Many industries utilize air for production purposes like mixing, pressurizing, atomizing and agitating applications. Applications include oil and gas, food, pharmaceutical, etc. By managing compressed-air systems and controlling airflow in such scenarios, users can improves production efficiency by up to 50 percent.
|Figure 1. A newly installed air compressor|
Compressed air flows as a result of pressure differential. This implies that pressure drop is the major cause of insufficient airflow. To maintain adequate airflow, much attention should be focused on the pressure losses that are caused by obstacles in the compressed air systems.
Common Obstacles to Proper Airflow
Obstacles in a compressed airflow system alter the pressure of the flowing air. As the push to optimize production continues, it becomes imperative for production personnel to always identify and combat such problems.
• Air Quality: Air cleanliness affects the required airflow. Atmospheric air contains a large amount of airborne contaminants ranging from dust, dirt, water vapor, and, in an oil related industry, oil vapor in the form of unburnt hydrocarbons.
In many applications, dirt and dust particles can pass through the air compressor and gradually form deposits on the interior surface of the compressor. As these deposits accumulate, friction increases and the compressor losses it ability to generate the required head for airflow.
|Figure 2. The author adjusting cooling water in an air compressor system.|
While many operators are concerned about the risk of dirt and dust particles, oil vapor and water vapor in the air stream poses a problem. During compression, oil vapor and water vapor escape with the compressed air, and after compression the air is cooled in the interstage cooler, resulting in condensed vapors. If this condensate is not removed, it causes corrosion and blockage to the compressed-air systems, thus reducing airflow and production efficiency. To prevent this, filters must be properly located in the system, and an interstage cooler with automatic drain traps must be fitted into the air compressor.
• Air Compressor Type and Operation: The air compressor can also be an obstacle to air flow. Air compressors make use of lubricating oil for sealing and lubrication, and use cooling water (mostly applied) for cooling. During operation, cooling water and lubricating oil may seep into the compressed air as a liquid or aerosol. The resultant leakage causes similar contamination problems as the condensed oil and water vapors.
In addition, the type of compresssor also affects proper airflow. A turbine-driven air compressor, for example, utilizes more lubricating oil and cooling water for operation than an electrically driven compressor. This infers that a turbine-drive compressor is more susceptible to lubricating oil and/or cooling water seepage.
• Improper Configuration of Distribution Systems: The main objective of proper sizing and configuration of distribution systems is to transport the maximum expected volumetric airflow from the compressor to the point of use with minimum pressure drop.
Poor distribution system configuration can lead to insufficient airflow, and thus affect the discharge pressure, robbing the user of expensive compressed air power. This is not limited to the interconnecting piping from the discharge of the air compressor to the header. It also applies to the air storage system and the distribution line conveying air to production areas. To prevent this, international quality standards and guidelines must be strictly adhered to when sizing distribution systems.
Quickly diagnosing and correcting application issues will help ensure that small problems don’t become big ones. Thus, it is important to always keep in mind the old truism: “A problem identified is half solved.” Table 1 provides guidance on troubleshooting five common problems.
Nwaoha Chikezie has previously worked as an operator (student trainee) with Port Harcourt Refining Company (PHRC) in Nigeria, and is currently working on several research projects involving flow systems design, including an initiative with the Caribbean African Student Exchange Initiative (CASEI). As part of his research, Mr. Chikezie has authored a number of engineering articles in leading international journals. Mr. Chikezie is a member of SPE, ASME, AIChe, IMechE, ICE, IGEM and Nigerian Gas Association (NGA). He can be reached at +234-703-135-3749, or firstname.lastname@example.org.
For another “best practices” article with troubleshooting remedies by Nwaoha Chikezie, see “Increasing Heat Exchanger Performance” on page 30.