Abstract:
A method for removing acid gas components from combustion gas and natural gas. The method includes bringing the gas mixture into contact with sea water and subjecting the gas mixture and sea water to turbulent mixing conditions. This causes the acid gas to be absorbed by the sea water. The sea water can be disposed of offshore without any detrimental effect on the environment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a Continuation of Application No. PCT/GB98/02775 filed Sep. 14, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the removal acid gases such as CO 2 , NO x , H 2 S, oxides of sulphur etc. from natural gas. 
     BACKGROUND OF THE INVENTION 
     Conventional systems for the absorption of acid gases employ a liquid solvent; typical solvents include amines such as methyldiethanolamine (MDEA), monoethanolamine (MEA) or diethanolamine (DEA), and mixtures of solvents. These solvents absorb CO 2 , NO x , H 2 S and other acid gases. The solvent is contacted with the sour gas mixture (gas mixture including acid gases) in a column which may be a packed column, a plate column or a bubble-cap column, or a column with some other form of contact medium. In these systems, the gas and liquid streams flow countercurrently. 
     The prior art absorption systems suffer the disadvantage that in order to achieve a significant degree of gas/liquid contact, the columns have to be large and their operation is hampered by excessive foaming. In addition, the subsequent stripping section which removes the acid gas from solution must also be large, to handle the large volume of solvent used. Since the operation normally takes place under high pressure and the fluids involved are highly corrosive, the capital costs of the large columns and subsequent stripping section is high. Furthermore, operating costs and maintenance costs are high. 
     It is an object of the present invention to provide a system for removing acid gas from natural gas which does not suffer from the disadvantages of the prior art, preferably with a high degree of efficiency and more economically than in existing methods. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a method of removing carbon dioxide and other acid gas components from natural gas which comprises: bringing the natural gas into contact with a liquid including a solvent or reagent for the carbon dioxide and other acid gases; subjecting the natural gas and liquid to turbulent mixing conditions thereby causing the carbon dioxide and other acid gases to be absorbed by the solvent or reagent; and separating a gas phase and a liquid phase. 
     The invention also extends to the apparatus for carrying out this method. 
     The turbulent mixing is very intense and results in extremely efficient gas liquid contact. The mixing regime is preferably turbulent shear layer mixing. The liquid entrained in the gas may be in the form of droplets for gas continuous fluid phase distribution. is The efficient mixing means that absorption can take place very rapidly and in a relatively small amount of solvent compared to that required in conventional absorption columns. This in turn means that the liquid duty in the equipment is dramatically reduced resulting in a consequential reduction in the size of any downstream regeneration section. At the same time, the mixing system used is simple and inexpensive compared to prior art systems, leading to reduced costs. Finally, an efficiency of approaching 100% for the removal of acid gas can be achieved for certain applications. 
     In addition, conventional absorbtion methods involve the evolution of heat which must then be removed from the system. While the method of the invention is capable of operation with a relatively low pressure drop across the mixing means, when greater pressure drop is employed, a cooling effect is achieved and this may render the need for additional cooling unnecessary. 
     The absorption may be achieved by simply dissolving the gas or by way of a chemical reaction with the solvent. 
     Preferably, the method is carried out as a continuous process with the natural gas and liquid flowing co-currently. The co-current flow eliminates the problems associated with foaming, since separation can easily be effected downstream of the contactor. Preferably, the method includes the step of treating the liquid phase to remove the absorbed acid gas components. 
     The turbulent mixing may be achieved by any convenient means, such as an ejector or a jet pump or more preferably in a turbulent contactor including a gas inlet, a liquid inlet, an outlet leading to a venturi passage and a tube extending from the outlet back upstream, the tube being perforated and/or being spaced from the periphery of the outlet. 
