Patent Publication Number: US-2022212136-A1

Title: Pressure vessel

Description:
The present invention relates to a pressure vessel for use for example in a thermal swing adsorbent plant or other cryogenic or higher temperature systems. 
     Temperature swing adsorption (TSA) is an adsorptive process for separating gas mixtures, in which the regeneration of an adsorbent used is effected by means of thermal energy. TSA is, for example, used in connection with exhaust gas cleaning or for processing gas mixtures such as natural gas. 
     In cryogenic and higher temperature systems, adsorption processes conducted within pressure vessels for example packed with an adsorbent bed comprising an adsorbent substrate are conducted until a predetermined amount of the adsorbent capacity has been used, i.e. a predetermined amount of contaminant has been adsorbed by the adsorbent. The adsorbed gas is then removed from the adsorbent, for example by rapidly reducing the pressure and/or increasing the temperature within the vessel. Because adsorption is in general a stronger function of temperature than pressure, thermal cycling is used in many situations as a regenerative means of removing adsorbed gas from the adsorbent substrate. 
     In many thermal swing adsorption systems this regenerative heating is carried out by flowing a stream of heated gas through the adsorbent bed. The bed is subsequently cooled by flowing a stream of cold gas through the bed. In the absence of other effects, the heat transfer involved in heating and cooling the bed poses few problems, due to the relatively high rate and turbulent gas flows characteristic of processes employing such beds. If however, there are solid metal walls containing the bed, the associated high heat capacities involved may not permit adequate heatup and cooldown of the walls within a reasonable time and/or with reasonable effort. When the bed is being used under such conditions, that portion of the bed in proximity with the vessel walls will tend to remain at a different temperature relative to the rest of the bed, being higher during cooldown and adsorption and lower during regeneration heating for appreciable lengths of the respective cycle steps. Thus, the vessel wall will act as a heat source during adsorption and as a heat sink during regeneration. The heat sink effect requires longer regeneration times in order to regenerate the adsorbent near the wall. The heat source effect causes adsorption near the wall to be weak, so that the adsorption front moves through the bed more rapidly in those areas. 
     For such applications it is therefore advantageous to insulate the pressure or adsorber vessels internally, for example by providing an insulating layer on the inside of the outer vessel wall. Internal insulation reduces regeneration gas demand, as the vessel walls will not be heated, and improves the regeneration of adsorbent materials close to the wall, because the temperature gradient to the wall is significantly reduced. Both effects enable more rapid and energy effective regeneration cycles, especially compared to externally insulated vessels. Internal insulation is thus especially advantageous for TSA vessels that require a short regeneration time and have high heat capacities in the vessel walls. A pressure vessel for use as a gas adsorbent vessel utilizing internal insulation is known from U.S. Pat. No. 3,925,041. According to this document, an internal insulation is provided on the inside of the casing of the vessel. 
     The internal insulation comprises a number of insulating layers, each made of a plurality of rigid preformed sheets abutting one another and arranged in rows and/or columns. In order to prevent gas flow into and through the insulation layers especially at gaps or transitions between abutting sheets, it is suggested in this document to bend over the edges of the sheets of a lower layer such that they extend into the gaps between the sheets of an upper layer, thereby providing gas flow barriers. Mounting and fixing such layers requires complex and precise handling, however, and is cost intensive. 
     The present invention seeks to provide more simple and cost effective means for preventing unwanted gas flow in and through insulation layers of an internally insulated pressure vessel. 
     This object is achieved with a pressure vessel comprising the features of claim  1 . 
     According to the invention, there is provided a pressure vessel comprising a cylindrical middle section, at a first end of which there is provided a top end cover, and at the second end of which there is provided a bottom end cover, the pressure vessel comprising an outer casing, wherein at least in the cylindrical middle section there is provided an insulation arrangement on the inside of the outer casing, the insulation arrangement comprising at least one insulation material layer, and a protective layer, especially a steel layer provided on the inside of the insulation arrangement, wherein at least one insulation material layer comprises a plurality of ceramic fibre plates, and/or the protective layer comprises a plurality of protective plates, especially steel plates, and wherein the cylindrical middle section is provided with a plurality of parallel rings extending circumferentially along the inside of the outer casing and adapted to secure the at least one insulation layer and/or the protective layer to the outer casing. 
     The pressure vessel according to the invention has excellent insulation properties, especially compared to pressure vessels with outer insulation. The insulation arrangement can be provided with a relatively small thickness, thereby minimizing the dimensions of the pressure vessel as a whole. Advantageously, the insulation arrangement can comprise only one insulation layer. A post treatment of the insulation arrangement is not necessary. For example, in prior art solutions internal insulation provided by concrete lining, such as refractory, must be enhanced by post-installation heat treatment to achieve required concrete qualities. Such an additional treatment is not necessary according to the invention. 
     The risk or frequency of gas bypassing the adsorbent by passing through insulation layers from feed to product side is avoided. Also, critical longitudinal welding seams provided on the cylindrical middle section or shell section of the pressure vessel are more easily accessible for maintenance purposes. For example, insulation can easily be removed and renewed only in specified segments. 
     Advantageous embodiments are the subject matter of the dependent claims. 
     According to a preferred embodiment, a ceramic paper layer is provided between the protective layer and the insulation arrangement. Especially in case of a steel layer as protective layer, such a ceramic paper layer ensures that the layers of the insulation arrangement are not damaged by the steel layer, especially during manufacture of the pressure vessel. 
     Advantageously, the cylindrical middle section of the pressure vessel is provided with a plurality of fixing elements adapted to secure the protective layer, especially the steel plates, and/or the insulation arrangement, especially the ceramic fiber plates, to one another and/or to the outer casing. Such fixing elements, which can be provided for example as clips or pins can effectively interact with the rings provided on the inside of the outer casing. 
     Advantageously, the top end cover and the bottom end cover comprise an internal insulation arrangement comprising bricks or a refractory or an inner skirt or a flexible insulation material. Such insulation arrangements are easily adaptable to complex shapes typically used in end covers, such as spherical or elliptical dished heads. 
     Expediently, gas flow passage means are provided in the top end cover and the bottom end cover of the pressure vessel. These can comprise protective shields between the gas flow passages and the internal insulation provided in the end covers and/or a basket gas distributor to ensure an even distribution of gas over the whole adsorbent bed in the cylindrical middle section. 
     Advantageously, the adsorbent bed is provided in the cylindrical middle section of the pressure vessel. 
     Advantageously, the adsorbent bed can be provided on a bed support, for example a wedge wire, to ensure optimal distribution of gas flow from the bottom end section. 
    
