Integrated apparatus for generating power and/or oxygen enriched fluid, and process thereof

Abstract: In an integrated power generation system, part of the air from a gas turbine compressor (1) is separated in a single nitrogen wash column (15) to remove oxygen and the gaseous nitrogen (21, 42)produced at the top of the column is sent back to a point upstream of the expander (5) of the gas turbine. The wash column may be fed with liquid nitrogen (17) from an independent air separation unit (A) in which air is separated by cryogenic distillation. Liquid (37) from the bottom of the wash column may be fed back to the air separation unit (A

Description: The present invention relates to an integrated apparatus for generating power and/or oxygen-enriched fluid and a process for the operation thereof. It also relates to an air separation apparatus and process All present oxygen production facilities extract oxygen from air. Air has the advantage of being free and available everywhere. One of the drawbacks is that because air is at atmospheric pressure, it contains a lot of water and CO2 at low partial pressure. And pressure drops in process cycles are energy-expensive close to atmospheric pressure. It is the reason why most oil, chemical or petrochemical processes operate in the range of 10-40 bar. The pressure drops are less costly, heat exchange is easier, and the size of plants is reduced, drastically decreasing overall cost. In the case of oxygen production, as air contains 80% nitrogen, a low pressure waste gas containing the nitrogen is normally produced. In case of cryogenic distillation, the cold heat contained in the waste nitrogen has to be recuperated through heat exchangers which are costly both in investment and related energy needs Some oxygen plants operate at higher than normal pressure with some means and additional investment to recover the energy lost in the waste nitrogen Figure 1 shows a basic power gas turbine arrangement in which an air compressor 1 sends air 3 at between 8 and 35 bar to a combustor 5 fed by fuel 6. The combustion gas 7 mixed with dilution air 4 forms mixture stream 8 which is expanded in gas turbine 9 having an inlet temperature between 900 and 1400°C and generates power. To achieve good combustion in the burner, a close to stoichiometric mixing is necessary to use fuel efficiently and produce minimum pollution. But in this case, combustion produces a hot gas at temperatures higher than 2000°C, well above what any kind of hot turbine can accept. For this reason, quench type cooling takes place by mixing this very hot flue gas 7 with compressed dilution air 4 from the compressor at the same pressure as stream 3 but much lower temperature. The dilution air flow 4 is of the same order of magnitude as the combustion air flow 3. Because this dilution air 4 does not participate in the combustion, oxygen is not necessary. So it is possible to extract the oxygen contained in the dilution air 4 as shown in figure 2. The air 4 is cooled, purified and distilled in separation unit 12 producing oxygen 10 and nitrogen 11. The nitrogen 11 is mixed with combustion gas 7. Generally the separation unit used is a double column comprising a thermally linked high pressure column and low pressure column. However it is known to use a single column with a top condenser and a bottom reboiler for this purpose. If the amount of nitrogen 11 is limited, it may alternatively be mixed with air stream 3 and sent to combustor 5 as described in US-A-4224045 or EP0717249. Another option is to send the nitrogen to be mixed with the fuel stream 6. It is an object of the invention to provide a integrated apparatus for generating power and/or oxygen-enriched fluid and a process for the operation thereof which possess advantages over the known art. According to the present invention, there is provided an integrated apparatus according to Claim 1. According to further optional aspects of the invention : the single column has no bottom reboiler and no top condenser. the apparatus comprises a second compressor and means for sending air from the second compressor to the single column. the external source of nitrogen enriched liquid is a second air separation unit comprising at least one distillation column the second air separation unit comprises a high pressure column and a low pressure column which are thermally linked. there are means for withdrawing the nitrogen enriched liquid from the high pressure column or the low pressure column, where necessary pressurizing it and sending it to the top of the single column in liquid form and/or means for sending the oxygen-enriched liquid from the bottom of the single column to the high pressure column and/or the low pressure column. there are means for sending air to the double column from one of the first, second or a third compressor. Alternatively there may be means for sending nitrogen enriched gas from the single column to the double column and/or means for sending nitrogen enriched gas from the double column to a point upstream of the expander. The apparatus may additionally include a gasifier, means