Fuel Optimization for Power, Heat and CHP Systems Including Emissions Regulations and Ambient Conditions

Combined Heat and Power systems have been used all around the world due to their effective and viable way of transforming energy from fossil fuel. Indeed, the advantage of lower greenhouse gas emissions compared to those obtained in conventional power or conventional heat generation systems have been an important factor giving CHP systems an advantage over these conventional ones. Certainly CHP has been, and continues to be, a good practice while renewable technologies become more economically. While these technologies emerge it is important to continue minimizing these greenhouse gas emissions from conventional and CHP units as much as possible. This paper deals with the fuel optimization of power, heat and CHP systems including emissions and ambient conditions constraints. Ambient conditions variations are evaluated before solving the optimization and then introduced to the problem to consider their effects.

Experimental Investigation of a Pilot Compression Chiller With Alternatives Refrigerants R401a and R134a

This paper reports the results of an experimental investigation on a pilot compression chiller (4 kW cooling capacity) working with R401a and R134a as R12 alternatives. Experiments are conducted on a single-stage vapor compression refrigeration system using water as a secondary working fluid through both evaporator and condenser. Influences of cooling water mass flow rate (170–1900 kg/h), cooling water inlet temperature (27–43°C) and chilled water mass flow rate (240–1150 kg/h) on performance characteristics of chillers are evaluated for R401a, R134a and R12. Increasing cooling water mass flow rate or decreasing its inlet temperature causes the operating pressures and electric input power to reduce while the cooling capacity and coefficient of performance (COP) to increase. Pressure ratio is inversely proportional while actual loads and COP are directly proportional to chilled water mass flow rate. The effect of cooling water inlet temperature, on the system performance, is more significant than the effects of cooling and chilled water mass flow rates. Comparison between R12, R134a and R401a under identical operating conditions revealed that R401a can be used as a drop-in refrigerant to replace R12 in water-cooled chillers.

Analysis of Clearances in Combined Screw Machines

Changes caused by differential expansion between the rotors and the casing occur in the high pressure clearances in both the compressor and expander sections when expansion and compression are performed together in a single oil free machine of the twin-screw type. These are more difficult to control than when the two functions are carried out in separate machines. The clearance changes affect both the performance and reliability of the machine but can be controlled by using different materials of construction for each section. Clearances, predicted by the assumption of linear expansion of the components, were included in a well-proven software package for performance estimation of both screw compressors and expanders and the results compared with experimental data. It was found that the clearance in the machine, being dependent on the temperature, could be estimated fairly accurately by matching measured discharge temperature and the temperature obtained by the estimation model. Therefore, a simple expansion analysis of the main machine clearances appeared to be an adequate tool for use in the design of these machines in order to optimise performance and prevent the machine seizing as a result of differential thermal expansion during operation.

3-E Analysis of a Heat Pump Driven by a Micro-Cogenerator

The cogeneration, or the combined production of electric (and/or mechanical) and thermal energy, is a well established technology, which has important environmental benefits and it has been noted by the European Community as one of the first elements to save primary energy, to avoid network losses and to reduce the greenhouse gas emissions. In particular, the study will be focused on the micro-cogeneration process with micro-combined heat and power system, or MCHP (electric power output ≤ 15 kW), which represents a valid and interesting application of this technology applicable, above all, to residential and light commercial users. This paper presents the Energy, Economic and Environmental (3-E) analysis of a natural gas-fired MCHP in combination with an electric heat pump (EHP). The 3-E analysis of the MCHP/EHP begins with the results of a detailed experimental activity developed in a test facility [1] for a wide range of conditions. Two operating conditions were simulated: a heating mode with co-production of electric and thermal energy, and a cooling mode with co-production of electric, thermal and cooling energy (tri-generation). The annual operating performance, also based on the typical features of the Italian market, is also discussed with a simplified approach.

Computing the Entropy Generation Rate for Turbomachinery Design Applications: Can a Diagnostic Tool Become a Predictive One?

