EP0308346A1 - Process and installation for the use of high viscosity refinery waste oil - Google Patents

Abstract

The invention relates to a process for the direct use as fuel at the point of production, in at least one burner (6), of a petroleum residue originating from a heat-treatment unit (1) such as a unit for fractionation or for conversion of a charge of hydrocarbons. In this process, the residue is taken from said unit (1) at a temperature greater than 300 DEG C and is directed via a heat-insulated pipe (12) to the burner (6). According to the invention, the flow of residue in the pipe (12) upstream of the burner is greater by 10 to 100% and preferably by 10 to 30% than the feed flow of said burner, thus by a fraction such that the increase in viscosity of this residue due to the heat losses between the production enclosure and the burner remains compatible with the use of said burner, while the part of said residue which is not used as fuel is recovered. <IMAGE>

Description

The present invention relates to the direct use, at the place of production, of a high viscosity petroleum fuel coming from a heat treatment unit, such as a unit for distillation or conversion of a hydrocarbon feedstock. . It relates more particularly to a process and an installation designed for the use as fuel, in at least one burner, of such a residue having a kinematic viscosity of between 0.005 and 1m² / s (that is to say say 5000 to a million centistokes) at 100 ° C.

The increase in crude oil costs and the growing need for light hydrocarbon cuts have led oil companies in recent years to modify the conditions for distillation and conversion processing of crude oil, in favor of the production of light products such as gas. , diesel and gasoline, to the detriment of the production of heavy fuels, to such an extent that even the residues of vacuum distillation of petroleum are considered today as noble fuels.

These operating conditions result in a final production of petroleum residue with a high density (at least 1 kg / dm³ at 15 ° C and, sometimes 1.1 kg / dm³), which have a viscosity at 100 ° C which can reach up to 1m² / s. Their economic value is therefore low and it is therefore interesting to be able to burn them directly in the refinery ovens, instead of the usual fuels. The combustion of the less viscous of them is generally carried out in the liquid phase, after preheating capable of lowering their viscosity to around 15.10⁻⁶m² / s or 15 cst, with steam assisted spray burners. For the others, combustion can be carried out in the solid phase, after grinding, if their softening points are high enough, or in the liquid phase but after fluxing with a lighter hydrocarbon cut, to obtain a lower viscosity, acceptable for industrial burners.

Direct combustion in the refinery of products with very high viscosity therefore poses serious problems, because, the maximum admissible viscosity at the level of conventional burners being of the order of 15.10⁻⁶m² / s (or 15 cst), this generally implies that the temperature of the residue to be burned can reach at least 300 ° C. and more. Combustible residues are certainly available at temperatures between 350 and 400 ° C, which makes them directly usable on site, but their transport to distant combustion plants, where they are used as fuel, results in loss of calories , which must be remedied by extensive insulation of the pipes, or even by heating the fuel before use, which is naturally very expensive.

This difficulty is further aggravated by the fact that maintaining a high viscosity fuel for a certain time at an elevated temperature, for example greater than 400 ° C., is capable of causing thermal cracking of the fuel, with the formation of gas. and coke that can settle in the pipes.

Finally, when the high viscosity fuel comes from a conversion unit such as a visbreaking unit, it is to be feared that its maintenance for a certain period of time at a temperature above 350-400 ° C. depending on the type of charge, does not lead to a prolongation of the reaction, with precipitation of asphaltenes in the pipes: with these petroleum fuels with very high viscosity, it is therefore very difficult to compensate for the inevitable heat losses by a rise in the initial temperature above 350 -400 ° C, due to the risk of blockage of the pipes by coke and asphaltenes. Clogging a pipe can lead to extremely high costs and even require the replacement of this pipe.

On the other hand, the higher the viscosity of the fuel, the higher the risk of blockage of the pipes following a drop in temperature below a certain limit is high: for fuels with a viscosity between 0.005 and 1m² / s at 100 ° C, this limit is generally around 200 ° C.

These clogging risks, resulting either from a too high temperature of the high viscosity petroleum residues, or from a too low temperature of these, makes their use practically impossible in current installations, because it imposes the imperative choice of a narrow range of temperatures, all the more difficult to maintain the greater the distance from the place of combustion.

The present invention aims to remedy these serious drawbacks by proposing a method capable of maintaining the temperature required to avoid pipe blockages, despite the heat losses between the places of recovery of high viscosity petroleum residues and their places of use as fuels inside the refinery or in its outbuildings.

The invention also aims to propose such a method which can be implemented without risk of accidental blockage of the pipes for transporting petroleum residues to their places of use as fuel, by limiting the heat losses of these pipes by a adequate insulation and by providing means suitable for maintaining a minimum temperature therein to avoid blockages which may result both from thermal cracking and from failure of the supply means.

