the turbine becomes very small. This, in turn, requires high rotational speed, multistaging and partial admission, especially if water is the working fluid. Toluene offers better design criteria for the turbine in the same temperature and power range (50–200 kW). For the very small range (10 kW) refrigerant 113 or similar should be used, otherwise severe design problems with the turbine will occur. In this power range, photovoltaics may also be considered. For high concentration systems with “Brayton cycles” (800–1000°C) only open-cycle gas turbine plants should be used.     

太阳能光伏-光热复合发电技术及其商业化应用

由于太阳能自身的间歇性和不稳定性,提高太阳能发电并网的质量成为近年来的研究热点。太阳能光伏-光热（photovoltaic/concentrated solar power,PV-CSP）复合发电技术作为一种新兴技术,相比于单独的太阳能光伏（PV）和太阳能热（CSP）发电技术具有诸多优势,目前已有多种技术形式实现了商业化。介绍了PV、CSP发电技术及PV-CSP复合发电技术,通过一些典型商业化PV-CSP复合电站的建设及运行情况,分析了当今商业化PV-CSP复合电站的应用现状,并综述了近年来对PV-CSP复合发电系统的技术和经济性研究情况。     

Exergetic analysis of solar concentrator aided coal fired super critical thermal power plant (SACSCTPT)

Comparative energetic and exergetic analysis of coal-fired supercritical thermal power plant (CSCTPT) and solar concentrator aided coal fired supercritical thermal power plant (SACSCTPT) have been carried out in this article. Optical analysis of Linear Fresnel reflecting (LFR) solar concentrator is used to predict the effect of focal distance and width of reflector upon the local concentration ratio and the tilt (θ) angles that are important parameters for SACSCTPT performance studies. Energetic and exergetic analysis for evaluating the effect of concentration ratio and inlet temperature of the fluid on LFR solar concentrator are carried out. An instantaneous increase in power generation capacity of about 20 % is observed by substituting turbine bleed streams to all the low pressure and high pressure feed water heaters of CSCTPT with solar concentrator aided feed water heaters (SAFWH). Coal consumption is increased by 3.35 % for reheat of the steam by substitution of high pressure feed water heaters with SAFWH. Energetic efficiencies of SACSCTPT appear high as compared to the solar alone thermal power plant and low as compared to coal-fired super critical thermal power plants. Furthermore, for a SAFWH, it is found that the land area requirement is 4.78 ha/MW.     

Economical study for hydrogen production from seawater using renewable energy in Egypt

This study looks into the possibilities of hydrogen production in the north coast and red-sea Zone, Egypt, to conver renewable energy to hydrogen (power to gas). The main purpose is to estimate the power needed for each kg of hydrogen production from seawater using renewable energy and then the quantity of desalinated seawater needed to cover this cost. We will discuss different scenarios; the main two scenarios are photovoltaic (PV) solar with reverse osmosis (RO) desalination and concentrating solar power (CSP) with multi-effect desalination (MED).     

Augmentation of thermal power stations with solar energy

A new concept of integration of a solar concentrator field with a modern thermal power station is proposed. Such a configuration would utilise the existing equipment and infrastructure as a base load facility and solar energy to reduce the fuel consumption during periods of insolation. The methodology suggested involves feed water heating using a solar concentrator field and consequent reduction of steam extraction presently used for the purpose. Study of retrofit to a 210-MW coal-fired plant indicates that saving of fuel upto 24·5% during periods of insolation can be achieved for feed water heating upto the present level, which is to a temperature of 241°C. The annual saving in coal would be around 47,000 tons at an estimated cost of about Rs. 3 crores. A doubling of the savings, by heating to a higher temperature level of 330°C, is feasible with presently available solar technology. Areas needing detailed study for achieving such an integration are indicated. The control system required to allow for fluctuations in the solar output is outlined. It is felt that the proposed system, where solar energy contributes a small but significant fraction of the total output of the plant, would be easier to control than one where the total energy is provided by solar radiation. A preliminary estimate indicates that the proposed system may cost about half of a stand-alone solar plant with back-up fuel and with the same solar input. However site-specific studies need to be carried out to confirm these figures.     

