Thermoeconomic Study of a Small Parabolic Trough Solar Plant

This work describes the thermoeconomic study of an integrated combined cycle parabolic trough power plant. The parabolic trough plant will economize boiler activity, and thus the thermoeconomic optimization of the configuration of the boiler, including the parabolic trough plant, will be achieved. The objective is to obtain the optimum design parameters for the boiler and the size of the parabolic field. The proposal is to apply the methodology employed by Duran [1] and Valde´s et. al. [2], but with the inclusion of the parabolic trough plant into the optimization problem. It is important to point out that the optimization model be applied to a single pressure level configuration. For future works, it is proposed that the same model be applied to different configurations of integrated combined cycle solar power plants. As a result the optimum thermoeconomic design will be obtained for a parabolic trough plant used to economize the HRSG.

Assessment of a Syngas-Diesel Dual Fuelled Compression Ignition Engine

Synthesis gas (Syngas), a mixture of hydrogen and carbon monoxide, can be manufactured from natural gas, coal, petroleum, biomass, and even from organic wastes. It can substitute fossil diesel as an alternative gaseous fuel in compression ignition engines under dual fuel operation route. Experiments were conducted in a single cylinder, constant speed and direct injection diesel engine fuelled with syngas-diesel in dual fuel mode. The engine is designed to develop a power output of 5.2 kW at its rated speed of 1500 rpm under variable loads with inducted syngas fuel having H2 to CO ratio of 1:1 by volume. Diesel fuel as a pilot was injected into the engine in the conventional manner. The diesel engine was run at varying loads of 20, 40, 60, 80 and 100%. The performance of dual fuel engine is assessed by parameters such as thermal efficiency, exhaust gas temperature, diesel replacement rate, gas flow rate, peak cylinder pressure, exhaust O2 and emissions like NOx, CO and HC. Dual fuel operation showed a decrease in brake thermal efficiency from 16.1% to a maximum of 20.92% at 80% load. The maximum diesel substitution by syngas was found 58.77% at minimum exhaust O2 availability condition of 80% engine load. The NOx level was reduced from 144 ppm to 103 ppm for syngas-diesel mode at the best efficiency point. Due to poor combustion efficiency of dual fuel operation, there were increases in CO and HC emissions throughout the range of engine test loads. The decrease in peak pressure causes the exhaust gas temperature to rise at all loads of dual fuel operation. The present investigation provides some useful indications of using syngas fuel in a diesel engine under dual fuel operation.

Towards Optimizing Building Energy Use to Reduce Electric System Carbon Emissions

In spite of heightened interest in anthropogenic climate change, little attention has been paid to optimizing a building’s carbon emissions at the source. Most work in building efficiency has assumed that generating plant carbon emissions are constant at their long-term average values. This study sought to improve our understanding of the temporal variations in carbon emissions on a diurnal time scale and their relation to electric system dispatch and load in order to motivate future work in optimizing building operation to reduce carbon emissions. Hourly fossil fuel plant emissions and load data, available from the EPA, were used to characterize power system performance for four US locations (IL, NY, TX, and CA). The study had set out with a hypothesis hoping to find a simple relationship between electric system load and emissions. It was found that there is a significant correlation between increased system load and decreased emissions rates, yet this correlation is not easily defined. During high load conditions, emissions reductions are related to the increased use of gas generators, or may be related to operating plants at more efficient part load ratios. The work conducted in this study shows that, while more complex than hoped for, there is indeed a strong relationship between electric system load and carbon emissions rates.

