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Diminishing fossil fuel reserves and a growing collective environmental awareness has led to the development of alternative methods of power generation such as Concentrated Solar Power (CSP). Although almost all existing CSP plants currently use water-cooled condensers, limited water supplies in the designated desert regions for such power plants,...
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Context 1
... implied that momentum recovery was occurring and was prominent. An example of the various pressure contributions is given in figure 10. For a steam mass flow rate of 0.18kg/s, the measured pressure drop is presented in conjunction with the large level of momentum pressure recovery that was determined using eqn. ...
Context 2
... only one flow rate was chosen to be presented here, with the other flow rates displaying similar trends. As can be seen in figure 10, the momentum pressure drop is a negative term and is thus a pressure recovery for condensation. The level of momentum recovery is quite large, of almost the same order of magnitude as the frictional term (albeit opposite in sense). ...
Context 3
... is this large level of momentum recovery that is responsible for the relatively small values of the measured pressure drops. For example, from figure 10, at a fan speed of 50% the measured pressure drop form inlet to outlet of the condenser is ≈ 0.0015Bar. The momentum pressure recovery is ≈ -0.0298Bar and the frictional pressure drop is ≈ 0.0313Bar. ...
Context 4
... momentum pressure recovery is ≈ -0.0298Bar and the frictional pressure drop is ≈ 0.0313Bar. Similarly from figure 10, at a higher fan speed of 100% the measured pressure drop is ≈ 0.00775Bar, the momentum recovery is ≈ -0.0433Bar and the frictional pressure drop is ≈ 0.051Bar. These figures explicitly quantify the level of momentum pressure recovery present during steam condensation, and demonstrate that it is of a similar order of magnitude as the frictional pressure drop. ...
Context 5
... experimentally-derived frictional pressure drop, from figure 10, and the other experimentally-derived frictional pressure drops (evaluated at the other flow rates from the initial measurements) are presented in figure 11. The corresponding theoretical two-phase frictional pressure drops, calculated with the Lockhart & Martinelli correlation are also presented in figure 11. ...
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Citations
... O'Donovan et al. [15,16] experimentally studied air-cooled condensers, albeit in a different geometry with shorter tubes than in the current study. They focused on condensation pressure and pressure drop at a fixed inclination, and did not measure thermal performance or compare different inclination angles. ...
An experimental study of convective steam condensation inside a large, inclined, flattened-tube air-cooled condenser for power plants is presented. This is the second of a four-part group of papers. The first part presents pressure drop and visualization results, while this study presents the experimental method along with heat transfer results. Follow-up papers present further heat transfer results and the effect of inclination.
The condenser in this study is steel with brazed aluminum fins. The condenser measures 10.72m in length, with a cross section of 214 mm x 18 mm. The condenser tube was cut in half lengthwise and covered with a polycarbonate viewing window in order to provide visualization access simultaneously with the heat transfer measurements. Inlet steam mass flux ranged from 6.2 – 9.5 kg m⁻² s⁻¹, and condenser capacity varied from 25 – 31 kW. The angle of inclination was varied from horizontal to 75o downward. The experiments were performed with a uniform fin-face velocity of crossflowing air at 2.2 m/s.
Condenser capacity was found to increase linearly with increasing downward inclination angle of the condenser, at a rate of 0.041% per degree of inclination below horizontal. This improvement was found to be the result of improved drainage and increased void fraction near the condenser outlet.
... The literature suggested some methods to enhance the condensing heat transfer rate (internal tabulators and internal fins) [20][21][22][23][24]; however, these methods are not very practical due to the small internal diameters and the very long tubes, which make it economically not efficient. Regarding the fin resistance, it has been intensively studied in literature to optimize the geometry, size and the spacing [25][26][27][28], which makes the current implemented fin-tube configuration the optimal design considering performance, cost, and manufacturing. ...
Restriction on water consumption is becoming an increasing problem for the power generation industry. As an alternative both to once-through cooling and to surface condenser/wet-cooling tower combination, utility companies and equipment manufacturers are considering, and even implementing, air-cooled condenser (ACC). However, the industry is quite reluctant to switch over to ACC for three important reasons: (a) lower power output, (b) higher capital cost, and (c) larger physical foot-print, all because of the same reason — it is not as efficient to transfer heat from condensing steam to air as it is to transfer to water. In other words, overall thermal resistance from condensing steam to the ambient air is significantly higher than to cooling water.
To get a clear and full understanding of the heat transfer process occur in air-cooling condenser, Detailed mathematical equations were derived to model the heat transfer process through the fined-tubes of the ACC. The total thermal resistance model was analyzed and investigated to identify the design components with highest affect in the process.
The paper proposes a viable cooling system based on novel heat pipe technology which addresses these problems. This technology employs boiling as the means to store and transfer heat energy. A detailed mathematical set of equations was derived to model the heat pipe thermal resistance. A comparison of the heat transfer performances of the ACC technology and the proposed method is presented.
