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Aug-2016

Reciprocating compressors in a hydrogen plant

A hydrogen producer chose moderate speed reciprocating compressors for its natural gas feed and hydrogen product services.

BENJAMIN WILLIAMS, Ariel Corporation
LAURENT RICHAUME, Air Liquide Engineering & Construction

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Article Summary

Since the early 1990s, emissions regulations throughout the world have led to increased demand for hydrogen. This is because hydrogen is required for many desulphurisation processes. Industrial gas companies have constructed a number of hydrogen plants throughout the world to meet the demands of the refining and petrochemical industries.

The majority of reciprocating compressors used in these hydrogen plants have been lubricated, long stroke, slow speed types. This is due to historical preference and the perception that these are the most reliable compressors available. It should be noted that other types of reciprocating compressors have also been used successfully in these facilities. These include vertical compressors and horizontal, short stroke, moderate speed types.

Although lubricated compressors are the most common type used in these facilities, there are times when the design of the hydrogen plant or its components cannot tolerate oil carry-over in the gas stream. In those cases, the decision must be made whether to use a lubricated compressor with a downstream coalescing (oil removal) system or a non-lubricated (dry piston) compressor.

When determining lubricated vs non-lubricated compressors, among the items that need to be considered are the impact of oil downstream of the compressor, initial and life cycle cost, and frequency 
of required maintenance. Typically non-lubricated compressors will have a higher initial capital cost due to the higher cost of wear part 
materials. Non-lubricated compressors typically require more frequent maintenance than a lubricated compressor.

Air Liquide made the decision to purchase packaged, non-lubricated, horizontal, balanced opposed, short stroke, moderate speed reciprocating compressors for the natural gas feed and hydrogen product services at a new hydrogen plant it was constructing in Campana, Argentina.

The hydrogen plant went on-line in November 2009. This article describes the compressor selections, provides a brief overview of their design characteristics and summarises their operational history.

Hydrogen production unit

Air Liquide built a new hydrogen unit (steam methane reformer technology) in Campana, Buenos Aires, Argentina. The unit supplies hydrogen and steam to the Esso Petrolera Argentina refinery for use in the production of gasoline.

Prior to this project, Air Liquide would typically purchase vertical, slow speed compressors for this type of facility. The decision to purchase moderate speed, short stroke compressors for the Campana project was 
based on delivery, compact packaging and capital cost. Spare parts availability and references for similar applications also contributed to the decision to purchase moderate speed reciprocating compressors.

The decision to use non-lubricated compressors for both the natural gas feed and hydrogen product services was based on differing requirements. Primarily, the natural gas feed service required non-lubricated compressors to prevent oil contamination of the Air Liquide process and process equipment. The hydrogen compressors needed to be non-lubricated due to customer requirements.

Compressor requirements

Operating details of compression requirements for the natural gas feed and hydrogen product are shown in Tables 1 and 2.

Compressor selections
Air Liquide purchased two 100% capacity, non-lubricated, non-cooled, short stroke, moderate speed, electric motor driven reciprocating compressors for each service. (Typically, Air Liquide will purchase either two 100% or three 50% units for hydrogen plants.)

The following is a brief description of the compressor selections and details of the calculated performance of each (see Tables 3 and 4).

Natural gas feed

Non-lubricated, short stroke, moderate speed, two stage, two throw compressor driven by a 500 kW, 750 rpm squirrel cage induction motor.
Cylinder data:    Stage 1    Stage 2
Cylinder bore dia., mm    358.78     244.48
Cylinder MAWP, BarG     56.2    87.6

Hydrogen product

Non-lubricated, short stroke, moderate speed, two stage, two throw compressor driven by a 500 kW, 750 RPM squirrel cage induction motor.

Cylinder data:     Throw 1      Throw 2
Cylinder bore dia., mm    244.48     244.48
Cylinder MAWP, BarG     87.6    87.6

Compressor design characteristics
As noted previously, the compressor frame models are the same for both services. The following overview applies to both the natural gas feed and hydrogen product compressors unless otherwise noted.
   
Compressor frames
Model: JGT/2
Compressor stroke, mm: 114.3
Piston rod diameter, mm: 50.8
Rated speed, rpm: 1500
Operating speed, rpm: 744
Average piston speed, m/s: 2.8
Rated tension rod load, kN: 165
(Average calculated tension rod loads were 119 kN and 103 kN, respectively)
API-618 Type “C” distance pieces (see Figure 1)

Cylinder bodies
Material: ASTM A395 ductile iron
Non-cooled
Unlined: ion-nitride hardened to approximately 57 Rc.
Surface finish: 0.15 ųm


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