    
     
       Preferred embodiments of the invention will now be described with reference to the accompanying drawing. Herein, 
         FIG. 1  shows a schematically simplified side sectional view of a preferred embodiment of the pressure vessel according to the invention, 
         FIG. 2  a more detailed sectional view of a portion of the cylindrical middle section of the pressure vessel of  FIG. 1 , and 
         FIG. 3  a schematical plan view of a section of the middle section, viewed from the inside of the vessel of  FIGS. 1 and 2 . 
     
    
    
     A preferred embodiment of a pressure vessel according to the invention is generally designated  100 . The pressure vessel  100  is of a generally cylindrical shape, and comprises a cylindrical middle section  120 . At an upper end it is provided with a top end cover  130 , and at a lower end with a bottom end cover  140 . Top end cover  130  and bottom end cover  140  are essentially provided as spherical or elliptical dished heads. Gas flow passage means  220  are provided in the top end cover  130 , and gas flow passage means  230  in the bottom end cover  140 . The gas flow passage means comprise basket gas distributors  224 ,  234 . In the lower section an inert ball filling for optimization of gas distribution may advantageously be provided. 
     An outer layer of the pressure vessel  100  is provided as an outer casing  180  extending over the top end cover  130 , the cylindrical middle section  120  and the bottom end cover  140 . The outer casing  180  is made of a metal such as carbon steel. 
     The top end cover  130  and the bottom end cover  140  are provided with internal insulation means on the inside of the outer casing  180 . The internal insulation means in the embodiment shown are provided as bricks  182 . Bricks provide an effective means of insulation, and can easily be adapted to complex shapes of the outer casing such as the dome shaped top and bottom end covers. Be it noted that the internal insulation means in the top end cover  130  and the bottom end cover  140  can also be provided for example as inner skirts, a refractory lining or as insulation plates covered with protective plates such as steel plates. 
     In the cylindrical section  120 , a plurality of rings  125  are provided on the inside of the outer casing. These rings  125  provide a plurality of parallely extending ridges, which serve to secure an insulation arrangement  190  and a protective layer in the cylindrical section  120 , as will be described in the following. These rings also serve to avoid gas bypasses though the insulation arrangement, as will also be further expanded on below. 
     As shown especially in  FIG. 2 , the insulation arrangement  190  comprises a first insulation material layer  192  adjacent to the inside of outer casing  180 . On the inside of first insulation material layer  192  there is provided a second insulation material layer  194 . 
     On the inside of the second insulation material layer  194  there is provided an additional intermediate layer  198 , which is preferably provided as a layer of ceramic paper. 
     Adjacent to the inside of the intermediate layer  198  there is provided a protective layer  196 , which is advantageously provided as a steel layer. The intermediate layer  198  between the steel layer  196  and the second or innermost insulation material layer  194  serves to protect the innermost insulation material layer  194  from damage during manufacturing of the insulation arrangement  190  and/or during operation of the pressure vessel. 
     The insulation material layers  192 ,  194 , the protective layer  196  as well as the intermediate layer  198  are advantageously provided in form of individual plates or sheets  192   a ,  194   a ,  196   a ,  198   a , which are secured to the outer casing  180  with the aid of the rings  125 , as will be explained in the following. Especially the plates  192   a ,  194   a  used for the insulation material layers are made of a flexible ceramic material. Such a flexible ceramic material my, for example, comprise a ceramic foam matrix, in which ceramic fibre materials are provided. 
     Advantageously, the axial distance H between neighbouring rings  125  can be constant over the whole cylindrical section  120 . For example, the axial distance H (as shown in  FIGS. 1 and 3 ) can be chosen to be 1000 mm. The plates/panels  192   a ,  194   a  of the insulation material layers  192 ,  194  and the steel layer  196 , as well as of the ceramic paper layer  198  are dimensioned such that they completely cover the area on the inside of the outer casing  180  between respective neighbouring rings  125 . For example, each of these panels can be provided with a height corresponding to the axial distance H between two neighbouring rings  125 . Any suitable arrangement is possible, with which complete covering of this area between two neighbouring rings  125  is achieved. It is also possible, for example, that the insulation material layers  192 ,  194  and/or the ceramic paper layer  198  are provided with a smaller size, such that, for example two such plates have a height corresponding to the axial distance H between two neighbouring rings  125 . Advantageously, the steel plates are provided with a height corresponding to axial distance H. 
