There are many choices to consider when looking to buy a new compressor for your industrial plant. The most common choices are reciprocating compressors, screw compressors, and centrifugal compressors. The best choice depends on the size of your facility and how you use compressed air.
If you have a very light compressed air load—and don’t operate many hours—then the simplest and most cost-effective solution might be to purchase reciprocating compressors. These units run start/stop, so they only cost you what you use, and if properly sized, the maintenance costs are minimal. But, they are typically suitable for only light loads with the occasional peaks. These compressors should not be run at high duty cycles, otherwise they will overheat and fail. As well, the air drying must be sized carefully to ensure the hot compressed air they produce doesn’t overwhelm the drying equipment.
If you have a fairly constant load for many hours at a time, with flow reductions due to breaks, such as lunch and coffee times or lighter evening and weekend load, then a system of screw compressors might be your best bet. These compressors can run fully loaded for hours at a time, but turn off during lighter loads, if set up correctly. You may choose between lubricated or oil free—this depends on your air quality requirements. Sometimes industrial processes need compressed air that is free from lubricant contamination … in this case, oil free compressors may be the proper selection. Screw compressors come with different control modes, with modulation being the least efficient. Various other control modes, some more energy efficient than others, reduce the power consumption of screw compressors at part loads. These can be variable displacement, load/unload, and variable speed. It is wise to consider which of these is the best fit for your facility. Sometimes outside help is required to determine the best fit.
For large industrial sites with constant high flow requirements, centrifugal compressors may be the best choice; these units are most suitable for base loading, constantly supplying high flows to industrial processes. These compressors are lubricant free and occupy a smaller footprint per kW than screw compressors. Often, however, the maintenance requirements and rebuilding costs are significantly more expensive than lubricated screws, however. Also, if these compressors must part load, due to a turn down of the flow, they might blow off and become very inefficient.
As you can see, there are many choices depending on your circumstances. In all cases, you should consider bringing in a specialist to help you make the right choices. Measurement of your system will help you properly size your system, your load characteristics and help determine what is right for your site. Most compressed air suppliers have some expertise available to help you with this, if you need assistance let them know.