Pirobloc provides efficient, safe and custom solutions to heat industrial fryers and other tecnologies used to process food. Some of the most frequent are:
Thermal fluids used as heat transfer fluids have wide applications in various food processing industries, including continuous industrial fryers and industrial ovens.
These fryers are used interchangeably for crisps, nuts, industrial pastry, fish, vegetables, corn and many other products such as nuggets, croquettes, pasties, etc.
For optimal efficiency, heating systems used in industrial food processing must provide consistent and uniform temperatures to maximise quality and yields.
With energy costs on the rise, food processing companies are looking for ways to increase thermal efficiency to protect the margins which are already tight in this highly competitive market.
Pirobloc has vast experience in the development of thermal oil heating systems for continuous industrial fryers and industrial ovens. Heating via thermal fluid heaters is the most efficient method currently on the market, as it guarantees better use of the heat generated, ensures that there are no interruptions in the production process and leads to lower energy consumption than other alternatives.
In practically all applications, vegetable oil usually requires temperatures close to 175ºC. Maintaining controlled and stable temperatures is critical, as it maximises production levels while improving the taste, texture and appearance of cooked products. In addition, a stable temperature makes it possible to reduce oil usage, further improving efficiency and reduce oil degradation, preserving high-quality taste.
There are different alternatives for the direct heating of vegetable oil to this temperature, including electrical heating resistors directly immersed in the vegetable oil or gas burners directly coupled to a combustion chamber. These two alternatives involve high energy consumption and, consequently, high costs.
On the other hand, there are indirect heating systems, which offer higher performance and lower energy consumption. Among these systems mentioned, the most preferable is a thermal fluid heater used in combination with an external thermal fluid exchanger which uses vegetable oil.
The submerged coil would be another option for indirect heating. Submerged heat exchangers are an energy-efficient solution, although the amount of maintenance and cleaning required is a disadvantage. To solve this problem there are systems that allow the coil to be lifted out of the fluid.
Indirect heating methods using thermal fluid heaters
Indirect heating methods use intermediate fluids such as steam or thermal fluid to carry out the heat transfer to the fryers.
In the case of steam, the latent heat is used to heat the process, which leads to lower efficiency in the heat transfer process compared to thermal fluid. This thermal fluid heating system is simple, but has many advantages over using steam. These advantages carry over when used in fryers; including greater safety as it works at lower pressure, less corrosion, greater operational flexibility, better control of the quality of the final product, etc. Due to these reasons, thermal oil is preferred to steam.
As mentioned above, indirect heating systems using thermal fluid heaters contribute to significant savings in energy use compared to other solutions and guarantee the highest standards of safety, control and hygiene.
In terms of cost, a thermal fluid heater is also the most economical alternative. Some products, such as crisps, require high thermal power for processing as 80% of the content of the potato is water. In order to achieve optimal frying quality, the water must be evaporated, which means providing a significant amount of energy. The overall efficiency of thermal fluid heating is around 90%, as the only energy loss is in the combustion flue. By using heat recovery systems, this energy can be recovered through an economiser as a preheating element of the combustion air.
Another of these advantages is the conservation of vegetable oil. Vegetable oil is susceptible to rapid degradation as a result of the high temperature at which it is used. The higher the film temperature of the vegetable oil, the sooner it will oxidise and degrade. When heating with electrical resistors or direct burners the vegetable oil reaches very high temperatures that exceed 500 ºC. This also speeds up the degradation process. With a thermal fluid/vegetable oil heat exchanger, the temperature of the former is around 230 ºC, ensuring a stable and extremely precise temperature of 175 ºC in the vegetable oil. This value is totally selectable depending on the product, achieving accuracies of +/- 1 C. In other words, the film temperature of the vegetable oil will be as low as possible as the heat source does not exceed 230 ºC.
On the other hand, the use of the external exchanger facilitates maintenance tasks and periodic cleaning of the equipment, since the tube bundle is completely external and easy to clean. The fact that the heat exchange takes place outside the deep fryer is a great advantage, since the oil carries waste residue as fine particles that tend to decant and settle at the base of the deep fryer.
Final product quality
The consistency and uniformity provided by the thermal fluid in the heating process offers numerous benefits in the final quality of the products. This is because an indirect heating system allows the temperature of the oven or fryer to be adjusted more precisely and with greater control, eliminating the temperature fluctuations typical in other systems, resulting in a higher quality finished product.
Improvements in product quality include better texture on outer layers, less moisture loss, or better final product weight, among other things.
In addition to the improvements in product quality, a heating solution that uses a thermal fluid heater offers other important advantages, such as greater environmental efficiency, increased safety for workers, noise reduction and easier maintenance of the equipment, resulting in a longer service life.
Construction and use
The design of the thermal fluid solution presented consists of two main components: a thermal fluid heater and heat exchangers.
The thermal fluid heater heats the fluid by burning gas. This thermal fluid is circulated through a centrifugal pump to a thermal oil – vegetable oil tubular heat exchanger. Finally, a vegetable oil pump, which is also centrifugal, is responsible for sending the hot vegetable oil into the fryer.
The following diagram shows the operation of these fryers with a heating system using a thermal fluid heater and external exchanger.
By frying or baking with indirect heating, fryers and ovens extend their service life, as well as that of the fluid used for heating.
As mentioned, the indirect heating system consists of a thermal fluid heater, a heat exchanger and the fryer or oven itself. This system uses a high temperature, low pressure method of heating, where the heat transfer fluid is sent to the heating device through the circulation pump and then the heat is supplied to the heater to be heated.
The combustion chamber can be designed vertically or horizontally and different heating fuels such as diesel, natural gas or other gases can be used, depending on the customer’s requirements and preferences.
The speed and flow of the heat transfer fluid can be precisely adjusted, so that the efficiency of the heat required for the production process is improved, while the temperature of the exhaust gases is significantly reduced, which contributes to maintaining a good working environment.
Pirobloc has extensive experience in the design and installation of thermal fluid solutions to provide heat efficiently and sustainably to frying ranges for processed food products.