EP3325138B1

EP3325138B1 - Device for mixing water and heavy fuel oil, apparatus and process for producing a water/heavy fuel oil micro-emulsion

Info

Publication number: EP3325138B1
Application number: EP16753252.2A
Authority: EP
Inventors: Marco Luigi FUMAGALLI
Original assignee: Eme International Lux SA
Current assignee: Eme International Lux SA
Priority date: 2015-07-23
Filing date: 2016-07-18
Publication date: 2021-09-15
Anticipated expiration: 2036-07-18
Also published as: EP3325138A1; ITUB20152434A1; WO2017013074A1

Description

Field of the invention

The present invention relates to a device for mixing water and heavy fuel oil, to an apparatus and to a process for producing a water/heavy fuel oil micro-emulsion.
At present, fuel oil is mainly used in stationary combustion for the production of steam for industrial uses or for generating electricity. Another very important use is that in large heavy fuel oil stationary engines for producing electricity in big power stations.
The Heavy Fuel Oils (HFOs) category includes both finished products, namely residual fuels, and the primary refinery streams from which they are blended.
The present invention is specifically related to residual fuel oils, namely low-grade fuels primarily used in industrial boilers and other direct source heating applications (e.g., blast furnaces) and as a principal fuel for large marine engines. The residual fuels are products that consist primarily of the residuum of the refining process after virtually all of the higher quality hydrocarbons have been distilled, cracked, or catalytically removed from crude oil feedstock. Historically, these residual fuels were based on residuals from atmospheric distillation. Different organizations may use different parameters and may have different numerical specifications for fuel grades. Based on viscosity, ASTM D396 classifies heavy fuel oils as oils number 4 to 6. In general, the boiling point and carbon chain length of the fuel increases with fuel oil number; the higher the molecular weight of the oil's component, the higher the level of polyaromatic compounds, polycycloparaffins and hetero-atoms (N, O, S and metals) increase, and the lower the level of paraffins; viscosity also increases with number and the heaviest oil has to be heated to get it to flow. Price usually decreases as the fuel number increases.
In the European Union the Engler degree is generally used to classify fuels: heavy fuel oils are oils having a viscosity greater than 12° Engler at 50°C.

Background of the invention

Since heavy fuel oils generate high calorie and are relatively inexpensive, a large amount of heavy fuel oil is consumed all over the world for facilities in various industries including stationary combustion for the production of steam for industrial uses or for generating electricity. Other uses includes large scale heating facilities. Nevertheless, the heavy fuel oils are very difficult to handle and use as fuels because are oleaginous, viscous, high boiling materials which do not flow easily and can cause problems in handling, atomization, etc., as well as problems such as the clogging of the pipework and other components of combustion boilers. Moreover, when such heavy fuel oils are burnt, a large volume of pollutants, such as, sulphur oxides, nitrogen oxides, carbon monoxide, soot and dust are generated. If no effective antipollution countermeasure is taken, these pollutants can contaminate the environment and pose a serious threat to the ecological system.
Even with properly maintained equipment of the latest design, substantial amounts of unburned carbon and other products of incomplete combustion are emitted. Heavy oils are typically atomized to enhance burning, but the droplets often burn incompletely. One way to improve combustion is to improve atomization, decreasing the heavy oil droplet size entering the flame front, allowing a smaller droplet to burn out completely during the limited time allowed for combustion. Another way to improve combustion is to introduce tiny water droplets into the oil in the form of an emulsion. These water droplets are vaporized to steam as the oil droplet starts to burn. The steam produced inside the oil droplet shatters it into many smaller droplets. A typical oil droplet is on the order of 50-100 microns in diameter and it has been found that water droplets in the range of 2-10 microns are very effective and gross water contents of 5-15 % wt or so in the fuel provide enough energy to shatter most or almost all the droplets and drastically reduce particulate emissions. NO_x emissions are usually reduced somewhat as well due to the fact that peak flame temperature is reduced slightly leading to a reduction in thermal NO_x formation. This technology allows not only a reduction in pollution combustion residues but also an increase in fuel efficiency and therefore a reduction in greenhouse gas emissions.
Water/heavy fuel oil micro-emulsions are nowadays known.
Public document JP2007152214 discloses a device according to the preamble of claim 1. It discloses an emulsified product preparation apparatus constituted of a long tilting cylindrical container, a spiral ribbon rotating body inserted between its upper end and bottom end, a feed port for feeding a mixed liquid of an emulsifier and water disposed on the uppermost wall of the cylindrical container, an oil feed port disposed on the upper wall immediately below the upper most wall, an emulsified product ejection port disposed on and protruded outwardly from the bottom of the cylindrical container, and an emulsified product returning pipe disposed between the oil feed port and a bottom opening of the cylindrical container parallel to and outside the cylindrical container for allowing a part of emulsified product to return to the oil feed port and then into the long cylindrical container.
In this field, the Applicant has observed that the manufacturing process for emulsion fuels is not straightforward. Indeed, the emulsion fuel cannot be produced simply by putting together water and fossil fuel.
The Applicant further observed that the dispersion of fine water and oil droplets, which are inherently mutually immiscible, is very unstable and goes back to the initial condition of the two-phase mixture over time. This phase separation phenomenon makes it difficult to accurately evaluate combustion efficiency for individual emulsion fuels.
The Applicant further observed that, since the phase separation phenomenon gradually proceeds over time, the combustion efficiency of the particular fuels involved varies depending on the time when the combustion experiment is performed.
The Applicant further observed that, currently, ultrafine emulsion fuel products are available, although there has not been any technology to maintain the products in a stable emulsified state. Emulsifying agents may be added to protect oil and water droplets in order to maintain the emulsified suspension. The development of these agents, however, is still in the fledgling stage and presents several challenges, including the possible effects on combustion.
The Applicant finally observed that the most urgent problem is how phase separation can be avoided to produce optimal emulsions and how the emulsified condition can be stabilized during a longer period.
The Applicant perceived that an higher level of emulsification can be promoted by circulating and/or recirculating a batch comprising heavy fuel oil, water and an emulsifying composition through a mixing device.
In particular, the Applicant has noted that circulating said batch in a mixing device provided with the features claimed and described further on is particularly advantageous in order to obtain a stable and homogeneous micro-emulsion.
The Applicant has conceived a mixing device, an apparatus comprising said mixing device and a process that allow the production of a water/heavy fuel oil micro-emulsion with excellent shelf-life, reduction in combustion-generated pollutants and efficient engine out-put, even with a high water content. Moreover, the emulsifying composition produced according to the process and/or by means of the mixing device or apparatus of the invention has very low environmental impact.
The Applicant has finally found that a mixing device provided with the features claimed and described further on is able to exert on the flowing liquid compression, centrifuging, dispersion and shear forces in order to promote emulsification.
The Applicant has verified that the rotor of the mixing device allows to increase the emulsification to highest levels.
The Applicant verified that the recirculation system(s) allows to increase the emulsification to highest levels.
The Applicant further verified that this recirculation system(s) allows to flexibly select the emulsification level of the batch, in particular adjusting the number of recirculation loops.

