Anna Sciazko

A comparative study of two various empirical methodologies for deriving kinetics of methane/steam reforming reaction

Despite methane/steam reforming is the conventional method for hydrogen production, there are widespread disagreements between formulations of the process kinetic derived in the literature. In the present research, the mathematical baseline of the classical calculation methodologies of the reaction kinetic are presented and compared. They include methodologies based on: I) the assumed constant partial pressure of steam and methane and II) the minimization of the summed relative standard deviation of the calculated reaction constant. Their results are compared with generalized least squares approach. The calculation methodologies are correlated with the planed experimental measurement set. This paper aims for the clarification of the observed differences and pointing the most suitable methodology for the decreasing the overall uncertainty of the model.

An attempt to minimize the temperature gradient along a plug-flow methane/steam reforming reactor by adopting locally controlled heating zones

Plug flow reactors are very common in the chemical process industry, including methane/steam reforming applications. Their operation presents many challenges, such as a strong dependence of temperature and composition distribution on the inlet conditions. The strongly endothermic methane/steam reforming reaction might result in a temperature drop at the inlet of the reactor and consequently the occurrence of large temperature gradients. The strongly non-uniform temperature distribution due to endothermic chemical reaction can have tremendous consequences on the operation of the reactor, such as catalyst degradation, undesired side reactions and thermal stresses. To avoid such unfavorable conditions, thermal management of the reactor becomes an important issue. To carry out thermal management properly, detailed modeling and corresponding numerical analyses of the phenomena occurring inside the reforming system is required. This paper presents experimental and numerical studies on the methane/steam reforming process inside a plug-flow reactor. To optimize the reforming reactors, detailed data about the entire reforming process is required. In this study the kinetics of methane/steam reforming on the Ni/YSZ catalyst was experimentally investigated. Measurements including different thermal boundary conditions, the fuel flow rate and the steam- to-methane ratios were performed. The reforming rate equation derived from experimental data was used in the numerical model to predict gas composition and temperature distribution along the steam-reforming reactor. Finally, an attempt was made to control the temperature distribution by adopting locally controlled heating zones.

Experimental and analytical evaluation of the drying kinetics of Belchatow lignite in relation to the size of particles

Water removal is a key technology for enhancing efficient utilization of lignite in power generation. An inherent characteristic of lignite, attributed to the large amount of water kept within the fuel, is the factor decreasing the thermal efficiency of lignite-fired power plants. This paper presents the research results on investigating the drying kinetics of Belchatow lignite excavated in the Central Poland in prior to developing a water removal system. Lignite drying test was conducted in superheated steam atmosphere at the temperature range of 110-170 °C. Spherically shaped samples, of which the diameter is 2.5 mm, was used. The experimental results were then analysed with previously conducted measurements of 5, 10, 30 mm samples to investigate the influence of particle size. The presented analysis shows the agreement of the evaluated drying rate at the CDRP to the experimental data. The obtained experimental results were used to predict the drying behaviour of the group of particles. The proposed investigation clarifies the size dependence of the drying characteristics of the multisize group of lignite particles.

An experimental verification of numerical model on superheated steam drying of Belchatow lignite

Due to low production costs, lignite is an important component of energy mixes of countries in its possession. However, high moisture content undermines its applicability as fuel for power generation. Drying in superheated steam is a prospective method of upgrading quality of lignite. The study aimed to validate the drying model of lignite from Belchatow mine in Poland. The experimental investigation on superheated steam drying of lignite was previously conducted. Spheres of 10 mm in diameter were exposed to the drying medium at the temperature range of 110-170oC. The drying behaviour was described in the form of moisture content, drying rate and temperature profile curves against time. With the application of basic coal properties (e.g. density, water percentage, specific heat) as well as the mechanisms of heat and mass transfer in subsequent stages of the process, the numerical model of drying was constructed. It was tentatively verified with reference to experimental results both in terms of drying parameters and temperature. The model illustrated drying behaviour in the entire range of conditions. Nevertheless, further development of numerical model is desirable regarding accuracy of the process parameters.

Influence of geological variations on lignite drying kinetics in superheated steam atmosphere for belchatow deposit located in the central Poland

Lignite-fired coal power plants suffer from a significant heat loss due to the high moisture content in this energy carrier. Water removal from fuel is an indispensable treatment for improving the combustion process, which will foster the efficient utilization of lignite. Superheated steam fluidized bed drying is expected for this purpose in a power generation sector. Understanding drying kinetics of lignite will greatly reinforce design process of a dryer. Physical features as well as the drying behaviour may be divergent among the lignite originated from different depths and positions in a certain mine. To reveal and clarify the influence of the geological features, the drying characteristics of several grades of lignite from the Belchatow mine in Poland were investigated. The attempts to clarify the influence of the divergent properties of the investigated samples on the drying kinetics in superheated steam were presented in this paper.