Method for separating gases in an oxy-fuel combustion process by using oxygen-permeable membranes

Abstract

The invention relates to a method for separating gases which comprises: a first step in which a gas fuel stream comprising combustible substances that produce gas products when oxidised, and an oxygen-rich inlet stream are passed through at least two modules of oxygen-separating ceramic membranes, such that the two streams come into contact through the membranes and exchange heat; a second step of selective diffusion of oxygen from the oxygen-rich stream to the fuel stream, such that the outlet streams from the membrane modules are an oxygen-depleted or completely oxygen-free stream and a partially or completely oxidised stream; and a third step of recovery of at least two separate outlet streams of at least two gases selected from oxygen, nitrogen, carbon dioxide and hydrogen.

Claims

1. A process to selectively generate and separate gases, comprising: a first step in which a gas-phase fuel stream and an oxygen rich input stream are passed through a first oxygen separation ceramic membrane module, wherein the gas-fuel stream comprises combustible substances whose oxidation gives rise to gaseous products, the oxygen rich input stream is either water vapor or a portion of an oxygen-depleted stream from a second oxygen separation ceramic membrane module, and the gas-phase fuel stream and the oxygen rich input stream come into contact through a first membrane, a heat exchange takes place between them, and a partially oxidized combustible gas stream is output, a second step of selective oxygen diffusion in which the partially oxidized combustible gas stream from the first oxygen separation ceramic membrane module and the water vapor are passed through the second oxygen separation ceramic membrane module, such that the output streams from the second oxygen separation ceramic member module are, on the one hand, an oxygen-depleted or completely oxygen-free stream and, on the other hand, a partially oxidized or completely oxidized stream, and a third step of recovery in which a third oxygen separation ceramic membrane module receives the oxygen-depleted stream from the second oxygen separation ceramic membrane module to extract oxygen such that one of at least two separate outlet streams of at least two gases is oxygen and another of the at least two separate outlet streams is selected from nitrogen, carbon dioxide and hydrogen.

2. The process according to claim 1, wherein in the second step the oxidation of the fuel is complete.

3. The process according to claim 1, wherein the gas exchange between the gas-phase fuel stream and the oxygen rich input stream to the membrane modules is carried out at a temperature between 600 C. and 1500 C.

4. The process according to claim 1, further comprising a pressurization step of the gas-phase fuel stream and the oxygen rich input stream in a first gas compressor device, at absolute pressures between 2 and 15 bar, obtaining pressurized input streams.

5. The process according to claim 1, further comprising a pre-heating step of the gas-phase fuel stream and the oxygen rich input stream with heat given off by the outlet streams, obtaining pre-heated pressurized input streams.

6. The process according to claim 1, wherein the flows of the gas-phase fuel stream and the oxygen-rich stream are arranged in countercurrent.

7. The process according to claim 1, wherein in the second oxygen separation ceramic membrane module, cross flows, co-current flows, or counter current flows are used.

8. The process according to claim 1, wherein: the gas-phase fuel stream leaving a first heat exchanger is pressurized and fed as an input stream to the first membrane module, the entire oxygen-rich input stream coming from a second heat exchanger is fed into the second oxygen separation ceramic membrane module, the oxygen-depleted stream leaving the second oxygen separation ceramic membrane module is metered by a system of valves that partially circulate this stream: to the first oxygen separation ceramic membrane module as a stream supplying oxygen as an oxygen-depleted stream containing an amount of oxygen less than the stoichiometric amount to completely oxidize the gas-phase fuel stream, and to the third oxygen separation ceramic membrane module as a stream supplying oxygen to the third oxygen separation ceramic membrane module and a turbine.

9. The process according to claim 8, wherein the oxygen depleted output stream from the second membrane module is recirculated to a turbine as a turbine input stream.

10. The process according to claim 8, wherein additional membrane modules are used, in addition to the first, second and third oxygen separation ceramic membrane modules, wherein the additional membrane modules purify the gas streams produced in the first oxygen separation ceramic membrane module and the second oxygen separation ceramic membrane module by removing oxygen therefrom, and the gas-phase fuel stream enters the additional modules as an entrainment stream.

11. The process according to claim 10, wherein the additional membrane modules have a countercurrent flow distribution to ensure the complete exchange of oxygen from the streams to be purified, to the gas-phase fuel streams.

12. The process according to claim 1, wherein the source of the gas-phase fuel stream is biomass, which is gasified by a thermochemical reactor, the input streams to the thermochemical reactor being: biomass an entrainment stream consisting of an inert gas.

13. The process according to claim 1, wherein the input stream, containing combustible materials, comprises one or more products selected from CO, H2, H2S, methane, liquefied petroleum gases, alcohols, olefins, peroxides, aromatic compounds, organic acids, organic amines, naphtha, asphalt, bituminous, diesel, vegetable, animal or mineral oils or fats, coals, and mixtures thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1. Diagram of the upgrading process of industrial streams from oxygen permeation ceramic membrane modules for the simultaneous production of CO.sub.2, N.sub.2 and O.sub.2.

(2) FIG. 2. Diagram of the revaluation process of industrial streams from oxygen permeation ceramic membrane modules for the simultaneous production of CO.sub.2, N.sub.2 and O.sub.2, in an alternative configuration of the C2 stream.

(3) FIG. 3. Diagram of the upgrading process of industrial streams from oxygen permeation ceramic modules for the simultaneous production of CO.sub.2 and O.sub.2.

(4) FIG. 4. Diagram of the upgrading process of industrial streams from oxygen permeation ceramic modules for the simultaneous production of CO.sub.2 and N.sub.2.

(5) FIG. 5. Diagram of the upgrading process of industrial streams from oxygen permeation ceramic modules for the simultaneous production of N.sub.2 and O.sub.2.

(6) FIG. 6. Diagram of the upgrading process of industrial streams from ceramic permeation membrane modules purifying the N.sub.2 and CO.sub.2 streams by means of ceramic membrane modules.

(7) FIG. 7. Diagram of the upgrading process of industrial streams from oxygen permeation ceramic modules integrated in a biomass gasification (or pyrolysis) process.