     One suitable contactor is a mixer supplied by Framo Engineering A/S and is described in EP-B-379319. 
     Preferably, the tube is located in a vessel, the vessel including the gas inlet, the liquid inlet and the outlet. In one possible regime, the natural gas is supplied to the tube, optionally directly, and, the liquid is supplied to the vessel, and so the natural gas stream draws the liquid into the venturi and the two phases are mixed. In another regime, the natural as is supplied to the vessel and the liquid is supplied to the tube, optionally directly, whereby the natural gas is drawn into the venturi by the liquid and the two phases are mixed. In a third regime, the liquid and the natural gas are supplied to the vessel, the liquid being supplied to a level above the level of the outlet, whereby the natural gas is forced out through the outlet via the tube, thereby drawing the liquid into the venturi so that the two phases are mixed. 
     Preferably, a solvent absorbs the carbon dioxide and other acid gases. Alternatively, a reagent reacts chemically with the carbon dioxide and other acid gases. Conceivably, the reagent is a biological reagent which removes the carbon dioxide and other acid gases biologically. In one variant of the invention, a plurality of acid gas components are absorbed by a plurality of respective solvents or reagents. 
     Preferably, the natural gas and the liquid are formed into a homogeneous mixture in the contactor, the homogeneous mixtures being cooled prior to separation into a gas phase and a liquid phase. Preferably, the cooled homogeneous mixture is separated into a gas phase and a liquid phase in a hydrocyclone. Preferably, the solvent in the liquid phase is subjected to a regeneration treatment to remove the absorbed acid gases. Preferably, the regenerated solvent-containing liquid phase is recycled to the contactor. Preferably, the regeneration is carried out by heating and/or by flashing off the absorbed gas component in a flash tank. Preferably, the post-mixing cooling and the regenerative heating are achieved, at least in part by mutual heat exchange. 
     In one alternative arrangement, a portion of the solvent, after extraction, is recycled to the contactor directly, without regeneration. Thus, part of the CO 2 -loaded solvent by-passes the regeneration section. This serves to increase the CO 2  loading of the solvent. It should be noted that optimisation of the process may not necessarily relate to the removal efficiency in terms of mole fraction of CO 2  removed, but rather the energy consumption required per unit mass of CO 2  removed. By increasing the CO s  loading of the solvent, it is possible to reduce the amount of solvent that needs to be handled by the regeneration section. 
     In the case of CO 2 , as the initial solvent loading level is increased, the CO 2  absorption efficiency drops. However, a considerable fraction of total liquid flow rate can be recirculated directly from the gas liquid separated before the drop in CO 2  removal becomes significant. 
     According to a more specific aspect of the invention, there is provided a method for removing acid gases from a natural gas which comprises: supplying the natural gas to a turbulent contactor; supplying a liquid including a solvent for the acid gases to the contactor; subjecting the natural gas and the liquid to turbulent mixing in the contactor to form a homogeneous mixture; allowing the acid gas to be absorbed by the solvent; cooling the homogeneous mixture; separating the cooled homogeneous mixture into a gas phase and a liquid phase in a hydrocyclone (or any other gas/liquid separator); removing the gas phase; subjecting the solvent in the liquid phase to a regeneration treatment to remove the absorbed acid gas; and recycling the regenerated solvent-containing liquid phase to the contactor. 
     Again, a portion of the solvent, after extraction may be recycled directed to the contactor. 
     Preferably, the regeneration is carried out by heating and/or by flashing off the absorbed gas component in a flash tank. Preferably, the post mixing cooling and the regenerative heating are achieved, at least in part by mutual heat exchange. Preferably, in instances where the natural gas is at a low pressure, the liquid is pumped to the contactor and thereby draws the natural gas with it through the contactor. Preferably, when the natural gas is at high pressures, it is conveyed to the contactor at a high pressure and thereby draws the liquid with it through the contactor. 
