EP0816476B1 - Fuel for conventional boilers based on vegetable oils and having a very low sulfur content - Google Patents

Abstract

New fuel composition for conventional boilers, having a high content of vegetable oil with a very low sulphur content, in which the two main components are: 10 - 60% (preferably 20 - 50%) wt. of a natural vegetable oil; a substantial amount of a petroleum cut comprising a heavy petrol, containing at least 25% vol. of mono- and di-aromatics and having a sulphur content of less than 0.05%(preferably less than 0.01%) wt. The use of the composition, alone or mixed with another boiler fuel, as a domestic fuel compatible with existing burners, is also claimed.

Description

The present invention relates to a fuel for oil-based boilers natural vegetable and containing very small quantities of sulfur, this fuel being capable of being burned in combustion plants, either directly or mixing with other fuels, without modifying the burners.

• de compatibilité avec les brûleurs des chaudières usuelles, car s'il existe sur le marché des brûleurs polycombustibles, ces brûleurs nécessitent un réchauffage du combustible, une adaptation de la ligne de transfert entre la cuve de stockage et le brûleur, voire une pulvérisation assistée, ce qui limite d'autant l'intérêt économique de brûler directement des combustibles à forte teneur en huile végétale, s'il faut modifier les équipements qui utilisent actuellement du fuel oil domestique;
• d'encrassement de la chaudière, dû à une mauvaise combustion;
• de miscibilité: l'huile végétale, qui est un triester, se mélange difficilement avec des produits plus légers, de nature chimique différente;
• de viscosité: la viscosité de l'huile végétale est particulièrement élevée, de l'ordre de 70.10^-6 m²/s à 20°C; or, pour un usage en tant que fioul domestique (dit encore fuel oil domestique ou "F.O.D."), les spécifications intersyndicales mentionnent, en particulier, une viscosité inférieure à 7,5.10^-6m²/s; ceci rend impossible l'incorporation directe d'huile végétale dans un tel fioul domestique ainsi que sa pulvérisation dans un brûleur classique pour FOD ;
• de mise en oeuvre, du fait des pertes de charge en lignes, liées à la viscosité naturelle des huiles végétales;
• d'opérabilité et de stabilité au stockage (oxydation et pollution bactérienne).

In order to replace fossil energy sources with renewable energies, research on fuels has been oriented for a few years towards the use of agricultural surpluses; but burning vegetable oil directly or incorporating high contents in a conventional fuel, is not without posing a whole series of problems:

• compatibility with the burners of conventional boilers, because if there are multi-fuel burners on the market, these burners require heating of the fuel, adaptation of the transfer line between the storage tank and the burner, or even assisted spraying, this all the more limits the economic advantage of directly burning fuels with a high vegetable oil content, if it is necessary to modify the equipment which currently uses domestic fuel oil;
• fouling of the boiler, due to poor combustion;
• miscibility: vegetable oil, which is a triester, hardly mixes with lighter products, of different chemical nature;
• viscosity: the viscosity of the vegetable oil is particularly high, of the order of 70.10 ^-6 m ² / s at 20 ° C; however, for use as domestic fuel oil (also known as domestic fuel oil or "FOD"), the inter-union specifications mention, in particular, a viscosity of less than 7.5.10 ^-6 m ² / s; this makes it impossible to incorporate vegetable oil directly into such a domestic fuel oil as well as to spray it into a conventional burner for FOD;
• of implementation, due to the pressure losses in lines, linked to the natural viscosity of vegetable oils;
• operability and storage stability (oxidation and bacterial pollution).

• soit des combustibles incorporant des matières végétales fortement modifiées, par exemple sous la forme d'ester méthylique de colza, mais les opérations de transestérification et de purification ainsi rendues nécessaire pour rendre le combustible compatible avec les chaudières existantes, entraínent bien entendu un important surcoût tant énergétique que financier ;
• soit des combustibles à faible teneur en huile végétale (généralement inférieure à 5 % en poids), la quantité d'huile végétale étant alors suffisamment faible pour que le mélange ne présente pas les inconvénients précités. Cette incorporation directe, mais à faible teneur, d'huile végétale dans un fioul domestique classique, voire dans un fioul encore plus lourd, ne participe que pour très peu à la diminution de la pollution, car les fiouls en question contiennent des teneurs en soufre relativement importantes, et la désulfuration (généralement par hydrotraitement) de ce type de fioul s'avère assez coûteuse. En effet, plus l'hydrocarbure possède un point d'ébullition élevé, plus son hydrotraitement est difficile et d'un coût élevé.

