57 research outputs found
Combined calcium looping and chemical looping combustion for postācombustion carbon dioxide capture: process simulation and sensitivity analysis
In this work, a combined calcium looping and chemical looping combustion (CaL--CLC)
technology is simulated at thermodynamic equilibrium conditions and the results in terms of
efficiency, power production, and solids circulation rates are compared with the case of using
CaL alone. In addition, a new solids looping configuration in the CaL--CLC process is
proposed with the purpose of mitigating the loss of calcium oxide conversion after high cycle
numbers. Simulations show an improved process efficiency of the CaL--CLC method
compared with CaL alone (34.2 vs. 31.2 % higher heat value) and an increased power output
(136 vs. 110 MWe additional power) due to the higher energy requirement to preheat the
reactants. A sensitivity analysis of the process operating parameters highlights the particular
importance of the temperature difference between reactors, which has a strong impact on the
required mass of solids circulating in the loops. Finally, partial carbon dioxide capture
scenarios are considered and indicate that lower capture levels are suitable to match regulation
targets
Simulation of a calcium looping CO2 capture process for pressurized fluidized bed combustion
The Canadian regulations on carbon dioxide emissions from power plants aim to lower the emissions from coalāfired units down to those of natural gas combined cycle (NGCC) units. Since coal is significantly more carbon intensive than natural gas, coalāfired plants must operate at higher net efficiencies and implement carbon capture to meet the new regulations. Calcium looping (CaL) is a promising postācombustion carbon capture (PCC) technology that, unlike other capture processes, generates additional power. By capturing carbon dioxide at elevated temperatures, the energy penalty that carbon capture technologies inherently impose on power plant efficiencies is significantly reduced. In this work, the CO2 capture performance of a calciumābased sorbent is determined via thermogravimetric analysis under relatively high carbonation and low calcination temperatures. The results are used in an aspenONEā¢ simulation of a CaL process applied to a pressurized fluidized bed combustion (PFBC) system at thermodynamic equilibrium. The combustion of both natural gas and coal are considered for sorbent calcination in the CaL process. A sensitivity analysis on several process parameters, including sorbent feed rate and carbonator operating pressure, is undertaken. The energy penalty associated with the capture process ranges from 6.8 ā11.8 percentage points depending on fuel selection and operating conditions. The use of natural gas results in lower energy penalties and solids circulation rates, while operating the carbonator at 202 kPa(a) results in the lowest penalties and drops the solids circulations rates to below 1000 kg/s
Experimental analysis of the unit cell approach for two-phase flow dynamics in curved flow channels
Flow behavior of gas\u8211liquid mixtures in thin channels has become increasingly important as a result of miniaturization of fluid and thermal systems. The present empirical study investigates the use of the unit cell or periodic boundary approach commonly used in twophase flows. This work examines the flow patterns formed in small tube diameter (<3 mm) and curved geometry flow systems for air\u8211water mixtures at standard conditions. Liquid and gas superficial velocities were varied from 0.1 to 7.0 (approx. \ub10.01) m/s and 0.03 to 14 (approx. \ub10.2) m/s for air and water respectively to determine the flow pattern formed in three geometries and dispersed bubble, plug, slug and annular flow patterns are reported using high-frame rate videography. Flow patterns formed were plotted on the generalized two-phase flow pattern map to interpret the effect of channel size and curvature on the flow regime boundaries. Relative to a straight a channel, it is shown that a \u8216C shaped\u8217 channel that causes a directional change in the flow induces chaotic advection and increases phase interaction to enhance gas bubble or liquid slug break-up thus altering the boundaries between the dispersed bubble and plug/slug flow regimes as well as between the annular and plug/slug flow regimes.NRC publication: Ye
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