Thermal Oil Or Electrically Heated Autoclaves. Which One is Right For You?

11.03.2021
Thermal Oil Or Electrically Heated Autoclaves. Which One is Right For You?

The heating type used in autoclaves differs depending on the required heating processes and energy cost. In additon to well-known direct steam heating, the following three methods are specifically used for hot air autoclave heating:

  • Thermal oil
  • Electric
  • Indirect steam

In this blog article, we will outline the main differences between electric heated and thermal oil heated autoclaves. The energy cost is usually the determining factor to choose between two heating methods. We cannot make a quick recommendation on one versus another as we have to look at them on a case-by-case basis. There needs to be an in-depth analysis of energy and operational cost of using autoclaves in different countries and regions.

THERMAL OIL HEATING:

The high temperature thermal oil is generated using thermal oil generators or boilers and the autoclave is heated by distributing the thermal oil through the heat exchanger mounted inside the autoclave. Using this method, the autoclaves can be heated up to 280-300°C.

The thermal oil generator can be powered by one of the following sources:

  • Electricity: The thermal oil generator uses clean electricity without any environmental emission.
  • Natural Gas: The natural gas provides lower cost and higher energy, and it is the most common source of energy for thermal oil generators. It has relatively low emmision values.
  • Diesel: It is a preferred source where natural gas is not available or in oil producing regions where diesel has lower cost. However, it has one of the highest emmision values and the use might be restricted without having sophisticed filter systems.
  • Coal: While it is a common source in coal rich regions, it requires extra operational costs, and it is the least enviromentally friendly and a high pollution source of energy.

When choosing the the suitable source of producing thermal oil, the following should also be considered:

  • The low cost and high energy and calorie level
  • The socio-economic and environmental rules and regulations of the installation area
  • The availibility of the energy source.

The Advantages of Thermal Oil Heated Autoclaves:

  • It can significantly reduce the operational costs where the electricity cost is high, particularly when the autoclave operates at high a number of cycles.
  • For high capacity heating autoclaves, it provides economical advantages.
  • Higher temperature values can be achieved at lower pressures. This becomes even more advantageous considering the risks of high pressure direct steam heat autoclaves.
  • Thermal oil heated autoclaves offer higher heat transfer compared to steam heated autoclaves.
  • Compared with direct steam autoclaves, the autoclaves face less corrosion.
  • The conditioning and treatment of discharged steam is not required for thermal oil heated autoclaves.
  • There is less instrumentation and less external piping which comes with lower risk of frostation.

The Disadvantages of Thermal Oil Heated Autoclaves:

  • It has a higher initial investment cost due to the cost of installing a thermal oil generator, than electrical heated autoclaves.
  • It has higher operational and maintenance costs than electrical heated autoclaves.
  • While the maximum heating temperature cannot exceed more than 300 ˚C with thermal oil, there is no temperature limit when using electrical autoclaves.
  • The piping and instrumentation is more critical with thermal oil potentially causing fire risk in case of leaks.
  • The oil used needs to be replaced as it loses heating function, viscosity and efficiency when used at a high number of cycles. The thickening of the oil may cause build-up in the heat exchange minimizing the heat transfer. The risk would be minimized by regularly replacing the oil.

ELECTRIC HEATING

Thermal Oil Heated Composite Autoclave

The autoclave heating is achieved using electric heating elements and distributing the hot air by motor circulation fan. Electric heating offers higher temperature levels compared to other heating methods.

The Advantages of Electrically Heated Autoclaves:

  • They offer low emmision and clean energy.
  • Electric autoclaves have less initial investment cost than thermal oil heated autoclaves.
  • They require less space compared to thermal oil or indirect steam heated autoclaves.
  • Electric autoclaves can be used at higher temperature in case higher curing temperatures are required.
  • They are safer and simpler to operate than thermal oil heated autoclaves.

The Disadvantages of Electrically Heated Autoclaves:

  • They may require higher electrical power supply and a higher capacity plant transformer as well as higher cost of in-plant power supply cabling.
  • They require a clean energy supply to prevent potential damages in heating elements due to voltage flactuations.

Summary:

It is important to thoroughly analyze the initial investment and operational costs when evaluating the possibility of using thermal oil heating for the autoclave curing process. The analysis and payback period should be compared against other heating options. Investing in the thermal oil generator and autoclave suitable for thermal oil heating should be decided accordingly.

In our experience, the rule of thumb would be that for any required heating capacity over 500 kW, a thermal oil heated autoclave should be considered as an alternative, and may become more economical and feasible. For any capacity below 500 kW, the electrically heated autoclaves offer better results for investors. In addition to the economical aspects, other factors, particularly the environmental regulations, should be assessed, as well as the safe supply of the power source (ie: electricity, natural gas, diesel). The economical feasibility of choosing the type of heating can be done by the autoclave manufacturer, while the other factors are studied by the investor.

With over 30 years in operation and a leading autoclave company, Akarmak offers state-of-the-art turnkey autoclave solutions for the glass lamination, composite, rubber, tire, and medical waste industries, with different heating methods. You may contact us for your autoclave needs and consult our recommendations as to what would be the best autoclave configuration for you.

Electrically Heated Composite Autoclave