Consultant - Screw compressor

With increase in automation across industries, the need for compressed air in the industrial sector is also increasing - and this dependency will only grow, going forward.

Having said that, the need for compressed air are many, based on various application in several industries.

Selection of the right compressor can be a daunting challenge with several technologies and options available in the market. In this article, we attempt to simplify the process of selecting the industry's most widely used air compressors; reciprocating and screw compressors for any given application.

But remember, when in doubt, always reach out to our Compressed Air Experts!

Factors to consider when selecting an air compressor:

• Quality of air
• Capacity of the compressor
• Duty cycle & utilization

Quality of Air

Industrial compressors have oil as the medium that cools, lubricates and seals gaps between the moving parts. As a result of this, compressed air is exposed to the oil and a part of it is carried over.

In specific applications, compressed air comes in direct contact with products such as food and pharma, this is where oil free air is preferred.

The quality of air based on the amount of this oil carried is represented by ISO 8573:2010. Class 3 allows for < 1 mg/m3 of oil carry over and a higher quality can be achieved through downstream filtration equipment.

Depending on your application requirement, the selection of the air compressor will vary.

Capacity of the Compressor Required

The capacity of an air compressor is a function of volumetric flow of air and the pressure to which it is compressed. This also determines the power rating (typically in kW or HP) of the air compressor.

Eg. A 22 kW (30 HP) air compressor can provide a flow of about 140 cfm (3.96 m3/min) at 7 bar g. (102 psi) pressure.

Few ways to determine the capacity requirement of a plant is through the OEM recommendation, past equipment experience or through air audit. Air audits enable companies to get valuable insights into their plant's compressed air utilization.

ELGi's air audits chart out a customized and comprehensive energy management plan for your needs. Reciprocating compressors are well suited for flow below < 50 cfm and for higher flow capacities, screw compressors are better suited, when comparing the two technologies.

Duty Cycle & Utilization

Duty cycle refers to the time a compressor is expected to run in a given hour at full capacity. Reciprocating compressors are designed to operate between 60-80% duty cycles and screw compressors are designed to operate at 100% duty cycle.

Life cycle cost of a compressor constitutes Initial Cost + Maintenance Cost + Energy Cost

(In a screw compressor, energy cost contributes to over 75% of the life cycle cost over 10 years' operation time).

It is critical to understand the life cycle cost of a compressor before making the purchase decision.

For more understanding on the life cycle cost of a compressor, refer to: https://blog.elgi.com/knowledge-center/identify-the-real-life-cycle-costs-of-your-air-compressor/

The amount of time a compressor runs in a day influences the energy cost. While looking to select a compressor with optimal life cycle cost, follow these guidelines:

• When utilization is < 4 hours/day select a reciprocating compressor
• When utilization is between 4 and 8 hours/day, a belt driven screw compressor is preferred
• When the utilization exceeds 8 hours/day, a direct driven screw compressor is the best fit.

You can also use the product selector on our website, to match the products for your requirements.