The calculation of the entropy generation rate ds/dt in turbomachinery passages is a straightforward task once the velocity and temperature fields are known. The global entropy generation rate in the passage, dS/dt = ∫V(x,y,z)(ds/dt)dxdydz, is of course directly related to the cascade efficiency, but its functional dependence on the local characteristics of the flowfield is not immediately detectable: the left-hand side is a single-valued quantity that cannot, as such, be used as the objective function of an inverse design procedure (because a local modification of a single detail of the blade geometry invariably produces non-negligible effects on the entire flow domain). On the contrary, knowledge of the local entropy generation rate in each point of a channel provides immediate useful insight into the relative importance of the different sources of irreversibility in the process. There are numerous examples of the application of entropy generation maps as a diagnostic design tool, i.e., to locate problematic areas that demand for design “improvements”: these are, though, basically heuristic and intrinsically non-systematic approaches. On the other hand, the adoption of a functional based on the local entropy generation rates is difficult both from a theoretical and from a practical point of view, and there is no example yet of a blade profile optimization in which the objective function is ∫V(x,y,z)(ds/dt)dxdydz, to be minimized over the design domain V. This paper presents a rational derivation of the relationships between the local and global entropy generation and the local features of the flow, and illustrates them by means of two examples derived from applications developed in the last years by the Turbomachinery Group led by the author at the University of Roma 1. The merits and limits of the use of such a “local” approach are critically discussed, and in the Conclusions a procedure is proposed for the development of an inverse design approach based on a properly constrained objective function based on ds/dt: though quite intensive from a computational point of view, there are indications that such an approach may become feasible on realistic geometries in the near future.

The Effects of Feeding Configurations to Water Flooding and General Performance of a Proton Exchange Membrane Fuel Cell

The performance of a Proton Exchange Membrane Fuel Cell (PEMFC) using different feeding configurations has been studied. Three bipolar plates, namely serpentine, straight channel and interdigitated designs, were arranged in different combinations for the PEMFC anode and cathode sides. Nine combinations in total were tested under different flow rates, working temperatures and loadings. The cell voltage versus current density and the cell power density versus current density curves were obtained. After operating the PEMFC under high current densities, the cell was split and the water flooding in the feeding channels was visually inspected. Experimental results showed that for different feeding configurations, interdigitated bipolar plate in anode side and serpentine bipolar plate in cathode side had the best performance in terms of cell voltage-current density curve, power density output rate, percentage of flooded area in the feeding channels, the pattern of flooding and the fuel utilization rate.

Scavenging Energy From Piezoelectric Materials for Wireless Sensor Applications

Wireless sensors are an emerging technology that has the potential to revolutionize the monitoring of simple and complex physical systems. Prior research has shown that one of the biggest issues with wireless sensors is power management. A wireless sensor is simply not cost effective unless it can maintain long battery life or harvest energy from another source. Piezoelectric materials are viable conversion mechanisms because of their inherent ability to covert vibrations to electrical energy. Currently a wide variety of piezoelectric materials are available and the appropriate choice for sensing, actuating, or harvesting energy depends on their characteristics and properties. This study focuses on evaluating and comparing three different types of piezoelectric materials as energy harvesting devices. The materials utilized consisted on PZT 5A, a single crystal PMN 32%PT, and a PZT 5A composite called Thunder. These materials were subjected to a steady sinusoidal vibration provided by a shaker at different power levels. Gain of the devices was measured at all levels as well as impedance in a range of frequencies was characterized. Results showed that the piezoelectric generator coefficient, g33, predicts the overall power output of the materials as verified by the experiments. These results constitute a baseline for an energy harvesting system that will become the front end of a wireless sensor network.

Influence of Steam Injection on Thermal Efficiency and Operating Temperature of GE-F5 Gas Turbines Applying VODOLEY System