(8) FIG. 8a is a perspective view of an oxygen permeation membrane module having 20 membranes with gas streams distributed in cross flow. Reference (70) shows the spacers between membranes and reference (72) shows the outer cover of the module.

(9) FIG. 8b is a plan view of the oxygen permeation membrane module in FIG. 8a.

(10) FIG. 8c is a sectional view of the oxygen permeation membrane module taken at B-B in FIG. 8b.

(11) FIG. 8d is a sectional view of the oxygen permeation membrane module taken at C-C in FIG. 8b.

(12) FIG. 8e is a partial sectional view of the oxygen permeation membrane module illustrating the highlighted portion of FIG. 8c.

(13) FIG. 8f is a partial sectional view of the oxygen permeation membrane module illustrating the highlighted portion of FIG. 8d.

(14) FIG. 9a is a perspective view of an oxygen permeation membrane module having 20 membranes with gas streams distributed in co-current or counter-current.

(15) FIG. 9b is a plan view of the oxygen permeation membrane module in FIG. 9a.

(16) FIG. 9c is a sectional view of the oxygen permeation membrane module taken at A-A in FIG. 9b for co-current flow distribution.

(17) FIG. 9d is a sectional view of the oxygen permeation membrane module taken at B-B in FIG. 9b for co-current flow distribution.

(18) FIG. 9e is a partial sectional view of the oxygen permeation membrane module illustrating the highlighted portion of FIG. 9c.

(19) FIG. 9f is a partial sectional view of the oxygen permeation membrane module illustrating the highlighted portion of FIG. 9d.

(20) FIG. 9g is a sectional view of the oxygen permeation membrane module taken at A-A in FIG. 9b for counter-current flow distribution.

(21) FIG. 9h is a sectional view of the oxygen permeation membrane module taken at B-B in FIG. 9b for counter-current flow distribution.

(22) FIG. 10a is a perspective view of an oxygen permeation membrane module of three passages, with 6 membranes per passage.

(23) FIG. 10b is a plan view of the oxygen permeation membrane module in FIG. 10a.

(24) FIG. 10c is a sectional view of the oxygen permeation membrane module taken at A-A in FIG. 10b for co-current flow distribution.

(25) FIG. 10d is a sectional view of the oxygen permeation membrane module taken at B-B in FIG. 10b for co-current flow distribution.

(26) FIG. 10e is a partial sectional view of the oxygen permeation membrane module illustrating the highlighted portion of FIG. 10c.

(27) FIG. 10f is a partial sectional view of the oxygen permeation membrane module illustrating the highlighted portion of FIG. 10d.

(28) FIG. 10g is a sectional view of the oxygen permeation membrane module taken at A-A in FIG. 10b for counter-current flow distribution.

(29) FIG. 10h is a sectional view of the oxygen permeation membrane module taken at B-B in FIG. 10b for counter-current flow distribution.

(30) FIGS. 11a-11f show the results of example 1 where a practical case of the first membrane module (6) has been studied with a mixture of COCO.sub.2 as a combustible gaseous stream and air as an oxygen-rich stream. Temperature profiles (T) and molar fraction of oxygen (Xo.sub.2) along the air chamber (L: longitudinal coordinate of the membrane module) for the oxygen permeation membrane module with oxygen deficit in the air stream (7) for different dilutions CO.sub.2 of the stream (7) with

(31) ${\mathrm{CO}}_{2}r=\frac{\mathrm{CO}2}{C1}.$
Results for a membrane module of a total membrane area of 380 cm.sup.2 and a supply of CO and CO.sub.2 (57.1% CO) for stream (5) with the input streams at 700 C.

(32) FIG. 11a is a block diagram representation of the first membrane module.

(33) FIG. 11b is a simplified view of the passage of the gas streams through the fuel (69) and (air (71) chambers for co-current flow configuration.

(34) FIG. 11c is a simplified view of the passage of the gas streams through the fuel (69) and (air (71) chambers for counter-current flow configuration.

(35) FIG. 11d is a graphical representation of the results for an air input at 25% of the stoichiometric amount.

(36) FIG. 11e is a graphical representation of the results for an air input at 50% of the stoichiometric amount.

(37) FIG. 11f is a graphical representation of the results for an air input at 75% of the stoichiometric amount.

(38) FIG. 12. Adiabatic flame temperature (T) for various fuels with air. They are important to understand the process mechanism and the results. F1: hydrogen, F2: methane, F3: natural gas, F4: acetylene, F5: ethane, F6: butane, F7: gasoline, F8: benzene, F9: kerosene, F10: light diesel, F11: medium diesel, F12: heavy diesel, F13: naphthalene, F14: pentadecane, F15: eicosan, F16: bituminous coal, F17: anthracite. (https://www.englneeringtoolbox.com/adlabatlc-flame-temperature-d_996.html).

(39) Light gas oil is defined as a by-product obtained from atmospheric distillation of petroleum that starts boiling between 175 and 200 C. and ends between 320 and 350 C.

(40) Medium gas oil: intermediate is defined as a by-product obtained from the distillation of petroleum, which boils within a range comprised between the boiling point of light gas oil and the boiling point of heavy gas oil.

(41) Heavy gas oil is defined as the residual product of petroleum distillation, whose boiling range is between 423 and 600 C.

(42) FIGS. 13a-13e show temperatures (T) for the oxygen permeation membrane module fed with different amounts of air (excess air to cause complete oxidation of the fuel). A represents the ratio between the introduced air (11) (oxygen rich stream) and the stoichiometric air to oxidize all the combustible material in the combustible gas stream (8). Results for a membrane module with a total membrane area of 380 cm.sup.2 and a CO and CO.sub.2 feed (9.5% CO) for (11) (oxygen rich stream) with the input streams at 700 C. The dots within the graphs indicate the cases where complete oxidation of the input fuel is achieved.

(43) FIG. 13a is a block diagram representation of the second membrane module.

(44) FIG. 13b is a graphical representation of the air output temperatures for co-current flows (14) (oxygen depleted stream).

