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(11) | EP 0 978 574 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Compositions of cationic surfactants and their use as antifouling agents for induced draft fans (IDF) |
| (57) The present invention relates to a cationic surfactant in the form of one or more
quaternary ammonium salts. Additionally, the present invention provides also the formulation
of a composition comprising one or more such quaternary ammonium salts and their use
as antifouling agents for induced draft fans for extracting burnt gases from steel
plant units. The composition according to the invention comprises at least one quaternary ammonium salt having at least one radical selected from alkyl, alkylaryl, or etherocycle, wherein said radical has an alkyl chain with 8 to 18 carbon atoms and is bonded to the nitrogen atom. The active agent is generally present in an amount of 15 to 60% by weight with respect to the total composition. |
[0001] The present invention relates to cationic surfactants in the form of quaternary ammonium salts or mixtures thereof, compositions comprising one or more of said quaternary ammonium salts, and the use thereof as antifouling agents for induced draft fans for extracting burnt gases from steel plant units.
[0002] One of the three basic methods for manufacturing steel is that using a (LD) converter with oxygen lances (for total or partial combustion), which is also called BOF (Basic Oxygen Furnace). Such a converter consists of the following units: converter, oxygen lances and the cooling system thereof, heat recovery hood and cooling system, as well as a gas scrubbing system (scrubber) and cooling system.
[0003] In the BOF process, oxygen is injected through a lance into the steel raw material at a rate of about 424,700 l/min. The steel raw material consists of hot metal from the blast furnace, scrap steel and fluorspar. The BOF process rapidly refines scraps and blast furnace iron into molten steel having the desired chemical composition and temperature. The injection period runs for 20 to 25 minutes for melting and burning off impurities.
[0004] Because of the high heat release, the gases leaving the furnace hood during the oxygen injection process are very hot. Part of the heat may be recovered from said gases by means of a waste heat recovery boiler directly mounted over the hood. The dust load in this system is higher than in other systems, and particularly in the range of 27 to 33 kg/ton of steel. The extremely small size of the particulate and the generally high zinc content (2-5%) make this dust undesirable for sintering.
[0005] In order to overcome this drawback the system is provided with gas scrubbers and gas coolers which remove particulate and heat from the gases. The large amount of fine particles produced is about 1-2% of the finished tonnage. The particulate is extremely fine, generally with size of 1-2 microns. Additionally, the more violent the process, the higher the level of dust. The volume of dust is also a function of the oxygen consumption rate, where the greatest dust volumes occur during injection with flux addition. The chemistry of the gas streams changes considerably during injection as a function of the loads and the resultant gases produced in the course of the process.
[0006] Usually, the gas cleaning during the BOF process is accomplished by means of electrostatic precipitators (BOF dry flow system) and/or high energy Venturi scrubbers (OG wet process system). The present invention can be applied to both dry and wet processes.
[0007] In general, the wet scrubber plant comprises a quencher (vessel or fixed throat venturi), and a variable throat venturi, where dirty gases are cleaned to an outlet dust loading of less than 3 g/m3 of dry gas.
[0008] The gases leaving the hood section at a temperature of about 1010°C pass through the quencher where they are cooled to less than 148°C. The thus cooled gases then enter a separate elbow pipe, where most of the water carrying solids is separated from the gas stream. This stream enters then a variable throat venturi system, the orifice of which dimensionally adjusts in order to maintain an optimum gas cleaning under the varying conditions of temperature, pressure and flow of the gas. Again, dirty water is separated from the gas stream which, optionally, enters a gas cooler and then arrives at the outlet fans.
[0009] The forced draft fans, which are driven by an electric motor, move the gas towards the scrubber and to the upper part of the blast furnace or to the vent.
[0010] The induced draft fans (IDF) are not provided with an electric motor, and it is the geometry and the physics of the system which create the gas suction from the system to the stack, based on the difference in temperature, and thus density and pressure, of burnt gases, thus driving the fans. The induced draft fans move the gas from the scrubber to the discharge vent or to the upper part of the blast furnace.