Energie- und CO2-Bilanzen von Solarkollektoranlagen

Energy systems based on solar collectors or other renewable energy sources are normally regarded as CO₂ zero-emission systems because nearly no fossil fuels are used to operate the systems. But the complete evaluation of an energy system concerning its CO₂ reduction potential must not be restricted to the emissions during the operation of the system. The cumulative energy demand and the cumulative CO₂ emissions during the life cycle have to be considered. In case of a solar collector system, in particular the production-determined emissions and emissions due to the requirement of auxiliary electric power for the collector pump are important. An energy analysis is this kind was performed for solar domestic hot water systems. It is shown that the consideration of the life cycle emissions reduces significantly the CO₂ reduction potential of solar collector systems whereby the design of the system has a major influence.     

Performance analysis of an air rock thermocline TES tank for concentrated solar power plants using the coupled DEM–CFD approach

Clean Technologies and Environmental Policy - One of the most common solutions currently available to meet future energy needs in the world is concentrated solar power (CSP) plants combined with...     

Failure analysis of a cracked concrete pipe in a 50 MW thermosolar power plant

Within the complexity of the design and execution of a solar power plant project, one of the main challenges falls on rainwater management, since there is the need to collect, conduct and store it for its use in the water-vapour cycle process. Therefore, the primary piping for rainwater transportation from the solar power plant is regarded as an essential installation for the operation of the plant. Within this framework, the appearance of pathologies in its conduction just a few months after the plant start-up is considered to be a critical problem, as it can endanger the electrical production of the facility.This problem has taken place at the solar power plant of “La Asturiana”, in Southern of Spain, with a solar field of 2 Mm² in size and a gross generation capacity of 50 MW.The need to understand the reason for the pathologies, in order to prevent their reappearance, justifies a detailed analysis of the adopted design, as well as its execution. The research is completed with novel techniques for in-situ tests, which enable us to obtain rigorous data to be used in computer models with the aim of reproducing, in a controlled way, the execution conditions in order to establish the causes of the failure.     

Low-temperature solar-plate-assisted heat pump: A developed design for domestic applications in cold climate

Solar energy and wasted heat in buildings are capable of supplying enough energy to answer the total demand of energy in dwellings. However, fluctuation in fuel prices and gas emissions are the main driving forces behind efforts. In this experimental study, a direct expansion solar-assisted heat pump system (DX-SAHP) using a bare ternary “retrofitted collectors with black paint” is investigated at the laboratory with a solar simulator and tested for domestic hot water (DHW) and space heating under quasi-static conditions. Unglazed solar collector absorber plates are used as an evaporator, and these are composed of two aluminium plates which are placed externally whilst another plate is mounted internally in the loft space of the house, where operating liquid from the heat pump is directly evaporated. The influence of outside temperature, solar irradiation and/or waste heat on the heating performance of DX-SAHP is investigated. The impact of the parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid is also assessed. Preliminary results elucidate that the refrigeration cycle can be a promising substitute for space heating and hot water when compared to the heat pump systems. This design technique results in higher solar collector/evaporator efficiency and lower system losses due to low evaporating temperature.     

Reversed Brayton cycle for food freezing at very low temperatures: Energy performance and optimisation

Freezing is a valuable method to increase food shelf life and to ensure high quality standards during long-term storage. Additional benefits to frozen food quality can be achieved by freezing at very low temperatures (< −50 °C): small ice crystal formation during fast freezing reduces food cell wall rupture, preventing water and texture loss during thawing. This paper presents the design of an innovative food freezing system operating at very low temperatures, based on a modified reversed Brayton cycle (rB cycle). The plant is composed of two interconnected sub-systems: a primary thermodynamic closed loop, operated by an rB cycle, and a secondary airflow loop which is devoted to food freezing by batch process. Relevant features of the designed rB cycle rely on the adopted environmentally safe working fluid, the optimised thermodynamics working conditions and the innovative cycle layout. A modelling framework for the system was developed to identify and design efficient operative settings for the plant components (turbo-machineries, heat exchangers, etc.) and to assess, via sensitivity analysis, the influence of the main design parameters on the global energy performance. The proposed system configuration, designed to maximise the coefficient of performance (CoP) value of the plant, was determined by means of nonlinear multivariable optimisation. In addition, the energy performance of the system can be increased by recovering waste heat available from the rB cycle.     

