Showing papers on "Thermal efficiency published in 1994"

The maximum power output and maximum efficiency of an irreversible Carnot heat engine

Abstract: The effect of thermal resistance, heat leakage and internal irreversibility resulting from the working fluid on the performance of a Carnot heat engine is investigated using a new cyclic model. The power output and efficiency of the heat engine are adopted as objective functions for heat engine optimization. The optimal performance of the heat engine is analysed systematically. Some significant results are obtained. For example, the maximum power output and maximum efficiency are determined. The efficiency of the heat engine at maximum power output and the power output of the heat engine at maximum efficiency are also calculated. Curves of the power output varying with the efficiency of the heat engine are obtained. These curves can indicate clearly the rational regions of efficiency and power output for an irreversible Carnot heat engine. It is pointed out that all the conclusions concerning a reversible Carnot heat engine, an endoreversible Carnot heat engine only affected by thermal resistance and an irreversible Carnot heat engine with internal irreversibility and/or heat leakage can be deduced from the results in this paper.

The Efficiency of Industrial Processes: Exergy Analysis and Optimization

Abstract: 1. Coefficients of Energy Transformation (CET) and Exergy Efficiency (CEE) for Different Industrial Systems. Thermodynamic approaches to evaluating system performance. Efficiency of mechanics, hydraulics an electrical technics. Coefficient of energy transformation (CET) and efficiency. 2. The Concepts and Values Needed for Determination of CEE. Energy and exergy. The particularities of the notions of "environment " and "surroundings" in exergy analysis. The exergy of steady matter flow. Chemical exergy and its parts. The exergy of industrial fuels. The exergy of solutions. Exergy of energy flows. 3. Coefficients of Exergy Efficiency. Kinds and characteristics of exergy losses. Generalised determination of the CEE: Statement of the problem. Approaches to determination of the CEE in thermodynamic systems. Calculation of transit exergy. Recommendations for determination of CEE at different levels of exergy analysis. 4. CEE Reflecting a System's Internal Thermodynamic Efficiency. CEE of closed engineering systems. CEE of the main processes in the systems for energy and material transformation. 5. Fields of Application of CEE. Basic concept. Creation of engineering systems - "to be or not to be? " Estimation of new phenomena for improvement of engineering systems. Thermodynamic analysis of engineering systems. Thermodynamic optimization of engineering systems. 6. Generalised Dependence of the Efficiency of the System on the Efficiency of the System Elements. Structure of engineering systems and the internal connection of its elements. Relationship of the efficiency of a system and its elements connected in series and in parallel. Relationship of the efficiency of a system and its elements in any complex connections. Application of the general formula relating efficiency of a system and efficiencies of its component parts for the analysis and thermodynamic optimization of engineering systems. 7. The functions of Technical Value and its Relationship with CEE. Application to Energy Storage and Upgrading by Separation and Mixing. Storage and upgrading of energy by separation and mixing (SUESAM) processes. The sorption heat pump (S.H.P.): Exergy analysis. Technical appraisal of a S.H.P. Technical appraisal of hybrid systems (absorption-compression) to upgrade industrial waste heat. 8. Efficiency in Techno-Economic and Ecological calculations. Selection of objective functions for thermodynamic and techno-economic optimization: Their relationship with efficiency. Comparison of the exergetic and operating cost optima of heat exchangers. Efficiency applications to costing in multi-product plants. Optimisation of equipment and operating costs. Efficiency of biological processes. References. Index.

Measurements of Emissions and Radiation for Methane Combustion within a Porous Medium Burner

Abstract: In this paper, we report the results of an experimental investigation of methane-air combustion within a porous medium burner for various equivalence ratios and flow rates. Measurements of emissions and radiant output are presented. The results indicate that CO and NOx, emissions increase with flame speed. For a given equivalence ratio, however, NOx, emissions are fairly constant over the range of flame speed studied. The radiant output increases but the radiant thermal efficiency decreases with flame speed.