[0011] Notwithstanding the presence of gas cleaning devices (dust separators, gas coolers, venturi scrubbers, dehumidifiers), the gas reaching the IDF still includes some small-sized particulate which is problematic and undesirable in that it creates deposits causing problems in the unit.
[0012] The impact of the particulate on the blades of the fan gives rise to erosion when it is still clean, and build up of fouling. In fact, in the gas scrubbing system of an LD process with oxygen, the extracting units are of the forced draft type between the converter and the scrubber, whereas they are of the induction type downstream of the scrubber and upstream of the stack.
[0013] Inhomogeneous deposits formed on the blades of the fan bring about vibrations of the shaft and thus a series of problems:
- decreased efficiency of the IDF;
- unforeseen shutdowns of the steel plant;
- maintenance costs (manual cleaning, blast-sanding of the blades);
- costs for part replacements.
[0014] The gas entering the IDF and the vent is saturated with water. This gives rise to condensation, and the relative phenomena should be considered as taking place in "aqueous media".
[0015] No chemical treatment is presently known or used which is suitable to solve the contamination problems of IDF by the impurities in the gases. At present, the method used in an effort to solve contamination problems is purely mechanical and consists in halting the IDF and manually cleaning it. The blades of the fans are simply subjected to sandblasting.
[0016] The same problems of contamination with impurities occur also in other systems of extracting fans in steel plants, foundries, and power plants and the invention also applies thereto.
[0017] The aim of the present invention is to solve the problems arising from impurities remaining in the gases by means of a chemical treatment. Unexpectedly, it was found that injecting cationic surfactants into the collector placed upstream of the fan solves or at least greatly reduces the above problems.
[0018] Particularly, in order to solve or at least relieve the problems of the prior art in the field of the present invention, the use of a quaternary ammonium salt or a mixture of quaternary ammoniums salts is suitable. The quaternary ammonium salts according to the invention have the following general chemical structure:
wherein:
R4 = C12-C14 alkyl, R3/R1 = -CH3, -C2H5, or C3H7, and R2= -CH2-C6H5,
particularly alkyl dimethyl benzalconium chloride, or
R4 = C8-C18 alkyl groups, R1 = -CH3 or C8-C18 alkyl groups, and R2/R3 = -CH3, -C2H5, or C3H7,
particularly dimethyl didecyl ammonium chloride, and cethyl trimethyl ammonium bromide,
wherein the chemical compounds of the formula (I) are defined as alkyl benzyl imidonium
halides; or
wherein R=-CH2-CH2-OH, -CH2-CH2-NH2, or -(CH2-CH2-NH)nH,
and Alk = alkyl radical, such as -CH3; -C2H5; alkyl radical of coconut fat acids; alkyl radical of tallow fatty acids; etcetera,
wherein the chemical compounds with formula (II) are defined as halides of alkyl benzyl
imidonium, particularly 2-methylbenzylimidonium chloride, 2-cocoalkyl-1-hydroxyethyl-1-benzylimidazolinium
chloride, and 2-tallowalkyl-1-hydroxyethyl-1-benzylimidazolinium.
[0019] In other words, according to the invention, the use of one or more quaternary ammonium salts having at least one of the following radicals bonded to the nitrogen atom: alkyl, alkyaryl, or etherocycle (imidazoliniunm, pyridinium, etc.) and containing an alkyl chain with 8 to up to 18 carbon atoms is provided.
[0020] The antifouling product (a quaternary ammonium salt or a mixture of such salts) is preferably in the liquid form, particularly a solution. This is the most convenient mode because a liquid product of suitable viscosity is available which can be easily supplied to the system by means of a positive displacement pump, such as for example a piston supply pump, etcetera. Moreover, the optimum injection point of the product in the system is preferably the burnt gas duct, immediately upstream of the extractor impeller (fan). The liquid product is injected into the gas stream by means of a suitable pump and spraying nozzle adapted to change the liquid to an aerosol, in such a way that the droplets reach the fans.
[0021] The quaternary ammonium salt or salts are present in the composition in an amount of 15 to 60% by weight based on the total composition, more preferably 25 to 45% by weight. The balance of the composition is water and solvents. Said solvents can be, among others, ethylene glycol, isobutylic alcohol, or isopropylic alcohol, or any other solvent not hindering the dispersion of the active agent in the liquid medium.
