AXIAL/RADIAL FLOW CONVERTER

Abstract

In a cooled axial/radial flow converter, in which process gas passes from an outer annulus via a catalyst bed to an inner centre tube, the catalyst bed is divided into identical modules stacked on top of each other. The process gas reaches the catalyst through openings facing the outer annulus, passes axially down the catalyst bed of each module, leaves the module through collectors in the bottom thereof, and flows to the centre tube. The catalyst bed is cooled by cooling panels, in which the process gas is pre-heated to the reaction temperature, while at the same time the heat of reaction is partly removed from the catalyst bed. The converter is especially suitable as ammonia converter.

Claims

1. A cooled axial/radial flow converter, in which process gas passes from an outer annulus via a catalyst bed to an inner centre tube, wherein the catalyst bed is divided into a number of identical modules stacked on top of each other, the feed flow of process gas reaches the catalyst through openings facing the outer annulus, passes axially down the catalyst bed of each module, leaves the module through collectors in the bottom thereof, and flows to the centre tube, and the catalyst bed is cooled by cooling panels, in which the process gas is pre-heated to the reaction temperature, while at the same time the heat of reaction is partly removed from the catalyst bed.

2. Converter according to claim 1, which is used as an ammonia converter.

3. Converter according to claim 1, wherein the module is an axial flow canister comprising a number of small exchanger plates and a number of main exchanger plates.

4. Converter according to claim 3, wherein cooling of the catalyst is achieved by insertion of vertical cooling plates installed radially in each canister.

Description

[0017] Cooling of the catalyst is possible by insertion of vertical cooling plates installed radially in each canister: Inside the panel, incoming gas is heated up to reaction temperature, at the same time removing heat of reaction from the catalyst. This principle is shown in the attached Figure.

[0018] The Figure is a side view and a top view of a preferred embodiment of the canister. In the side view, a represents the total height, b is the height from the bottom to the top of the exchanger plates, and c is the catalyst height. Further, d represents the outlet profiles of the canister.

[0019] In the top view of the canister, it is seen that this embodiment of the canister comprises both a number of small exchanger plates (1) and a number of main exchanger plates (2). In this embodiment, the number of small plates is larger than that of main plates.

[0020] Alternatively, the flow pattern can be simple adiabatic, and inter-bed cooling can be provided by installing a heat exchanger in the inner chamber. In this way, several reaction steps within the same pressure shell will be possible.

[0021] The selection depends on the intended servicing.

[0022] One possible application of the novel axial/radial flow converter of the invention is to use it as an ammonia converter, as will be described in more detail below. The Haber-Bosch ammonia synthesis belongs to the autothermic process category, meaning that it is an exothermic chemical reaction for which the temperature is maintained by the heat of reaction alone. In order to achieve this condition, gas flow and heat exchange are arranged to reduce the increase in temperature associated with the exothermic reaction and to suppress the need for an external source of heat once the reaction is started.

[0023] Cooling of the catalyst in ammonia production is well-known from the classical TVA converter. In the catalyst section of the TVA converter, the pre-heated gas flows up inside a large number of small tubes. There it absorbs part of the heat generated by the chemical reaction on the catalyst. At the top of the converter the synthesis gas, now brought to a sufficient temperature, reverses its direction and flows down the catalyst bed where the reaction occurs. However, the TVA converter had full axial flow, resulting in a high pressure drop and the need for parallel converters to obtain high production capacities.

[0024] The axial/radial flow converter according to the invention, preferably for use as an ammonia converter, has a main flow pattern similar to that of a radial flow converter, which means that gas passes from an outer annulus via a catalyst bed to an inner centre tube. However, the flow pattern in the catalyst bed is different in that the catalyst bed is divided into a number of modules stacked on top of each other. The feed flow to each module reaches the catalyst through ports facing the outer annulus. Then it flows axially down the catalyst bed and exits the module through collectors in the bottom and flows to the centre tube where all reactants are collected.

[0025] The catalyst bed is cooled by cooling panels in which the feed gas is pre-heated to the reaction temperature while, at the same time, removing the heat of reaction from the catalyst bed.

[0026] For an ammonia converter, a number of advantages can be obtained, such as a lower pressure drop in the converter if that is desired. Further it may be possible to utilize smaller catalyst sizes, i.e. below 1.5 mm.

[0027] A higher conversion in the first bed(s) can also be obtained due to intra-bed cooling. Further there is a possibility of obtaining the same conversion in one bed as previously was obtained over the first two beds.

[0028] The bed can be loaded outside the converter. In fact, it may be loaded in the catalyst plant, then reduced, sealed and shipped and finally mounted directly in the converter shell.

[0029] The axial/radial converter of the invention is suitable for revamp purposes as well as for grassroots projects. In the latter case, however, a full diameter converter cover is required.

[0030] The idea underlying the present invention is to combine the virtues of the TVA converter and the radial flow converter, but keeping the flow pattern outside the new bed exactly the same as in Applicant's radial flow converters, also for the convenience of revamp.

[0031] The flow concept may also be used for other types of converters, for which a low pressure drop is desired or in case the catalyst shrinks during the reduction process.