MXPA98001378A - Separation of - Google Patents

Abstract

The present invention relates to: An oscillating vacuum adsorption apparatus 2 for separating a gas mixture includes a line 6 along which the vacuum is capable of being attracted. The apparatus is provided with a plurality of eductors 24, 26, 28 and 30 each connected to the pipe 6, and in parallel with the other eductors, and with the respective check valves 48, 50, 42 and 54. The valves of retention 48, 50, 52 and 54 are placed and operate in order to select the number of eductors 24, 26, 28 and 30 in communication with the pipe 6. In this way the degree of vacuum to which the apparatus is subjected can be varied.

Description

"SEPARATION OF GAS" BACKGROUND OF THE INVENTION This invention relates to gas separation. In particular, it relates to a vacuum oscillating adsorption apparatus for separating a gaseous mixture, for example, air. There is a continuous investigation for cheaper methods of air separation. Some of these methods are aimed at improving the thermodynamic efficiency of air separation processes. Others are aimed at finding economic sources of energy. One of these sources is the waste heat that is typically fired from an oxidation reaction. It is known how to use this waste heat to raise the steam and to expand the pressurized steam in a turbine, which can be coupled directly with a compressor that is part of the air separation plant or that can alternatively be coupled with a power generator electric Alternatively, a stream of compressed nitrogen from the air separation plant can be raised in temperature by the waste heat and expanded in an expansion turbine. The expansion turbine can be coupled directly with a compressor that is part of the air separation plant, or with an electric power generator. A disadvantage of these provisions is that they are added very considerably to the total capital cost of the plant and may tend not to be lent for use when there is a need to vary the output of electric power. Japanese Patent Application Number 54-162967A discloses a process in which a gas enriched with oxygen containing 40 volume percent oxygen is separated by means of the membranes of air. The gas enriched with oxygen is the permeation gas. A vacuum is attracted to the side of the permeation gas of the membranes in order to facilitate separation of the gas enriched with oxygen. The gas enriched with oxygen is supplied to an oven. The residual heat from the furnace is used to raise the steam. The steam flows through an eductor that attracts the vacuum. This arrangement however is inappropriate for practical use because the steam contaminates the product enriched with oxygen. It is therefore necessary to decouple the liquid water from the gas enriched with the resulting oxygen. It is also necessary to ensure that the vapor does not contain impurities that could be dangerous in the presence of the gas enriched with oxygen.

The way of separating the air by vacuum oscillating adsorption is already well known. A motor-driven vacuum pump such as a Rootes blower is used to attract vacuum. These empty shadows have a tendency to fail. In addition, the vacuum oscillating adsorption apparatus that includes this vacuum pump tends to have relatively deficient characteristics and is therefore not suitable to be used to fill a variable demand for a gaseous product. One object of the present invention is to provide an apparatus that improves at least one and preferably all of these disadvantages.

SUMMARY OF THE INVENTION In accordance with the present invention, an oscillating vacuum adsorption apparatus is provided for separating a gas mixture, including a line of pipe through which the vacuum is able to be attracted, wherein there is a plurality of eductors each connected to the line of pipe and in parallel with the other eductors and one or more first connection-disconnection valves associated with the eductors, placed and operable to select the number of eductors in communication with the pipeline.

