EP3585872B1

EP3585872B1 - A method for degasification of diathermic oil

Info

Publication number: EP3585872B1
Application number: EP18712479.7A
Authority: EP
Inventors: Gilberto TANI
Original assignee: Oil Service Srl
Current assignee: Oil Service Srl
Priority date: 2017-02-22
Filing date: 2018-02-21
Publication date: 2022-06-15
Anticipated expiration: 2038-02-21
Also published as: EP3585872A1; WO2018154618A1; IT201700019798A1

Description

The invention relates to the sector of maintenance of industrial systems that use oils at high temperatures and, more in detail, the invention relates to a method for degasification of diathermic oil, i.e., the elimination of gases present therein.
The apparatus that implements this method is not included in the invention.
In systems that use oil at high temperature, over 250 °C, it is fundamental to eliminate any gases or light fractions that can be released from the oil and that can cause various problems.
The formation of gases in diathermic oils is caused by deterioration of these oils, whose molecules, through a phenomenon of cracking (thermal shock), break up and generate light fractions (gases) and/or heavy fractions (sludge). Cracking is caused by a sudden increase in the temperature, which makes it impossible for the oil to absorb heat, hence causing thermal shock.
The presence of light fractions or gases inside a diathermic oil system lowers the flash point of the oil, as well as lowering the general safety conditions of the entire system, with the risk of fire in the event of accidental leakages of the high temperature fluid.
Gas and light fractions are currently eliminated through a method based on an oil distillation process, thanks to the use of apparatus similar to distillers. These apparatus, once connected to a bypass of the circuit, allow elimination of the gases via the presence of a vacuum chamber. However, this procedure is implemented with the system operating and the oil passes through the vacuum chamber at the operating temperature of around 250°C - 270°C, temperature maintained constant for the entire process.
Document DE 22 05 466 A1 refers to a method for degasification of diathermic oil, comprising the steps of:

diverting a partial flow or the main flow of the diathermic oil from the operating circuit;
send said flow through the degasification apparatus wherein the volatile components of the diathermic oil are removed under vacuum, thus increasing the flash point;
re-introducing said oil into its operating circuit.

The main drawbacks of this method essentially depend on the high operating temperatures of the oil, which remain constant for the whole of the duration of the distillation process.
Unfortunately, elimination of the gases generated by the diathermic oil implemented through this distillation method, and at such high temperatures, does not guarantee optimal removal of the gas from the fluid and does not cause the flash point to increase to a value able to restore acceptable safety conditions.
As the vacuum chamber itself causes stress to the fluid already degraded by cracking phenomena, an increase of temperature during operation starting from an oil at 250° C and more, causes further thermal shock that further cracks and degrades the molecules.
Finally, the distillation process at such high temperatures is hazardous for the operators and for the entire system.
The invention aims to overcome these limits, defining a new method able to obtain elimination of the gases and light fractions at low temperatures without further stress and degradation to the oil, avoiding possible further degradation of the molecules, simultaneously restoring the system to safe conditions and significantly lowering the risk of fire, hence also guaranteeing greater safety for the operators.
These objects are achieved with a method for degasification of diathermic oil in a circuit of use, characterized in that it comprises the following steps:

collecting a sample of diathermic oil from said circuit of use and analytically determining the temperature value corresponding to the flash point of said diathermic oil;
analytically determining the distillation curve of said sample of diathermic oil and acquiring the related temperature values of distillation of the volume of the substances contained;
diverting said diathermic oil from said circuit of use;
regulating the temperature of said diathermic oil taking it to a temperature value lower than the flash point to favour the formation of gases that develop around this temperature;
applying the vacuum to said diathermic oil, at a preset pressure value and for a time interval predetermined by the distillation curve, so as to totally suck the gas released in said conditions;
collecting the gas released via the application of vacuum and sending it to a discharge point;
re-introducing said diathermic oil into its circuit of use;
regulating the temperature of said diathermic oil again, increasing it by a value Δt and bringing it to a value higher than the previous one, and repeating the subsequent steps for n values of predetermined incremental temperature until reaching the temperature of use of said diathermic oil in said circuit.