for sending oxygen from the air separation unit and a carbon containing substance to the gasifier and means for sending fuel from the gasifier to the combustor. According to a still further aspect of the invention, there is provided a process according to Claim 11. Further features of the process may include : said column having no bottom reboiler and no top condenser. sending air from a second compressor to the single column. the external source being a second air separation unit comprising at least one column the external source comprises a high pressure column and a low pressure column which are thermally linked withdrawing the nitrogen enriched liquid from the high pressure column, pressurizing and sending it to the top of the column of the first air separation unit. sending the liquid from the bottom of the single column to the second air separation unit, optionally to the high pressure column or low pressure column of the second air separation unit. sending air to the second air separation unit from one of the first, second or a third compressor. sending nitrogen enriched gas from the column of the first air separation unit to the second air separation unit . means for sending nitrogen enriched gas from the second air separation unit to a point upstream of the expander. wherein the column of the first air separation unit operates at between 8 and 35 bara. the highest pressure of a column of the second air separation unit is between 5 and 25 bara. the volume of air sent from the first compressor to the first air separation unit and the volume of nitrogen enriched gas sent upstream of the expander differ by no more than 10%,preferably 5%. all the nitrogen originates from the first air separation unit or alternatively the nitrogen originates from the first air separation unit and the external source. the external source being the second air separation unit The invention will now be described in further detail with reference to the figures 3 to 6 which are schematic flow sheets of an integrated air separation unit for use in an integrated power generation system and with reference to figures 7 and 8 which are schematic flow sheets of air separation units suitable for integration according to the invention. It will be appreciated that the units of Figures 7 and 8 could be used as integrated air separation unit for supplying nitrogen enriched gas to a gas turbine. Cryogenic technology is the basic technology for large air separation plants. In the process of figure 3, air is compressed to between 8 and 35 bara in compressor 1. Air stream 3 is sent to combustor 5 where it is burnt with fuel 6. Air stream 4 is cooled in heat exchanger 8, purified in purifying unit 14 and then cooled in heat exchanger 13 to a temperature suitable for cryogenic distillation. It is then sent to a first air separation unit, in this case a wash column 15 which is a single column fed at the top by a liquid nitrogen wash stream 17 which may be pure or contain up to 5% oxygen. Various sources for the liquid are shown in figures 4 to 6. The single column 15 contains a number of separation stages, which may be composed of trays or structured packing. Liquid 37 containing between 27 to 40mol.% oxygen is removed from the bottom of column 15. Nitrogen enriched gas 21 containing between 85 and 100mol.% nitrogen is removed from the column at a pressure between 8 and 25 bara, warmed in exchangers 13,8 , reactivates air purification 14,compressed and sent to the combustion chamber 5 or else mixed either with the combustion gas as shown (stream 11) or with air stream 3. The mixture thus formed is sent to expander 9 producing external work. The nitrogen is compressed in a booster 16 at ambient temperature but may be compressed at sub-ambient or super-ambient temperatures so as to make up for the pressure drop in the exchangers and column.. Alternatively air stream 4 may be boosted to the operating pressure of column 15 any of the temperatures described. A less economical option would be to expand the feed air 3 slightly before sending it to the combustor. When the air separation from our gas turbine by-pass is performed using a liquid nitrogen wash column 15(figure 3), the following advantages are obtained: all heat exchanges (hot and cold) and purification are carried out at elevated pressure thus reducing investment and energy drop cost. the nitrogen wash column 15 is fed by nitrogen enriched liquid 17, and very impure oxygen 37is removed in liquid rich phase. These liquids easily can be pumped and expanded, thus rendering this wash column pressure totally independent of the rest of the process nitrogen enriched gas flow 21 at the outlet of the wash column 15 is almost equal to the air flow 4 at the inlet of this column, thus maintaining the perfect balance of the gas turbine. In the version of figure 4,the liquid nitrogen for the wash column 15 is derived from a second air separation unit 41 comprising a double column with a high pressure column 25 and a low pressure column 27 thermally linked via a reboiler condenser 29 as in standard plants. The system may