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The VIP Compressor - A Solution to Reliable High Speed OperatiWilliam C. Wirz

Dresser-Rand, Painted Post, N.Y., U.S.A

The Recip - a State of the Art Compressor4 5 November 1999, Dresden

bstract:gh Speed Compressors offer opportunities for clients to lower total installed cost by having a smaller compressor in physical size, bw (MMSCFD) of larger, slower speed reciprocating compressors. While lower total installed cost cannot be disputed with high-speempressors, there is an overriding concern of lifetime costs and maintenance due to the high rotative speed. It is clear that developm

ue high speed, reliable, reciprocating compressor is needed to provide consumers with the opportunity compress gas at lower cost. ll identify the Dresser-Rand "VIP" compressor as a solution to the need to compress gas reliably at very low cost.

ntroductionresser-Rand Company is a joint venture company owned by Halliburton and Ingersoll-Rand. Both companies ng history in providing equipment for the Oil and Gas, Petrochemical Markets. In the areas of gas compressioears of design and operating experience are brought to bear in the development of new solutions to meet spe

the client. Specific compression solutions include: non-lubricated service, high pressure, gas transmission, gathering, sour gas service, hazardous gas compression. To specifically address the need for a solution to relia

ompress gas at higher rotative speeds, Dresser-Rand embarked on the design of the "VIP - (Valve-In-Piston)"ompressor. After nearly 5 years of applying this cylinder design in a variety of compression applications, clientxperienced increased reliability and lower operating costs than other high speed units in similar service.

he "VIP" Design

ylinder Design

ntil the introduction of the "VIP" cylinder there were basically two types of compressor cylinder designs: Barrealve-in-Head. The "Barrel" cylinder configuration (Figure 1.) is designed with the compressor valves radially aylinder bore. These cylinders typically have the highest percent of clearance due to the need to feed the valvecallops or cylinder liner port cuts. Piston design is conventional, cylindrical in shape, and attached to a piston rollars and a piston nut.

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Figure 1. Typical "Barrel" Type Compressor Cylinder

Figure 2. Typical "Valve in Head" Cylinder Cross-section

he Valve-In-Head cylinder configuration (Figure 2.) has the compressor valves at each end of the cylinder. Thonfiguration generally provides lower percent of clearance over a "barrel" type cylinder offering a performancedvantage. However, an inherent maintenance concern exists with an unusually large outer head, which must bmoved for routine service of the piston and compression rings. Sealing gas pressure is also a concern. Large

bolts on the outer head are required to contain the gas pressure. As a result, this configuration of cylinder is stricted to lower pressure applications.

he VIP (Valve - In - Piston) cylinder configuration (Figure 3.) is different than either the "barrel" and "Valve-In-onfiguration and must be understood to make a comparison. The VIP has two stationary suction valves mounte cylinder bore. These valves serve two purposes: The first is to act as a suction valve allowing gas to enter t

ompressor cylinder during the expansion stroke. The second is to act as frame and outer heads containing theompression during the compression stroke. The discharge valves are in motion and are attached to the pistonerve two purposes: The first is to act as discharge valves allowing compressed gas to exit the compressor afteompression. The second is the discharge valve assembly serves as the piston providing the structure to suppoompression rings and being a robust component utilised to compress the gas to the required higher pressure. nswept" volume or clearance effect the performance of any cylinder. Clearance is at a minimum when compa

arrel" or "Valve-In-Head" design (Figure 4.)

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Figure 3. VIP Cylinder

Figure 4. Clearance Comparison "Conventional" vs. "VIP" Cylinder Design

he only volumes that are unswept by the piston are: The frame and outer end "bump" clearances and the cleae valve assembly. Note also that the amount of seals required to contain the gas within the cylinder are at a malve covers have been completely eliminated removing them as a potential source of gas leakage as well as aaintenance concern.

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esigning the VIP for RELIABILITYhe Compressor Valve

ithout a doubt the heart of any compressor cylinder and the continued ability of the cylinder to compress gas y the compressor valve. The VIP valve is a derivative of the proven, "PF" valve design, which has been utiliseresser-Rand high-speed compressor applications since 1985. The VIP valve is a ported plate design, which uetallic, Hi-Temp, plate, trochoidal in shape (Figure 5.)for optimum reliability.

Figure 5. VIP Compressor Valve Plate

Finite element analysis, life cycle testing have demonstrated that the shape of this plate in combination witmaterial used optimises the reliability of the valve by forcing the valve plate to impact on the area of thecompressor valve plate with the most material.

The VIP is different in that the discharge valve is in motion. Recognising this, the discharge valves were firanalysed utilising Finite Element Analysis in a static condition with 3-D, 20 node, structural solid elements.analysis was verified with strain gage work (Figure 6.) and finally the entire assembly run and loadeddynamically on the Dresser-Rand closed loop.

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Figure 6. VIP Seat - Strain Gage

This design work under laboratory conditions clearly demonstrated the reliability of the valve assemblies.

The VIP Cylinder

The VIP Cylinder is simple in design. It is a single wall casting and resembles little more than a "cast tube"makes the cylinder easy to cast by having the foundry difficulties attributed to double wall and water-cooledcylinder designs eliminated.

