Marcus Thern

Experimental and Theoretical Results of a Humidification Tower in an Evaporative Gas Turbine Cycle Pilot Plant

The Evaporative Gas Turbine Pilot Plant has been in operation at Lund Institute of Technology in Sweden since 1997. In this cycle low-grade heat in the flue gases is utilized for water evaporation into the compressed air in the humidification tower. This result in, amongst others, power augmentation, efficiency increase and lower emissions. This article presents the experimental and theoretical results of the humidification tower, in which simultaneous heat and mass transfer occurs. A theoretical model has been established for the simultaneous heat and mass transfer occurring in the humidification tower and it has been validated with experiments. The humidification tower in the pilot plant can be operated at several operating conditions. An after-cooler makes it possible to chill the compressor discharge air before entering the humidification tower. The saturation temperature of the incoming compressed air can thereby be varied from 62 to 105°C at the operating pressure of 8 bar(a). It has been shown that the air and water can be calculated throughout the column in a satisfactory way. The height of the column can be estimated with an error of 10% compared with measurements. The results from the model are most sensitive of the properties of the diffusion coefficient, viscosity and thermal conductivity due to the complexity of the polar gas mixture of water and air.

Waste Heat Recovery from Multiple Heat Sources in a HD Truck Diesel Engine Using a Rankine Cycle - A Theoretical Evaluation

Few previous publications investigate the possibility of combining multiple waste heat sources in a combustion engine waste heat recovery system. A waste heat recovery system for a HD truck diesel engine is evaluated for utilizing multiple heat sources found in a conventional HD diesel engine. In this type of engine more than 50% of heat energy goes futile. The majority of the heat energy is lost through engine exhaust and cooling devices such as EGRC (Exhaust gas recirculation cooler), CAC (Charge air cooler) and engine cooling. In this paper, the potential of usable heat recuperation from these devices using thermodynamic analysis was studied, and also an effort is made to recuperate most of the available heat energy that would otherwise be lost. A well-known way of recuperating this heat energy is by employing a Rankine cycle circuit with these devices as heat sources (single loop or dual loop), and thus this study is focused on using a Rankine cycle for the heat recovery system. Furthermore, this paper investigates the possibilities and challenges involved in coupling these different sources in a single Rankine cycle and the selection of suitable working fluid for this Rankine cycle. The study shows that with recuperation from these multiple sources it is possible to recover 5-10% of the otherwise wasted heat energy, which results in ~5% power increase. REFPROP was used for studying fluid properties, and the commercial software IPSEpro is used to build and simulate the Rankine cycle. (Less)

Effect of A/B-site substitution on oxygen production performance of strontium cobalt based perovskites for CO2 capture application

Oxy-fuel combustion is one of the proposed technologies which have the potential to achieve zero CO2 emission. Strontium cobalt based perovskite oxygen carriers are promising materials for air separation with a high selectively for oxygen. And these perovskites can produce an oxygen enriched carbon dioxide stream for an oxy-fuel combustion process. The relatively low oxygen production yield may be a drawback of this type of material for this technology. This paper presents an effective approach by A/B-site substitution to improve the oxygen production performance of the perovskites. In this study, a series of different A/B-site substituted SrCo0.8Fe0.2O3−δ were prepared by an EDTA–citrate sol–gel combustion synthesis method. Fixed-bed experiments and TGA measurements were performed to study the effects of A/B-site substitution on cyclic oxygen adsorption/desorption performance of the synthesized samples. The experimental results indicate that the oxygen desorption amounts of different A-site substituted perovskites decrease in the order of BaCo0.8Fe0.2O3−δ > Ba0.5Sr0.5Co0.8Fe0.2O3−δ > SrCo0.8Fe0.2O3−δ > Sr0.5Ca0.5Co0.8Fe0.2O3−δ > MgCo0.8Fe0.2O3−δ. Moreover, B-site substitution by different transition metal ions can significantly modify oxygen adsorption capacity and oxygen desorption performance of SrCo0.8Fe0.2O3−δ. Furthermore, oxygen desorption performance can be improved when Fe ions of the perovskite SrCo0.8Fe0.2O3−δ are substituted by Zr, Cr, Zn, and Ni ions.

