Journal of Energy Engineering

This paper studies and compares the results of a simple and fast heuristic method, genetic algorithm (GA), and the exhaustive search method (ES) concerning the minimization of fuel consumption of a natural gas compressor station (CS). The results, obtained for an input data set [natural gas flow rate of 150 million standard cubic meters per day (MMSCMD), suction pressure of 5.45 MPa, and discharge pressure of 6.9 MPa], showed that for a CS with similar turbo-compressor (TC) units, all of the applied methods achieved the same solution (fuel consumption rate of $3.620\mathrm{kg}/\mathrm{s}$). By contrast, for a CS with dissimilar TC units, the GA and ES methods attained a lower fuel consumption rate ($3.738\mathrm{kg}/\mathrm{s}$) than that obtained by the heuristic method ($3.753\mathrm{kg}/\mathrm{s}$). The effect of changing the CS flow rate, suction, and discharge pressures on optimal fuel consumption rate was also investigated. In the first case study, a 100 MMSCMD (or 100%) increase in the flow rate, 8.3 bar (or 13%) increase in discharge pressure, and 8.3 bar (or 14%) reduction in the suction pressure of the CS caused the optimal fuel consumption rate to increase by $2.41\mathrm{kg}/\mathrm{s}$ (or 99%), $1.02\mathrm{kg}/\mathrm{s}$ (or 33%), and $1.72\mathrm{kg}/\mathrm{s}$ (or 60%), respectively. In the second case study, for the same changes of flow rate, discharge, and suction pressures mentioned previously, the optimal fuel consumption rate increased by $2.72\mathrm{kg}/\mathrm{s}$ (or 112%), $1.03\mathrm{kg}/\mathrm{s}$ (or 32%), and $1.71\mathrm{kg}/\mathrm{s}$ (or 58%), respectively.

This paper presents the experimental work carried out in winter for a double slope solar still with external reflectors. Experiments were performed in Dhahran, a city in the eastern province of Saudi Arabia at latitude 26°N. Four inclined mirrors were placed around the still to reflect extra solar irradiance onto the solar still. Numerical analysis was also carried out using heat and mass transfer inside the solar still and was validated with the experimental results. The external reflectors were shown to significantly enhance the productivity of the solar still and an increase in the distillate by approximately 82% was observed in this study. The present study is a partial implementation of two patents submitted recently in the field of solar distillation.

A simple yet extensible electrical system model, suitable for studying the effects of renewable energy integration, is presented. The model uses publically available historical data to create a representative sample time-series of system loads. Historical conditions are scaled to future target years in accordance with projected system-wide electrical load growth. Renewable energy generation is evaluated regionally and subregionally from coincident climatic conditions, combined with regionally appropriate generator transform functions. Renewable energy generation is scaled to target years based on legislated requirements or projected growth. Future dispatchable generation requirements and conditions are developed as the difference between the projected load and projected renewable energy deployment. A case study conducted in the eastern Canadian province of Nova Scotia is presented. Legislated renewable energy targets will significantly increase the ramp rates required of dispatchable generation.

Dimethyl carbonate (DMC) has advantages of solubility in diesel and high oxygen content. Its application in diesel engines has won increasing popular focus. A DMC/diesel blend with 10% DMC by volume (D10) is prepared to investigate its combustion process and emissions. Although the volumetric energy density drops slightly with the addition of DMC, minor adjustments of the injection parameters would achieve the output power of the original engine. The heat release process is more concentrated because the addition of low boiling point DMC boosts the atomization and mixing with air of the blended fuel. Hence the indicated thermal efficiency of D10 increases remarkably as compared with reference diesel. The emissions of hydrocarbons and carbon monoxide are apparently reduced for D10. Nitrogen oxide (${\mathrm{NO}}_{\mathrm{x}}$) emissions increase owing to the addition of oxygenated fuel DMC, but this is reduced by the decline in engine load. The oxygen from the D10 blend plays a role in reducing particulate matter (PM) emissions. There is a scope for balancing the ${\mathrm{NO}}_{\mathrm{x}}$ and PM emissions.

The present article analyzes the potential contribution of a hybrid energy system in a scenario with a high deployment of wind farms. The hybrid energy system consists of a small/medium-sized nuclear reactor (SMR), a biomass processing plant, and an optional hydrogen production plant. The SMR operates at full power constantly and is able to switch its thermal output to supply the steam turbine for electricity generation or to supply the biomass production plant for heat processes. The hybrid energy system management is electricity demand following, so the sum of the electricity generated by both the hybrid energy system and the aggregated wind farm tends to meet electricity demand. The hydrogen production plant is considered to be an electricity consumer and operates during times of wind power surplus. Wind farm capacities of 100–2,000 MW were investigated. For these, the optimal SMR size in the hybrid energy system varies from 200 to $300{\mathrm{MW}}_e$. The increase in SMR size is limited owing to the maximum heat demand for the biomass processing plant, which is $\mathrm{1,033}{\mathrm{GWH}}_{th}$ annually (expected heat for biomass processing within a radius of 80 km). For a 1,000 MW wind farm, the (standard) deviations between wind farm output and electricity demand are reduced by 32 percentage points with the aid of the hybrid energy system without the hydrogen production plant. An additional reduction of 30 percentage points is achieved using the hydrogen plant, but this then has a very low utilization (15%).

