Recirculation method

As the production lives of secondary methods lose their efficiency, further techniques have been tested and found to continue to release additional amounts of oil. These methods are considered tertiary methods and are generally associated with chemical or gaseous recirculation methods of recovery. Some instances of in-situ thermal recovery have been used but not on a large extent. 

The recirculation methods were developed from the static methods. The main part of the recirculation apparatus is a thermostated equilibrium cell. The equilibrium cell has facilities for mechanically driven circulation through external loop(s) of either the lighter (i.e., the top) phase or the heavier (the bottom) phase, or of both phases. Magnetically operated high-pressure pumps usually achieve the circulation. 

Figure 14. Apparatus for measurement of adsorption of surfactant onto rock core by the recirculation method. (Reproduced with permission from reference 35. Copyright 1992 Society of Petroleum Engineers.)...

The other type of flow system is the vapour recirculation method. In this method a two-phase mixture is placed in a vessel at a specific temperature. Vapour is then withdrawn from the cell and recirculated through the liquid. This contact between vapour and liquid provides a fairly rapid approach to equilibrium. Again after equilibrium is reached samples of gas and liquid are withdrawn and analysed. Some provision is usually made to keep the pressure constant during sampling. 

Hiza, Herring, and co-workers have discussed several single-pass and recirculation methods for studying vapour-liquid and vapour-solid equilibrium... 

As an alternative to on-line gas analysis, simple and reliable techniques such as dynamic measurements [15, 45], stationary measurements [46] and the recirculation method [47] have been developed for on-line OUR determination in mammalian cell cultures. In the dynamic method, a DO profile is dynamically created by changing the gas composition. The DO concentration is increased to a first DO set point by... 

In the recirculation method, the culture broth is circulated through a recycle loop, located outside the bioreactor, at a certain flow rate. The difference between the DO concentrations in the bioreactor and the external loop is proportional to the pumping rate and the OUR of the culture. This method requires (1) optimization of the pumping rate to provide a relatively large difference between the two DO concentrations without causing an O2 limitation for the cells and (2) accurate determination of the external loop volume. 

The features and benefits of recirculation method at water processing can be demonstrated by taking as an example the sand filter. Traditionally, to be effective, sand filter should have the height of sand bed to be 0.7-2.0 m, flow rates in slow sand Alters should be between 0.1 and 0.2 m/h, and that in quick sand filters should be between 5 and 20 m/h. 

Recirculation methods. When investigating equilibrium between fluid phases the system of interest is enclosed in a thermostatted stirred vessel with provision for recirculating both the phases [64]. The vapour phase is recirculated via a vapour sampling bomb and back to the equilibrium vessel where it bubbles up through the liquid. The liquid phase may also be recirculated via a liquid sample bomb. When it is considered that equilibrium has been reached, the pressure is noted and representative samples of the vapour and liquid phases are sealed off in the sample bombs, the contents of which are analysed. 

Concerning the acid measurements of solid samples, the experiments of acid-base titrations by base probes can be performed in various liquids, as above reported. In this case, the HPLC line, comprising the pump and detector coupled to a personal computer for the collection, storage, and processing of the data, works according to a recirculating method (Fig. 17.4). 

Fig. 17.5 Example of raw data obtained from the acid-base titration in liquid by recirculation method. The points representing the base probe injection are indicated by a cross (Ref [9])...

Fig. 17.6 Example of isotherms of adsorption of PEA on two siUca-niobia samples at low (Si-Nb/5org) and high (Si-Nb/45org) niobia content collected in water at 17 °C by the recirculation method (from Ref [9])...

Climate conditions, environmental impacts, availability of liquids, financial means, and legal regulations are the main criteria when selecting the liquid recirculation method. The two most preferred options from the standpoint of environmental impact are buried trenches and vertical wells. They offer minimum exposure pathways, good all-weather performance,... 

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