In this context, the so-called "green" fuels that are emerging today are only:

• or fuels incorporating highly modified plant materials, for example in the form of rapeseed methyl ester, but the transesterification and purification operations thus made necessary to make the fuel compatible with existing boilers, of course entail a significant additional cost as energetic than financial;
• or fuels with a low vegetable oil content (generally less than 5% by weight), the quantity of vegetable oil then being sufficiently small so that the mixture does not have the abovementioned drawbacks. This direct, but low-content incorporation of vegetable oil into conventional domestic fuel oil, or even into even heavier fuel oil, contributes only very little to the reduction of pollution, because the fuel oils in question contain sulfur contents relatively large, and the desulphurization (generally by hydrotreatment) of this type of fuel oil turns out to be quite expensive. In fact, the more the hydrocarbon has a high boiling point, the more difficult it is to hydrotreat it and the higher its cost.

In general, the prior art mentions mixtures of vegetable oils with extremely diverse petroleum cuts: this is the case, for example, of the 'patent WO94 / 19430 which, in order to solve certain possible foaming problems in these mixtures, proposes the addition of anti-foaming additives and which in doing so quotes, extremely broadly, families of hydrocarbons (ranging from light gasoline to heavier fuels), which can be mixed with vegetable oils; this patent does however, does not solve the viscosity and compatibility problems with boilers usual.

WO 95/25152 discloses a fuel comprising an oil cut of the diesel type, as well as a vegetable oil mixed with at least 5% by weight of a monoester of fatty acid or resinic acid, intended in particular to lower the viscosity to low fuel temperature.

Therefore, in order to avoid the problems associated with increased viscosity and desulfurization costs when using petroleum fractions more and more heavy, and in order to ensure compatibility with the burners of conventional boilers, a judicious choice of the oil cut is fundamental.

• non seulement de réaliser des combustibles pour chaudières à forte teneur en huiles végétales naturelles non transformées, grâce à l'adjonction, dans la formulation du combustible, d'une coupe pétrolière originale, habituellement non destinée à ce type de combustible pour chaudière,
• mais également de tirer profit du fait que, d'une part, lesdites huiles végétales ne contiennent pratiquement pas de composés soufrés et que, d'autre part, la coupe précitée s'hydrotraite de façon relativement facile, pour réaliser à un coût raisonnable des combustibles originaux, qui préservent les caractéristiques de propreté de l'huile végétale.

Thus, during its work in the field of alternative fuels, the Applicant established that, quite surprisingly, it was possible:

• not only to produce fuels for boilers with a high content of unprocessed natural vegetable oils, thanks to the addition, in the fuel formulation, of an original petroleum cut, usually not intended for this type of boiler fuel,
• but also to take advantage of the fact that, on the one hand, said vegetable oils contain practically no sulfur compounds and that, on the other hand, the abovementioned cut hydrotreats relatively easily, to achieve at a reasonable cost original fuels, which preserve the cleanliness characteristics of vegetable oil.

We thus manage to correct the drawbacks of mixtures of vegetable oils and conventional fuel oils, in particular with regard to viscosity, resistance to cold and sulfur emissions in combustion effluents.

• une quantité substantielle d'au moins une huile végétale naturelle, à une teneur généralement comprise entre 10% et 60% en poids et, de préférence, entre 20% et 50% en poids,
• une quantité substantielle d'au moins une coupe pétrolière de type essence lourde, contenant au moins 25% en volume de composés aromatiques de type monoaromatiques et diaromatiques, et possédant une teneur en soufre inférieure à 0,05% en poids et, de préférence, inférieure à 0,01% en poids.

The present invention therefore relates to a new fuel for conventional boilers with a high vegetable oil content and a very low sulfur content, characterized in that its two main constituents are:

• a substantial amount of at least one natural vegetable oil, at a content generally between 10% and 60% by weight and, preferably, between 20% and 50% by weight,
• a substantial amount of at least one petroleum cut of the heavy petrol type, containing at least 25% by volume of aromatic compounds of the monoaromatic and diaromatic type, and having a sulfur content of less than 0.05% by weight and, preferably, less than 0.01% by weight.

