Study of natural gas powered solid oxide fuel cell simulation and modeling

Solid oxide fuel cell (SOFC) system has been proposed to address the issue of waste gas emission due to gas flaring in oil and gas industry. System has unique advantage of consuming the waste gases and generating electricity as bye product. To analyze and quantify the proposed benefits, a robust cell performance model is highly desirable. A detailed understanding of SOFC component including electrode, electrolyte, interconnect, fuel processing and electrochemical reactions are first step in accurate determination of characteristic performance of the system. For this purpose, a review of modeling philosophies of SOFC system was undertaken in this study. Specifically, SOFC simulation and modeling using commercial software such as Aspen Plus, Aspen Hysys was focused in detail. SOFC models available in literature are either mathematical model or numerical models and ever evolving and improving. SOFC simulation rely on split approach due to absence of built-in module. Authors have developed an Aspen Hysys simulation model using split approach and discussed briefly here. Split approach approximates the SOFC phenomena, thereby inducing error. To overcome this deficiency, authors are developing a MATLAB based user model that can be integrated using 'user unit operation' available in Hysys. Details of the MATLAB program approach is included

A preliminary study of pyrolysis kinetics among various types of oil palm wastes

Oil palm waste such as empty fruit bunch (EFB), mesocarp fibre (MF) and palm kernel shell (PKS) are some of the abundant wastes produced by oil palm mills which have great potential to replace fossil fuel through the application of thermochemical processes like torrefaction which produces solid biofuel and pyrolysis that produces bio-oils. The study of the kinetics of a reaction indicates the activation energy and frequency factor of the reaction are often applied in the design of a reactor. In this study, the kinetics of pyrolysis of oil palm wastes were investigated with the aid of a derivative thermogravimetric graph (DTG) using thermogravimetric analyzers. Modelfitting methods including Arrhenius, Coats-Redfern (CR) and Kennedy-Clarke (KC) models were applied to obtain the kinetic parameters which are activation energy (E) and pre-exponential factor (A). As a result, it is clear that the CR model provides the most accurate estimates of the kinetics of the pyrolysis of oil palm wastes

Evaluation of oil palm waste mild pyrolysis kinetic parameters

With the goal of contrasting model-fitting and model-free methods for the kinetics of mild pyrolysis for empty fruit bunches (EFB), EFB were thermal decomposed and the profile was analysed using thermalgravimetric analysis (TGA). Coats-Redfern (CR) and Kissinger-Akahira-Sunose (KAS) methods were selected to represent model-fitting and model-free methods respectively. The activation energies (Ea) calculated for CR ranged between 22.45 and 26.31 kJ mol−1 (regression coefficient, R2 of 0.93 to 0.95) while the average Ea for KAS was 3.98 kJ mol−1. Compared with other typical model fuels, the mild pyrolysis of EFB from this work shows higher thermal instability, hence more reactive compared to previous works. Furthermore, the KAS method is more reliable in representing the mild pyrolysis process due to its higher overall regression coefficients showing that the assumptions of the KAS method are more accurate

The study of torrefaction in air and steam biomass gasification for syngas production through process simulation

Torrefaction is a process where biomass is converted to solid biofuel that can be sustainably used for energy generation to produce syngas. Limited information was found for a system with the combination of torrefaction and gasification. Therefore, a study by using a thermodynamic tool was conducted to study the best conditions of such system for empty fruit bunch (EFB). Four case studies were conducted for air gasification with and without torrefaction as Cases 1 and 2 respectively, steam gasification with and without torrefaction as Cases 3 and 4 respectively with varying equivalence ratio (ER), and steam-to-biomass (S/B) ratio applied in a process simulation model that is thermodynamic-based. It was found that the best case is Case 3 which increases the syngas concentration and higher heating value (HHV) by 4% and 0.4%, respectively, compared to Case 1. Therefore, steam gasification with torrefaction is the best method for syngas production

The effects of additives on the pelletization of raw and torrefied food waste

This study evaluates the effect of various binders on the pelletization of raw and torrefied food waste (FW) towards its physical properties, including density, moisture reabsorption, and tensile strength of the formed pellets. Three binders; starch, lignin, and vegetable oil, were used to make the raw and torrefied FW pellets. It was found that the addition of lignin helps to improve the density of both, raw and torrefied FW pellets by 40% for raw FW pellets and up to 27% improvement for the torrefied FW pellets. In addition, increasing the concentration of lignin may also reduce moisture reabsorption from 48% to 40% of raw FW pellets, and the sorption was further reduced for the torrefied FW pellets. The addition of lignin improves the tensile strength, mainly the torrefied FW pellets. Results show that lignin inclusion demonstrates significant enhancement to the physical properties of FW pellets

Torrefaction of oil palm fronds (OPF) as a potential feedstock for energy production processes