(45) FIG. 13c is a graphical representation of the air output temperatures for countercurrent flows (14).

(46) FIG. 13d is a graphical representation of the maximum temperatures inside the module for co-current flows (10).

(47) FIG. 13e is a graphical representation of the maximum temperatures inside the module for countercurrent flows (10).

(48) FIGS. 14a-14g show oxygen extracted depending on the process conditions and the membrane area (A) used for the third membrane module. The extraction of oxygen (E.sub.O2) was calculated by means of the ratio of oxygen extracted to oxygen entering the membrane module. Air input 22.4 m.sup.3.sub.CN/h (CN: normal conditions).

(49) FIG. 14a is a block diagram representation of the third membrane module.

(50) FIG. 14b is a graphical representation of process conditions with 50 mbar of vacuum pressure and air at atmospheric pressure.

(51) FIG. 14c is a graphical representation of process conditions with 50 mbar of vacuum pressure and air at 2.5 bar.

(52) FIG. 14d is a graphical representation of process conditions with 50 mbar of vacuum pressure and air at 5 bar.

(53) FIG. 14e is a graphical representation of process conditions with 100 mbar of vacuum pressure and air at atmospheric pressure.

(54) FIG. 14f is a graphical representation of process conditions with 100 mbar of vacuum pressure and air at 2.5 bar.

(55) FIG. 14g is a graphical representation of process conditions with 100 mbar of vacuum pressure and air at 5 bar.

(56) FIG. 15. Conventional configuration of a flat plate heat exchanger.

EXAMPLES

(57) FIGS. 1 to 7 show examples of various embodiments for the process and installation of the invention.

(58) All embodiments of the installation of the invention use the same references for the elements common to all of them, which are detailed below:

(59) The installation has two main conduits or input streamlines: an input material streamcombustible gaseous stream(C1) and an oxygen rich stream (C2).

(60) The installation has several outlet conduits or lines: the oxygen-depleted stream (C3) and each of the gaseous streams that are obtained depending on the process application.

(61) The combustible gaseous stream (C1) is driven by a first gas compressor (2).

(62) The input stream to the first compressor (2) is the input combustible gaseous stream (1). The output stream of the first compressor (2) is the pressurized fuel gas phase stream (3).

(63) The pressurized combustible gaseous stream (3) is heated until the input temperature, to the membrane modules by means of a first heat exchanger device (4).

(64) The input stream to the first heat exchanger (4) is the combustible gaseous stream (3) coming from the first compressor (2).

(65) The output stream of the first heat exchanger system (4) is the preheated pressurized combustible gaseous stream (5).

(66) The oxygen-rich stream (C2) (27) is driven by a second gas compressor (28).

(67) The input stream to the second compressor (28) is the oxygen rich input stream (27).

(68) The output stream from the second compressor (28) is the pressurized oxygen-rich input stream (30).

(69) The pressurized oxygen-rich stream (30) is heated until the input temperature of the membrane modules by means of a gas heat exchanger (31).

(70) The input streams to the heat exchanger device (31) are the oxygen-rich stream (30) coming from the compressor (28) and an oxygen-depleted stream (32) coming from the turbine (33).

(71) One of the output streams of the heat exchanger system (31) is the oxygen-depleted stream (C3), which reaches the outlet through streamline (35). One of the output streams of the heat exchanger system (31) is the oxygen-rich stream (34) To optimize the pressurization (and depressurization) of the oxygen-rich line, the compressor (28) and the turbine (33) can be connected to the same shaft (29).

Example 1

(72) FIG. 1 shows a diagram of a particular example of the process and the installation to carry it out.

(73) The installation has in this particular case three main oxygen permeation ceramic membrane modules (M.sub.1, M.sub.2 and M.sub.3), also designated as (6), (10) and (15). These modules have parallel flat membranes whose total area is distributed in different sections within each module. The arrangement of the streams, the geometry of the module, and the trajectory of the streams of each module are focused to optimize the process it houses and to optimize the heat transfer between the different streams that pass through it.

(74) The input material stream (C1) (gasified stream, or fuel gas phase stream) contains combustible substances whose complete oxidation by reaction with oxygen produces gaseous compounds. The oxygen-rich input stream (C2) is composed primarily of O.sub.2 and N.sub.2.

(75) The combustible gaseous stream (3) is heated until the input temperature to the first membrane module (6) by the first heat exchanger device (4). The input stream to the heat exchanger (4) is the combustible gaseous stream (3) coming from the compressor (2). The output stream of the heat exchanger (4) is the heated pressurized combustible gaseous stream (5).

(76) The oxygen-rich stream (C2) (30) is heated until the input temperature of the M.sub.1 module by means of a second heat exchanger (31). The input streams to the heat exchanger (31) are the oxygen-rich stream (30) coming from the compressor (28) and the oxygen-depleted stream (32) coming from the turbine (33). In this case there are two output streams from the second heat exchanger system (31), which are an oxygen-rich stream (34) and the oxygen-depleted output stream (35).

(77) The metering or control of the volumetric flow of the incoming and outgoing gaseous streams to the oxygen permeation membrane modules (6) and (10) is carried out by means of a valve system (38 and 39). This dosage must be carried out considering that a quantity of air containing oxygen quantities less than the stoichiometric quantity is introduced to the first membrane module (6) to completely oxidize the fuel gas, while a quantity of air containing an excess of oxygen with respect to the stoichiometric quantity is introduced to the second membrane module (10). Consequently, the heated oxygen-rich stream (34) is divided into two streams (36 and 37). The input stream to the metering valve (38) of the first membrane module (6) is an oxygen-rich stream (36). The output stream from the metering valve (38) of the first membrane module is an oxygen-rich stream (7). The input stream (37) to the metering valve (39) of the second membrane module (10) is an oxygen-rich stream (37). The output stream from the metering valve (39) of the second membrane module (10) is an oxygen-rich stream (11).

