Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
  • F17D—PIPE-LINE SYSTEMS; PIPE-LINES
  • F17D1/00—Pipe-line systems
  • F17D1/005—Pipe-line systems for a two-phase gas-liquid flow

Definitions

• the invention relates to a device for splitting a two-phase inlet stream consisting of a light phase fluid and a heavy phase fluid, for instance vapor and liquid, into two or more two-phase outlet streams.
• the device will ensure that the desired vapor/liquid ratio is obtained for each of the outlet streams.
• the total flow rates of each outlet stream do not necessarily need to be identical.
• the invention is suited for but not limited to the application of splitting a two- phase process stream flowing in a pipe or channel to parallel heat exchangers, furnace tubes, air coolers, chemical reactors or piping systems.
• the devices for splitting a two-phase process stream can be divided into 6 general types:
• Type 1 Symmetrical piping splits using standard piping tee's.
• the traditional way of splitting a two-phase stream is to make symmetrical piping splits using standard piping tee's and to rely on the phases to distribute evenly to each branch pipe.
• An example of a symmetrical piping split for splitting a two-phase stream into four outlet streams is shown on the isometric drawing in figure 1.
• the two-phase inlet stream is flowing in the inlet pipe 1.
• Pipe 1 is routing the two-phase stream to the first tee 3 where the stream is divided into two outlet streams.
• a 90° elbow 2 is located upstream the Tee 3.
• the pipe 1 shall preferably be perpendicular to the plane defined by the tee 3 as shown.
• Each of the two outlet streams from tee 3 is further divided into two outlet streams in the tee's 5a and 5b. Upstream the tee 5a is an elbow 4a and upstream the tee 5b is an elbow 4b.
• the symmetric piping split is probably the most widely applied method for dividing a two-phase inlet stream into two or more outlet streams.
• this principle has failed to distribute the liquid and vapor evenly to the outlet streams in many cases resulting in unequal vapor to liquid ratio in the outlet streams.
• a major problem with the symmetrical piping split in standard piping tee's is that the performance of the stream split does depend upon flow regime in the upstream pipe and that it is not always possible to stay inside the desired dispersed flow regime at all relevant operating conditions.
• Dispersed flow regime is a flow regime inside a flow channel or pipe with a uniform distribution of small liquid droplets in a continuous vapor phase or of small vapor bubbles in a continuous liquid phase (Bubble Flow).
• the performance of the symmetrical piping split may depend upon the presence of pipe fittings upstream the split as already mentioned.
• a major limitation of the symmetrical piping split is that the flow rate of the outlet streams needs to be close to identical to avoid significant differences in vapor to liquid ratio of the outlets streams.
• Another limitation is that a two-phase stream can only be split symmetrically into 2,4,8,16, etc. outlet streams. It is thus not possible to make 3,5,6,7,9...etc. outlet streams.
• Type 2 Use of special inserts such as vanes, baffles or static mixers in piping tee's.
• a first example is given in US patent 4,396,063 where a static mixer is located just upstream of a tee consisting of a Y branched conduit.
• dispersed flow is preferred. In the dispersed flow regime the two- phase mixture will more or less act as a single-phase fluid. The small liquid droplets tend to follow the vapor flow at approximately the same velocity or visa versa. Therefore in the dispersed flow regime a good splitting performance is often achieved in a piping tee.
• the use of a static mixer upstream the tee provides surfaces with a certain projected area perpendicular to the flow direction in the inlet pipe.
• static mixers disturb the desired dispersed flow regime, if present, and results in separation of liquid and vapor which is unwanted.
• the use of static mixers introduces additional pressure drop in the process system which may result in additional operating cost due to increased power consumption in pumps and/or compressors.
• static mixers are susceptible to fouling caused by contaminants such as scale and corrosion products.
• This flow splitter also includes a static mixer 22 located in the inlet pipe upstream a tee 14 where the inlet stream 30 is divided into two outlet streams 74 and 76. Between the static mixer 22 and tee 14 a horizontal stratifier 24 is located. The stratifier is collecting fluids from six different elevations. The fluids collected at the lowest and first elevation are sent to outlet stream 76, the fluids collected at the second elevation are sent to the outlet stream 74, the fluids collected at the third elevation are sent to outlet stream 76, etc. Like for the mixer of the first example the mixer of the present example will tend to separate the liquid from the vapor which is unwanted. The static mixer may also increase the operating costs and be susceptible to fouling.
• the stratifier collecting the fluids will only work if the vapor and liquid are distributed uniformly across the pipe cross section which will not be the case in real applications.
• the Mixer/Stratifier assembly was tested in a steam/water field application described in US patent 5,810,032. The result of the test was that a better split of the steam and water was obtained in standard impacting tee than with the Mixer/Stratifier assembly.
• Type 3 Devices which rely on a certain flow regime to be established upstream the split.
• flow regime maps are mainly based on two-phase flow regime data for air and water in small diameter piping ( ⁇ 2 inch). Therefore for instance in a hydrocarbon/hydrogen system at elevated pressures and temperatures like in a hydroprocessing unit the flow regime maps may be inaccurate.
• thermodynamic models for prediction of liquid and vapor amounts and properties In addition to the uncertainty in the flow regime maps comes the uncertainty in the thermodynamic models for prediction of liquid and vapor amounts and properties. This uncertainty may be significant for instance for complex hydrocarbon systems where the hydrocarbons are characterized by use of pseudo components and where an equation of state is used to predict the degree of vaporization and the fluid properties.
• piping systems in process plants are often complex systems with pipe fittings like expansions, contractions, elbows, check valves, etc.
• pipe fittings like expansions, contractions, elbows, check valves, etc.