Summary

In a first aspect, the invention relates to a device according to claim 1, a device for mixing heavy fuel oil and water with emulsifying composition, comprising:

at least one duct for a flow of liquid, said duct extending along a main development direction and presenting an inlet opening and an outlet nozzle, wherein the inlet opening comprises a first inlet for water with emulsifying composition and a second inlet for heavy fuel oil;
a helix shaped rotor arranged in at least a portion of said duct and coaxial with the main development direction, said rotor being configured for defining a helix shaped advancement path for said liquid.

The structure of the mixing device according to the invention makes the flow to be subject to compression, centrifuging, dispersion and shear forces and makes the molecules to impact against the inner walls of the duct, greatly improving emulsification. These actions are possible thanks to the helix shaped rotor configured for defining a helix shaped advancement path for the liquid flowing in the duct.
According to the invention, the mixing device comprises at least a cone shaped septum placed in the duct upstream of the rotor and coaxial with the main development direction, said cone shaped septum being provided with a plurality of apertures made through its conical wall.
In an aspect according to the preceding aspects, said apertures are arranged around the main development direction.
In an aspect according to the preceding aspect, said cone shaped septum comprises two, three or four series of apertures arranged along respective circular paths defined at the conical wall of the cone shaped septum.
In an aspect according to the preceding aspects, the mixing device comprises a plurality of cone shaped septa arranged in series upstream of the helix shaped rotor.
In an aspect according to the preceding aspects, said cone shaped septum tapers towards the outlet nozzle.
In an aspect according to the preceding aspects, the apertures are shaped as slots.
In an aspect according to the preceding aspects, each aperture defines an advancement direction for the liquid flowing inside the duct that is inclined with respect to the main development direction.
In an aspect according to the preceding aspects, the mixing device further comprises heating elements configured to heat the duct at a predetermined temperature and/or thermal insulating elements configured to maintain a predetermined temperature inside the duct, for example comprised between 40°C and 80°.
In an aspect according to the preceding aspects, the mixing device further comprises at least one divergent section and/or one convergent section.
In an aspect according to the preceding aspects, said cone shaped septum is disposed at one divergent section.
In an aspect according to the preceding aspects, said mixing device ends with a convergent section defining said outlet nozzle.
In an aspect according to the preceding aspects, the first inlet is arranged inside the second inlet.
In an aspect according to the preceding aspects, the first inlet is coaxial with the second inlet.
In an aspect according to the preceding aspects, the first inlet and/or the second inlet are coaxial with the main development direction.
In an aspect according to the preceding aspects, the first inlet is connected with a nozzle for water with emulsifying composition.
In an aspect according to the preceding aspects, a first channel is in fluid communication with the first inlet.
In an aspect according to the preceding aspects, a second channel is in fluid communication with the second inlet.
In an aspect according to the preceding aspect, an outlet from the second channel is arranged around the nozzle.
In an aspect according to the preceding aspects, the mixing device further comprises a choking arranged upstream of the rotor and/or upstream of the cone shaped septum.
In an aspect according to the preceding aspect, the choking is defined by a cone shaped septum having a central opening.
In an aspect according to the preceding aspects, the mixing device further comprises power generating means, for example a motor, disposed outside said duct and configured for rotating said helix shaped rotor.
In an aspect according to the preceding aspects, the helix shaped rotor is arranged inside the duct at a section having a constant section area.
In an aspect according to the preceding aspects, the outlet nozzle of the duct is provided with an external conical wall and with a cone.
In an aspect according to the preceding aspect, the cone is supported by brackets and defines, together with the external conical wall, a choking in the passage section for the liquid.
In an aspect according to the preceding aspects, the cone is defined by a tapering angle of about 40°.
In an aspect according to the preceding aspects, the external conical wall is distanced from the cone by a distance defined perpendicularly to the external conical wall and/or the cone. Such distance decreases along the main direction.
In an aspect according to the preceding aspects, the decrease of said distance is due to the orientation of the external conical wall with respect to the cone.
In an aspect according to the preceding aspects, the external conical wall has a tapering angle which is greater than the tapering angle of the cone, preferably has a tapering angle of about 50°.
In a second aspect, the invention relates to an apparatus for preparing a water/heavy fuel oil micro-emulsion according to claim 14, said apparatus comprising:

at least one heavy fuel oil feeding unit;
at least one emulsifying composition feeding unit;
at least one water feeding unit;
at least one mixing tank in fluid communication with the heavy fuel oil feeding unit, with the emulsifying composition feeding unit and with the water feeding unit;
a mixing device according to one or more of the preceding aspects and/or of the appended claims operatively connected to said mixing tank and disposed upstream of the mixing tank.