(78) The first membrane module (6) is intended to produceaccording to this particular embodimentnitrogen from the combustible gaseous stream and an oxygen-rich stream. The input streams to the membrane module (6) are the combustible gaseous stream (5), which comes from the exchanger (4) and the oxygen-rich stream (7) which comes from the metering valve (38). The output streams from the membrane module (6) are the partially oxidized combustible gasified stream (8) and the oxygen-depleted stream (9) whose composition is practically pure N.sub.2. In this embodiment of the process, the oxygen-rich stream (7) is introduced in an amount less than the minimum amount to oxidize all the combustible material carried by the combustible gaseous stream (5). Considering that an amount of oxygen less than the stoichiometric amount of the combustible gaseous stream (5) has been introduced, the chamber of the combustible gaseous stream will maintain a very low oxygen pressure (of the order of mbar) and, therefore, the driving force of the oxygen transport process will be very high. In this module (6) it must be ensured that the outgoing oxygen-depleted stream (9) is practically pure nitrogen and that the heat transfer between the streams that pass through the module is efficient. For this purpose, the input streams to the M.sub.1 module (6) (the combustible gaseous stream (5) and the air stream (7)) are arranged in counter-current. The oxygen exchanged through the membrane reacts with the combustible material by increasing the temperature, thereby improving the oxygen transport properties of the material. If necessary and in order to avoid excessive heating due to the oxidation of combustible gases, it is possible, optionally, to recirculate part of the carbon dioxide or nitrogen obtained in the process and thus dilute the combustible gaseous stream (5) and absorb the oxidation heat. Considering that the combustible material of the combustible gaseous stream (5) has a composition of CxHyOz, the maximum nitrogen production that could be achieved is

(79) $\frac{2x+y/2\text{-}z}{2}.Math.\frac{0.Math.79}{0.Math.21}$
mole of N.sub.2 for each mole of combustible material. The variables x, y, z can take any value that is technically possible.

(80) The second membrane module (10) is intended to completely oxidize the combustible gaseous stream (8) that leaves the first membrane module (6) partially oxidized. For this purpose, an excess (in flow rate) of the oxygen rich stream with respect to the minimum amount to oxidize all the combustible material carried by the combustible gaseous stream (8), is introduced into the process. The input streams to the second membrane module (10) are the combustible gaseous stream (8), which comes from the outlet of the first membrane module (6), and the oxygen-rich stream (11). The output streams from the second membrane module (10) are the combustible gaseous stream (13), which is mainly composed of CO.sub.2 and water vapor (unless the combustible material of the gasified stream be CO, in which case the output combustible gaseous stream will be composed mostly of CO.sub.2), and the oxygen stream (14), depleted in oxygen with respect to C2. The oxygen exchanged through the membrane reacts with the combustible material increasing the temperature, thereby improving the oxygen transport properties of the material. The amount of air introduced into the second module (10) M.sub.2 must be high enough to ensure that the exchanged oxygen causes complete combustion of all the combustible material contained in the combustible gaseous stream (i.e., that at the outlet of M.sub.2 the hydrocarbon and carbon monoxide content of this stream is negligible) and to avoid excessive heating of the module due to combustion processes, through a dilution effect and heat distribution in a large volumetric flow rate. Finally, for this module (10) the gases can be distributed in cross flows, in co-current flows or in countercurrent flows. The final choice of the module is subject to the needs: for example, considering that oxidation processes can generate excessive temperatures within the module, a co-current distribution may be necessary to allow a more gradual dosage of the oxygen exchanged by the membranes of the module and, in this way, reduce and control the progress of oxidation reactions to avoid excessive temperature increases.

(81) The third membrane module (15) is intended to extract oxygen from an oxygen-rich stream. The input stream to the membrane module (15) is the oxygen-depleted stream (14) relative to the stream (C2) coming from the second membrane module (10). The output streams from the third membrane module (15) are the oxygen-depleted stream (16) and the extracted oxygen (17). The oxygen is extracted by imposing a vacuum in the entrainment chamber and thus achieving a high driving force. As no additional phenomena occur, this module works isothermally as long as it is well thermally insulated.

(82) The completely oxidized combustible gaseous stream (13) coming from the second membrane module (10) is mainly composed of carbon dioxide and water vapor. For the separation thereof, the water vapor is condensed by cooling the stream to room temperature (15-25 C.). A heat exchanger device (22) is used for this purpose. The input stream to the heat exchanger system (22) is the completely oxidized combustible gaseous stream (13) coming from the second membrane module (10). The output stream to the heat exchanger system (22) is the completely oxidized combustible gaseous stream (23).

(83) A condenser-separator (24) is optionally used to evacuate the condensed liquid water from the completely oxidized combustible gaseous stream (23) coming from the third module (15) and which has passed through the heat exchanger (22). The input stream to the condenser-separator (24) is the completely oxidized combustible gaseous stream (23) that comes from the heat exchanger device (22). The output streams of the condenser-separator (24) are the completely oxidized combustible gaseous stream (25), mainly composed of CO.sub.2, and a liquid water stream (26).

(84) Alternatively, in the case where the starting combustible gaseous stream (C1) is a mixture of CO and CO.sub.2, the completely oxidized combustible gaseous stream (13) coming from the second membrane module (10) will be composed mainly of CO.sub.2, thus that the separator condenser (24) is not needed and the output stream (23) of the heat exchanger device (22) would be the final CO.sub.2 stream.

(85) The oxygen stream (17) extracted from the third module (15) must be cooled before being introduced into a vacuum generation system (20). For this purpose, a device with at least one heat exchanger (18) is required to lower the temperature of the oxygen stream to approximately room temperature. The input stream to the heat exchanger device (18) is the oxygen stream (17) that comes from the outlet of the third membrane module (15). The output stream of the heat exchanger device (18) is an oxygen stream (19). Finally, the vacuum generation unit (20) drives the oxygen and pressurizes it, inducing a depression or vacuum upstream. The input stream for the vacuum generation system (20) is the oxygen stream (19) that comes from the heat exchanger device (18). The output stream for the vacuum unit (20) is the oxygen stream at the required service pressure.