The proposed cooling system suggests a solution for each of the three components of the thermal resistance, the super-hydrophobic coating of the steam ducts internal surfaces increased the condensing heat transfer rate by an order of magnitude, the proposed design of the heat pipes improved the external heat transfer, and the installation mechanism improves the fin efficiency by eliminating the contact resistance between steam duct and the heat pipe.
... A brief description of the experimental arrangement and measurement procedure is presented . For a more detailed description of both, the reader is referred to previously published papers by the authors [27,28]. ...
... This ensures vacuum conditions are maintained throughout. Further details of this arrangement, which is typical of operational ACCs, can be found in [27,28]. ...
... A brief description of the experimental set-up is provided, followed by an overview of the test-procedure. For a more detailed description, the reader can refer to a previously published paper by the authors' which provides a more thorough explanation of the test procedure and test facility [9]. ...
Limited water supplies in proposed concentrated solar power (CSP) plant locations have instigated the need for air-cooling of the condensers in the Rankine cycle. The current industry standard for air-cooling in power plants is the A-frame air-cooled condenser (ACC), the installation of which has increased exponentially in the last 15 years. This has occurred despite the fact they suffer from significant inefficiencies and weather effects. This paper introduces a modular air-cooled condenser (MACC) design which seeks to minimise these inefficiencies. A thermodynamic analysis is carried-out to determine the outcome of installing this MACC design in a CSP plant. Firstly, a series of measurements performed on a full-scale prototype MACC under vacuum conditions representative of an operational ACC are presented. Condenser temperature and pressure were measured as fan speed was varied, for a range of steam flow rates, to determine the qualitative and quantitative relationship between fan rotational speed and condenser steam-side conditions. Results show that for a fixed steam flow rate and constant ambient temperature, condenser temperature and pressure decrease as fan speed increases. The relationships, developed from the measurements, between fan speed and condenser temperature-pressure were then used to evaluate the gross output from a 50 MW steam turbine and, ultimately, evaluate the net plant output. Results show that increasing fan speed leads to an increase in plant output up until a certain point, at which further increases in output are offset by larger fan power consumption rates. Thus, an optimum operating point exists. The effects of ambient temperature were also examined and were seen to have a significant impact on firstly, steam-side conditions and consequently, plant output. Increases in ambient reduce plant output. However, by varying the fan speed to achieve the optimum operating point for any given ambient, the losses can be minimised.
... This leaves potential for the four row design to have a higher heat to power ratio. Another reason to reduce the number of tube rows is due to the phenomenon of backflow, an inherent issue with a multi-row condenser design which is explained in further detail in [5] and [6]. Both condenser designs were characterised for two fan scenarios, the fans forcing the air through the condenser (forced draft, FD) and the fans inducing the flow through the condenser (induced draft, ID). ...
... Figure 1 is a pictorial view of the prototype test facility. Suspended in the frame structure (5) is the prototype condenser (3) and each prototype can be coupled with the fan array (6). The fan array consists of four axial fans of 0.91m diameter. ...
This paper aims at developing a novel air-cooled condenser for concentrated solar power plants. The condenser offers two significant advantages over the existing state of the art. Firstly, it can be installed in a modular format where pre-assembled condenser modules reduce installation costs. Secondly, instead of using large, fixed speed fans, smaller speed controlled fans are incorporated into the individual modules. This facility allows the operating point of the condenser to change in order to maximise plant efficiency at all times. Two condenser designs were proposed and full-scale prototype modules were manufactured for experimental testing. Both designs comprise a bank of circular finned tubes, coupled to an array of axial fans. The air-side thermal and aerodynamic characteristics were measured using a purpose built steady-state test facility. The measurements were correlated and compared well with existing correlations in the relevant literature, thus validating their use in thermodynamic models to predict power plant performance. A plant performance analysis was conducted combing the experimental measurements with output data from a 50MW concentrated solar power plant. This analysis firstly verified that the plant efficiency can be continually maximised by altering the condenser fan speed. Furthermore, under certain conditions plant output can be increased by over 10% by varying fan speed by 10% of the full speed. The study also provides a comparison of the two designs in terms of their effect on the plant output power. With respect to the thermodynamic efficiency and cost-efficiency, the four row condenser substantially outperforms the initial six row design. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/)
... FD forced draft ID induced draft LCOE levelised cost of electricity, V/kWh MACC modular air-cooled condenser Another investigation by the authors [13] highlights and explains a fundamental design problem with a single pass, multi-row condenser commonly known as backflow. This phenomenon is less prevalent in heat exchangers with fewer tube rows, and so it was deemed necessary to extend the investigation on circular finned tube designs beyond the original six row design and study the performance of circular finned tube heat exchangers with fewer tube rows. ...
