Why Satisfactory Compressor Installation Relies on the Design
If you’re beginning the process of a compressor installation, then it’s ideal to fully understand the design first. The foundation is very important, which is detailed more below.
Compressors are those interesting mechanical devices that help to increase pressure in various compressible fluids. They are used across a wide variety of industries to power tools, instrument or shop air, abrasive blast equipment, and paint sprayers. And they find excellent use in propelling gas through pipelines, phase shifting refrigerants for refrigeration and air conditioning, etc.
Just as with pumps, compressors come in 2 major varieties: kinetic or dynamic or centrifugal and positive-displacement types. In places where centrifugal varieties principally represent pumps, compressors are usually of the positive-displacement type.
Compressors also come in different sizes, from the unit that fits in a glovebox and inflates tires to the turbocompressor or giant reciprocating machines used extensively in pipeline service. Positive-displacement compressors are of 2 distinct types: the rotary types such as the rotary vane and helical screw, as well as the reciprocating types with the predominant piston style.
This post will focus more on reciprocating compressors, what it is, and why its installation relies heavily on the design. But first, a little background information.
Basics of Reciprocating Compressor
A reciprocating compressor refers to a positive-displacement mechanical and electrical device that uses a piston to easily compress gas in order to deliver it at incredibly high pressure.
These compressors are often some of the most expensive – and highly critical – systems found at production facilities. And for these reasons, they deserve lots of attention. This is because petrochemical plants, transmission pipelines, refineries, and several other industries depend heavily on this equipment.
Industrial facilities should expect varying reliability and lifecycle costs from their respective installations due to several factors, including – but not limited in any way to – the overall quality of the initial design/specification, operational factors, and adequacy of maintenance practices.
Numerous types of compressors can be found across a wide variety of industrial facilities. Some of the gases compressed by reciprocating compressors include:
- Oxygen, hydrogen, etc. for processing chemicals
- Air for powering air systems and compressed tools
- Light hydrocarbon fractions in refining
- Numerous gases are employed for transmission or storage, etc.
Reciprocating compressors are generally employed where high compression ratios – i.e., discharge to suction pressures – are needed in every stage with zero high flow rates while the process fluid is dry.
Importance of Foundation Design in Reciprocating Compressors
The importance of foundation design in reciprocating compressors cannot be overemphasized. This is because a highly satisfactory compressor installation, in most cases, depends significantly on how well the support structure or foundation was designed.
A deficient foundation design can cause excessive vibration, which leads to severe equipment damage. This is why it is never safe to cut corners on foundation design because considerable amounts of that money would be spent on high maintenance and costs linked with lost production.
As a result of the basic design of the reciprocating compressor, both its reciprocating and rotating masses generate inertia forces as well as moments that must be readily absorbed by the foundation and can’t be eliminated completed. The compressor manufacturer can choose to reduce the magnitude of these moments and forces by adding several counterweights to the crossheads without totally eliminating them.
Besides the imbalanced moments and forces, the foundation must be capable of absorbing the moments generated by the gas torque. The gas pressure forces create this torque as the reciprocating compressor goes through a revolution. The compressor manufacturer must offer the magnitude of the resulting moments and forces while the gas torques.
Foundation design engineers have found ways of using unbalanced moments and forces in their numerous design calculations. According to the most recent experience, when gas torques create moments, they considerably impact foundation design.
Excellent design practices, as well as highly detailed information for reciprocating compressor foundations and support structures, can be found in the titled: ‘Design of Structures and Foundations for Vibrating Machines’ authored by George Pincus, Suresh Arya, and Michael O’Neill.
It is possible to use finite-element analysis computer programs with dynamic simulation capability to evaluate the forced vibration response and natural foundation frequency for where foundations or highly complex offshore structures can be critical.
For high-speed reciprocating compressors installed in a region with enough soil capable of supporting a pickup truck, it pays to stick to the following rules:
- The weight of the concrete foundation should be up to 3-5 times – at least – the weight of the equipment.
- Concrete should only be poured into a very neat or clean excavation with zero formed side faces.
- It is typically far better to increase width and length instead of depth in order to meet weight requirements.
- For a design less than 50 percent of allowable static conditions, use soil bearing.
Types of Reciprocating Compressors
There are several options with reciprocating compressors, based on the particular application they will be used for.
- Single-Acting Reciprocating Compressor
A single-acting reciprocating compressor comes with a basic inlet valve as well as a discharge valve. Both valves are spring-loaded and one-way. The one-way inlet valve sucks in air when the piston moves downward, while the one-way discharge valve opens up only after enough external force has been applied.
Most single-acting compressors come with only one compression cycle for every crankshaft turn since valves can only be found right at the top of the cylinder. Single-acting reciprocating compressors are the most popular types of compressors and are employed for several reasons.
Single-acting reciprocating compressors are also incredibly affordable, especially when compared to other varieties of compression technology such as rotary screw compressors, etc.
- Double-Acting Reciprocating Compressor
Double-acting reciprocating compressors also come with inlet and discharge valves positioned at either end of the cylinder. This results in 2 compression cycles with every turn the crankshaft completes.
The design of double-acting reciprocating compressors – which rarely or mostly comes with less than 100 horsepower – makes it incredibly efficient. And this is why this type of compressor is highly prominent in the manufacturing industry.
However, this compressor’s power has an exceedingly large footprint that is not too practical, especially when space considerations are highly significant. Double-acting reciprocating compressors also create lots of vibration and generally require vibration isolation features or equipment. And the entire system must be set on a pretty solid foundation.
As you can see, the crucial importance of foundation design with compressor installation should never be joked with in any way.
When foundation design is inadequate, it may bring about severe damage to the equipment due to excessive vibration. Therefore, no expenses must be spared on foundation design effort so that lots of money will not be spent on high maintenance.
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