Using an eductor or eductors to attract the vacuum, the capital and operating costs of a vacuum pump driven by a conventional engine are avoided. In addition, the maintenance and shutdown periods associated with each of the pumps can be greatly reduced. The vacuum oscillating adsorption method and apparatus according to the invention does not make it necessary to use a steam turbine or a gas expansion turbine. further, because the gas stream produced is typically not adsorbed, it does not need to contact the pressurized steam that attracts the vacuum and therefore there is no risk of contamination of the gas produced by the steam. The vapor can be provided at any convenient elevated pressure. Pressures within the range of 5 to 60 bar are generally appropriate. The apparatus according to the invention is particularly suitable for supplying a gas stream enriched with oxygen to support the convulsion of a part of a stream of hydrogen sulphide in a Claus process. In this example, the gas stream enriched with oxygen is preferably supplied separately from an air stream to a burner that discharges to an oven in which the combustion of hydrogen sulfide and the reaction between sulfur dioxide is carried out resulting and the residual hydrogen sulfide to form sulfur vapor. In this example, the source of the pressurized steam supplied to the eductor may be a residual heat burner associated with the furnace. The Claus process is only one example of a process in which the flow of feed fluid varies and therefore the demand for oxygen varies. When oxygen is supplied to this process, it is desirable that it has the ability to vary its flow. A specific advantage of the apparatus according to the invention is that it lends itself to the production of the gas stream produced at a variable flow rate and therefore it can easily follow changes in the flow regime of an acid gas stream to the Claus process. The first connection-disconnection valves preferably work automatically. Preferably, the vacuum oscillating adsorption apparatus according to the invention also includes a plurality of second automatically operable switching-disconnection valves each capable of operating to position a different adsorbent bed in communication with the pipeline, and a medium to select the duration of each period for which each of the second operable shut-off valves automatically opens in accordance with the number of eductors that will communicate with the pipeline during that period. Preferably, there is a means for automatically selecting the number of first automatically operable switching-disconnection valves that open in accordance with the demand for the production gas. The vacuum oscillating adsorption apparatus preferably includes a plurality of adsorbent beds that operate out of phase one with the other. During each period in which the event is subjected to a vacuum, another bed receives a flow of gas mixture and adsorption of prefence or more rapidly one compartment of the gas mixture (in comparison with the other components). It is desirable in a vacuum oscillating adsorption apparatus according to the invention to supply variations in the duration of the periods in which each bed is subjected to vacuum, making concomitant variations in the flow regime of the gas mixture to be separated. towards the apparatus (typically by means of a flow control valve in a line of pipe for the gas mixture communicating with the apparatus) or preferably by arranging for a period of rest if necessary, at the end of the adsorption steps selected.