• the general flow regime is disturbed and it may require long straight pipe runs to reestablish the general flow regime.
• an elbow tends to separate the phases with the dense liquid phase running near the large radius wall of the elbow and the lighter vapor running near the small radius wall of the elbow.
• a first example of such a two-phase stream splitter is given in US patent 4,516,986.
• the splitter consists of an inner pipe 12 inserted in the main pipe 10.
• a baffle 13 is located in the annular area between the inner and main pipes.
• the intended flow regime in the main pipe is the Annular Flow regime where liquid is flowing in an annular ring near the pipe wall and the vapor is flowing at high velocity in the center of the pipe.
• Part of the liquid flowing near the pipe wall is intended to be collected in the closed end volume 14.
• From the closed end volume 14 the liquid is routed through an external line 15 through a control valve 23. Vapor is collected from the annular vapor volume 30 downstream the baffle 13 and send through the pipe branch 11 where it is combined with the liquid from the control valve.
• a flow meter 20 in the two-phase stream in pipe branch 11 is used to control the liquid flow. It is not described how the flowmeter can accurately measure vapor/liquid ratio. In order to measure vapor/liquid ratio separate flow measurements of the vapor and liquid flow would normally be required. For other flow regimes than Annular Flow such as for example Slug Flow the split performance of the device may be poor. Even if Annular Flow is the dominating flow regime in the main pipe 10 any pipe fittings such as elbows upstream the splitter would disturb the flow. Therefore a certain straight pipe section is needed upstream the splitter which may take up additional space in the process unit. Also there may be limitations in flow rate rangeability.
• the vapor/liquid ratio is expected to be a function of total flow rate in each branch line.
• the higher flow rate in a branch line the more vapor will be sucked into the pipe and thus the higher vapor to liquid ratio. If the flow regime during certain operating modes is different than expected, for instance Stratified Flow, then severe maldistribution of the phases to the outlet branches is the result.
• a third example is given in US patent 4,574,837 where a certain phase distribution in a horizontal main pipe 10 is assumed to be known. Openings at different elevations are provided in the main pipe to allow fluids to flow first to an annular chamber 12 and then further to a branch pipe 13.
• the vapor/liquid ratio of the stream in the branch pipe is set by selection of appropriate flow areas of the openings at the top and the bottom of the pipe 10 respectively. The higher flow area at the top of the pipe relative to the flow area at the bottom the higher vapor to liquid ratio is achieved in the branch pipe.
• the device will only work for the Stratified Flow and Wavy Stratified Flow regimes.
• the device will only generate a split stream with the desired vapor to liquid ratio when the liquid level in the main pipe is as foreseen. Consequently the device will only work for low flow velocities and for fixed vapor/liquid ratio and properties. Most commercial applications are characterized by high flow velocities and significant variation in vapor/liquid ratio and properties.
• Type 4 Devices which utilize centrifugal forces.
• centrifugal two-phase flow splitter has a tangential fluid inlet 28 into a swirl chamber 23.
• a central hub 38 and vanes 39 which directs the swirling vapor and liquid towards the outlet apertures 36 and into the outlet channels 37. It is not easily understandable what the driving force for distribution of the liquid phase is.
• the fluid inlet is not symmetrical since there is only one inlet 28 at one side of the device.
• the liquid is swirling along the inner wall of the swirl chamber but due the asymmetric design a uniform flow and thickness of the liquid layer/film is not expected. Consequently some of the vanes 39 are expected to collect more liquid than others resulting in less than optimal liquid distribution to the outlet channels 37.
• Type 5 Devices which utilize an external energy source to generate dispersed flow.
• EP patent 0003202 B1 An example of such an apparatus is given in EP patent 0003202 B1.
• a motor 32 and a rotating stirring device on a shaft 28 is used to disperse the liquid and vapor mixture upstream the split where the inlet stream is split into outlet channels 4a, 4b and 4c.
• the device is likely to work since a Dispersed Flow regime can be generated by addition of shaft work to shaft 28 no matter of variations in flow rates and fluid properties.
• the main problem with this type of apparatus is to obtain a good seal between the shaft 28 and pipe/bend 21 which is not an easy task (not an inexpensive design) in high pressure applications like hydrocracking (up to 300 bar). Also the initial cost, the maintenance cost of the rotating equipment and the cost of power consumption for the motor are all high.
• Type 6 Devices which first separates vapor and liguid in the inlet stream and then distributes each phase to the outlet streams
• a first example of a flow splitter for splitting a two-phase inlet stream into three outlet streams using a conventional vapor/liquid separator and conventional instrumentation is shown in figure 2.
• a two-phase inlet stream is flowing through line 11 to a separator 10 where the liquid phase 13 is separated from the vapor phase 12.
• the vapor phase is routed via the vapor outlet line 14 to parallel control valves 15a, 15b and 15c.
• the position or lift of the control valves is controlled by the flow controllers 16a, 16b and 16c to obtain the desired vapor flow rate through each control valve.
• the flow measurements are obtained by use of any conventional methods such as orifice plates or venturi tubes combined with a ⁇ P transmitter.
• the flow controllers are cascaded with a pressure controller 17.
• the pressure controller is changing the flow set points to the flow controllers 16a, 16b, 16c in order to maintain the desired pressure in separator 10.
• the liquid phase 13 is routed via the liquid outlet line 18 to the parallel control valves 19a, 19b and 19c.
• the position or lift of the control valves is controlled by the flow controllers 20a, 20b and 20c to obtain the desired liquid flow rate through each control valve.
• Flow measurements are obtained by use of any conventional methods such as for instance an orifice plate combined with a ⁇ P transmitter.
• the flow controllers are cascaded with a level controller 21.