In particular, said value ΔT is between 20° and 30°C.
Alternatively, said step of regulating the temperature of said diathermic oil comprises the step of heating said diathermic oil, or the step of cooling said diathermic oil.
According to possible aspects of the invention, between the step of diverting said diathermic oil from its circuit of use and the step of adjusting its temperature, there is provided a step of mechanical filtration and a step of magnetic filtration for said diathermic oil.
Moreover, said step of collecting the gas released and sending it to a discharge point comprises a step of physical-chemical filtration of said released gas.
Advantageously, before said step of physical-chemical filtration of said released gas, there is provided a step of condensation thereof.
The process for degasification of diathermic oil described above offer important advantages with respect to conventional methods.
Treatment of the oil does not take place in constant conditions of operating temperature of the system, but in programmed situations in which the temperature of the oil can be regulated and modulated according to processing needs. Therefore, it starts from lower temperatures around the flash point (detected by the analyses), to slowly and gradually reach the operating temperature. In this way the gas is eliminated naturally following the normal start-up process of the diathermic oil system, without incurring any further stress and degradation of the fluid.
In any case, it is possible to start with treatment of the oil in conditions of operating temperature of the system, through the use of blast chillers.
Advantageously, through the process at controlled temperatures according to the invention:

the oil is preserved from further stresses that could further degrade and break up its molecules already broken up by the cracking phenomenon;
the treatment time is considerably reduced;
safe operating condition of the system is restored;
the flash point of the oil is increased again and consequently the risk of fire in the system is reduced;
high levels of safety are guaranteed for the operators;
the system does not require to be topped up with new oil.

The first steps of the process according to the invention are steps of analysing and evaluating the diathermic oil to be treated: determining the flash point and the distillation curve are the most important operations of the entire procedure, and are carried out analytically in the laboratory using ASTM methods applied to a sample of diathermic oil collected from the system.
By determining the flash point of the oil, it is possible to understand if gases have formed.
The flash point of a new diathermic oil corresponds to around 200°C and its reduction to 130°C is tolerated. If this value drops further, it means that gas has formed inside the oil, which is thus easily inflammable in the event of leakage from the circuit and in contact with an external ignition source.
The distillation curve instead allows an evaluation in percentage of the volume of gas generated in the oil to be implemented, indicatively detecting it in several concentration levels (considering 0% the starting point of gas formation, and then measuring 2%, 5% and 10%).
For example, for a new oil, 2% of the volume must distil at a temperature higher than 300°C if this value drops below the operating temperature of the oil (around 250°C), it becomes a significant value indicating a very high concentration of gas.

The following table (Table 1) provides an example of the flash points and of the distillation curves detected on five different samples of diathermic oils.

(Table 1)

	SAMPLE A	SAMPLE B	SAMPLE C	SAMPLE D	SAMPLE E
Type of oil	Mineral	Mineral	Synthetic	Synthetic	Mineral
Flash point °C (T0)	120	75	80	130	100
Distillation curve: start (IBP)°C	180	150	130	200	140
2%	220	200	210	270	190
5%	270	240	245	300	240

As can be noted there are low flash points (close to 130°C) and values of the distillation curve at 2% all below 300°C. These values show that the various diathermic oils have generated gases and in different amounts.
The central step of the degasification process takes place in a bypass, parallel to the system, with the circulation pump of the system operating, and can be carried out both with the system not at operating temperature, and hence with cold diathermic oil, and with the system active, with diathermic oil at the operating temperature.
We shall first examine the case in which the process for degasification is implemented with the system not at operating temperature, with cold diathermic oil.
The first step provides for regulating the temperature of the oil, using the heating means of the system, taking it to the temperature T0 lower than the flash point measured.
After reaching the temperature T0, the vacuum is applied to the diathermic oil, with a preset pressure value P0 and for a predetermined time interval Δt0, both values defined by the distillation curve, sufficient to suck all the gases released at the given temperature T0.
After suction has terminated and the gases have been sent to the discharge point, the diathermic oil is re-introduced into the system at the temperature T0.
The subsequent steps substantially involve the same operations of applying the vacuum carried out at different levels of incremental temperature T1, T2, T3,... Tn increasing in steps of an interval ΔT between 20° and 30° C.
The oil is gradually heated inside the system using its own heating means.
The process ends when the operating temperature of the oil is gradually reached and all the gases have been collected.
We shall now examine the case in which the process for degasification is implemented with the system operating, therefore starting from a diathermic oil collected from the system directly at the operating temperature.
The first step involves reducing the temperature of the oil, taking it to the temperature T0 lower than the flash point measured.
The oil is normally cooled using blast chillers of known type, positioned in series, inside which the oil is made to flow before reaching the step of applying the vacuum.
Through these blast chillers, the temperature of the diathermic oil collected from a system that is operating, and therefore presumably around 250°C, can be lowered to around 70°C, temperature usually lower than the flash points found on many diathermic oil systems.
After reaching the temperature T0, the vacuum is applied to the diathermic oil with a given value and for a given time interval, determined by the distillation curve and necessary to suck all the gases released at that given temperature.
After suction has terminated and the gases have been sent to the discharge point, the diathermic oil is re-introduced into the system at the temperature T0 and immediately taken to the operating temperature using the heating means of the system.
The subsequent steps substantially involve the same operations of applying the vacuum carried out at different incremental temperature levels T1, T2, T3,... Tn increasing in steps with an interval ΔT between 20° and 30° C.
Each time the oil is collected from the system at its operating temperature it must be cooled to a temperature always lower than the operating temperature, but each time higher than the temperature of the previous treatment step.
The process always ends when all the gases have gradually been collected.
As indicated in the table below (Table 2), modulation of the vacuum (measured in bar) varies as a function of the incremental temperatures of the oil T0, T1, T2, ... Tn to which the oil is taken during the method for degasification.
The temperature increases, from one step to the next, are between 20° and 30° C. (Table 2)

