EP0128792B1 - Combustion process and apparatus particularly suited for the combustion of heavy fuel - Google Patents

Abstract

The clean combustion of a combustible material is facilely carried out by (i) in situ generating a dispersing first stream of hot combustion gases by establishing a first downstream axially extending, axially symmetrical helical flowstream of combustion-supporting gases in a first combustion reaction zone and by introduction and combustion of a combustible fluid feedstream therein, (ii) serially directly contacting and intimately admixing the material cleanly combustible hereby with said first stream of hot combustion gases at a zone of reduced pressure thereof defining the inlet end of a second combustion reaction zone and whereat and downstream thereof said first stream of hot combustion gases is also in the configuration of an axially symmetrical helical flowstream, (iii) the amounts of said combustion-supporting gases and said combustible fluid being such as to effect essentially instantaneous dispersion and entrainment of fine particles of said cleanly combustible material at and downstream of said point of direct contact with said first stream of hot combustion gases, (iv) establishing a second downstream axially extending, axially symmetrical helical flowstream of combustion-supporting gases in said second combustion reaction zone, and (v) whereby said cleanly combustible material dispersed and entrained within said first stream of hot combustion gases is introduced into and combusted within said second stream of combustion-supporting gases in said second combustion reaction zone.

Description

The present invention relates to a method and a device for clean combustion and applies in particular to the burning of heavy fuels.

• soit un combustible issu de la distillation d'un pétrole brut tel qu'un fuel 4 à 6 selon norme ASTM (Burner Fuel Specification D 396 - cf Perry et Chilton Chemical Engineers Handbook - Fifth Edition 9.9) ou ce pétrole brut lui-même,
• soit une émulsion,
• soit une suspension partiellement ou totalement combustible d'un solide dans un liquide ou un gaz.

By heavy fuels is meant in particular:

• either a fuel resulting from the distillation of a crude oil such as a fuel 4 to 6 according to standard ASTM (Burner Fuel Specification D 396 - cf Perry and Chilton Chemical Engineers Handbook - Fifth Edition 9.9) or this crude oil itself,
• either an emulsion,
• either a partially or completely combustible suspension of a solid in a liquid or a gas.

By clean combustion is meant combustion without final emission of carbonaceous particles.

We know that this defect represents a major drawback when using heavy fuels. It results in the fact that the formation of solid residues is observed, adding to any ash.

Because, to date, this problem has not been resolved satisfactorily to the knowledge of the plaintiff.

However, the applicant has claimed, in FR-A-2 257 326, a method of contacting substances having different phases according to which at least one phase is used to form a well-vortex flow with axial symmetry and at less a phase is introduced along the axis of symmetry of said well-vortex flow, up to the zone in relative depression of said well-vortex flow, the momentum of the volume elements of the well-vortex flow relative to that of the volume elements of the axial phase being such that said well-vortex flow causes both the disintegration, the dispersion and the taking over of the axial phase and its possible treatment by the well-vortex flow.

In FR-A-2 276 086, a method and a device have been claimed for the generation of hot gases by carrying out combustion in the zone in relative depression of a symmetrical helical flow.

It was therefore naturally thought to supply the device according to the first patent with a hot gas obtained according to the method of the second.

But it is understandable that we encountered technical problems, in particular in the area of high temperatures.

This is what led the plaintiff to claim, in EP-A-7 846, a new arrangement of the elements which amounts to making, in situ, the generation of hot gases in a first zone by imposing on said gases the form a well-vortex flow and introduce the material to be treated into the zone in relative depression of this flow, so as to avoid subjecting the sensitive parts of the device to the prolonged action of hot gases.

This solution allowed the use of temperatures higher than those of resistance of conventional steels, leading to remarkable results as regards the size distribution of the drops obtained and consequently the vaporization speed of these drops.

However, it is known that the use of heavy fuels encounters problems due to the inhomogeneity of the spraying, which results in particular in the formation of black particles (soot, cenospheres, etc.).

The object of the present invention is to overcome these drawbacks.