• the level controller is changing the flow set points to the flow controllers 19a, 19b and 19c in order to maintain the desired liquid level in separator 10.
• Finally the vapor streams from valves 15a, 15b and 15c is combined with the liquid streams from valves 19a, 19b and 19c to generate the three two-phase outlet streams 22, 23 and 24.
• the instrumentation for the two-phase stream splitter shown in figure 2 is rather complex and as the complexity and number of components such as transmitters, control valves and controllers are increased the risk of failure and upsets is also increased. Some downstream systems may be damaged if the vapor to liquid ratio is too high or too low during such failure or upset in the control system. Examples are the risk of tube rupture or coke buildup in a furnace tube due to overheating of the tube in case the vapor to liquid ratio of the stream flowing inside the tube is suddenly increased. Another example is the risk of rapid coke build-up in parallel catalytic hydroprocessing reactors if the reactor is operated with too low vapor to liquid ratio resulting in hydrogen deficiency even in a short period of time. Also the complexity of the control system and the large size of the separator vessel 10 results in a high cost of the splitter.
• This two-phase flow splitter includes a separator vessel 10 which has a two-phase inlet nozzle 11.
• An impingement plate 14 is located below the inlet nozzle to break down the high velocity of the inlet stream.
• Two or more chimneys 12 are provided in the separator. The upper ends of the chimneys are open to allow vapor to enter the chimney.
• Apertures 13 are provided in the chimneys for liquid entrance to the chimney.
• Caps 16 are located above the chimney openings to prevent direct liquid entrance at the chimney top.
• the flow of liquid to each chimney is determined by the liquid head above the apertures 13 and the flow area of the apertures. For a given liquid level in the vessel the flow of liquid to each chimney will almost be constant.
• the liquid flow rangeability of the splitter can be broadened by providing apertures at more elevations. However if apertures at more elevations are provided then the liquid distribution performance at the design point is reduced relative to the splitter with apertures in one elevation only.
• splitters where the liquid level is the driving force for even liquid distribution to each outlet stream are given in US patent 4,662,391; JP patent 03113251 A2; JP patent 02197768 A2.
• a third example of stream splitters with separation of the liquid and vapor phases are given in US patent 5,250,104.
• the two-phase mixture flowing in pipe 14 is separated in separator 12.
• the vapor phase is divided into two streams in tee 20.
• Each of the two vapor streams is passed through an orifice 22 and 24.
• the liquid is collected in the sump 30 and is passed though the two parallel liquid lines 32 and 34.
• the pressure drop for vapor flow, ⁇ Pv, through the orifice is almost proportional to the squared volumetric vapor velocity.
• _, through the liquid lines 32 and 34 consist of a static term, ⁇ P S L, due to the difference in elevation of the liquid level in sump 30 and the liquid tube ends 40 and 42 and a frictional term, ⁇ P F ⁇ _- ⁇ P F L is almost proportional to the squared volumetric liquid flow rate. Since the vapor and liquid path through the splitter are parallel paths the pressure drop needs to be identical:
• the flow area of the vapor orifices and the liquid tubes are sized for a certain vapor flow rate Qv and a certain liquid flow rate Q .
• ⁇ Pv is 125% higher than foreseen. Since the liquid flow is unchanged ⁇ PFL is also unchanged.
• ⁇ P S L therefore has to be increased by 1.25x ⁇ Pv. The result is that the liquid level in sump 30 needs to be reduced significantly and at some point there will be no liquid level in the sump and both vapor and liquid will enter the liquid lines 32 and 34. In such a case poor distribution of liquid to the parallel lines 32 and 34 will be the result.
• the invention is a device for splitting a two-phase inlet stream into two or more outlet streams.
• the device can be designed to maintain close to identical vapor to liquid ratio in each of the outlet streams.
• the splitter of the present invention in one embodiment, is shown in figure 3A, 3B and 3C.
• the inlet stream is routed via an inlet pipe to a separator vessel.
• an impingement plate is provided below the inlet pipe entrance in the vessel to break down the high velocity of the stream and to direct the stream towards the inner walls of the separator where liquid will impinge and separate from the vapor phase.
• separation of the liquid and vapor phases is achieved.
• suction channels are in fluid communication with the two outlet pipes through which the outlet streams are leaving the separator.
• the lower ends of the suction channels are submerged in the liquid phase.
• the suction channels are provided with apertures in the side walls. Vapor is flowing though the apertures which are above the liquid level in the separator. When vapor is flowing through these apertures a pressure drop across the wall of the suction channel is generated. Consequently liquid is lifted up into the suction channel. The liquid is mixed with the vapor inside the suction channel and the two-phase mixture is flowing upwards through the channel and is leaving the separator and two-phase stream splitter through the outlet pipes.
• the liquid level in the separator is mainly determined by the vapor flow rate entering the vessel. At low vapor flow rates the liquid level is high and at high vapor flow rates the liquid level is low. The liquid level is almost unaffected by the liquid flow rate.
• the splitter of the present invention can be designed to maintain close to identical vapor to liquid ratio in the outlet streams.
• the splitter may be designed to maintain specific and different vapor to liquid ratios in the outlet streams.
• the splitter of the present invention can be designed for any split ratio.
• the invention will also work if the actual split ratio during some operating periods is different than the split ratio that the splitter was designed for.
• the splitter of the present invention will function equally well at all flow regimes in the inlet piping.
• D) The splitter of the present invention is not sensitive to the layout of the upstream or the downstream piping systems. For instance the performance is unaffected by the presence of pipe fittings like elbows or valves upstream the splitter.
• the splitter of the present invention represents a simple and robust design. It has no instrumentation and no moving parts. It requires only low maintenance and no attention from the plant operators.