T0 = 100 °C T1 =130 °C T2 = 150 °C T3 = 180 °C T4 = 200 °C T5 = 230 °C Tn = ...°C

VACUUM bar -0.85 -0.80 -0.75 -0.70 -0.65 -0.60 ....

As is apparent from the table provided by way of example below (Table 3), the time interval for application of the vacuum is also determined, at the different incremental temperatures of the oil T0, T1, T2, ... Tn, based on the amount of diathermic oil present in the system, expressed in litres, and based on the distillation curve.

(table 3)

AMOUNT OF OIL	Time at T0 = 100 °C	Time at T1 = 130 °C	Time at T2 = 150 °C	Time at T3 = 180 °C	Time at T4 = 200 °C	Time at T5 = 230 °C	Time at Tn = ... °C
up to 6,000 litres/hour	3h	3h	2h	2h	1h	30 min.	....
from 6,000 to 12,000 litres	5h	4h	4h	4h	3h	2h	....
from 12,000 to 20,000 litres	8h	8h	6h	6h	5h	4h	....

Both when the process for degasification takes place with the system switched off and with the system operating, the gas and the light fractions extracted from the oil must be treated before being emitted into the atmosphere. This treatment takes place with an activated charcoal filter, advantageously preceded by a step of condensation to liquid state, and subsequent removal, of the light fractions composed of a mixture of hydrocarbons. Said step of condensation also allows the life of the activated charcoal filter to be extended and prevents the release of unpleasant odours into the environment.
A preferred embodiment of the method defined above using apparatus that implement this method is described below by way of non-limiting example and with the aid of the figures, wherein:

Fig. 1 schematically illustrates an apparatus (not part of the invention) that implements the method for degasification of diathermic oil;
Fig. 2 schematically illustrates a connection in series of three blast chillers;
Figs. 3a and 3b illustrate two gas chromatograms of a first sample of diathermic oil (n° 402), respectively before and after the treatment;
Fig. 4 illustrates the gas chromatograms of Figs. 3a and 3b superimposed;
Figs. 5a and 5b illustrate two gas chromatograms of a second sample of diathermic oil (n° 332), respectively before and after the treatment;
Fig. 6 illustrates the gas chromatograms of Figs. 5a and 5b superimposed;
Figs. 7a and 7b illustrate two gas chromatograms of a sample C of diathermic oil, respectively before and after the treatment using a conventional method;
Fig. 8 illustrates the gas chromatograms of Figs. 7a and 7b superimposed;
Figs. 9 and 10 schematically illustrate two possible variants of the apparatus of Fig. 1 (not part of the invention);
Fig. 11 schematically illustrates a component of the apparatus of Fig. 9 (not part of the invention).

With particular reference to Fig. 1, there is illustrated a diagram of the main components of an apparatus for degasification of diathermic oil arranged to implement the method described above, in the case of use in a bypass with a system that is not operating.
Said apparatus essentially comprises:

a vacuum chamber 1 provided with an inlet IN and with an outlet OUT for said diathermic oil;
a vacuum pump P1 connected to said vacuum chamber 1 and adapted to remove the gases released from said diathermic oil;
an activated charcoal filter F to retain the gases released from said diathermic oil placed downstream of said vacuum chamber 1, preferably downstream of said vacuum pump P1;
a pump P2 for collecting said treated diathermic oil from said vacuum chamber 1.