Oil palm fronds (OPF) and trunks contribute the highest biomass availability compared with other oil palm wastes. At the moment, they are usually left on the ground around the plantation area to decompose naturally and fertilize the soil. Previous researchers have focused on torrefaction of wood residues and other agricultural biomass with less attention has been paid to the utilization of Malaysia’s biomass such as OPF. Therefore, in this study, torrefaction of OPF was conducted in a tubular reactor at temperatures between 200 and 300 °C and residence time of 30 min. The results reveal an improved heating value as the temperature was increased, from 16.81 to 20.32 MJ/kg after the torrefaction process. The van Krevelen diagram also proved that torrefaction OPF could be classified as an intermediate, between raw OPF and coal. This proves the potential of OPF as one of the alternative feedstocks for energy production process through torrefaction

Evaluation of biofuel from the torrefaction of Malaysian food waste

The alarming issues related to the depletion of conventional fossil-based fuel resources have sparked interest in the search for alternative resources. Being a developing country facing tremendous growth, Malaysia is generating large amounts of food waste (FW). In this paper, an investigation of the potential of FW conversion to solid, coal-like fuel is carried out through torrefaction. The torrefaction process was carried out at temperatures between 260 and 320 °C and residence times of 15 to 45 min. The results showed that a higher torrefaction temperature leads to an increase in mass loss of the initial solid FW, which is also observed with increasing residence time. The loss of solid mass, nevertheless, increased the higher heating value (HHV) of the torrefied FW. A significant improvement was also observed in the volatile matter (VM) and moisture content (MC) of torrefied FW, which both decreased, while the carbon (C) content was increased. This suggests the improvement in the fuel properties of FW and its potential as a renewable energy source

Co-gasification of coal and empty fruit bunch in an entrained flow gasifier : A process simulation study

Co-gasification of coal and biomass is a proven method to improve gasification performance and a platform towards being independent of fossil fuel in power generation. Thus, this research was conducted to assess the feasibility of coal and EFB as fuels in co-gasification using Aspen HYSYS. A sequential model of an EFG was developed to predict the syngas composition and the optimum operating condition of the gasifier. The process was modelled with a set of five reactors to simulate various reaction zones of EFG in accordance with its hydrodynamics. The model considers devolatilization, char and volatile combustion, char gasification and water-gas shift reactions. The model prediction has exhibited excellent agreement with the experimental results. Three parameters of BR, Top and S/F were considered to account for their impacts on syngas composition in the process. The CE, CGE, PE and HHV were adopted as the indicators of process performance. The optimal values of BR, Top and S/F were 50%, 950°C and 0.75, respectively. While the value of CE reached above 90% and the maximum value of CGE, PE and HHV was obtained. This finding should be helpful in designing, operating, optimizing and controlling any co-gasification process especially in the entrained flow system

Thermodynamic evaluation of the aqueous stability of rare earth elements in sulfuric acid leaching of monazite through pourbaix diagram

The objective of this study is to construct Pourbaix diagram (Eh-pH diagram) for Lanthanum (La), Cerium (Ce) and Neodymium (Nd) elements at elevated temperatures. The Pourbaix diagram is able to map the stability area of the aqueous system, which will be useful to determine the process conditions that favor dissolution and possible rare earth (RE) metals that may be present in the system. In this work the process condition is based on the sulfuric acid leaching of monazite concentrate and it is carried out using HSC Chemistry 8.0 software. Addition of the sulfate ions from the sulfuric acid as the leaching solvent, introduces soluble metal-sulfate complexes. With temperature increase, the stability of these complexes increases. This can be observed based on the increased area in the Eh-pH diagram. Comparing the 3 rare earth elements in this study, it was determined that at elevated temperatures the order of stability is Ce>Nd>La

The effect of operating temperature and equivalence ratio in an entrained flow gasification of EFB

Biomass is a renewable and sustainable source of energy that can be used to generate electricity and other forms of power. Rapid economic growth in developing countries, growing energy demand, high dependence on global and local transportation, pollution, depletion of sources, and endangered national security of energy importing countries have raised the awareness of the need for non-fossil based renewable energy sources. This paper presents the effect of operating temperature and equivalence ratio (ER) on the gasification of empty fruit bunch (EFB) in an entrained flow reactor. EFB is one of the most abundant biomass source in Malaysia, being the second largest palm oil processing nation in the world. The temperature ranges of between 700 °C to 900 °C and ER of 0.2 to 0.4 were studied to find the most optimum condition for biomass gasification in an entrained flow gasification system. It was found that the production of synthesis gas increases as the temperature increased, along with the carbon conversion and higher heating value of gas product. The most optimum operating temperature and ER for biomass gasification in the entrained flow gasifier were found at 900°C and 0.3 respectively