     As is especially visible in  FIG. 2 , the respective plates  192   a ,  194   a ,  196   a ,  198   a  above a ring  125  can rest on this ring  125  with their lower edges. As their height corresponds to the axial distance H, they will also engage the lower side of a neighbouring ring  125  with their upper edges, as also shown in  FIG. 2  for the plates  192   a ,  194   a ,  196   a ,  198   a  below the ring  125 . 
     Advantageously, pins or clamps  135  can be provided on the inner edges of rings  125  for fixing the steel plates on the insulation plates, and thus the insulation arrangement  190  on the outer casing  180 . 
     By means of providing rings  125 , in addition to the support for the plates on the inside of the outer casing  180 , as discussed, an effective deflection and/or barrier means counteracting gas bypasses between the protective steel layer  196  and the outer casing  180 , i.e. through the insulation arrangement  190 , can be effectively avoided. Should, for example, gas passing through the pressure vessel flow into the space between the protective steel layer  196  and a steel ring  125  and thus through the insulation arrangement  190 , this flow will be interrupted at a neighbouring ring  125 , so that such a gas flow bypassing the main gas flow through an adsorbent bed provided in the cylindrical section  120  can be minimized or avoided. 
     Be it noted that the number of insulation layers  192 ,  194  can be adapted according to the required insulation effect. For example, only one insulation layer can be provided between the outer casing  180  and the protective steel layer  196 . Also, more than two such layers can be provided. 
     As is schematically shown in  FIG. 3 , it is advantageously possible to provide the plates of insulation material  192   a ,  194   a  in a different orientation from that of the protective steel plates  196   a . For example, rectangular insulation plates  192   a ,  194   a  can be provided with a width W and a height H/2 smaller than W, such that their horizontal extension is larger than their vertical extension. As also shown in  FIG. 3 , for example two insulation plates  192   a ,  194   a  may be provided above one another, such that the height of two neighbouring plates  192   a  with height H/2 corresponds to the axial distance H between two neighbouring rings  125 . Such two insulation plates  192   a  can also be slightly displaced from one another in circumferential direction, as indicated by displacement W. 
     Be it noted that in order to visualize plates  192   a ,  194   a ,  196   a  in  FIG. 3  only parts of the respective layers are shown. 
     On the other hand, it is advantageous to provide the protective plates  196   a  with a height H and a width K such that their height corresponds to the axial distance between two neighbouring rings  125 . K can be equal to H/2, and W can be equal to H, so that all plates  192   a    194   a ,  196   a  are of the same size. However, different values for H/2, W and K may also be chosen. 
     The inside of pressure vessel  100  is filled with an adsorption bed, which is not shown in the figures. Advantageously, there is provided a bed support, for example a wedge wire  250  (shown in  FIG. 1 ), on which the adsorbent bed can be positioned. In this case, an inert ball filling in the bottom section  140  of the vessel is not necessary. 
     Advantageously, the flow passage means  220 ,  230  comprise basket gas distributors  224 ,  234  and protective shields  222 ,  232  inserted into gas flow nozzles, as is well known in the art. 
     Advantageously, the nozzles are equipped with protective shields as a protective measure against thermal shocks. 
     LIST OF COMPONENTS 
     
         
           100  pressure vessel 
           120  cylindrical middle section 
           125  rings 
           130  top end cover 
           140  bottom end cover 
           180  outer casing 
           182  bricks 
           190  insulation arrangement 
           192  first insulation material layer 
           194  second insulation material layer 
           196  protective layer 
           198  intermediate layer (ceramic paper layer) 
           192   a , 194   a , 196   a , 198   a  plates or sheets 
           220 , 230  gas flow passage means 
           222 , 232  protective shields 
           224 , 234  basket gas distributors 
           250  wegde wire 
         H height 
         W,K widths