Renewable energy has a significant role to play in helping the world achieve the greenhouse gas emission reduction necessary to achieve the pathway to a 2°C increase in global temperature. Electricity generation from wind and solar resources can contribute immensely to the decarbonization of power generation, but these resources are intermittent. High penetration of intermittent renewable power generation can cause grid stability and control issues for network operators, with fast response fossil fuel power plant necessary to provide security of supply and maintain grid stability. Increasingly natural gas-fueled distributed power generation is being installed to provide the necessary grid support. However, hybrid power plants comprised of a fossil fuel power generating system, a renewable power generation system and energy storage can provide both the low CO 2 electricity required to meet environmental constraints, and the despatchability and stability required by grid operators. Integrated Solar Combined Cycle Power Plants (ISCCs), comprising a Concentrated Solar Power plant and a natural gas fired combined cycle plant, have the potential to simultaneously reduce fossil fuel consumption, provide secure, highly predictable electricity generation, and reduce the cost of integrating renewable energy into a power system. While a number of ISCCs have been built at a larger scale (above 150MW power output), the concept has rarely been adopted for smaller scale distributed power applications. In addition, the traditional ISCC concept uses a steam bottoming cycle, which consumes water, and often locations where distributed ISCC could be utilized suffer from a scarcity of fresh water. This paper evaluates whether replacing the steam bottoming cycle with an Organic Rankine Cycle (ORC) alternative can provide a simpler, lower cost distributed ISCC solution that can be utilized on smaller and island grid systems, or mini- and micro-grids, to provide an affordable, water-free, low carbon power generation system.

For SCR (selective catalytic reduction) applications both aqueous ammonia and urea reagents are used for NOx reducing agents in exhaust systems. For both diesel engines and small boilers, the reagent injection systems often consist of a few, and in some cases, a single injector, located on the wall of the exhaust pipe or duct. Often numerical modeling is performed to determine the location and orientation of the injectors and to predict the NRMS (normalized root mean square) of the gas phase reducing specie distribution prior to the catalyst. Aqueous ammonia and aqueous urea have significantly different processes from the point of injection to the formation of the gas phase reducing species. Evaporation characteristics are important, but for urea, the molecule must also decompose into ammonia and isocyanic acid. For modeling purposes, a simplifying assumption is frequently made to treat the liquid reagent as liquid water and assume that the evaporation of liquid water satisfactorily emulates the processes of forming the gas phase reducing species for both aqueous ammonia and aqueous urea reagents. In reality, the reagent droplets are binary component mixtures and treating the droplets as a single component, namely water, may significantly depart from reality. Additionally, the evaporation processes for aqueous ammonia and aqueous urea have significantly different behaviors. This paper addresses the potential errors associated with using a single component water drop for emulating the evaporation of aqueous ammonia and aqueous urea. This is accomplished by analyzing binary component evaporation for both aqueous ammonia and aqueous urea. Additionally, the time for the gas phase chemical decomposition of urea into ammonia and isocyanic acid is evaluated for various conditions. Typical decomposition times are compared to droplet evaporation times. Finally, the paper attempts to provide guidelines for determining when treating the drops as a single component may be sufficiently accurate, and when the complexity of modeling binary component evaporation is necessary.

A shell and tube heat storage (1 MJ) has been designed computationally to enhance the heat transfer rate from heat transfer fluid (HTF) to the storage media. Concrete and water are considered as the sensible storage material and HTF, respectively. The system can be used to store the solar energy in the day time, which will be available in the absence of sunlight. Finite element based software, named COMSOL Multiphysics, is used for the study. The parameters analyzed, are tube outside diameter, radial distances between the tubes, number of tubes and inlet temperature of HTF. After a simulation time of 3000s, the increase of tube diameter from 1.03 to 1.71 cm is found to increase the average storage bed temperature by 6.3%. For the radial distances between the tubes to be 6 cm, the stored energy is maximum. The stored energies for 5 and 4 cm are 2.4 and 12.4% less than 6 cm, respectively, after duration of 6000s. The average bed temperature reaches to the steady state condition at 5147s with 19 tubes, whereas, with 25 tubes it takes 30.2% less time. Finally, the shell and tube heat storage has been optimized for higher heat transfer rate.