The fuel according to the present invention may optionally contain, in preferably less than 20% by weight, a complement of compounds hydrocarbons whose distillation interval is preferably between that of petroleum and vegetable oil cutting, and the sulfur content of which is also less than 0.05% by weight and preferably less than 0.01% by weight.

The invention also relates to fuel mixtures including fuel that has just been defined.

• une viscosité d'une valeur choisie entre 1,1 et 1,5.10^-6 m²/s, puisque le mélange final doit présenter une viscosité généralement inférieure à 7,5.10^-6 m²/s à 20°C;
• un bon pouvoir solvant vis-à-vis de l'huile végétale, ce pouvoir solvant étant lui-même lié à la teneur en composés aromatiques présents dans la coupe.

The petroleum cut necessarily involved in the formulation of the fuel according to the present invention will advantageously have the following characteristics:

• a viscosity of a value chosen between 1.1 and 1.5.10 ^-6 m ² / s, since the final mixture must have a viscosity generally less than 7.5.10 ^-6 m ² / s at 20 ° C;
• a good solvent power with respect to vegetable oil, this solvent power itself being linked to the content of aromatic compounds present in the cut.

The available capacity of the refinery must also be taken into account. hydrotreatment reactors for this type of cut, as well as the other types of valuation likely to apply to said cut.

It is therefore advantageous to use petroleum fractions rich in aromatic compounds of the heavy gasoline type. These cuts may come, among other things, from a non-hydrogenating conversion of the FCC type (catalytic cracking in the fluid state), catalytic reforming, steam cracking, or pyrolysis. Indeed, the cuts thus obtained are free of heavy polyaromatic compounds with 3 or more cycles, (amount less than 0.5% by weight and preferably less than 0.1% by weight); they are also free of nitrogen compounds. In addition, they can comprise up to 25% and more of monoaromatic and diaromatic compounds; these will be present in a volume ratio of a chosen value, preferably between 8 and 12. Finally, this cut of hydrocarbons, after hydrotreatment (hydrodesulfurization), that is to say after passage in the presence of a hydrotreating catalyst in a reactor containing hydrogen with a pressure greater than 10 × 10 ⁵ Pa (10 bars), contains less than 0.05% and, preferably, less than 0.01% by weight of sulfur.

Particularly advantageous use will be made of the heavy petrol obtained from catalytic cracking insofar as this gasoline is difficult to recover in the fuels of the petrol or diesel engine type and therefore inexpensive.

The vegetable oil which can be used in the fuel according to the invention is preferably an oil from a plant that can be cultivated with a high yield at hectare. It can be advantageously chosen from the group comprising sunflower, palm oil, coconut oil, soybean oil, rapeseed oil and their mixtures. Preferably, the vegetable oil is rapeseed oil.

In general, the ratio between the volume of heavy petrol rich in aromatic compounds and the volume of vegetable oil in the mixture will be between 0.5 and 10 and preferably between 0.8 and 5.

• il incorpore en quantité substantielle de l'huile végétale d'origine agricole, et donc des hydrocarbures dits "renouvelables" et peu polluants;
• il peut incorporer aisément de 10 à 60 % en poids d'huile végétale sans nécessiter la modification de(s) brûleur(s) de chaudière, et ceci grâce à l'adjonction dans un rapport volumétrique déterminé d'une famille particulière d'hydrocarbures généralement destinée à d'autres fins;
• de par sa composition, il est respectueux de l'environnement: il incorpore une huile végétale ne contenant par nature ni soufre, ni azote, ni composés aromatiques fortement condensés à trois cycles ou plus, ainsi qu'une coupe d'hydrocarbures assurant la compatibilité avec les chaudières existantes et qui, elle aussi, est exempte de soufre;
• il améliore la combustion et le rendement des chaudières, du fait de l'apport d'oxygène qui résulte de l'incorporation de l'huile végétale;
• il est relativement économique, parce que la coupe pétrolière à basse teneur en soufre est fabriquée sans faire intervenir un hydrotraitement trop coûteux;
• il est compatible au stockage avec les autres hydrocarbures de type fioul domestique ou équivalent;
• il est utilisable en remplacement ou en complément des fiouls domestiques généralement utilisés sur chaudière;

