|Content Type||Conference Paper|
|Title||A Multi-Discipline Approach to Closed System Treatment|
|Authors||Darrell Hartwick, Don Hutchinson, and Mylene Langevin, Buckman Laboratories|
|Source||CORROSION 2004, March 28 - April 1, 2004 , New Orleans, La|
|Copyright||2004. NACE International|
|Keywords||cleaning, closed system, filtration, glycol, molybdate, nitrite.|
Traditionally, closed system treatment programs have involved adding corrosion inhibitor and periodically testing for the residual. However, to be effective, these treatment programs must also include cleaning (either prior to being put into service or to remove existing corrosion products) as well as monitoring. The systems being protected are generally of very high value and a comprehensive program, which assesses everything from pre-commissioning to ongoing performance, must be considered. This paper will discuss the various aspects that should be evaluated as part of a closed system treatment program.
Hot and chilled (closed) water systems are found in many applications, ranging from space heating in commercial and industrial sites, to residential applications, as well as providing cooling at these same sites. Closed loops frequently receive little attention from the water management team, in spite of the fact that their failure is potentially more inconvenient and costly.
Before beginning a discussion of the various aspects of a closed system treatment program it is worthwhile to examine the different roles of closed loop systems.
As the name implies, hot water loops provide heat to manufacturing processes or simply to warm an area. In order to get heat into the water, boilers (or other controllable sources of heat) are used. While both fire-tube and water-tube boilers are employed in this application, the most common type of boiler remains the fire-tube type. Although, over the past decade, small, high efficiency watertube boilers have gained a significant portion of the market. Regardless of the boiler type, they can suffer corrosion damage, and to a lesser extent, scaling.
While most people assume that closed systems are free of oxygen, the reality is that they contain varying amounts. In a loop with low make-up, the only source is from in-leakage of air (around seals, etc.) and corrosion rates can be low. However, in systems where there is a significant amount of make-up, or poor air removal, the problem can be very severe. The presence of oxygen and temperature speeds up the corrosion processes and this can result in the formation of considerable amounts of sludge, which in turn can lead to reduced efficiency and equipment damage, as it settles out in low flow areas, such as the boiler.
It is worth noting that there is not a single specific temperature that hot water circuits operate at. The temperatures can range, from as low as 50ºC (120ºF) to those that run as high as 150ºC (300ºF) but, typically are between 80ºC - 85ºC (175ºF - 185ºF). Hydronic, or radiant heating, designs are becoming very popular in residential applications for both heating and snowmelting, and normally work at much lower recirculating water temperatures, i.e. 50ºC (120ºF) to 82ºC (180ºF). It is common for properly designed hydronic loops to operate in the 43 to 60ºC (110 - 140ºF) zone, while for snowmelt systems the temperature range is at, or below, the bottom end of the hydronic heating range.
If hot water systems are given little consideration, chilled water circuits receive even less attention, although their importance has increased as the number of electronic devices in the typical office has boosted the heat load in the work environment. At the same time, employees have come to expect comfortable working conditions, which have further expanded the demands on chilled water loops.
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