• a) on introduit, dans une première zone, un courant gazeux comburant selon des trajectoires hélicoïdales symétriques par rapport à leur axe commun et on introduit un courant de fluide combustible, de manière à réaliser une première phase de combustion dispersante ;
• b) on force l'écoulement résultant à travers un passage restreint, dans une seconde zone, de manière à lui donner la forme d'un écoulement puits-tourbillon symétrique ;
• c) on introduit la substance combustible à traiter dans la zone en dépression relative dudit écoulement puits-tourbillon et l'on provoque une seconde combustion grâce à un second courant gazeux comburant hélicoïdal dans la seconde zone, les quantités de gaz comburant et combustible introduits dans la première zone étant suffisantes pour provoquer la pulvérisation obtenue par transfert de la quantité de mouvement de la première phase de combustion dispersante, puis la vaporisation de la substance à traiter à l'entrée de la seconde zone.

According to the method of the invention:

• a) a combustion gas stream is introduced into a first zone along symmetrical helical paths relative to their common axis and a stream of combustible fluid is introduced, so as to produce a first phase of dispersing combustion;
• b) the resulting flow is forced through a restricted passage, in a second zone, so as to give it the form of a symmetrical well-vortex flow;
• c) the combustible substance to be treated is introduced into the zone in relative depression of said well-vortex flow and a second combustion is caused by a second helical oxidant gas stream in the second zone, the quantities of oxidant gas and fuel introduced into the first zone being sufficient to cause the spraying obtained by transfer of the momentum of the first dispersing combustion phase, then the vaporization of the substance to be treated at the entrance to the second zone.

In practice, the combustible substance introduced into the second zone is given a low initial speed, preferably less than 10 m / s and if possible at 5 m / s, so as not to have to increase the initial amount of movement too much. hot dispersing gas phase, the ratio of the momentum of said hot dispersing gas phase to that of the combustible substance being at least 100 but generally lying preferably between 1,000 and 10,000.

The spraying thus takes place by transfer of the momentum and an isore-distributed dispersion is obtained at the entrance to the second instantaneous zone practically instantaneous in a spectrum of fine particles which are thus in the best conditions for homogeneous and rapid vaporization. This spraying will be called a spraying spray.

According to the invention, this avoids the pitfall of poor dispersion of a hardly flammable substance and incomplete combustion at high temperature.

The present invention thus allows a spray quality which leads to clean combustion of heavy fuels, which, as already said, has not been possible until now.

Optionally, the second gas stream is introduced tangentially to form a helical stream which can be made well-vortex by a restricted passage delimiting the second zone. In this case, a material to be treated can be introduced axially into the zone in relative depression of this second flow. This substance is, for example, a mineral solution or suspension, based on synthetic or natural carbonates, silicas, silico-aluminates, but it can also be of an organic nature, it can also be a residual water to be decontaminated.

The first gas stream used to produce the well-vortex flow is advantageously constituted by air.

The first fuel introduced can be supplied either in gaseous form or in the form of a spray cloud which is obtained by any known means such as a spray nozzle of the type described in the work by K. MASTERS entitled "SPRAY DRYING and published by George Godwin Limited-London (second edition - 1972), either by a device of the well-vortex flow type.

This first fuel is preferably chosen for its ease of combustion.

It is therefore located in the range of expensive fuels, having regard to heavy fuels, and it will therefore be advantageous to reduce the proportion thereof relative to said heavy fuel.

The second fuel to be treated, such as heavy fuel or combustible suspension, is introduced axially into the zone in relative depression of the well-vortex flow coming from the first zone, so as to promote the suction effect due to said zone in relative depression.

The second fuel is generally a fuel corresponding to types 4 to 6 of the ASTM standards.

The second symmetrical well-vortex flow is obtained using an oxidizing gas such as air.

The helical currents introduced into a zone are advantageously under low pressure, preferably at a pressure less than 10 ⁵ Pa relative to the pressure prevailing directly downstream of said zone when said pressure is equal to atmospheric pressure.

• une première chambre (1) de combustion correspondant à la zone 1
• une chambre de mise en contact et de combustion (2) correspondant à la zone 2.

The method according to the invention can be implemented by a device according to EP 7846 which comprises (Fig. 1)

• a first combustion chamber (1) corresponding to zone 1
• a contacting and combustion chamber (2) corresponding to zone 2.

