Many industrial processes involve mixing and distribution of fluids, and proper mixing and homogeneous distribution of fluids is especially important to ensure economic operation at high throughput rates in catalytic reactors or fractionation columns. However, various difficulties typically arise with high volume throughput, and especially where the fluid has multiple phases (e.g., liquid and vapor). Consequently, numerous approaches have been tried to circumvent at least some of the problems.
For example, many fixed bed reactors and other vessels with concurrent downflow of one or more fluid phases employ inlet diffusers. Inlet diffusers are typically located at the inlet nozzle and are generally configured to effect a distribution of the fluid onto a cross-sectional area in the vessel below (see e.g., U.S. Pat. No. 3,685,971 to Carson). Where appropriate, inlet diffusers may be utilized in combination with additional devices, and particularly distribution trays (see e.g., U.S. Pat. No. 3,146,189 to Halik, et al.). While such configurations often provide at least some homogeneous distribution of a liquid over a target area, all or almost all of them exhibit significant shortfalls when vapor and liquid phases need to be homogeneously distributed.
To circumvent at least some of the problems with homogeneous distribution of vapors and liquids, inlet diffusers may be configured to achieve at least partial disengagement of the entering vapor and liquid phases (see e.g., U.S. Pat. No. 3,378,349 to Shirk, et al., or U.S. Pat. No. 4,579,647 to Smith). Such inlet diffusers, which typically improve homogeneous distribution of vapor and liquids at least to some degree, are, however, often not satisfactory when the vapor and liquid may enter the inlet diffuser with significant momentum and in a very non-homogeneous manner. Vapors and liquids may be homogenized to help improve distribution as described, for example, in U.S. Pat. No. 4,126,539 to Derr, et al., by providing perforated plates in combination with passageways defined by concentric frustoconical sections. However, and especially where the liquid and vapor have a relatively high momentum, liquid may pass primarily through the orifices located near the points where the liquid impacts the perforated plate. Furthermore, a non-uniform vapor velocity profile may result in vapor recirculation zones above the perforated plate, with consequent inhibition of the liquid flow through orifices located below these vapor recirculation zones.
Alternatively, as described in U.S. Pat. No. 3,915,847 to Hutchings, a perforated plate together with a tube sheet and distribution conduits may be employed to assist homogeneous distribution of vapor and liquid. However, maldistribution of liquids and vapors may still persist in such configurations due to liquid impingement upon and/or vapor recirculation above the perforated plate. Moreover, such configurations typically inhibit personnel access to a vessel, as such configurations are not readily withdrawn through the top nozzle of the vessel.
In still other approaches, mixing devices may include a configuration with chevron-type vanes, wherein the device is disposed between the outlet of a mixing chamber and an imperforate deck as described in copending U.S. patent application Ser. No. 10/031,856, filed on Nov. 8, 2002, now U.S. Pat. No. 7,125,006, which is incorporated by reference herein. While such devices typically improve mixing and distribution of liquids and vapors, circumferentially asymmetric fluid distribution may still occur, especially when the liquid and vapor stream enters the mixing and distribution device asymmetrically.
Thus, although there are numerous mixing and distribution devices known in the art, all or almost all of them suffer from one or more disadvantages. Therefore, there is still a need for improved methods and apparatus for mixing and distributing fluids.
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