• the splitter of the present invention is an open system, which is not susceptible to fouling. Use of the splitter in a process unit will thus not affect the overpressure protection philosophy. For hydroprocessing units, equipment located upstream the splitter can thus still be overpressure protected by relief valves located downstream the splitter.
• the pressure drop of the splitter is low (-0.05 bar at the design conditions) no matter how high the pressure drop of the downstream systems might be.
• the splitter of the present invention represents a compact and cost efficient design.
• Figure 1 represents prior art and is an isometric view of a piping system involved in a symmetric piping split.
• the inlet stream is split into 4 outlet streams by use of three standard piping tee's.
• Figure 2 also represents prior art and is a process flow sketch of a vapor/liquid separator with instrumentation used for splitting the inlet stream into three outlet streams.
• Figure 3A, 3B and 3C represents one embodiment of the present invention.
• Figure 3A is a side sectional view of the embodiment taken along line A-A.
• Figure 3B is a cross sectional view taken along the line B-B.
• Figure 3C is an overhead view taken along the line C-C.
• FIG 4 is a process flow sketch showing a first example of an application of the splitter of the present invention.
• the splitter is used to split a two-phase stream to three parallel process systems consisting of heat exchangers, instrumentation and furnace tubes.
• FIG. 5 is a process flow sketch showing a second example of an application of the splitter of the present invention.
• the splitter is used to split a two-phase stream to two parallel trickle bed chemical reactors.
• Figure 6A, 6B and 6C represents a further embodiment of the present invention and illustrates alternative suction channel designs.
• Figure 6A is a cross sectional view of the embodiment taken along line A-A.
• Figure 6B is a side sectional view taken along line B-B.
• Figure 6C is a side sectional view taken along line C-C.
• Figure 7A and 7B represent a further embodiment of the present invention where the splitter is built as an integral part of a chemical reactor.
• Figure 7A is a side sectional view of the bottom part of the chemical reactor.
• Figure 7B is a cross sectional view of the suction channel taken along line A-A of figure 7A.
• Figure 8 represents one embodiment of the present invention where the splitter is build as an integral part of a shell and tube heat exchanger.
• Figure 8 is a side sectional view of the heat exchanger and splitter.
• Chemical reactors such as trickle bed reactors may be arranged in parallel configuration. In high pressure applications this may be done to reduce the reactor diameter and thus the overall reactor cost.
• revamp of process plants where more catalyst volume needs to be added to an existing plant the addition of a new chemical reactor in parallel rather than in series with an existing one is often very attractive from an economic point of view. The reason is that if the new reactor is added in series with the existing one then the total reactor pressure drop increases significantly. This may result in the need for expensive replacement/upgrade of pumps and/or compressors. On the other hand if the new chemical reactor is added in parallel then the pressure drop may actually be reduced to allow for higher through-put in the plant even with the same pumps and compressors. History has shown that attempts of splitting a two-phase stream in many cases has failed to produce outlet streams of equal vapor to liquid ratios. Examples of the consequences of unequal vapor to liquid ratio in the outlet streams are:
• the furnace tubes receiving the high vapor to liquid ratio stream gets hotter than the furnace tubes receiving the low vapor to liquid ratio stream due to the lower heat capacity of vapor relative to liquid. Therefore the maximum allowable tube metal temperature may be reached even below the heat duty that the furnace was rated for. The furnace can thus not transfer the heat that it was originally designed for.
• the consequences may be lower production rate from the process unit. In hydrocarbon service the hotter tube metal temperature results in increased coke formation rate on the tube wall. The result may be that premature shut down of the unit for decoking the furnace tubes is needed.
• the vapor and liquid is distributed to each parallel furnace tube by automatic control systems such as flow control valves then in case of failure of the control system one or more furnace tubes may suddenly not receive any liquid feed at all. The consequence could be overheating and rupture of the furnace tube.
• the splitter of the present invention can be designed to handle any required split ratio.
• Split ratio is defined as the total mass flow of an outlet stream divided by the total mass flow of the inlet stream.
• the invention can be designed for a 50%/50% split but also for a 5%/95% split. Since the two-phase splitter is an open system without any control valves and with low overall pressure drop, it is the hydraulic capacity of the downstream flow systems and not the two-phase splitter itself which sets the split ratio. When properly designed the splitter will ensure that the vapor to liquid ratio in each of the outlet streams are close to identical even if the split ratio deviates from the split ratio that the two-phase splitter was designed for. The reason is explained here:
• a stream splitter has been designed to split a two-phase inlet stream into two outlet streams with split ratios of 30% / 70% for suction channel A and B respectively.
• split ratios 30% / 70% for suction channel A and B respectively.
• the split ratio could maybe be 40% / 60% instead of the 30% / 70% that the two-phase splitter was designed for. In that case more vapor than originally anticipated is flowing through the apertures in the side of suction channel A. The pressure drop from the outside to the inside of suction channel A is therefore larger. Consequently more liquid is lifted up into the suction channel.
• the split ratio for a given suction channel during certain operating modes is higher than anticipated then the higher vapor flow will result in a higher liquid flow. Similarly if the split ratio for a given suction channel is lower than anticipated then the lower vapor flow will result in a lower liquid flow. The result is that the vapor to liquid ratio in the outlet pipe is only affected by the changed split ratio to a low extent.
• FIG 4 shows a process flow sketch of a process system with parallel heat exchangers, instrumentation and furnace tubes.
• the cold two-phase feed stream 50 needs to be heated up by heat exchange with the hot streams 58 and 65 and by use of furnace 61.
• the cold stream 50 is first split into three streams 52, 53 and 54 by use of the splitter 51 of the present invention.
