Supercritical CO2 Power Cycle Symposium May 24-25, 2011

Boulder, Colorado Successful Operational Experience Sealing Supercritical CO2

Marquardt, Jason, T John Crane Incorporated

6400 W. Oakton Morton Grove, IL 60043

jtmarquardt@johncrane.com

Abstract

Enhanced Oil Recovery (EOR) using Supercritical CO2 has been around for decades and these pipeline applications have traditionally been handled using centrifugal pumps with non-contacting dry gas seals (John Crane has well over 1 million running hours in these applications). As the interest in CO2 capture and storage has greatly increased, new challenges have appeared as a result of the higher operating pressures, higher rotational speeds, increased temperatures, and resulting higher seal leakages for these new applications. Due to the unique properties of CO2 at supercritical conditions, there are several issues to consider regarding the sealing of the turbo-machinery selected for these applications. John Crane will present on its over twenty (20) years of field application experience applying dry gas seals and their respective seal support system requirements for SCO2 service. 1. Field Experience Since the late eighties, CO2 applications have been successfully handled with non-contacting dry gas seals optimized for fluids operating at or near their point of vaporization. API 682 recognizes these types of seals as dual unpressurized seals (or Tandem arrangements). Tandem seals have a pair of seal faces each able to take the full pressure requirements of the application with a full backup seal for safety reasons. Depending on a variety of factors including regional climate, whether the equipment is indoors or outdoors, availability of nitrogen, etc. the seal support system may include a nitrogen buffer in the primary vent, a nitrogen buffer on the secondary vent, or both. The most common arrangement simply has a heated, filtered flush (Plan 12) with a low flush rate and a system to monitor vapor leakage in the primary vent (Plan 76). These applications can be broken down into three (3) categories: Low speed applications ( 8000 rpm). Table 1 below is an experience list for non-contacting gas seals applied in CO2 service.

OEM Shaft Dia (in) Location Seal SizePress Max (psi)

Speed Max Cont

Temp Max (F)

Floway Pumps 1.187 Houston, TX. 2.187 225 3600 350Man Turbo 2.755 Beula, ND 4.187 1600 26400 350

Ingersoll Rand 2.756 Denver City, TX 4.187 1950 2100 72Ingersoll Rand 2.756 Denver City, TX 4.187 1950 2100 72

Bingham 2.635 Denver City, TX 3.937 1950 2100 72Bingham 2.635 Denver City, TX 3.937 1950 2100 72

Production Pump 2.635 Texas 3.687 2000 3960 220Production Pump 2.635 Texas 3.687 2000 3960 220

United 4.750 Texas 6.187 2200 2100 100United 4.750 Texas 6.187 2200 2100 100

United Centrifugal 4.750 NA 6.187 2200 1780 350United Centrifugal 4.750 NA 6.187 2200 1780 350

FlowServe 4.750 NA 6.187 2200 2160 125FlowServe 4.750 NA 6.187 2200 2160 125

Ingersoll Rand 2.375 Denver City, TX. 3.687 2200 3000 110Ingersoll Rand 2.375 Denver City, TX. 3.687 2200 3000 110

Man Turbo 2.755 Beula, ND 4.187 2500 26400 350American Pump 3.265 Dallas, TX. 4.437 2500 4000 100American Pump 3.265 Dallas, TX. 4.437 2500 4000 100

Bingham 2.635 Corsicana, TX. 3.687 2400 4000 350Bingham 2.635 Corsicana, TX. 3.687 2400 4000 350

BWIP 2.505 Texas 3.687 2400 3560 350BWIP 2.505 Texas 3.687 2400 3560 350MHI 4.724 Japan 6.375 3118 7700 400MHI 4.724 Japan 6.375 3118 7700 400

High Peripheral Speed

Table 1 Supercritical CO2 Experience List The partial SCO2 experience list demonstrates the vast majority of the existing field experience is with low speed (pipeline applications) with sealing pressures between 1900 2500 psig, and rotational speeds of 3600 rpm or less. Large quantities of these seals have been supplied throughout west Texas and New Mexico and this technology is considered mature with very little field application uncertainty. The applications highlighted in yellow represent the moderate and high speed applications representative of where the market demands are going. It should be noted that although all test results for these more challenging applications has been extremely positive, there are still a relatively small quantity of these seals in circulation as compared to the low speed applications. Filtration of the seal flush is critical to seal reliability. A duplex filtration system with a 3 micron nominal filter element is recommended. The duplex filtration system allows uninterrupted operation in the event the filter element needs to be replaced. A detailed fluid analysis is also required for proper filter element selection. It is helpful to view these applications on a Pressure-Enthalpy diagram to see the state of the fluid (liquid, vapor, or supercritical). Traditionally the applications with low vapor pressure margins or low to moderate speed supercritical applications are handled with pumps. Not until recently have turbo machinery OEMs begun applying compressors for these services. Regardless of the type of equipment, John Crane believes that the non-contacting dry gas seal is the preferred solution for this service. Figure 1 below displays field operating points on a CO2 Pressure-Enthalpy diagram.

