CO2 Recovery Process Research Articles

Monitoring and Predicting CO2 Flooding Using Material Balance Equations

Abstract In order to operate a CO2 flooding scheme successfully, it is necessary to get accurate information about the reservoir dynamic performance and the fluids injected. Although some numerical simulation studies have been conducted, the complicated drive mechanisms and actual reservoir performance have not been fully understood. Thus, there is a strong industrial need to develop models using different perspectives to provide valuable and complementary insights into the reservoir performance during the CO2 flooding process. The objective of this study is to develop models using material balance equations (MBE) to analyze the field data before and after CO2 injection. After matching the historical field data, the proposed model can be applied to evaluate, monitor and predict the overall reservoir dynamic performance during the CO2 flooding process. To accurately account for the complex displacement process involving compositional effect and multiphase flow, the PVT properties of reservoir fluids and the four-phase fluid relative permeability relationship are integrated into the model. This study has investigated the effects of a number of factors, such as the reservoir pressure, the amount of CO2 injected, the CO2 partition ratios in reservoir fluids, the possibility of the existence of a free CO2 gas cap, the proportion of reservoir fluids contacted by CO2, the oil swelling and the oil relative permeability improvement. The model has been applied to analyze the Weyburn CO2 flooding project. The study has shown that the proposed MBE model is an effective complementary tool to analyze overall reservoir performance in tertiary CO2 recovery processes. The results show that:there exists a free CO2 gas cap under reservoir conditions, even if the reservoir pressure is larger than MMP (minimum miscible pressure) in the Weyburn Field;the CO2 partition ratios in oil, water and gas phases and the proportions of reservoir fluids contacted by CO2 largely affect the drive mechanism and production performance; andthe effect of CO2 solubility in water under actual reservoir conditions cannot be neglected. The proposed new model is the first one in developing and applying MBE to evaluate the overall dynamic performance for the CO2 flooding process and a valuable insight into reservoir responses during this process has been achieved. Introduction CO2 flooding is considered one of the most effective tertiary recovery processes in light/medium oil reservoirs and has achieved widespread use in the petroleum industry. However, the complicated displacement mechanisms and reservoir performance involved in the CO2 injection process have not been completely understood. Monitoring reservoir performance and obtaining accurate information regarding reservoir fluid and injected fluid using field data will help understand the mechanisms and manage the CO2 injection project efficiently. There are two types of methods that monitor and evaluate reservoir performance: numerical simulation and MBE. MBE is a classic reservoir engineering tool. It is applied to analyze the reservoir performance based on the law of conservation of matter. Compared with MBE, reservoir numerical simulation is a more modern technique for modelling reservoir performance.

Carbon dioxide capture from flue gas by pressure swing adsorption at high temperature using a K‐promoted HTlc: Effects of mass transfer on the process performance

AbstractUsing hundreds (640) of simulations obtained from a cyclic adsorption process simulator, two heavy reflux (HR) pressure swing adsorption (PSA) cycles were analyzed at the periodic state for the capture and concentration of CO2 from flue gas at high temperature (575 K), using a K‐promoted hydrotalcite like compound (HTlc). Since the values of the adsorption (ka) and desorption (kd) mass transfer coefficients of CO2 in the K‐promoted HTlc were uncertain, this study focused only on the effects of ka and kd on the process performance. Both, a 5‐bed 5‐step stripping PSA cycle with light reflux (LR) and HR from LR purge and a 4‐bed 4‐step stripping PSA cycle with HR from countercurrent depressurization were studied using a vacuum swing cycle with the high pressure fixed at 137.9 kPa and the feed set at 15 vol % CO2, 75 vol % N2, and 10 vol % H2O. For the 5‐bed process, increasing both ka (= 0.0058 s−1) and kd (= 0.0006 s−1) by a factor of five increased both the CO2 purity and CO2 recovery, achieving a CO2 purity of nearly 90% at a CO2 recovery of 72% and feed throughput (θ) of 57.6 L STP/h/kg. Increasing ka and kd by a factor of ten further increased both the CO2 purity and CO2 recovery, achieving for the first time a CO2 purity greater than 90% at a CO2 recovery of 85% and θ of 57.6 L STP/h/kg. Making kd = ka (= 0.0058 s−1) resulted in a CO2 purity of 89% with a CO2 recovery of 72% at a θ of 57.6 L STP/h/kg; and increasing that value by a factor of five led to a CO2 purity of 91% at a high CO2 recovery of 88% and θ of 57.6 L STP/h/kg. These results suggested that the performance was desorption limited. For the 4‐bed process, when ka and kd were both increased by a factor of five, the CO2 purity increased to 98% at a θ of 201.7 L STP/h/kg, but the CO2 recovery decreased to 5%. Overall, it was proven that mass transfer effects were important to the performance of this high temperature CO2 recovery process, with higher but acceptable values of ka and kd leading to CO2 purities of greater than 90%, a needed limit for process viability. © 2006 American Institute of Chemical Engineers Environ Prog, 2006

Bench-Scale CO2 Recovery from Moist Flue Gases by Various Alkali Carbonates Supported on Activated Carbon

As described in the previous papers, K2CO3 supported on activated carbon sorbed CO2 from moist feed gas at 353 K to form KHCO3 and the entrapped CO2 was then efficiently released by steam flushing at 423 K, followed by condensation of the excess steam through a heat exchanger to afford CO2 in high purity. In the present study, various alkali carbonates supported on activated carbon were employed to recover CO2 from moist gases at different temperatures. Carbon dioxide can be sorbed at higher temperatures in the order of the impregnated salt, Na2CO3 K2CO3 > Cs2CO3, providing a more energy-conservative CO2 recovery process for moist flue gases at 313–393 K than conventional amine absorption methods.

CO<sub>2</sub>回収を部分的に行う多重熱利用サイクル発電システムの構成と特性

A multi-cascade heat utilizing power generation system is proposed in which carbon dioxide (CO2) generated is partially recovered by adopting the oxygen (O2) combustion method. In the system, a gas turbine is driven by high-temperature working fluid (air) generated by burning fuel. The turbine outlet gas, which has still considerable energy, is used to generate high-pressure super-heated steam and middle-pressure one at a waste heat boiler (WHB). The high-pressure steam is used for driving an expansion turbine, until its pressure becomes the same as the one of the middle-pressure super-heated steam produced at the WHB. Both the middle-pressure steams are utilized as the working fluid of the CO2-recovering non-polluting high-efficiency gas turbine power generation system, in which the heat energy is also utilized cascade-wisely. It was shown that the system had the net power generation efficiency of 48.4% at the lower calorific value base with CO2 recovery rate of 30.1%, and that this efficiency was remarkably high compared with that of a convensional combined-cycle power generation sys-tem in which a CO2 recovery process is incorporated so as to attain the same CO2 recovery rate.