CFD modeling of gas–solids flow in a large scale circulating fluidized bed furnace

Heat Transfer Performance in a Superheater of an Industrial CFBC Using Fuzzy Logic-Based Methods

The heat transfer coefficient in the combustion chamber of industrial circulating flidized bed (CFB) boilers depends on many parameters as it is a result of multifactorial mechanisms proceeding in the furnace. Therefore, the development of an effective modeling tool, which allows for predicting the heat transfer coefficient is interesting as well as a timely subject, of high practical significance. The present paper deals with an innovative application of fuzzy logic-based (FL) method for the prediction of a heat transfer coefficient for superheaters of fluidized-bed boilers, especially circulating fluidized-bed combustors (CFBC). The approach deals with the modeling of heat transfer for the Omega Superheater, incorporated into the reaction chamber of an industrial 670 t/h CFBC. The height above the grid, bed temperature and voidage, gas velocity, and the boiler’s load constitute inputs. The developed Fuzzy Logic Heat (FLHeat) model predicts the local overall heat transfer coefficient of the Omega Superheater. The model is in good agreement with the measured data. The highest overall heat transfer coefficient is equal 220 W/(m²K) and can be achieved by the SH I superheater for the following inputs l = 20 m, t_b = 900 °C, v = 0.95, u = 7 m/s, M-C-R = 100%. The proposed technique is an effective strategy and an option for other procedures of heat transfer coefficient evaluation.

Simulation of biomass-steam gasification in fluidized bed reactors: Model setup, comparisons and preliminary predictions

A user-defined solver integrating the solid-gas surface reactions and the multi-phase particle-in-cell (MP-PIC) approach is built based on the OpenFOAM software. The solver is tested against experiments. Then, biomass-steam gasification in a dual fluidized bed (DFB) gasifier is preliminarily predicted. It is found that the predictions agree well with the experimental results. The bed material circulation loop in the DFB can form automatically and the bed height is about 1m. The voidage gradually increases along the height of the bed zone in the bubbling fluidized bed (BFB) of the DFB. The U-bend and cyclone can separate the syngas in the BFB and the flue gas in the circulating fluidized bed. The concentration of the gasification products is relatively higher in the conical transition section, and the dry and nitrogen-free syngas at the BFB outlet is predicted to be composed of 55% H₂, 20% CO, 20% CO₂ and 5% CH₄.

Application of the Numerical Techniques for Modelling Fluidization Process Within Industrial Scale Boilers

The numerical simulation of the large scale industrial circulating fluidized bed (CFB) boilers, working under air- and oxy-fuel combustion are presented in this paper. Moreover, two-dimensional experimental rig used for numerical model validation is described. For three-dimensional numerical simulations two industrial compact CFB boilers were selected installed in Polish Power Plants. Numerical simulations were carried out using three-dimensional model where the dense particulate transport phenomenon was simultaneously modelled with combustion process. The fluidization process was modelled using the hybrid Euler-Lagrange approach. Within the paper, readers can find information about used computational technique and a number of reference to specific work. The impact of radiative heat transfer on predicted temperature profile within the CFB boiler was investigated in presented work. Moreover, the novel model for retrieving radiative properties of gases under oxy-fuel combustion process was used. The evaluated temperature and pressure profiles during numerical simulations were compared against measured data collected during boiler air-fuel operation. Collected data was also used for validating numerical model of the oxy-fuel combustion model. Stability of the model and its sensitivity on changes of composition of the oxidizer were studied. This simulations were evaluated to check the response of the numerical model on changing the combustion conditions from air- to oxy-fuel combustion process. The comparison of the pressure and temperature profiles for all considered cases gave comparable trends in contrary to measured data.