In an aspect according to the preceding aspect, the emulsifying feeding unit is in direct fluid communication with the water feeding unit upstream of said mixing device.
In an aspect according to the preceding aspects, the apparatus further comprises a recirculation conduit configured for recirculating the batch in the mixing tank comprising said heavy fuel oil, said emulsifying composition and said water.
In an aspect according to the preceding aspect, said recirculation conduit comprises a mixing device according to one or more of the preceding aspects and/or of the appended claims.
In an aspect according to the preceding aspects, the mixing tank comprises heating elements configured to heat the mixing tank at a predetermined temperature and/or thermal insulating elements configured to maintain a predetermined temperature inside the mixing tank, for example comprised between 40°C and 80°C.
In an aspect according to the preceding aspects, the apparatus further comprises a storage tank disposed downstream of the mixing tank and an additional recirculation conduit configured for recirculating the batch in the storage tank comprising said heavy fuel oil, said emulsifying composition and said water, said additional recirculation conduit comprising a mixing device according to one or more of the preceding aspects and/or of the appended claims.
In an aspect according to the preceding aspect, the storage tank comprises heating elements configured to heat the storage tank at a predetermined temperature and/or thermal insulating elements configured to maintain a predetermined temperature inside the storage tank, for example comprised between 40°C and 80°C.
In a third aspect, the invention relates to a process according to claim 15, a process for preparing a water/heavy fuel oil micro-emulsion, comprising:

feeding a predetermined amount of a heavy fuel oil into a mixing device according to one or more of the preceding aspects and/or of the appended claims;
feeding a predetermined amount of an emulsifying composition into said mixing device;
feeding a predetermined amount of water into said mixing device;
feeding a mixing tank with a batch obtained in said mixing device, the batch comprising said heavy fuel oil, said emulsifying composition and said water.

In an aspect according to the preceding aspect, the emulsifying composition is fed into a water tank in order to form a pre-mix of water and emulsifying composition.
In an aspect according to the preceding aspect, the process further comprises feeding water and emulsifying composition from the water tank into the mixing device.
In an aspect according to the preceding aspect, the process further comprises:

recirculating the batch in the mixing tank through a recirculation conduit;
discharging the fuel micro-emulsion batch.

In an aspect according to the preceding aspects, recirculating the batch in the mixing tank comprises recirculating the batch through a further mixing device according to one or more of the preceding aspects and/or of the appended claims. In an aspect according to the preceding aspect, the recirculation step is carried out about five or six times.
In an aspect according to the preceding aspects, discharging the fuel micro-emulsion batch comprises feeding the fuel micro-emulsion batch from the mixing tank to a storage tank.
In an aspect according to the preceding aspects, the process further comprises:

recirculating the fuel micro-emulsion batch in the storage tank through an additional recirculation conduit and through a further mixing device according to one or more of the preceding aspects and/or of the appended claims.

In an aspect according to the preceding aspect, the recirculation step of the fuel micro-emulsion batch is carried out continuously in the additional recirculation conduit.
In an aspect according to the preceding aspects, the water/heavy fuel oil micro-emulsion comprises:

from 4.0 to 40.0 % by weight of water,
emulsifying composition, preferably in amount of at most 1.1% by weight, and
heavy fuel oil to make it up to 100%.

In one embodiment, the emulsifying composition may comprise at least:

tannic acid at a concentration of from about 30.0% to about 50.0% of the weight of the composition,
sorbitan monostearate at the concentration of from about 2.0% to about 4.0% of the weight of the composition, and dodecanoic acid at the concentration of from about 0.5% to about 1.5% of the weight of the composition, and
hydrogen peroxide at 50% by volume at the concentration of from about 2.5 to about 3.5% of the weight of the composition and di-tert-butyl peroxide at the concentration of from about 0.3% to about 2.5% of the weight of the composition.

In an aspect according to the preceding aspects, the emulsifying composition may comprise at least:

tannic acid at a concentration of from about 38.0% to about 47.0% of the weight of the composition,
sorbitan monostearate at the concentration of from about 2.5% to about 3.1% of the weight of the composition, and dodecanoic acid at the concentration of from about 0.8% to about 1.2% of the weight of the composition,
hydrogen peroxide at 50% by volume at the concentration of about 3.0% of the weight of the composition and di-tert-butyl peroxide at the concentration of from about 0.5% to about 2.0% of the weight of the composition,
ethylene glycol at the concentration of about 20.0% of the weight of the composition,
ammonium nitrate at the concentration of from about 0.5% to about 0.9% of the weight of the composition,
an ethanethiol at the concentration of from about 1.5% to about 3.0% of the weight of the composition, and
glutaraldehyde at the concentration of from about 0.05 to about 0.1 % of the weight of the composition.

In an aspect according to the preceding aspects, the present emulsifying composition consists of:

tannic acid at a concentration of from about 38.0% to about 47.0% of the weight of the composition,
sorbitan monostearate at the concentration of from about 2.5% to about 3.1% of the weight of the composition, and dodecanoic acid at the concentration of from about 0.8% to about 1.2% of the weight of the composition,
hydrogen peroxide at 50% by volume at the concentration of about 3.0% of the weight of the composition and di-tert-butyl peroxide at the concentration of from about 0.5% to about 2.0% of the weight of the composition,

ethylene glycol agent at the concentration of about 20.0% of the weight of the composition,
ammonium nitrate at the concentration of from about 0.5% to about 0.9% of the weight of the composition,
an ethanethiol at the concentration of from about 1.5% to about 3.0% of the weight of the composition, and
glutaraldehyde at the concentration of from about 0.05 to about 0.1 % of the weight of the composition.