[0022] In a preferred embodiment, the product is a mixture of two quaternary ammonium salts, with a content of active material of 35.6%, in 8% ethylene glycol, and 56.4% water. Particularly, in this embodiment, the active material is a mixture of two quaternary ammonium salts according to the invention, that is salt A = dimethyl-didecyl-ammonium chloride, and B = 2-coco-alkyl-1-hydroxyethyl-benzyl-imidazolinium chloride, where A+B can vary from 100% A and 0% B to 0% A and 100% B.
[0023] For the product according to the invention, and particularly according to the preferred embodiment, the recommended dosage is 1 to 100 g of the product for 1000 Nm3 of gas, corresponding to 1 to 36 g of active material for 1000 Nm3 of gas. The optimum and preferred dosage is 15 to 30 g for 1000 Nm3 of gas, corresponding to 5 to 11 g of active material for 1000 Nm3 of gas.
[0024] However, any solvent, and preferably mixtures of solvents, suitable for obtaining a stable solution, can be used in the product of the invention.
[0025] It is obvious that for a product in the form of a solution, the dosage is to be intended as proportional to the dose range as indicated, i.e. a function of the active material content of the solution.
[0026] For a better understanding of the field of application of the present invention, non-limitative reference will be made to the figure which is the diagram of a suppressed-combustion BOF. However it is pointed out that the figure is only by way of an example and has no limitative effects on the scope of the invention.
[0027] The burnt gas extractors of a steel plant (oxygen converters) or blast furnace can in fact have a critical operability as a function of the amount of particulate polluting the gas. Steel plant gases, i.e. gases leaving the oxygen converters, are particularly rich in solid particles. This is the result of the high turbulence caused by the oxygen lance.
[0028] The particulate depends on the nature of the raw materials, among which the quality of metal scraps has an important role. The metal scraps come from inner or outer recycles, and can thus contain different impurities, such as zinc oxides if scraps of electroplated steel are present in a relatively high quantity.
[0029] In any case, it is to be noted that problems are the result of the residual particulate in that usually the extractor moves a large gaseous mass which has been cleaned by a plant placed upstream. The gases are purified either by electrostatic precipitators or by a wet scrubber system (venturi system for scrubbing gases).
[0030] If the gases have a calorific power, such as in blast furnace gases or gases from "suppressed combustion" oxygen conversion, they have to be purified in order to meet the requirements making them suitable to be used as fuels.
[0032] If the gases have no calorific power, such as in oxygen conversion with total combustion, the IDF passes the gases to the stack. In the diagram of the figure representing a suppressed combustion BOF, it can be seen that depending on the various stages of the processing, the extractor can either send the gases to the stack or to the gasometer, by adjusting appropriate valves.
[0033] The purpose of the wet scrubber in a total combustion oxygen steel plant is to purify the gases to such a level as to permit restitution to the atmosphere, in accordance with the laws relevant to air pollution.
[0034] In addition to being scrubbed, gases are also water-cooled, in order to decrease their volume and accordingly the bulk of the extractor and its relevant power consumption.
[0035] The active agent, the composition and their use thus conceived are susceptible of numerous modifications and variations all of which are within the scope of the inventive concept; in addition, all the details may be replaced with other technically equivalent elements.
[0036] The results of the invention will be better understood on the basis of the following examples, given only by way of an indication and not a limitation of the scope of protection of the present invention.
Comparative Example
[0037] In a large steel plant in Southern Italy, the status of the IDF was defined by the following parameters:
A. IDF life: 3 years, equivalent to 23,000 castings;
B. IDF costs: 43,000$ per year;
C. 5 sand blastings per year (one per 1,500 castings) at a cost of 4,000$ a year.
D. 5 castings per year, as a result of production losses, because of unexpected shutdowns due to excessive vibrations. Equivalent cost: 23,000$ per year.
First Embodiment
[0038] The use of the invention in the IDF according to the comparative example has changed the status parameters of the IDF as follows:
A'. IDF life: 6 years
B'. IDF costs reduced to 21,500$ per year;
C'. sand blastings reduced to one per 3,000 castings, at a cost of 2,000$ per year.