Models for predicting the performance of Brayton-cycle engines

Abstract: Gas turbine performance is the result of choices of type of cycle, cycle temperature ratio, pressure ratio, cooling flows, and component losses. The output is usually given as efficiency (thermal, propulsive, specific thrust, overall efficiency) versus specific power. This paper presents a set of computer programs for the performance prediction of shaft-power and jet-propulsion cycles: simple, regenerative, intercooled-regenerative, turbojet, and turbofan. Each cycle is constructed using individual component modules. Realistic assumptions are specified for component efficiencies as functions of pressure ratio, cooling mass-flow rate as a function of cooling technology levels, and various other cycle losses. The programs can be used to predict design point and off-design point operation using appropriate component efficiencies. The effects of various cycle choices on overall performance are discussed.

Finite-time thermodynamic analysis of a radiative heat engine with internal irreversibility

Abstract: A relation between the design parameters of an internally and externally irreversible radiative heat engine is presented to find the maximum power and the efficiency at maximum power output. It was found that the ratio of the reservoir temperatures must be less than half of the cycle-irreversibility parameter and the ratio of area of the heat exchangers must be less than 1.0 for optimum thermal efficiency and maximum power output. Increasing the cycle-irreversibility parameter and the heat-transfer area of the cold side improve thermal efficiency and maximum power output.

Staged air, low NOx burner with internal recuperative flue gas recirculation

Abstract: A gas-fired burner 10 incorporating a mixing chamber for mixing air, fuel, and recirculated flue gas with reduced heat loss from the recirculated flue gas is disclosed. The burner is configured for the staged introduction of combustion air to provide a fuel-rich combustion zone and a fuel-lean combustion zone. Internal recirculating flue gas channels 80 deliver cooled flue gas to the primary fuel-rich combustion zone. A valve assembly 150 may be provided to control the flow of flue gas. Secondary air passages 40 concentrically arranged within the recirculating flue gas channels 80 deliver superheated, staged air to the secondary fuel-lean combustion zone. Heat is transferred from the hot flue gas to the counterflowing cooler secondary air. The burner achieves reduced NO x emission levels in high temperature applications which use preheated combustion air with no or minimal loss in thermal efficiency from flue gas recirculation.

Analysis of a Basic Chemically Recuperated Gas Turbine Power Plant

Abstract: This paper investigates a basic'' Chemically Recuperated Gas Turbine (a basic'' CRGT is defined here to be one without intercooling or reheat). The CRGT is of interest due to its potential for ultralow NO[sub x] emissions. A computer code has been developed to evaluate the performance characteristics (thermal efficiency and specific work) of the Basic CRGT, and to compare it to the steam-injected gas turbine (STIG), the combined cycle (CC) and the simple cycle gas turbine (SC) using consistent assumptions. The CRGT model includes a methane-steam reformer (MSR), which converts a methane-steam mixture into a hydrogen-rich fuel using the waste'' heat in the turbine exhaust. Models for the effects of turbine cooling air, variable specific heats, and the real gas effects of steam are included. The calculated results show that the Basic CRGT has a thermal efficiency higher than the STIG and simple cycles not quite as high as the combined cycle.

Split stream boiler for combined cycle power plants

Abstract: A process and equipment for generating useful power comprising a special split stream heat recovery boiler 108 in combination with a gas turbine 20 and a steam turbine 80 to form a combined cycle. A steam-injected gas turbine 20 and alternately a condensing steam turbine 116 may be utilized. A topping high temperature and high pressure topping steam turbine 80 optionally may be included. Chemical heat recuperation via natural gas reformation may be incorporated within the boiler 108 to increase cycle efficiency further and to lower NOx formation without excess CO. The heat recovery boiler 206 yields increased efficiency and power output heretofore unexpected for the combined cycle compared to conventional combined cycle equipment.

Indirect-fired gas turbine bottomed with fuel cell

Abstract: An indirect-heated gas turbine cycle is bottomed with a fuel cell cycle with the heated air discharged from the gas turbine being directly utilized at the cathode of the fuel cell for the electricity-producing electrochemical reaction occurring within the fuel cell. The hot cathode recycle gases provide a substantial portion of the heat required for the indirect heating of the compressed air used in the gas turbine cycle. A separate combustor provides the balance of the heat needed for the indirect heating of the compressed air used in the gas turbine cycle. Hot gases from the fuel cell are used in the combustor to reduce both the fuel requirements of the combustor and the NOx emissions therefrom. Residual heat remaining in the air-heating gases after completing the heating thereof is used in a steam turbine cycle or in an absorption refrigeration cycle. Some of the hot gases from the cathode can be diverted from the air-heating function and used in the absorption refrigeration cycle or in the steam cycle for steam generating purposes.