Further aspects of the invention are presented below.
In an aspect according to the preceding aspects, the overall batch comprising the heavy fuel oil, the emulsifying composition and the water may be of about 5000 liters.
In an aspect according to the preceding aspects, the predetermined amount of emulsifying composition in the overall batch may be of about 50 liters, preferably of about 25 liters.
In an aspect according to the preceding aspects, the water is fed into the mixing tank in a mixed state with the emulsifying composition and with heavy fuel oil.
In an aspect according to the preceding aspects, the predetermined amount of water in the overall batch may be of about 1100 liters.
In an aspect according to the preceding aspects, water can be any type of purified water, such as distilled, deionized or demineralized, or waste water; preferably is tap water or waste water.
In an aspect according to the preceding aspects, the pressure of the water and emulsifying composition entering the mixing device may be comprised between about 100 and 150 bar, preferably may be of about 120 bar.
In an aspect according to the preceding aspects, the predetermined amount of heavy fuel oil in the overall batch may be of about 3850 liters, preferably of about 3875 liters.
In an aspect according to the preceding aspects, the pressure of heavy fuel oil entering the mixing device may be of about 120 bar.
In an aspect according to the preceding aspects, the overall batch comprising the heavy fuel oil, the emulsifying composition and the water may be of about 5000 liters.
In an aspect according to the preceding aspects, the percentage of heavy fuel oil, emulsifying composition and water of the batch in the mixing tank may be as follows:

In an aspect according to the preceding aspects, recirculation through the additional mixing device is performed for a number of times comprised between about three and between about nine, preferably of about five or six.
In an aspect according to the preceding aspects, the pressure of fluid entering the additional mixing device may be comprised between about 1,5 and 2,5 bar, preferably may be of about 2 bar. The time required for performing this recirculation may be of about 4 min (each loop).
In an aspect according to the preceding aspects, the water is heated before reaching the mixing tank, preferably at a temperature comprised between about 40°C and 80°.
In an aspect according to the preceding aspects, the emulsifying composition is heated before reaching the mixing tank, preferably at a temperature comprised between about 40°C and 80°.
Further characteristics and advantages will be clear from the detailed description of a preferred but not exclusive embodiment of an apparatus and a process for producing a water/heavy fuel oil micro-emulsion in accordance with the present invention.

Description of drawings

Such description will be set forth hereinbelow with reference to the set of drawings, provided merely as a non-limiting example, in which:

Figure 1 is a schematic view of the apparatus for preparing a water/heavy fuel oil micro-emulsion according to the invention;
Figure 2 is an exploded sectional view of a mixing device according to the invention belonging to the apparatus of Figure 1;
Figure 3 is a sectional view of a mixing device according to the invention belonging to the apparatus of Figure 1;
Figure 4 is a front view of a mixing device according to the invention belonging to the apparatus of Figure 1.

Detailed description

Referring to the attached schematic figure 1, the apparatus for preparing a water/heavy fuel oil micro-emulsion is identified by reference numeral 1. The apparatus 1 comprises a heavy fuel oil feeding unit 2, an emulsifying composition feeding unit 3, a water feeding unit 4 and a mixing tank 5 provided with a recirculation conduit 6 and a discharge duct 7. The discharge duct 7 allows the mixing tank 5 to be in fluid communication with a storage tank 8. The storage tank 8 is provided with an additional recirculation conduit 9 and with an additional discharge duct 10.
The heavy fuel oil feeding unit 2 comprises a heavy fuel oil tank 11, a first conduit 12 having a first end connected to the heavy fuel oil tank 11 and a second end connected to the mixing tank 5. A first pump 13 is placed in the first conduit 12 to pump the heavy fuel oil from the respective tank 11 towards the mixing tank 5. The water feeding unit 4 comprises a water tank 14 and a second conduit 15 having a first end connected to the water tank 14 and a second end connected to the mixing tank 5. A second pump 16 is placed in the second conduit 15.
The emulsifying composition feeding unit 3 comprises an emulsifying composition tank 17 and a third conduit 18 having a first end connected to the emulsifying composition tank 17 and a second end connected to the water tank 14. A third pump 19 is placed in the third conduit 18 to pump the emulsifying composition from the emulsifying composition tank 17 to the water tank 14. In other words, the water tank 14 is fed with emulsifying composition. Inside the water tank 14 water and emulsifying composition are mixed and in the second conduit 15 departing from the water tank 14 emulsifying composition and water flow. The second pump 16 pumps water and emulsifying composition from the water tank 14 towards the mixing tank 5. Heating elements, not shown, are operatively connected to the water tank 14 and/or to the second conduit 15 to heat the emulsifying composition and water.
Further heating elements, not shown, are operatively connected to the emulsifying composition tank 17 and/or to the third conduit 18 to heat the emulsifying composition.
As shown in figure 1, the second conduit 15 is connected to the first conduit 13 at a connection point placed downstream of the first and second pumps 13, 16 and upstream of the mixing tank 5. A mixing device 20 is placed at the connection point. The mixing device 20 will be described in detail further on. Downstream the mixing device 20 a common conduit 21 is present through which the batch comprising heavy fuel oil, emulsifying composition and water flow towards the mixing tank 5.
The mixing tank 5 presents an upper portion 22 and a bottom portion 23. The bottom portion 23 can be shaped like an hopper.
The common conduit 21 enters through an upper wall of the mixing tank 5 and a terminal end 24 of said common conduit 21 is located in the upper portion 22. A first valve 25 is placed in the common conduit 21 between the connection point and the mixing tank 5.
The recirculation conduit 6 presents a first end connected to the bottom portion 23 of said mixing tank 5 and a second end connected to the upper portion 22 of the mixing tank 5.
The first end of the recirculation conduit 6 can be the terminal end of the common conduit 21 disclosed above. A fourth pump 26 is located in the recirculation conduit 6 to pump the batch comprising water, emulsifying composition and heavy fuel oil from the bottom portion 23 of the mixing tank 5 to the upper portion 22 of the mixing tank 5. The recirculation conduit 6 further comprises a second valve 27 arranged between the mixing tank 5 and the fourth pump 26 and a third valve 28 arranged between the fourth pump 26 and the mixing tank 5.
The mixing tank 5 comprises heating elements (not shown) configured to heat the mixing tank 5 at a predetermined temperature, for example a temperature comprised between 40°C and 80°C, preferably between 50°C and 70°C. The mixing tank 5 further comprises thermal insulating elements (not shown) configured to maintain a predetermined temperature inside the mixing tank 5, for example comprised between 40°C and 80°C, preferably between 50°C and 70°C. Such a temperature, together with the recirculation via the recirculation conduit 6, helps the batch to get homogeneous and maintain its properties.
As previously said, a discharge duct 7 departs from the mixing tank 5. The discharge duct 7 has a first end connected to the mixing tank 5 and a second end connected to the storage tank 8.
A fifth pump 29 is located in the discharge duct 7, as well as a fourth valve 30. The fifth pump 29 is configured to pump the batch comprising water, emulsifying composition and heavy fuel oil from the mixing tank 5 to the storage tank 8. As illustrated in figure 1, the fourth valve 30 is located between the mixing tank 5 and the fifth pump 29.
The storage tank 8 is connected with the additional recirculation conduit 9. The additional recirculation conduit 9 has a first end connected to a bottom portion 31 of the storage tank 8 and a second end connected to an upper portion 32 of the storage tank 8.
A sixth pump 33 is located in the additional recirculation conduit 9 to pump the water/heavy fuel oil micro-emulsion from the bottom portion 31 of the storage tank 8 to the upper portion 32 of the storage tank 8. A fifth and a sixth valve 34, 35 are located in the additional recirculation conduit 9. The fifth valve 34 is located just downstream the storage tank 8 between the first end of the additional recirculation conduit 9 and the sixth pump 33, while the sixth valve 35 is located between the sixth pump 33 and the second end of the additional recirculation conduit 9.
The storage tank 8 comprises heating elements (not shown) configured to heat the storage tank 8 at a predetermined temperature, for example a temperature comprised between 40°C and 80°C, preferably between 50°C and 70°C. The storage tank 8 further comprises thermal insulating elements (not shown) configured to maintain a predetermined temperature inside the storage tank 8, for example comprised between 40°C and 80°C, preferably between 50°C and 70°C. Such a temperature, together with the recirculation via the additional recirculation conduit 9, helps the batch to get homogeneous and maintain its properties.
Downstream the storage tank 8, there is an additional discharge duct 10. The additional discharge duct 10 has a first end 36 connected to the bottom portion 31 of the storage tank 8 and a terminal end 37. A seventh pump 38 is disposed in the additional discharge duct 10 to pump the batch comprising water, emulsifying composition and heavy fuel oil from the first end 36 of the additional discharge duct 10 to its terminal end 37. Further, a seventh valve 39 is located in the additional discharge duct 10 upstream the seventh pump 38.
The mixing device 20 according to the invention is represented in figures 2-3. The mixing device 20 is substantially shaped like a cylindrical body and delimits internally a duct 40 extending along a main development direction X-X of the cylindrical body. The mixing device 20 comprises an inlet opening 41 and an outlet nozzle 42. The inlet opening 41 comprises a first inlet 43 for water with emulsifying composition and a second inlet 44 for heavy fuel oil.
The first inlet 43 is connected to the second conduit 15 and is fed with water with emulsifying composition and the second inlet 44 is connected to the first conduit 12 and is fed with heavy fuel oil.
Inside the mixing device 20, a fuel micro-emulsion (i.e. water/heavy fuel oil micro-emulsion) batch starts to form thanks to the structure of the mixing device 20 itself. Said batch exiting the mixing device 20 is then sent, through the common conduit 21, to the mixing tank 5. The water/heavy fuel oil micro-emulsion comprises:

