FR2731504A1 - Low pollution burner fuel supply system - Google Patents

Abstract

Fuel pumped (6) from storage (5) enters a reservoir (1) with heating facilities (15) and level control (7). The pumped (19) fuel (18), pressure regulated (23, 22), enters the mixer (21) together with water and e.g., sodium carbonate neutraliser solution, from similarly equipped reservoirs (2, 3). All flows are metered (20). The mixer feeds (24) a by-passable (30) re-heater (25), initially filled (27) with fuel only, and thence is pumped (33) via the emulsifier (34) to the burner(s) (36). Surplus fuel returns (37) via a reducing valve (38) to a venturi passage in the mixer, powerfully aspirating the infeeds and ensuring thorough mixing. The emulsifier tube contains a central stack of perforated disks between two helical springs. Cavitation and pulsation in the inlet passage cause resonant vibration of both stack and individual disks, giving a colloidal emulsion.

Description

Fuel oil supply device reducing pollution
The invention relates to a method and a device for supplying a burner with a liquid mixture containing a hydrocarbon fuel and water.

Such a method and such a device are used in particular for supplying oil burners to heating installations. It is known that the presence of water allows a more complete combustion of the hydrocarbons, which gives a better yield and a strong reduction in the unburnt solids (soot).

Liquid and gaseous natural hydrocarbons contain sulfur which, when burned, becomes sulfur dioxide and then sulfur dioxide, which combines with water to give sulfuric acid H2SO4. Likewise, nitrogen and oxygen in the air combine, under the effect of the flame temperature, to form nitrous and nitric oxides and finally nitric acid. There is no need to insist on the corrosive nature of sulfuric and nitric acids and on the dangers involved in their dissemination in the atmosphere. In large installations, the acid gases are washed with water containing a neutralizing reagent. The waste water from washing is discharged into the wild or into the sewers, which again leads to pollution. In addition, the washing efficiency is not always perfectly satisfactory.

The object of the invention is to remedy these drawbacks.

The invention relates in particular to a process of the kind defined in the introduction, and provides that the mixture is brought to the burner in the form of an emulsion the aqueous phase of which contains at least one neutralizing agent capable of converting the acid vapors produced in the non-corrosive burner flame.

At the temperature of the burner flame, which is generally between 900 and 1600 "C, the acid vapors react very quickly and completely with the neutralizing agent and consequently do not cause corrosion or pollution. The reaction leads to the formation neutral sulphates and nitrates which are deposited on the walls of the flue gas exhaust pipes and can be recovered by the usual cleaning and sweeping procedures to be used, for example, as fertilizer in agriculture.

In the emulsion, each fuel droplet is immediately surrounded by the neutralizing agent in solution ready to react with the acid vapors produced by combustion.

Optional, complementary or alternative characteristics of the invention are set out below - Said neutralizing agent is chosen from alkali, alkaline-earth and ammonium hydroxides and carbonates. In the case of a carbonate, in particular sodium carbonate, the reactions produce the corresponding sulphate and nitrate, and carbon dioxide which are released into the atmosphere.

- The emulsion is colloidal.

The invention also relates to a device for implementing the method as defined above, comprising a mixer, means for introducing into the mixer the constituents of the mixture to be produced, fuel, water and neutralizing agent, at metered relative flow rates, an emulsifier receiving the mixture produced by the mixer, a circulation pump placed in series with the emulsifier so as to produce an emulsion flow rate greater than the flow rate consumed by the burner, a supply line supplying pumps the burner with the flow rate of emulsion necessary for the burner and a return line bringing the excess flow rate from the pump to the mixer so as to be mixed therewith.

This device can be used both to supply a single burner and to supply several burners in parallel. In the latter case, the reference to the burner must be understood as a reference to all of the burners supplied by the device.

The device according to the invention may include at least some of the following features - The mixer has a first inlet for the emulsion coming from the return line, suitable for forming an emulsion jet, an outlet for the mixture substantially coaxial with the first inlet, other inputs for the components arranged laterally with respect to the first inlet, and means arranged between the first inlet and the outlet for producing a suction at said other inlets, in cooperation with said emulsion jet.

