Hazards of Water in Refinery Process Systems

A similar incident involving steam condensation was reported in the Hazard of Water in Refinery Process Systems [6], where the caption on a photo of a badly damaged tank states, A vacuum vent and one open hatchway was not enough to prevent damage when steam condensed and pulled in the top two courses of this 35 ft. diameter by 21 ft. high wash tank. ... 

Standard Oil Company (Indiana), Hazards of Water in Refinery Process Systems, Chicago, 111.,... 

The Hazards of Water in Refinery Process Systems booklet [IJ states that confined water will increase 50 psi (345 kPa) for every degree Fahrenheit in a typical case of moderate temperatures. In short, a piece of piping or a vessel that is completely liquid-full at 70° F and 0 psig will rise to 2,500 psig if it is warmed to 120° F. This concept is displayed better in Figure 3-8. 

The Hazard of Water in Refinery Process Systems [6] illustrates the benefits of a vapor space with increasing temperature of water. If water is confined in a piping system with a vapor space, and then heated, the pressure rises more slowly until it becomes too small due to compression or disappears due to the solubility of air in water. If a simple water system piping has a vapor space of 11.5% air at 70°F (21°C) and atmospheric pressure (0 psi or 0 kPa), if it is heated to 350°F (177°C) the pressure will rise to 285 psi (1954 kPa) with only a 1.2% vapor space remaining. Pressures shoot up in the next 20°F as the vapor space compresses to near 0%. 

Another means of protecting against the explosion hazard in flammable atmospheres is to employ gas detectors. The principle is that the gas detectors detect flammable gas/air mixtures at a low percentage, typically 10%, of the LEL and cause an alarm to sound. If the concentration reaches 25% or so of the LEL, the system automatically initiates a shutdown of the process. This type of technique is commonly used in process plants such as oil and gas refineries, LEG storage tank farms, chlorine doping rooms in water treatment plants, and on vehicles such as electric fork lift trucks operating in Zone 1 and 2 areas. 

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