Conceptual Design of a Mid-Sized Semi-Closed Oxy-Fuel Combustion Combined Cycle

This paper presents the study of a mid-sized semi-closed oxy-fuel combustion combined cycle (SCOC-CC) with net power output around 108 MW. The paper describes not only the power balance and the performance of the SCOC-CC, but also the conceptual design of the SCOC turbine and compressor. A model has been built in the commercial heat and mass balance code IPSEpro to estimate the efficiency of semi-closed dual-pressure oxy-fuel combustion combined cycle using natural gas as a fuel. In order to obtain the real physical properties of the working fluids in IPSEpro, the code was linked to the NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP). The oxy-fuel turbine was modeled with the in-house Lund University package LUAX-T. Important features such as stage loading, loss modeling, cooling and geometric features were included to generate more accurate results. The oxy-fuel compressor has been modeled using a Chalmers university in-house tool for conceptual design of axial compressors. The conceptual design of the SCOC-CC process has a net efficiency of 47 %. The air separation unit and CO2 compression reduce the cycle efficiency by 10 and 2 percentage points, respectively. A single-shaft configuration was selected for the gas turbine simplicity. The rotational speed chosen was 5200 rpm and the turbine was designed with four stages. All stage preliminary design parameters are within ranges of established industrial axial turbine design limits. The main issue is the turbine exit Mach number; the stage must be lightly loaded in terms of pressure ratio to maintain the exit Mach number below 0.6. The compressor is designed with 18 stages. The current value of the product of the annulus area and the blade rotational speed squared (AN2) was calculated and found to be 40*10^6.

Dynamic Modeling of a Parabolic Trough Solar Thermal Power Plant with Thermal Storage Using Modelica

ABSTRACT Concentrating solar power (CSP) technology with thermal energy storage is a renewable and emerging technology. In this work, dynamic models for analyzing and evaluating energy storage concepts and its interaction with the solar field and the power block have been developed. A physical model of a 50 MW CSP plant has been implemented in the modeling language Modelica. The models are developed in a modular, flexible structure with a well-defined interface to easily replace and test modules of various detail and complexity. Models include turbine island, steam generator, solar field, and thermal energy storage system. In addition, a decentralized control configuration has been developed. Results have been successfully validated against the reference plant key steady-state data. Dynamic response of the power block has shown expected behavior, and transient durations were comparable with settling times predicted in literature. Furthermore, the performance of the plant has been evaluated during a typical summer day including effects such as variation of solar irradiance, charging and discharging the heat storage system, and dumping excess heat in the solar field. The summer day scenario results agreed with published performance of the plant.

A new IPSEpro library for the simulation of binary mixtures of real fluids in power cycle analysis

Increasing efforts to produce power from renewable resources and improve the efficiency of current industrial processes have turned the spotlight on organic Rankine cycles (ORC). The use of refrigerant mixtures in these cycles offers a wide range of possibilities for fluid selection and optimization. Moreover, zeotropic mixtures are reported to yield better cycle performances due to their better thermal match with the source and sink streams. In this work a new IPSEpro® library for the simulation of power cycles using binary mixtures was developed. With this library the working fluid can be defined as the mixture of any pair of suitable fluids contained in the Refprop database.

Aerodynamic Considerations in the Thermodynamic Analysis of Organic Rankine Cycles

Due to the increasing interest of producing power from renewable and non-conventional resources, organic Rankine cycles are finding their place in today’s thermal energy mix. The main influencers on the efficiency of an organic Rankine cycle are the working fluid and the expander. Therefore most of the research done up to date turns around the selection of the best performance working media and the optimization of the expansion unit design. However, few studies consider the interaction of the working fluids in the turbine design, and how this fact can affect the overall thermodynamic cycle analysis. In this work we aim at including the aerodynamic behavior of the working fluids and their effect on the turbine efficiency in the thermodynamic analysis of an organic Rankine cycle. To that end, we proposed a method for the estimation of the characteristics of an axial in-flow turbine in an organic Rankine cycle simulation model. The code developed for the characterization of the turbine behavior under the working fluid properties evaluated the irreversibilities associated to the aerodynamic losses in the turbine. The organic Rankine cycle was analyzed by using IPSEpro process simulator. A set of candidate working fluids composed of selected organofluorines and organochlorines was chosen for the analysis. The thermophysical properties of the fluids were estimated with the equations of state implemented in Refprop. Results on the energy and exergy overall performances of the cycle were analyzed for a case study with standard source and sink temperatures. For each fluid the number of stages and geometry of the turbine were optimized. It was observed that some working fluids that could initially be considered as advantageous from a thermodynamic point of view, had an unfavorable impact on the turbine efficiency, thus increasing the irreversibilities of the cycle. We concluded that if the influence of the working fluid on the turbine performance is underestimated, the real performance of the organic Rankine cycle could show unexpected deviations from the theoretical results. (Less)

