WO2026003689A1

WO2026003689A1 - Decreasing wash oil evaporation inside a compressor

Info

Publication number: WO2026003689A1
Application number: PCT/IB2025/056349
Authority: WO
Inventors: Bolaji OLAYIWOLA; Mohammad Shariati; Chandresh Patel
Original assignee: Nova Chemicals International SA
Current assignee: Nova Chemicals International SA
Priority date: 2024-06-28
Filing date: 2025-06-23
Publication date: 2026-01-02
Anticipated expiration: 2026-12-28

Abstract

A system and a method for decreasing fouling inside a compressor are provided. An exemplary method includes mounting a port in a casing disposed over a wheel in a compressor stage at a greatest diameter or downstream of a greatest diameter of the wheel, wherein the wheel includes a stator, and impeller, and a diffuser. An atomizer is mounted in the port, wherein the atomizer generates a flared spray pattern. A center axis of the flared spray pattern is tilted to an angle downstream of the wheel and wash oil is injected through the atomizer.

Description

DECREASING WASH OIL EVAPORATION INSIDE A COMPRESSOR

TECHNICAL FIELD

This disclosure relates to systems and methods for decreasing the evaporation of wash oil in a compressor to improve the mitigation of fouling.

BACKGROUND ART

Cracked gas compressors (CGCs) are important unit-operations in ethylene plants that provide the driving force used for conducting back-end separation and purification of the ethylene produced during thermal cracking of hydrocarbon. During operations, the compressor efficiency is generally reduced by fouling due to polymerization of reactive species in the cracked gas in the high temperature environment due to heat of compression. Accumulation of this fouling materials results in decrease of the available flow area for the cracked gas, and thus reduced throughput. To maintain the same throughput when the compressor was clean and when it was fouled, the power input to the compressor must be raised. This will result in high suction pressure, which propagates backward to the furnace and causes reduction of ethylene yield. One method used in the industry to reduce fouling material in the compressor is by wash oil injection. Wash oil is a hydrocarbon solvent with solvency for polymeric foulants. The conventional way of injecting the wash oil into the compressor is through the suction or return bend of each stage or both.

SUMMARY OF INVENTION

An embodiment described herein provides a system for decreasing fouling inside a compressor. The system includes a compressor stage that includes a wheel. The wheel includes a stator, and impeller, and a diffuser. A casing is disposed over the compressor stage and a port is disposed in the casing disposed proximate to or downstream of a greatest diameter of the wheel. An atomizer is mounted in the port, wherein the atomizer injects a wash oil onto the wheel in a flared spray pattern, wherein a center axis of the flared spray pattern is tilted at an angle to a downstream side of the wheel.

Another embodiment described herein provides a method for decreasing fouling inside a compressor. The method includes mounting a port in a casing disposed over a wheel in a compressor stage at a greatest diameter or downstream of a greatest diameter of the wheel, wherein the wheel includes a stator, and impeller, and a diffuser. An atomizer is mounted in the port, wherein the atomizer generates a flared spray pattern. A center axis of the flared spray pattern is tilted to an angle downstream of the wheel a wash oil is injected through the atomizer. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a schematic drawing of a compressor system, for example, used for the gas product from a cracker (cracked gas).

Figure 2 is a cutaway drawing of the two compressor stages, 3 and 4, described with respect to Figure 1.

Figure 3 is a drawing of a compressor stage showing injection points for the injection of wash oil to mitigate fouling.

Figure 4 is a cutaway view of the injection of wash oil through a casing of a compressor at a wheel in a compressor stage, such as proximate to the second wheel.

Figures 5A and 5B are modeled views showing the trapping of wash oil in the diffuser for a single wheel.

Figures 6A and 6B are modeled views of the modification of the injection pattern.

Figures 7A-7E are views of the computational geometry of the compressor system used for the modeling.

Figure 8 is a velocity contour plot of process gas inside a four-wheel compressor stage.

Figures 9A and 9B are tangential and radial velocity contour plots of process gas inside the compressor.

Figure 10 is a modeled view of the distribution of the wash oil droplets when injected into the compressor stage through the suction, similar to the baseline case.

Figures 11A and 1 IB are comparisons between a perpendicular spray pattern and a tilted spray pattern.