BRIEF DESCRIPTION OF THE DRAWINGS The apparatus in accordance with the invention will now be described by way of example with reference to the accompanying drawing, which is a schematic flow diagram of a plant including a vacuum oscillating adsorption apparatus and an oven for react the hydrogen sulfide with oxygen.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawing, the illustrated plant includes an apparatus 2 of vacuum ascending adsorption. Vacuum oscillating adsorption is the term applied to the oscillating pressure adsorption where the minimum desorption pressure that is obtained is lower than the atmospheric pressure. The vacuum adsorption apparatus 2 may be any of a kind already known. In this example, it is of the kind shown in Figure 1 of the US Patent Number 5,122,164 and can trigger one of the cycles illustrated in Figures 2, 3 and 4 of the American Patent Number 5,122,164. U.S. Patent Number 5,122,164 is incorporated herein by reference. It should be noted, however, that the vacuum pump 16 shown in Figure 1 of US Pat. No. 5,122,164, has been omitted and replaced by a group of steam eductors as will be discussed below. The vacuum oscillating adsorption apparatus 2 has associated therewith a first pipe 4 for a gas produced enriched with gaseous oxygen, typically containing at least 90 volume percent oxygen, a second pipe 6 through which it attracts the vacuum and a third pipe 8 through which the air is fed to the plant. A compressor 10 is placed inside the first pipe 4. During operation, a continuous flow of the gas enriched with oxygen is provided by the compressor 10 to a burner 12 which is discharged to an oven 14 that forms part of a plant to recover the sulfur by the Claus process of a gas stream containing hydrogen sulfide. The burner 12 is also supplied with an air flow through a pipe 16 and a flow of an acidic gas mixture, typically comprising at least 40 volume percent hydrogen sulfide, and typically other combustible gases such as hydrocarbons and ammonia, and also carbon dioxide, through a pipe 18. The relative flow of the oxygen molecules to hydrogen sulfide and other fuel molecules to the burner 16, is placed in such a way that a part of the hydrogen sulfide it burns with the result that sulfur dioxide and water vapor are formed. A certain amount of the sulfur dioxide reacts in the furnace 14 with the residual hydrogen sulphide to form sulfur vapor and water vapor. The configuration and operation of the furnace 14 and the burner 12 is described essentially in the Patent Number EP-A-0 701 967 with the exception that the air is supplied to the burner instead of the carbon dioxide. European Patent Application Number 0 701 967 is incorporated herein by reference. A gas mixture comprising hydrogen sulfide, sulfur dioxide, steam, sulfur vapor, carbon dioxide and nitrogen leaves the furnace 14 through an outlet 20, at a temperature of up to 1650 ° C. The gas mixture flows to a waste heat boiler 22 where it is cooled and where the steam rises to a high pressure. The resulting cooled gas mixture flows through the remainder of the Claus plant (not shown in the drawing) typically comprising units 14, 16, 18, 20 and 22 shown in Figure 1 of Patent Number EP-A- 0 701 967. The reader should refer to the Patent Number EP-A-0 701 967 for additional information about these units and their operation. At least part of the high-pressure steam raised in the waste heat burner 22 is distributed to a group of four readers 24, 26, 28 and 30, placed in parallel with respect to each other. The educators 24, 26, 28 and 30 have throats 32, 34, 36 and 38, respectively. The grooves 32, 34, 36 and 38 communicate with the conduits 40, 42, 44 and 46, respectively, each of which is connected to the second pipe 8. The conduits 40, 42, 44 and 46 have connecting valves. - disconnects that are automatically workable 48, 50, 52 and 54, respectively, placed on them. During operation, when all of the automatically operating on-off valves 48, 50, 52 and 54 are opened, the flow of the high pressure steam through each of the eductors 24, 26, 28 and 30, causes a vacuum is attracted in each of the conduits 40, 42, 44 and 46, and in the second pipe 6. Referring again to Figure 1 of the US Patent Number A-5 122 164 and its description therein, The vacuum oscillating adsorption apparatus includes two adsorbent beds A and B in parallel with one another. The adsorbent bed A is able to be placed in communication with a vacuum source, opening the valve 2A, and the adsorbent bed B is similarly able to be placed in communication with the vacuum source by opening the valve 7B. When the vacuum oscillating adsorption apparatus 2 shown in the accompanying drawing is provided by the apparatus shown in Figure 1 of US Patent Number A-5 122 164, and let's say valve 2A is opened, bed A is subjected to to a vacuum drawn towards the second pipe 6 shown in the accompanying drawing. Initially, during the opening of the valve 2A, the adsorbent bed A is at a pressure considerably greater than the minimum pressure obtained in the vacuum oscillating adsorption process. By submitting bed A to a vacuum, the minimum pressure is achieved. The time required from the opening of the valve 2A shown in Figure 1 of the US Patent Number A-5 122 164 until the time when the minimum pressure is achieved, depends on how many more valves 48, 50, 52 and 54 are opened together If all four valves 48, 50, 52 and 54 are opened together, the time required is minimum; if only one is opened, the time required is maximum. An intermediate time can be achieved when either two or three of the valves 48, 50, 52 and 54 open together. When the valve 7B of the apparatus shown in Figure 1 of US Pat. No. A-5 122 164 is opened, the bed B is subjected to vacuum, and the time required to reach a minimum pressure can be varied by selecting which of the valves 48, 50 , 52 and 54 are open. The longer the time required to reach the minimum pressure, the longer the duration of each cycle of the oscillating vacuum adsorption process and the lower the supply rate of oxygen enriched air from the apparatus 2. In practice, a Claus plant for sulfur recovery from the acidic gas stream it is subjected to a load that varies widely and difficulties arise for the operation of oscillating conventional pressure or oscillating adsorption oxygen generators to fill this charge. The method and apparatus according to the invention, however, can follow a variable demand for oxygen. The apparatus shown in the accompanying drawing can be positioned such that when the acidic gas supply rate