(86) Finally, the oxygen-depleted stream (16) is introduced into a turbine (33) for its energy upgrading. The outlet stream from the turbine (33) is the oxygen-depleted stream (32) that comes from the third membrane module (15). To optimize the pressurization (and depressurization) of the oxygen-rich line, the compressor (28) and the turbine (33) can be connected to the same shaft (29).

(87) FIG. 11 shows the results of this embodiment relative to the first membrane module (6) with a mixture of COCO.sub.2 as combustible gaseous stream (5) and air as oxygen-rich stream (7). FIG. 11.a shows a view of the first membrane module. FIGS. 11.b and 11.c show a simplified view of the passage of gas streams through fuel (69) and air (71) chambers for a co-current flow distribution (solid lines in FIGS. 11. d, 11.e and 11.f) and countercurrent (dashed lines in FIGS. 11.d, 11.e and 11.f) respectively. FIG. 11.d shows the results of the temperature profiles in the air chamber (71) and the molar fraction of oxygen in the air chamber (71) along the longitudinal coordinate of the membrane module considering an air inlet (7) corresponding to 25% of the minimum amount to achieve oxidation of all the combustible material of the input fuel gas stream (5). FIG. 11.e shows the results of the temperature profiles in the air chamber (71) and the oxygen molar fraction in the air chamber (71) along the longitudinal coordinate of the membrane module considering an air inlet (7) corresponding to 50% of the minimum amount to achieve oxidation of all the combustible material in the input fuel gas stream (5). FIG. 11.f shows the results of the temperature profiles in the air chamber (71) and the oxygen molar fraction in the air chamber (71) along the longitudinal coordinate of the membrane module considering an air inlet (7) corresponding to 75% of the minimum quantity to achieve oxidation of all the combustible material in the input fuel gas stream (5). The results show that, for the cases considered by example 1, considering a total fixed membrane area, for the first membrane module (6) the countercurrent flow arrangement allows to generate nitrogen streams whose oxygen content is less than 1%, while in the co-current case, diluting excessively the fuel stream (5) causes the module not to heat efficiently and, therefore, oxygen does not permeate because the membrane resistance acts as a limiting factor. It is observed that in the co-current case, as the oxidation reactions take place, the heat is used to heat both the COCO.sub.2 stream and the air stream. On the other hand, oxygen is consumed in the same direction, such that for the co-current case, the temperature increases as the driving force decreases and, due to this, the phenomena of oxygen transport through the membrane is activated as the driving force decreases. On the other hand, in the countercurrent case, the direction of the fuel causes the heating of the module to occur in the opposite direction in which the driving force decreases.

(88) This means that the hottest areas and the areas with the greatest driving force are in the same area of the module. Consequently, for countercurrent distribution, the oxygen transport phenomena through the membrane are activated as the driving force increases.

(89) FIG. 13 shows the results of example 1 where a practical case of the second membrane module (10) has been studied with a mixture of COCO.sub.2 as combustible gaseous stream (8) and air as oxygen-rich stream (11). A practical case has been studied for the arrangement of flows in co-current (FIGS. 13.b and 13.d) and counter-current (FIGS. 13.c and 13.e) in the second membrane module (10). FIGS. 13.b and 13.c show the temperatures of the outlet air stream (14) (oxygen depleted stream) as a function of the air stream input temperature (11). FIGS. 13.d and 13.e show the maximum temperatures inside the module as a function of the air stream input temperature (14) (stream depleted in oxygen). The results show that, for the cases considered in example 1, considering the total fixed membrane area, for the second membrane module (10) to achieve complete oxidations of the waste stream without reaching excessive temperatures that could degrade the module, requires introducing high air excess and high input temperatures.

(90) FIG. 14 shows the results of example 1 where a practical case of the third membrane module (15) has been studied. Air has been considered as the oxygen rich stream (14). The results show that, for the assumptions considered in example 1, the pressure of the input air stream to the third membrane module and the imposed vacuum significantly improve the extraction of oxygen by reducing the membrane area required for the process.

Example 2

(91) A second alternative of the process according to the invention is shown in FIG. 2.

(92) This variant of the process presents an alternative in terms of the dosage of the oxygen rich stream in the modules M.sub.1 and M.sub.2. In this case, the oxygen-rich stream (11) in the heat exchanger device (31) is introduced into the second membrane module (10). The oxygen-depleted stream (14) leaving the second membrane module (10) is metered by a metering valve system (44, 45 and 46) to recirculate this stream from the first membrane module (6), to the third module membrane (15) and the turbine (33). So, the depleted oxygen stream (14) that comes from the second membrane module (10) is divided into three streams (41, 42 and 43) that are introduced into the metering valves. The input stream to the first metering valve (44) is a fraction of the depleted air stream (41). The input stream to the second metering valve (45) is a fraction of the depleted oxygen stream (42) with respect to (C2) and the output stream is the oxygen-rich stream (48) entering the third membrane module (15). The oxygen-depleted stream (16) coming from the third membrane module (15) and the output stream from the first metering valve (47) are joined and introduced into an oxygen-depleted stream (40) that is introduced into the turbine (33). The input stream to the third metering valve (46) is a fraction of the oxygen-depleted stream (43) coming from the second membrane module (10). The output stream from the third metering valve is the oxygen-rich stream (7) entering the first membrane module. This stream (7), as in the case of example 1, must contain an amount of oxygen less than the stoichiometric amount to completely oxidize the combustible stream (5), it is supplied to the third membrane module (15) as stream (48) which supplies oxygen to the module (15) and to the turbine (33). In this way, the metering of the metering valves (44, 45, and 46) is carried out considering that the depleted oxygen output stream (9) must be practically pure N.sub.2 and the amount of oxygen (21) that is desired to be produced.

Example 3

(93) FIG. 3 shows a particular example of a process according to the invention, an alternative to the process for producing O.sub.2 and CO.sub.2. In this case, the first membrane module is dispensed with, with respect to the first two examples (FIG. 1 and FIG. 2). It is observed that the combustible gaseous stream (5) leaving the first heat exchanger (4) is the input stream to the second membrane module (10). In this case all the heated oxygen-rich stream (11) in the second heat exchanger system (31) is introduced into the second membrane module (10).

