A two-fluid model simulation of an industrial moving grate waste incinerator.

CFD modelling and simulation is an effective means of optimizing the design and operation of moving grate waste incinerators. Conventional approach models the grate combustion and the furnace combustion separately by using an in-bed/over-bed coupling procedure. In this paper, a comprehensive two-fluid reacting model that integrates the gas-solid grate incineration and the gas turbulent combustion in one scheme is developed for industrial incinerators. Realistic grate geometry and direct simultaneous coupling of the fuel bed and the freeboard gas phase are realized. According to different treatments of the solid phase, the whole incinerator is divided into three regions, namely the packed bed region, the fall region and the furnace region. The kinetic theory of granular flow (KTGF) is introduced to describe the rheological properties of waste particles, and the Ergun model is used for the gas-solid drag. Thermal conversion of wastes is characterized by the heterogeneous reactions of moisture evaporation, devolatilization, char-O2 combustion and the homogeneous reactions of hydrocarbons combustion. Distributions of temperatures and gas species are predicted and validated by measurements. Particle properties are calculated to reveal the grate incineration characteristics. Effects of waste throughput on the incineration are also investigated. Overall, the present model provides a new methodology of in-bed and over-bed integration for the moving grate incinerator simulation.

CFD simulation of MSW combustion and SNCR in a commercial incinerator.

A CFD scheme was presented for modeling municipal solid waste (MSW) combustion in a moving-grate incinerator, including the in-bed burning of solid wastes, the out-of-bed burnout of gaseous volatiles, and the selective non-catalytic reduction (SNCR) process between urea (CO(NH2)2) and NOx. The in-bed calculations provided 2-D profiles of the gas-solid temperatures and the gas species concentrations along the bed length, which were then used as inlet conditions for the out-of-bed computations. The over-bed simulations provided the profiles of incident radiation heat flux on the top of bed. A 3-dimensional benchmark simulation was conducted with a 750 t/day commercial incinerator using the present coupling scheme incorporating with a reduced SNCR reduction mechanism. Numerical tests were performed to investigate the effects of operating parameters such as injection position, injection speed and the normalized stoichiometric ratio (NSR) on the SNCR performance. The simulation results showed that the distributions of gas velocity, temperature and NOx concentration were highly non-uniform, which made the injection position one of the most sensitive operating parameters influencing the SNCR performance of moving grate incinerators. The simulation results also showed that multi-layer injections were needed to meet the EU2000 standard, and a NSR 1.5 was suggested as a compromise of a satisfactory NOx reduction and reasonable NH3 slip rates. This work provided useful guides to the design and operation of SNCR process in moving-grate incinerators.

[Clinical observation on acupuncture combined with motortherapy for early treatment of cerebral palsy high risk infants].

OBJECTIVE: To observe the effect of early treatment with acupuncture and motortherapy on developmental quotient (DQ) of cerebral palsy high risk infants. METHODS: Sixty cerebral palsy high risk infants were divided into an acupuncture combined with motortherapy group (treatment group) and a control group, 30 cases in each group. Changes of DQ were investigated by the children mental development scale. RESULTS: The DQ in the treatment group was significantly higher than that in the control group (P < 0.001), with a very significant difference between the two groups in the different grades of DQ (P < 0.005). Incidence of cerebral palsy in the treatment group significantly lower than that in the control group (P < 0.005). CONCLUSION: Acupuncture combined with motortherapy can effectively improve intelligence level and motor function, and reduce the incidence of cerebral palsy for cerebral palsy high risk infants at early stage.