It is known that the loss of calories from a liquid moving in a conduit varies in the opposite direction from the volume conveyed. In other words, the larger the volume of liquid delivered, the lower the heat losses reported per unit volume. To bring a heavy petroleum residue to a temperature sufficient for its use as a fuel on the very places of production, the invention therefore proposes to convey this fuel in a pipe maintained at a temperature above 280 ° C and preferably at 300 ° C, with a flow rate greater than its flow rate of use and recover the unused fraction.

The invention therefore relates to a process for the direct use at the place of production as fuel, in at least one burner, of an oil residue with a viscosity of between 0.005 and 1m² / s at 100 ° C and whose temperature necessary to obtain a viscosity of 15.10⁻⁶m² / s (that is to say 15 centistokes) is greater than 280 ° C, this residue coming from a heat treatment unit such as a fractionation unit or conversion of a hydrocarbon feed, process in which said residue is taken from said unit at a temperature above 300 ° C and is conveyed by a heat-insulated pipe to said burner, this process being characterized in that the flow rate of said petroleum residue in said pipe upstream of the burner, is 10 to 100% and preferably 10 to 30% higher than the feed rate of said burner by a fraction such as the increase in viscosity of this residue due to heat losses, between the production site and said burner, remains compatible with the use of said burner, and in that the part of said residue not used as fuel is recovered.

The fraction not used as fuel from petroleum residue can be streamed, then stored in a tank maintained at an adequate temperature, but advantageously, it will be recycled directly and without streaming at the production unit.

The temperature for taking off the petroleum residue will advantageously be between 300 and 350 ° C., while that of the arrival of the fuel at the burner will advantageously be between 280 ° C. and 320 ° C., due to the inevitable heat losses in this part of the region. 'installation.

The critical viscosity not to be exceeded during feeding of the burner will be 30.10⁻⁶ m² / s and, preferably, 15.10⁻⁶ m² / s, and the flow rate of the residue in the pipe which transports it to its place of use will be adjusted so as to maintain the viscosity at below this limit. The flow rate chosen will naturally depend on the length and diameter of this pipe.

According to a particularly advantageous mode of use of the method according to the invention, the risks of blockage of the conduits associated with keeping the residue at too high a temperature are avoided by bringing the temperature of the fuel removed using a heat exchanger. in the unit at a set temperature guaranteeing thermal stability of the residue throughout the installation and between 280 and 350 ° C, and compensating for the corresponding temperature decrease by an increase in the flow rate of the residue in the pipe upstream of the burner.

In practice, the flow rate of the residue in the fuel line will therefore be made independent of the fuel consumption at the burner; the regulation of this flow rate can advantageously be carried out using viscosity or temperature probes making it possible to vary the flow rate of the petroleum residue in the pipe upstream of the burner as a function of the viscosity of the residue in said pipe.

The invention also relates to an installation for the direct use as fuel, in at least one burner, of an oil residue having a viscosity of between 0.005 and 1m² / s at 100 ° C. and the temperature of which is necessary to obtain a viscosity of 15.10⁻⁶m² / s is greater than 280 ° C, coming from a heat treatment unit such as a fractionation or conversion unit of a hydrocarbon feed, this installation comprising a means for removing said residue in said unit, at a temperature equal to or lower than that prevailing in this unit, at least one burner for burning said residue, an insulated pipe joining said production enclosure to said burner and at least one means for conveying said residue in said pipe , installation characterized in that said means for conveying said residue is such that the flow rate of this residue in said pipe is 10 to 100% greater than the feed flow rate of said burner by a fraction such that the viscosity increase of this residue due to the thermal losses of said pipe between the place of production and the point of use remains greater than 15.10⁻⁶m² / s, that is to say remains compatible with its use as fuel in said burner, and in this that means are provided for limiting the supply of the burner to the desired fraction of the flow rate in said pipe and for recovering the excess fraction of said residue not used as fuel.

Preferably, said pipe will comprise heat-insulating means capable, on the one hand, of avoiding heat losses and, on the other hand, in the event of shutdown of the industrial unit, of maintaining the temperature of said residue in said pipe at above a pumpability threshold which will be between 180 and 250 ° C and preferably between 180 and 220 ° C. These insulating means may include a thermal insulator and, between this thermal insulator and the pipe, a buffer zone equipped with means for heating the pipe, for example using steam tracing lines or using electric heating resistors, activated automatically when the temperature of said pipe drops below the threshold thus predetermined.

Preferably, an enclosure forming a pressurization buffer tank and thermally insulated in a manner known per se will be disposed on the circuit of said pipe between the enclosure for producing the residue and the burner for using this residue as fuel. The volume of this enclosure will advantageously be such that it can provide one hour of supply to the burner (s) so as to prevent any shutdown of the producing installation.