Upstream of said vacuum chamber 1 there are provided filter means F1 and F2 of the inflowing diathermic oil, adapted to carry out initial cleaning of the oil and facilitate the subsequent work of the vacuum pump.
Said filter means comprise a metal mesh filter F1 for sludge, and a magnetic filter F2 for ferrous impurities.
Said apparatus also comprises a liquid trap TR interposed between said vacuum chamber 1 and said vacuum pump P1, adapted to retain, by sedimentation, any residues of oil sucked with said vacuum pump P1.
According to prior art, said apparatus comprises a vacuum relief valve Vr that has the task of regulating the inflow of outside air into said trap TR. Said vacuum relief valve Vr substantially prevents implosion of the trap TR, and consequently of the vacuum chamber 1, placing the whole vacuum circuit of the apparatus in communication with outside environment upon reaching a minimum preset vacuum pressure inside the vacuum chamber 1. Opening or closing of said vacuum relief valve Vr can take place automatically or via manual regulation by an operator.
In the case in which the method for degasification of diathermic oil is implemented with the system operating, blast chillers A1, A2 and A3 connected in series are placed upstream of the vacuum chamber 1, as illustrated by way of example in Fig. 2.
With particular reference to Figs. 9 and 11, said apparatus comprises a condensation device C interposed between said vacuum pump P1 and said activated charcoal filter F.
Said condensation device C comprises a refrigerator 2 loaded with Freon, a plate heat exchanger 3, a sensor 4 to detect the temperature, an electronic regulation and control unit 5.
Said plate heat exchanger 3 comprises two inlets (a first inlet for the gases released from the vacuum pump P1 and a second inlet for the cooling Freon) and two outlets (a first outlet for the heated Freon and a second outlet for the cooled gases with the condensed light fractions removed). Said two inlets and said two outlets are placed opposite so as to obtain the best possible heat dissipation.
The condensation procedure takes place via a preliminary setting of the temperature required to reduce the light fractions (2° - 5° C) via the electronic regulation and control unit 5.
The detection sensor 4 and the electronic control unit 5 act on the condensation device C switching the refrigerator 2 on and off based on the temperature required to maintain the temperature set on the gases exiting from the plate heat exchanger 3.
Said condensation device C also allows any moisture and water vapour present in the gases released to be eliminated. In this case the condensation temperature to be set with the electronic regulation and control unit 5 is between 10° and 20° C.
With particular reference to Fig. 10, said apparatus comprises a calibrated valve Vc for recovery of the gases released from said diathermic oil placed downstream of said vacuum pump P1 along a circuit for connection with the trap TR, or more generically with the outlet OUT of said vacuum chamber 1. This calibrated valve Vc allows the vacuum pressure inside said vacuum chamber 1 to be regulated to be able to improve the performance of the apparatus, the result of the method for degasification and its safety.
By inserting said calibrated valve Vc between the outlet of the vacuum pump P1 and the outlet OUT of the vacuum chamber 1, the gas exiting from the vacuum pump P1 is recovered; in this way, no air is sucked from outside using the vacuum relief valve Vr and consequently no air and gas are conveyed into the vacuum pump P1, into activated charcoal filter and into the condensation device C, if present.
The apparatus described can be operated manually by an engineer who, as a function of the information collected on the state of the oil and of the system before the start of operation, regulates the heating or cooling means and the vacuum pump based on the tables described above.
Alternatively, said apparatus can comprise a control unit capable of performing the aforesaid regulations automatically. After the necessary data has been entered, said control unit can regulate the vacuum value and the operating temperature directly.
By way of example, the analytical steps of investigation carried out on five samples of oil and the related tables for implementation of the method and management of the apparatus according to the invention are set down below.

Test no. 1:

SAMPLE - A: Mineral Oil
Flash point:	120°C
Distillation curve:	Ibp: 180°C
	2 %: 220°C
	5%: 270°C

Applied Vacuum Table Sample A

	T0 = 100 °C	T1 = 130 °C	T2 = 150 °C	T3 = 180 °C	T4 = 200 °C	T5 = 230 °C
VACUUM bar	-0.85	-0.80	-0.75	-0.70	-0.65	-0.60

AMOUNT OF OIL	Time at T0 = 100 °C	Time at T1 = 130 °C	Time at T2 = 150 °C	Time at T3 = 180 °C	Time at T4 = 200 °C	Time at T5 = 230 °C
up to 6,000 litres	2h	2h	1h	1h	40 min.	30 min.
from 6,000 to 12,000 litres	4h	4h	2h	2h	1 ½ h	1h
from 12,000 to 20,000 litres	6h	6h	4h	4h	3h	2h