additionally include an argon separation column fed by the low pressure column. The operating pressures preferably vary between 5 and 25 bara for the high pressure column.. The air for the double column comes from a compressor 30 and is sent to the high pressure column 25 after cooling in exchanger 33. Alternatively the air for the double column may be derived at least in part from compressor 1 of the gas turbine or from an independent compressor feeding the single column, as shown in Figure 8. Oxygen enriched and nitrogen enriched liquids 32,34 are sent from the high pressure column to the low pressure column as reflux. The system may use a Claude turbine, a turbine feeding air to the low pressure column or a nitrogen turbine to produce refrigeration. Gaseous oxygen 36is produced from the low pressure column either directly or by vaporizing liquid oxygen. Waste nitrogen 38 is withdrawn from the low pressure column. Liquid nitrogen 17 from the top of the high pressure column 25 is sent to the top of wash column 15 optionally following pumping in pump 35. Liquid 37 from the bottom of column 15 is expanded in a valve 39 and sent to the bottom of the high pressure column or to the low pressure column . It could for example be mixed with reflux stream 32 A standard cryogenic oxygen plant has a double column including high pressure column with liquid nitrogen at the top and oxygen rich liquid at the bottom. If one installs a gas turbine next to an oxygen plant to produce electric power (for the oxygen plant or not) or to produce a combination of power and steam (cogeneration), the existing air separation plant can operate in conjunction with an additional air separation plant so as to supply a new product to the gas turbine. With the arrangement of figure 4, some liquid nitrogen or poor liquid 17 can be withdrawn from the existing medium pressure column or any other point of the process such as the low pressure column. It can be pumped to the relevant pressure in order to feed the additional plant which is a nitrogen wash column .The corresponding rich liquid 37 will be returned to the low pressure column as the normal rich liquid. Thus some extra oxygen molecules will be fed to the column, allowing increased oxygen production (at the same or reduced purity, depending on the boosting ratio). Obviously, this interesting process can be used in a grass root plant. In this case, a dedicated cold box will be better suited than a standard plant. Because oxygen is to be replaced by nitrogen or air for the gas turbine, some additional compressed air is needed. It can be (figure 5) either : injected into the cold box 41 of the air separation unit via compressor 30. The necessary pressure will be lower but a second air purification 38 is necessary. injected at the inlet of the expander 9 (before or after the hot exchanger 8). No purification is necessary but the corresponding oxygen will be wasted (which is not a problem if the by-pass flow is sufficient for oxygen demand. mixed with the by-pass air 4 before the nitrogen wash step(before or after the hot exchanger 8). In that case the existing purification 14 can be used to purify the air. In certain cases and depending on the final oxygen pressure required, a nitrogen (or air) recycle compressor 43 fed by nitrogen enriched gas from the high pressure and/or low pressure columns is necessary to adjust the separation power requirement of the oxygen separation and compression cycle. To maintain the advantages of the global pressurized cycle, this compressor 43 will preferably receive air or nitrogen at medium pressure (above 3 bar). Refrigeration from oxygen will be recovered in the cold box 41 or within the cold exchanger 13. Because the gas at the top of nitrogen wash column is nitrogen, it can be used partly 21' to help the final distillation instead of the recycle compressor. Thus nitrogen enriched gas 45 from a column 25,27 of the air separation unit can be sent to compressor 47 and then to the expander 9. The flow to the turbine can be readjusted as before with air or waste nitrogen recompression 47. It might have an advantage over a nitrogen recycle compressor as this compressed nitrogen will not need any final cooling (figure 6). It will be appreciated that the external source for the liquid nitrogen could be a remote storage tank periodically replenished by tanker trucks or a liquefier in which gaseous nitrogen e.g. from a pipeline is condensed rather than an air separation unit. The oxygen enriched liquid from the first air separation unit may then be sent to another column or another user, or to liquefy after expansion the gaseous nitrogen from the pipe-line. In the case where the external source is a second air separation unit, this may be a single column air separator generating liquid nitrogen, a standard double column with or without minaret ,an external condenser of an air separation column, a double column in which oxygen enriched liquid from the bottom of the low pressure column is fed to a top condenser of the low pressure column, a triple column in which rich liquid from a high pressure