Initial Residence Time Research Articles

Hydrogen production by sewage sludge gasification in supercritical water with high heating rate batch reactor

Sewage sludge gasification in supercritical water was studied with high heating rate batch reactor. Effect of temperature, pressure, residence time and catalyst were investigated. The hydrogen yield, gasification efficiency, carbon gasification efficiency and hydrogen yield potential were mainly affected by temperature. The maximum values of them reached 20.66 mol/kg, 73.49%, 61.16% and 41.34% without catalyst at 750 °C and 30 min respectively. The modified detailed kinetics indicated steam reforming, water-gas shift and pyrolysis promoted the formation of H2 and CO2 when temperature was ranged from 550 to 750 °C at the initial residence time. As residence time increased, the water-gas shift was dominant. Meanwhile, the formation of CO and CH4 were inhibited when temperature and residence time increased. The addition of mixed catalysts promoted the three reactions and formation of hydrogen better at lower reaction condition. The mixed use of both catalysts could enhance the gasification and the formation of hydrogen better. The increased loading of RNi-Mo2 could enhance the formation of hydrogen better because the heterogeneous catalyst could promote steam reforming and alkali catalyst could promote water-gas shift reaction better.

Optimization of the ethane thermal cracking furnace based on the integration of reaction network

The cracking furnace is the core of an ethylene plant. An optimization method is built based on the integration of reaction network. Starting from atomic scope, an algebraic procedure is used to seek all possible reactions and establish the reaction network. Based on this, the reaction network is integrated and simplified to identify the variation rate of every component. The calculation procedure is developed to identify the variation of each component’s concentration and the selectivity and identify the optimal furnace parameters. For the studied furnace, the residence time corresponding to the minimum by-product production is identified to be 0.4 s, and its by-product generation is 4.3% less than that at the initial residence time (0.3 s).

Control of the solids retention time by multi-staging a fluidized bed reactor

Fluidized bed reactors are often operated with particles of different size and density present simultaneously (e.g. inert bed material and fuel particles in fluidized bed combustion, or catalyst particles and polymer particles in fluidized bed polymerization). This paper presents a general concept to separate a single fluidized bed reactor into two reaction zones by introducing a primary chamber in the bed where flotsam particles are fed and spend a certain initial residence time. The feasibility of the concept is experimentally proven in a fluid-dynamically down-scaled unit, both in terms of functionality (ability to maintain two separate reaction regions and to avoid backflow from the secondary to the primary region of the solids fed) and of operability (ability to control the residence time distribution of the solids fed in the primary chamber through operational parameters such as pressure and bed height). Numerical simulations show that the residence time distribution is sensitive to the degree of segregation in the primary chamber, and that the heat transfer between the two reaction regions by means of bulk solids mixing is still sufficient to sustain an endothermic process in one zone by an exothermic process in the other.