Over the past decade, several technical developments (such as hydraulic fracturing) have led to an exponential increase in discovering new domestic natural gas reserves. Raw natural gas composition can vary substantially from source to source. Typically, methane accounts for 75% to 95% of the total gas, with the rest of the gas containing ethane, propane, butane, other higher hydrocarbons, and impurities, with the most common including H 2 O, CO 2 , N 2 , and H 2 S. All natural gas requires some treatment, if only to remove H 2 O; however, the composition of natural gas delivered to the commercial pipeline grids is tightly controlled. Sub-quality natural gas reserves, which are defined as fields containing more than 2% CO 2 , 4% N 2 , or 4 ppm H 2 S, make up nearly half of the world’s natural gas volume. The development of sub-quality, remote, and unconventional fields (i.e. landfill gas) can present new challenges to gas separation and purification methods. Adsorbent technologies, such as the use of activated carbons, zeolites, or metal-organic frameworks (MOFs), may hold the key to more efficient and economically viable separation methods. This work proposes to prove the applicability of the multi-component potential theory of adsorption (MPTA) to a real world natural gas adsorbent system to properly characterize the adsorbent’s selectivity for an individual gas component using only the single component isotherms. Thus, the real-world gas separation/purification application of a specific adsorbent for a given gas stream can be obtained simply and effectively without the need for large experimental efforts or costly system modifications until after an initial computational screening of perspective materials has been completed. While the current research effort will use natural gas, which is the world’s largest industrial gas separations application, to validate the MPTA, the tools gained through this effort can be applied to other gas separation effort.

Multiphase flows frequently occur in many important engineering and scientific applications, but modeling of such flows is a rather challenging task due to complex interfacial dynamics between different phases, let alone if the flow is oscillating in the porous media. Using humid air as the working fluid in the thermoacoustic refrigerator is one of the research focus to improve the thermoacoustic performance, but the corresponding effect is the condensation of humid air in the thermal stack. Due to the small sized spacing of thermal stack and the need to explore the detailed condensation process in oscillating flow, a mesoscale numerical approach need to be developed. Over the decades, several types of Lattice Boltzmann (LB) models for multiphase flows have been developed under different physical pictures, for example the color-gradient model, the Shan-Chen model, the nonideal pressure tensor model and the HSD model. In the current study, a pseudopotential Multiple-Relaxation-Time (MRT) LBM simulation was utilized to simulate the incompressible oscillating flow and condensation in parallel plates. In the initial stage of condensation, the oscillating flow benefits to accumulate the saturated vapor at the exit regions, and the velocity vector of saturated vapor clearly showed the flow over the droplets. It was also concluded that if the condensate can be removed out from the parallel plates, the oscillating flow and condensation will continuously feed the cold surface to form more water droplets. The effect of wettability to the condensation was discussed, and it turned out that by increasing the wettability, the saturated water vapor was easier to condense on the cold walls, and the distance between each pair of droplets was also strongly affected by the wettability. It’s expected that this study can be used to optimize and redesign the structure of thermal stack in order to produce more condensed water, also this multiphase approach can be extended to more complicated 3D structures.

Optimized operation of gas turbines is discussed for a fleet of eleven LM2500PE engines at a Statoil North Sea offshore field i n Norway. Three engines are generator drivers whilst eight engines are compressor drivers. Several of the compressor drive engines are running at peak load (T5.4 control), hence the production rate is limited by the available power from these engines. The majority of the engines discussed run continuously without redundancy, hence gas turbine uptime is critical for the field’s production and economy. Two of the compressor drive engines are instrumented with a new static P2 probe in order to have an inlet depression measurement and thus be able to monitor compressor air flow. Compressor air flow has been used as an additional parameter to efficiency, in order to have better analysis methods and better documentation of deterioration rates. The performance gain with online water wash at high water-to-air ratio and upgraded inlet air filter systems, as well as successful operation at longer intervals between offline wash/maintenance stops are thus documented. An approach for developing a compressor map for mass flow based on field measurements, predictions and deterioration has been performed, as well as correction methods for engine load and ambient conditions in order to be able to compare performance points in various conditions and engine control modes. When monitoring compressor air flow, the Reynolds number effects on axial compressor performance can be analyzed. Understanding the gas turbine performance deterioration is of vital importance. Trending of its deviation from the engine baseline facilitates load-independent monitoring of the gas turbine’s condition. Instrument resolution and repeatability are key factors in order to have reasonable results on the performance analysis. Based on previous tests and analysis, the compressor air flow rate is the most sensitive parameter for detecting performance deterioration. Unfortunately, gas turbines for offshore operation, are normally not equipped with any air flow measurement devices.