The structure of the mixing device 20 is described in the following.
The cylindrical body comprises a first portion 45 wherein the first and the second inlet 43, 44 are defined, a second portion 46 comprising one or more cone-shaped septa 47, a third portion 48 comprising a rotor 49 and a fourth portion 50 defining the outlet nozzle 42 for the batch. The first portion 45 is connected to the second portion 46, which is connected to the third portion 48. The third portion 48 is connected to the fourth portion 50. The connection among the first, the second, the third and the fourth portion 45, 46, 48, 50 can be made through threaded couplings.
The inlet opening 41 has a substantially circular shape. The inlet opening 41 has a diameter Din of about 50 mm and has a cross section area Ain of about 1960 mm².
The first inlet 43 is disposed at a central portion of the inlet opening 41, while the second inlet 44 is shaped as an annulus around the first inlet 43. The first and the second inlet 43, 44 are coaxial with the main development direction X-X of the duct 40. The first inlet 43 has a diameter Dfi of about 5 mm and a cross section area Afi of about 20 mm².
The difference between the diameter Din of the inlet opening 41 and the diameter Dfi of the first inlet 43 is therefore of about 45 mm. The cross section area Asi of the second inlet 44 is of about 1940 mm².
The duct 40 has a total length Ltot of about 1250 mm; therefore, the ratio between the total length Ltot of the duct 40 and the diameter Din of the inlet opening 41 is of about 25.
The duct 40 is formed by a plurality of duct sections reciprocally aligned along the main direction X-X. Said plurality of sections comprises divergent sections, convergent sections and sections provided with constant cross section areas. The duct 40 comprises a first section 51 arranged between the inlet opening 41 and a cone shaped septum 47. The first section 51 has an overall constant diameter D1 equal to the diameter Din of the inlet opening 41 and a length L1 of about 200 mm (ratio between the length L1 of the first section 51 and the diameter Din of the inlet opening 41 equal to 4). The first section 51 comprises a first channel 52 in fluid communication with the first inlet 43 and a second channel 53 in fluid communication with the second inlet 44. Water with emulsifying composition flows inside the first channel 52 and heavy fuel oil flows inside the second channel 53. The first channel 52 has a circular cross section and is coaxial with second channel 53 and with the main direction X-X. The cross section of the second channel 53 is shaped as an annulus around the first channel 52. The first and the second channels 52, 53 have respective constant diameters. The first channel 52 has a terminal end wherein a nozzle or spray dryer 54 is disposed. The nozzle or spray dryer 54 is configured for spraying the water with the emulsifying composition inside the duct 40. The water with the emulsifying composition exiting the nozzle 54 is mixed with the heavy fuel oil exiting the second channel 53. By spraying the water with emulsifying composition the dimensions of the drops of water and emulsifying composition get smaller and therefore the contact surface between heavy fuel oil and water and emulsifying composition increases. Such an increase in the contact surface allows a better mixing between heavy fuel oil with water and emulsifying composition. Downstream of the nozzle 54 a drilled septum or a grill 100 is located.
Downstream of the nozzle 54 the first section 51 defines a choking of the passage section of the liquid in the duct 40. The choking allows a better mixing of the heavy fuel oil and water with emulsifying composition. The choking is defined by a cone shaped septum 55 with a central opening. The cone shaped septum 55 tapers in the flow advancement direction. The central opening has a diameter Lw of about 12,5 mm and therefore the ratio between said diameter Lw and the diameter Din of the inlet opening is of about 0,25.
The first section 51 opens in a second section 56 having a greater diameter with respect to the first section 51. The second section 56 is a divergent section and has a tapering angle Ω2 of about 45°. The second section 56 has a length L2 of about 150 mm and therefore the ratio between its length L2 and the diameter Din of the inlet opening 41 is of about 3.
A plurality of cone shaped septa 47 are arranged in the second section 56 in series to each other. As illustrated in figure 3, the cone shaped septa 47 are three. Each cone shaped septum 47 is formed by a conical wall exhibiting through apertures 57. The apertures 57 are shaped as slots. The passage of the fluid through the apertures 57 of the cone shaped septa 47 generates a turbulent motion of the fluid that makes it possible a better mixing of heavy fuel oil with water and emulsifying composition in order to obtain the water/heavy fuel oil micro-emulsion.
Preferably, as illustrated in figure 4, the apertures 57 are disposed at the conical wall following a regular pattern around the main development direction X-X. The cone shaped septum 47 comprises series of apertures 57. Each series of apertures 57 is arranged along a circular path coaxial with the main development direction X-X. Each circular path can be defined by a respective diameter. As shown in figure 3, the second section 56 comprises a first cone shaped septum 47 having two series of apertures 57, a second cone shaped septum 47 arranged downstream the first cone shaped septum having three series of apertures 57 and a third cone shaped septum 47 arranged downstream the second cone shaped septum having four series of apertures 57.
The apertures 57 consecutively disposed along a same circular path are distanced by a value of distance different from a value of distance defined between apertures 57 consecutively disposed along a different circular path. The third cone shaped septum 47 is shown in figure 4. The third cone shaped septum 47 has four series of apertures 57 disposed along a respective circular path defined at its conical wall. A first circular path of apertures 57 is defined in a central portion of the third cone shaped septum 47. Adjacent apertures 57 consecutively arranged along said first circular path are distanced by a first distance L1c. Around the first circular path is defined a second circular path of apertures 57. Adjacent apertures 57 consecutively arranged along said second circular path are distanced by a second distance L2c greater than the first distance L1c. Around the second circular path is defined a third circular path of apertures 57. Adjacent apertures 57 consecutively arranged along the third circular path are distanced by a third distance L3c greater than the second distance L2c. Around the third circular path is defined a fourth circular path of apertures 57. Adjacent apertures 57 consecutively arranged along the fourth circular path are distanced by a fourth distance L4c greater than the third distance L3c. Such apertures 57 enables the water, the heavy fuel oil and the emulsifying composition to further mix with each other in order to obtain a water/heavy fuel oil micro-emulsion. Further, each aperture 57 defines an advancement direction for the liquid flowing inside the duct 40 that is inclined with respect to the main development direction X-X (see figure 3).
