High-pressure
entrained-flow gasifier technology is used to convert
solid carbonaceous feedstocks into synthesis gas, which can be used
in an integrated gasification combined cycle power plant or as a feedstock
for chemical or synthetic fuel production. Computational fluid dynamics
(CFD) models, once validated, can be used to help design full-scale
reactors. Model validation entails the comparison of model predictions
to lab-scale or pilot-scale measurements. However, experimental measurements
of high-pressure pilot-scale gasifiers usually consist only of wall
temperatures and outlet gas temperature and composition, which are
of limited use for model validation when the gasifier is operating
well, providing information only about operating temperature, heat
loss, and equilibrium gas composition. These do not provide a strong
validation of the CFD model, whose main purpose is to make predictions
of the flame size and shape and its ability to convert solid fuel
to gas efficiently in a small volume. This paper presents a model
validation based on data generated using CanmetENERGY’s 1 MWth high-pressure entrained-flow gasifier. To provide a stronger
validation, the approach taken here is to compare the model predictions
to the pilot-scale measurements over a range of operating conditions
comprising higher (approximately 90%) carbon conversion and lower
(approximately 80% or lower) carbon conversion. In effect, the comparison
includes operating conditions for which gasification reactions are
extended or delayed toward the outlet in order to capture key effects.
It is found that the present CFD model is able to track the performance
of the gasifier over the range of operating conditions and provides
insight into the causes for limited carbon conversion.
This study presents a reduced order model (ROM) that describes the behavior of a commercial-scale short-residence gasifier which uses a multielement injector feed system. The state-of-the-art injection technology disperses the feed across the crosssection of the gasifier to enhance the mixing efficiency, thereby allowing a reduction in the reactor size and capital cost. A reactor network is integrated into the ROM to capture the laminar and mixing zones formed by each nozzle and subsequently the merging point of the multiphase flow coming from all of the nozzles. The results of the ROM are in reasonable agreement with the limited data reported for a short-residence time commercial-scale gasifier, that is, residence time, carbon conversion, and cold gas efficiency. Moreover, the performance of the gasifier is examined under changes in the operating pressure, number of injectors, flow nonuniformity, and plugging in the fuel's injection tubes. The ROM provides valuable insights on the operation of the commercial-scale gasifier and potential safety concerns that can be used to design suitable and safe operation policies for the system. Furthermore, sensitivity analyses on the model, design, and operational parameters are performed to assess the suitability of the model assumptions and identify the most important factors influencing carbon conversion, particle residence time, and temperature profiles.
Transmission heavy crude oil carries water-wetted solid particles. Studies have shown that these particles can accumulate on the pipe floor and cause under-deposit corrosion and that the incidence of accumulation is strongly correlated to locations downstream of overbends. Computational fluid dynamics (CFD) analysis of light and heavy crude oil flows in a representative segment of a real transmission pipeline suggested that the deposition patterns in heavy oil flow are a result of low near-wall velocity, especially downstream of overbends, which prevents the flow from sweeping particles along the pipe floor, not the tendency of particles to fall to the pipe floor. The objective of the present study was to provide information that would help establish mitigation strategies. The present parametric study used the CFD model to predict the decrease in near-wall velocity at the pipe floor downstream of overbends for different pipe diameters and oil flow rates and properties. This information provided the basis for mapping the transition from light oil behavior to heavy oil behavior. The results were condensed to a chart that provides the reduction in near-wall velocity downstream of overbends as a function of the Reynolds number. It indicated a sharp overbend effect as the Reynolds number decreased below 30,000.
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