Line freezing

Absolute prevention of line freezing can be obtained only when the dew point of the line air is below any temperature to which it may be exposed. Freezing is always possible if there is line condensation. For example when air lines are run outdoors in winter weather or pass through cold storage rooms, the ambient temperatures will change the dew point and cause any moisture in the air to condense and freeze. 

If a firewater line needs to be temporarily isolated and an isolation means is not available on the immediate portion of the system needing work, a unique solution is to use a liquid nitrogen low temperature coil line freezing apparatus. This mechanism causes an ice plug to form in the line, effectively sealing the line from leakage, during the period the temporary isolation is needed. 

Figure 3.2 Variation of fluidized bed freezer capacity with bed depth (solid line = freezing capacity, broken line = mass per unit power consumption). Adapted from Persson, ASHRAE Journal, June 1967. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., www.ashrae.org.

Maintenance Considerations Equipment Inspection Premodification Periodically in Service Trip and Alarm Testing Maintenance Procedures Specialty Contractors Line Freezing Hot Tapping or Stopple On-Stream leak repair... 

The drains after the dump valve should be heat traced. The water content is high, and with a high acid gas content, these lines freeze easily. As we have seen, hydrates readily form in acid gas mixtures. 

Additive to prevent carburetor icing and gas line freeze... 

Because spontaneous evaporation into a dry atmosphere causes cooling of the remaining water, the damp clothes on the washing line freeze in cool weather, and early peoples were afforded the equivalent of modem refrig-eration. The early Egyptians, living in the exceptionally dry desert air, were probably quite familiar with ice manufactured by this method. 

For removing water floating on a chlorinated hydrocarbon bottom layer, two or three drain valves at easily accessible positions should be provided. The valves should be fitted close to the tank sides to avoid the danger of the drain lines freezing up. Product tanks should be fitted with pressure-vacuum valves and with self-closing dip and sample hatches. 

Frost line (freeze line) n. In the extrusion of blown film, a ring-shaped transition zone of frosty appearance located at the level at which the film reaches its final diameter and is changing from melt to solid. 

Ice is obviously hazardous in a day-to-day sense because it can cause people to slip and fall. But ice (and ice compounds) can also be hazardous from a process point of view. Particular concerns are to do with line freezing and hydrate formation. 

The sample line is not winterized (sample line freezes during water batching or when the sample flow is shut ofO. 

---