A Compact External Combustion Engine With High Part-Load Efficiency

An external combustion engine design using steam is described which has good efficiency at full power and even better efficiency at the low power settings common for passenger vehicles. The engine is compact with low weight per unit power. All of its components fit in the engine compartment of a front-wheel drive vehicle despite the space occupied by the transaxle. It readily fits in a rear-drive vehicle. Calculated net efficiencies, after accounting for all losses, range, depending on engine size, from 28–32% at full power increasing to 33–36% at normal road power settings. A two-stage burner, 100% excess air, and combustion temperature below 1500°C assure complete combustion of the fuel and negligible NOx. The engine can burn a variety of fuels and fuel mixes, which should encourage the development of new fuels. Extensive software has been written that calculates full power and part-load energy balances, structural analysis and heat transfer, and performance in specified vehicles including using SAE driving cycles. Engines have been sized from 30 to 3200 hp. In general, fuel consumption should be at least 1.5 times lower than gasoline engines and about the same as diesels operating at low to moderate load settings. Due to this analysis, a prototype, when built, should perform as expected.

Thermo-Economic Analysis of Microalgae Co-Firing Process for Fossil Fuel-Fired Power Plants

A thermoeconomic analysis of microalgae co-firing process for fossil fuel-fired power plants is studied. A process with closed photobioreactor and artificial illumination is evaluated for microalgae cultivation, due to its simplicity with less influence from climate variations. The results from this process would contribute to further estimation of process performance and investment. The concept of co-firing (coal-microalgae or natural gas-microalgae) includes the utilization of CO2 from power plant for microalgal biomass culture and oxy-combustion of using oxygen generated by biomass to enhance the combustion efficiency. As it reduces CO2 emission by recycling it and uses less fossil fuel, there are concomitant benefits of reduced GHG emissions. The by-products (oxygen) of microalgal biomass can be mixed with air or recycled flue gas prior to combustion, which will have the benefits of lower nitrogen oxide concentration in flue gas, higher efficiency of combustion, and not too high temperature (avoided by available construction materials) resulting from coal combustion in pure oxygen. Two case studies show that there are average savings about $0.386 million/MW/yr and $0.323 million/MW/yr for coal-fired and natural gas-fired power plants, respectively. These costs saving are economically attractive and demonstrate the promise of microalgae technology for reducing greenhouse gas (GHG) emission.

A Roadmap for Rural Electrification in Developing Countries Using MiViPPs (Microutility Virtual Power Plants)

In this paper we present a road-map for rural electrification in developing countries by means of Renewable Energy based MiViPPs (Microutility virtual power plants). First and foremost a feasibility and viability analysis of the various upcoming and alternative renewable energy options is performed with respect to rural environmental constraints and demands. Renewable Energy based DDG’s (Decentralized Distributed Generation Units) offer the potential for affordable, clean electricity with minimal losses and effective maintenance and local cost recovery. But Independent DDG projects are fraught with their own issues mainly stemming from the unreliable and intermittent nature of the generated power and high costs. We propose an alternative approach to rural electrification which involves off grid DDG units operated at the local level taking advantage of feasible renewable energy technologies, which can effectively serve rural areas and reduce the urgency of costly grid extension. In MIVIPP model, a multitude of decentralized units (renewable energy based units and a non-renewable energy based unit for last mile backup) are centrally controlled and managed as part of an interconnected network, resulting into a virtual power plant that can be operated as a distributed power plant large enough to reliably serve all the local electricity demands in a cost effective manner. Finally, by a set of simulation results we establish how an automated MIVIPP (based on an Intelligent Auto Control System) effectively addresses all the issues pertaining to Dispersed DDG units by leveraging the scalability achieved by mutually augmenting the supplies from different Renewable Energy Based DDG units.

Converting Low-Grade Heat Into Power Using a Supercritical Rankine Cycle With Zeotropic Mixture Working Fluid

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power is proposed and analyzed in this paper. A supercritical Rankine cycle does not go through two-phase region during the heating process. By adopting zeotropic mixtures as the working fluids, the condensation process happens non-isothermally. Both of the features create a potential in reducing the irreversibility and improving the system efficiency. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle improves the cycle thermal efficiency, exergy efficiency of the heating and the condensation processes, and the system overall efficiency.

