Application Note: Using a Leister LHS Air Heater with Compressed Air

When is it Appropriate to Use a Compressed Air Supply?

​STANMECH typically recommends that Leister’s LHS air heaters be supplied with air by a blower. This is because a blower-based process heat system, when correctly sized and installed, will be far more energy efficient than an equivalent compressed air system. The associated cost-savings increase with the power rating of the heater—larger heaters require larger volumetric air flows resulting in more savings.
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However, when broken down to its basics, LHS air heaters simply require a consistent supply of air flow regardless of its source. As long as the system is capable of providing an uninterrupted supply of air that meets the minimum flow requirements for the heater, the LHS air heaters can be operated safely using compressed air. 

The top 4 reasons for using compressed air instead of a blower are:

• Footprint: While air compressors are typically much larger than the equivalent blowers needed for the LHS air heaters, they are also usually located much farther away from the point of use. Conversely, STANMECH recommends that blowers be placed as close as possible to their associated heaters. If space is severely constrained at the point of use, a compressed air supplied system may be the best option regardless of increased operating costs.
• Noise Levels: Air compressors are typically much louder than the equivalent blowers needed however, once again, they are usually located away from the point of use. If noise levels in the work area are a concern, it may be worth considering using a compressed air supply.
• Up Front Cost: Many facilities already have a compressed air system installed, if there is adequate capacity available there is very little additional cost up front for supplying air to a process heat system. Keep in mind that, due to the inherent energy inefficiency of compressed air compared to a blower, this will lead to increased operating costs over time. Any blower supplier should be capable of completing an ROI analysis for installing a blower to replace compressed air in your application.
• Alternate Gas Supply: It is rare, but some applications require the use of a gas other than atmospheric air (i.e., A clean room application may require the supply of Nitrogen or an inert gas). In these cases there is no alternative to using a compressed gas supply.

Best Practices for Operating a System with Compressed Air

Before operating a Leister LHS air heater with compressed air, there are two critical system details which must be verified.

1. Does the compressed air system have the required volumetric air flow capacity? Every LHS air heater has a specified minimum volumetric air flow for safe operation. It is critical that the compressed air system be capable of supplying this volumetric air flow to the heater sustainably and consistently. STANMECH recommends that the LHS air heaters only be operated on compressed air systems with capacity beyond the minimum requirement. This will ensure that air will be supplied consistently to the tool if another operation in the plant begins using compressed air while the heater is functioning.
   
   Additionally, if the heater is not being operated with closed-loop controls (See our article on Temperature Control of Air Heaters) it is important that the compressed air system is capable of supplying enough air to ensure the maximum operating temperature of the tool is not exceeded. LHS air heaters have a maximum operating temperature of 650°C.
   
   
2. Is the operating pressure of the compressor safe for the LHS heater? The LHS air heaters have a maximum inlet pressure rating of 100 kPa (14.5 PSI). If the compressor will produce air that exceeds the maximum rated pressure a regulator must be installed to prevent damage to the tool.

Once the above questions have been answered and any issues addressed, the heater can be installed into the system. There are Leister adapters available to make an easy compressed air connection to the LHS air heaters. However, non-Leister fittings/adapters are acceptable if they are rated appropriately for the pressure and do not restrict the volumetric air flow below safe levels.

In order to get the most out of the life of your tool, STANMECH strongly recommends the following:

• Clean Air: Compressed air is often contaminated by dirt, grit, oil, and water. Filters should be installed to minimize the amount of these contaminants that pass through the tool’s heating element.
• Proper Shutdown Procedure: A cool down cycle should be initiated prior to cutting off air to the tool. Power to the heater must be switched off while the air flow continues until the exhaust from the heater reaches the ambient temperature. Failing to properly cool the heater can not only damage the heating element due to thermal shocking, but in some cases the heat can back up into the housing and damage the circuit board as well. The length of the cool down cycle required will be dependent upon the operating temperature and the volumetric air flow. If uncertain, a 5 minute cool down cycle is usually adequate.
• Consistent Air Flow: It is imperative that the heater never be operated when there is no air flow. A safety should be put in place to turn off power to the heater immediately should the air compressor fail to provide the required minimum air flow. Residual air from the compressor tank should be allowed to continue to flow through the tool to act a makeshift cool down cycle.

If you have any more questions about operating your LHS heater with compressed air, please contact STANMECH Technologies Inc. Our experts will be happy to discuss your application in detail.