Blade for gas turbine

Abstract: A gas-turbine moving blade made of a Ni-base superalloy containing less grain boundary strengthening elements, in which a blade portion is formed of a single crystal and the rest is formed of columnar crystals, and a gas turbine including the moving blade. A thermal efficiency of the gas turbine can be improved to 35% or more, and a thermal efficiency of complex power generation with a steam turbine can be improved to 45% or more.

Hybrid internal combustion engine

Abstract: A method and apparatus for improving efficiency and reducing emissions of an internal combustion engine coupled to an inertial load An apparatus is provided for controlling the energy exchange between engine and load so that the maximum conversion efficiency is obtained for both directions of energy flow Valve controls make the engine a variable displacement expander or compressor so that kinetic energy received from the load by the engine may be stored as compressed air and returned to the load by the engine These controls eliminate all fuel consumption and emissions when power is not required by the load, and utilize the stored energy in conventional engine operation

Gas Turbine Cycles With Solid Oxide Fuel Cells—Part I: Improved Gas Turbine Power Plant Efficiency by Use of Recycled Exhaust Gases and Fuel Cell Technology

Abstract: The energy conversion efficiency of the combustion process can be improved if immediate contact of fuel and oxygen is prevent4ed and an oxygen carrier is used. In a previous paper (Harvey et al., 1992), a gas turbine cycle was investigated in which part of the exhaust gases are recycled and used as oxygen-carrying components. For the optimized process, a theoretical thermal efficiency of 66.3% was achieved, based on the lower heating value (LHV) of the methane fuel. One means to further improve the exergetic efficiency of a power cycle is to utilize fuel cell technology. Solid oxide fuel cells (SOFC) have many features that make them attractive for utility and industrial applications. In this paper, the authors will therefore consider SOFC technology. In view of their high operating temperatures and the incomplete nature of the fuel oxidation process, fuel cells must be combined with conventional power generation technology to develop power plant configurations that are both functional and efficient. In this paper, the authors will show how monolithic SOFC (MSOFC) technology may be integrated into the previously described gas turbine cycle using recycled exhaust gases as oxygen carriers. An optimized cycle configuration will be presented based upon a detailed cyclemore » analysis performance using Aspen Plus[trademark] process simulation software and a MSOFC fuel cell simulator developed by Argonne National Labs. The optimized cycle achieves a theoretical thermal efficiency of 77.7%, based on the LHV of the fuel.« less

Methods and systems for improving thermal efficiency, determining effluent flows and for determining fuel mass flow rates of a fossil fuel fired system

Abstract: Methods and systems are disclosed for: (1) determining and improving the thermal efficiency of a fossil fuel power plant, such as a combustion turbine system, by indirect assessment of input fossil fuel flow rate, and direct observation of various gaseous effluents; (2) determining total effluent gas flow rates; (3) determining input fuel mass flow rates; and (4) determining flow rates of various constituent gases making up the effluent gas.

Monitoring Feedwater Flow Rate and Component Thermal Performance of Pressurized Water Reactors by Means of Artificial Neural Networks

Abstract: The fouling of venturi meters, used for steam generator feedwater flow rate measurement in pressurized water reactors (PWRs), may result in unnecessary plant power derating On-line monitoring of these important instrument channels and the thermal efficiencies of the balance-of-plant components are addressed The steam generator feedwater flow rate and thermal efficiencies of critical components in a PWR are estimated by means of artificial neural networks The physics of these systems and appropriate plant measurements are combined to establish robust neural network models for on-line prediction of feedwater flow rate and thermal efficiency of feedwater heaters in PWRs A statistical sensitivity analysis technique was developed to establish the performance of this methodology

The Effects of Load Height on the Emissions from a Natural Gas-Fired Domestic Cooktop Burner

Abstract: A single production cooktop burner was studied at three levels of thermal input, to determine the effects of load height on its efficiency and gaseous emissions. In this work, load height was defined as the vertical distance from the center of the base of the load vessel to the top of the burner ports. To simulate practical operation as closely as possible, the production gas injector was used, so that primary aeration varied with thermal input in these experiments. The Australian Gas Association regulations limit the operating range of load height for this burner to values between 7mm (CO/CO2 40%). Minimum NO2 emission rates of 8.7,8.0 and 8.8 ng/J were observed at load heights of 25, 40 and 48 mm respectively, at thermal inputs of 0.49, 0.83 and 1.65 kW respectively. A new measure of pollutant emission was proposed, to provide a means of assessing the “balance” between the requirements for lower emission rate and higher thermal efficiency. The total emission of a ...

