Counter-current reactors

In order to take advantage of this purification effect and to optimise the water content of the iodine-rich phase, CEA has proposed to use a counter-current reactor to perform the Bunsen reaction. This idea arises from the consideration that, aside from S02, the chemical system includes two almost immiscible solvents (excess water and excess iodine) and two solutes (H2S04 and HI). Bunsen reactor... 

In its most recent assessment of the cycle, which is reported here, CEA chose to make an optimistic assumption about the composition of the HI/I2/H20 mixtures that are treated inside the iodine section. A 2 HI/6 I2/9 H20 composition, instead of the usual 2 HI/8 I2/10 H20 mentioned above, was assumed to be produced from Bunsen section, thanks to the counter-current reactor described above. Although not proven, this assumption is consistent with experimental results obtained so far on HI/H2SC>4/I2/H20 mixtures, in CEA (Lovera, 2009) as well as elsewhere (Lee, 2008). 

With this assumption, and using a modified Neumann model for HI/I2/H20 mixtures description, CEA (Leybros, 2009) devised a flow sheet for the iodine section which decomposes almost all incoming HI and therefore returns relatively pure products (the iodine return flow contains only 4 molar% water and less than. 3 molar% HI) to the Bunsen section, an important feature for the counter-current reactor. Secondary helium heat is provided to the boiler of the column (235 kj/mol), whereas all other heat needs are fulfilled through internal heat recovery, with the help of a heat pump which transfers heat from the products of the distillation column to its feed. Mainly because of the presence of this heat pump, the iodine section uses 60 kj/mol of electric power on top of the helium heat. 

The most unusual development in reactor design in dilute acid hydrolysis of cellulose hydrolysis is that of a counter-current reactor. It is defined as a mov-... 

Fig. 5. Profiles of sugar concentration in co-current and counter-current reactors. Substrate yellow poplar reaction conditions acid concentration = 0.08 wt% sulfuric acid, u = 1.0 cm/ min, VO = 1.0 cm/min, T = 230 °C, reactor length = 6 inches...

A continuous counter-current reactor system has shown great promise as a process reactor in the dilute acid hydrolysis of cellulose. However, the findings on this unique reactor system have been limited to the theoretical aspects and the proof-of-concept laboratory experiments. It has to be developed into an upscale process reactor before it is adopted into the biomass conversion process. To this end, a pilot-scale process study is being conducted at NREL. This is only the first step. To be noted here is that reactors of similar design are being used in industry it took years of developmental work, however, before they were put into commercial service. It would probably take about the same degree of investment in this case. In addition to the reactor issue, there are other important issues that need to be addressed in the dilute acid process. 

Figure 6.14 A counter current reactor/heat exchanger. [After E. A. Grens and R. A. McKean, Chem. Eng. Sci., 18, 291, with permission of Pergamon Press, Inc., London, England, 1963.]...

Mensah P, Carta G (1999) Adsorptive control of water in esterification with immobilized enzymes. Continuous operation in a periodic counter-current reactor. Biotechnol Bioeng 66 137-146... 

Gaikwad and Naik (2000) studied a combination of WAO and adsorption that has been successfully used to demonstrate the removal of sulphates from DWW. Studies were done in a counter current reactor containing 25 cm base of small crushed stones supporting a 20 cm column of bagasse ash as an adsorbent. The wastewater was applied from the top of the reactor and air was supplied at the rate of 1.0 L/min. The treatment removed... 

The tubeside temperature profiles of tube 1 for the three types of mixed flow system, together with the profile for the co-and counter-current reactors, are given in figure 4. In all cases, the tube in the bundle representing the worst conditions has been used. An important observation is that it is not always... 

Comparison between co-current and counter-current reactor configurations. (a)Temperature profiles of hot gas and reforming sections and (b) methane conversion, HRF and permeation flow. 

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