Simulation of Indoor Air Flow Fields in Buildings With Large Interior Spaces With Stratified Air Conditioning and Perforated Side Wall Diffusers

The energy consumption of AC (air conditioning) systems in large buildings is normally higher than the energy consumption in smaller buildings, and its indoor air flow field is also more complex than that in small building. To study the air flow mode and the indoor air flow fields in large spaces is of great significance to the energy conservation of AC systems and thermal comfort of the occupants. This paper presents an example using a large building that uses stratified air conditioning delivered through the linear slot sidewall diffusers and perforated sidewall diffusers. Using CFD simulation methods, three air flow field situations were simulated: (1) total air volume supplied from linear slot diffusers located in the middle of a side wall, (2) 50% flow through the linear slot diffusers the remainder supplied through the perforated sidewall diffusers, (3) 30% of the volume supplied with linear slot diffusers, 70% supplied through the perforated sidewall diffusers. The simulated results show that the third airflow mode is the optimal one for the three modes, which is good for achieving energy conservation and a comfortable building thermal environment in buildings with large spacial areas.

Second-Law Analysis in a Steam Power Plant for Minimization of Avoidable Exergy Destruction

Performance analysis of a 500 MWe steam turbine cycle is performed combining the thermodynamic first and second-law constraints to identify the potential avenues for significant enhancement in efficiency. The efficiency of certain plant components, e.g. condenser, feed water heaters etc., is not readily defined in the gamut of the first law, since their output do not involve any thermodynamic work. Performance criteria for such components are defined in a way which can easily be translated to the overall influence of the cycle input and output, and can be used to assess performances under different operating conditions. A performance calculation software has been developed that computes the energy and exergy flows using thermodynamic property values with the real time operation parameters at the terminal points of each system/equipment and evaluates the relevant rational performance parameters for them. Exergy-based analysis of the turbine cycle under different strategic conditions with different degrees of superheat and reheat sprays exhibit the extent of performance deterioration of the major equipment and its impact to the overall cycle efficiency. For example, during a unit operation with attemperation flow, a traditional energy analysis alone would wrongly indicate an improved thermal performance of HP heater 5, since the feed water temperature rise across it increases. However, the actual performance degradation is reflected as an exergy analysis indicates an increased exergy destruction within the HP heater 5 under reheat spray. These results corroborate to the deterioration of overall cycle efficiency and rightly assist operational optimization. The exergy-based analysis is found to offer a more direct tool for evaluating the commercial implication of the off-design operation of an individual component of a turbine cycle. The exergy destruction is also translated in terms of its environmental impact, since the irretrievable loss of useful work eventually leads to thermal pollution. The technique can be effectively used by practicing engineers in order to improve efficiency by reducing the avoidable exergy destruction, directly assisting the saving of energy resources and decreasing environmental pollution.

Minimizing On-Peak and Off-Peak Demands for a Thermal Storage System: Forecast Model Analysis to Predict Next Day Daily Average Load and Model Application

Thermal storage systems were originally designed to shift on-peak cooling production to off-peak cooling production to reduce on-peak electricity demand. Recently, however, the reduction of both on- and off-peak demands is becoming an exceedingly important issue. Reduction of on- and off-peak demands can also extend the life span and defer or eliminate the replacement of power transformers due to potential shortage of building power capacity caused by anticipated equipment load increases. Next day daily average electricity demand is a critical set point to operate chillers and associated pumps at the appropriate time. For this paper, a mathematical analysis of the annual daily average cooling of a building was conducted, and three real-time building load forecasting models were developed: a first-order autoregressive model, a random walk model, and a linear regression model. A comparison of results shows that the random walk model provides the best forecast. A complete control algorithm integrated with forecast model for a chiller plant including chillers, thermal storage system and pumping systems was developed to verify the feasibility of applying this algorithm in the building automation system. Application results are introduced in this paper as well.