Sibel Özdoğan

Autothermal reforming as a hydrocarbon fuel processing option for PEM fuel cell

Abstract In this paper, we discuss the results of a preliminary systematic simulation study: the effect of operating parameters on the product distribution and conversion efficiency of high and low molecular weight hydrocarbon mixtures in autothermal reforming (ATR). The HYSYS simulation software has been utilized for the simulations and calculations of the fuel processing reactions. It is desired to produce hydrogen-rich reformate gas with as low as possible CO formation, which requires different combinations of TATR, S/C and O/C ratios. Fuel properties only slightly effect the general trends.

Correlations towards prediction of petroleum fraction viscosities: an empirical approach

New empirical correlations have been developed to predict viscosities of petroleum fractions (C5–C15) at 40°C under atmospheric pressure. Viscosities, densities and quantitative hydrocarbon analyses of 42 petroleum fractions were experimentally determined. Viscosities were correlated with density and/or average molecular weight data.

Simulation of Biomass and/or Coal Gasification Systems Integrated With Fuel Cells

This paper presents the results of a system simulation study. The HYSYS 3.1 - ASPEN code has been used for simulation. The system consists of a fixed bed gasifier followed by reforming and clean-up units. The produced hydrogen gas is fed to a PEM fuel cell. The gasified hydrocarbons are hazelnut shells, bark, rice straw, animal waste, and two lignites. Hydrocarbon properties, gasification, and reforming process parameters all affect the system efficiency. The effect of the moisture content and oxygen to carbon ratio of the hydrocarbon fees on the fuel processing and overall system efficiencies are presented. The overall efficiency of the system increases with increasing hydrocarbon fees oxygen to carbon ratio; this tendency is more evident at higher moisture levels.

Correlations for the sulfur contents of Turkish coals exposed to ashing and devolatilization conditions at 750°C and 950°C

Abstract Total sulfur, sulfur forms, CaO, MgO and ash were analyzed in 19 selected Turkish coals with widely varying characteristics (from bituminous coal to low grade lignite) according to the American Society for Testing and Materials (ASTM) standards. The combustible sulfur contents of coals, the sulfur retained in the coal ash, the volatile sulfur content, and the sulfur retained in the coal char (the non-volatile sulfur content) were determined at two different temperatures, namely 750°C and 950°C. Formulae were developed to correlate the before-mentioned coal properties with the combustible sulfur and char sulfur contents of coals at 750°C and 950°C. Correlations based on the sulfur forms and CaO and MgO contents gave the least erroneous results.

Simulation Study of a PEM Fuel Cell System with Steam Reforming

Abstract This article summarizes the results of a study for a 100 kWe DC electrical power PEM fuel cell system. The system consists of a pre-steam reformer, a steam reformer, high and low temperature shift reactors, a preferential oxidation reactor, a PEM fuel cell, a combustor, and an expander. Acceptable net electrical efficiency levels can be achieved via intensive heat integration within the PEM fuel cell system. The calculations take into account the auxiliary equipment such as pumps, com pressors, heaters, coolers, heat exchangers and pipes. The process simulation package “Aspen-HYSYS 3.1’’ has been used. The operation parameters of the reactors have been determined considering all the technical limitations involved. A gasoline type hydrocarbon fuel has been studied as hydrogen rich gas source. Thermal efficiencies have been calculated for all of the major system components for selected operation conditions. The fuel cell stack efficiency has been calculated as a function of cell numbers (500, 750, 1000, and 1250 cells). Efficiencies of all of the major system components along with auxiliary unit efficiencies determine the net electrical efficiency of the PEM fuel cell system. The obtained net electrical efficiency levels are between 34 (500 cells) to 41% (1250 cells). #Contributed by the Organizing Committee for the First International Exergy, Energy and Environment Symposium (IEEES-1). Paper presented at IEEES-1, Izmir, Turkey,13-17 July 2003. Manuscript received by IJGE on 2003-12-23; final revision received on 2004-02-10. Corresponding guest editors: I. Dincer and A. Hepbasli.

Estimation of CO2 emission factors of coals

New formulae have been developed to estimate CO2 emission potentials of coals from easily obtainable coal properties such as heating value, volatile matter and fixed carbon contents. The magnitude of CO2 emission per unit amount of coal combusted as well as per unit amount of coal heating value were selected as CO2 emission potential indicators of coals. Within this frame proximate, ultimate and calorific value analysis results of 39 Turkish coals with widely varying rank characteristics were evaluated via regression analyses. Simple formulae with mean differences less than 3% were obtained. Published data of 122 coals from abroad were used to check some of the developed formulae and to search for less erroneous correlations.

The behavior of sulphur forms of three lignites exposed to pyrolysis temperatures between 350 and 950 °C

Three selected Turkish lignites were pyrolyzed at seven different temperatures between 350 and 950 °C for 7 min. The lignites and their chars were analyzed quantitatively for their total sulphur content and sulphur forms. The alkaline oxide contents of the lignites and selected char samples were determined. Calcium compounds, which prevail in all of the parent lignites, undergo various chemical changes during pyrolysis. The results clearly indicate that both the temperature and the calcium oxide contents affect the behavior of various sulphur forms during pyrolysis. The organic sulphur decomposition and formation is the most difficult to predict.

Formation and dispersion of toxic combustion by-products from small-scale combustion systems

Pollutants of primary interest are SOx, CO, NOx, methane and other volatile organics, and particulate matter. First- and second-law efficiencies have been evaluated. Next, the turbulent flows of exhaust gases through the stack have been modeled for both natural draft stacks and stacks equipped with forced draft fans. Velocity and temperature profiles in the stacks and for the plumes have been obtained from the numerical model for specified meteorological conditions.

Correlations towards prediction of petroleum fraction viscosities: a semi-theoretical approach

Abstract A new semi-theoretical method based on Enskogs hard sphere theory for dense fluids and the principle of corresponding states is presented for predicting viscosity of petroleum fractions (C 5 –C 15 ) at 40°C under atmospheric pressure. Viscosities, densities, normal boiling points and quantitative hydrocarbon analyses of 42 petroleum fractions were experimentally determined. The critical properties and the average molecular weights of the petroleum fractions were calculated by the Riazi Daubert equation. The predictions were compared with experimental data. Satisfactory results were obtained. The average error of the 42 petroleum fractions could be decreased to below 3.4% utilising only density and average boiling point as input parameters. The addition of hydrocarbon group weight fractions as additional input parameters decrease the average error to around 2.6%. When acyclic rich and cyclic rich samples are handled separately, the average errors are below 2%.

Solar, industrial process-heat applications in selected Turkish industries

We discuss the potential and economic feasibility of solar, industrial processheat applications in the Turkish food, textile and chemical industries. The study covers 18 sites and end-use temperatures up to 120 and 150 °C. A solar system composed of parabolic troughs but without thermal storage and to be backed up by the existing conventional boiler is chosen. The system-size range investigated is 500–20,000 m2. The economic criteria applied are net present value analysis and the determination of internal rate of return. Break-even net fuel prices and break-even system sizes, which make the net present value equal to zero, are also calculated. Levelized energy-costs analysis and the method of the discounted pay-back period have been included in the study.