Countercurrent exchange

About: Countercurrent exchange is a research topic. Over the lifetime, 2255 publications have been published within this topic receiving 28687 citations. The topic is also known as: Countercurrent exchange.

Modeling of moving-bed coal gasifiers

Abstract: A mathematical model of an atmospheric countercurrent moving-bed coal gasifier was developed and used for air+steam gasification. The model considers an adiabatic reactor in a stationary state with different temperatures for the solid and the gas and uses a shrinking unreacted core model to describe the solid-gas reactions. The system of differential equations for the mass and energy balances is solved by using a fourth order Runge-Kutta-Merson method with variable step size. The effect of the reaction scheme in the combustion zone on the longitudinal temperature profiles predicted by the model is studied. A parametric study is performed on the effect of reactivity with steam, CO 2 , and O 2 , of particle size, and of the emissivity of the ash layer on the longitudinal temperature profiles, the maximum temperature, and the gas composition. The effect of operating conditions on the gas compositions, low heating value, and thermal efficiency of the process is also studied

Parametric Study of the Membrane Process for Carbon Dioxide Removal from Natural Gas

Abstract: In this work, the cross-flow model is compared with the cocurrent flow model and the countercurrent flow model for the process of removing CO 2 from natural gas. According to the comparison result, the cross-flow model is used for the analysis of the process of CO 2 removal from the natural gas. Analysis results indicate that the membrane area is not a monodrome function of the selectivity and both the effects of the fast gas (CO 2 ) permeability and the slow gas (CH 4 ) permeability on membrane area and CH 4 recovery are studied. Similar analysis is carried out for the operating pressures. Both the single stage system and the two-stage system with a recycle are studied. In order to reduce the membrane area required, membranes with high permeability and selectivity less than 100 are preferable. With increasing feed side pressure and decreasing permeate side pressure, the membrane area required decreases and the CH 4 recovery increases. For the single-stage system using a commercial membrane with selectivity of 20, the CH 4 recovery is lower than 90% at a product purity of 98%. Only when the membrane with selectivity higher than 50 is used, the separation of CH 4 recovery >98% and product purity >98% target can be fulfilled by the single stage system. Using the two-stage system with a membrane selectivity of 20, the separation target can be achieved. In the two-stage system, the permeate gas of the first stage has to be compressed before it can be sent to the next stage. The compression energy required between stages is estimated to be 107.5 KJ/m 3 (STP) of feed for the process discussed in this paper. Even considering the conversion factor between heat and electricity of 3-4, the energy consumption of a two-stage membrane system is still much less than that of the amine absorption process which is about 600-900 KJ/(m 3 (STP) of feed).

Study of Fluid Dynamics of Mass-Transfer Apparatuses Having Stream-Bubble Contact Devices

Abstract: To increase the efficiency of mass-21transfer apparatuses, a stream-bubble contact device with intensive countercurrent contact between the gas (vapor) and liquid in each element is proposed. This way of effecting phase contact helps increase mass-transfer coefficients and, consequently, increase efficiency of masstransfer processes significantly. In the proposed contact device, hydraulic resistance is low. The profile and parameters of liquid drops atomizing may differ markedly, depending on the design and process parameters of the contact device and of the apparatus as a whole.