Artificial versus Natural Reuse of CO2 for DME Production: Are We Any Closer?

This work uses a mathematical optimization approach to analyze and compare facilities that either capture carbon dioxide (CO₂) artificially or use naturally captured CO₂ in the form of lignocellulosic biomass toward the production of the same product, dimethyl ether (DME). In nature, plants capture CO₂ via photosynthesis in order to grow. The design of the first process discussed here is based on a superstructure optimization approach in order to select technologies that transform lignocellulosic biomass into DME. Biomass is gasified; next, the raw syngas must be purified using reforming, scrubbing, and carbon capture technologies before it can be used to directly produce DME. Alternatively, CO₂ can be captured and used to produce DME via hydrogenation. Hydrogen (H₂) is produced by splitting water using solar energy. Facilities based on both photovoltaic (PV) solar or concentrated solar power (CSP) technologies have been designed; their monthly operation, which is based on solar availability, is determined using a multi-period approach. The current level of technological development gives biomass an advantage as a carbon capture technology, since both water consumption and economic parameters are in its favor. However, due to the area required for growing biomass and the total amount of water consumed (if plant growing is also accounted for), the decision to use biomass is not a straightforward one.     

Review on numerical modeling of active magnetic regenerators for room temperature applications

The active magnetic regenerator (AMR) is an alternative refrigeration cycle with a potential gain of energy efficiency compared to conventional refrigeration techniques. The AMR poses a complex problem of heat transfer, fluid dynamics and magnetic field, which requires detailed and robust modeling. This paper reviews the existing numerical modeling of room temperature AMR to date. The governing equations, implementation of the magnetocaloric effect (MCE), fluid flow and magnetic field profiles, thermal conduction etc. are discussed in detail as is their impact on the AMR cycle. Flow channeling effects, hysteresis, thermal losses and demagnetizing fields are discussed and it is concluded that more detailed modeling of these phenomena is required to obtain a better understanding of the AMR cycle.     

COMPROMISE: AN EFFECTIVE APPROACH FOR SOLVING MULTIOBJECTIVE THERMAL DESIGN PROBLEMS

In this paper, the application of the compromise Decision Support Problem Technique to the design of a Rankine power cycle to be used in a solar powered irrigation system is described. The system consists of a solar collector cycle coupled with a simple Rankine cycle. The uniqueness or the present approach lies in the interfacing of the thermal system simulation routines with a multi-objective optimization algorithm^1.2, as opposed to the traditional iterative design procedure. The problem, though simple in a mathematical sense, is complete in that it is representative of the complexities associated with the design or thermal systems dealing with thermodynamic property changes.     

Air-stable,earth-abundant molten chlorides and corrosion-resistant containment for chemically-robust,high-temperature thermal energy storage for concentrated solar power

A dramatic reduction in man-made CO₂ emissions could be achieved if the cost of electricity generated from concentrated solar power (CSP) plants could become competitive with fossil-fuel-derived electricity. The solar heat-to-electricity conversion efficiency of CSP plants may be significantly increased (and the associated electricity cost decreased) by operating CSP turbines with inlet temperatures ≥750 °C instead of ≤550 °C, and by using thermal energy storage (TES) at ≥750 °C to allow for rapidly dispatchable and/or continuous electricity production. Unfortunately, earth-abundant MgCl₂–KCl-based liquids currently being considered as low-cost media for large-scale, high-temperature TES are susceptible to oxidation in ambient air, with associated undesired changes in liquid composition and enhanced corrosion of metal alloys in pipes and tanks containing such liquids. In this paper, alternative high-temperature, earth-abundant molten chlorides that are resistant to oxidation in ambient air are identified via thermodynamic calculations. The oxidation resistance, and corrosion-resistant containment, of such molten chlorides at 750 °C are then demonstrated. Such an air-tolerant strategy, involving chemically-robust, low-cost TES media paired with effective containment materials, provides a critical advance towards the higher-temperature operation of, and lower-cost electricity generation from, CSP plants.     