To understand the effect of an air injector on airlift performance, an experimental study of the influence of air exit-port arrangement on the mass flow rate of solids and lifting efficiency was performed. An airlift with a riser 1,500-mm long and 40-mm diameter was designed and tested. At a constant submergence ratio, the mass flow rate of solids and lifting efficiency were significantly affected by the air exit-port arrangement. As the air flow rate increased, the mass flow rate of solids increased to a maximum value and then decreased slightly. The curve relating the air flow rate to lifting efficiency was $m$-shaped, i.e., it contained two local maxima. The air flow rate at the second efficiency maximum was approximately equal to the air flow rate at which the solid mass flow rate was maximal. When the measurement results were expressed in dimensionless form, the relation between the volume flow of slurry and air flow rate was approximately the same for all air exit-port arrangements, and was in good agreement with a theoretical model that was presented based on the Bernoulli equation.

This paper examines the effects of passive solar heating produced by a direct passive solar system consisting of windows for direct insolation in a residential building located in Nis, Serbia. A mathematical model is presented to calculate the temperature in the room of a building with a direct passive solar system, depending on the size of the opening, window slope (slanting or vertical position), orientation of the room, and the size of the eave above the window (if it is installed). Using the proposed mathematical model, the inner air temperatures of a thermally insulated residential building with a direct passive solar system are analyzed for different building orientations during the period between January and March of 2008. Two software packages are developed to support the proposed mathematical model.

Deregulation of the energy sector has created new markets for producers as well as opportunities for consumers to meet their needs in a more customized way. Yet, traditional building energy management systems operate statically by adjusting air or water flow in heating and cooling systems in response to predetermined triggers, in relation to large deviations in the zone temperature from the equipment’s set-point temperature. The writers provide decision support to managers of buildings through dynamic control of the installed equipment that seeks to minimize energy costs. Assuming that the building’s occupants have comfort preferences expressed by upper and lower limits for the temperature, the writers model the effect of active equipment control (through changes to either the set point or valve flow) on the zone temperature, taking into account the external temperature, solar gains, building’s shell, and internal loads. The energy required to change the zone temperature in each time period is then used to calculate the energy cost in the objective function of an optimization problem. By implementing the model for actual public buildings, the writers demonstrate the advantages of more active equipment-management in terms of lower costs and energy consumption.

Dwindling energy resources and associated environmental costs have resulted in a serious need to design and construct energy-efficient buildings. One of the strategies to develop energy efficient structural materials is the incorporation of phase-change materials (PCM) in the structural element. This paper presents details of a finite-element-based framework that is used to study the thermal performance of structural precast concrete wall elements with and without a layer of phase-change material. The simulation platform developed can be implemented for a wide variety of input parameters. In this study, two different locations in the continental United States, representing different ambient temperature conditions, two different types of concrete—normal weight and lightweight—two PCM types, and different PCM layer thicknesses are considered with an aim of understanding the energy flow across the wall member. The energy flow through the inside face of the wall, which determines the indoor HVAC energy consumption, is used as the defining parameter. Phase-change materials incorporating lightweight concrete wall design reduces HVAC costs in hot climates compared with the use of normal concrete. An ad hoc optimization scheme is also implemented where the PCM thickness is fixed but its location and properties are varied. Numerical results show (1) a slightly better response for PCM placed closer to the inside face of the wall compared with other locations, especially for hotter climates, and (2) energy savings are possible with small changes in baseline values, information that a PCM manufacturer can possibly use to design the next generation of phase-change materials.

In this work, a tiny-oil ignition cyclone burner is proposed for a 300-MW down-fired pulverized coal-fired boiler to reduce oil consumption during the start up and low load operation of the boiler. Numerical simulations are carried out to investigate the gas-solid two-phase flow in the burner. The Reynolds stress model (RSM) is employed to model the swirling gas flow in a cyclone burner, and the stochastic Lagrangian method is used to calculate the movement of the particle. A Foster Wheeler (FW) cyclone burner is also simulated to compare with the tiny-oil ignition cyclone burner. The results show that the gas flow characteristics in the FW cyclone burner agree well with previous studies, indicating that the calculation models employed for the swirling flow is reasonable and acceptable. The tiny-oil ignition cyclone burner has the same operation characteristics with the FW cyclone burner in the industrial applications, as the differences of the vent air ratio and the separation efficiency between the two burners are less than 10%. But the tiny-oil ignition cyclone burner would produce a more favorable effect on the coal particle ignition, coal combustion, and the NOx reduction than FW cyclone burner.

Smart microgrid systems are distributed energy production systems intended to increase local renewable energy use and power supply reliability and lower transmission loss and carbon dioxide emissions. Optimal energy management operation strategies are essential to smart microgrid systems. This research formulates an optimization model for smart microgrid systems and establishes optimal operating strategies. The operating framework was tested on a smart microgrid system currently being developed at the Institute of Nuclear Energy Research, Taiwan. The smart microgrid system is equipped with energy storage devices (batteries) as well as photovoltaic and wind power generation systems. Sensitivity analyses of electricity demand growth and storage device investment were conducted for the smart microgrid model. The results show that optimal battery investment should be determined based on battery efficiency, power supply, load, and the rate of load change.