Hot Oil Systems

The systems using heat transfer oils with boiling temperatures between 260 ° C and 390 ° C are called hot oil systems. It is preferred in areas where high operating temperatures are needed such as chemical industry, drying and cooking.

The most important factor in the preference of hot oil is that other systems require high pressures to reach the same temperature. In hot oil systems, the pressure at the top is about 1 bar. In this way, the security measures required by other high pressure systems are minimized.


Matters To Be Considered In Hot Oil Installation

  1. Thermal Oil Expansion Tank:

It should be at least 1/3 of the oil volume in the hot oil boiler serpentines and the entire installation, that is, the entire moving oil volume except the expansion tank.

= (Installation + Boiler Serpentine Volume+ Degasser) X 1/3

  1. Reserved Thermal Oil Tank:

It should be at least 1.5 times the volume of the entire oil except the reserve tank in the hot oil system.

= (Installation + Boiler coil volume + Degasser + 1/2 Expansion Tank) X 3/2

  1. Thermal Oil Circulation Pumps:

It should be a steel cast horizontal type pump, specially designed for high temperatures, preferably with an oil or air cooling system, keeping the oil speed in the range of 2.5-3 m / sec and always turbulent the oil flow.

  1. Thermal Oil Filling Pumps:

Gear, manual or electric pumps selected according to the viscosity of the thermal oil at room temperature should be used.

  1. Armature and Fittings Group:

Steel casting or nodular cast iron equipment should be used, preferably PN25 or higher class, resistant to the maximum temperature value of the hot oil boiler.

  1. Filters:

It is an equipment that should be used in the installation to keep foreign substances carried with the oil. It will not bring much resistance to hot oil movement, its surface should be large and cleanable. It can be operated safely by placing a manometer at the entrance and exit.

  1. Thermal Oil Level Indicator:

It is absolutely necessary to see the expansion that may occur in the system and must be in a structure suitable for the characteristics of the oil and the temperature of the oil in the expansion tank.

  1. Piping and Pipe Fittings:

It is an indispensable part of the hot oil installation, these parts should definitely be at or above the P235GH standard of steel drawn boiler pipe. Alloy steels should be preferred for temperatures above 300 ° C.

Cast pipe parts should never be used due to their fragility.

The piping should be inclined properly and an air discharge pipe and valve should be placed in places where air can be collected. The entire installation should be insulated with min 50mm thick rock wool.

  1. Equipments:

The necessary equipment in the hot oil installation for safe and controlled operation are as follows;

* Burner start-stop thermostat;

It is a temperature stimulator that turns the burner on or increases the power level in case of a rise in the oil temperature of the hot oil boiler, which we set the working and stop temperature of, the burner is reduced or stopped.

* Maximum temperature thermostat;

In cases where the temperature of the hot oil rises due to unnoticed reasons, for example, the pump is stopped, the oil is blocked, if the differential process is not equipped with a warning system or does not work, the temperature of the stationary oil will rise suddenly. The maximum temperature thermostat is a necessary safety equipment as it will strengthen the safety chain and prevent both the burning of oil and possible damage.

* Differential process in low pressure process or flow control automatic;

When the oil circulation slows down or stops, they switch the burner off so that the stagnant oil in the coils does not burn. Thus, the burning of thermal oil with high economic value is prevented.

* Expansion tank lower level electrode;

When the oil level drops to a critical level, the pump will not be able to make air, the turbulent movement of the oil will not continue and the partially stationary oils will burn and lose their properties, so it first cuts off the electricity of the burner and rings the warning alarm. At this moment and after that, if the temperature of the thermal oil is above 90 ° C, the pump continues to operate, if the oil temperature is at or below 90 ° C, the pump stops with the burner. After controlling the system gain, it protects the system elements and the facility by not allowing the system to work until it is added to the oil.

* Flue thermostat;

When the oil circulation stops for any reason and the burner continues to operate, the rising flue gas temperature cuts off all the electricity in the system except pump automation, ringing the alarm. The system can be restarted if the gain takes the necessary precautions and the warning source eliminates the fault.

  1. Thermal Oil to be used in the System:

Industrial oils that are made of mineral oils that do not deteriorate at high temperatures and that do not deteriorate in time at high temperatures should be used. The operating temperature of the oil to be used in closed systems must be at least 10% above the safety temperature of the boiler.

  1. Expansion Tank:

It is the only area where the thermal oil in the system meets the air. In order to prevent oxidation, the temperature of the oil in the tank should not exceed 75-80 ° C. The design of the system should be made in accordance with this temperature limitation. The expansion tank should be vertical type and should be placed out of operation at a certain extent from the highest point of the installation in a way that does not interfere with the discharge line.

The expansion tank should not be isolated, it should be protected from severe cold by building a closed enclosure section against the possibility of frost, and it should be ensured that the oil does not fall below the flow temperature limit (-5 ° C to -10 ° C) with the electric resistance heater that is automatically activated.

Connection of the expansion tank and the installation; It is best to make it at least 1 1/2 “or 2” after the degasser before the suction of the circulation pump.

  1. Thermal Oil Storage Reserve Tank:

Reserve tank; It should be placed at a depth where all the oil in the installation will be discharged with natural flow. There should be a level gauge above the reserve tank. Oil should be pumped into the system from the lowest point with a hand pump or gear pump. An air release valve should be placed in places where there is a possibility of air retention in the system, and care should be taken that these are open during filling.

  1. Tube Elongation:

It is important to consider the elongations that may occur in the pipes in the hot oil installation due to high temperatures. Due to the high temperature difference, the elongations should be calculated clearly and compensators of suitable type and characteristics should be placed at the relevant points.

  1. Air Evacuation Installation:

It is made to evacuate the steam and gas collected at the top points of the system. It should be done in order not to cause injury in possible hot and steamy gas outputs.

15. Making Divisions:

In order to discharge all oil and other substances in the installation when necessary, a blowdown installation should be made at the lowest point suitable for the device or installation.

  1. Hot Oil Boiler Rooms

It must be separate from the main building, independent and built on the ground. It must have an emergency exit door other than the entrance door. It must have ventilation ducts and systems suitable for the needs and capacity of the combustion unit. In the case of using natural gas, a gas leak detection device is required.


The boiler room should have lower air ducts for fresh air intake that will provide more air input and output than the combustion air required by the combustion unit, and upper air ducts where the dirty air can easily exit.