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Air vs. Steam Atomization Part 4 – Atomization Reliability

Posted on August 8th, 2017 by in Chemical Manufacturing Excellence

Air-Steam-Atomization-4

Previous posts discussed sustainability as related to process control, the incineration process and the atomization process, whereby discussion indicated that it might make sense to atomize with air instead of steam. However, the plant air compressor motor operates continuously at full speed while the compressor regularly loads and unloads to maintain sufficient air pressure in the plant air receiver located downstream of the compressor and plant air dryer. It is desirable to atomize using hot compressed air from the compressor discharge, which is upstream of the final air compressor cooler. However, the pressure at this location varies from full pressure (when the compressor is loaded) to effectively zero pressure (when unloaded). This wide pressure variation is unacceptable for continuous incinerator operation.

The existing control strategy loads the compressor when the plant air receiver pressure falls below a certain pressure and unloads when it reaches a higher pressure. This causes the pressure in the plant air receiver to rise and fall with each loading and unloading cycle. Another alternative is to install a variable speed drive to reduce the speed of air compressor – effectively reducing the capacity of the air compressor and forcing the air compressor to remain loaded. This can be done by controlling the plant air receiver pressure by varying the compressor motor speed. As a subtle point, controlling the plant air receiver pressure near its lowest acceptable pressure will tend to reduce the electrical energy consumption required to produce plant air while still maintaining an adequate air supply.

That problem resolved, the incinerator cannot fully rely on atomization air, because there is always the possibility of an occasional upset that causes the air compressor to unload. This eventuality can be addressed with appropriate interlocks to valves that switch between air and steam atomization but fail-safe to steam atomization, which is usually more reliable. A double block and bleed arrangement (with check valves) would likely be appropriate to ensure that steam never reaches the air compressor where it can cause damage.

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All opinions shared in this post are the author’s own.

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