Figure 1 Pressure-Enthalpy Diagram (Field Operating Points) 1.1 Low Speed Applications A typical low speed application would be a pipeline application utilizing centrifugal pumps with operating speeds below 4000 rpm. The seal configuration is classified by the API 682 community as a dual unpressurized (Tandem) arrangement. The double ended pumps require a relatively unsophisticated seal support system consisting of a heated, filtered flush (Plan 12) at a low flush rate (1-2 gpm) and a vapor monitoring system for the primary vent gas leakage (Plan 76). The gas seal solution/support system has proven to be much more reliable and easier to manage and has very low seal leakage as compared to conventional contacting (wet) seal solutions. The contacting seal solution requires a very high flush rate to prevent the seals from burning up, has a more complex (and costly) seal support system and results in very high seal leakage which is an emissions problem. Depending on the regional climate, pump insulating and or flush line heat tracing may be required to maintain process temperature. A typical P&ID diagram for a double ended pump applied with a gas seal solution in SCO2 service is shown below in Figure 2. These applications have been applied successfully since the late eighties and have accumulated over 1 million hours of operation.

Figure 2 Typical P&ID Diagram for SCO2 Pump Application 1.2 Moderate Speed Applications As the pressure requirements have continuously increased to reach deeper reinjection reservoirs and handle increased pipeline pressures, centrifugal pump OEMs have been developing high speed pumps to handle these demands. Regardless of the ambient temperature of the application, the losses and heat generated by the seal due to viscous drag of the rotating seal components (churning heat) can result in significant temperature rise in the seal chamber. John Crane has developed empirical formulas to estimate this churning heat for dry gas seals in high density fluids based on the Bilgen-Boulos equations for high Reynolds numbers [1,2]. The churning heat estimated for one moderate speed application with a sealing pressure of 3118 psig and rotation speed of 7700 rpm resulted in estimated losses of 15 16 kW. Although not insignificant, field testing demonstrated that a low, filtered flush (1-2 gpm) without the heating requirement similar to the low speed applications as shown above in Figure 2 is appropriate. 1.3 High Speed Applications In the last few years, several inquiries have been received for development work for high speed centrifugal pumps, centrifugal compressors, and Turbo expander OEMs to establish products for the expanding SCO2 market. Specifically transportation (higher pipeline pressure requirements), storage (high pressure reinjection for enhanced oil recovery and sequestration) and carbon capture (power plants) are the areas of interest. The high rotational speeds for these new applications along with the high density of the SCO2 fluid are expected to create considerable churning losses due to windage. These applications will require some form of additional cooling which can be remedied by proper design of the seal support system. One such application for an integrally geared compressor with a suction pressure of 2300 psig, available seal gas at a temperature of 350 F, and rotational speed of 26000 rpm led to estimated churning losses of 50 60 kW. Analysis of the temperature rise in the seal chamber shows an increase in the mass flow rate feeding the seals is required to keep the temperature rise at the seal to within the limits of the seal design. Cooling of the seal supply gas (typically fed discharge gas) is also required. There are several commercially available programs for estimating the fluid state properties at these conditions to be used in the analysis. The result is that a high flush rate of approximately 1.5 acfm (10 gpm) is required in addition to cooling

the seal supply fluid temperature to approximately 125 F to manage the temperature inside the seal chamber. The seal fluid flush rate required for this application is considerably higher than typical low/moderate speed applications previously discussed and must be accounted for in the design of the seal support system. 2. Development Activities John Crane has performed a significant amount of testing on both liquid and SCO2 at sealing pressures up to 3000 psig and rotational speeds up to 3600 rpm. The purpose of this testing was to correlate leakage data gathered from the testing with John Crane developed proprietary CFD software (CSTEDY) used to calculate seal leakage. The results demonstrated very close correlation between the software predicted seal leakages and actual test leakages. Further testing is planned for high pressure/high speed applications to correlate the estimated churning heat based on the empirical formulas developed by John Crane for gas seals against actual test data. This testing is planned for late 2011. 3. Conclusion Traditional CO2 applications have been handled successfully for decades with proven non-contacting gas seal technology (dual unpressurized seal arrangements) and relatively uncomplicated seal support systems (Plan 12 and Plan 76). Application pressures are on the rise for several reasons including higher pipeline pressure requirements, SCO2 storage applications (enhanced oil recovery and sequestration) and the expanding carbon capture demands from power plant exhaust. As rotational speeds increase, it is necessary to consider the churning heat generated from viscous drag of the rotating seal components. The design of the seal gas support system is a critical component regardless of the application. For applications with high expected churning losses, a provision for cooling to manage the temperature rise in the seal chamber is required. A properly designed seal support system is required to accomplish this. Regardless of application speed, a detailed fluid analysis and properly selected filter element is required for improving seal reliability. 4. Acknowledgements While the author of this paper has applied the aforementioned seals and support systems into the field, it could not have been done without the hard work of engineers working in John Cranes research and development group (K. Meck, G. Zhu) in establishing guidelines for estimating churning losses in high speed gas seal applications. 5. References [1] E. Bilgen, R. Boulos, Functional Dependence of Torque Coefficient of Coaxial Cylinders on Gap Width and Reynolds Numbers, Transaction ASME J.Fluids, 1973. [2] F. Kreith, Heat Transfer of a Disc Rotating in an Enclosure, International Journal of Heat and Mass Transfer, 1968. [3] K. Meck, G. Zhu, Internal Proprietary John Crane R&D Document 10002300: CO2 Sealing Design Methodology, 2011.