Example 4

(94) FIG. 4 shows a particular examplewith possible variants, as read at the end of the paragraphof a process according to the invention to produce N.sub.2 and CO.sub.2. It is observed that in this case the third membrane module is dispensed with, with respect to the first two examples (FIG. 1 and FIG. 2). It is observed that the oxygen-depleted output stream (14) from the second membrane module (10) is recirculated to the turbine (33) as an input stream.

(95) Additionally, depending on the final application of the gaseous streams obtained, the process can optionally incorporate a pressurization system for the different streams that are produced as shown in the figure. Therefore, a variant of this embodiment would be an embodiment in which the nitrogen and carbon dioxide streams obtained are not pressurized and therefore the compressors (49) and (51) would not be present.

(96) In the case that the stream is pressurized, for the CO.sub.2 pressurization system (49), the input stream is the CO.sub.2 stream (25) that comes from the condenser-separator (24) and the output stream is a CO.sub.2 stream (50) at the required operating pressure. The nitrogen (9) (oxygen depleted stream) that leaves the first membrane module (6) is cooled to practically room temperature by means of a heat exchanger (73), from which it leaves as an N.sub.2 stream (74). Finally, a N.sub.2 pressurization system (51) is provided. The input stream to this pressurization system (51) is the N.sub.2 stream (74) leaving the heat exchanger (73). The output stream of the N.sub.2 pressurization system (51) is the N.sub.2 stream (52) at the required operating pressure.

(97) Dosing or volumetric flow control of the incoming and outgoing gaseous streams to the oxygen permeation membrane modules (6) M.sub.1 and M.sub.2 (10) is carried out by means of a system of valves (38 and 39) as in Example 1.

Example 5

(98) FIG. 5 shows a particular example of a process according to the invention to produce N.sub.2 and O.sub.2. In this case, the second membrane module is dispensed with, with respect to the first two examples (FIG. 1 and FIG. 2). The partially oxidized combustible gaseous stream (8) leaving the first membrane module (6) and the oxygen depleted rich stream (16) leaving the third membrane module (15) are introduced into a combustor (53) to finish the oxidization of the fuel material of the partially oxidized fuel gas stream. The output stream from the combustor (54) is introduced into the turbine (33).

(99) Dosing or volumetric flow control of the incoming and outgoing gaseous streams to the oxygen permeation membrane modules M.sub.1 and M.sub.2 is carried out by means of a system of valves (38 and 39) as in the case of example 1.

(100) The nitrogen (9) (oxygen-depleted stream) that leaves the first membrane module (6) is cooled and pressurized in the same way and with the same components that are used in example 4, shown in FIG. 4.

Example 6

(101) FIG. 6 shows a particular example of a process according to the invention that includes two additional membrane modules (M.sub.4 and M.sub.5) (56) and (59) for the purification of the N.sub.2 and CO.sub.2 streams. The N.sub.2 (9) (oxygen depleted stream) and CO.sub.2 (13) streams produced in the first membrane module (6) and the second membrane module (10) respectively can contain significant amounts of oxygen considering the purity required in their subsequent applications. Oxygen permeation membrane modules will be used for the removal of oxygen that the streams to be purified may contain, wherein the stream to be purified (55) enters the module as a stream that supplies oxygen to the system for N.sub.2, and (57) for the CO.sub.2). As shown in the figure, the combustible gaseous stream (55) enters these modules as an entrainment stream from the additional modules. The input streams to the first additional module (56) are the combustible gaseous stream (55) and the stream (oxygen depleted) of N.sub.2 to be purified (9) that comes from the outlet of the first membrane module (6). The output streams of the first additional membrane module (56) are the combustible gaseous stream (57) and the purified N.sub.2 stream (58). The input streams to the second additional module (59) are the combustible gaseous stream (57) that comes from the outlet of the first additional membrane module (56) and the CO.sub.2 stream to be purified (13) (it is the combustible gaseous stream, after combustion in the first modules (M.sub.1 and M.sub.2), therefore it contains CO.sub.2 and excess O.sub.2 (which is the one removed in the additional modules) coming from the outlet of the second membrane module (10). The output streams of the second additional membrane module (59) are the combustible gaseous stream (5) and the purified CO.sub.2 stream (60). Finally, the oxygen extracted from the streams to be purified will cause a slight oxidation in the combustible gaseous stream which will cause a slight increase in temperature. The additional membrane modules (56 and 59) have a countercurrent flow distribution to ensure complete oxygen exchange from the streams to be purified to the combustible streams.

(102) According to a further alternative, another way of purifying the CO.sub.2 and/or N.sub.2 streams can be the use of polymeric oxygen permeation membranes. In this case, the streams to be purified must be cooled to atmospheric temperature and pressurized in order to carry out the process.

(103) The completely oxidized combustible gaseous stream (13) that comes from the second membrane module (10) is mainly composed of carbon dioxide and water vapor, as in the case of example 1. The same components and procedure are used for its separation as in the case of example 1.

(104) Dosing or volumetric flow control of the incoming and outgoing gaseous streams to the oxygen permeation membrane modules M.sub.1 and M.sub.2 is carried out by means of a system of valves (38 and 39) as in the case of example 1.