Downstream the second section 56, the duct 40 comprises a third section 58 having a constant diameter D3 of about 175 mm and a length L3 of about 50 mm. Therefore, the ratio between the diameter D3 of the third section 58 and the diameter Din of the inlet opening 41 is of about 3,5 and the ratio between length L3 of the third section 58 and diameter Din of the inlet opening 41 is of about 1. The cone shaped septa 47 develops also inside the third section 58.
Downstream the third section 58, the duct 40 comprises a fourth section 59 having a constant diameter D4 of about 125 mm and a length L4 of about 575 mm. The fourth section 59 is defined at the third portion 48 of the cylindrical body of the mixing device 20. Therefore, the ratio between the diameter D4 of the fourth section 59 and the diameter Din of the inlet opening 41 is of about 2,5 and the ratio between the length L4 of the fourth section 59 and the diameter Din of the inlet opening 41 is of about 11,5.
In the fourth section 59 a helix shaped rotor 49 is arranged. The helix shaped rotor 49 is rotated by power generating means 60 (schematically shown in figure 3), for example by a motor, disposed outside said duct 40. The helix shaped rotor 49 can be rotated at a speed of about 300-500 rpm. The helix shaped rotor 49 comprises a plurality of screw shaped portions 61. In figure 3 is shown a helix shaped rotor 49 having seven screw shaped portions 61. Each screw shaped portion 61 has a maximum diameter DX that is substantially equal to the diameter D4 of the fourth section 59 and a distance LX with the adjacent screw shaped portion 61 that is of about 60 mm. The ratio between the distance LX and the diameter Din of the inlet opening 41 is therefore of about 1,2. Each screw shaped portion 61 is configured to guide the batch in the duct 40 along a portion of a globally helix shaped advancement path. Such a helix shaped advancement path enables the water, the heavy fuel oil and the emulsifying composition to further mix with each other in order to obtain a water/heavy fuel oil micro-emulsion. Further, the rotating motion of the helix shaped rotor 49 creates a turbulent motion of the fluid advancing in the duct 40, thus enabling a better mixture of heavy fuel oil with water and emulsifying composition in order to obtain the water/heavy fuel oil micro-emulsion. The helix shaped rotor 49 has a length LR parallel to the main development direction X-X of the duct of about 450 mm. Therefore, the ratio between the length LR of the helix shaped rotor 49 and the diameter Din of the inlet opening 41 is of about 9.
Downstream the fourth section 59, the duct 40 comprises a fifth section 62 defining the outlet nozzle 42 of the duct 40. The fifth section 62 is defined at the fourth portion 50 of the cylindrical body of the mixing device 20 and is provided with an external conical wall 63 and with a cone 64. The cone 64 is supported by brackets 65 and defines, together with the external conical wall 63 of the duct 40, a choking in the passage section for the liquid. According to the cross section of figure 3, the cone 64 is defined by a tapering angle Ω5 of about 40°. The external conical wall 63 is distanced from the cone 64 by a distance D5 defined perpendicularly to the external conical wall 63 and/or the cone 64. Such distance D5 decreases along the main direction X-X. The decrease of the distance D5 is due to the orientation of the external conical wall 63 with respect to the cone 64. As it can be seen from figure 3, the external conical wall 63 has a tapering angle ΩW which is greater than the tapering angle Ω5 of the cone 64. The tapering angle ΩW is of about 50°. The outlet nozzle 42 has a diameter Dout of 35 mm and therefore the ratio between the diameter Dout of the nozzle 42 and the diameter Din of the inlet opening is of about 0,7. The outlet nozzle 42 has a cross section area of about 962 mm².
The mixing device 20 comprises heating elements 101 configured to heat the duct 40 at a predetermined temperature, for example a temperature comprised between 40°C and 80°C, preferably between 50°C and 70°C. The heating elements 101 are schematically represented in figure 1. The mixing device 20 further comprises thermal insulating elements (not shown) configured to maintain a predetermined temperature inside the duct 40, for example a temperature comprised between 40°C and 80°C, preferably between 50°C and 70°C. Such temperature allows a better mixing of the heavy fuel oil with the water and with the emulsifying composition.
Auxiliary mixing devices 20', 20" provided with the same structure detailed above may be installed in the recirculation conduit 6 downstream of the fourth pump 26 and/or in the additional recirculation conduit 9 downstream of the sixth pump 33 (see figure 1). Auxiliary mixing devices 20', 20" installed in such positions are fed with only one fluid. Such fluid is water/heavy fuel oil micro-emulsion. In other words, both the first and second inlet 43, 44 of the auxiliary mixing devices 20', 20" are fed with water/heavy fuel oil micro-emulsion. Such auxiliary mixing devices 20', 20" allows a better mixing of the water/heavy fuel oil micro-emulsion.
A control unit, not shown, is operatively connected to pumps 13, 16, 19, 26, 29, 33, 38, and valves 25, 27, 28, 30, 34, 35, 39, to heating elements, to thermal insulating elements and to suitable sensors (of temperature, pressure, flow, ecc.) operatively connected to the apparatus 1 in order to control the process for preparing a water/heavy fuel oil micro-emulsion implemented by said apparatus 1. In use and according to the process of the invention for preparing a water/heavy fuel oil micro-emulsion, a predetermined amount of heavy fuel oil is pumped by means of the first pump 13 into the mixing device 20 through the first conduit 12.
In use, the mixing device 20 is further fed with a predetermined amount of water and emulsifying composition. The water and emulsifying composition are pumped by means of a second pump 16 into the mixing device 20 after having been mixed in a tank, such as the water tank 14. The water and emulsifying composition are pumped into the mixing device 20 through the second conduit 15. The pressure of fluid entering the mixing device 20 may be of about 120 bar.
While pumping the heavy fuel oil, a predetermined amount of the emulsifying composition is pumped by the third pump 19 into the water tank 14.
In one embodiment, the emulsifying composition may comprise at least:

