Process Engineering Beginner's Guide

CHAPTER TENEXTRACTING WORK FROM STEAM

In 1968 I was working for the long since forgotten American Oil Company in Texas City on their Delayed Coker. To cut the coke out of the giant coke drums, a high-pressure water drill stem was slowly lifted by means of an air operated motor. The source of the air to turn the motor was the plant air system. Plant air was about 60 psig and ambient temperature. The plant air, having done its job of spinning the turning motor, was exhausted to the atmosphere. The thing I noticed about the air lift motor was that it was iced over. Now this was Texas City in July, not the Arctic in December. It was 90% humidity and 95°F. Why the ice?

Did you know that the fundamental nature of the universe is hidden from us? For example, the energy that drives an air motor does not come from the pressure of the air. It can’t! Because low-pressure air contains more energy than high-pressure air, if the air is at the same temperature at both pressures, and if the air is not moving! Meaning, there’s no kinetic energy stored up in the air.

For the molecules of air to move further away from each other takes energy – potential energy. Does that mean that if we allow air to expand from a little box at 60 psig into a big box at two psig, the larger box will be colder? It certainly will. Maybe that partly explains why the air motor in Texas City got cold. But it certainly does not explain where the energy came to spin the motor.

The energy to spin the lift motor came not ...