The chamber (1) has an envelope (3) closed at its upstream part by a bottom plate (4), an annular space (6) delimited internally by a perforated wall (7), a restricted passage (10), at least a pipe (8) for tangential supply of a gaseous phase and a means for injecting fuel (5) inside the chamber (1), the casing (3) ending downstream by a convergent ( 9) in which ends, along the axis of symmetry of rotation of the chamber (1), an injection device (11), substantially at the level of the restricted passage (10), the contacting chamber (2) extending downstream the chamber (1) along the same axis of rotational symmetry and being provided with a perforated wall (12) defining an annular space (13) with its envelope (14), space in which leads to at least one tangential inlet ( 15).

This device can also comprise (FIG. 2) a second treatment chamber (16) of a substance introduced by a second injection device (17) disposed substantially at the level of a second restricted passage (18).

In the chamber (1), a hot gas is generated by combustion of a first fuel.

At the restricted passage (10) separating the chamber (1) from the chamber (2), the material to be treated is introduced and the well-whirlpool effect located downstream of the restricted passage is used to disperse the fuel into very fine elements volume.

• la température minimale de pulvérisation vaporisante du combustible lourd est compris entre 150 et 300 °C, à l'issue de la zone d'isorépartition,
• la température de la phase gazeuse issue de la zone 1 est compris entre 400 et 1 000 °C.
• le rapport massique de la quantité d'air introduit dans la zone 2, par rapport à celle de l'air introduit dans la zone 1, est compris entre 1 et 100, cette dernière valeur étant fonction de la température finale visée en zone 2
• le rapport massique de la quantité de combustible introduit dans la zone 1, par rapport à celle introduite dans la zone 2, est compris entre 0,01 et 0,1.

In a simple case where the oxidizing gases consist of air and where the first fuel is a gaseous hydrocarbon, the normal operating conditions for this device are as follows:

• the minimum spraying temperature for heavy fuel is between 150 and 300 ° C, at the end of the isorepartition zone,
• the temperature of the gas phase from zone 1 is between 400 and 1000 ° C.
• the mass ratio of the amount of air introduced into zone 2, relative to that of the air introduced into zone 1, is between 1 and 100, the latter value being a function of the final temperature targeted in zone 2
• the mass ratio of the quantity of fuel introduced into zone 1, relative to that introduced into zone 2, is between 0.01 and 0.1.

• de la nature du courant gazeux comburant introduit dans la zone 1 : par exemple oxygène au lieu d'air,
• de la nature du combustible introduit dans la zone 1 : par exemple hydrogène. Dans le cas où on vise une température dans la zone 1 plus élevée, de l'ordre de 1 000 à 2 500 °C notamment lorsqu'on utilise l'oxygène comme comburant, on met en oeuvre préférentiellement le dispositif illustré à la Fig. qui présente une chambre 1, dans laquelle débouchent tangentiellement les entrées 19 reliant la chambre 1 à des tores de distribution 20 alimentés par des tubulures 21.

Of course, these operating conditions may be modified depending on:

• the nature of the oxidizing gas stream introduced into zone 1: for example oxygen instead of air,
• the nature of the fuel introduced into zone 1: for example hydrogen. In the case where a temperature in the higher zone 1 is aimed at, of the order of 1000 to 2500 ° C., in particular when oxygen is used as oxidizer, the device illustrated in FIG. which has a chamber 1, into which the inlets 19 tangentially open connecting the chamber 1 to distribution toroids 20 supplied by pipes 21.

The cooling of the chamber 1 is ensured by a circulation of cooling liquid comprising an annular circulation space 22 around the chamber 1.

This annular circulation space 22 can be replaced by a tubular assembly 23 hollowed out in the thickness of the walls of the chamber 1, as illustrated in FIG. 4, in particular on a small scale.

The temperature of the gas phase, coming from the second zone, will largely depend on the envisaged application.

Finally, all these conditions will also depend on the nature of the fuel to be vaporized.

Example 1

Using the device illustrated in FIG. 1, the tests summarized in the following table were carried out:

During test 8, the gas from the system was rehomogenized in temperature in order to be able to carry out a thermal balance.

Experimental data

• Entrée : 54,4 kg/h x 1,096 kJ/kg °C x 950 °C = 56 848 kJ/h
• Génération : 19,9 kg/h x 41 840 kJ/kg = 832 616 kJ/h
• Sortie : 1123 kg/h x 1,075 kJ/kg °C x t °C d'où t °C = 735 °C

Calculation of the outlet temperature by balance in zone 2

• Input: 54.4 kg / hx 1.096 kJ / kg ° C x 950 ° C = 56 848 kJ / h
• Generation: 19.9 kg / hx 41,840 kJ / kg = 832,616 kJ / h
• Outlet: 1123 kg / hx 1.075 kJ / kg ° C xt ° C hence t ° C = 735 ° C

The temperature measured at the center of the gas outlet pipe is 850 ° C, which taking into account the experimental inaccuracies in the measurements is entirely in agreement with a temperature rise of 735 ° C for a gas that has previously been overpressed.