Figure 12 is a plot of the fraction of the total wash oil that did not evaporate in each wheel when the injection was split between suction and casing compared to 100% injection at the suction.

Figures 13A and 13B are modeled pressure and temperature profiles in the compressor.

Figure 14 is a block flow diagram of a method for decreasing fouling inside a compressor.

DESCRIPTION OF EMBODIMENTS

Compressor fouling is often reduced through injection of wash oil into the compressor. Wash oil is a blend of hydrocarbons they can prevent fouling by dissolving the fouling material as is formed, coating surfaces to prevent adhesion of fouling, or both. Wash oil often comprises a high percentage of aromatic compounds, such as 90 weight %. The fouling that forms in a compressor system is generally polymeric, such as components formed from butadiene, styrene, and ethylene in the cracked gas stream.

To improve wash oil performance, its flow may be split between the suction and casing. For example, the port at the casing may be installed perpendicular to the compressor shaft, facing downward. Although this design is easy, it could result in erosion. In addition, some of the wash oil droplets could get trapped in a u-bend on the diffuser, resulting in increased residence time of the droplets in the u-bend and consequently, increased evaporation of the wash oil. To decrease evaporation of the wash oil, the way the wash oil is injected at the return channel is important.

Embodiments described herein decrease the evaporation of wash oil inside the compressor through modification of the design of the atomizer used to inject wash oil into the casing, for example, changing the injection angle of the atomizer and tilting its axis at an angle towards the compressor discharge. With this modification, most of the injected wash oil droplets make their way through the return channel and travel to the next wheel instead of being trapped in the u-bend of the diffuser.

Figure 1 is a schematic drawing of a compressor system 100, for example, used for the gas product from a cracker (cracked gas) 102. The cracked gas 102 is introduced to a first stage suction drum 104, which separates a liquid stream 106 from a feed stream 108, which is a gaseous stream fed to a compressor train 110. In this example, the compressor train 110 includes 5 compressor stages, labeled 1-5.

As described herein, a wash oil stream 112 can be added to the feed stream 108 to mitigate fouling from polymerization of materials in the cracked gas. Similarly, the wash oil stream can be added to the feed streams to each of the compressor stages 1-5. To control the temperature of the gases in each of the compressor stages 1-5, a boiler feed water stream is injected into gas stream through ports on casings.

After the addition of the wash oil stream 112 which the feed stream 108 is sent to compressor stage 1. In embodiments described herein, the wash oil stream 112 is used as a direct injection stream 114 into the casing of one or more of the compressor stages 1-5 to directly mitigate fouling inside the compressor. This is discussed further with respect to Figure 2, which shows a drawing of a compressor 116 that includes compressor stages 3 and 4. Fouling is further mitigated by controlling the temperature in the compressor stages 1-5 through the injection of a boiler feed water stream 118.

From each of the compressor stages 1-5, the compressed gas is fed to a corresponding intercooler 120. The cooled compressed gas is then fed from the intercooler 120 to a corresponding flash drum 122. Each flash drum 122 separates a second liquid stream 124 from the cooled compressed gas stream from the corresponding intercooler 120, which then provides a gas feed stream to the next compressor stage 2-5.

Figure 2 is a cutaway drawing of the two compressor stages, 3 and 4, 116 described with respect to Figure 1. Like numbered items are as described with respect to Figure 1. These compressor stages 202 and 204 correspond to compressor stages 3 and 4 described with respect to Figure 1. Compressor stage 3 202 has four compressor wheels 206-212, wherein each compressor wheel 206-212 has a tighter clearance, increasing the pressure through that wheel over the last wheel. Similarly, compressor stage 4 204 also has four compressor wheels 214-220 that each have tighter clearance then the last wheel. As each compressor stage is at higher pressure than the previous stage, the clearances in each compressor stage are tighter than the previous compressor stage. The compressor wheels 206-220 are mechanically coupled to a rotor 222 that passes through the compressor 116 and is used to drive all of the compressor stages 1-5 (Figure 1). The compressor wheels 202- 220 are enclosed in a compressor casing 224.