- The first inlet has an axial nozzle with a tubular wall, the other inlets being arranged and distributed around said tubular wall.

- The means for producing a suction comprise a constricted passage of the venturi type.

- The constricted passage is followed by a plate placed across the path of the mixture and pierced with a multiplicity of orifices offering in total a passage section less than the minimum section of the constricted passage.

- Each of said orifices has a median constriction.

- The emulsifier has a substantially coaxial inlet and outlet between which a first throttled passage is successively disposed, deflector means placed in the path of the mixture to be struck by it and mounted so as to be able to oscillate in the axial direction, and a second strangled passage.

- The deflector means comprise an alternating stack of two types of plates pierced with a multiplicity of orifices having respectively a cylindrical shape and a constricted shape, the constricted orifices having a minimum section at least equal to the section of the cylindrical orifices, the orifices constricted by a plate being axially aligned with the cylindrical orifices of the preceding plate and offset transversely with respect to those of the following plate, two adjacent plates defining between them a free volume into which their orifices open.

- The stack of plates is maintained in a middle position between the first and second passages throttled by elastic retaining means.

- The plates of the stack are mounted so as to slide individually along the cylindrical internal wall of an emulsifier body and are applied against each other by the elastic retaining means.

- Means for reheating the mixture are interposed in the path of the latter between the mixer and the emulsifier.

- The circulation pump is placed upstream of the emulsifier and a pressure limiter is provided downstream of it to establish the supply pressure of the burner at a value between 1 and 2 bars.

- The mixer has an inlet for the fuel and at least one inlet for the water and for the neutralizing agent, connected to respective tanks.

- The mixer has an inlet for most of the water and another inlet for a concentrated solution of the neutralizing agent.

The characteristics and advantages of the invention will be explained in more detail in the description below, with reference to the accompanying drawings, in which - FIG. 1 represents a functional diagram of a device according to the invention; - Figure 2 is an axial sectional view of a mixer that can be part of this device; and - Figure 3 is a partial view in axial section of an emulsifier that can be part of this device.

The device illustrated in FIG. 1 comprises three tanks 1, 2 and 3 intended to contain fuel oil, water and a concentrated solution of neutralizing agent, for example sodium carbonate, respectively. The fuel oil is brought into the tank 1 by a pipe 4 opening at the top of it, from a storage tank 5, thanks to a pump 6.

The tank 5 and the pump 6 can be part of a conventional heating installation which has been modified to include the device according to the invention. An overflow pipe 7 returns from the tank 1 to the tank 5 and makes it possible to maintain a constant level in the tank. The water tank 2 is supplied by a pipe 8 which can be connected to a distribution network 9 and which is provided with a non-return valve 10 and a float valve 11 also ensuring a constant level. A solenoid valve 12 controlled by two detectors 13 of the water level in the tank intervenes in the event of failure of the float valve.

The reservoir 3 has at its top a filling opening 14 through which one can introduce solid sodium carbonate and water to produce the concentrated solution of neutralizing agent. As a variant, this solution can be introduced via a pipe (not shown) from a storage tank (not shown), the liquid level being maintained by means of sensors 13 similar to those of the tank 2.

Each of the tanks 1, 2 and 3 is provided with a resistor 15 making it possible to reheat its content when the temperature is very low or, in the case of fuel oil, to lower its viscosity when it contains heavy hydrocarbons.

The indications below are valid for each of the three tanks. The lower part 16 of the tank is conical and is connected to a drain pipe provided with a valve 17. Above the conical part 16 is connected an outlet pipe 18 containing a pump 19 and a flow meter 20 and connected to a input of a mixer 21 common to the three circuits. A return line 22 is connected to the outlet line 18, downstream of the pump 19 and upstream of the flow meter 20, and returns to the reservoir, at a point higher than the start of the line 18. This return line 22 contains a pressure regulator 23 which makes it possible to send each fluid to the mixer 21 at a determined pressure, and consequently to keep the ratios of the flow rates of the various fluids constant.

At the outlet of the mixer 21, a line 24 brings the oil-water-neutralizing agent mixture to a reheating tank 25 provided with a heating resistor 26 intended to keep the mixture sufficiently fluid. The lower part of the tank 25 has the same shape as that of the tanks 1 to 3 and also has a pipe and a drain valve.

