Population balance model of heat transfer in gas–solid particulate systems

A population balance model is derived for heat transfer processes in gas–solid systems with intensive motion of particles in order to describe the temperature distribution of particulate phase. The model involves collisional particle–particle and particle–wall heat transfers, and continuous gas–particle, gas–wall and wall–liquid environment heat transfer processes. Collisional heat transfers are characterised by collision frequencies and random heat exchange parameters with general probability distributions with support [0, 1], describing the heat transfer efficiency between the colliding solid bodies. An infinite hierarchy of moment equations, describing the time evolution of moments of the temperature of particle population is derived from the population balance equation, which can be closed at any order of moments. The properties of the model and the effects of parameters are examined by numerical experiments using the second order moment equation model of a spatially homogeneous fluidized bed.     

Intermediate storage in batch/continuous processing systems under stochastic operation conditions

A mathematical model and model-based method is presented to design the intermediate storages aiming to buffer the operational differences between the batch and continuous subsystems in processing systems. The occurrence times of the inputs are assumed to be described by a Poisson process, while the amounts of the material transferred by the batch units allowed changing according to general probability distributions. Based on the stochastic differential equation model of operation, integral equations for determining the overflow and underflow probabilities of a finite storage are formulated for both infinite and finite operation horizons that provide the basis for the rational design of such intermediate storages. Analytical solutions to the integral equations for infinite horizons are derived in the cases of constant and exponentially distributed inputs. For the batch sizes described by general distribution functions, solutions to the integral equations are obtained in the form of approximating functions generated by stochastic simulation. A number of numerical experiments with exponential, normal and lognormal distributions of the batch sizes are presented and analyzed. The effects of process parameters on the design are also investigated.     

The efficiency of municipal wastewater treatment with the reconstructed activated sludge method

Centralized wastewater treatment policy is a common challenge in Hungary. With the recent technology improvement of the Debrecen Wastewater Treatment Plant, the original activated sludge function system’s maximum load is doubled, making it able to treat the effluents of 7 settlements total. The introduced new technical constructions however required strict attention to be successfully integrated into the existing system. Retrofitting the overall processes caused disturbances affecting certain parameters in the biological treatment, thus modifying water quality of the effluent. Our experiments had aimed to control the performance of the plant after the reconstruction during test phase for more than a year period. It has been found that a slight increase of removal efficiency was achieved in the observed parameters of COD, BOD₅, TP, SS, while TN remained in a moderate degree of enhancement. Retention effectiveness has begun to escalate significantly after a year of operation.