• lorsque la combustion dans la chambre (1) a lieu, la paroi interne de la chambre (2) est toujours froide et très propre et le reste durant toute l'expérience ;
• lorsque l'on coupe l'alimentation du combustible dans la zone (1), on observe :
  • que les parois de la chambre (2) se salissent très rapidement (chemisage de fuel liquide fondu noir), à mesure que la température des gaz de pulvérisation décroît,
  • que la flamme change d'aspect (devient plus éclairante) et que les gaz de combustion se chargent d'imbrûlés,
  • que l'on atteint facilement l'extinction dans la chambre (2).

The advantage of the present invention can be easily understood in the following manner:

• when the combustion in the chamber (1) takes place, the internal wall of the chamber (2) is always cold and very clean and the rest during the whole experiment;
• when the fuel supply is cut off in zone (1), we observe:
  • the walls of the chamber (2) get dirty very quickly (lining of black molten liquid fuel), as the temperature of the spraying gases decreases,
  • the flame changes its appearance (becomes more illuminating) and the combustion gases become charged with unburnt,
  • that one easily reaches extinction in the chamber (2).

• diamètre : 180 mm
• longueur : 500 mm

et que, en paroi froide, il se dégage donc de l'ordre de 63 x 10⁶ kJ/h.m³, valeur très élevée par rapport à celles qui caractérisent les brûleurs classiques. De telles dimensions sont normalement incompatibles avec une combustion de combustible lourd, surtout à de tels débits, en présence de paroi froide ce que la coupure d'alimentation du combustible en zone (1) confirme d'ailleurs systématiquement.It is important to note that, for approximately 20 kg / h of totally burnt fuel, the chamber (2) has the following dimensions:

• diameter: 180 mm
• length: 500 mm

and that, on a cold wall, it therefore emerges on the order of 63 × 10 ⁶ kJ / hm ³ , a very high value compared to those which characterize conventional burners. Such dimensions are normally incompatible with combustion of heavy fuel, especially at such flow rates, in the presence of a cold wall, which the fuel supply cut-off in zone (1) systematically confirms.

The device therefore allows the “clean” combustion of a heavy fuel (type No. 4 ASTM) with an additional fuel in the chamber (1), of the order of 1 to 10% by mass (relative to the heavy fuel )

Example 2

• Pour 1000 kg/h de nonadécane : chaleur de vaporisation = 356 kJ/kg à 25 °C, chaleur de combustion = 44 279 kJ/kg

The operating conditions were determined:

• For 1000 kg / h of nonadecane: heat of vaporization = 356 kJ / kg at 25 ° C, heat of combustion = 44,279 kJ / kg

These conditions are collated in the table below:

This system makes it possible to generate hot gases containing little or no solid particles from the least noble fuels and we can easily imagine the economic benefits in applications such as: drying, heating, production of steam and electricity, and in general all use of heavy DC fuels ”, distillation residues, combustible suspensions, etc.

One observes, in fact, a “much less luminous gas flame (that is to say containing less radiant solid particles) when the vaporizing atomization of the fuel is carried out with hot gas than in the case where one is content with a simple spraying into the combustion air.

• 1) très peu de pression motrice nécessaire (< 3 x 10⁵Pa par exemple si la combustion a lieu aux environs de la pression atmosphérique), donc dispositifs simples de pompage non soumis à l'abrasion
• 2) pas de système d'ajutage pulvérisant soumis à une abrasion forte
• 3) possibilité de co-injection de produit traitant in situ, dans la flamme même, les éventuels sous- produits indésirables naissant dans la combustion (S0₂ par exemple).

