Typical industrial heating systems use water or steam as a heat carrier. But, at higher temperatures, both steam and water need high operating pressures. This may not always be desirable from an installation or safety standpoint.
Because the piping system requires more thickness that increases weight and thermal stresses. It needs special manufacturing techniques and safety procedures. This increases costs.
When considering industrial heating systems where high-temperature process output is required, maintaining high-temperature is important.
Liquid heat transfer medium has a definite advantage here. High-temperature levels can be maintained using synthetic heat transfer fluids or heat transfer oils without increasing operating pressure.
The heat transfer oils are capable of withstanding very high temperature. Organic thermal oils can operate in temperature up to 6000F and some synthetic heat transfer fluids can even go up to 8000F. The thermal fluid used in heat transfer could be glycols or specially designed oil and high operating temperatures are easily achieved at quite low operating pressures.
Thermal oil boiler heat exchangers use such liquid medium or thermal fluids for heat transfer. A thermal oil boiler fires through a helical coil and generates energy from the hot products of combustion by heating the coil through radiation and convection.
The coil heats thermal oil or fluid that is pumped through the thermal oil boiler. The thermal oil heats coils in various types of heat exchangers. Unlike a water or steam boiler, this heating process of oil boiler heat exchangers does not heavily pressurize the system.
Components of Heat Exchanger Systems
Operating heat exchanger systems is not difficult if the components of a system are understood, how to start-up & shutdown the system properly and general operational procedures.
System components and their function - The system is made up of …
- A pump that pushes the heat transfer fluid through an insulated piping system to a heater to the processing equipment.
- A piping system that carries the fluid from one location to another in the most direct path. These could be rigid or flexible, made of steel, copper, aluminum or brass pipes depending on the type of thermal fluids used
- There is an expansion tank on the system to allow for the expansion of the hot oil as it gets hot and contraction when the hot oil is cooled.
- Filtration units to remove particles from the system, some systems have in-line or sidestream (preferred method) filtration units. The in-line filters 100% of the flow, where the side stream takes 10% or less of the system flow rate.
- Heaters which are classified by the amount of BTU produced per hour and the fuel that is used to generate the heat such as electric, gas, oil, and wood.
Operation Procedure
A. Start Up
1. The system pump is started to get the fluid flowing through the system.
2. Once a good flow is ensured, heat is applied in increments. The reason for this is to ensure that a turbulent flow is maintained through the heater (where the hot oil can remove just as much heat as the heater can supply to the coil in the heater) so that there is no thermal cracking of the oil. The increments are continued until the heat transfer fluid gets to a viscosity of 10 cP (centipoise) or less.
3. Once the heat transfer fluid is 10 cP or less, the heater can be dialed to the required operating temperature.
B. Shut Down
1. The heater is turned off
2. The pump continues to circulate the heat transfer fluid to remove any residual heat that is in the heater, the process, and the pipes. For some systems, this may take awhile depending on the system size. The reason for this is to make sure that when the pump gets turned off, the residual heat in the various components of the system does not thermally crack the heat transfer fluid.3. Once the temperature has dropped to 200°F (93°C) the residual heat has been removed the pump is shut off.
Oil Heat Exchanger Problems
Normal leakage in thermal fluid systems. This consist of fluid seeping out from threaded fittings, flange gaskets, mechanical seals and valve stem and pump shaft packing glands. Any droplets formed will cool rapidly on exposure to air.
Extremely low volume leaks may produce a light gray smoke. This is an indication that the fluid is oxidizing immediately on exposure to air. This smoke may cause respiratory irritation if inhaled for a period of time as can any type of smoke.
Catastrophic Equipment Failure may result in the rapid release of large quantities of thermal fluid.
If the total system pressure is low and the fluid is operating below its atmospheric boiling point, then the leak will consist of liquid that may spray a short distance before falling to the ground.
Higher system pressure may produce a finer spray that ejects a greater distance from the equipment; however, the relatively larger surface area of the droplets and their velocity will result in rapid cooling.
A severe potential for fires can exist if the thermal fluid flow is interrupted without causing the heater to shut down. Under this no-flow condition, the temperature of the fluid inside the still energized heater increases rapidly to well above its boiling point. Any equipment failures may result in spontaneous ignition of the leaking fluid.
These are some of the oil heat exchanger problems and each needs to be handled carefully.