Traditionally, water is used in thermal power plant for heat rejection processes such as in the steam condenser for use in a Rankine cycle. Typically, research has shown that approximately 2 litres of water are required to generate 1 kWh of electricity on a wet-cooling system; which on a bigger scale could translated to more than 11000000 m 3 per year of make-up water for a 600 MWe coal-fired plant. The ever-increasing cost of water resources as well as the water resource scarcity have paved a path to dry-cooling systems which alternatively provide a significant cooling potential. However, dry-cooling systems performance are generally driven by the atmospheric conditions which at time do not meet the desired cooling temperatures resulting in significant drop in their performance. Recent developments in cooling technology suggest that hybrid systems (dry-wet) be used to insure good and manageable performances while maintaining the cost of operation at admissible range. In light of the recent draught experienced in South Africa, attention was drawn to evaluation of deluged systems performance as well as water consumption to increase the public awareness in the field. In this study, a deluged bundle was used to experimentally determine the cooling performance characteristic as well as water consumption for performance management. The above is then considered on a bigger scale to in order to open floor for further discussion on future strategies in term of the South African policy on water usage.

In this paper, a novel nodalized reduced order model (NROM) has been developed to analyze the linear stability in a heated channel using supercritical water (SCW) as a coolant. The presented reduced order model is developed based on the two-phase flow system approach. The model is much simplified, which reduced the requirement of computational efforts and resources. In the heated channel, the SCW’s density shows a dramatic downfall near the pseudo-critical temperature, based on which it has been divided into n number of nodes. The one-dimension partial differentiation conservation equations of energy, mass and momentum are used and have been linearized by a small perturbation applied on its steady-state solution. These PDEs are converted into the corresponding time-dependent, nonlinear ordinary differential equations (ODEs) by using weighted residual method applied under some appropriate assumptions and approximations. These sets of ODEs (n+1 equations) are then solved analytically by using a state space approach to capture the stability boundary (SB) in terms of trans-pseudo-critical phase change number ( N tpc ), pseudo-subcooling number ( N spc ) by applying a constant external pressure drop (Δ P tpc ) condition across the channel. The NROM results are found to be in good agreement with the methodology and have been verified by numerical simulation. To extend this as a nonlinear stability analysis, the different types of the Hopf Bifurcation regime are also reported.

Reduced mechanisms are needed for use with computational fluid dynamic codes (CFD) utilized in the design of combustors. Typically, the reduced mechanisms are created from the detailed mechanisms which contain numerous species and reactions that are computationally difficult to handle using most CFD codes. Recently, it has been shown that the detailed Aramco 2.0 mechanism well predicted the available experimental data at high pressures and in high-CO 2 diluted methane mixtures. Further, a 23-species gas-phase mechanism is derived from the detailed Aramco 2.0 mechanism by path-flux-analysis method (PFA) by using CHEM-RC. It is identified that the reaction CH 4 +HO 2 ⇔ CH 3 +H 2 O 2 is very crucial in predicting the ignition delay times under current conditions. Further, it is inferred that species C 2 H 3 and CH 3 OH are very important in predicting the ignition delay time of lean sCO 2 methane mixtures. Also, the 23-species mechanism presented in this work is performing on par with the detailed Aramco 2.0 mechanism in-terms of simulating ignition delay times, perfectly-stirred-reactor estimates under various CO 2 dilutions and equivalence ratios, and prediction of turbulence chemistry interactions. It is observed that the choice of equation-of-state has no significant impact on the ignition delay times of supercritical CH 4 /O 2 /CO 2 mixtures but it influences supercritical H 2 /O 2 /CO 2 mixtures considered in this work.

