Chemistry of inorganic compounds – Nitrogen or compound thereof – Ammonia or ammonium hydroxide
Reexamination Certificate
1998-12-10
2001-03-06
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Ammonia or ammonium hydroxide
C423S361000, C422S187000, C422S198000, C422S198000, C422S198000, C422S211000, C518S700000, C518S713000
Reexamination Certificate
active
06197271
ABSTRACT:
The present invention relates to a chemical reactor for use in equilibrium limited exothermic gas phase reactions, such as methanol synthesis or ammonia synthesis and to a process for conducting exothermic vapour phase reactions.
The evolution of ammonia and methanol reactors from the 1960s to the 1980s is outlined in a paper entitled “Review these developments in ammonia and methanol reactors” by Umberto Zardi which was published in the August 1982 edition of “
Hydrocarbon Processing”
at pages 129ff. The first reactor described in this paper is the single bed Ammonia Casale axial reactor, designed for ammonia production, in which the synthesis gas flows under high pressure and temperature axially through a single catalyst bed mounted in a cylindrical reactor. Subsequent developments include the introduction of multi-bed designs and reactors utilising radial as well as axial flow through the beds.
Thus, EP-A-0026057 describes an integrated process for the production of ammonia or methanol in which an appropriate synthesis gas is passed through a series of catalyst beds and, between each bed, the gas is quenched, by the injection of quench gas between the beds. Quenching the reaction mixture between catalyst beds helps to shift the equilibrium of the exothermic gas phase reaction(s) in a favourable direction and to alleviate the undesirable effects of the presence of pockets of vapour of elevated or reduced temperature. These effects include, in the case of hot pockets, deterioration of catalyst and, in the case of cold pockets, possible snuffing of the reaction. Similarly, EP-A-0248284 relates to a reactor for use in the production of ammonia, in which the reactor comprises a number of catalyst beds wherein cooler quench gas is supplied to the reactor between each bed. The purpose of this quench gas is the same as in EP-A-0026057, i.e. to shift the equilibrium of the exothermic gas phase reaction(s) in a favourable direction and to alleviate the undesirable effects of non-uniform temperature distribution within the catalyst beds.
The efforts of the prior art to counteract the problem of temperature inhomogeneity in catalyst beds during equilibrium limited exothermic gas phase reactions have not been entirely successful and there is a need in the art for a reactor design which will yield increased catalyst life and performance.
According to the present invention there is provided a reactor for conducting an exothermic vapour phase reaction comprising:
a) a pressure vessel having inlet means for supply of a gaseous reactant or reactants and outlet means for recovery of a product-containing stream therefrom;
b) a plurality of beds of a heterogeneous catalyst effective for catalysis of the exothermic vapour phase reaction in the path of a material passing from the inlet means to the outlet means, each bed being supported within the pressure vessel by a respective support means;
c) a vapour collection chamber and a vapour redistribution chamber between the or each successive pair of beds, the vapour collection chamber being arranged to collect a vaporous reaction mixture from an exit end of one bed of the pair and the vapour redistribution chamber being arranged to redistribute vapour over the inlet end of the other bed of the pair;
d) a diaphragm extending across the interior of the pressure vessel and separating the vapour collection chamber from the vapour redistribution chamber;
e) at least one pair of nested trough members, the or each pair comprising an inner trough member and an outer trough member associated with the diaphragm and extending at least partially thereacross, the inner trough member and the outer trough member being nested so as to define a space therebetween, the inner trough member opening to the vapour collection chamber and having one or more first apertures along its length and the outer trough member communicating laterally on each side with the vapour redistribution chamber by means of one or more second apertures opening laterally of the outer trough member along a respective side thereof, the space between the inner trough member and the outer trough member providing a tortuous passageway for vapour from the vapour collection chamber to the vapour redistribution chamber through the at least one first aperture, through the space between the inner trough member and the outer trough member, and then through the at least one second aperture to discharge laterally into the vapour redistribution chamber; and
f) a quench gas conduit associtated with the or each pair of trough members and being provided with one or more third apertures along its length arranged to discharge quench gas into the vapour flowing along the tortuous pathway.
The pressure vessel may be of any size and shape but is preferably circular in cross-section. Preferably the inlet means and the outlet means are axially spaced one from another so that the overall direction of flow of reactants and products is from one end portion of the reactor to the other.
In one arrangement the beds of catalyst are substantially cylindrical.
The trough members may be of any suitable section provided that lateral discharge of vapour into the vapour redistribution chamber is possible. A preferred form of trough member is arcuate in section. Preferably the angle subtended by the arc of an arcuate section trough member is from about 120° up to about 180°. Semi-circular section trough members may be used. Alternatively the trough members may be part-elliptical, for example, semi-elliptical in section. If desired, the trough members may be formed with one or more planar faces. For example, it is envisaged that a trough member with a flat bottom and arcuate sides could be used, or a trough member with a flat bottom and inclined planar sides, which may be inclined, usually outwardly inclined to the bottom of the trough member. The angle of inclination between the sides and the bottom of the trough may be any suitable angle, for example from about 30° to about 90°.
In one preferred arrangement the quench gas conduit associated with the or each respective pair of trough members is mounted at least partially within the inner trough member of the pair.
The first and second apertures in the inner and outer trough members respectively may be of any suitable shape, e.g., circular, elliptical or rectangular, as may also be the third aperture or apertures in the quench gas conduit. The inner and/or outer trough members may each have only a single first or second aperture respectively, the aperture being provided in the form of an elongate slot. However, it will normally be preferred for ease of construction to provide a plurality of apertures along the length of the respective trough member. Similarly, although the quench gas conduit may have a single elongate slot to serve as the third aperture, it will normally be preferred to provide a plurality of third apertures along the length of the conduit for ease of construction and to enable the quench gas conduit to retain sufficient structural strength.
When the diaphragm and associated nested trough members are the only means of vapour redistribution provided between successive catalyst beds of the reactor it is preferred that the position of the second apertures be arranged such that the radial displacement, with respect to the nearest point on a reference axis lying in the plane of the diaphragm and also in a perpendicular plane bisecting the outer trough member along its longitudinal axis, of the second apertures from the plane of the diaphragm is not more than about 45°. However, this angle may be greater than 45° when further means of vapour redistribution are provided between catalyst beds, as will be explained further below.
The second apparatus may be arranged in one or more rows on each side of the outer trough member so that the discharge of quenched reaction mixture to the vapour redistribution chamber is through a set of one or more rows of second apertures on one side of the outer trough member and through a corresponding set of one or more rows of second apert
Early Simon Robert
Harrison George Edwin
Kippax John Wilson
Griffin Steven P.
Kvaerner Process Technology Limited
Medina Maribel
Senniger Powers Leavitt & Roedel
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