Technology
In the current industry, there are many processes in which the calorific contribution by means of a direct system is not practicable; for example, when the material to be warmed is inflammable, when a thermal decomposition is possible or when the rate of consumption is considerable, or still when it is necessary to obtain a constant heating in a high temperature. Then, we have to resort to the method of indirect heating by using like transmitter agent of heat, water, vapour, organic products or dissolved masses of salt or metals, according to the required temperatures.
A substance which will be used as heat carrier will have to satisfy, initially, the following conditions:
- to be cheap and easy of obtaining
- good thermal stability
- Mustn't degrade the building materials of the system
- low volatility
- good properties of heat transfer
- Under solidification point and low viscosity
The agent transmitter of heat with the most favourable calorific properties is the water. She allows passing on big quantities of heat which can go up to 100ºC without pressure, and over this temperature, in the form of water under pressure or steam. Although, the price of the water treatment is considerable, this product is easy to obtain and its price is not high.
Nevertheless, the increase of temperatures imposes considerable conditions to the facilities and to the materials. To 180 ºC, the water develops a steam pressure of 10 bar, reaching 50 bar for a temperature of 260 ºC. It implies a series of requirements (civil work, conduction of heat) and inevitable risks. On the other hand, the problems of corrosion, maintenance and water treatment are well known. As a consequence and as we will see it later, the indirect system of heating by steam meets a visible regression.
With the heat transmitters' agents of organic type, also so called thermal fluids, it is possible to operate with very low pressures, inside a range of temperatures up to 350ºC. The problems of corrosion are non-existent, and the low risks facilitate the location of the boilers in the own ships of work without needs of special civil work. On the other hand, on having been employed always in liquid phase, without changes of state during the process, he allows an important energy saving by comparison with the traditional and conventional steam circuit (pérdidas entálpicas de los condensados).
According to their origin and their characteristics, we stand out the thermal synthetic fluids of mineral type. The first group forms by oil product which we added additives in order to obtain improvements in the definite properties. The thermal oils of mineral type are combinations, also modified. The main difference between both groups is the range of working temperature which is more raised in thermal oil of synthetic types.
The technology of the thermal fluid is conceptually very simple and it was strongly imperative in all the sectors and the industrial processes.