• the outlet stream 52 is passed through train A which consists of the shell sides of shell and tube heat exchangers 55a, 55b, 55c and 55d and the tube pass 67 of furnace 61.
• the outlet stream 53 is passed through train B which consists of the shell sides of shell and tube heat exchangers 56a, 56b, 56c and 56d and the tube pass 68 of furnace 61.
• the outlet stream 54 is passed through train C which consists of the tube sides of shell and tube heat exchangers 57a, 57b and 57c and control valve 69.
• the outlet streams 62, 63 and 60 from train A, B and C respectively are combined in the product stream 64.
• the design vapor and liquid flow rates and properties for the splitter 51 is given in table 1.
• the splitter 51 was designed for a split ratio of 40%/40%/20% to train A, B and C respectively. Identical vapor to liquid ratio of each of the outlet streams 52, 53 and 54 was aimed at. When the actual split ratio is identical to the design split ratio of 40%/40%/20% the vapor to liquid ratio in the three outlet streams 52, 53 and 54 will be close to identical. However it turned out that the pressure drop for a given flow rate was 20% higher for train A than anticipated. The difference in flow resistance was due to different piping layout and slightly different exchanger and furnace design for the two parallel trains A and B. Also it turned out that the pressure drop for a given flow rate was 30% lower for train C than originally anticipated. The lower flow resistance of train C was due to higher flow requirement controlled by control valve 69. Due to the different flow resistance of the parallel flow systems the split ratio became different than foreseen.
• %DVLR - - N f abs[VL ⁇ - VL l 0% (2)
• VLj, and VL f ⁇ ed are the volumetric vapor to liquid ratios of outlet stream i and the inlet feed stream respectively, and where Nsplit is the number of outlet streams from the splitter.
• the given splitter design shows excellent performance over a very wide range of vapor and liquid flow rates even when the flow resistance of the downstream systems are different than originally designed for.
• the vapor to liquid ratio varies from 1.3 to 21.5 and the pressure drop of the trains vary from 1.3 bar to 20.9 bar.
• the average %DVLR caused by the 20% higher flow resistance of train A and the 30% lower flow resistance of train B is as low as 2.97 %.
• Table 2 Performance of splitter 51 with different than expected flow resistance of downstream systems.
• the performance of the splitter is affected by the mechanical tolerances during fabrication and installation of the splitter. Especially the relative elevation of the suction channels and the flow area of the apertures in the suction channels affect the performance.
• a second example of an application of the splitter of the present invention is shown in the process flow diagram in figure 5.
• An existing trickle bed reactor 75 loaded with 190 m 3 catalyst particles is too small to produce the desired product at the desired rate. Therefore 90 m 3 additional catalyst volume needs to be added.
• a new reactor 74 is installed in parallel with the existing reactor 75.
• a splitter 71 of the present invention is used to split the two-phase feed stream 70 into two outlet streams 72 and 73 which are fed to the reactors 75 and 74 respectively.
• the split ratio is 32%/68% to reactor 74 and 75 respectively. Downstream the reactors the outlet stream 76 from reactor 74 is combined with outlet stream 77 from reactor 75 into the product stream 78.
• the suction channels in splitter 71 are intended to be at same elevation but in this example the suction channel A corresponding to stream 72 is elevated 10mm higher than the Suction channel B corresponding to stream 73. Also the flow area of the apertures in Suction channel A is 2% larger than intended and the flow area of the apertures in Suction channel B is 2% lower than intended. Both the elevation difference of the suction channels and the difference in the flow area of the apertures will increase the vapor to liquid ratio of stream 72 relative to stream 73.
• the splitter 71 has been designed for the vapor and liquid flow rates and properties given in table 3.
• %DVLR vapor to liquid ratio
• the operating conditions evaluated are given in table 4 and corresponds to 50%, 100% and 200% of the vapor and liquid design flow rates respectively.
• the results from the evaluation such as ⁇ P across the splitter, ⁇ P across the reactors, the vapor to liquid volumetric ratio for streams 72 and 73 and the %DVLR are also given in table 4.
• Table 4 Performance of splitter with worst case fabrication and installation tolerances.
• the splitter was designed to produce outlet streams with identical vapor to liquid ratios.
• the stream splitter can also be designed to produce outlet streams of different vapor to liquid ratios.
• the splitter could be designed to split a two-phase inlet stream into three outlet streams with split ratios of 20% / 20% / 60% and with vapor to liquid volumetric ratios of 10/12/20.
• identical vapor to liquid ratio is however desired in the outlet streams.
• the separation of vapor and liquid in the separator of the present invention does not necessarily need to be as good as in a traditional phase separator. It is sufficient that the bulk part of the liquid is separated from the vapor. Smaller liquid droplets passing with the vapor will be distributed to the suction channels also since the vapor is distributed evenly.
• the separator of the two-phase stream splitter can therefore be designed for higher linear vapor velocities and thus smaller cross sectional area than traditional phase separators. Also, the required liquid hold-up time is significantly lower for the separator of the two- phase stream splitter than for a traditional separator with instrumentation like the one shown in figure 2.
• the size and cost of the pressure vessel of splitter 51 from figure 4 designed for the vapor and liquid rates and properties in table 1 is compared with the size and cost of the pressure vessel of a conventional phase separator as shown in figure 2.
• the conventional phase separator is also designed for the vapor and liquid flows and properties from table 1. The results are given in table 5.
• Table 5 Comparison of size and cost of the pressure vessel of the splitter and of a conventional separator.
• the cost given in table 5 is the cost of the vessel plus internals such as the suction channels.
• the installation cost including foundation, erection, insulation, piping and instrumentation etc. is not included.
• the total installed cost is typically 3-4 times the equipment cost given in table 5.