As described with respect to Figure 1, a portion of the wash oil stream 112 can be injected into the inlet 226 of compressor stage 3 202 to mitigate fouling. Similarly, a portion of the wash oil stream 112 can be injected into the inlet 228 of compressor stage 4 204. However, as discussed herein, the wash oil from the wash oil stream 112 injected into the inlet 226 and 228 may not effectively mitigate fouling through the compressor wheels 206- 220, as droplets of the wash oil can be trapped in low velocity zones leading to evaporation. Once the wash oil evaporates, it is no longer effective at mitigating fouling.

In embodiments described herein, a portion of the wash oil stream 112 is injected through a port in the compressor casing 224 over one or more of the compressor wheels 206-212 and 214-220 in each of the compressor stages 3 202 and 4 204. Similarly, a portion of the wash oil stream 112 is injected through a port in the compressor casing over compressor wheels in other compressor stages 1-2 and 5.

As described with respect to Figure 1, the inlet 226 and 228 of each of the compressor stages may be fluidically coupled to corresponding flash drums 122. The outlets may be coupled to corresponding intercoolers 120.

Figure 3 is a drawing of a compressor stage 300 showing injection points 302 and 306 for the injection of wash oil to mitigate fouling. In this example, a first injection 302 of wash oil placed along an inlet 304 to the compressor stage 300. A second injection 306 is directly into the compressor stage 300, for example, through the casing over the second wheel 308 in the compressor stage 300 In various embodiments described herein, the amount of wash oil injected into the injection points 302 and 306 is controlled to decrease the amount of evaporation of the wash oil.

Figure 4 is a cutaway view of the injection of wash oil through a casing of a compressor at a wheel in a compressor stage, such as proximate to the second wheel 406. Like numbered items are as described with respect to Figures 2 and 3. As shown by arrows 404, the gas flows by an impeller 406 into a diffuser 408, then into a return channel 410.

The wash oil 402 is injected into a port 412 through the compressor casing 224 and provides the wash oil to an atomizer 414. The atomizer 414 can spray the wash oil 402 in a number of patterns, such as a cone pattern that has a center axis that is perpendicular to the rotor 222 that the wheel is attached. However, the perpendicular injection may result in erosion of the diaphragm. Further, as described herein, the perpendicular injection may lead to oil droplets being trapped in the diffuser 408, as discussed further with respect to Figures 5A and 5B.

In embodiments described herein, the atomizer 414 sprays the wash oil 402 in a tilted pattern directed towards the return channel 410 downstream of the wheel. Further, other patterns besides cone shapes are used in embodiments, such as a fan spray, for example, directed downstream of the wheel. This lowers the amount of oil trapped in the vicinity of the diffuser, decreasing the evaporation of the oil. In various embodiments, any number of commercial atomizers may be used, for example, flood jet atomizers available from Spraying System Co. of Glendale Heights, Illinois, USA. In some embodiments, the port 412 holding the atomizer 414 is retractable for cleaning and replacement. For example, the port 412 may be a quill that can be pulled through a double block and bleed system allowing the compressor stage 300 to remain operational while the atomizer 414 is replaced.

Figures 5A and 5B are modeled views showing the trapping of wash oil in the diffuser for a single wheel. As described above, in a perpendicular injection, a portion of the wash oil droplets may be trapped in the u-bend on the diffuser instead of traveling to the return channel, as shown in Figure 4, resulting in increased residence time of the droplets in the u-bend and consequently, increased evaporation of the wash oil.

Figures 6A and 6B are modeled views of the modification of the injection pattern. Figure 6A is a modeled view of the perpendicular injection. Figure 6B is a modeled view of the tilted injection, for example, at an angle, shown as 0 in Figure 6B. In various embodiments, the angle is controlled to decrease spray of the wash oil droplets to the bend of the diffuser and have the droplets in the direction of the gas flow. This aids in decreasing the amount of evaporation of the wash oil. For example, the evaporation of wash oil inside the compressor can be decreased through modification atomizer design and injection angle. This is achieved by reducing the spray angle of the atomizer and tilting its axis at an angle towards the compressor discharge. With this modification, most of the injected wash oil droplets make their way to the return channel and travel to the next wheel instead of being trapped in the u-bend of the diffuser. As discussed herein, in some embodiments, the spray is a substantially flat fan, e.g., less than about 5° thick, with the fan pointed at the angle 0 in the direction of the gas flow.