Trigeneration: Thermodynamic performance and cold expander aerodynamic design in humid air turbines

Improving electrical efficiency has been proposed as the most convenient means of reducing, e.g. CO2 emission from power plants. Increasing fuel utilization through combined heat and power generation is another useful measure for emission reduction. Trigeneration technology for the production of heat, power and cooling is an interesting alternative for further improvement of fuel utilization. Previous studies at The Department of Heat and Power Engineering in Lund. Sweden, have shown that wet cycles are the best candidates, with a high potential to achieve fuel utilization higher than 100%, based on the fuels lower heating value [1, 2, 8]. Apart from high fuel utilization, trigeneration technology can produce cooling without the use of harmful cooling agents. The basic principle of trigeneration is to interrupt the expansion at an elevated pressure level and extract heat from the working medium. The final expansion then takes place at low temperature admission levels resulting in a very low temperature at the turbine exhaust. In this paper results from both thermodynamic analysis of the humid air turbine concept in conjunction with trigeneration. and the expander design criterion required for realization of the last section of the expander are presented. The thermodynamic study gives the boundary conditions for the cold turbine design. Optimum conditions for the inlet to the cold expander are a pressure of 2 to 3 bar and a temperature of 47 (Less)

Theoretical and experimental evaluation of a plate heat exchanger aftercooler in an evaporative gas turbine cycle

The evaporative gas turbine pilot plant (EvGT) has been in operation at Lund Institute of Technology in Sweden since 1997. This article presents the experimental and theoretical results of the latest process modifications made, i.e. the effect of the installation of an aftercooler. The purpose of the aftercooler is to increase the performance of the cycle by utilizing more low-level heat in the humidification tower. The chosen aftercooler is of plate heat exchanger type, which, is very compact, has high thermal efficiency and low pressure drop. The installation of an aftercooler lowers the temperature of the air entering the humidification tower. This also lowers the temperature of the circulating humidification water, which facilitates the extraction of more low-level heat from the economizer. This low-level heat can be utilized to evaporate more water in the humidification tower and thus increase the gas flow in the expander. The pilot plant has been operated at different loads and the measured results has been evaluated and compared with theoretical models. The performance of a plate heat exchanger in power plant applications has also been evaluated. Experience from the measurements has then been used for the potential cycle calculations. It has been shown that the aftercooler lowers the flue gas temperature in the pilot plant to 93 (Less)

Evaluation of Different Turbocharger Configurations for a Heavy-Duty Partially Premixed Combustion Engine

The engine concept partially premixed combustion (PPC) has proved higher gross indicated efficiency compared to conventional diesel combustion engines. The relatively simple implementation of the concept is an advantage, however, high gas exchange losses has made its use challenging in multi-cylinder heavy duty engines. With high rates of exhaust gas recirculation (EGR) to dilute the charge and hence limit the combustion rate, the resulting exhaust temperatures are low. The selected boost system must therefore be efficient which could lead to large, complex and costly solutions. In the presented work experiments and modelling were combined to evaluate different turbocharger configurations for the PPC concept. Experiments were performed on a multi-cylinder engine. The engine was modified to incorporate long route EGR and a single-stage turbocharger, however, with compressed air from the building being optionally supplied to the compressor. Experimental combustion heat release rates and boundary conditions were used to validate a simulation model. This model was then used to compare three different turbochargers: two single-stage turbochargers and one two-stage. The whole speed and load range was covered in the simulations to determine the engine performance. The influence of high EGR rates as well as the effect of charge air and EGR cooler gas outlet temperatures were also investigated. The simulation results showed that the two-stage turbocharger was able to give the highest load over the whole speed range with a brake mean effective pressure of 25.6 bar, whereas the two single-stage turbochargers reached 22.2 and 23.1 bar respectively. The average brake efficiency was 39.3, 39.7 and 40.2 %. It was found that decreasing the inlet temperature is critical for obtaining high loads and system efficiencies. Finally, it was shown that the optimal amount of EGR was dependent on the turbocharger efficiency and cooler temperatures.