Vacuum application time Table Sample A

Test no. 2:

SAMPLE - B: Mineral Oil
Flash point:	75°C
Distillation curve:	Ibp: 150°C
	2 %: 200°C
	5%: 240°C

	T0= 100 °C	T1 = 130 °C	T2 = 150 °C	T3 = 180 °C	T4 = 200 °C	T5 = 230 °C
VACUUM bar	-0.85	-0.80	-0.75	-0.70	-0.65	-0.60

Applied Vacuum Table Sample B

AMOUNT OF OIL	Time at T0 = 100 °C	Time at T1 = 130 °C	Time at T2 = 150 °C	Time at T3 = 180 °C	Time at T4 = 200 °C	Time at T5 = 230 °C
up to 6,000 litres	3 ½ h	2 ½ h	1 hour	1 ½ h	1h	40 min.
from 6,000 to 12,000 litres	5 ½ h	4 ½ h	2 hours	2 ½ h	2h		1 ½ h
from 12,000 to 20,000 litres	7 ½ h	6 ½ h	4 hours	4 ½ h	4h		2 ½ h

Vacuum application time Table Sample B

Test no. 3:

SAMPLE - C: Synthetic oil
Flash point:	80°C
Distillation curve:	Ibp: 130°C
	2 %: 210°C
	5%: 245°C

	T0 = 100 °C	T1 = 130 °C	T2 = 150 °C	T3 = 180 °C	T4 = 200 °C	T5 = 230 °C
VACUUM A bar	-0.85	-0.80	-0.75	-0.70	-0.65	-0.60

Applied Vacuum Table Sample C

AMOUNT OF OIL	Time at T0 = 100 °C	Time at T1 = 130 °C	Time at T2 = 150 °C	Time at T3 = 180 °C	Time at T4 = 200 °C	Time at T5 = 230 °C
up to 6,000 litres	3h	2h	1h	1h	1h	40 min.
from 6,000 to 12,000 litres	4 h	4 h	2 h	2 h	2 h	1 ½ h
from 12,000 to 20,000 litres	7 h	6 h	4 h	4 h	4 h	2 ½ h

Vacuum application time Table Sample C

Test no. 4:

SAMPLE - D: Synthetic oil
Flash point:	130°C
Distillation curve:	Ibp: 200°C
	2 %: 270°C
	5%: 300°C

	T0 = 100 °C	T1 = 130 °C	T2 = 150 °C	T3 = 180 °C	T4 = 200 °C	T5 = 230 °C
VACUUM A bar	-0.85	-0.80	-0.75	-0.70	-0.65	-0.60

Applied Vacuum Table Sample D

AMOUNT OF OIL	Time at T0 = 100 °C	Time at T1 = 130 °C	Time at T2 = 150 °C	Time at T3 = 180 °C	Time at T4 = 200 °C	Time at T5 = 230 °C
up to 6,000 litres	2 h	2 h	1 h	2 h	1 h	1 h
from 6,000 to 12,000 litres	4 h	4 h	2 h	3 h	2 h	1 ½ h
from 12,000 to 20,000 litres	6 h	6 h	4 h	5 h	4 h	2 ½ h

Vacuum application time Table Sample D

Test no. 5:

SAMPLE - E: Mineral Oil
Flash point:	100°C
Distillation curve:	Ibp: 140°C
	2 %: 190°C
	5%: 240°C

	T0 = 100 °C	T1 = 130 °C	T2 = 150 °C	T3 = 180 °C	T4 = 200 °C	T5 = 230 °C
VACUUM A bar	-0.85	-0.80	-0.75	-0.,70	-0.65	-0.60

Applied Vacuum Table Sample E

AMOUNT OF OIL	Time at T0 = 100 °C	Time at T1 = 130 °C	Time at T2 = 150 °C	Time at T3 = 180 °C	Time at T4 = 200 °C	Time at T5 = 230 °C
up to 6,000 litres	3 ½ h	3 h	1 ½ h	1 h	40 minutes	40 minutes
from 6,000 to 12,000 litres	5 ½ h	5 h	2 ½ h	2 h	1 ½ h	1 ½ h
from 12,000 to 20,000 litres	7 ½ h	7 h	4 ½ h	4 h	3 h	3 h