D'. no production losses
Second Embodiment
[0039] The use of the invention in an IDF has allowed the following saving:
- cleaning of gas extractors = 50 million a year
- sand blasting of gas extractors = 16 million a year
- balancing of extractors = 100 millions a year
Total costs = 166 millions a year
from which the cost of the chemical treatment (i.e. the invention) is to be subtracted.
[0040] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.
WORDS IN THE FIGURE
1. Composition comprising at least one quaternary ammonium salt having at least one radical
group selected in the class containing alkyl, alkylaryl, or etherocycle, said radical
having an alkyl chain of 8 to 18 carbon atoms, and being bonded to the nitrogen atom,
where the at least one quaternary ammonium salt is present in an amount of 15 to 60%
by weight based on the total composition.
2. Composition according to claim 1, wherein the at least one quaternary ammonium salt
is present in an amount of 25 to 45% by weight based on the total composition.
3. Composition according to claim 1 or 2, comprising at least one quaternary ammonium
salt selected in the class containing those quaternary ammonium salts of the formula
(I):
wherein:
wherein:
R4 = C12-C14 alkyl, R3/R1 = -CR3, -C2H5, or C3H7, and R2= -CH2-C6H5.
4. Composition according to claim 1 or 2, comprising at least one quaternary ammonium
salt selected in the class containing quaternary ammonium salts of the formula (I):
wherein:
wherein:
R4 = C8-C18 alkyl groups, R1 = -CH3 or C8-C18 alkyl groups, and R2/R3 = -CH3, -C2H5, or C3H7.
5. Composition according to claim 1 or 2, comprising at least one quaternary ammonium
salt selected in the class containing quaternary ammonium salts of the formula (II):
wherein:
wherein:
R=-CH2-CH2-OH, -CH2-CH2-NH2, or -(CH2CH2-NH)nH and Alk = alkyl radical, alkyl radicals of coconut and tallow fatty acids.
6. Composition according claim 3, comprising at least a quaternary ammonium salt, wherein
said at least one salt is alkyl dimethyl benzalkonium chloride.
7. Composition according claim 4, comprising at least one quaternary ammonium salt, wherein
said at least one salt is dimethyl decyl ammonium chloride.
8. Composition according claim 4, comprising at least one quaternary ammonium salt, wherein
said at least one salt is cethyl trimethyl ammonium bromide.
9. Composition according claim 5, comprising at least one quaternary ammonium salt, wherein
said at least one salt is 2-methyl benzyl imidonium chloride.
10. Composition according claim 5, comprising at least one quaternary ammonium salt, wherein
said at least one salt is 2-cocoalkyl-1-hydroxyethyl-1-benzylimidazolinium chloride.
11. Composition according claim 5, comprising at least one quaternary ammonium salt, wherein
said at least one salt is 2-tallowalkyl-1-hydroxyethyl-1-benzylimidazolinium chloride.
12. Composition according claim 1, comprising as the quaternary ammonium salts, dimethyl
didecyl ammonium chloride and 2-cocoalkyl-1-hydroxyethyl-1-benzylimidazolinium chloride,
wherein the content of the active material is 35.6%, solvent 8%, and water 56.4%.
13. Composition comprising at least one quaternary ammonium salt according to one of claims
1 to 12, in liquid form.
14. Use of the composition according to one of the preceding claims as antifouling agent
in plants provided with induced draft fans for extracting burnt gases from steel plant
units.
15. Use of the composition according to claim 14, wherein the antifouling agent is injected
in the gaseous stream directly upstream of the fan.
16. Use of the composition according to claim 14 or 15, wherein the dosage of the at least
one quaternary ammonium salt is 1-36 g per 1000 Nm3 of gas.
17. Use of the composition according to claim 16, wherein the dosage of the at least one
quaternary ammonium salt is 5-11 g of quaternary ammonium salt per 1000 Nm3 of gas.
18. Use of the composition according to claim 14 or 15, wherein the dosage of the product
is 1-100g of product per 1000 Nm3 of gas.
19. Use of the composition according to claim 18, wherein the dosage of the product is
15-30g of product per 1000 Nm3 of gas.