Furthermore, the device for introducing the main fuel imposes little pressure drop on its flow. It therefore allows the injection of a mixture consisting of several phases (slurries or dense pneumatic transport) or of several of these co-sprayed mixtures (coaxial introduction for example) which has the following advantages compared to current techniques

• 1) very little driving pressure required (<3 x 10 ⁵ Pa for example if combustion takes place at about atmospheric pressure), therefore simple pumping devices not subject to abrasion
• 2) no spraying nozzle system subjected to strong abrasion
• 3) possibility of co-injection of product treating in situ, in the flame itself, any undesirable by-products arising in combustion (S0 ₂ for example).

• séparément : solution, bouillie, transport pneumatique
• ou en mélange : suspension stabilisée.

Co-injected products (such as very fine carbonates) can be:

• separately: solution, slurry, pneumatic transport
• or as a mixture: stabilized suspension.

4) possibility of treatment, with hot gases, of coal-based mixtures, these gases containing oxygen, with a view either to the total combustion of the carbon, or to its partial combustion in the presence of oxidants of this carbon aimed to its "gasification" (water vapor and / or carbon dioxide for example).

A possible diagram of this gasification treatment is illustrated in FIG. 5 where P is a device according to the invention, suitable for this type of supply (diagram in principle in FIG. 6).

In a preliminary zone P, combustion is carried out with oxygen of a hydrocarbon Cm Hn, in the possible presence of C0 ₂ .

At the restricted passage characterizing the device according to the invention, a solid carbonaceous material such as ground coal is introduced, either wet or put in pneumatic transport by C0 ₂ , or any other means.

In Figure 5 are explained the respective feed rates of zones P and A: for 1 of carbon, we introduce W Cm Hn, X0 ₂ , Y CO ₂ , ZH ₂ , Cm Hn denoting either hydrogen or a hydrocarbon.

In zone A, gasification of the solid carbonaceous material is carried out with the C0 ₂ introduced and the combustion gases coming from the preliminary zone P. It is optionally possible to introduce into zone A other reagents such as hydrogen for example .

Finally, in zone B, rapid quenching is carried out by a third body such as water.

This system makes it possible to produce a synthesis gas whose composition depends on the operating conditions of P and A.

Claims (7)

1. A process for clean combustion comprising :

a) introducing a gaseous combustion-supporting flow (8) into a first zone (1) along helical paths which are symmetrical with respect to their common axis and introducing a flow of combustible fluid (5) so as to provide for a first dispersing combustion phase,

b) forcing the resulting flow through a restricted passage (10) into a second zone (2) so as to impart thereto the form of a symmetrical axial flow-vortex flow configuration, and

c) introducing the substance to be treated (11) into the zone which is in a condition of relative depression of said axial flow-vortex flow configuration, the process being characterised in that said substance to be treated is combustible and that combustion thereof is caused by means of a second gaseous combustion-supporting flow (15) in the second zone (2) and that the amounts of fuel and combustion-supporting gas which are introduced into the first zone are sufficient to cause atomisation produced by transfer of the momentum of the first dispersing combustion phase and then vaporisation of the substance to be treated at the intake of the second zone.

2. A process according to claim 1 characterised in that the combustible substance is introduced into the second zone at an initial velocity which is lower than 10 m/s, advantageously lower than 5 m/s, the ratio of the momentum of the dispersing gaseous phase to that of the combustible substance being at least equal to 100 and preferably between 1 000 and 10000.

3. A process according to one of claims 1 and 2 characterised in that the helical flows introduced into a zone are at a relative pressure lower than 10⁵ Pa with respect to the pressure obtaining directly downstream of the system of said zone when said pressure is equal to atmospheric pressure.

4. A process according to any one of claims 1 to 3 characterised in that :

the minimum vaporising atomisation temperature of the heavy fuel results in a temperature of between 150 and 300 °C at the outlet of the isodistribution zone,

the temperature of the gaseous phase issuing from the first zone is between 400 and 1 000 °C,

the ratio by mass of the amount of air introduced into the zone 2 with respect to the amount of air introduced into the zone 1 is between 1 and 100, and

the ratio by mass of the amount of fuel introduced into the zone 1 with respect to the amount of fuel introduced into the zone 2 is between 0.01 and 0.1.

5. Use of the process according to one of claims 1 to 3 for treating products by the injection of a mixture consisting of a plurality of phases.

6. Use of the process according to one of claims 1 to 3 for the treatment of products by the injection of a plurality of co-atomised mixtures.

7. Use of the process according to one of claims 1 to 3 for treating carbon-based mixtures.

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