[Q&A] 2017.7.18

For heat exchangers that have not been used for a long time, perform purging and unflanging； Slightly open the material bypass line to maintain material flow ；

1. All cooling water heat exchangers must be supplied with cooling water regardless of whether they are in use or not, and the supply must not be interrupted. The upper and lower bypass valves are slightly open. 2. A small amount of steam is supplied to all unused steam heaters, with the condensate being continuously drained via drain lines. 3. For heat exchangers that are not used for a long time, the medium inside them should be emptied.

1. All cooling water heat exchangers must be supplied with cooling water regardless of whether they are in use or not, and the supply must not be interrupted. The upper and lower bypass valves are slightly open. 2. A small amount of steam is supplied to all unused steam heaters, with the condensate being continuously drained via drain lines. 3. For heat exchangers that are not used for a long time, the medium inside them should be emptied.

Water-side protection measures include: ① It is recommended to install a filter on the inlet pipeline to remove impurities larger than 1 mm； 　　②Flow switches or pressure/differential pressure sensors are installed on the water inlet or outlet pipelines to shut down the compressor when the set values are not reached ； 　　③Temperature sensors are installed on the inlet or outlet pipes; a value of >7°C is set for the inlet pipe, or >2°C for the outlet pipe – the compressor shuts down when the temperature falls below these values. 　　Protection measures on the refrigerant side include: ① Installing a hot refrigerant vapor bypass valve between the compressor exhaust pipe and the evaporator inlet pipe; this valve opens when the evaporation temperature drops to a certain value ； 　　②A suction pressure control valve is installed on the compressor’s suction line; when the evaporation temperature drops to a certain level, this valve closes, thereby preventing the evaporation temperature from dropping any further ； 　　③A condensation pressure control valve is installed between the condenser and the receiver; when the condensation temperature drops to a certain level, this valve closes, causing the condensate to accumulate in the air-cooled condenser and thus occupying the condensation area, which in turn raises the condensation pressure.

For a properly operating plate heat exchanger, there is no need to consider anti-freezing measures; it is sufficient to ensure that proper insulation is in place in order to maintain the heat exchange efficiency； For the deactivated plate exchangers, it is required to empty the contents and fill them with nitrogen to a slight positive pressure. For other condensers that are out of service, the heat exchange medium should be completely drained, the unit should be disconnected from the system, and nitrogen should be introduced for protection.

With a slight recirculation flow, normal operation is usually fine; there’s no need to shut it off, drain it, dry it out or install a blind flange

1. Add heat tracing, 2. Maintain circulation； 3. Improve insulation

Increase the flow rate of the cold medium; drain the liquid from the drain when it is shut down

If not in use, drain the medium completely; if in use and prone to freezing, ensure proper insulation and heating