Example 7

(105) FIG. 7 shows a particular example of a process according to the invention that integrates the process described in example 1, shown in FIG. 1, in a biomass thermochemical upgrading process. In this case, the source of the combustible stream (C1) is biomass. The biomass is gasified by means of a thermochemical reactor (64). The input streams to the thermochemical reactor (64) are biomass (61), a carrier stream (63), which is composed of an inert gas and can contain water vapor to improve the process (if necessary) and an oxygen rich stream in (62) (unless the thermochemical process is a pyrolysis process, in which case no component is introduced that could cause the oxidation of the material). The output streams of the thermochemical reactor (64) are the gasified stream (66) and the ashes contained in the biomass (65). The gasified stream (66) is led to a fractionation tower (67) to separate the light gases from the heavy gases. The output streams are the light gas streams (68), each of the product streams in which the fractionation is distributed (74, 75, 76, 77) and the liquid stream of heavy compounds (78). In this case, the liquid heavy compound stream (78) represents the starting combustible stream for the membrane modules. Since the stream enters the process in the liquid phase, in this case the stream is driven by a hydraulic pump (79) at operating pressure (considering the pressure drops of the different downstream equipment). The input stream to the hydraulic pump (79) is the heavy liquid stream (78) that comes from the fractionation tower (67). The output stream of the hydraulic pump (79) is the pressurized heavy liquid stream (80). In this case, to bring the combustible stream to the membrane modules conditions, evaporation is required before heating the stream to the operating temperature. For this purpose an evaporator (12) is arranged to gasify the combustible stream. The inlet stream to the evaporator (12) is the heavy compound liquid stream (80) that comes from the hydraulic pump (79). The output stream of the evaporator (12) is the gasified stream of heavy compounds (3). A good design of the membrane modules can generate sufficient amounts of the CO.sub.2 and O.sub.2 streams to be considered for feeding the thermochemical reactor.

Example 8

(106) Membrane module to produce N.sub.2 (not shown in the figures) from air as an oxygen-rich stream and a combustible gaseous stream composed of CO and CO.sub.2. The initial input fuel gas stream is composed of 57.10% CO in CO.sub.2. The initial input combustible gaseous stream is diluted with CO.sub.2 to reduce the increase in temperature due to oxidation reactions such that

(107) $r=\frac{F_{CO2}}{F_i},$
where r is the molar ratio between the input flow rate of diluted CO.sub.2 (F.sub.CO2) and the initial fuel gaseous input flow rate (F.sub.i). Different dilutions from r=2.5 to r=10 have been tested. All the streams enter at 700 C. The airline is pressurized to 2.5 bar absolute pressure. Amounts of air at 25%, 50% and 75% of the stoichiometric amount of air have been used. The considered membrane module has 5 membranes of 380 cm.sup.2 per membrane. Co-current and counter-current flow distribution has been considered. The longitudinal distance between the inlet of the module chambers and the outlet of each chamber is 20 cm. The transport of oxygen through the membrane has been simulated from the following equation:

(108) $\begin{array}{cc}{J}_{O2}\left(x\right)=K\left(T\left(x\right)\right).Math.\ln \left(\frac{p_{air}.Math.x_{O2,air}}{p_{\mathrm{drag}}.Math.\left(x_{O2,\mathrm{entrainment}}+t\mathrm{ol}\right)}\right)& \end{array}$
wherein J.sub.O2 is the molar flow of oxygen per unit area, K is the permeability constant, pair is the total pressure in the air chamber, p.sub.entrainment is the pressure in the entrainment chamber and x.sub.O2, is the mole fraction of oxygen in chamber i (i is general and indicates the chamber in question, it can be air or entrainment.), T is the temperature, x is the longitudinal coordinate and tol is a parameter to avoid indeterminates in the calculation set at 10.sup.5. K is calculated as a function of temperature to be able to predict the improvement in permeation as the temperature increases.

(109) The heat transmission has been carried out considering the thermal conduction between the two membrane walls, using the equation:

(110) $\begin{array}{cc}\mathrm{Heat}=k_{MEMB}.Math.\frac{dA}{dx}.Math.\left(T_{\mathrm{entrainment}}\left(x\right)-T_{air}\left(x\right)\right)& \end{array}$
wherein k.sub.MEMB is the thermal conductivity of the membrane, dA is the membrane area differential, dx is the length differential, T.sub.i(x) is the temperature in chamber i (air or entrainment) at position x, and x represents the longitudinal position.

(111) The oxidation reaction that takes place in the entrainment chamber (69) is: CO+0.5O.sub.2.fwdarw.CO.sub.2. The heat of reaction has been calculated using the reaction enthalpy of the combustion reaction. Results are shown in FIG. 11.

Example 9

(112) Membrane module for complete oxidation of a stream with combustible material from air as an oxygen-rich stream and a combustible gaseous stream composed of CO and CO.sub.2. The gaseous combustible stream is made up of 9.5% CO in CO.sub.2. The temperature of the input streams was varied such that the air stream was introduced at temperatures from 600 C. to 815 C. and the entrainment current was introduced at 600 C. and 700 C. The airline was pressurized at 2.5 bar absolute pressure. Air is introduced in excess, where A is the molar ratio between the input air molar flow rate (F.sub.air) and the stoichiometric air molar flow rate (F.sub.stoichiometric air), such that

(113) $A=\frac{F_{aire}}{\mathrm{Fstoichiometric}\mathrm{air}}$
Different air excesses were tested, from A=5 to A=20. The considered membrane module has 5 membranes of 380 cm.sup.2 per membrane. Co-current and countercurrent distribution has been considered. The output temperatures of the air stream and the maximum temperature the system reaches were measured. The longitudinal distance between the inlet of the module chambers and the outlet of each chamber is 20 cm. The transport of oxygen through the membrane was simulated using the following equation:

(114) $\begin{array}{cc}{J}_{O2}\left(x\right)=K\left(T\left(x\right)\right).Math.\ln \left(\frac{p_{air}.Math.x_{O2,air}}{p_{\mathrm{entrainment}}.Math.\left(x_{O2,entrainment}+\mathrm{tol}\right)}\right)& \end{array}$
wherein J.sub.O2 is the molar flow of oxygen per unit area, K is the permeability constant, p.sub.air is the total pressure in the air chamber, p.sub.entrainment is the pressure in the entrainment chamber and x.sub.O2, is the mole fraction of oxygen in chamber i (air or drag), T is the temperature, x is the longitudinal coordinate and tol is a parameter to avoid indeterminates in the calculation, set at 10.sup.5. K is calculated as a function of temperature to be able to predict the improvement in permeation as the temperature increases.