column feeds a medium pressure column and liquid from the medium pressure column feeds the low pressure column for example of the type shown in FR1 061 414, EP0717249 or EP 538118. The second air separation unit serving as an external source may produce other liquids in addition to the nitrogen and other gaseous products. Gases may be produced at high pressure by pumping and vaporizing liquids withdrawn from columns of the second air separation unit. One advantage of the present system is that the first air separation unit and the second air separation unit can operate independently by providing storage tanks for the liquid nitrogen from the second air separation unit and the oxygen enriched liquid from the first air separation unit. Thus when the second air separation unit is not operational, the first air separation unit draws liquid nitrogen from the storage. Similarly when the first air separation unit is not operational the oxygen enriched liquid is removed from the storage and sent to the second air separation unit. In the process of figure 7, air stream 4 is purified in purifying unit 14 and then cooled in heat exchanger 13 to a temperature suitable for cryogenic distillation. It is then sent to a first air separation unit , in this case a wash column 15 which is a single column fed at the top by a nitrogen enriched liquid wash stream 17 which may be pure or contain up to 5mol.% oxygen. Wash column 15 operates at a pressure between 4 and 25 bara. Liquid 37 containing between 27 to 40mol.% oxygen is removed from the bottom of column 15. Gaseous nitrogen 21 is removed from the column at a pressure between 8 and 25 bar, warmed in exchangers 13,8 , reactivates air purification 14 and is compressed in a booster 16 at ambient temperature but may be compressed at sub-ambient or super-ambient temperatures so as to make up for the pressure drop in the exchangers and column. A second air separation unit which may be a source of the liquid 17 is shown in figure 8. An existing plant fed by 1000Nm3/h of air consists of a double column where all the refrigeration is supplied by a high pressure nitrogen turbine (not shown) fed by 210 Nm3/h nitrogen enriched gas from column 25 which provides the refrigeration for liquid production and an air turbine 28 sending 80Nm3/h air to the low pressure column which provides refrigeration for the apparatus. The amount of oxygen enriched gas 36 initially produced from low pressure column 27 is 210Nm3/h and this can be increased to 265Nm3/h by adding a wash column 15 as described above to produce a plant as shown in figure 8, no longer using the nitrogen turbine and increasing the amount of air flowing in the other turbine by 20% to cover thermal losses. In the version of figure 8, the nitrogen enriched liquid 17 for the single wash column 15 is derived from an air separation unit comprising a double column with a high pressure column 25 and a low pressure column 27 thermally linked via a reboiler condenser 29 as in standard plants. The system may additionally include an argon separation column fed by the low pressure column. The operating pressures preferably vary between 5 and 25 bar for the high pressure column. The 1000Nm3/h of air for the double column come from a dedicated compressor 30 and are sent partly to the high pressure column 25 after purification in 31 cooling in exchanger 33 and partly (100Nm3/h) to the turbine 28 which feeds the low pressure column 27. Oxygen enriched and nitrogen enriched liquids 32,34 are sent from the high pressure column to the low pressure column as reflux. The system may additionally use a Claude turbine or a nitrogen turbine to produce refrigeration. 265Nm3/h of gaseous impure oxygen 36 is produced from the low pressure column either directly or by vaporizing liquid oxygen. 735m3/h of waste nitrogen 38 is withdrawn from the low pressure column. 180Nm3/h of nitrogen enriched liquid 17 from between 0 and 10 theoretical trays below the top of the high pressure column 25 is sent to the top of wash column 15 following pumping in pump 35. 180Nm3/h of liquid 37 containing 55Nm3/h oxygen from the bottom of column 15 is expanded in a valve 39 and sent to the bottom of the high pressure column or alternatively to the low pressure column. This liquid typically contains between 30 and 40 mol.% oxygen. 300Nm3/h of air is sent to the bottom of the further column 15 from a separate compressor 40 following compression and cooling 46, another source of compressed air or the main compressor 30 and 300Nm3/h of nitrogen enriched gas 42 is removed from the top. This nitrogen may be used as a product stream. With the arrangement of figure 8, some liquid nitrogen or poor liquid 17 can be withdrawn from the top of the medium pressure column or a few theoretical trays below the top of that column or any other point of the process such as the low pressure column. It can be pumped or expanded to the relevant pressure in order to feed the nitrogen wash column .which may operate at a pressure which is equal to, greater than or less than the pressure of the high pressure column 25. The corresponding