Cooling water systems are designed to cool an installation in the event of a nearby fire. This can be necessary if the contents of a tank or pressure vessel are likely to expand with heat.
The National Fire Protection Association (NFPA) has drawn up several standards. Examples of these are: NFPA-11 (Low-, Medium-, and High-Expansion Foam Systems) NFPA-13 (Installation of Sprinkler Systems) and NFPA-15 (Water Spray Fixed Systems for Fire Protection). These standards provide requirements for such things as piping systems, support spacing, area coverage and spray density. In this context the spray density is the amount of water required per surface area per minute.
Generally, a cooling water system will consist of a pump that provides the necessary water, a piping system, and a collection of deluge nozzles (sprinklers). A good design ensures that all the required surface area of the vessel are wetted with sufficient water. This involves a selection of nozzles with a sufficient coverage and capacity. On vertical vessels (and the upper half of horizontal cylindrical or spherical vessels) a certain amount of area can be covered by water running down. The NFPA-15 standard does set limits to how far the nozzles can be spaced when relying on rundown.
Modelling and Hydraulic Calculation
We can use BOSfluids to perform hydraulic calculations of steady state flows in a cooling water system that includes many deluge nozzles (sprinklers). BOSfluids includes a deluge nozzle element that can be used to model the sprinklers. Setting up a steady state flow model is easy and because of the 3D modelling, effects such as pressure loss with height and in bends are automatically accounted for.
With the newly introduced Flood-and-Drain module, it is now also possible to perform a dynamic calculation of the forces involved in filling such a system. With such a surge analysis, we can ensure that a cooling water system doesn’t get damaged due to the dynamic forces when it’s first turned on.
All in all, creating a cooling water system design involves many different choices and possible solutions. DRG can help you achieve an optimal design according one of the many applicable safety codes or standards.
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