Steam surface condensers may require several different relief devices for safe operation. Atmospheric relief devices are typically utilized for the safe relief of over-pressure on the shell-side (LP steam). This is to protect and prevent steam surface condensers, often including steam turbine exhaust hoods, from exceeding specified design pressures. In addition to shell-side safety devices, relief devices for the tube-side (cooling water), such as water box pressure & vacuum relief, venting and air removal valves, all perform a similar function. This paper provides a thorough background to all the types of condenser safety relief devices currently available. The latest applicable standards, codes and guidelines for these safety relief devices are reviewed, in conjunction with the current methodology for the correct design and sizing of such devices. Several sample calculations and working examples for the correct sizing of safety devices are provided for reference. The paper includes a review of the relative attributes and considerations for the appropriate selection of each of these types of safety devices, e.g. rupture discs versus atmospheric relief valves for shell-side protection. The paper concludes with a comprehensive review of the latest guidelines for the installation, operation, and maintenance for these safety devices, including guidance on other aspects such as preferred locations, exhaust & vent piping, routine inspection, and testing requirements.

Surface tension and solution evaporation of aqueous solutions of sodium lauryl sulfate (SLS), ECOSURF™ EH-14, and ECOSURF™ SA-9 under natural convection is examined through experimental methods. SLS is an anionic surfactant while EH-14 and SA-9 are environmentally-friendly nonionic surfactants. Surfactants are known to affect evaporation performance of solutions and are studied in relation to water loss prevention and heat dissipation. Surfactants could be useful under drought conditions which present challenges to water management on a yearly basis in arid areas of the world. Recent water scarcity in the greater Los Angeles area, south eastern Africa nations, eastern Australia and eastern Mediterranean countries has high cost of water loss by evaporation. Surfactants are studied as a potential method of suppressing evaporation in water reservoirs. Surfactants are also studied as performance enhancers for the working fluid of heat dissipation devices, such as pulsating heat pipes used for electronics cooling. Some surfactants have been shown to lower thermal resistances and friction pressure in such devices and thereby increase their efficiency. The static surface tensions of the aqueous-surfactant solutions are measured with surface tensiometer using Wilhelmy plate method. The surfactants are shown to lower surface tension significantly from pure water. The surface tension values found at the Critical Micelle Concentration are 33.8 mN/m for SLS, 30.3 mN/m for EH-14, and 30.0 mN/m for SA-9. All three surfactants reduced natural convection water loss over 5 days with SLS showing the greatest effect on evaporation rates. The maximum evaporation reduction by each surfactant from distilled water with no surfactants after 5 days is 26.1% for SLS, 20.8% for EH-14, and 18.4% for SA-9.

High-temperature Gas-cooled Reactor Pebble-bed Module (HTR-PM) is under construction in Shidao Bay, Shandong of China. It is supposed to be the world’s first pebble-bed modular commercial demonstration plant for High Temperature Gas-cooled Reactor (HTGR). In HTR-PM project, water-Rankine cycles have been used in the power conversion system. Meanwhile, supercritical carbon dioxide (S-CO2) Brayton cycle has shown great potentials for future HTGR technology. Comparing with typical helium Brayton cycle, in S-CO2 cycle where critical properties of carbon dioxide are utilized, compressor work may reduce significantly and thermal efficiency may improve greatly. Furthermore, the general sizes of S-CO2 cycle equipment, such as heat exchanger and turbine, would be orders of magnitude smaller than water-Rankine system at similar power output. Therefore, parameters study of S-CO2 were conducted in this paper for future HTGR. Firstly, a physical model of S-CO2 Brayton cycles was built and the performance of cycles were analyzed. Secondly, compression ratio, temperature ratio, the inlet temperature of turbine, inlet parameters of compressor, and recuperated effectiveness were discussed as key cycle parameters. For heat capacities of CO2 are significantly different as a function of temperature and pressure, flow recompression was considered. Calculation was based on a split-flow cycle configuration. The split flow ratio was also analyzed. Finally, the parameters of S-CO2 cycle were optimized for HTGR. In conclusion, S-CO2 Brayton cycle will be a good option for future HTGR.