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Figure 7. - VIP Cylinder - Strain Gage

However, as simple as the cylinder is, the reliability and soundness of the design needed to be verified. Cydesign takes on the following steps: hand calculations to determine wall thickness etc., Finite Element Ana(FEA) to verify stress levels and utilisation of metal in areas where it is most useful, and finally a strain gagor burst test of the cylinder to verify and correlate the design work. The Finite Element Analysis as shown(Figure 7) indicates the area of higher stress. Note that the burst test of the same cylinder (Figure 8.) showfailed area in identical location to what was predicted utilising FEA. This is excellent correlation. Note that fthe burst tests conducted, VIP cylinders have withstood pressures in excess of four times the design press

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Figure 8. - VIP burst test results

The VIP - Application

The VIP has been and is applied at a variety of speeds, heavy and light mole weight gases, sour and sweeservice, low and high-pressure.

The VIP is designed for speeds up to 1800 revolutions per minute. All of the internal components are suitafor sour gas service to National Association of Corrosion Engineers (NACE) MR0175-94 "Sulfide StressCracking Resistant Metallic Materials for Oilfield Equipment".

Clearance is easily added to the VIP cylinder to "tune" the performance to the specific client operating conThis is accomplished by easily adjusting the outer end inlet valve outward from the moving discharge assemuch the same way as clearance outer heads are done on conventional "barrel" type cylinders. In additionmounted fixed clearance heads as well as bypasses to inlet mechanisms are also available.

The VIP Frame and Running Gear

The solution that Dresser-Rand was addressing in the development of the VIP was directed toward the cylend. This is primarily due to existing Dresser-Rand running gear designs that are very reliable for high-speoperation. Therefore, the VIP cylinder was adapted to proven, reliable Dresser-Rand running gears such a

Dresser-Rand CUB, KOA, and HOS.

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Testing

The final verification of any design is to test. Dresser-Rand has a closed loop test facility (Figure 9.) which the capability of running a given compressor at various pressures and speeds. It is on this closed loop thatperformance measurements are taken to verify the performance prediction. In addition, this closed loop seas a full scale endurance test apparatus. Problems in design, should they arise, are addressed here beforeequipment is placed in the field.

Figure 9. VIP Compressor on Dresser-Rand Closed Loop

Dresser-Rand Company owns large rental compression fleet (Figure 10).

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Figure 10. VIP Installed in the Dresser-Rand Rental Fleet.

Part of the design verification is to place newly designed and laboratory tested in the field, utilising DresseRands rental fleet, to gain "real life" operational data. This fleet typically serves the "gas patch" where adveoperating conditions including wind, weather, and unattended operation is the norm.

Successful testing using both lab endurance testing combined with field testing equates to a more reliable

compressor when it is sold to our clients.The "VIP" - Cost Effective!

Comparing a VIP with other cylinder designs, one can observe that fewer parts are utilised on a VIP versu"barrel" or "Valve-in-Head" design cylinder. This can be seen in the preceding figures. Fewer parts means cost. In addition, a part commonality between cylinder bore sizes is a plus when considering some inventocommon wearing or replacement parts. This design therefore has an overall effect of lower installed cost dfewer parts and lower long term operating costs because of parts commonality.

The "VIP" - A Reliable Compressor!

One of the main concerns is the reliability of high-speed compression equipment. Dresser-Rand sought todevelop a compressor to address this concern. Successful designs, laboratory testing, and field testing proa sound basis on which to introduce a new compressor to market. However, the variation of applications, athe environments in which a compressor must run are more typically encountered when more units are plain the field either through rental compression or sale to clients.

Since 1994, Dresser-Rand has placed more than 400 VIP cylinders into services ranging in speeds up to 1rpm, bore sizes up to 23 inches, gases ranging from Hydrogen to Carbon Dioxide, and sweet and sour (H2gas service. These cylinders along with their running gear, have an average running time well over 17000hours. Some units have more that 50000 hours of service with no more than routine wear parts replacemeEven with routine wear parts replacement down time is minimised due to the ease at which parts are remofrom the cylinder.

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Durability of the compressor valve design is key. VIP valves have been known to function without damagewith harmful debris entering the cylinder and being lodged in the valve! This is due to the embeddability of valve plate material and the robust design of the seat and guard.

This VIP Compressor has been proven to be extremely robust even in more than difficult services.

Conclusion

By identifying a need by the client for a cost effective and more reliable high speed compressor, Dresser-Rembarked on the design of the VIP. Through proper design method, laboratory and field testing, Dresser -has sold more than 400 VIP cylinders flanged to proven Dresser-Rand frame and running gear. The VIP

compressor has been proven reliable in many applications and various conditions of service. As a result ofVIP reliability, maintenance costs are low.

The success of the VIP is now demonstrated. It is clear that the VIP compressor cylinder design contributegreatly toward improved compressor reliability and lower maintenance costs.

VIP cylinders can be applied at various speeds, strokes, piston rod diameters, and operating conditions wisignificant changes to proven frame and running gear. This includes Dresser-Rand running gear, but also compressor running gear.

Acknowledgements

The author wishes to thank the work associates at Dresser-Rand Company for successfully introducing thiproduct to the marketplace. Also the author wishes to thank the clients who first made the decision to try thVIP compressor. Someone always has to go first and for making that decision they should be recognised bindustry. Finally, a wholehearted thanks goes to the inventor of the VIP, Mr. Robert Bennitt, and Dresser-RCompany for supporting this development and product introduction with the necessary enthusiasm andresources.

References

1. Huang, J.Y. and Miller, T.M. The application of finite element analysis to VIP compressor cylinderdesign, Proceedings of Purdue University Compressor Technology Conference 1994.

2. Bennitt, R. VIP compressor, Dresser-Rand Technology Conference, presented October 22-23, 1993. Blazejewski, T. The Development of a Valve-in-Piston (VIP) compressor cylinder and its application

both the gasfield and process gas industries. IMechE Conference, 13-14 May 1996

Refer questioContac

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