An industrial gas turbine has the characteristic that turbine output decreases on hot summer days when electricity demand peaks. For GE-F5 gas turbines of Mashad Power Plant when ambient temperature increases 1° C, compressor outlet temperature increases 1.13° C and turbine exhaust temperature increases 2.5° C. Also air mass flow rate decreases about 0.6 kg/sec when ambient temperature increases 1° C, so it is revealed that variations are more due to decreasing in the efficiency of compressor and less due to reduction in mass flow rate of air as ambient temperature increases in constant power output. The cycle efficiency of these GE-F5 gas turbines reduces 3 percent with increasing 50° C of ambient temperature, also the fuel consumption increases as ambient temperature increases for constant turbine work. These are also because of reducing in the compressor efficiency in high temperature ambient. Steam injection in gas turbines is a way to prevent a loss in performance of gas turbines caused by high ambient temperature and has been used for many years. VODOLEY system is a steam injection system, which is known as a self-sufficient one in steam production. The amount of water vapor in combustion products will become regenerated in a contact condenser and after passing through a heat recovery boiler is injected in the transition piece after combustion chamber. In this paper the influence of steam injection in Mashad Power Plant GE-F5 gas turbine parameters, applying VODOLEY system, is being observed. Results show that in this turbine, the turbine inlet temperature (T3) decreases in a range of 5 percent to 11 percent depending on ambient temperature, so the operating parameters in a gas turbine cycle equipped with VODOLEY system in 40° C of ambient temperature is the same as simple gas turbine cycle in 10° C of ambient temperature. Results show that the thermal efficiency increases up to 10 percent, but Back-Work ratio increases in a range of 15 percent to 30 percent. Also results show that although VODOLEY system has water treatment cost but by using this system the running cost will reduce up to 27 percent.

A Novel Brayton Cycle With the Integration of Liquid Hydrogen Cryogenic Exergy Utilization

Stored or transported liquid hydrogen for use in power generation needs to be vaporized before combustion. Much energy was invested in the H2 liquefaction process, and recovery of as much of this energy as possible in the re-evaporation process will contribute to both the overall energy budget of the hydrogen use process, and to environmental impact reduction. A new gas turbine cycle is proposed with liquefied hydrogen (LH2) cryogenic exergy utilization. It is a semi-closed recuperative gas turbine cycle with nitrogen as the working fluid. By integration with the liquid H2 evaporation process, the inlet temperature of the compressor is kept very low, and thus the required compression work could be reduced significantly. Internal-fired combustion is adopted which allows a very high turbine inlet temperature, and a higher average heat input temperature is achieved also by internal heat recuperation. As a result, the cycle ha ry attractive thermal performance with the predicted energy efficiency over 79%. The choice of N2 as the working fluid is to allow the use of air as the oxidant in the combustor. The oxygen in the air combines with the fuel H2 to form water, which is easily separated from the N2 by condensation, leaving the N2 as the working fluid. The quantity of this working fluid in the system is maintained constant by continuously evacuating from the system the same amount that is introduced with the air. The cycle is environmentally friendly because no CO2 and other pollutant are emitted. An exergy analysis is conducted to identify the exergy losses in the components and the potential for further system improvement. The biggest exergy destruction is found occurring in the LH2 evaporator due to the relatively higher heat transfer temperature difference. The energy efficiency and exergy efficiency are 79% and 52%, respectively. The system has a back-work ratio only 1/4 of that in a Brayton cycle with ambient as the heat sink, and thus can produce 30.14 MW (53.9%) more work, with the LH2 cryogenic exergy utilization efficiency of 54%.

AB Initio Simulation on Grotthuss Mechanism

Ab initio simulations on Grotthuss mechanism have been carried out. Using the simulation results together with the existing experimental data, all the popular propositions for Grotthuss mechanism, including the one recently proposed by Noam [1], have been checked. Combining with the charge distribution calculation and the movement of the positive charge center inside the protonated water cluster during the proton diffusion process, only one mechanism is shown probable, while all the other proposed mechanisms are excluded. According to this probable mechanism, the high mobility of proton inside water is caused by the high diffusion rate of H5O2+, while the diffusion of H5O2+ is mainly induced by the thermal movement of water molecules at the second solvation shell of H5O2+ cation and the Zundel polarization inside the cation ion. Furthermore, the external field and thermo-dynamic effects play important roles during the transport process by affecting the reorientation of water molecules at the neighborhood of the second solvation shell of H5O2+ to induce the Zundel polarization and by providing the energy for the cleavage of the hydrogen bond between a newly formed water molecule and H5O2+. Because the weight (fraction) of H5O2+ among protonated water clusters decreases as temperature increases, this proposed mechanism is considered to play the dominant role only when temperature is below 572 K, above which, protons transport by other mechanisms become dominant.