     The invention also extends to apparatus for carrying out such a method, comprising: a turbulent contactor having a liquid inlet, a gas inlet and a fluid outlet; a cooler for the fluid stream from the fluid outlet; a hydrocyclone arranged to separate the cooled fluid stream into a gas phase and a liquid stream; a regenerator arranged to treat the separated liquid stream; and a recycle line arranged to convey the regenerated liquid stream to the contactor. 
     The apparatus may include a recycle line for the liquid stream from the separator to the contactor, by-passing the regenerator. There may also be a further separator, for example, in the form of a flash tank, in lo the recycle line to allow absorbed gas to be released from the liquid. 
     The apparatus may include a pump arranged to supply liquid to the liquid inlet of the contactor. Preferably, the regenerator is a heater and/or a flash is tank. Preferably, the contactor is a turbulent contactor as described above, or alternatively an ejector or a jet pump. 
     The invention may be considered to extend to the use of a turbulent contactor to remove acid gas from natural gas by forming a homogeneous mixture of the gas mixture with a solvent for the acid gas in the contactor, allowing the acid gas to be absorbed by the solvent, and subsequently separating a gas phase and a liquid phase, the liquid phase thereby containing the acid gas. 
     The improved efficiency possible for the removal of acid gases makes the present invention particularly valuable as awareness is increased of the potential damage to the environment that can be caused by acid gases. 
     Furthermore, the small size of the apparatus compared to conventional absorption columns render the invention especially applicable to use in marine applications, such as on board shuttle tankers. 
     The invention may be put into practice in various ways and two specific embodiments will be described by way of example to illustrate the invention with reference to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram of the process for use when the gas is under low pressure; 
     FIG. 2 is a flow diagram of the process for use when the gas is under high pressure; 
     FIG. 3 is a block diagram of the apparatus as used in the batch test procedure; 
     FIG. 4 is a view of the turbulent contactor as used in the batch test procedure; 
     FIG. 5 shows an alternative mixer arrangement; 
     FIG. 6 is a view of a jet pump which can be used as an alternative to the contactor; and 
     FIG. 7 is a block diagram of an alternative embodiment of a process according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In one embodiment of the invention, a continuous process operation for the removal of carbon dioxide (and other acid gases) from exhaust gas is shown in FIG. 1. A liquid solvent stream  1 , for example MEA (monoethanolamine), is conducted by a pump  2  to a contactor  3  (though this could be an ejector) capable of inducing turbulent mixing. A natural gas stream  4 , including the CO 2  which is to be removed, is drawn into the contactor  3  by the low pressure generated in the venturi by the liquid stream after it has passed through the pump (stream  1   a ). This arrangement provides an automatic means of self-regulation as the gas mixture to solvent ratio can be maintained for varying flow rates. At the outlet of the contactor  3  the liquid solvent and the natural gas stream are in the form of a homogeneous mixture (stream  5 ) and the mass transfer of the CO 2  from the gas phase to the liquid occurs very rapidly. 
     The mixed two phase stream  5  is then conveyed to a cooler  6  and on into a hydro cyclone  7 . The gas stream  8  is taken off and the liquid stream  9  passes on to a regeneration system. At this point in the circuit all the CO 2  is in the liquid phase (stream  9 ) and the gas stream  8  is free of CO 2 . 
     The regeneration of the liquid solvent is achieved by boiling off the CO 2  in a heater  10 . The CO 2  is taken off as a gas stream  11  and the liquid solvent is optionally passed through a flash tank (not shown) to remove any residual dissolved gas before being recycled into the feed stream  1 . The liquid solvent in stream  1  is topped up from the reservoir  12  as necessary to maintain a regular flow rate around the system. 
     It will be clear to a person skilled in the art that the cooler  6  and the heater  10  may be combined to form a heat exchange unit. 
     An alternative system for the removal of CO 2  from a high pressure natural gas stream is shown in FIG. 2. A high pressure natural gas stream  20  containing the CO 2  which is to be removed is conveyed to a contactor  21  similar to that shown in FIG.  4 . The high pressure of the gas draws a controlled amount of liquid solvent, for example MEA, from the recycle stream  22  and, if necessary, from a reservoir  23  into the contactor  21 . 