Preferably, the installation will include means heat extraction to bring the temperature of the residue in the buffer tank to a set temperature generally greater than 300 ° C, or that of the supply line to the burner to a set temperature generally greater than 280 ° C, taking into account the fact that this temperature differential of 20 ° C between the buffer tank and the burner is a minimum on this type of pipe, regardless of the insulation thereof.

In addition, the supply to the buffer tank being adjusted to a set temperature, the flow rate of the line upstream of the burner can be regulated using a probe measuring the viscosity or the temperature of the fuel.

For safety, a separate fuel supply circuit for the burner from an auxiliary tank may also be provided. This backup circuit will use, for example, a fuel of the usual type to supply the burner.

Control and command means will advantageously be provided for automatically switching the supply of the burner from the main circuit to the backup circuit, when certain parameters reach critical values. The control means will, for example, continuously measure the flow rate, the pressure, the temperature and / or the viscosity of the residue at the level of the burner and will transfer the supply thereof to the backup circuit as soon as a preset threshold has been reached. one or more of these parameters was reached.

• la figure 1 est un schéma d'une installation utilisant ce procédé ;
• la figure 2 est une coupe transversale de la conduite d'acheminement du résidu pétrolier aux brûleurs, montrant les moyens dont elle est équipée pour y maintenir la tem­pérature au-dessus d'un seuil acceptable, tant en fonction­nement normal qu'en cas de panne d'alimentation en résidu pétrolier.

The appended schematic drawings illustrate a form of implementation of the method according to the invention. In these drawings:

• Figure 1 is a diagram of an installation using this method;
• FIG. 2 is a cross section of the pipe for conveying the petroleum residue to the burners, showing the means with which it is equipped for maintaining the temperature there above an acceptable threshold, both in normal operation and in the event of failure supply of petroleum residue.

We will first refer to Figure 1.

On the circuit shown, the bottom of a fractionation tower 1 is connected as usual, by a line 2 to a pump 3, which evacuates to the storage (not shown), by a line 4, the distillation residue to high viscosity, which one wishes to use as fuel.

On line 4, heat exchangers are provided which recover part of the calories from this fuel and, in particular, exchanger 5 adapts its temperature to the ceiling value above which blockages could occur as a result of thermal cracking. , or precipitation of asphaltenes. For this purpose, the flows in the lines 7 are controlled by a probe 30 which continuously measures the viscosity of the fuel at any point of the circuit and controls the valves 9 taking into account the losses of calories between the location of this probe and that of the exchangers.

According to the invention, at least part of the fuel is used directly to supply burners such as 6 of an oven or of another installation.

To this end, lines such as 7, mounted in diversion on line 4, on either side of the exchanger 5, supply a reserve buffer tank 8, capable of remedying variations in production. Valves 9, mounted on lines 7, make it possible, by varying the flow rate of these lines, to adjust the temperature of the fuel which feeds the tank 8. An automatic adjustment system for this temperature can advantageously be provided.

The bottom of the tank 8 is connected by a line 10 to a pump 11, connected by a line 12, equipped with a valve 14, to the line 13 for supplying the burners 6. The burners 6 can be supplied by a direct line , but it is preferable to provide a circulation loop with a return downstream of the regulating valve 32 to the primary circuit. The pump flow 11 is defined as a function of the flow rate necessary to supply the burners and of the thermal losses of lines 12 and 13. The fraction of the residue not used as fuel can be returned by line 15, fitted with a valve 27 to line 4 and storage , but it will preferably be recycled to tower 1 by line 16, fitted with a valve 28, so as to compensate for the losses due to the fuel circulation loop. It will be noted that a fluxing agent can be introduced into line 4 through line 31, in order to lower the viscosity of the fuel with a view to its storage.

Due to the excess fuel passing through the line 12, the heat losses on this line can be reduced enough for the viscosity of this fuel to supply the burners 6 to remain compatible with the conditions of use of these burners.

A safety circuit is provided for supplying the burners 6 with the aid of a fuel stored in a tank 20, when the supply by the line 12 is faulty. This circuit comprises a reservoir 20 of auxiliary fuel, connected to the line 13 supplying the burners 6 by a line 17 equipped with a pump 18, a heater 19 and a valve 21.

A device 22 controls the flow rate, the temperature, the pressure and / or the viscosity of the supply flow to the burners 6 and simultaneously controls the closing of the valve 14 and the opening of the valve 21 and the actuation of the pump 18 , when the measured value of one or more of these parameters reaches a predetermined threshold.

Such an installation therefore allows, using simple means, the direct use as fuel of high viscosity petroleum residues.

It is however necessary to provide for a complete breakdown of the supply means of line 12. Indeed, this would then risk cooling the fuel, which, immobilized, would solidify, which would then have extremely serious consequences for installation.

