Simulations of Coal Combustion in a Pressurized Supercritical CO₂ Circulating Fluidized Bed

Abstract

The supercritical CO2 (S-CO2) power cycle circulating fluidized bed (CFB) integrated with pressurized combustion is a promising power generation technology with high efficiency and low exhaust heat discharge. In multiphase particle-in-cell (MP-PIC) simulations, a 3-D Eulerian–Lagrangian model with a coal combustion process was developed to investigate the combustion characteristics in CFB with S-CO2 wall boundaries under the pressurized conditions of 0.3–0.9 MPa compared with the atmospheric pressure condition (0.1 MPa), with the distribution of pressure, temperature, heat flux, pollution emissions, as well as boiler efficiency being comprehensively illustrated. Furthermore, effects of the excess air ratio corresponding to various pressures on combustion characteristics were deeply analyzed. Results showed that the pressurized combustion compared with the atmospheric pressure condition offered an enhanced combustion and heat transfer, lower pollution emissions, and increased combustion efficiency. Increasing the operating pressure obviously increased the furnace temperature and heating surfaces heat flux, indicating the enhancement of combustion and heat transfer, and meanwhile, emissions of CO, NO, and N2O decreased. Additionally, increasing the operating pressure contributed to the significant improvement of highly efficient coal combustion and the reduction of heat loss, and increasing the excess air ratio could also increase the combustion efficiency by up to 2.65% with more pronounced elevation at lower pressure.

Gas–Solid Hydrodynamics and Combustion Characteristics in a 600 MW Annular CFB Boiler for Supercritical CO2 Cycles

“…In the CPFD calculations, a computational particle consists of a certain quantity of real particles with similar properties including the type, position, and temperature, and the computational complexity could be reduced after such treatment . This method has been widely used in CFB boiler simulations on the combustion and gas–solid flow. ,− For instance, Gu et al carried out full-loop CFD simulations to investigate the gas–solid flow and oxy-fuel combustion characteristics on the lab-scale (0.1 MWth), pilot-scale (150 MW), and industrial-scale CFB boilers (330 MWe) using this method. Xie et al modeled a 75 t/h industrial-scale CFB boiler to perform the combustion process of municipal solid waste and coal based on the MC-PIC method.…”

“…As the most significant equipment in the power generation system, the boiler has great changes in the configuration and heating surface arrangement to adapt to the above-mentioned new S-CO 2 cycle. In the case of a CFB boiler, one of the most typical boilers, the inlet working fluid temperature is about 200 °C higher than that of the steam one, which affects the heat transfer boundary conditions leading to the different structure and heating surface arrangement. , For coal-fired generating units with the same power generation, the turbine in the S-CO 2 power cycle produces more shaft work leading to a working fluid flow rate of about 7–9 times that of the steam, and the configuration design of the S-CO 2 boiler faces the challenge of a larger working fluid flow and greater pressure drop. The design calculation shows that the heat distribution varies greatly compared with the water steam CFB boiler.…”

Study on Dynamic Characteristics of Residual Char of CFB Boiler Based on CPFD Method

“…The related chemical equations and reaction rates are shown in Tables 3 and 4. A detailed description of the reaction mechanism can be found in the relevant literature [20][21][22][23][24][25][26]. Table 3.…”

Numerical Comparison of Thermal Energy Performance between Spouted, Fluidized and Fixed Beds Using Supercritical Co2 as Fluidizing Agent

“…[10], in which supercritical CO 2 (sCO 2 ) was used as the heat transfer fluid (HTF). The density of sCO 2 is similar to that of a common liquid [11,12]. Compared with traditional steam Rankine turbines [13,14], sCO 2 Brayton cycle technology has higher thermal efficiency and medium density, thereby allowing to reduce the size of the compressor, the heat exchanger, and the turbine, and making the system more compact and easy for construction.…”