     At the outlet of the contactor  21  the two phases are in the form of a homogeneous mixture (stream  24 ) and the mass transfer of the CO 2  from the gas phase to the liquid solvent takes place. The residence time may be as little as 0.1 seconds since the reaction kinetics for the absorption of CO 2  by MEA are very rapid, although this will vary with the solvent used and the gas to be transferred from the gas to the liquid. 
     The two phase mixture (stream  24 ) passes through a cooler  25  to a hydro cyclone unit  26 . The gas stream free of CO 2  is taken off in stream  27  and the remaining liquid stream  28  including the CO 2  is passed to a regeneration system. 
     The liquid stream  28  is fed into a heater  29  to remove the CO 2  as a gas stream  30 . This regenerates the solvent for re-use in the system. This solvent (stream  22 ) is then drawn into the contactor  21  by the low pressure generated in the venturi by the high pressure natural gas (stream  20 ) as explained above. Any shortfall in the solvent liquid is made up by addition from the reservoir  23 . As in the first embodiment, the heater  29  and the cooler  25  can be combined to form a heat exchange unit. 
     The contactor used in both the above embodiments is shown in FIG.  4 . The turbulent contactor  100  comprises a vessel  101  having a gas inlet  102 , a liquid inlet  103  is and an outlet  104  leading to a venturi passage  105 . There is a tube  106  (which may or may not be perforated) extending from the outlet  104  back into the vessel  101 . 
     In a first arrangement, the natural gas is supplied to the vessel  101  and the liquid solvent is supplied to the tube  106  whereby the gas is drawn into the venturi by the liquid and the two phases are mixed. 
     In a second arrangement, the liquid solvent is supplied to the vessel  101  and the gas mixture is supplied to the tube  106 , whereby the liquid is drawn into the venturi by the gas and the two phases are mixed. 
     In a third arrangement, the liquid solvent and the natural gas are supplied to the vessel  101 , the solvent being supplied to a level above the level of the outlet  104 , whereby the gas is forced out through the outlet  104  via the tube  106 , thereby drawing the solvent into the venturi so that the two phases are mixed. 
     A fourth variant is shown in FIG.  5 . This embodiment is similar to that shown in FIG. 4, but the contactor  110  is inverted. It comprises a vessel  111  with a liquid inlet  112 , a gas inlet  113  and an outlet  114  leading to a venturi passage  115 . There is a tube  116  (which may or may not be perforated) extending from the outlet  114  back into the vessel  111 . The tube  116  may be connected directly to the gas inlet  113 . 
     The contactors referred to in the above embodiments may be replaced by jet pump arrangements which are capable of inducing turbulent mixing. FIG. 6 shows a jet pump  120  comprising a first fluid inlet  121  for the high pressure fluid and a second fluid inlet  122  for the low pressure fluid. The high pressure fluid draws the low pressure fluid along the length of the jet pump  120  to the outlet  123 . The fluids are well mixed into a homogenised mixture in the region  124  at the outlet of the high pressure inlet  121 . 
     An alternative embodiment is shown in FIG.  7 . Here the Co 2 -containing gas is supplied to the contactor  201  via a gas inlet  202  and solvent is supplied via a solvent inlet  203 . The two phases are mixed in the contactor  201  and subsequently in a contact pipe  204 . The homogeneous mixture is fed via a line  205  to a separator  206  where separation into a cleaned gas stream  207  and a CO 2  loaded solvent stream  208  is effected. 
     The loaded solvent is conveyed to a flash tank  209  where some of the absorbed CO 2  comes out of solution and is removed via line  210 . The partially loaded solvent is conveyed to a desorption column  211  via line  212  where the solvent is regenerated and returned to the contactor  201  via line  213 . 
     However, a portion of the partially-loaded solvent is recycled, without regeneration, via recycle line  214 , directly to the contactor  201 . This serves to increase the loading of the solvent in the system and thus enables the duty of the regeneration operation to be reduced. 