Increasing the share of intermittent renewable energy sources in a power system poses challenges in terms of increased net load variability and maintaining grid stability and security. Operational flexibility of coal-fired power plants in China has played an essential and promising role in accommodating these nonequilibrium in the power grid. In the study, focusing on condensate throttling coupled with thermal storage tank measures, dynamic simulations of an entire 660 MW supercritical coal-fired power plant were developed via the GSE software. Then, the dynamic characteristics of main thermodynamic parameters and output power were described and compared, and operational flexibility performances of these measures were discussed. It turns out that: when condensate water flowrate decreases, the largest power ramp rate, power capacity, and energy capacity are 12.68 MW min −1 , 12.76 MW, and 1084.70 MJ, respectively, and when condensate water flowrate increases, the largest power ramp rate, power capacity, and energy capacity are −5.49 MW min −1 , −5.65 MW, and −695.94 MJ, respectively, which means condensate throttling without thermal storage tank measure is more suitable for power-up regulation than power-down regulation, but the shortest duration time is 130 s, which will restrict the operational flexibility regulation. However, coupling with thermal storage tanks, the deaerator water level can maintain a longer time. Meanwhile, at feedwater bypass 60% coupled with thermal storage tank, the largest power ramp rate, power capacity, and energy capacity are −3.62 MW min −1 , −3.81 MW, and −897.31 MJ, respectively, and at condensate water bypass 60% coupled with thermal storage tank, the largest power ramp rate, power capacity, and energy capacity are 7.74 MW min −1 , 7.88 MW, and 1829.38 MJ, respectively, and these parameter values are greater than condensate water flowrate directly increases or decreases 60%, which means condensate throttling coupling with thermal storage tanks can improve operational flexibility performances. The work is expected to reveal the performance parameters and strategies to provide detailed guidance of using turbine energy storage to improve operational flexibility of the coal-fired power plants.

The Wells turbine is a self-rectifying device that employs a symmetrical blade profile, and is often used in conjunction with an oscillating water column to extract energy from ocean waves. The effects of solidity, angle of attack, blade shape and many other parameters have been widely studied both numerically and experimentally. To date, several 3-D numerical simulations have been performed using commercial software, mostly with steady flow conditions and employing various two-equation turbulence models. In this paper, the open source code Open-FOAM is used to numerically study the performance characteristics of a Wells turbine using a two-equation turbulence model, namely the Menter SST model, in conjunction with a transient fluid solver.

Scarcity and restrictions in the use of cooling water has prompted power plant developers to explore multiple sources of cooling mediums to condense turbine exhaust steam in a steam surface condenser. The cooling mediums can have different chemistries dictating selection of different tube and tubesheet materials. The flowrate, inlet temperature and temperature rise for the cooling mediums can be different. Some cooling mediums may not be available during certain times of the year. The resulting steam surface condenser will include multiple smaller tube bundles of various sizes operating with different flowrates and temperatures. The challenges in designing a condenser that employs multiple sources of cooling medium with different chemistries, flowrates and inlet temperatures are enormous. To ensure reliable operation a number of thermal, hydraulic and mechanical design issues must be carefully evaluated. Determining performance of the entire condenser at off-design conditions with variations in flowrates and inlet temperatures of one or more cooling water streams (or absence thereof) can be complicated. This paper highlights the major concepts that need to be addressed while designing a steam surface condenser that employs multiple sources of cooling medium to condense the turbine exhaust steam. Critical thermal, hydraulic and mechanical design issues that can impact the performance and reliability of the overall condenser are addressed.

Power and freshwater demand are increasing as populations around the world keep growing. Due to the environmental impact of using fossil fuels and limited resources, using solar thermal in desalination application is a valuable option. In this paper, an innovative new design of low temperature multi-effect desalination coupled with mechanical vapor compression (LT-MED-MVC) powered by supercritical organic Rankine cycle utilizing a low-grade solar heat source using evacuated tube collectors is analyzed. The proposed design has the potential to desalinate water of high salt concentrations or brine with high salinity more than 100,000 ppm or effluent streams from a power plant with low energy consumption and high efficiency when compared to the previously discussed systems. The performance of the LT-MED-MVC was found to be better than similar systems found in the literature. The specific power consumption for MVC is lower than 4 kWh/m 3 for seawater feed salinity of 100,000 ppm, 14 forward feed effects, and a recovery rate of 50%. The overall system efficiency is about 14%. The impact of increasing the number of effects, motive steam temperature, pressure of supercritical-ORC and salt concentration on the specific power consumption, solar collector area, and the system efficiency are also analyzed.