The initial filling of the tank 25 can be carried out through a filling pipe 27 opening at its upper end, this pipe connecting to the return pipe 22 of the fuel tank 1. The mixture can leave the tank 25 by two outlet pipes in parallel, a line 28 located immediately above the lower conical part and a line 29 located above, each provided with a solenoid valve and a manual shut-off valve. After a period of rest of the installation during which water has been able to collect at the base of the tank, the pipe 28 is closed and the pipe 29 is opened to send to the burner a mixture which is not excessively rich in When the burner is lit, you can close the line 29 and open the line 28 to send the excess water to the burner without causing the flame to go out.

Two pipes 30 and 31, respectively fitted with a manual valve and a solenoid valve, connect the pipe 24 and the pipe 29 (into which the downstream end of the pipe 28 opens) so as to allow the mixture to short-circuit the reservoir 25 in the event of failure. The lines 29, 30 and 31 meet in a line 32 containing a pump 33 followed by an emulsifier 34, the pump 33 bringing into the emulsifier a flow rate of mixture greater than that consumed by the burner, under the pressure necessary for operation. of the emulsifier, between 10 and 25 bars depending on the viscosity of the mixture. A corresponding flow rate of emulsion leaves the emulsifier via a line 35 which is then subdivided into a line 36 for supplying one or more burners not shown and a return line 37 bringing the excess emulsion to the mixer 21. The line 37 contains a pressure reducer or pressure limiter 38 which brings the supply pressure of the burner to a value between 1 and 2 bars. A return line 39 coming from the burner or burners is connected to the line 37, downstream of the regulator 38 and upstream of a non-return valve 40.

The circuit of Figure 1 may include various solenoid valves, shut-off valves and regulating valves, in addition to those mentioned above.

As seen in Figure 2, the mixer 21 comprises four tubular parts 50, 51, 52 and 53, arranged along the same axis so as to define an axial path of fluid.

The axial bore of the part 51 is threaded in its upstream part and receives a region 54 externally threaded from the part 50. This region 54 is connected upstream to a region 55 of larger diameter, by a radial shoulder 56 which comes s '' press on the end 57 of the part 51. In the enlarged region 55, the axial bore of the part 50 has a thread 58 to receive a connection (not shown) connecting the mixer to the downstream end of the return pipe 37 .

The region 54 is extended downstream by a tubular wall 59 located inside the part 51. An annular space 60 is thus defined around the wall 59, inside the part 51, which communicates with four passages 61 opening laterally outside this part and arranged 900 from each other around the axis of the mixer. The passages 61 are internally threaded so as to connect respectively to the downstream ends of the three pipes 18 for leaving the tanks 1 to 3 and to a pressure sensor.

The part 52 is disposed immediately downstream of the part 51, its bore being in the form of a venturi with an upstream part 62 whose diameter decreases progressively from that of the bore of the part 51 and a downstream part 63 which increases progressively from the final value of the part 62, the latter having a curvilinear profile whose convexity is turned towards the inside and the part 63 being substantially frustoconical. The downstream end of the part 52, and the upstream end of the part 53, which faces it, have respective counterbores for housing the peripheral edge of a metal disc 64 which extends across the axial path and which is pierced with a multiplicity of orifices 65 constricted in the form of a venturi, the sum of the minimum passage sections of the orifices 65 being less than the minimum passage section in the part 52. Immediately downstream of the disc 64, the bore of the part 53 has a frustoconical shape decreasing diameter. Next, this bore comprises a cylindrical part provided with a thread 66 for receiving an outlet connector, not shown, connected to the upstream end of the pipe 24.

The parts 52, 64 and 53 are applied axially against each other and on the downstream end of the part 51 by a nut 67 provided with an internal flange 68, which is screwed onto a stainless steel tube 69, surrounding the part 52 and partly part 53, and itself screwed onto a region 70, externally threaded, of part 51 so as to bear on a shoulder 71 thereof turned downstream. The flange 68 is supported on a shoulder 72 of the part 53, also turned downstream, the part 53 and the tube 69 bearing one on the other by frustoconical surfaces 73.