Gas Turbine Cycles With Solid Oxide Fuel Cells—Part II: A Detailed Study of a Gas Turbine Cycle With an Integrated Internal Reforming Solid Oxide Fuel Cell

Abstract: The energy conversion efficiency can be improved if immediate contact of air and fuel is prevented. One means to prevent this immediate contact is the use of fuel cell technology. High-temperature solid oxide fuel cells (SOFC) have many features that make them attractive for utility and industrial applications. However, in view of their high operating temperatures and the incomplete nature of the fuel oxidation process, such fuel cells must be combined with conventional power generation technology to develop power plant configurations that are both functional and efficient. Most fuel cell cycles proposed in the literature use a high-temperature fuel cell running at ambient pressure and a steam bottoming cycle to recover the waste heat generated by the fuel cell. With such cycles, the inherent flexibility and shorter start-up time characteristics of the fuel cell are lost. In Part 1 of this paper, a pressurized cycle using a solid oxide fuel cell and an integrated gas turbine bottoming cycle was presented. The cycle is simpler than most cycles with steam bottoming cycles and more suited to flexible power generation. In this paper, the authors will discuss this cycle in more detail, with an in-depth discussion of all cycle component characteristics andmore » losses. In particular, they will make use of the fuel cell's internal fuel reforming capability. The optimal cycle parameters were obtained based on calculations performed using Aspen Technology's ASPEN PLUS process simulation software and a fuel cell simulator developed by Argonne National Laboratory. The efficiency of the proposed cycle is 68.1%. A preliminary economic assessment of the cycle shows that it should compare favorable with a state-of-the-art combined cycle plant on a cost per MWe basis.« less

Performance Evaluation of Low Heat Rejection Engines

Abstract: Improving the performance of the Chinese B135 six-cylinder direct injection turbocharged and turbocompounded Low Heat Rejection Engine (LHRE) was based on experimental and analytical studies. The studies were primarily applied on a B1135 single-cylinder LHR engine and a conventional water-cooled B1135 single-cylinder engine. Performance of the B1135 LHRE was worse than that of the conventional B1135 due to a deterioration in the combustion process of the B1135 LHRE. The combustion process was improved and the fuel injection system was redesigned and applied to the B135 six-cylinder LHRE. The new design improved the performance of the LHRE and better fuel economy was realized by the thermal energy recovered from the exhaust gases by the turbocompounding system.

Thermal power engine and its operating method

Abstract: A method for improving the total production of useful energy in an energy utilization system of a thermal power engine (1) that is liquid-cooled and is used for the production of thermal energy as well as mechanical energy. In the energy utilization system, thermal energy is taken from the coolant of the engine cooling system. At least a part of the coolant from the engine is led to a vaporization space (5) where, either by lowering the pressure or by increasing the amount of thermal energy within that space (5), a part of the coolant is transformed to vapor. The vapor is used within the energy utilization system for energy transport and/or as a medium for recovering energy.

Performance and exhaust emissions of a compression ignition engine operating on ester fuels at increased injection pressure and advanced timing