• the splitter of the present invention represents a compact and low cost option relative to the use of a conventional phase separator.
• FIGS 3A, 3B, 3C, 6A, 6B, 6C, 7A, 7B and 8 represent alternative structures of the splitter of the present invention.
• the figures are presented only to exemplify the invention and alternatives. They are not intended to limit the scope of the concepts disclosed herein or to serve as working drawings. They should not be construed as setting limits on the scope of the inventive concept.
• the relative dimensions shown by the drawings should not be considered equal or proportional to commercial embodiments.
• the splitter 30 shown in figure 3A, 3B and 3C is a splitter for splitting an inlet stream 41 into two outlet streams 42 and 43.
• the splitter 30 consists of a vessel 31 with an inlet pipe 32 and two outlet pipes 44 and 45.
• the inlet pipe 32 is connected to the wall of vessel 31 to form a fluid tight seal.
• the lower end of pipe 32 is open to allow the inlet stream 42 to enter into vessel 31.
• Below the inlet pipe 32 is an impingement plate 33 with side walls 40.
• the impingement plate 33 and the side walls 40 form a flow channel which first split the inlet stream 41 into two streams and then direct these two streams towards the cylindrical wall of vessel 31.
• Each suction channel consists of a circular pipe with open upper and lower ends. The lower end of the suction channel is submerged in the liquid 39.
• the upper end or outlet of the suction channel 34 is connected to the outlet pipe 44 and the upper end or outlet of suction channel 35 is connected to the outlet pipe 45 to form two flow channels out of vessel 31. Fluid tight seals are provided between the walls of vessel 31 and the outlet pipes 44 and 45.
• Suction channel 34 is provided with apertures 37 in the sides of the pipe and Suction channel 35 is provided with apertures 36 in the side of the pipe.
• the two-phase inlet stream 41 enters the vessel 31 through pipe 32.
• the two-phase jet hits the impingement plate 33 which brakes down the high velocity of the stream and directs the stream towards the cylindrical walls of vessel 31.
• the liquid phase 39 separates from the vapor phase 38.
• the liquid phase collects in the heavy phase collection region in the bottom of the vessel while the vapor phase is in the light phase collection region in the upper part of the vessel.
• the vapor 38 is now flowing through the fraction of the apertures 36 and 37 in the sides of the suction channels that are above the liquid surface. The flow through the apertures results in a pressure drop from outside the suction channel to inside the suction channel and therefore liquid is lifted up into the suction channel.
• Liquid 39 is flowing through the lower open ends of suction channels 34 and 35 and through the fraction of the apertures 36 and 37 that are below the liquid surface in vessel 31.
• the liquid mixes with the vapor in the suction channels and the two-phase mixture flows upwards inside the suction channels to the outlets thereof and out of vessel 31 through the outlet pipes 44 and 45.
• the feed inlet is preferably located symmetrically between the suction channels as indicated in figure 3A. This will result in the minimum cross sectional area of the vessel required for vapor/liquid separation and it will also distribute small liquid droplets that are taking the vapor path more evenly.
• the splitter is preferably designed so that the feed inlet stream impinges or impacts plates and walls as shown in figures 3B and 3C. When the inlet feed stream impinge plates and walls, liquid tends to separate from the vapor phase and also it is prevented that the high velocity inlet jet reaches the liquid surface in the vessel which could result in liquid re-entrainment and waves.
• the total area of the apertures in the suction channels is selected to obtain the desired liquid level in the vessel.
• a larger area of the apertures results in a lower pressure drop of the vapor and therefore a higher liquid level so that the lower pressure drop matches the vertical height that the liquid needs to be lifted up.
• a smaller area results in a lower liquid level.
• the area of the apertures in each suction channel can be used to set the vapor to liquid ratio of the outlet stream from that suction channel. If the area of the apertures in a suction channel A is increased relative to the area of the apertures in another suction channel B then the vapor to liquid ratio of the outlet stream from suction channel A is increased relative to the vapor to liquid ratio from suction channel B.
• the cross sectional area and shape of each suction channel also affects the liquid level in the vessel and the vapor to liquid ratio of each outlet stream.
• the apertures in the suction channels shown in figure 3A are circular holes. However these apertures can also be vertical slots or have other shapes such as V-shape, triangular, rectangular, polygonal, ellipsoidal, etc.
• the area of the apertures does not necessarily need to be evenly distributed over the height of the suction channel. For instance a suction channel may have a smaller area of the apertures near the bottom end and a larger area of the apertures near the top end.
• suction channels shown in figure 3A and 3B have circular cross sections but the suction channels can also have many other cross sectional shapes such as triangular, rectangular, ellipsoidal, polygonal, etc. Also the cross sectional area of the suction channels may vary along the length of the suction channel.
• the bottom ends of the suction channels shown in figure 3A are open for liquid flow. However in many cases improved splitting performance can be achieved if the bottom ends of the suction channels are closed and all liquid therefore needs to pass through the apertures in the sides of the suction channels that are below the liquid surface.
• the suction channels of the splitter shown in figure 3A and 3B are vertical. However the Suction channels do not need to be entirely vertical. It is sufficient that the Suction channel has a vertical component, or, in other words, that the liquid is constrained by the suction channel to flow upwards past the apertures for inlet of vapor before reaching the outlet of the suction channel leading into one of the outlet pipes 44 and 45.
• the vessel 31 of the splitter in figure 3A, 3B and 3C is a horizontal cylindrical vessel with ellipsoidal heads.
• the separator or vessel of the present invention may have any shape and orientation.
• Other examples of vessel shapes and orientations are vertical cylindrical vessels, spherical vessels, box shaped vessels with rectangular cross sections, etc.