     The invention is further illustrated by reference to the following examples. These serve to verify the operating principles of the two embodiments described. In the series of batch experiments conducted, the gas stream was a mixture of nitrogen (N 2 ) and CO 2  and the liquid solvent was a mixture of MEA and water. The reservoir pipe was kept under pressure using nitrogen gas. The contactor used was a FRAMO contactor generally as described in EP 379319 and shown in FIG.  4 . The mixer injection pipe was adjusted to yield gas/liquid ratios in the range of about 3 to 5, depending upon the total flow rate. 
     A schematic diagram for the series of experiments is shown in FIG.  3 . The contactor  51  is charged with an amount of the liquid solvent mixture from the reservoir  54  which is controlled by a valve  55 . A gas source  50  of the experimental N 2 /CO 2  gas mixture is conveyed to the contactor  51  via a pipe  52  controlled by a valve  53 . 
     At the outlet of the contactor  51  there is a 1 metre section of pipe  56  in which the mass transfer occurs. This section provides the residence time for the contacting materials. A set of 2 simultaneously acting fast closing valves  57  and  58  form a 1.5 metre analysis section  59  where the gas/liquid mixture can be captured, separated and sampled. At the top end of the analysis section there is a sampling point where a sample of the gas can be drawn off (not shown). At the lower end of the section there is a further sampling point where a sample of the liquid can be drawn off (not shown). The lower section of the sampling section is provided with means for cooling the liquid sample prior to its removal (not shown for clarity). 
     A further valve  60  separates the sampling section from a reservoir pipe  61  and is used to control the flow rate through the system. The reservoir pipe  61  is pressurised to a predetermined pressure by an independent nitrogen gas source  62  via a pipe  63  controlled by a valve  64 . This pressure will be lower than that in the contactor to provide a pressure difference which will force the fluids through the system. The reservoir pipe  61  is inclined with respect to the horizontal to enable the liquid collected to be drained off via a pipe  65  controlled by a valve  66  to a measurement drum  67  which is used to determine the amount of liquid passing through the system on each run. The drum  67  has a drainage pipe  68  controlled by a valve  69 . 
     In operation, the contactor  51 , pipe section  56  and analysis section  59  are filled with the suitable strength solvent solution. The simultaneously acting valves  57  and  58  are closed and valve  60  is set to a position carefully adjusted to yield the required mass flow rate through the system for the predetermined pressure difference between the contactor and the reservoir pipe. 
     The contactor  51  is pressurised with the test gas of CO 2 -rich nitrogen to a pressure of 50 barg. The reservoir pipe  61  is pressurised with nitrogen to a predetermined value typically between 16 and 48 barg, providing a range of flow rates through the system. 
     Before the experiment starts, a sample of the test gas is taken to determine the level of CO 2  in the gas. 
     The experiment commences with the activation of the simultaneously operating valves  57  and  58 . The liquid and the gaseous solution flow co-currently through the system to the reservoir pipe  61 . The pressure in the contactor is maintained at 50 barg during the 10 second test run by manual supply of the test gas from a cylinder fitted with an accurate manometer. This makes it possible to record the amount of spent gas for each experiment. 
     After 10 seconds the 2 operating valves  57  and  58  are closed simultaneously. A sample of gas from the analysis section is extracted from the upper sampling point immediately after the valves have closed. This is then tested for content of CO 2  by gas chromatography. The machine used was a Chromopack Model CP-2002 gas chromatograph. 
     In order to verify the mass balance, a liquid sample of the amine solution in the analysis section is taken from the lower sampling point. Before the sample is taken the liquid in the analysis section is cooled using nitrogen gas surrounding the pipe section  59 . The liquid sample is analyzed using a titration technique specially developed for CO 2 . 
     At the end of each run, the liquid from the reservoir pipe  61  is released into the measurement drum  67  to measure the amount of liquid expended in the course of the run. 
     The results of the tests are shown in Table 1 below: 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 mol % 
                 gas 
                 liquid 
                 total 
                   