Vacuum application time Table Sample E

As methods of increasing the flash point based on high temperature processes are available on the market, it is necessary to compare the efficacy of the low temperature approach forming the subject matter of the present invention with the conventional high temperature approach.
The result of the analysis conducted on two samples of diathermic oil before and after the treatment is shown below, implemented using the method for degasification at low temperature according to the invention with the aim of increasing the flash point.
The two samples of diathermic oil are n° 402 manufactured by the company Silicart with an initial flash point of 118°C and n° 332 manufactured by the company Clea with an initial flash point of 110°C.
As analyses carried out in gas chromatography-mass spectrometry on the two samples show (Figs. 3a and 3b, 5a and 5b), the chemical composition of the light fraction, the one responsible for lowering the flash point, of the two diathermic oils, undergoes a significant reduction, in particular with regard to the more volatile component.
This depletion of the light fraction is shown by the increase of the flash point value of the two samples passing from 118°C to 145°C for sample n° 402 (Silicart), and from 110°C to 168°C for sample n° 332 (Clea).
The two gas chromatograms, corresponding to analysis of the headspace of the two samples, have been superimposed (Figs. 4 and 6) and the chromatogram before the treatment has been highlighted in blue, while the chromatogram after the treatment has been highlighted in red.
As can be seen, there is a significant reduction in the volatile component, the one responsible for lowering the flash point, in both the samples subjected to low temperature treatment.
Analyses were then conducted on a sample C of diathermic oil before and after the treatment using a conventional high temperature method aimed at increasing the flash point.
The data recorded are:

Flash point before the treatment: 55 °C
Flash point after the high temperature treatment: 70 °C.

As shown by the analyses carried out in gas chromatography-mass spectrometry on the sample C, the chemical composition of the light fraction, the one responsible for lowering the flash point, is practically identical.
The gas chromatogram in black refers to headspace analysis of the oil C after the treatment, while the gas chromatogram in red refers to headspace analysis of the same oil C, before the treatment.
As can be noted by superimposing the chromatograms (Fig. 8), no appreciable differences are identified in the volatile component of the diathermic oil analysed before and after the purification treatment.
Consequently, the high temperature treatment is not effective in reducing volatile substances, i.e. in increasing the flash point.
The very small increase of the flash point following the treatment could therefore be explained based on incomplete removal of the volatile components from the spent diathermic oil.
Therefore, it can be concluded that the best approach to increase the flash point through elimination of the volatile component is the low temperature approach.

Claims

A method for degasification of diathermic oil in a circuit of use, characterized in that it comprises the following steps:
- collecting a sample of diathermic oil from said circuit of use and analytically determining the temperature value T0 corresponding to the flash point of said diathermic oil;

- analytically determining the distillation curve of said sample of diathermic oil and acquiring the related temperature values of distillation and volume of the substances contained;

- diverting said diathermic oil from said circuit of use;

- regulating the temperature of said diathermic oil, taking it to the temperature value T0 lower than the flash point to favour the formation of gases that develop around this temperature T0;

- applying the vacuum to said diathermic oil, at a preset pressure value P0 and for a time interval Δt0 predetermined by the distillation curve so as to totally suck the gas released in said conditions;

- collecting the gas released via the application of vacuum and sending it to a discharge point;

- re-introducing said diathermic oil into its circuit of use;

- regulating the temperature of said diathermic oil again, increasing it by a value Δt and taking it to a value Ti higher than the previous one, and repeating the subsequent steps for n values of predetermined incremental temperature T1, T2, T3,..., Tn until reaching the temperature of use of said diathermic oil in said circuit.
The method according to claim 1, characterized in that said value Δt is between 20°C and 30°C.
The method according to claim 1, characterized in that said step of regulating the temperature of said diathermic oil comprises the step of heating said diathermic oil.
The method according to claim 1, characterized in that said step of regulating the temperature of said diathermic oil comprises the step of cooling said diathermic oil.
The method according to claim 1, characterized in that between the step of diverting said diathermic oil from its circuit of use and the step of regulating its temperature, there is provided a step of mechanical filtration of said diathermic oil.
The method according to claim 5, characterized in that after said step of mechanical filtration there is provided a step of magnetic filtration for said diathermic oil.
The method according to claim 1, characterized in that said step of collecting the gas released and sending it to a discharge point comprises a step of physical-chemical filtration of said released gas.
The method according to claim 7, characterized in that before said step of physical-chemical filtration of said released gas there is provided a step of condensation thereof.