Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-12-16
2001-09-11
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S241000, C137S802000
Reexamination Certificate
active
06288269
ABSTRACT:
The present invention relates to an apparatus for introducing a fluid into a process stream. In particular, though not exclusively, the present invention relates to an apparatus for introducing a fluid into a vinyl acetate reactor.
BACKGROUND OF THE INVENTION
Vinyl acetate may be produced by reacting acetic acid, oxygen and ethylene in the presence of a catalyst. The activity of the catalyst may be enhanced by using a promoter such as aqueous potassium acetate. Typically, the reaction is carried out in a fixed bed reactor containing the catalyst. A reactant process stream comprising acetic acid vapour, ethylene and oxygen is fed into the reactor through an inlet. The inlet comprises a pipe having a bend of an angle of between 45 to 90° upstream of the reactor. As reactant molecules flow past the bend in the pipe, they accelerate by varying amounts. This distorts the velocity distribution of the reactant molecules and, as a result, the velocity profile of the process stream is asymmetric.
The catalyst promoter is also introduced into the reactor through the pipe. Conventionally, this is achieved using a spray nozzle which is mounted to an end of a rigid support arm. The support arm is positioned downstream of the bend, and extends perpendicularly into the pipe from the pipe wall. The promoter is introduced into the pipe as liquid droplets from the nozzle; which partially evaporate whilst in the pipe. The promoter is carried by the reactant process stream into the reactor for distribution over the catalyst bed. However, because of the distorted velocity profile of the reactant process stream, the promoter is not deposited evenly over the catalyst. The problem is compounded by the support arm, which, by being configured at right angles to the direction of flow, further distorts the velocity profile of the reactant process stream.
BRIEF DESCRIPTION OF THE INVENTION
We have alleviated the problem by providing a new apparatus for introducing fluid into a process stream.
According to the present invention, there is provided apparatus for introducing a fluid into a process stream which apparatus comprises:
(a) a pipe for conducting said process stream, said pipe having a bend; and
(b) a nozzle for introducing said fluid into said process stream downstream of said bend characterised in that said pipe has a flow-correction device downstream of said bend and said nozzle is mounted downstream of said flow-correction device to an end of a support arm which extends into said pipe in a direction substantially parallel to the direction of said pipe downstream of said bend.
The pipe bend may have an angle of 40 to 120° preferably, of about 45 to 100°. In a preferred embodiment, the pipe bend has an angle of about 90°.
In use, a process stream is fed into the pipe at a location upstream of the pipe bend. This process stream flows through the pipe, and past the pipe bend. Fluid is also introduced into the pipe through the nozzle. The nozzle fluid is introduced at a location downstream of the bend, and is carried along by the flow of the process stream. The nozzle is mounted on a support arm which extends into the interior of the pipe in a direction substantially parallel to the direction of the pipe downstream of the bend. Thus, the support arm causes minimal disturbance to the flow of process stream as it flows past the bend. Preferably, the support arm takes the form of a tube, which is coupled to a supply of nozzle fluid.
Preferably, the nozzle fluid is a liquid.
As the process stream flows past the bend, the molecules accelerate by varying amounts. This distorts the velocity distribution of the process stream and, as a result, the process stream velocity profile is non-uniformly asymmetric. The bend may also cause the process stream to swirl. At least one of these disadvantages may be alleviated by mounting a flow-correction device in the pipe of the present invention.
In one embodiment, the flow-correction device comprises a body having a plurality of longitudinal channels. In use, the body is positioned downstream of the pipe bend and configured such that the channels are substantially parallel with the direction (longitudinal axis) of the pipe downstream of the bend. As the process stream flows through the channels, any swirl in the flow pattern is reduced. The velocity distribution of the process stream, however, remains unchanged.
In a preferred embodiment of the invention, the flow-correction device comprises a plate having perforations. The perforations may take the form of pores or apertures which, preferably, are evenly spaced apart from one another. For example, the plate may comprise a plurality of holes with diameters of 5 to 30 mm, preferably, 8 to 12 mm. These holes may be spaced apart by about 5 to 30 mm, preferably, 12 to 17 mm. In a preferred embodiment, the plate has a plurality of 10 mm diameter holes spaced 14.7 mm apart. In use, the plate reduces the free area of flow through the pipe such that process stream passing through the perforations experiences a drop in pressure. The pressure drop may be equivalent to about 5 to 20 velocity heads based on the pipe inlet flow. The pressure drop causes an increase in turbulence and a near equal flux through the holes of the plate. As a result, distortions in the velocity profile of the process stream are reduced or eliminated.
The nozzle is positioned downstream of the flow-correction device. Thus, the nozzle fluid introduced into the pipe is carried along the pipe by a flow of process stream whose flow pattern has been corrected either for swirling and/or non-uniformity in the velocity distribution profile.
Where a plate having perforations is employed as a flow-correction device, the nozzle may be coupled to the plate. In one embodiment, the plate having perforations is provided with a hole. In use, the nozzle is inserted through the hole and held in place, for example, by retaining means. The retaining means may take the form of a guide sleeve which is coupled to the plate. The guide sleeve can be used to ensure that the nozzle is placed in the same position every time it is used. Preferably, the guide sleeve ensures that the tip of the nozzle just protrudes from the underside of the plate. This allows nozzle fluid to be introduced into the optimum mixing zone of the pipe.
The present invention may be employed as an inlet for a fixed bed reactor, for example, to contact process stream and nozzle fluid with a catalyst bed positioned therein. In one embodiment, the present inlet is coupled to a fixed bed reactor for the production of vinyl acetate. In this embodiment, a process stream comprising acetic acid vapour, ethylene and oxygen is fed into the reactor, whilst a promoter of, for example, potassium acetate solution, is introduced into the reactor as a nozzle fluid. The promoter may evaporate on entering the pipe and is carried by the flow of reactants into the reactor for deposition over the catalyst bed. It has been found that fluid deposits more evenly over the catalyst bed as a vapour rather than a liquid. Thus, in a preferred embodiment, the distance between the nozzle and catalyst bed is adjusted to maximise the residence time of the nozzle fluid in the inlet. This ensures that the a relatively large proportion of the nozzle fluid is evaporated before entering the reactor.
The present invention may further comprise a distributor, for example, in the form of a plate. The plate is preferably circular and, when mounted over a portion of a catalyst bed, provides a bluff surface which is substantially perpendicular to the direction of the pipe downstream of the bend. The plate removes some of the dynamic pressure of the incoming process stream
ozzle fluid mixture through turbulent eddies and promotes back-mixing of the process stream
ozzle fluid mixture by setting up recirculation within the reactor head-space. This ensures that the nozzle fluid is adequately dispersed in the process fluid, and can be deposited onto the catalyst bed in an even manner. The plate may be mounted on support members which may be secured to th
BP Chemicals Limited
Deemie Robert W.
Killos Paul J.
Nixon & Vanderhye
LandOfFree
Apparatus for introducing fluid into a process stream does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for introducing fluid into a process stream, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for introducing fluid into a process stream will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2437444