API RP 520 provides guidance for blowdown design arrangements. The temperature of blowdown liquids has to be considered when selecting the materials for a blowdown system to avoid undue thermal effects. Similarly disposal to an open pit poses the hazards of exposed combustible liquids and gases. A blowdown to a tank is generally avoided since entrained gases, or failure or undersized relieving devices, may cause the tank to rupture. The blowdown could be routed to storage tanks, an open pit, burn pit, another process facility, or the pressurized sewer. Ideally liquid blowdowns should be routed to facilities that are specifically designed to handle large quantities of liquid materials. A liquid release out of the flare may result in a flare out, and if the flare is elevated, a shower of liquids on the process facilities can result. A liquid blowdown should never be sent the facility flare that is designed to only handle gaseous materials. Blowdown is similar to depressurization but is relevant to liquids instead of gases. Nolan, in Handbook of Fire and Explosion Protection Engineering Principles (Second Edition), 2011 12.3 Blowdownīlowdown is the removal of liquid contents of vessels and equipment to prevent its contribution to a fire or explosive incident. This constantly measures the level of solids in the water and instigates an automatic variable blowdown on a continuous or intermittent basis. The third and most automatic system is the conductivity-controlled blowdown. Again, regular checks need to be carried out to monitor the quality of water in the boiler. It is necessary for water quality to be checked frequently and the rate of continuous blowdown adjusted as may be found necessary.Ī second method is a time-controlled valve allowing regular intermittent blowdown of the boiler. The simplest is a preset continuous blowdown valve to maintain a suitable water quality in the boiler. On medium and large plants additional systems are employed. On small boilers the required operation of the main blowdown valve may be sufficient to control the quality of water within the boiler. E Walker CEng, BSc, MIMechE, R J Blaen, in Plant Engineer's Reference Book (Second Edition), 2002 10.16.3 Blowdownīlowdown on a boiler is mandatory.
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