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21 Oct The Introduction of HTF Expansion Slot and Setting Regulations

The expansion slot is the most multifunctional device in HTF heating system. Understanding the function, design, installation and use of expansion slot plays a critical part in the long-term stable operating of the system.
The expansion slot is primarily a safety device that can prevent the overpressure of heating system due to thermal expansion of HTF. There are seven functions of expansion slot presented as follow:
1. HTF will expand in volume as heating temperature increases, and the function of expansion slot is to contain the extra fluid resulted from volume expansion. HTF then expand, slow down and reside in the slot, and that is why it is called expansion slot.
2. The expansion slot can re-supply appropriate amount of fluid to the system when the quantity of fluid is inadequate due to HTF leaking and low boiling substance steaming during operation.
3. The expansion slot can act as exhaust slot to release the gas generated during dehydrating, boiling fluid and high-temperature operations.
4. The expansion slot also can be the nitrogen seal slot for some specific systems.
5. The expansion slot is installed at the top of heating system and replenishes the pressure head. It can let the suction inlet of circulating pump have quite fluid column pressure and avoid cavitation.
6. The cold fluid in expansion slot can replace the hot ones in heating furnace under the emergency condition of power outage. The cold fluid absorbs and cools the heat from furnace to protect furnace and avoid overheating of fluid film.
7. Fluid can be filled into expansion slot and then flow to heating furnace and system. Expansion slot functions as intermediary slot in this case.
Important setting regulations for multifunctional expansion slot:

A. The volume, pressure, liquid level and temperature of expansion slot

Volume: The volume capacity of expansion slot should be at least 1.3 times the expanded HTF volume after being heated to the highest possible temperature. Systems without emergency power supply unit need bigger slots that have more room for cold fluid to absorb and cool the furnace heat under the condition of unexpected power outage.
Pressure: The design pressure of expansion slot should at least be 0.6MPa.
Liquid level: At ambient temperature the liquid level of filling fluid should be at 1/4 of the overall height of expansion slot liquid level, and the liquid level of fluid is better between 1/4 and 3/4 of the overall height under the operating temperature. Glass liquid level meter is not allowed.
Temperature: The expansion slot should not be thermal preserved, and its temperature should be controlled under 70℃.

B. There are HTF inlet, outlet and connector at the bottom of expansion slot and noncondensable gas inlet, nitrogen inlet and vent pipe outlet at the top. There are overflow holes on the upside, which should not be placed higher than the highest liquid level. The expansion slot should also have temperature, pressure, liquid level meter connector, liquid level warning device connector and manhole.

C. The expansion slot should be installed at the highest position of the entire heating system, and its bottom should be higher than any of the heating devices and leaves at least a 1.5M leeway above the highest point where transport pipes are. It cannot be installed right above the HTF furnace to avoid fire hazard caused by overflow.

D. At least one of the expansion pipes connected to slot should not have valve. The diameter of pipes should comply with the design requirements and should not be narrowed. The angle of bend should not be less than 120° when expansion pipes need to bend.

E. No matter what type the HTF is, expansion slot should be filled with nitrogen at some pressure level or other inert gases to lengthen HTF service life and prevent it from oxidative deterioration .

Dear customers, if you have any other questions about expansion slot, please contact Schultz Chemical (Shanghai) Co. Ltd. It is Schultz’s promise that our technicians will answer all your questions in detail and provide you with technical support.