• the inlet and outlet streams enter and exit through the top wall of vessel 31 in figure 4.
• the inlet and outlet streams may enter and exit through other walls such as the bottom or side walls.
• the splitter 80 consists of a vertical cylindrical vessel 81.
• the splitter has an inlet stream 88 entering via pipe 87 through the side wall of vessel 81.
• a vertical splash plate 86 is located downstream this inlet.
• the splitter has three outlet streams 91, 92 and 85.
• the outlet stream 91 is flowing via outlet pipe 99 through the top wall of vessel 31.
• Outlet pipe 99 is connected in a leak free manner to suction channel 82.
• Suction channel 82 has a circular cross section and is tapered so that the cross sectional area of the channel decreases downwardly.
• the Suction channel 82 is provided with four vertical slots 94.
• the Suction channel 82 is open for liquid flow in the bottom end.
• the outlet stream 92 is flowing via outlet pipe 98 through the side wall of vessel 31.
• Outlet pipe 98 is connected in a leak free manner to suction channel 83 by use of a 90° bend 97.
• Suction channel 83 has a square cross section.
• the suction channel 83 is provided with four V-shaped slots 93.
• the Suction channel 83 is open for liquid flow in the bottom end.
• the outlet stream 85 is flowing through outlet pipe 100 through the bottom wall of vessel 31.
• Outlet pipe 100 is connected in a leak free manner to suction channel 84 by use of a 180° bend 96.
• Suction channel 84 has a circular cross section and is provided with square apertures 95. The Suction channel 84 is closed for liquid flow in the bottom end and all liquid therefore has to flow through the square apertures 95.
• the two-phase inlet stream 88 enters the vessel 81 through pipe 87.
• the two-phase jet hits the splash plate 86 which brakes down the high velocity of the stream and results in some degree of phase separation.
• the liquid phase 90 separates from the vapor phase 89.
• the liquid phase collects in the bottom of the vessel while the vapor phase is in the upper part of the vessel.
• the vapor 89 is now flowing through the apertures 93, 94 and 95 in the sides of the suction channels 83, 82 and 84 respectively.
• the vapor flow through the apertures results in a pressure drop from outside the suction channel to inside the suction channel and therefore liquid is lifted up into the suction channel.
• Liquid 90 is flowing through the lower open ends of suction channels 82 and 83 and through the fraction of the apertures 93, 94 and 95 that are below the liquid surface in vessel 81.
• the liquid mixes with the vapor in the suction channels and the two-phase mixture flows inside the suction channels and out of the vessel 81 through the outlet pipes 98, 99 and 100.
• the splitting performance of the present invention quantified as %DVLR as defined in equation (2) is reduced in high vapor to liquid ratio applications.
• the performance of the present invention can be significantly improved by use of inserts inside the suction channels to increase the pressure drop for the two phase flow inside the suction channel.
• Use of one or more orifices in the suction channel is one example of such inserts for increasing the pressure drop and for improvement of splitting performance.
• the use of inserts inside the suction channel has an effect on the two-phase flow pattern in the suction channel. For instance the use of orifices tends to eliminate the unwanted Slug Flow where liquid slugs and vapor pockets periodically is flowing in the suction channel.
• splitters 30, 51 , 71 and 80 in figure 3A, 3B, 3C, 4, 5, 6A, 6B and 6C all have their own separator or vessel.
• present invention may be used as an integral part of other process equipment such as for instance shell and tube heat exchangers and chemical reactors.
• FIG. 7A and 7B is showing an example of a splitter of the present invention which is an integral part of a chemical trickle bed reactor 110.
• Figure 7A is showing the bottom part of this trickle bed reactor.
• the catalyst particles 103 are loaded inside a cylindrical pressure shell 101 with hemispherical heads 102.
• the catalyst is supported by a catalyst support grid or screen 104.
• the catalyst support grid/screen is designed so that the catalyst particles can not move through the screen but the vapor and liquid can.
• Below the catalyst support grid/screen two vertical suction channels 107 are located. Each suction channel is provided by eight slots 108.
• the suction channels are also provided with inserts to increase the pressure drop of the suction channel. These inserts consist of four orifices 109, 110, 111 and 112 for each suction channel.
• Each suction channel 107 is connected to an outlet nozzle 105 in a leak free manner by use of channels 106 with bends.
• vapor and liquid is flowing co-currently down through the bed of catalyst particles 103 and through the catalyst support grid/screen 104.
• Below the catalyst support grid/screen 104 is an open space where the liquid phase 113 separates from the vapor phase 114.
• the liquid phase 113 collects in the bottom of the reactor.
• the vapor 114 is now flowing through the fraction of the slots 108 that are above the liquid surface. The flow through the slots results in a pressure drop from outside the suction channel to inside the suction channel and therefore liquid is lifted up into the suction channel.
• Liquid 113 is flowing through the opening of the lower orifices 112 and through the fraction of the slots 108 that are below the liquid surface.
• the liquid mixes with the vapor in the suction channel and flow through the suction channel and the orifices and out of the reactor 110 through the nozzles 105.
• FIG. 8 is showing an example of a splitter of the present invention which is an integral part of a shell and tube heat exchanger 120.
• the shell and tube heat exchanger consist of:
• the length of shell 121 has been slightly increased compared to normal heat exchanger designs to provide room for a two-phase splitter of the present invention on the shell side downstream the last flow baffle and downstream the 180° bends of the U-tubes 124.
• the splitter consists of two essentially vertical suction channels 126 with holes 127 in the walls. The bottom end of the suction channels 127 are open and available for liquid flow.
• the tube side fluid is entering the exchanger through nozzle 129 and is routed through and inside the U-tubes and exits the exchanger through nozzle 130.