In one embodiment, the emulsifying composition may comprise at least:

tannic acid at a concentration of from about 38.0% to about 47.0% of the weight of the composition,
sorbitan monostearate at the concentration of from about 2.5% to about 3.1% of the weight of the composition, and dodecanoic acid at the concentration of from about 0.8% to about 1.2% of the weight of the composition,
hydrogen peroxide at 50% by volume at the concentration of about 3.0% of the weight of the composition and di-tert-butyl peroxide at the concentration of from about 0.5% to about 2.0% of the weight of the composition,
ethylene glycol at the concentration of about 20.0% of the weight of the composition,
ammonium nitrate at the concentration of from about 0.5% to about 0.9% of the weight of the composition,
an ethanethiol at the concentration of from about 1.5% to about 3.0% of the weight of the composition, and
glutaraldehyde at the concentration of from about 0.05 to about 0.1% of the weight of the composition.

In one embodiment, the present emulsifying composition consists of:

tannic acid at a concentration of from about 38.0% to about 47.0% of the weight of the composition,
sorbitan monostearate at the concentration of from about 2.5% to about 3.1% of the weight of the composition, and dodecanoic acid at the concentration of from about 0.8% to about 1.2% of the weight of the composition,
hydrogen peroxide at 50% by volume at the concentration of about 3.0% of the weight of the composition and di-tert-butyl peroxide at the concentration of from about 0.5% to about 2.0% of the weight of the composition,
ethylene glycol agent at the concentration of about 20.0% of the weight of the composition,
ammonium nitrate at the concentration of from about 0.5% to about 0.9% of the weight of the composition,
an ethanethiol at the concentration of from about 1.5% to about 3.0% of the weight of the composition, and
glutaraldehyde at the concentration of from about 0.05 to about 0.1% of the weight of the composition.

