EFFECT OF PAC ON MBR PERFORMANCE DURING THE TREATMENT OF SYNTHETIC WASTEWATER CONTAINING ORGANIC COMPOUNDS

S t r e s z c z e n i e W artykule zaprezentowano przygotowanie modelu procesu zgazowania roślin energetycznych. Przeprowadzono badania eksperymentalne zgazowania analizowanej biomasy z wykorzystaniem zgazowarki ze złożem stałym. Najwyższą wartość opałową gazu uzyskano ze zgazowania Miskanta olbrzymiego (3.84 MJ/m3n). Pozyskane dane eksperymentalne posłużyły do walidacji modelu zbudowanego przy użyciu oprogramowania Aspen Plus. Zbudowany model właściwie odzwierciedla proces zgazowania w analizowanym reaktorze. Względne różnice między wartościami opałowymi gazów ze zbudowanego modelu oraz z eksperymentu nie przekroczyły 1%. K e y w o r d s : Energy crops; Gasification; Modeling; Experimental research. 3/2017 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 135 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 3/2017 A . S k o r e k O s i k o w s k a , W . U c h m a n , S . W e r l e 136 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 3/2017 authors concluded that gasification, compared with direct combustion and anaerobic digestion, performs best in almost all analyzed categories (global warming potential, non-renewable energy use, acidification, eutrophication and respiratory organics). The only category in which the anaerobic digestion is better is non-renewable energy use. What is more, in the analyses concerning natural gas as a fuel, using Miscanthus instead of natural gas to generate electricity reduces non-renewable energy use and global warming. Gasification process can be a valuable method of energetic utilization of energy crops planted in the areas of wasteland for the purpose of phytoremediation of soil. The resulting process gas, after the removal of impurities, can potentially be used for the production of electricity and heat in a cogeneration system. There is little research on the gasification of various types of energy crops which should be deeply revised due to high potential of this technology to positively impact the environment. A mathematical model of the gasification process should also be developed for integration with energy system models to provide broad system analysis of possible use of energy crops as a source of energy for combined heat and power plant. To reach the stated goal, first, experimental research on gasification of the selected plant species in a fixed bed generator using air as a gasifying agent was performed. The model of gas generator was then built and verified based on the measured data. The modeling of the gasification process, owing to a variety of chemical reactions and the heterogeneity of the process, is not an easy problem. However, numerical models allow multi-criteria analysis and thermodynamic optimization of energy systems to be conducted (considering, e.g., thermodynamic or economic criteria), significantly reducing the risk associated with investment in this type of system. Numerical models allow to determine the performance characteristics of the devices included in the systems as well as those of the whole integrated systems to be determined, considering many significant quantities. In the case of gasification systems, these are, e.g., the type (composition) of fuel, the type of gasifying medium, and the process of purification or cooling of the resulting process gas. There are two approaches to the construction of gas generator models to be found in the literature. One approach involves the construction of models, which considers the kinetics and dynamics of the gasification process and is mainly based on modeling through CFD (computational fluid dynamics) methods; the second is based on equilibrium models, most often using minimization of the Gibbs function. The main advantages of the latter approach are the much smaller time investment for the construction of the model and realization of the calculations, the lack of a need to know a number of key kinetic parameters of the process and the less time-consuming analysis; however, this approach is more simplified and does not map the complex physicochemical kinetics occurring in the real process [21, 22]. In this study, the second approach was chosen. Regardless of the choice of the modeling method, one of the most important stages of the modeling process is the validation of the model on the basis of real experimental data. This increases the credibility and verification of the correctness of the operation of the built numerical models. 2. EXPERIMENTAL STUDY The laboratory stand used for energy crops gasification is a laboratory-scale fixed-bed gasification facility. It consists of the reactor (5 kg maximum feedstock) operating with small overpressure. The produced gas passes through a basic gas cleaning apparatus, and the samples are taken to the analysis. The molar fraction of gas composition was measured online using the following analyzers: ABB Uras14, utilizing infrared absorption to measure the concentration of CO and CO2, Siemens Ultramat 6E, utilizing infrared absorption to measure concentration of CH4 and Siemens Calomat, utilizing conductivity to measure concentration of H2. The laboratory stand was described in detail in [23]. The gasification process was conducted for the air excess ratio λ = 0.18. The scheme of the gasification facility is presented in Figure 1. The main properties of the gasified biomass are presented in Table 1. The main differences are visible when the phytoremediation potential is concerned, which was described in detail in [8], however it is not significant in this work. The main results of the experiment are presented in Figures 2 and 3. The highest share of CO and CH4 was obtained for Miscanthus x giganteus which results in the highest LHV of produced gases. The results of the experimental study were discussed in detail in [23]. M O D E L I N G O F E N E R G Y C R O P S G A S I F I C A T I O N B A S E D O N E X P E R I M E N T A L D A T A E N V I R O N M E N T 3 /2017 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 137 3. MODEL OF THE GASIFICATION UNIT For the construction of the model of the gasification unit, Aspen Plus software was used [24]. The main aim of building the model in this study was to reflect the processes occurring in the gas generator, wherein the achievement of the objective was evaluated by comparing the composition and the calorific value of the gas from the model with the values obtained from measurements on the experimental stand. During the analysis, many different structures of the model of the gasification system were considered (from simplified to complex), and the final structure was the result of the minimization of the objective function. It was assumed in the model that the gasification process is carried out isothermally and in steady-state Figure 1. Scheme of the laboratory stand e Table 1. Properties of the analyzed energy crops Quantity Miscanthus x giganteus Sida hermaphrodita Panicum virgatum Spartina pectinata Ultimate analysis, % (dry basis)