超临界二氧化碳循环发电技术应用

超临界二氧化碳循环可应用于火力发电、核能发电、太阳能热发电等多种发电技术领域,作为新型的动力循环系统替代目前广泛使用的汽轮发电机组或燃气轮机发电机组。在进入商业化应用之前,需要对超临界二氧化碳循环技术在各种应用场景下的优势及其潜在的社会和经济效益进行探讨。通过分析超临界二氧化碳循环的特点和优势,探索其与化石能源、核能、太阳能、生物质能、余热等各种热源相结合的可行性,提出多种发电系统方案,可为今后超临界二氧化碳循环的商业化应用提供参考。随着超临界二氧化碳循环技术不断成熟,设备成本进一步降低,其系统简化、结构紧凑、效率高等优势将更加突显。     

Multi-objective optimization of steam power plants for sustainable generation of electricity

A unified framework that combines process simulation and multi-objective optimization is presented to simultaneously maximize the annual profit, while minimizing environmental impact (i.e., greenhouse gas emissions) of steam power plants with fixed flowsheet structures. The proposed methodology includes the selection of suitable primary energy sources (i.e., fossil fuels, biomass, biofuels, and solar energy) for sustainable electricity generation. For solving the problem of optimal selection of energy sources, a linear model is developed and included within a highly nonlinear simulation model for the parameter optimization of steam power plants that is solved by using genetic algorithms. This approach is robust and avoids making discrete decisions. Life cycle assessment technique is used to quantify the greenhouse gas emissions resulting from different combinations of energy sources and operating conditions of the power plants. The thermodynamic properties for liquid water and steam are calculated rigorously using the IAPWS-IF 97 formulation. An example problem of an advanced regenerative-reheat steam power plant is presented to illustrate the proposed method, which provides the Pareto optimal solutions, the types and amounts of primary energy sources as well as the optimal values of the operating conditions of the plant that simultaneously maximize the profit while minimizing environmental impact.     

燃气电厂噪声污染及控制

从几个方面对燃气电厂噪声控制过程和方法进行探讨:正确理解环评批复要求;合理设置燃气电厂总体布局工艺;系统分析燃气电厂噪声设备声源特性;准确模拟燃气电厂噪声;合理制定燃气电厂噪声控制措施;应用新技术需进行科学试验、验证;与各设计方配合内容等。上述燃气电厂噪声控制技术,在众多燃气电厂得到推广应用,取得良好效果。     

Leistungsfähige Spiegel für solarthermische Kraftwerke

High efficient mirrors for Concentrating Solar Power plants Mirrors are an essential component of CSP plants. Wet chemically coated silver mirrors supplied by Flabeg GmbH achieve an average specular and solar weighted reflectivity of 94.4%. Almost 30 years of field experience prove the durability of the coating. First surface mirrors could provide higher reflectivity, but so far either the necessary durability is not met or the costs are not competitive. Another approach to increase reflectivity is to equip the mirror with an antisoiling coating. This type of mirror is currently under field testing, showing already promising results. New paint systems for silvered mirrors will expand the locations for power plants to the shore or into tropical regions.     

Performance analysis of a solar cooling plant based on a liquid desiccant evaporative cooler

Summer air conditioning represents a growing market in buildings worldwide, with a significant growth rate observed in European commercial and residential buildings. Available heat driven cooling technologies can be used in combination with solar thermal collectors to reduce the load caused by air conditioning on the electric utilities and to reduce the environmental impact. This work reports a performance analysis of an open cycle solar cooling plant. The plant, installed in Northern Italy, is based on a liquid desiccant evaporative cooler coupled with a solar field. Experimental tests run during summer show average primary energy ratio and primary energy saving index of about 1.6 and 30%, respectively. Though this performance is satisfactorily, the regeneration unit always operated near the lower bound of the nominal temperature range. Therefore, optimization of the solar system design could lead to higher performance.     

Analysis of solar absorption cooling systems with low generator temperatures

Closed cycle absorption cooling systems have been analysed using water-lithium bromide and ammonia-water as working fluid pairs. An open cycle system using water-lithium bromide has also been analysed and compared with the closed cycle system. A flat plate collector has been considered for heat supply to the generator of the closed cycle systems. The effect of high flow ratios on the overall solar collector area required has been studied. It has been shown that the daily operating time of a cooling system can be increased by employing relatively high flow ratios.