Archive for the ‘Gas Drying and Arresting’ Category
Gas Drying and Flame Arresting
Introduction
Effectively preventing a Flash-back event is of considerable importance for both your safety and to prevent damage to your equipment. Over the last two years we have invested considerable amounts of time, studying the flashback event to best understand how to prevent it in the first place and should it occur how to minimize its effect to ensure it is safely managed.
Background As a start, let have a look at some of the background information, so we can understand what were are working with. Firstly, lets look at the the flame speed.
Based on the research conducted by William Rhodes we know that the flame speed of this gas is:
SIX SEQUENCES: Recorded timing for 10 feet of tubing was consistent - 1.225 milliseconds = 10,000 ft in 1.226 seconds, or 8160 ft/sec div 1088 ft/sec (speed of sound not compensated for our 1150 ft above sea level) was mach 7.5
For those who have studied this gas closely know that this Propagation Rate is extremely fast, in fact 1000’s time fast than any other gas.
Secondly, in the absence of any other gases, meaning Hydrogen – Oxygen – Hydrogen in perfect ratio, like it is made, the gas collapses back into water creating a vacuum. Our experimentation has shown that this is a two stage process, where there is at first a large (sonic) expansion, then resulting in a vacuum.
Due to the Gas Propagation Speed, and the fact that oxygen is present with in the gas, hydrogen arrestors used with bottled hydrogen gas are unsuitable and too unreliable for use.
Water is one of the most effective way to prevent a flash-back, though this is dependent on the flame not being able to propagate between the bubbles. In order to maximise the drying effect, it is important to bounce the gas off as many edges as possible, similar to a labyrinth.
The more corners the gas is required to turn the dryer it becomes. As seen in the picture above, the gas is required to turn many times. Our testing showed that after five turns or level the gas would exit well dried.
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In this picture you will see how the gas is able to move through the water via connect bubble streams. |
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In the early investigation a coil arrangement was setup, which was partly filled with water. As the gas moved through the coil it carried a small body of water in front of it until the surface tension was broken, allowing the gas to move past. As the gas entered the coil it carried water in sections, providing a water barrier between each stream of gas. As seen in this picture the flame is arrested depending on where these stream was broken. Gravity was used to push the water back down the coil once it has broken away from the gas flow. From a design point of view this is very impractical for the following reasons:
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Building Gas Drying and Arresting Systems
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