The fuel according to the invention has various advantages

• it incorporates a substantial quantity of vegetable oil of agricultural origin, and therefore so-called "renewable" and low-polluting hydrocarbons;
• it can easily incorporate from 10 to 60% by weight of vegetable oil without requiring the modification of boiler burner (s), and this thanks to the addition in a determined volumetric ratio of a particular family of hydrocarbons generally intended for other purposes;
• due to its composition, it is respectful of the environment: it incorporates a vegetable oil containing by nature neither sulfur, nor nitrogen, nor aromatic compounds strongly condensed with three or more cycles, as well as a cut of hydrocarbons ensuring compatibility with existing boilers, which is also sulfur-free;
• it improves the combustion and the efficiency of boilers, due to the oxygen supply which results from the incorporation of vegetable oil;
• it is relatively economical, because the low-sulfur petroleum cut is produced without involving too costly hydrotreatment;
• it is compatible with storage with other hydrocarbons of the domestic fuel oil type or equivalent;
• it can be used as a replacement or in addition to the domestic fuel oils generally used on boilers;

This fuel is therefore particularly suitable for combustion on a boiler located in an environmentally sensitive area.

Advantageously, the fuel according to the present invention can be mixed with another cut of hydrocarbons, preferably free of sulfur, such as, for example, heavy diesel from a hydrocracking process, or an ester of a vegetable oil.

The subject of the invention is also the use of the fuel in accordance with the invention in boilers and / or furnaces of the collective and / or industrial type, without modifications to said boilers or said ovens.

The examples which follow illustrate the characteristics and advantages of the invention. They are not limiting.

Examples

(A): Huile de colza ("HC") raffinée, mais non transformée, commercialisée sous l'appellation LUBRIROB par la société ROBBE à Compiègne ; son point d'écoulement est inférieur à -21°C et sa viscosité est de 75.10^-6 m²/s à 20°C.

(B): Essence lourde ("EL") de craquage catalytique, ayant subi un hydrotraitement, d'intervalle de distillation compris entre 150 et 240°C, de masse volumique égale à 831 Kg/m³ à 15°C, de viscosité égale à 1.1. 10^-6 m²/s à 20°C, de teneur en composés mono et diaromatiques égale à 51% en volume et de teneur en soufre égale à 0,002 % en poids.

(C1): Fioul domestique ("BTS") à basse teneur en soufre, dont l'intervalle de distillation est compris entre 170 et 371°C, de masse volumique égale à 857 Kg/m³ à 15°C et de teneur en soufre égale à 0,05 % en poids.

(C2): Fioul domestique ("FOD"), dont l'intervalle de distillation est compris entre 165 et 380°C, de masse volumique égale à 863 Kg/m³ à 15°C et de teneur en soufre égale à 0,2 % en poids.

(C3): Gazole dit lourd ("GO"), dont l'intervalle de distillation est compris entre 230 et 350°C, de masse volumique est égale à 848Kg/m³ à 15°C et de teneur en soufre égale à 0,24 % en poids.

The products used in the fuel formulations mentioned in the table below are the following:

(A): Rapeseed oil ("HC") refined, but not transformed, sold under the name LUBRIROB by the company ROBBE in Compiègne; its pour point is less than -21 ° C and its viscosity is 75.10 ^-6 m ² / s at 20 ° C.

(B): Heavy gasoline ("EL") of catalytic cracking, having undergone a hydrotreatment, of distillation interval ranging between 150 and 240 ° C, of density equal to 831 Kg / m ³ at 15 ° C, equal to 1.1. 10 ^-6 m ² / s at 20 ° C, content of mono and diaromatic compounds equal to 51% by volume and sulfur content equal to 0.002% by weight.

(C1): Domestic fuel oil ("BTS") with low sulfur content, the distillation interval of which is between 170 and 371 ° C, with a density equal to 857 Kg / m ³ at 15 ° C and sulfur equal to 0.05% by weight.

(C2): Domestic fuel oil ("FOD"), the distillation interval of which is between 165 and 380 ° C, with a density equal to 863 Kg / m ³ at 15 ° C and a sulfur content equal to 0, 2% by weight.

(C3): Diesel said heavy ("GO"), the distillation range of which is between 230 and 350 ° C, density is equal to 848Kg / m ³ at 15 ° C and sulfur content equal to 0 , 24% by weight.