The modification of the spray cone angle and spray angle decreases the evaporation of the injected wash oil, resulting in better utilization of the wash oil. Further, the improved utilization of the wash oil will decrease fouling in the compressor, resulting in better performance and longer service time, reduce downtime for cleaning, reduce pressure drop increase associated with fouling, and improved throughput. Computational Fluid Dynamic (CFD) Modeling

The CFD modeling of the wash oil injection into the compressor stage was performed using AN SYS Fluent 2022 and 2023. AN SYS Fluent is available from Ansys, Inc., of Canonsburg, Pennsylvania, USA.

Figures 7A-7E are views of the computational geometry of the compressor system used for the modeling. The geometry used for the study is a compressor stage with 4 wheels. Figures 7A-7C show the compressor configuration for a single compressor stage. Figures 7D and 7E show the wheel configuration in the compressor stage used for the modeling.

The properties of the cracked gas and wash oil used for the simulation as well as the process conditions of the simulation are as shown in Table 1 and Table 2, respectively. Table 1: Properties of Cracked Gas and Wash Oil Table 2: Process Conditions

For the CFD modeling, a baseline or control case, 100% of the wash oil was considered to be injected at the suction of the compressor. Six test cases that were simulated in the CFD modeling are shown in Table 3.

Table 3: Test Cases Modeled by CFD

For the baseline case, a hollow cone atomizer with a spray angle of about 90° was used. For the other cases, a hollow cone atomizer with spray angle of 45° was used. As described herein, 45° is the spray cone angle while 15° in the table refers to the angle between the cone axis and the vertical line perpendicular to the compressor shaft (axis). The spray nozzle used at inlet had a cone angle of 90°. The angle between the spray cone axis and the horizontal line was 30°.

Figure 8 is a velocity contour plot of process gas inside a four-wheel compressor stage. A low velocity region can be seen on the outer radius of the u-bends after wheel 1 - wheel 3, termed RC1-RC3, herein. The location and size of the low velocity region are slightly different due to change in the width of each return channel and change in the velocity magnitude and profile. Figures 9A and 9B are tangential and radial velocity contour plots of process gas inside the compressor. When 40% of the wash oil is injected through the casing, due to strong centrifugal force and lower radial and axial velocity, some of the wash oil droplets stay in the low radial/ high tangential velocity region for some time and significant mass of the droplets evaporate until they reach a droplet size that can be carried over by the main stream gas flow.

Figure 10 is a modeled view of the distribution of the wash oil droplets when injected into the compressor stage through the suction, similar to the baseline case. Only a small amount of the wash oil droplets makes it to the 3rd and 4th wheels of the compressor stage. Table 4 shows fraction of wash oil injected at the suction that did not evaporate in each wheel for the case of 100% injection (baseline).

Table 4: Fraction of Wash Oil Injected at the Suction That Did Not Evaporate.

Figures 11A and 1 IB are comparisons between a perpendicular spray pattern and a tilted spray pattern. Figure 11A shows the trapping of the wash oil droplets when injected through the casing at wheel 2, RC2, and perpendicular to the main shaft. Figure 1 IB shows the modeling results for the case when the atomizer was tilted at 15° towards the compressor discharge, which represents case 2 and case 5 in Table 3. By tilting the atomizer at 15° towards the compressor discharge, the wash oil droplets were pushed by the gas flow into the mainstream and are carried to the next wheel.

Figure 12 is a plot of the fraction of the total wash oil that did not evaporate. The fraction of total wash oil injected that did not evaporate was used to quantity the performance. In this case, II was defined as the ratio of fraction of wash oil injected that did not evaporate in each wheel for different experimental conditions to that of baseline, which is 100% wash oil injection at the suction.

The best case gave IT > 1, which indicates that some oil was carried over from a previous wheel. Of all the cases, case 4 and case 5 provided the highest performance. For these cases, the amount wash oil injected that did not evaporate in wheel 3 and wheel 4 is more than that with 100% wash oil injection at the suction. For case 4, 60% of the wash oil was injected at the suction and 40% was injected at the casing on top of wheel 2 with the atomizer tilted towards the compressor discharge at 15°. For case 5, 70% of the wash oil was injected at the suction and 30% was injected at the casing on top of wheel 2 with the atomizer tilted towards the compressor discharge at 15°. For these cases, some of the wash oil injected at the casing on top of wheel 2 still made it to wheel 3 and wheel 4 as liquid droplets.