Housing 74, 75, 76 and 77 are provided to receive O-rings intended to seal between the shoulder 56 and the end 57, between the shoulder 71 and the upstream end of the tube 69, between the part 53 and this same tube and between the flange 68 and the shoulder 72.

The emulsion produced by the emulsifier 34, at a flow rate imposed by the pump 33, and not used by the burner, returns to the mixer through line 37 and is injected there through the tubing 59. The jet then arrives in the defined venturi by the surfaces 62 and 63 and sucks the constituents coming from the reservoirs 1, 2 and 3 through the passages 61 and the annular space 60. A mixture of good uniformity is thus obtained, further improved by the perforated disc 64 which n 'is only necessary for large flows.

The emulsifier 34, partially shown in FIG. 3, comprises a tubular body 80 of stainless steel at the upstream end of which are mounted brass parts 52, 53 and 67 identical to the parts designated by the same reference numbers and described below. above in connection with the mixer 21. The thread 66 of the part 53 receives an inlet connector (not shown) connected to the downstream end of the pipe 32, and the nut 67 is screwed onto the body 80, its flange 68 pressing on the shoulder 72 of the part 53 so as to bring this to bear on the end of the body, by frustoconical surfaces of cooperation 73. The countersinking of the downstream end of the part 53 receives the upstream end of the part 52, adjacent to the rounded part 62 of the bore of the latter, while the countersinking of the part 53 ensures the centering of a helical spring 81.

Other parts, not shown, identical to parts 52, 53 and 67, are mounted at the downstream end of the tubular body 80, symmetrically of the first ones with respect to the median radial plane of the body. The part 52 arranged downstream ensures the centering of a spring 82 similar to the spring 81. A multiplicity of discs 83, 84 are stacked in the body 80, between the springs 81 and 82, so as to each extend across the body. These discs are held in place, tight against each other, by the two springs. Several discs 83, and several discs 84 different from the previous ones, are stacked alternately. Each disc 83 has a peripheral frame 85 which fits into the body 80 and has an axial length sufficient to ensure its sliding guide. Radially inside the frame, the disc 83 forms a thin plate pierced with a multiplicity of holes cylindrical 86. Each disc 84 has an axial thickness greater than that of the perforated plate of the discs 83 and less than that of the frames 85, and is clamped axially between the frames of two neighboring discs 83, a flat free volume 87 separating two consecutive plates . In this volume 87 open the orifices 86 of the adjacent disc 83, as well as orifices 88, of choked shape, of the adjacent disc 84. The orifices 88 have a minimum passage section at least equal to the passage section of the orifices 86. The orifices 88 of a disc 84 are axially aligned with the orifices 86 of the preceding disc 83 and offset transversely with respect to those of the disc 83 Housing not shown may be provided to receive sealing O-rings between at least some of the frames 85 and the body 80.

The variations in the passage section in the parts 53 and 52 produce cavitation phenomena in the mixture entering the emulsifier, and pressure pulsations which in turn cause a resonance vibration of the discs 83 and 84, both in their whole as compared to each other. This results in the formation of an emulsion in which the particles of the dispersed phase are in the form of micelles of colloidal dimensions. Such an emulsion allows better spraying of the fuel by the burner and increases the contact surface between the fuel and the combustion air, improving the combustion efficiency. At the same time, the neutralizing agent is distributed uniformly in all the sprayed droplets, which allows complete neutralization of the acid vapors formed.

It is understood that the ratio of the flow rates of fuel and neutralizing agent to be introduced into the mixer must be adjusted as a function of the quantities of acid vapors to be neutralized. The quantity of sulfuric vapors is itself determined by the quantity of sulfur contained in the fuel, while the quantity of nitric vapors is linked to the operating conditions of the burner. For example, one tonne of fuel oil containing 1% sulfur contains 10 kg, or 312.5 gram atoms, of sulfur, producing 312.5 moles of sulfuric acid, the neutralization of which requires as many moles of sodium carbonate. , about 33 kg, depending on the reaction
H2SO4 + Na2CO3 g Na2SO4 + C 2 + H2O.

