Modelling of an industrial Nickel powder decomposer

Abstract

The nickel carbonyl, primarily known as Nickel tetracarbonyl gas, is decomposed when it is subjected to high temperature at an elevated pressure to produce nickel powder and carbon monoxide. The nickel powder thermal decomposer process has been used in the industry for nickel purification for over a hundred years. However, theoretical dynamic modelling on this process is limited and the few ones are primarily based on empirical models. In this work, a theoretical and empirical dynamic modelling of nickel carbonyl thermal decomposer is presented. Theoretical modelling was carried out on the nickel thermal decomposer process based on mass and energy conservations, and both steady state and dynamic models were developed for the process. A steady-state model was proposed to describe the relationship between gas temperature and nickel carbonyl (Ni(CO)4) decomposition percentage along the reactor. A partial differential equation (PDE) model was developed to describe the dynamic profiles of the process variables. Simulations were performed to explore the dynamic effects of process variables. The results indicate that feed flowrate affects the gas temperature and the dynamics of temperature gets slower from sections(1-4). The simulated results also show that one zone wall temperature mainly affects the internal temperature at the same zone with the impact also seen spread across to other sections. The obtained theoretical models help to enhance our understanding of the process, provide the needed information for process design, optimization and improved process control. The model also gave background information about the important variables for empirical modelling. Based on the industrial test data, empirical models were proposed for the nickel thermal decomposer process for the purposes of enhancing process control . The sections(1-4) internal temperature profiles of the decomposer were modelled as a function of 4 wall temperature input and input feed flowrate into the decomposer process. The obtained empirical models describe the dynamics of the internal temperature profile. The models show that the feed flowrate has effect on the internal temperature of the Nickel powder thermal decomposer and its effect increases as the gas mixture flows through from section 1 to section 4 of the decomposer. The input feed gas flowrate has negative gains on the internal temperatures of 4 sections. The wall temperature input has positive gains on the internal temperature of the same section but its impact spreads across other sections. The obtained empirical models were evaluated by comparing the model predicted data with industrial measured data and model residuals were also calculated. The results indicate that the obtained models match the industrial data reasonably well. The obtained models provide a necessary basis for applying advanced process control and thereby improving process quality and production efficiency