               
               
                   
                 CO 2  in 
                 flow 
                 flow 
                 flow 
                   
               
               
                 MEA 
                 exit 
                 rate 
                 rate 
                 rate 
                 gas volume 
               
               
                 wt % 
                 gas 
                 (m 3 /hr) 
                 (m 3 /hr) 
                 (m 3 /hr) 
                 fraction 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 50 
                 0.005 
                 10.34 
                 4.63 
                 14.97 
                 0.69 
               
               
                 50 
                 0.003 
                 11.76 
                 3.92 
                 15.68 
                 0.75 
               
               
                 50 
                 0.005 
                 12.12 
                 3.92 
                 16.04 
                 0.76 
               
               
                 50 
                 0.002 
                 10.87 
                 3.92 
                 14.79 
                 0.73 
               
               
                 50 
                 0.006 
                 10.08 
                 3.96 
                 14.04 
                 0.72 
               
               
                 50 
                 0.007 
                 11.7 
                 3.6 
                 15.3 
                 0.76 
               
               
                 50 
                 0.019 
                 10.44 
                 3.24 
                 13.68 
                 0.76 
               
               
                 50 
                 0.006 
                 7.2 
                 3.24 
                 10.44 
                 0.69 
               
               
                 50 
                 0.007 
                 15.48 
                 3.24 
                 18.72 
                 0.83 
               
               
                 25 
                 0.009 
                 10.08 
                 4.68 
                 14.76 
                 0.68 
               
               
                 25 
                 0.005 
                 9 
                 3.96 
                 12.96 
                 0.69 
               
               
                 25 
                 0.006 
                 9 
                 3.96 
                 12.96 
                 0.69 
               
               
                 25 
                 0.003 
                 6.84 
                 3.6 
                 10.44 
                 0.66 
               
               
                 25 
                 0.005 
                 14.04 
                 4.32 
                 18.36 
                 0.76 
               
               
                 5 
                 2.03 
                 14.4 
                 3.6 
                 18 
                 0.80 
               
               
                 5 
                 0.5 
                 15.12 
                 3.24 
                 18.36 
                 0.82 
               
               
                 5 
                 2.95 
                 17.28 
                 3.24 
                 20.52 
                 0.84 
               
               
                 5 
                 3.65 
                 18.72 
                 1.8 
                 20.56 
                 0.91 
               
               
                 5 
                 1.63 
                 12.6 
                 3.96 
                 16.56 
                 0.76 
               
               
                 5 
                 2 
                 14.76 
                 3.96 
                 18.72 
                 0.79 
               
               
                 5 
                 2.13 
                 15.84 
                 3.6 
                 19.44 
                 0.81 
               
               
                 5 
                 0.31 
                 7.92 
                 3.6 
                 11.52 
                 0.69 
               
               
                 5 
                 1.25 
                 7.92 
                 3.6 
                 11.52 
                 0.69 
               
               
                 5 
                 2.32 
                 10.44 
                 3.6 
                 14.04 
                 0.74 
               
               
                 5 
                 2.67 
                 11.16 
                 3.6 
                 14.76 
                 0.76 
               
               
                 5 
                 3.4 
                 18 
                 3.6 
                 21.6 
                 0.83 
               
               
                   
               
             
          
         
       
     
