Compressors are used for a number of purposes on remediation projects including:
- Operation of pneumatic pumps for groundwater extraction or chemical injection
- Air sparging or bio-sparging where compressed air is injected into the subsurface to remediate petrochemical saturated soil or impacted groundwater
- Ozone injection where compressed air is used to create ozone for injection
A number of parameters need to be determined prior to selecting a compressor for a specific purpose.
Some of the typical parameters are as follows:
- Pressure required
- Flow required at a specific pressure
- Moisture content allowed
- Hydrocarbon content allowed
- Outlet temperature allowed
- Noise level allowed
- Compressor runtime based on pressure and flow requirements
- Expected service life of compressor components
- Maintenance required
- Cost of maintenance compared to other suitable compressor types
- Power available to operate the compressor
- Material composition and friction loss of piping to be connected to the compressor
- Expected duration of the project
- Budget allowed for purchase
These days a lot of remediation projects are awarded based solely on the low bid. I remember a project we lost due to cost and the winning bidder had combined 6 small rotary vane compressors to create the required flow for the project compared to our one large, much more expensive, screw compressor. After about six months of operation the compressors began to fail but they got the project and we did not. So needless to say if you are going to use "or equivalent" in bids and make sure you are getting an equivalent performance for the expected project duration.
Air sparging is a very common remediation method that requires the compressor to run continuously. The projects typically require 6 months to 3 years to complete depending on the size and concentration of the plume. Rotary screw compressors have been the typical choice for these applications until the last decade where the rotary claws have become more popular. Reciprocating and rotary vane compressors typically do not hold up well under continuous run applications for long periods of time (years). Reciprocating compressors are typically used in small product recovery pumps systems where compressor run times are short.
There are some really good quality vane compressors but they cost a lot more than the dry carbon vane type I typically saw used on remediation sites. Their use would typically be similar to that of the rotary screw compressors.
Air outlet temperature is a concern for most air sparging applications. Air\air after-coolers are used to cool the air prior to going through the regulators, flow meters and low temperature manifold piping typically used on these projects. Oil mist and moisture are also a concern on most environmental applications. Water and oil coalescing filters are used to remove oil and water where oil flooded rotary screw or reciprocating compressors are used.
Oil less air compressors are available but typically do not last as long as oil flooded units. On short duration projects they may be fine and typically have lower cost. Some of the pros and cons of the compressors being discussed herein are presented below:
|Rotary Screw Compressor||
|Rotary Vane Compressor (Dry Carbon Vane Type)||
|Rotary Claw Compressor||
Remediation projects typically take longer to complete than early estimates predict. It is important to get good equipment from the beginning as O&M budgets seem to get used up pretty quickly and additional costs associated with equipment problems are likely not in the usual estimate. In this environment of the "low bid wins no matter what" make sure you specify quality equipment that will last the life of the project (when properly maintained).
In Part 6 we will discuss pumps. The pumps discussed will include centrifugal, diaphragm, progressive cavity, and liquid rings.