(115) The heat transmission was carried out considering the thermal conduction between the two membrane walls, using the equation:

(116) $\begin{array}{cc}\mathrm{Heat}=k_{MEMB}.Math.\frac{dA}{dx}.Math.\left(T_{\mathrm{entrainment}}\left(x\right)-T_{aire}\left(x\right)\right)& \end{array}$
where k.sub.MEMB is the thermal conductivity of the membrane, dA is the membrane area differential, dx is the differential length, T.sub.i(x) is the temperature in chamber i (air or entrainment) at position x and x represents the longitudinal position. The oxidation reaction that occurs in the entrainment chamber (69) is: CO+0.5O.sub.2.fwdarw.CO.sub.2. The reaction heat was calculated using the reaction enthalpy of the combustion reaction. The results are shown in FIG. 13.

Example 10

(117) Membrane module for obtaining oxygen from air as an oxygen rich stream and imposing a vacuum.

(118) This example is intended to illustrate the third membrane module of Examples 1, 2, 3, 5, 6, and 7. In these cases, it is an O.sub.2 permeation from an O.sub.2 rich stream.

(119) The temperature of the input stream was varied from 900 C. to 1050 C. Different pressurizations of the airline were tested from 1 bar to 5 bar absolute pressure.

(120) Two vacuum pressures have been tested: 50 mbar and 100 mbar. Different membrane areas were studied (from 0.5 m.sup.3 to 10 m.sup.3). The equivalence between membrane area and number of membranes was carried out considering 380 cm.sup.2 membranes. The oxygen transport through the membrane was simulated using the following equation:

(121) 0$\begin{array}{cc}{J}_{O2}\left(x\right)=K\left(T\left(x\right)\right).Math.\ln \left(\frac{p_{\mathrm{air}}.Math.x_{O2,air}}{p_{vacuum}}\right)& \end{array}$
wherein J.sub.O2 is the molar flow of oxygen per unit area, K is the permeability constant, pair is the total pressure in the air chamber, p.sub.vacuum is the pressure in the entrainment chamber and x.sub.O2, is the mole fraction of oxygen in chamber i (air or vacuum), T is the temperature, and x is the longitudinal coordinate. K is calculated as a function of temperature to be able to predict the improvement in permeation as the temperature increases. The results are shown in FIG. 14.

Example 11

(122) Flat oxygen permeation membrane modules were designed with various configurations shown in FIGS. 8, 9 and 10. These figures are not intended to give a sample of fixed geometries and planes for the membrane modules but to clarify the internal distribution of the gas streams through the module. Likewise, there are more construction details that can be modified depending on the needs of the module. For example, the number of membranes in the module depending on the needs of the process area or the number of lanes to conduct the currents to the module chambers or extract the gas from the module chambers (identified by the holes FIG. 8.b, FIG. 9.b and FIG. 10.b) can be increased depending on the final dimensions of the module in order to ensure a good distribution of the gas streams in each of the chambers.

(123) FIG. 8 shows the geometry of a flat membrane module (with 20 membranes) with a cross-flow distribution. FIG. 8.c shows the B-B cross section (FIG. 8.b) of the membrane module with cross-flow distribution with the paths of the gaseous stream that passes through the module in the B-B direction. FIG. 8.d shows the C-C cross section (FIG. 8.b) of the membrane module with cross-flow distribution with the paths of the gas stream that passes through the module in the C-C direction (perpendicular to the B-B direction). FIGS. 8.c and 8.d illustrate that the gas streams enter from the top and bottom part of the module and are extracted in the same way with the aim of minimizing pressure drops and equitably distributing the incoming gas stream by the different chambers of the module.

(124) FIG. 9 shows the geometry of a flat membrane module (with 20 membranes) valid for both a co-current distribution and a counter-current flow distribution. The cross sections AA and BB (FIG. 9.b) are parallel planes, so that the gas streams shown in the figures obtained by these cut planes (9.c-h) circulate in the same path with the same direction for the distribution of flows in co-current (FIGS. 9.c and 9.d) or with opposite directions for the distribution of counter-current flows (FIGS. 9.g and 9.h). FIGS. 9.c and 9.d illustrate the gas stream paths using the membrane module in a co-current flow configuration. FIG. 9.e is an enlarged view of FIG. 9.c to detail the flow distribution in the module. FIG. 9.f is an enlarged view of FIG. 9.d to detail the flow distribution in the module. FIGS. 9.g and 9.h illustrate the gas stream paths using the membrane module in a countercurrent flow configuration. FIGS. 9.c-h illustrate that the gas streams enter from the top and bottom of the module and are extracted in the same way with the aim of minimizing head losses and equitably distributing the input gas stream through the different chambers. of the module.

(125) FIG. 10 shows the geometry of a flat membrane module where gas streams pass through the membrane module several times in its longitudinal direction. This geometry allows both a co-current distribution and a counter-current flow distribution. Considering as one passage each time the gas stream passes through the membrane in its longitudinal direction, FIG. 10 represents a module of 3 passages through the module with 6 membranes per passage. The shear planes AA and BB (FIG. 10.b) are parallel planes, so that the gas streams shown by the figures obtained by these shear planes (10.c-h) go in the same trajectory with the same direction for the co-current flow distribution (FIGS. 10.c and 10.d) or with opposite directions for the distribution of counter-current flows (FIGS. 10.g and 10. h). FIGS. 10.c and 10.d illustrate the gas stream paths using the membrane module in a co-current flow configuration. FIG. 10.e is an enlarged view of FIG. 10.c to detail the flow distribution in the module. FIG. 10.f is an enlarged view of FIG. 10.d to detail the distribution of flows in the module.

(126) FIGS. 10.g and 10.h illustrate the gas stream paths using the membrane module in a countercurrent flow configuration. The gases enter the module from the inner side for the distribution of co-current flows (FIGS. 10.c and 10.d) and for FIG. 10.g and the upper part for FIG. 10.h. The gases leave the module through the upper part thereof for the distribution of co-current flows (FIGS. 10.c and 10.d) and for FIG. 10.g and the lower part for FIG. 10.h.