Important Factors to Know in Compressor Design
It’s ideal to understand quality compressor design to ensure quality results. Here’s everything you need to know.
Most compressors are designed to deal with large and significant changes in temperature and pressure that generally occur in several gas mixtures.
Therefore, the reliability of a compressor depends heavily on gas loads, rotor weights, the thermal growth within the bearing house, and that of the cylinder versus the rotor shaft. All these also make the compressor design complicated.
Crucial Factors to Know in Compressor Design
Several factors are essential in compressor design. Here they are in no particular order:
Gas Composition
Compressors are employed in various applications, including myriads of chemical process variations, natural gas or air compression, etc. Compressor materials must combat sulfide stress cracking, hydrogen embrittlement, moisture, as well as numerous other corrosive conditions.
Aside from the compressor housing material, the elastomers and seals must be capable of resisting the overall effects of different gases that pass through the compressors.
The NACE (National Association of Corrosion Engineers) looked into this by developing an industry standard. The latter helps define compressor design that contributes to resisting some of the crucial elements found in many gases.
- The need for lubrication
Every gas compressor must not be devoid of proper lubrication. This is because oil helps protect the compressor’s bearings from corrosive elements present in gases. The oil also provides lubricity essential in maintaining expected bearing life.
During compression, there’s a constant possibility of water condensation within the bearings. When water condenses, it can easily wash away the bearings’ oil, so they become unprotected.
Particulate contamination also has an adverse impact on roller bearings and can badly shorten the life spans of these bearings.
Pressure Variation
It is highly essential for compressor housing to be robust enough to deal with the overall pressure within the compression chamber consistently.
Compression cycles create uninterrupted pressure pulses that can be harmful to the compressor. It is also vitally essential to take note of the numerous external forces – such as the thermal growth and weight from the connected piping – that act on compressors.
These forces significantly add loads and moments to the flanges, which are non-essential to the compressor’s housing. This is why the materials used in constructing the compressor must be pliable and strong enough to adequately maintain reliability.
Temperature Variation
It is not uncommon for gas temperatures to considerably increase by some degrees within a compression cycle. Nevertheless, thermal expansion affects every component within the gas stream.
The overall design of the compressor must help reduce the effect that the components’ thermal growth has on the compressor’s efficiency. It must also affect the compressor’s ability to perform or function in a faithful manner with minimal downtime.
This is where water jacket cooling comes in. Water jacket cooling helps ensure the predictability of thermal growth while making the compressor design more efficient.
Ambient conditions also affect the overall reliability of gas compressors. This is why compressor systems designed for environments typical to the Canadian province of Northern Alberta may be unable to withstand that of desert areas in the United Arab Emirates or the Middle East.
The Reliability of Compressor Design
Basic compressor design has hardly changed since the first ones constructed in the ’60s and ’70s hit the market. Many compressors of these periods are still in active operation today, which attests to the equipment’s overall reliability.
Compressor design has several moving components. This includes bearings, seals, the rotor, and vanes that always rotate in one direction, which help prevent the bulk of the fatigue linked with other compressor types.
The following are the materials current designs of compressors utilize for more reliable equipment:
- The rotor
This one-piece shaft is expertly shaped to an incredibly close tolerance, with one primary goal: to enhance efficiency and prevent ruinous failures. The one-piece design of the rotor supports its overall weight with zero deflection while efficiently resisting bending caused by gas loads.
- The vanes or rotor blades
They are constructed from high-strength aramid fiber steeped in phenolic resin. This material has a low thermal expansion ratio, which increases the compressor’s efficiency due to the tightly-held clearances it affords.
The average life span of a compressor blade is not more than 2 years. However, rotor blades have been known to last more than 5 years due to proper lubrication and lower operating temperatures.
- The cylinder head and body
They are usually constructed with ASTM A395 liquid-cooled ductile iron. The elasticity of this material perfectly deals with every temperature change. The material is also highly resilient to pressure changes that often occur during the compression cycle.
Considerable Improvement in Compressor Design Reliability
The custom-designed bearings are one notable improvement in reliability over the original or initial compressor design. Thanks to technological advances in heat-treating control and material science improvements, the life expectancy of bearings within a distinctive application are more than 30,000 hours.
Every component exposed to process gas is specially designed to resist sulfide stress cracking and hydrogen embrittlement. Thanks to the ductile iron construction of both the cylinder and head, handling pressure and temperature variances are now a walk in the park.
The iron construction also complies with the NACE MR0175 criteria for preventing sulfide stress crack that H2S causes. All rotors have NACE-compliant options.
However, it is important to maintain a thin film of fresh lubricating oil on internal components in order to protect them from the process gas. This is why the once-through lubrication system employed with the sliding vane compressor injects small amounts of oil at every point.
All the injected oil is finally ejected from the compressor discharge and downstream, where it is removed from the entire process using a specifically-designed separator.
Balancing is a crucial operating factor in compressor manufacture. Every out-of-balance force must be removed immediately in order to prevent the severe vibration that may otherwise develop when the compressor operates at high speeds.
Conclusion
These are the essential factors to know in compressor design, without which compressor systems may fail. Knowing and considering them when designing compressors help ensure the longevity of the entire system while minimizing downtime to the barest minimum.
From industry standards like Ariel compressor parts to Clark and Cooper Bessemer compressor parts, we carry compressor parts you can trust and the service you can count on.