Date: Nov 08, 2016
By Mark Krisa, Global Air System Performance Leader, Ingersoll Rand® Compression Technologies and Services
How a facility manages its compressed air condensate influences operational reliability and, because of the hazardous waste contained within condensate, affects a plant’s impact on the environment because of the hazardous waste contained within condensate. It is important that compressed air systems have a condensate management network in place. Understanding the environmental factors that produce more or less condensate, the drain and piping systems, and identifying what condensate is made of are all integral to properly maintaining a compressed air system.
How condensate is formed and managed in a compressed air system
When atmospheric air is compressed, the amount of water that can exist in a vapor state is reduced, causing the surplus water to condense into a liquid. This water mixes with other airborne constituents consumed from the environment along with traces of lubricant/coolant from the compressor. The resulting emulsification is referred to as compressed air condensate.
The volume of condensate that is extracted from a compressor is based on the difference between how much water was present in the atmospheric air ingested into the compressor and how much water can remain in a vapor state at the temperature and pressure of the compressed air. Consequently, a compressed air system will generate more condensate on a hot summer day than on a cold winter day.
Identifying the appropriate condensate drain for an application
While there are a large number of drain manufacturers, there are only a few common types of drains for compressed air systems. Drains can be categorized as manual drains, timer based drains or capacity sensing drains.
Some low cost units can be sensitive to contamination and may fail easily due to obstruction. This needs to be considered during purchase, weighing both application conditions and degree of maintenance. One common issue to be cognizant of is the use of strainers installed ahead of a drain valve. Although in theory the strainer will collect larger particulate and protect the drain from failing due to obstruction, the strainers are often neglected and become clogged. It is important that if a strainer is installed, a manual valve and piping arrangement is also installed ahead of the drain to facilitate easy isolation for servicing and testing.
Proper piping to navigate condensate from drains to collection areas
Condensate piping must be configured to facilitate easy removal of every drain for service or inspection. A bypass should be installed on the discharge side of every drain to support testing the drain operation. This should include a tethered hose for systems to periodically test the condensate discharge rate using a scaled collection device over a fixed period of time.
The quantity of condensate removed from the compressed air system will change based on the volume of compressed air consumed and the ambient conditions. On a hot, summer day, a 100 horsepower compressor with a refrigerated air dryer can generate more than 45 gallons of condensate in an eight-hour shift. The same system during a subfreezing winter day would generate less than one gallon of condensate during a shift. Some maintenance programs may periodically measure the rate of condensate removal relative to operating conditions to establish a performance baseline. This data could be used to identify a deviation from the desired performance and facilitate a more prognostic approach to maintaining compressed air system performance.
It is a good practice to periodically test condensate for concentration of major constituents and pH level. This data can be helpful in troubleshooting quality issues associated with contamination. It is not uncommon to assume compressed air condensate as the source of contamination for a process related issue only to find that the actual source of the problem is a local airborne pollutant or lubricant. This is a common misdiagnosis in paint applications that can be very sensitive to silicone or hydrocarbons.
Identifying condensate properties and disposing hazardous waste
Compressed air condensate can be acidic or basic depending on the environment. This can influence the rate of material degradation or corrosion. Knowing more about the condensate properties is valuable when selecting materials for the compressed air system such as piping, plastic tubing, valves, and fittings. Condensate should be tested both during the summer and winter to account for changes in the concentration of water present in the atmosphere. When attempting to diagnose an issue associated with the presence of specific compounds in the condensate, sampling frequency may also need to account for wind and the ingestion of airborne contaminants from processes outside of the compressor’s intake. Depending on the chemical compositions of neighboring exhaust, temperature inversions may also be influential, causing an increased density of contaminants during morning hours when the ground is still cold and air temperatures start increasing.
Compressed air condensate is an emulsification of water, hydrocarbons and other potential airborne contaminants, therefore it is considered a hazardous waste and must be processed accordingly. Condensate cannot be discharged directly to a municipal sewage system and must be treated to reduce the concentration of contaminants to an acceptable level. Some facilities have a central wastewater treatment process that can treat the waste, but it is important to consider the cost associated with treating the condensate compared to other methods.
One alternative option is to use a condensate separation product dedicated to the air compressors to reduce oil from condensate down to an environmentally acceptable level. It is important to investigate details regarding the type of oil introduced into the condensate and the requirements to separate it from the water. Some oils will separate based on dwell time while others may require chemicals to separate the oil from the water. Some may choose a distillation type product that uses an electric heater to boil the water off as steam, leaving only the residual waste liquid to be processed as hazardous waste. For some installations, there is no access to a drainage system so the water from the oil/water separator is discharged through an exterior wall and allowed to pool in the soil. Unfortunately, the water is not pure and will typically still have low concentrations of oil. Over time, the water will evaporate leaving behind the oil and eventually enough oil will accumulate for the soil to be classified as hazardous waste, requiring costly disposal.
Having a condensate management process, key data about a manufacturing facility and awareness of temperature conditions give maintenance staff the opportunity to address a both a system’s performance and issues before there is a bigger problem. Proactively correcting condensate issues can help to reduce excess condensate carrying over into the network, saturating the piping system and contaminating production equipment. These factors will help facilities abide by hazardous waste regulations and optimize reliability of their compressed air systems.