• the shell side fluid is entering the exchanger through nozzle 131 and may be a single phase or a two-phase stream. In addition to heat transfer, condensation or vaporization may take place in the exchanger.
• the shell side fluid is flowing on the outside of the U-tubes.
• the liquid phase 133 collects in the bottom of the shell 121.
• the vapor 134 is now flowing through the fraction of the holes 127 that are above the liquid surface.
• the vapor flow through these holes results in a pressure drop from outside the suction channel to inside the suction channel and therefore liquid is lifted up into the suction channel.
• Liquid 133 is flowing through the open bottom end of the suction channels 126 and through the fraction of the holes 127 that are below the liquid surface.
• the liquid mixes with the vapor in the suction channel and flow through the suction channel and out of the exchanger 120 through of the nozzles 125.
• a two-phase inlet stream is split to parallel downstream piping systems and process equipment.
• the present invention can also be used inside process equipment to distribute vapor and liquid evenly to parallel passes in the equipment.
• One example is the use of the present invention in the inlet header of heat exchangers or air coolers for equal distribution of vapor and liquid to the parallel tubes in the exchanger.
• suction channel connected to each outlet pipe from the splitter there is only one suction channel connected to each outlet pipe from the splitter.
• more than one suction channel may be used per outlet stream. If more than one suction channel is used per outlet stream then the suction channels connected to an outlet stream do not necessarily need to be identical.
• a splitter designed for splitting a two-phase inlet stream into two outlet streams may have a total of five differently sized suction channels with three suction channels all connected to a first outlet stream and the remaining two suction channels connected to the second outlet stream.
• the use of differently sized suction channels to the same outlet stream may result in improved splitting performance.
• the splitter of the present invention may also be used to split a two-phase mixture of immiscible liquids such as a hydrocarbon liquid phase and an aqueous liquid phase into two or more outlet streams with the desired oil to water ratio of each outlet stream.
• immiscible liquids such as a hydrocarbon liquid phase and an aqueous liquid phase
• the invention relates to a splitting device for splitting or dividing a two-phase inlet stream consisting of a light and a heavy phase into two or more outlet streams with the desired light to heavy phase ratio of each outlet stream.
• the splitting device consists of a separation vessel or container with one or more inlets. In the vessel partial or complete separation of the light and the heavy phases take place.
• the vessel is provided with at least two hollow suction channels with a lower end and an upper open end.
• Apertures in the side of each suction channel are provided at at least one elevation between the lower and the upper ends.
• the lower end of the suction channel is submerged in the heavy phase while the upper open end of the suction channel is in the light phase and is connected in a leak tight manner by flow channels to downstream systems.
• the suction channels must have a vertical component so that during operation at least a fraction of the area of the apertures is elevated above the interphase level.
• light phase is flowing through the fraction of the area of the apertures that is above the interphase level and is thereby creating a pressure drop from outside to inside of the suction channel. Due to this pressure drop heavy phase is lifted up into the suction channel through any lower open end and through any apertures that are located at levels below the interphase level.
• the heavy phase is mixed with the light phase.
• the two-phase stream is flowing through the suction channel and through said flow channels to the downstream system.
• Inserts or flow restrictions may be used inside the suction channels to increase the pressure drop and to modify the two-phase flow regime in the suction channel.
• the inserts may be orifices with circular flow openings.
• the bottom end of the suction channel may be closed and all heavy phase needs to flow through the apertures in the side of the suction channels that are located below the inter-phase level.
• the vessel or container may be an integral part of other process equipment used for other purposes such as performing chemical reactions or exchange of heat in addition to the purpose of stream splitting.
• Said downstream systems may be parallel flow passes in the same piece of equipment which the splitter is an integral part of.
• Said downstream systems may be process systems consisting of piping, instrumentation and equipment.
• the suction channels may have circular cross sections.
• the apertures in the side of the suction channels may be either circular holes or rectangular slots.
• the vertical height from the bottom of the suction channel to the highest elevated aperture preferably is between 100 mm and 1500 mm.
• the no-slip two-phase flow velocity in the upper end of the suction channels is preferably between 0.5 m/s and 15 m/s during at least one operating phase.
• One or more suction channels may be connected to each downstream system.
• the device may advantageously be used to split a two-phase vapor/liquid mixture to parallel heat exchangers.
• the device may advantageously be used to split a two-phase vapor/liquid mixture to parallel furnace tubes.
• the device may advantageously be used to split a two-phase vapor/liquid mixture to parallel chemical reactors.
• the device may advantageously be used to split a two-phase vapor/liquid mixture to parallel air coolers.
• the device may advantageously be used to distribute vapor and liquid to parallel heat exchange tubes or channels in a two-phase heat exchanger or air cooler.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Separating Particles In Gases By Inertia (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

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• 2004
  • 2004-06-24 DE DE602004015999T patent/DE602004015999D1/de not_active Expired - Lifetime
  • 2004-06-24 CN CNB2004800178329A patent/CN100561036C/zh not_active Expired - Lifetime
  • 2004-06-24 EP EP04738943A patent/EP1651904B1/de not_active Expired - Lifetime
  • 2004-06-24 WO PCT/DK2004/000446 patent/WO2004113788A1/en active IP Right Grant
  • 2004-06-24 AT AT04738943T patent/ATE405790T1/de not_active IP Right Cessation
  • 2004-06-24 EA EA200600090A patent/EA007546B1/ru unknown
  • 2004-06-24 ES ES04738943T patent/ES2315667T3/es not_active Expired - Lifetime
  • 2004-06-24 JP JP2006515729A patent/JP4722840B2/ja not_active Expired - Lifetime

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