rich liquid 37 will be returned to the low pressure column as the normal rich liquid. Thus some extra oxygen molecules will be fed to the column, allowing increased oxygen production (at the same or reduced purity, depending on the boosting ratio) In this way, the nitrogen molecules sent from the double column to the wash column are replaced by oxygen molecules. This means that the amount of impure oxygen which can be produced by the double column is increased by up to 25% The pressure drop for nitrogen waste gas 38 from the low pressure column reduces because less nitrogen enters the double column when the wash column 15 is used. The pressure drop for the oxygen 36 is substantially increased and it may be necessary to use additional heat exchangers for the heat exchange between the air and the oxygen or to reallocate the existing passages in the heat exchanger 33 In certain cases and depending on the final oxygen pressure required, a nitrogen (or air) recycle compressor is necessary to adjust the separation power requirement of the oxygen separation and compression cycle. To maintain the advantages of the global pressurized cycle, this compressor will preferably receive air or nitrogen at medium pressure (above 3 bar). Refrigeration from oxygen will be recovered in the cold box 41 or within the cold exchanger 13. The single column may be contained in a second cold box B together with the exchanger 44 in which the feed liquid nitrogen is heated following pressurization against the bottom liquid of the single column and the exchanger 46 in which the feed air for the single column is cooled against the product gaseous nitrogen from the single column. Because the gas at the top of nitrogen wash column is nitrogen, it can be used partly to help the final distillation instead of the recycle compressor. The air may be cooled using the gaseous nitrogen from the top of the single column. The second air separation unit may include an argon column or a mixing column. With an apparatus of this sort, it becomes possible to increase the capacity of the existing second air separation unit (i.e. the double or triple column) by 25% for impure oxygen by adding the single air separation column. The combined air separation unit and single column will produce a greater proportion of oxygen and consequently a lesser proportion of waste nitrogen than the air separation unit alone. For this reason, more oxygen can be produced with less waste nitrogen. In general, the waste nitrogen circuits are the bottleneck for increased oxygen production by simple feed air flow boosting. There are new separation power requirements for purifying the additional oxygen introduced in the air separation unit. This extra power can be obtained, either by decreasing the purity of part or all of the oxygen produced ; or by reducing the total amount of gas expanded in one or more turbines to produce less refrigeration (thus possibly reducing liquid production), taking into account that the further column will require additional cooling.

Claims: An integrated apparatus for generating oxygen enriched fluid (37) and/or power comprising a first air separation unit (15), a gas turbine comprising a combustor (5) and an expander (9), a first compressor (1), means (3) for sending air from the first compressor to the combustor and optionally to the first air separation unit, means for sending combustion gases from the combustor to the expander, means for sending a nitrogen enriched gas (1) from the first air separation unit to a point upstream of the expander and means (16) for either compressing the nitrogen enriched gas sent to a point upstream of expander, further compressing the air sent to the first air separation unit from the first compressor if there are said means for sending air from the first compressor to the first separation unit or expanding the air sent to the combustor from the first compressor characterized in that the first air separation unit comprises a single column (15) and the apparatus comprises means for sending nitrogen enriched liquid (17) from an external source (25,27) to the top of the single column, the external source being external to the single column, and means for removing the nitrogen enriched gas from the top of the single column and for removing oxygen-enriched fluid (37) from the bottom of the column. An apparatus as claimed in Claim 1 wherein said single column (15) has no bottom reboiler and/or no top condenser. An apparatus as claimed in Claim 1 or 2 comprising a second compressor and means for sending air from the second compressor to the single column. An apparatus as claimed in Claim 1,2 or 3 wherein the external source is a second air separation unit (A) comprising at least one column (25,27). An apparatus as claimed in Claim 4 wherein the second air separation unit (A) comprises at least a high pressure column (25) and a low pressure column (27) thermally linked with one another and means (30) for feeding air to the high pressure column and the liquid nitrogen is derived from one of the columns (25,27). An apparatus as claimed in Claim 5 