Figures 13A and 13B are modeled pressure and temperature profdes in the compressor. Generally, the pressure and temperature in a compressor stage increases from wheel 1 to wheel 4, which impacts the rate of formation of the fouling. Therefore, wetting the surface of wheel 3 and 4 with the wash oil is important because any fouling material formed can either be removed by dissolution or prevented from attaching to the surface of the wheels.

Figure 14 is a block flow diagram of a method 1400 for decreasing fouling inside a compressor. The method begins at block 1402 with the mounting of a port in a casing of a compressor stage, wherein the port is disposed over a greatest diameter of a wheel in a compressor stage in the compressor, wherein the wheel comprises a stator, and impeller, and a diffuser. In some embodiments, the compressor stage has four wheels, and the port is disposed over a first wheel. In some embodiments, the compressor stage has four wheels, and the port is disposed over a second wheel.

At block 1404, an atomizer is mounted on the port, wherein the atomizer generates a flared spray pattern. In various embodiments, the atomizer has a maximum spray angle for the flared spray pattern of about 15° to about 60°. In some embodiments, the atomizer has a maximum spray angle for the flared spray pattern of about 45°.

At block 1406, a center axis of the flared spray pattern is tilted to an angle downstream of the wheel. In some embodiments, the flared spray pattern is tilted towards the outlet of the compressor stage at an angle of 15°. In some embodiments, the atomizer generates a flared spray pattern that is tilted. In some embodiments, the atomizer itself is tilted relative to the center axis of the port.

At block 1408, a wash oil is injected through the atomizer onto the wheel. In some embodiments, a portion of the wash oil is injected into a suction line to the compressor stage while a second portion of the wash oil is injected into the atomizer. For example, 60% of the wash oil can be injected into the suction line while 40% of the wash oil is injected through the atomizer, or 70% of the wash oil can be injected into the suction line, while 30% of the wash oil is injected through the atomizer. Embodiments

In an embodiment, combinable with any other embodiment, the port includes a valve system that allows the atomizer to be retracted while the compressor is operational.

In an embodiment, the valve system includes a double block and bleed system.

In an embodiment, the atomizer is mounted on a retractable line.

In an embodiment, the flared spray pattern covers an angle of between about 15° and about 60° around the center axis.

In an embodiment, the flared spray pattern includes a fan pattern.

In an embodiment, the flared spray pattern covers an angle of about 45° around the center axis.

In an embodiment, the center axis of the flared spray pattern is tilted at an angle of 15° toward a discharge from the compressor stage.

In an embodiment, the port is disposed in the casing proximate to a first wheel in the compressor stage.

In an embodiment, the port is disposed in the casing proximate to a second wheel in the compressor.

In an embodiment, combinable with any other embodiment, the system includes an injection port on a suction line to the compressor, wherein the injection port is to inject wash oil into the suction line to the compressor.

In an embodiment, about 60% of the wash oil is injected into the suction line of the compressor stage and about 40% of the wash oil is injected through the atomizer at the casing.

In an embodiment, 70% of the wash oil is injected into the suction line of the compressor stage and about 30% of the wash oil is injected through the atomizer at the casing.

Another embodiment described herein provides a method for decreasing fouling inside a compressor. The method includes mounting a port in a casing disposed over a wheel in a compressor stage at a greatest diameter or downstream of a greatest diameter of the wheel, wherein the wheel includes a stator, and impeller, and a diffuser. An atomizer is mounted in the port, wherein the atomizer generates a flared spray pattern. A center axis of the flared spray pattern is tilted to an angle downstream of the wheel a wash oil is injected through the atomizer.

In an embodiment, the method includes selecting the atomizer with a maximum spray angle of about 15° to about 60° for the flared spray pattern.

In an embodiment, the method includes selecting the atomizer with a maximum spray angle of about 45° for the flared spray pattern.