Abstract: Effects of increased injection pressure and advanced injection timing on the performance and exhaust emission characteristics of a direct injection, naturally aspirated John Deere 4239D engine operating on methyl soyoil ester (IV (iodine value) = 125−135) and methyl tallow ester (IV = 47−53) were studied. The test engine was fully instrumented to provide all the required measurements for determination of the needed performance and exhaust emission variables. Four treatment combinations consisting of two levels of injection pressure (18.6 MPa and 24.1 MPa) and two levels of injection timing (19° before top-dead-centre (BTDC) and 14° BTDC) were employed. The physical and chemical properties of the test fuels were earlier determined in accordance to the ASTM and AOCS standards. Results indicated that the engine operating on ester fuels at the manufacturer's injection pressure-timing setting (18.6 MPa and 14° BTDC) had lower carbon monoxide and unburned hydrocarbon carbon emissions and smoke levels, despite a slight increase in brake specific fuel consumption, as compared with when it was operating on No. 2 diesel fuel (control fuel). There were no significant differences in the engine brake specific fuel consumption and brake thermal efficiency between the ester fuels. However, between the two ester fuels, the saturated ester fuel (methyl tallow ester) showed slightly lower carbon monoxide and unburned hydrocarbons emissions, and higher smoke levels. The engine performance and exhaust emission characteristics of the engine operating on the ester fuels at advanced injection timing were better than when operating at increased injection pressure. Poor fuel combustion near the maximum operating power level was indicated with the engine operating on ester fuels at increased injection pressure. Complete fuel combustion was suppressed during high fuel flow probably due to the lack of oxygen within the spray envelope. Thus, fuels in some locations within the spray envelope that were too rich to burn escaped as unburned hydrocarbons, or burned incompletely causing high carbon monoxide and smoke levels in the exhaust emissions. Operating the engine at such conditions for extended periods could give rise to deposits problems in the combustion chamber. The engine performance and exhaust emission characteristics between the two ester fuels were almost similar at advanced injection timing and increased injection pressure.

Energy efficient afterburner

Abstract: A small energy efficient afterburner for oxidizing the byproducts of incomplete combustion is disclosed. Gases are forced into a firebox, where a heating element maintains a temperature above the flash point for the more common and undesirable pollutants. Typical temperatures are 500° C. to 800° C. for burning hydrocarbons coming from internal combustion engines or wood stoves. After gases pass through the firebox, they are forced into a chamber adjacent to the firebox intake, so that heat energy may be transferred to the incoming gases, thereby greatly increasing the thermal efficiency of the device. Greater efficiencies are achieved by putting a catalytic surface in the firebox, and by insulating the afterburner exterior.

Power process utilizing humidified combusted air to gas turbine

Abstract: A process for producing mechanical power utilizing compressed humidified hot air and a fuel, which are mixed together and combusted and the resulting hot combustion gas is expanded through a gas turbine. The air is initially compressed and intercooled (34) against a water stream, and then further compressed and passed directly to a heat recovery unit (40) where it is humidified (42) using the water from the compressed air intercooling step. The compressed humidified air is further heated and combined with a fuel in a combustor (46), and the resulting hot combustion gas is expanded through a gas turbine (48) to produce mechanical power needed for driving the air compression. The hot turbine exhaust gas is cooled (51) against the compressed humidified air stream (43) and against the water stream (41), and then discharged to the atmosphere. By eliminating a usual separate air aftercooling and saturator unit upstream of the air combined humidifying and heating step, process thermal efficiency for the present process is increased and equipment cost reduced.

Ammonia absorption refrigeration cycle for combined cycle power plant

Abstract: A power plant utilizing combined mode steam and gas turbines runs a refrigeration cycle powered by the energy in the rejected heat from the steam turbines and/or other waste heat source to cool the ambient inlet air to the gas turbines to have them operate more efficiently

LNG Power Recovery

Abstract: The thermal efficiency of a Carnot cycle is limited by the maximum and minimum temperatures available. The construction of LNG (liquid natural gas) terminals and the need to vaporize LNG offers a c...

Hybrid central receiver

Abstract: A hybrid combined cycle power plant including a solar central receiver (7) for receiving solar radiation and converting it to thermal energy The power plant includes a molten salt heat transfer medium (8) for transferring the thermal energy to an air heater (9) The air heater (9) uses the thermal energy to preheat the air from the compressor (12) of the gas cycle The exhaust gases from the gas cycle are directed to a steam turbine (16) for additional energy production

Cogeneration system and control therefor with auxiliary heating elements and thermal barrier

Abstract: A cogeneration system that is particularly suited to residential use comprises an internal combustion engine, preferably diesel, coupled to a generator, preferably of the induction type. The generator and the engine are thermally isolated from each other so that the engine can run hotter (and thus more efficiently) without adversely affecting the generator. A supplemental electric heater supplies additional heat when the thermal output of the engine is insufficient. A dual stage controller for the heater controls its operation for enhanced efficiency. A generator controller enables the generator to serve the additional function of starting the engine when heat is called for, thus obviating a separate starting motor and related equipment. The system provides a high operating efficiency.