A comparative study of hydrodynamics and gasification performance of two types of spouted bed reactor designs | |
| Author | Salam, P. Abdul |
| Call Number | AIT Diss. no.ET-05-01 |
| Subject(s) | Hydrodynamics Spouted bed processes |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ET-05-01 |
| Abstract | A comparative hydrodynamic and gasification study of spouted bed reactors having central jet (conventional) and circular slit (modified) distributors has been carried out. Specifically the study aimed: (i) to carry out a comparative hydrodynamic study of spouted beds with central jet and circular slit distributors, (ii) to carry out a comparative study on gasification of charcoal in spouted beds with central jet and circular slit distributors, and (iii) modeling of hydrodynamic behaviour and gasification performance of spouted beds with central jet and circular slit distributors by using Artificial Neural Network (ANN). The hydrodynamic study compared the minimum spouting velocity, pressure drop across the bed and across the distributor at minimum spouting velocity and maximum spoutable bed height of the central jet spouted bed with the circular slit spouted bed. Central jet and circular slit distributors with four different air inlet areas were used. Three sizes of crushed coconut shell particles, two sizes of sand, two sizes of dolomite and one size of silica gel, in a specially constructed transparent spouted bed of 13.3 cm inner diameter, were used for the study. The results of the hydrodynamic study showed that (i) for a particular bed height and air inlet area, the minimum spouting velocity of circular slit spouted bed is significantly (i.e. 1.2 - 3 .8 times) higher than that of central jet spouted bed, (ii) as bed height increases, the minimum spouting velocity of central jet and circular slit spouted beds tends to become equal, (iii) the pressure drop across the bed of circular slit spouted bed at minimum spouting velocity is almost independent of its air inlet area, (iv) for a given particle size and air inlet area, maximum spoutable bed height for central jet spouted bed is higher than that of circular slit spouted bed, and (v) for a specific particle size, as the air inlet area increases the maximum spoutable bed height decreases in case of central jet distributor, whereas the bed height is almost constant in case of circular slit distributor. A comparative experimental study on air gasification of charcoal in spouted bed reactors having central jet (conventional) and circular slit (modified) distributors was also carried out. The gasification study showed that: (i) for a particular superficial spouting velocity, the bed temperature of central jet spouted bed is higher than that of circular slit spouted bed, (ii) the circular slit distributor design is associated with higher CO concentration (i.e. 12.31 - 16.02 vol.% for central jet and 15.32 - 18.42 vol.% for circular slit) in the gas and higher carbon conversion in comparison with the central jet distributor, (iii) char carry over rate in case of circular slit spouted bed is higher than that of central jet spouted bed, (iv) at higher spouting velocities, the gasification efficiency of the circular slit spouted bed is slightly more as compared to the central jet spouted bed, (v) the gasification efficiency of both the types of spouted bed designs is low (i.e. 40 to 52 % for central jet and 43.6 to 54.1 % for circular slit) because of higher energy loss associated with the char carry over (i.e. 14 - 28 % for central jet and 24 -36 % for circular slit); in practical systems, the carry over loss could be reduced by recycling the char particles, and (vi) the efficiency of the circular slit spouted bed with carry over recycling is expected to be significantly higher compared to central jet spouted bed for gasification of solid fuels . A two-layered artificial neural network (ANN) model was developed for predicting the minimum spouting velocity (Ums), minimum fluidization velocity (Umf) and charcoal gasification efficiency. The model was trained by using a backpropagation learning algorithm. About two-thirds of the available data was used for training the model and the remaining was used to test and validate the model. The neural network model developed predicts the Ums and Umf values better than the correlations available in the literature. The model developed in this study also closely predicts the gasification efficiency. The position of flow regime of circular slit spouted bed was also compared with the flow regimes of central jet spouted bed and fluidized bed. The knowledge of the flow regime of the circular slit spouted bed is important for identifying and designing practical applications of spouted bed with circular slit distributor. The flow regime of the tested circular slit spouted bed falls within the flow regime of the central jet spouted bed. This implies that the circular slit spouted bed could be used for similar applications of central jet spouted bed. |
| Year | 2005 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ET-05-01 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Energy Technology (ET) |
| Chairperson(s) | Kumar, S.;Bhattacharya, S. C.; |
| Examination Committee(s) | Tabucanon, Mario T.;Surapong Chirarattananon;Basu, Prabir; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2005 |