Combined Cycle Gas Turbine (CCGT) power plant offer operators both environmental and economic benefits. The high efficiency achievable across a wide load range reduces both fuel costs and CO 2 emissions to atmosphere. However, the scale of the power generation plays a major role in determining both cost and efficiency: a modern large centralized CCGT of 600MW output or more will have a full load efficiency in excess of 60% and a very competitive installed cost on a US$/kW basis. The smaller gas turbines required for distributed power applications are not optimized for combined cycle operation, with potential full load efficiencies of a combined cycle scheme ranging from a little over 40% to the high 50s depending on the power output of the gas turbine, the exhaust gas conditions and the plant configuration, while the installed cost is around twice that of a large centralized CCGT on a US$/kW basis. The drawback of a conventional combined cycle plant design is the need for water, which is a scarce commodity in some regions. Air cooling of the CCGT plant can be used to reduce water consumption, but make-up water will still be required for the steam system to compensate for steam losses, blowdown etc. While the lower exhaust gas temperatures of the smaller gas turbines impact the combined cycle efficiencies achievable, they do allow Organic Rankine Cycle (ORC) technology to be considered for an alternative combined cycle configuration. This paper compares both the capital and operating costs and performance of combined cycle power plants for distributed power applications in the 30MW to 250MW power range based on conventional steam and various different ORC configurations.

The influence of mesh resolution, the abilities of various eddy viscosity models, and near wall flow treatments on predicting the flow coefficients of poppet valves, operating in water are investigated in this paper. The computational fluid dynamics (CFD) models are solved using STAR-CCM+ 12.04. Grid-convergence is studied first, followed by quantitative assessments of the ability of standard k-ε model, realizable k-ε model, EB k-ε model, Lag EB k-ε model, V2F model and k-ω-sst model, and different wall treatments, such as high y + wall treatment, two-layer wall treatment and all y + wall treatment, embedded in the solver. The flow discharge coefficient (C q ) of poppet valves predicted by CFD models are compared to physical measurements. It was demonstrated in the study that grid resolutions normal to the wall and mesh quality are key factors. Advanced near wall flow treatments produce similar or worse predictions when using the standard k-ε model, and the effects of the near wall flow treatments are marginal for the realizable k-ε model. The ability of turbulence models varies greatly in predicting flow in different valves and lift levels. The realizable k-ε model is the optimal option for the considered valve flows giving an acceptable error within ±5%.

The paper investigates the cavitation in micro-turbomachinery, using a small-sized water system. Unsteady numerical model is architected to predict cavitating flows through a 7.5 cm axial hydro-turbine working at 2.8 m water head. Based on the validated simulations, specific turbine designs (regular design and rim-drive turbines) are simulated with cavitating flow conditions including different rotation speeds (1000–5000 rpm) and outlet pressures (0, -24, -48, -96, kPa gage). Phase change interactions (liquid water and vapor) were considered by adding the physics models of Volume of Fluid (VOF) multiphase, cavitation, and Large Eddy Simulation (LES) turbulence. Records featured spatial variation in the cavitation pattern between the two designs. Rim-drive turbine stands against cavitation along the rim integration lines, but it starts the hub cavitation earlier than the regular turbine. The proposed rim-drive bests the regular geometry before cavitation, and the relative efficiency gap increased to be 16% at extreme cavitation condition.

Augmentation in heat transfer is very useful for various engineering and scientific applications due to the call for energy and cost saving. The heat transfer and pressure drop characteristics in annuli of double pipe heat exchanger using helical and plain surface ring turbulators are studied through experimental investigation. The effect of helical surface ring turbulators and plain surface ring turbulators are studied for varied range of pitch ratio (4.0–6.4), Reynolds Number (3,000–10,500) and two different diameter ratios (0.475 and 0.54). Water (hot fluid) flows in the inner tube and air (cold fluid) flows through the annulus. The tests are conducted for air with uniform wall temperature condition. The heat exchanger with least pitch and least diameter ratio is found to exhibit the highest Nusselt number and pressure drop. Results indicate that maximum enhancement is obtained for smallest diameter ratio 0.475 and pitch ratio 4.0 at lowest Reynolds Number. Also, thermal performance factor is always greater than unity for the DPHE using helical surface turbulators. Correlations have been developed for enhancement in Nusselt number and friction factor; show the good agreement with experimental test data within test range.