to the Claus plant is at a maximum, all four valves 48, 50, 52 and 54 open together. Typically and only one of the valves 48, 50, 52 and 54 is opened, the rate of oxygen production can be about half. Therefore, the oxygen production rate can be reduced in steps or directly up to about half. The number of different oxygen delivery regimes that are possible depends on the number of steam eductors that are used. In order to effect the operation of the valves 48, 50, 52 and 54, the apparatus shown in the accompanying drawing is provided with a valve controller (not shown). Typically there is a single valve controller which in addition to switching the valves 48, 50, 52, and 54 for connection and disconnection in accordance with a predetermined program also similarly connects and disconnects all the connection-disconnection valves shown in Figure 1 of US Patent Number A-5 122 164. If desired, a flow meter can be placed in the acidic gas pipe 18 and positioned to generate a signal representative of the flow rate through it. This signal is transmitted to the valve controller which determines which of the valves 48, 50, 52 and 54 are open at any time. Alternatively, if the flow rate of the acidic gas is varied by changing the setting of the flow control valve (not shown) the valve controller can respond directly to this change in setting. The valve controller can also adjust the operation of the adsorption steps of the vacuum swing adsorption process according to the adjustment of the bed regeneration steps where the adsorption beds are subjected to a vacuum. If the time required from the opening of the valve 2A or 7B shown in Figure 1 of the US Patent Number A-5 122 164 until the time when a minimum pressure is achieved is increased by reducing the number of valves 48, 50, 52 and 54 that are opened, steps are taken to ensure that the impurities do not penetrate the adsorbent bed during an adsorption step and thus reduce the purity of the gas enriched with oxygen produced to less than that specified for it. For example, referring to Figure 2 of U.S. Patent No. A-5 122 164, the selection of a reduced number of valves 48, 50, 52 and 54 will typically lengthen the period of time required for the bed to be placed on the right hand side. , as shown in Figure 2C, is regenerated during step 3 of the vacuum oscillating adsorption cycle illustrated. If desired, by referencing the accompanying drawing, a flow control valve 56 may be placed in the supply air pipe 8 and its adjustment selected in accordance with the number of valves 48., 50, 52 and 54 that are open. If there is a small number of these valves, the adjustment of the flow control valve 56 is selected in order to reduce the flow rate of the air to the vacuum oscillating adsorption apparatus 2. Accordingly, the duration of the adsorption step carried out by the left-hand bed as shown in Figure 2C of the US Patent Number A-5 122 164, can be adjusted to match the duration of the regeneration step taken. out by the bed on the right. Alternatively, the flow control valve 56 can be omitted and the adsorption step allowed to terminate before the vacuum regeneration step (Figure 2C of US Patent Number A-5 122 164) when the vacuum oscillating adsorption apparatus is producing oxygen at a decreased rate. In these examples, during those periods of the cycle in which the adsorption step has ended but the regeneration step continues, the adsorption bed is isolated from the feed gas and from the product reservoir. In this way, referring again to Figure 1 of US Pat. No. A-5 122 164, with bed A having completed the adsorption step before bed B has been regenerated, valves A and C are closed. 4A. Bed A therefore lies in isolation until the end of the regeneration of bed B after which both beds move to the next step of the vacuum swing adsorption cycle. Different means may be employed to detect when the adsorption step is completed. For example, the partial pressure of oxygen in the pipe 4 of the product can be monitored, or the pressure in the respective adsorption bed can be monitored. The oxygen supply pressure typically falls within the range of 1.5 to 2 bar and steam is typically supplied to the eductors at a pressure of about 40 bar even when lower or higher vapor pressures may be used. Various modifications and additions can be made to the plant shown in the accompanying drawing. For example, the air supply pipe 8 can be provided with a blower (not shown) to assist air flow. Alternatively, the compressor 10 may be omitted and replaced by a compressor (not shown) in the air supply line 8. Arrangements can be made to isolate any of the eductors 24, 26, 28 and 30 that are not currently being used to evacuate an adsorbent bed from the steam supply. Those eductors 24, 26, 28 and 30 that are in line can be placed to discharge their steam towards a chimney. If desired, some or all of the steam may be supplied from a source other than the waste heat burner 22. For example, a certain amount of the steam may be supplied from one or more sulfur condensers that are part of the Claus plant. Another modification that can be made is to omit one of the valves 48, 50, 52 and 54. Accordingly, an eductor is permanently in communication with the second pipe.

Claims (5)

R E I V I N D I C A C I O N S

1. The vacuum oscillating adsorption apparatus for separating a gas mixture, which includes a pipe through which a vacuum is capable of attracting, where there is a plurality of eductors each connected to the pipe and in parallel with the other eductors, and one or more first connection-disconnection valves associated with the eductors, positioned and capable of operating to select the number of eductors in communication with the pipeline.

2. The vacuum oscillating adsorption apparatus according to claim 1, wherein the first connection-disconnection valves are automatically operable.

3. The vacuum oscillating adsorption apparatus according to claim 1, further including means for automatically selecting the number of first connection-disconnection valves that are open in accordance with the demand for the gas produced. The vacuum oscillating adsorption apparatus according to claim 1, further including a flow control valve in another line for feeding the gas mixture to be separated to the apparatus and the means for adjusting the valve setting of flow control to provide variations in the duration of that period. 5. The device d? Vacuum oscillating adsorption according to claim 2, further comprising means for allowing a period of rest at the end of a selected adsorption step.