... The array of smaller fans in the MACC overcomes this issue by producing a more uniform flow of air across all of the heat exchanger surface. Other additional benefits of the MACC include the ability to maintain optimum condenser pressure and temperature with variable fan speed control, reduced fan power consumption and maintenance costs compared to conventional ACC systems [14,15]. ...
Air-cooled condensers overcome one of the main issues facing the construction of concentrated solar power plants by replacing water with air as the medium for cooling of the steam turbine waste heat. The recent development of modular air-cooled condensers as an improvement on conventional designs means that the effect of wind on their performance needs to be quantified. This study examines these effects by numerically modelling the condenser at the system level and using the results to build a mathematical model to predict the optimal condenser configuration. These types of mathematical models can be easily used by a power plant designer to quickly predict what the performance of the power plant will be based on the condenser geometry using data from numerical models of appropriate size and boundary conditions. The designer can then make a trade-off between the plant performance and initial capital costs in commissioning the power plant.
It has been found that when trying to optimise the performance, the historical wind condition distributions for a specific location should be used as significantly different condenser designs and orientations are required at different locations due to these distributions of local wind conditions.
Water consumption becomes a continously increasing issue in the design and operation process of concentrated solar power plants. If a conventional wet cooling tower is used, the cooling system has the largest share of water consumption. By utilizing a dry cooling system instead, water consumption can be decreased by over 90 %. In return, operating and maintenance costs increase while the thermal efficiency is reduced. Hybrid cooling systems aim at a tradeoff between water consumption and efficiency by combining at least two cooling mechanisms in one or more components. Due to the increasing complexity of the systems a demand for optimized operation plans emerges. This thesis attemps to solve the problem by introducing a distpatch and operation optimizer for hybrid cooling systems aiming to maximize the power generation, while minimizing water consumption at the same time. The value of water can be adjusted, so that higher water savings can be achieved at the costs of reduced electrical yield. The cooling optimizer is designed to optimize operational plans over a finite time horizon up to 24 h. It can be applied for online-optimization in a real power plant or to investigate cooling systems theoretically. The latter can be achieved by utilizing the optimizer in yield assessment calcualtions. One major advantage of the solution, proposed in this thesis, is that the cooling optimizer is independent of the CSP-Plant and hybrid cooling system, meaning that the solution can be applied to arbitrary power plant configurations and cooling systems without adjusting the solution algorithm. The only requirement is that a model of the plant and cooling system is available to the optimizer, such that the performance of the optimizer can be customized by setting corresponding parameters. The viability of the developed algorithm is demonstrated by implementing a testbench including the cooling operation optimizer into a simulation tool for yield assesment calculations (YACOP) and investigating a 50 MW parabolic trough power plant with different hybrid cooling systems. To evaluate the performance of the optimizer, two hybrid cooling systems both equipped with a cold thermal energy storage have been designed and analyzed within the scope of this thesis. It has been determined, that the application of a cold thermal energy storage in parallel to a dry cooling component is energetically reasonable. The application in parallel to a wet cooling tower aims at a decrease in water consumption. Depending on the cooling components and the value of water given to the optimizer, water consumption can be decreased and eletricity generation can be increased. However, water consumption always comes at the costs of reduced electrical yield, which can partly be compensated by applying the cooling operation optimizer. Economical investigations can be executed as a post processing step in YACOP after applying the simulation with optimization of the cooling operation plans, when information on investment, operation and maintenance costs are at hand.
This paper describes a 1-D thermofluid network modelling methodology for air-cooled condensers (ACCs). This study focuses on modelling a utility-scale ACC system at steady-state conditions applying a 1-D network modelling approach and using a component-level discretization approach. This allowed for each cell to be modelled individually, accounting for steam duct supply behaviour, and for off-design conditions to be investigated. The developed methodology was based on existing empirical correlations for condenser cells and adapted to also model double row dephlegmators, previously not observed in literature. A large 64-cell ACC system was modelled, which had a fan inlet elevation of 54m and a 10.363mfan diameter. The model was validated to site data with agreement in results. The model was also compared to the existing lumped approach, and differences were observed due to the steam ducting distribution.
The effect of increasing ambient air temperature from 25-35°C was investigated, with decreasing heat rejections and increasing backpressure observed. Condensers’ heat rejection decreased with higher air temperatures, while dephlegmators’ heat rejection increased due to the increased outlet vapour pressure and flow rates from condensers. Heat transfer coefficients were also investigated, with a decrease in overall heat transfer coefficient at higher air temperatures. Off-design conditions were simulated, including hot air recirculation and wind effects through edge cells which would be due to fan failure or crosswinds. Differences in performance were found between the developed model and existing lumped approach when considering wind effects which arose when comparing wind-affected cells and non-affected cells.