Before reaching the mixing device 20, the emulsifying composition and/or the heavy fuel oil is pre-heated by the heating elements to a controlled temperature between 40°C and 80°C.
The control unit controls and drives the first, second and third pumps 13, 16, 19 in order to obtain a correct and predefined ratio between the emulsifying composition, the heavy fuel oil and the water to be pre-mixed in the mixing device 20.
The mixing tank 5 is filled with the predetermined amount of water/heavy fuel oil micro-emulsion. The time required to fill the mixing tank 5 with said predetermined amount of water/heavy fuel oil micro-emulsion may be of about 24 min.
After having been mixed in the mixing device 20, the water/heavy fuel oil micro-emulsion reaches the mixing tank 5.
The first and second pumps 13, 16 are then stopped.
At this stage, the overall batch comprising the heavy fuel oil, the emulsifying composition and the water may be of about 5000 liters.
The predetermined amount of the emulsifying composition in the overall batch may be of about 50 liters, preferably of about 25 liters.
The predetermined amount of water in the overall batch may be of about 1100 liters.
The predetermined amount of heavy fuel oil in the overall batch may be of about 3850 liters, preferably of about 3875 liters.
The percentage of heavy fuel oil, emulsifying composition and water of the batch in the mixing tank 5 may be as follows:

At this stage, the second valve 27 is opened and the fourth pump 26 pumps the water/heavy fuel oil micro-emulsion in the recirculation conduit 6. Such a recirculation is carried out a predetermined number of times, preferably five or six times. The time required for performing this recirculation is of about 24 min (about 4 min for each loop). The flow rate in the recirculation conduit can be of about 20,8 L/s (liters per second). In the embodiment wherein an auxiliary mixing device 20' is provided in the recirculation conduit 6, the micro-emulsion pass through such auxiliary mixing device 20' during each recirculation step. The pressure of fluid through the recirculation conduit 6 may be of about 2 bar.
Then, the second valve 27 is closed, the fourth valve 30 is opened and the fifth pump 29 is activated. The fifth pump 29 pumps the micro-emulsion in the storage tank 8 through the discharge duct 7. When the micro-emulsion is in the storage tank 8, the seventh valve 39 is closed, the fifth and the sixth valves 34, 35 are opened and the sixth pump 33 is activated. The sixth pump 33 pumps the micro-emulsion in the additional recirculation conduit 9. Such a recirculation step is carried out continuously, i.e. without interruption as long as the micro-emulsion is in the storage tank 8. The pressure of fluid through the additional recirculation conduit 9 may be of about 2 bar. In the embodiment wherein an auxiliary mixing device 20" is provided in the additional recirculation conduit 9, the micro-emulsion pass through such auxiliary mixing device 20" during the recirculation step.
The micro-emulsion can be extracted from the storage tank 8 through the additional discharge duct 10. In the extraction step, the fifth valve 34 is closed (no recirculation in the additional recirculation conduit) and the seventh pump 38 is activated.
The closure and opening of the valves 25, 27, 28, 30, 34, 35, 39 and the activation or deactivation of the pumps 13, 16, 19, 26, 29, 33, 38 are controlled by the control unit.
As previously mentioned, at the end of all the recirculation steps, the fuel micro-emulsion batch is discharged through the additional discharge duct 10. The process can be started again with another batch to be emulsified.

Claims

Device (20) for mixing heavy fuel oil and water with emulsifying composition, comprising:
- at least one duct (40) for a flow of liquid, said duct extending along a main development direction (X-X) and presenting an inlet opening (41) and an outlet nozzle (42), wherein the inlet opening (41) comprises a first inlet (43) for water with emulsifying composition and a second inlet (44) for heavy fuel oil;

- a helix shaped rotor (49) arranged in at least a portion (45, 46, 48, 50) of said duct (40) and coaxial with the main development direction (X-X), said helix shaped rotor (49) being configured for defining a helix shaped advancement path for said liquid;
characterized in the device further comprising:
- at least a cone shaped septum (47) placed in the duct upstream of the helix shaped rotor (49) and coaxial with the main development direction (X-X), said cone shaped septum (47) being provided with a plurality of apertures (57) made through its conical wall.
The device of claim 1, wherein said apertures (57) are arranged around the main development direction (X-X).
The device of claim 1 or 2, wherein said cone shaped septum (47) tapers towards the outlet nozzle (42).
The device of claim 1 or 2 or 3, wherein said cone shaped septum (47) comprises two, three or four series of apertures (57) arranged along respective circular paths defined at the conical wall of the cone shaped septum (47).
The device of anyone of claims 1 to 4, comprising a plurality of cone shaped septa (47) arranged in series upstream of the helix shaped rotor (49).
The device of anyone of claims 1 to 5, wherein each aperture (57) defines an advancement direction for the liquid flowing inside the duct that is inclined with respect to the main development direction (X-X).
The device of one of the preceding claims, further comprising heating elements (101) configured to heat the duct (40) at a predetermined temperature inside the duct (40).
The device of one of the preceding claims, wherein the first inlet (43) is arranged inside the second inlet (44).
The device of one of the preceding claims, wherein the first inlet (43) is connected with a nozzle (54) for water with emulsifying composition.
The device of claim 9, wherein a second channel (53) is in fluid communication with the second inlet (44) and an outlet from the second channel (53) is arranged around the nozzle (54).
The device of one of the preceding claims, wherein the outlet nozzle (42) of the duct (40) is provided with an external conical wall (63) and with a cone (64).
The device of the preceding claim, wherein the cone (64) defines, together with the external conical wall (63), a choking in the passage section for the liquid.
The device of the preceding claim, wherein the external conical wall (63) is distanced from the cone (64) by a distance (D5) defined perpendicularly to the external conical wall (63) and/or the cone (64), wherein such distance (D5) decreases along the main direction (X-X).
Apparatus (1) for preparing a water/heavy fuel oil micro-emulsion, comprising:
- at least one heavy fuel oil feeding unit (2);

- at least one emulsifying composition feeding unit (3);

- at least one water feeding unit (4);

- at least one mixing tank (5) in fluid communication with the heavy fuel oil feeding unit (2), with the emulsifying composition feeding unit (3) and with the water feeding unit (4);

- a mixing device (20) according to one or more of the preceding claims operatively connected to said mixing tank (5) and disposed upstream of the mixing tank (5).
Process for preparing a water/heavy fuel oil micro-emulsion, comprising:
- feeding a predetermined amount of a heavy fuel oil into a mixing device (20) according to one or more of claims 1 to 13;

- feeding a predetermined amount of an emulsifying composition into said mixing device (20);

- feeding a predetermined amount of water into said mixing device (20);

- feeding a mixing tank (5) with a batch obtained in said mixing device (20), the batch comprising said heavy fuel oil, said emulsifying composition and said water.