     In all cases the gas feed composition was 10.5 mol per cent CO 2  in nitrogen. 
     The results show that virtually all the CO 2  is absorbed from the gas to the liquid solvent for the 50% and 25% mixture for all the flow rates tested. Only on reduction of the MEA concentration to a mere 5% by weight does the amount of CO 2  remaining in the gas reach appreciable levels. 
     From the measurements at the 5% level, it can be seen that the absorption efficiency decreases with an increasing gas flow rate and gas volume fraction. This result is expected since the already lean solvent mixture (only 5% MEA) has a diminishing capacity to absorb all of the CO 2 . 
     The gas chromatograph measurements of the CO 2  were verified using the data obtained from the titration of the liquid sample. A mass balance calculation on the CO 2  through the system showed that the CO 2  which was in the test gas had been transferred to the liquid. 
     In a second set of experiments, the contactor  51  was only pressurised to a low pressure (in the range 0.5 to 2 barg) and the reservoir pipe  61  was left open to atmospheric pressure. This gave a driving force of between 0.5 and 2 bar. The only change to the apparatus from the first set of experiments is the addition of a small hydrocyclone at the top of the gas pipe to separate the gas and liquid after reaction. This means that there are no entrained droplets in the gas sample. In these experiments, the liquid solvent mixture is a 50% solution of MEA and the gas feed composition was 9.4 mol per cent CO 2  in nitrogen. As for the first set of experiments, the test run lasted for 10 seconds and the pressure in the contactor was maintained by manual supply of the test gas. The results are shown in table 2 below. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 (1) -this experiment had a run time of 20 seconds. 
               
             
          
           
               
                   
                 mol % 
                 gas 
                 liquid 
                 total 
                   
               
               
                   
                 CO 2  in 
                 flow 
                 flow 
                 flow 
                 gas 
               
               
                 Mixer P 
                 exit 
                 rate 
                 rate 
                 rate 
                 volume 
               
               
                 (barg) 
                 gas 
                 (m 3 /hr) 
                 (m 3 /hr) 
                 (m 3 /hr) 
                 fraction 
               
               
                   
               
             
          
           
               
                 0.5 
                 0.59 
                 2.16 
                 4.68 
                 6.84 
                 0.316 
               
               
                 0.5 
                 0.87 
                 1.80 
                 4.32 
                 6.12 
                 0.294 
               
               
                 0.5 
                 0.80 
                 2.16 
                 3.96 
                 6.12 
                 0.353 
               
               
                 1 
                 0.80 
                 3.24 
                 4.68 
                 7.92 
                 0.409 
               
               
                 1 
                 0.95 
                 3.24 
                 4.32 
                 7.56 
                 0.429 
               
               
                 1 
                 1.20 
                 3.42 
                 4.32 
                 7.74 
                 0.442 
               
               
                 1.5 
                 1.10 
                 4.68 
                 4.32 
                 9.00 
                 0.520 
               
               
                 1.5 
                 0.76 
                 4.68 
                 4.14 
                 8.82 
                 0.531 
               
               
                 1.5 
                 1.27 
                 5.04 
                 4.32 
                 9.36 
                 0.538 
               
               
                 2 
                 0.73 
                 6.12 
                 5.22 
                 11.34 
                 0.540 
               
               
                 2 
                 1.10 
                 6.48 
                 5.76 
                 12.24 
                 0.529 
               
               
                 2 
                 0.82 
                 6.12 
                 5.40 
                 11.52 
                 0.531 
               
               
                 0.5 
                 0.13 
                 2.52 
                 3.96 
                 6.48 
                 0.389 
               
               
                 0.5 
                 0.61 
                 3.60 
                 3.96 
                 7.56 
                 0.476 
               
               
                 0.5 (1) 
                 0.45 
                 2.16 
                 3.69 
                 5.85 
                 0.369 
               
               
                   
               
             
          
         
       
     
     The small pressure difference driving the fluids through the system results in there being more liquid relative to the gas than in the previous experiments. Even at these lower gas volume fractions, most of the carbon dioxide is removed from the gas phase. It will be noted that there is no real trend from a pressure difference of 0.5 to 2.0 bar so it will be apparent that this method is applicable down to lower pressure differences than 0.5 bar. Such pressure differences may be present, for example, in exhaust gas systems.