comprising means for withdrawing the nitrogen enriched liquid from the high pressure column (25), means (35) for pressurizing at least part of the withdrawn nitrogen enriched liquid and means for sending the pressurized liquid (17) to the top of the single column (15) of the first air separation unit. An apparatus as claimed in at least one of Claims 4 to 6 comprising means for sending at least part of the liquid (37) from the bottom of the single column (15) of the first air separation unit to the second air separation unit. An apparatus as claimed in one of Claims 4 to 7 comprising sending air to the second air separation unit from at least one of the first, second or a third compressor (1,30). An apparatus as claimed in one of Claims 4 to 8 comprising means for sending gaseous nitrogen from the single column of the first air separation unit to the second air separation unit. An apparatus as claimed in one of Claims 4 to 9 comprising means for sending nitrogen enriched gas (45) from the second air separation unit to a point upstream of the expander (9). A process for generating power and/or oxygen enriched fluid using an integrated apparatus according to claim 1 and comprising the steps of compressing air in a first compressor (1), sending air from the first compressor to a combustor (5) and optionally to a first air separation unit (15), sending a nitrogen enriched gas (21) from the first air separation unit to a point upstream of an expander (9) of a gas turbine, sending fuel (6) to the combustor, sending combustion gas from the combustor to the expander and either compressing the nitrogen enriched gas (21) sent to a point upstream of expander, further compressing the air sent to the first air separation unit if the air is sent from the first compressor to the first separation unit or expanding the air sent to the combustor from the first compressor characterized in that the first air separation unit comprises a single column (15) and the process comprises feeding the single column of the first separation unit with air (4), sending nitrogen enriched liquid (17) from an external source (25,27) to the top of the column, the external source being external to the single column, and removing nitrogen enriched gas (21) from the top of the column and an oxygen enriched fluid (37) from the bottom of the column. A process as claimed in Claim 11 wherein said single column is a column (15) having no bottom reboiler and no top condenser. A process as claimed in Claim 11 or 12 comprising sending air from a second compressor to the first air separation unit (15). A process as claimed in Claim 11,12 or 13 wherein the external source comprises a second air separation unit comprising at least one column (25,27). A process as claimed in Claim 14 wherein the second air separation unit comprises at least a high pressure column (25) and a low pressure column (27) thermally linked with one another and the nitrogen enriched liquid (17) is derived from one of the columns. A process as claimed in Claim 15 comprising withdrawing the nitrogen enriched liquid from the high pressure column (25), pressurizing at least part of it and sending at least part of the pressurized liquid to the top of the single column (15) of the first air separation unit. A process as claimed in one of Claims 14 to 16 comprising sending liquid (37) from the bottom of the single column to the second air separation unit. A process as claimed in one of Claims 14 to 17 comprising sending air to the second air separation unit from one of the first, second or a third compressor (1,30). A process as claimed in one of Claims 14 to 18 comprising sending nitrogen enriched gas from the single column (15) of the first air separation unit to the second air separation unit. A process as claimed in Claim 14 to 19 comprising means for sending nitrogen enriched gas (45) from the second air separation unit to a point upstream of the expander (9). A process as claimed in any of Claims 11 to 20 wherein the single column (15) of the first air separation unit operates at between 8 and 25 bara. A process as claimed in any of Claims 14 to 21 wherein the highest pressure of any column (25) of the second air separation unit (41) is between 5 and 25 bara. A process as claimed in any of Claim 11 to 22 in which the volume of air sent from the first compressor (1) to the first air separation unit (15) and the volume of nitrogen enriched gas sent upstream of the expander (9) differ by no more than 10%. A process as claimed in any one of Claims 11 to 23 wherein all the nitrogen enriched gas sent upstream of the expander (9) originates from the first air separation unit. A process as claimed in any one of Claims 11 to 23 wherein the nitrogen enriched gas sent upstream of the expander (9) originates from the first air separation unit and the external source.

Inventors: BRUGEROLLE JEAN-RENAUD, BRUGEROLLE, JEAN-RENAUD
Applicants: AIR LIQUIDE, L'AIR LIQUIDE, S.A. A DIRECTOIRE ET CONSEIL DE SURVEILLANCE POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE
Application year: 2000
Main classification: F25J3
IPC codes: F25J3