To this quantity should be added that necessary for the neutralization of nitric vapors.

The device according to the invention can comprise two reservoirs instead of three for the constituents of the mixture, the neutralizing agent being dissolved in all of the water.

Claims (17)

Claims 1. Method for supplying a burner with a liquid mixture containing a hydrocarbon fuel and water, characterized in that the mixture is brought to the burner in the form of an emulsion the aqueous phase of which contains at least one solution a neutralizing agent capable of converting the acid vapors produced in the burner flame into non-corrosive substances. 2. Method according to claim 1, characterized in that said neutralizing agent is chosen from alkali, alkaline-earth and ammonium hydroxides and carbonates. 3. Method according to one of claims 1 and 2, characterized in that the emulsion is colloidal. 4. Device for implementing the method according to one of the preceding claims, comprising a mixer (21), means for introducing into the mixer the constituents of the mixture to be produced, fuel, water and neutralizing agent, at relative flow rates dosed, an emulsifier (34) receiving the mixture produced by the mixer, a circulation pump (33) placed in series with the emulsifier so as to produce an emulsion flow rate greater than the flow rate consumed by the burner, supply (36) bringing from the pump to the burner the flow rate of emulsion necessary for the latter and a return line (37) bringing back the excess flow rate from the pump to the mixer so as to be mixed with said constituents. 5. Device according to claim 4, characterized in that the mixer has a first inlet (50) for the emulsion coming from the return line, suitable for forming an emulsion jet, an outlet (53) for the substantially mixing coaxial with the first inlet, other inlets (61) for the components arranged laterally with respect to the first inlet, and means (52) arranged between the first inlet and the outlet to produce suction at said other inlets, in cooperation with said emulsion jet. 6. Device according to claim 5, characterized in that the first inlet comprises an axial nozzle (59) with a tubular wall, the other inlets being arranged and distributed around said tubular wall. 7. Device according to one of claims 5 and 6, characterized in that the means for producing a suction comprise a throttled passage (62, 63) of the venturi type. 8. Device according to claim 7, characterized in that the constricted passage is followed by a plate (64) placed across the path of the mixture and pierced with a multiplicity of orifices (65) offering in total a passage section less than the minimum section of the constricted passage. 9. Device according to claim 8, characterized in that each of said orifices has a median constriction. 10. Device according to one of claims 4 to 9, characterized in that the emulsifier has an inlet (53) and a substantially coaxial outlet between which are successively disposed a first constricted passage (52), deflector means (83, 84) placed in the path of the mixture to be struck by it and mounted so as to be able to oscillate in the axial direction, and a second throttled passage. 11. Device according to claim 10, characterized in that the deflector means comprise an alternating stack of two types of plates (84, 84) pierced with a multiplicity of orifices (86, 88) having respectively a cylindrical shape and a shape constricted, the constricted orifices having a minimum section at least equal to the section of the cylindrical orifices, the constricted orifices of a plate being axially aligned with the cylindrical orifices of the preceding plate and offset transversely with respect to those of the following plate, two neighboring plates defining between them a free volume (87) into which their orifices open. 12. Device according to claim 11, characterized in that the stack of plates is maintained in a middle position between the first and second passages throttled by elastic retaining means (81, 82). 13. Device according to claim 12, characterized in that the plates of the stack are mounted so as to slide individually along the cylindrical internal wall of an emulsifier body (80) and are applied against each other by elastic retaining means. 14. Device according to one of claims 5 to 13, characterized in that means (25, 26) for reheating the mixture are interposed in the path of the latter between the mixer and the emulsifier. 15. Device according to one of claims 5 to 14, characterized in that the circulation pump is arranged upstream of the emulsifier and that a pressure limiter (38) is provided downstream of it to establish the burner supply pressure at a value between 1 and 2 bars. 16. Device according to one of claims 5 to 15, characterized in that the mixer has an inlet for the fuel and at least one inlet for the water and for the neutralizing agent, connected to respective tanks (13). 17. Device according to claim 16, characterized in that the mixer has an inlet for most of the water and another inlet for a concentrated solution of the neutralizing agent.