The following table brings together the results concerning the combustion of 6 different mixtures numbered from (1) to (6) on a community type boiler (power greater than 500 KW): The contents of A, B and C are expressed in% by volume. (1) (2) (3) (4) (5) (6) (A) ("HC") 5 15 20 40 30 40 (B) ("EL") 80 60 40 40 (C1) ("BTS") 85 30 10 (C2) ("FOD") 95 (C3) ("GO") 10 Combustible
Sulfur content (% by mass) 0.19 0.04 0,004 0.005 0.02 0.04 Viscosity + - + + + + Combustion + - + + + + SO ₂ emission in smoke (in ppm) 35 10 0 0 10 8

This table shows, in particular (see column (2)), that, without adding the cut (B), the incorporation in substantial quantity of vegetable oil in a fuel oil, even at low sulfur content, does not allow the use of a boiler without modification, because the viscosity becomes too high.

This table also shows that the fuels (3) and (4) consisting exclusively of heavy gasoline of catalytic cracking and vegetable oil have remarkably low sulfur contents; no SO ₂ emission was detected in the combustion fumes.

In addition, the green fuels described in (3) to (6) can be burned in a boiler usually using domestic fuel oil, without modifying the installation of initial boiler, and in particular of burner (s). They also have good storage stability. Finally, while it is well known to those skilled in the art that the burning rapeseed oil, even on a modified burner, poses a big problem of start-up (given the low intrinsic volatility of the product), adding variable proportion of cut B, mixed with significant quantities of oil of rapeseed, considerably improves the ignition by electrodes, when starting the burner.

Claims (13)

1. Fuel for conventional boilers with a high vegetable oil content and a very low sulphur content, characterised in that its two main constituents are:

   a substantial quantity of at least one natural vegetable oil, in a content which is generally between 10 and 60 wt.% and preferably between 20 and 50 wt.%,

   a substantial quantity of at least one petroleum cut of the heavy naphtha type containing at least 25% by volume of aromatic compounds of the monoaromatic and diaromatic type and possessing a sulphur content lower than 0.5 wt.% and preferably lower than 0.01 wt.%.
2. Fuel according to claim 1, characterised in that the petroleum cut of the heavy naphtha type rich in aromatic compounds has a viscosity selected between 1.1 and 1.5 .10^-6 m²/s at 20°C.
3. Fuel according to any of the preceding claims, characterised in that its viscosity is lower than or equal to 7.5.10^-6 m²/s at 20°C.
4. Fuel according to any of the preceding claims, characterised in that the ratio by volume between the petroleum cut and the vegetable oil is between 0.5 and 10, preferably between 0.8 and 5.
5. Fuel according to any of the preceding claims, characterised in that it contains a complement, in a quantity preferably lower than 20 wt.% of hydrocarbon compounds of which the distillation range is preferably between that of the petroleum cut and that of the vegetable oil and of which the sulphur content is also lower than 0.05 wt.% and preferably lower than 0.01 wt.%.
6. Fuel according to any of the preceding claims, characterised in that the petroleum cut of the heavy naphtha type rich in aromatic compounds contains monoaromatic compounds and diaromatic compounds present in a ratio by volume preferably selected between 8 and 12.
7. Fuel according to any of the preceding claims, characterised in that the petroleum cut of the heavy naphtha type rich in aromatic compounds contains less than 0.5 wt.% and preferably less than 0.1 wt.% of heavy polyaromatic compounds containing 3 or more cycles.
8. Fuel according to any of the preceding claims, characterised in that the petroleum cut rich in aromatic compounds results from an operation of hydrotreatment of cuts selected from the group comprising the heavy naphtha issuing from catalytic cracking, the heavy naphtha from catalytic reforming, the heavy naphtha from steam cracking, the heavy naphtha from pyrolysis or a mixture of one or more of these naphthas.
9. Fuel according to claim 6, characterised in that the petroleum cut rich in aromatic compounds is preferably heavy naphtha issuing from catalytic cracking.
10. Fuel according to any of the preceding claims, characterised in that the vegetable oil is selected from the group comprising sunflower oil, palm oil, copra oil, soya oil, rape oil and mixtures thereof and is preferably rape oil.
11. Fuel according to any of the preceding claims, characterised in that the petroleum cut is completed by a further cut of hydrocarbons such as a heavy diesel fuel having a low sulphur content or a domestic fuel oil.
12. Use in a boiler running on domestic fuel oil of a fuel according to any of the preceding claims, without modification of this boiler.
13. Use of the fuel according to any of claims 1 to 9, characterised in that said fuel is used in a mixture with another fuel for boilers.