In an embodiment, combinable with any other embodiments, the method includes tilting the center axis about 15° from vertical towards a discharge from the compressor.

In an embodiment, the method includes mounting the port proximate to a first wheel in the compressor.

In an embodiment, the method includes mounting the port proximate to a second wheel in the compressor.

In an embodiment, combinable with any other embodiment, the method includes mounting a second port in a suction line to the compressor stage and injecting a portion of the wash oil into the suction line into the compressor stage.

In an embodiment, the method includes injecting about 60% of the wash oil into the port on the suction line and about 40% of the wash oil into the atomizer at the casing.

In an embodiment, the method includes injecting about 70% of the wash oil into the port on the suction line and about 30% of the wash oil into the atomizer at the casing.

Other implementations are also within the scope of the following claims.

INDUSTRIAL APPLICABILITY

Cracked gas compressors (CGCs) are important unit-operations in commercial ethylene plants. This disclosure relates to systems and methods for decreasing the evaporation of wash oil in a compressor to mitigate of fouling.

Claims

1. A system for decreasing fouling inside a compressor, comprising: a compressor stage comprising a wheel, comprising: a stator; an impeller; and a diffuser; a casing disposed over the compressor stage; a port in the casing disposed proximate to or downstream of a greatest diameter of the wheel; and an atomizer mounted in the port, wherein the atomizer injects a wash oil onto the wheel in a flared spray pattern, wherein a center axis of the flared spray pattern is tilted at an angle to a downstream side of the wheel.

2. The system of claim 1, wherein the port comprises a valve system that allows the atomizer to be retracted while the compressor is operational.

3. The system of claim 2, wherein the valve system comprises a double block and bleed system.

4. The system of claim 2, wherein the atomizer is mounted on a retractable line.

5. The system of claim 1, wherein the flared spray pattern covers an angle of between about 15° and about 60° around the center axis.

6. The system of claim 1, wherein the flared spray pattern comprises a fan pattern.

7. The system of claim 1, wherein the flared spray pattern covers an angle of about 45° around the center axis.

8. The system of claim 1, wherein the center axis of the flared spray pattern is tilted at an angle of 15° toward a discharge from the compressor stage.

9. The system of claim 1, wherein the port is disposed in the casing proximate to a first wheel in the compressor stage.

10. The system of claim 1, wherein the port is disposed in the casing proximate to a second wheel in the compressor.

11. The system of claim 1, comprising an injection port on a suction line to the compressor, wherein the injection port is to inject wash oil into the suction line to the compressor.

12. The system of claim 11, wherein about 60% of the wash oil is injected into the suction line of the compressor stage and about 40% of the wash oil is injected through the atomizer at the casing.

13. The system of claim 11, wherein 70% of the wash oil is injected into the suction line of the compressor stage and about 30% of the wash oil is injected through the atomizer at the casing.

14. A method for decreasing fouling inside a compressor, comprising: mounting a port in a casing disposed over a wheel in a compressor stage at a greatest diameter of the wheel or downstream of a greatest diameter of the wheel, wherein the wheel comprises a stator, and impeller, and a diffuser; mounting an atomizer in the port, wherein the atomizer generates a flared spray pattern; tilting a center axis of the flared spray pattern to an angle downstream of the wheel; and injecting a wash oil through the atomizer.

15. The method of claim 14, comprising selecting the atomizer with a maximum spray angle of about 15° to about 60° for the flared spray pattern.

16. The method of claim 14, comprising selecting the atomizer with a maximum spray angle of about 45° for the flared spray pattern.

17. The method of claim 14, comprising tilting the center axis about 15° from vertical towards a discharge from the compressor.

18. The method of claim 14, comprising mounting the port proximate to a first wheel in the compressor.

19. The method of claim 14, comprising mounting the port proximate to a second wheel in the compressor.

20. The method of claim 14, comprising: mounting a second port in a suction line to the compressor stage; and injecting a portion of the wash oil into the suction line into the compressor stage.

21. The method of claim 20, comprising injecting about 60% of the wash oil into the port on the suction line and about 40% of the wash oil into the atomizer at the casing.

22. The method of claim 20, comprising injecting about 70% of the wash oil into the port on the suction line and about 30% of the wash oil into the atomizer at the casing.