In order to remedy this drawback, it is judicious not only to cover the pipe 12 with a thermal insulator 24, as can be seen in FIG. 2, but to interpose between this insulator and the pipe 12 a warming buffer zone 25, in which electrical heating resistors 26 or steam lines are arranged, the valves of which are capable of opening automatically to maintain the temperature above a threshold generally between 180 and 220 ° C. A temperature sensor (not shown), arranged on the line 12, controls the supply of the resistors 26, or of the steam circulation valves, as soon as the recorded temperature drops below the threshold.

Claims (13)

1.- Process for the direct use at the place of production as fuel, in at least one burner (6), of an oil residue of kinematic viscosity between 0.005 and 1 m² / s at 100 ° C and whose temperature necessary to obtain a viscosity of 15.10⁻⁶ m² / s is greater than 280 ° C, coming from a heat treatment unit (1) such as a fractionation or conversion unit of a hydrocarbon charge, process in wherein said residue is taken from said unit (1) at a temperature above 300 ° C and is conveyed by a thermally insulated pipe (12) to said burner (6), method characterized in that the flow rate of said residue in said pipe (12 ) upstream of the burner is 10 to 100% and preferably 10 to 30% higher than the feed rate of said burner, by a fraction such as the increase in viscosity of this residue due to heat losses between the enclosure production and said burner remains compatible with the use of said burner, and in that the part of said residue not used as fuel is recovered. 2.- Method according to claim 1, characterized in that the temperature of the fuel taken from the heat treatment unit is brought back using a heat exchanger, to a set temperature guaranteeing the thermal stability of the residue and between 280 and 350 ° C, and in that the decrease in fuel temperature is compensated by a flow rate from the supply line (12) to the burner, greater than that required by said burner. 3.- Method according to claim 2, characterized in that the flow rate of the petroleum residue in the pipe upstream of the burner varies as a function of the viscosity of the residue in said pipe. 4.- Method according to one of claims 1 to 3, characterized in that at least 10% of the fraction of said petroleum residue not used as fuel is recycled to said unit (1). 5.- Method according to one of claims 1 to 3, characterized in that at least 10% of the fraction of said petroleum residue not used as fuel is flowed, then stored in a storage tank. 6.- Installation for direct use as fuel in at least one burner (6) of an oil residue having a viscosity of between 0.005 and 1 m² / s at 100 ° C and the temperature of which is necessary to obtain a viscosity of 15.10 ⁻⁶ m² / s is greater than 280 ° C, coming from a heat treatment unit (1) such as a fractionation or conversion unit of a hydrocarbon charge, this installation comprising a means for removing said residue in said unit (1) at a set temperature above 300 ° C, at least one burner (6) for burning said residue, a thermally insulated pipe (12) joining said production enclosure to said burner and at least one means (11) for conveying said residue in said pipe, installation characterized in that said means (11) for conveying said residue is such that the flow rate of this residue in said pipe is 10 to 100% greater than the feed flow rate of said feed burner, of a fraction such as acc ojection of viscosity of this residue due to the heat losses of said pipe between the place of production and the point of use remains greater than 15.10⁻⁶ m² / s, that is to say compatible with its use as fuel in said burner, and in that means (14, 13) are provided for limiting the supply to the burner to the desired fraction of the flow rate in said pipe and for recovering the excess fraction of said residue not used as fuel. 7.- Installation according to claim 6, characterized in that it comprises means for recycling to said unit (1) part of the fraction of said petroleum residue not used as fuel. 8.- Installation according to claim 6, characterized in that it comprises means for fluxing and storage of the fraction of said petroleum residue not used as fuel. 9.- Installation according to one of claims 6 to 8, characterized in that a buffer tank (8) is provided on the circuit of said pipe (12) between the enclosure (1) for producing said residue and the or said burners (6). 10.- Installation according to claim 9, characterized in that it comprises heat extraction means (5) for bringing the temperature of the residue in the buffer tank (8) to a set temperature above 300 ° C. . 11.- Installation according to claim 6, characterized in that the flow rate of the line (12) upstream of the burner is regulated using a probe measuring the viscosity or the temperature of the fuel. 12.- Installation according to one of claims 6 to 11, characterized in that it comprises an auxiliary circuit for supplying fluxed fuel compatible with the said burner (s) (6) from an auxiliary tank (20) and means (22) for automatically switching the supply of the burner (s) (6) to said auxiliary circuit when the flow rate, the pressure and / or the temperature of said residue on the supply to the burners reach a preset threshold. 13.- Installation according to one of claims 6 to 12, characterized in that said thermally insulated pipe (12) comprises, in addition to the thermal insulation (24) sheathing this pipe, a heating zone (25) equipped with heating means (26) actuated automatically when the temperature of said pipe drops below a predetermined threshold.

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